What reacts with dilute sulfuric acid. Physical and chemical properties of sulfuric acid
Concentrated acid, safety precautions when working.
SULFURIC ACID. PHYSICAL AND CHEMICAL PROPERTIES.
Physical properties: Anhydrous sulfuric acid is a colorless oily liquid that crystallizes at 10.5 0 C. It is miscible with water in any ratio. When dissolved in water, a large amount is released
warmth. In this case, sulfuric acid hydrates are formed.
Because the dissolution of H 2 SO 4 in water is accompanied by the release of a large amount of heat; this operation must be carried out with great care. To avoid splashing of the heated surface layer of the solution, sulfuric acid should be poured into the water.
Concentrated sulfuric acid vigorously absorbs moisture and is therefore used to dry gases.
CHEMICAL PROPERTIES OF SULFURIC ACID.
It is a dibasic acid.
Structural formula:
Concentrated sulfuric acid - energetic oxidizing agent :
1. When heated, it oxidizes most metals, including copper, silver, and mercury. Depending on the activity of the metal, the reduction products can be: S 0 , SO 2 , H 2 S, but more often until SO2.
For example: When interacting with copper and other low-active metals upon heating, it forms SO 2.
Cu + 2 H 2 SO 4 = CuSO 4 + SO 2 + H 2 O
Reductant oxidizer
Cu 0 - 2ē - Cu +2 1 ok, I'm glad
SO 4 2- + 4H - +2ē - SO 2 0 +2H 2 O 1 Ave. Sunday ok
In the cold, concentrated sulfuric acid (above 93%) does not interact with active metals such as aluminum, iron, and chromium.
This phenomenon is explained by the passivation of metals. This feature of sulfuric acid is widely used for transporting the latter in iron containers.
2. When boiled, it oxidizes non-metals such as sulfur and carbon:
S + 2 H 2 SO 4 = 3 SO 2 +2 H 2 O
C + 2 H 2 SO 4 = CO 2 + 2 SO 2 + 2 H 2 O
3. Water-removing effect (charring).
PROPERTIES OF DILUTATE SULFURIC ACID.
1. Changes the color of the indicator.
2. Interacts with basic and amphoteric oxides:
Na 2 O + H 2 SO 4 = Na 2 SO 4 + H 2 O
ZnO + H 2 SO 4 = ZnSO 4 + H 2 O
3. With bases (neutralization reaction):
H 2 SO 4 + 2KOH = K 2 SO 4 + H 2 O
3H 2 SO 4 + 2 Al(OH) 3 = Al 2 (SO 4) 3 + 6 H 2 O
4. With salts:
H 2 SO 4 + Ba(NO 3) 2 = BaSO 4 ↓+ 2 HNO 3
Conclusions:
1.Anhydrous sulfuric acid is a colorless oily liquid that crystallizes at 10.5 0 C. It can be mixed with water in any proportion.
2. Because the dissolution of H 2 SO 4 in water is accompanied by the release of a large amount of heat; this operation must be carried out with great care. To avoid splashing of the heated surface layer of the solution, sulfuric acid should be poured into the water.
3. Concentrated sulfuric acid vigorously absorbs moisture and is therefore used for drying gases.
4.Sulfuric acid is a dibasic acid.
5. Concentrated sulfuric acid - energetic oxidizing agent .
· When heated, it oxidizes most metals, including copper, silver, and mercury. Depending on the activity of the metal, the reduction products can be: S 0 , SO 2 , H 2 S, but more often until SO2.
· .In the cold, concentrated sulfuric acid (above 93%) does not interact with active metals such as aluminum, iron, chromium.
· When boiled, it oxidizes non-metals such as sulfur and carbon.
· Water-removing action (charring).
6. PROPERTIES OF DILUTATE SULFURIC ACID.
· Changes the color of the indicator.
· Interacts with:
· with basic and amphoteric oxides.
· With bases (neutralization reaction).
· With salts.
Sulfates. Qualitative reaction to sulfate ion
The reagent for sulfate ion is barium chloride.
Barium chloride BaCl2 precipitates from dilute solutions of sulfates a white crystalline, insoluble precipitate of barium sulfate:
BaCl 2 + Na 2 SO 4 = BaSO 4 ↓ + 2 NaCl
Ba 2+ + SO 4 2- = BaSO 4 ↓
pharmacopoeial reaction.
Technique: to 2 drops of sodium sulfate solution Na2SO4 add barium chloride solution BaCl2 and observe the precipitation.
Conclusions:
1. The reagent for sulfate ion is barium chloride.
2.Barium chloride BaCl2 Precipitates a white, crystalline, insoluble precipitate of barium sulfate from dilute solutions of sulfates.
Any acid is a complex substance whose molecule contains one or more hydrogen atoms and an acid residue.
The formula of sulfuric acid is H2SO4. Consequently, the sulfuric acid molecule contains two hydrogen atoms and the acidic residue SO4.
Sulfuric acid is formed when sulfur oxide reacts with water
SO3+H2O -> H2SO4
Pure 100% sulfuric acid (monohydrate) is a heavy liquid, viscous like oil, colorless and odorless, with a sour “copper” taste. Already at a temperature of +10 °C it hardens and turns into a crystalline mass.
Concentrated sulfuric acid contains approximately 95% H2SO4. And it hardens at temperatures below –20°C.
Interaction with water
Sulfuric acid dissolves well in water, mixing with it in any proportion. This releases a large amount of heat.
Sulfuric acid can absorb water vapor from the air. This property is used in industry for drying gases. The gases are dried by passing them through special containers with sulfuric acid. Of course, this method can only be used for those gases that do not react with it.
It is known that when sulfuric acid comes into contact with many organic substances, especially carbohydrates, these substances become charred. The fact is that carbohydrates, like water, contain both hydrogen and oxygen. Sulfuric acid takes these elements away from them. What remains is coal.
In an aqueous solution of H2SO4, the indicators litmus and methyl orange turn red, which indicates that this solution has a sour taste.
Interaction with metals
Like any other acid, sulfuric acid is capable of replacing hydrogen atoms with metal atoms in its molecule. It interacts with almost all metals.
Diluted sulfuric acid reacts with metals like an ordinary acid. As a result of the reaction, a salt with an acidic residue SO4 and hydrogen is formed.
Zn + H2SO4 = ZnSO4 + H2
A concentrated sulfuric acid is a very strong oxidizing agent. It oxidizes all metals, regardless of their position in the voltage series. And when reacting with metals, it itself is reduced to SO2. Hydrogen is not released.
Сu + 2 H2SO4 (conc) = CuSO4 + SO2 + 2H2O
Zn + 2 H2SO4 (conc) = ZnSO4 + SO2 + 2H2O
But gold, iron, aluminum, and platinum group metals do not oxidize in sulfuric acid. Therefore, sulfuric acid is transported in steel tanks.
The sulfuric acid salts that are obtained as a result of such reactions are called sulfates. They are colorless and easily crystallize. Some of them are highly soluble in water. Only CaSO4 and PbSO4 are slightly soluble. BaSO4 is almost insoluble in water.
Interaction with bases
The reaction between acids and bases is called neutralization reaction. As a result of the neutralization reaction of sulfuric acid, a salt containing the acid residue SO4 and water H2O are formed.
Examples of sulfuric acid neutralization reactions:
H2SO4 + 2 NaOH = Na2SO4 + 2 H2O
H2SO4 + CaOH = CaSO4 + 2 H2O
Sulfuric acid reacts with neutralization with both soluble and insoluble bases.
Since there are two hydrogen atoms in the sulfuric acid molecule, and two bases are required to neutralize it, it is classified as a dibasic acid.
Interaction with basic oxides
From the school chemistry course we know that oxides are complex substances that contain two chemical elements, one of which is oxygen in the oxidation state -2. Basic oxides are called oxides of 1, 2 and some 3 valence metals. Examples of basic oxides: Li2O, Na2O, CuO, Ag2O, MgO, CaO, FeO, NiO.
Sulfuric acid reacts with basic oxides in a neutralization reaction. As a result of this reaction, as in the reaction with bases, salt and water are formed. The salt contains the acid residue SO4.
CuO + H2SO4 = CuSO4 + H2O
Interaction with salts
Sulfuric acid reacts with salts of weaker or volatile acids, displacing these acids from them. As a result of this reaction, a salt with an acidic residue SO4 and an acid are formed
H2SO4+BaCl2=BaSO4+2HCl
Application of sulfuric acid and its compounds
Barium porridge BaSO4 is capable of blocking X-rays. Filling the hollow organs of the human body with it, radiologists examine them.
In medicine and construction, natural gypsum CaSO4 * 2H2O and calcium sulfate crystalline hydrate are widely used. Glauber's salt Na2SO4 * 10H2O is used in medicine and veterinary medicine, in the chemical industry - for the production of soda and glass. Copper sulfate CuSO4 * 5H2O is known to gardeners and agronomists, who use it to combat pests and plant diseases.
Sulfuric acid is widely used in various industries: chemical, metalworking, oil, textile, leather and others.
Acid with metal is specific to these classes of compounds. During its course, the hydrogen proton is reduced and, in conjunction with the acid anion, is replaced by a metal cation. This is an example of a reaction that produces a salt, although there are several types of interactions that do not follow this principle. They proceed as redox reactions and are not accompanied by the release of hydrogen.
Principles of reactions of acids with metals
All reactions with metal lead to the formation of salts. The only exception is, perhaps, the reaction of a noble metal with aqua regia, a mixture of hydrochloric acid and any other interaction of acids with metals leads to the formation of a salt. If the acid is neither concentrated sulfuric nor nitric, then molecular hydrogen is released as a product.
But when concentrated sulfuric acid reacts, the interaction with metals proceeds according to the principle of an oxidation-reduction process. Therefore, two types of interactions between typical metals and strong inorganic acids were experimentally identified:
- interaction of metals with dilute acids;
- interaction with concentrated acid.
Reactions of the first type occur with any acid. The only exceptions are concentrated and nitric acid of any concentration. They react according to the second type and lead to the formation of salts and products of the reduction of sulfur and nitrogen.
Typical interactions of acids with metals
Metals located to the left of hydrogen in the standard electrochemical series react with other acids of varying concentrations, with the exception of nitric acid, to form a salt and release molecular hydrogen. Metals located to the right of hydrogen in the electronegativity series cannot react with the above acids and interact only with nitric acid, regardless of its concentration, with concentrated sulfuric acid and with aqua regia. This is a typical reaction between acids and metals.
Reactions of metals with concentrated sulfuric acid
Reactions with dilute nitric acid
Dilute nitric acid reacts with metals located to the left and to the right of hydrogen. During the reaction with active metals, ammonia is formed, which immediately dissolves and reacts with the nitrate anion, forming another salt. The acid reacts with metals of medium activity to release molecular nitrogen. With low-active ones, the reaction proceeds with the release of divalent nitrogen oxide. Most often, several sulfur reduction products are formed in one reaction. Examples of reactions are provided in the graphical appendix below.
Reactions with concentrated nitric acid
In this case, nitrogen also acts as an oxidizing agent. All reactions end with the formation of a salt and the release of redox reactions. Schemes for the flow of redox reactions are proposed in the graphical appendix. In this case, the reaction with low-active elements deserves special attention. This interaction of acids with metals is nonspecific.
Reactivity of metals
Metals react with acids quite readily, although there are several inert substances. These are also elements that have a high standard electrochemical potential. There are a number of metals that are built on the basis of this indicator. It is called the electronegativity series. If the metal is to the left of hydrogen in it, then it is able to react with dilute acid.
There is only one exception: iron and aluminum, due to the formation of 3-valent oxides on their surface, cannot react with acid without heating. If the mixture is heated, the metal oxide film initially reacts, and then it itself dissolves in the acid. Metals located to the right of hydrogen in the electrochemical activity series cannot react with inorganic acid, including dilute sulfuric acid. There are two exceptions to the rule: these metals dissolve in concentrated and dilute nitric acid and aqua regia. Only rhodium, ruthenium, iridium and osmium cannot be dissolved in the latter.
In the writings of the monk-alchemist Vasily Valentin, who lived in the 15th century, whom many historians of chemistry consider a mythical figure, it was recommended to obtain “spirit from salts” (“spiritus salis”) - by calcining a mixture of rock salt and iron sulfate. At the same time, a liquid was distilled off, which amazed the imagination of alchemists: it smoked in the air, caused coughing, and corroded fabric, paper, and metal. What substance are we talking about? What other interesting properties and why does this substance have? These are the questions we have to answer.
Sulfuric acid is a strong acid. This is explained by the structure of its molecule since the electron density from hydrogen atoms shifts to oxygen and sulfur atoms, which have greater electronegativity, which allows hydrogen protons to be easily split off.
Physical properties of sulfuric acid
100% H2SO4 (monohydrate, SO3×H2O) crystallizes at 10.45 C; boiling point 296.2 C; density 1.9203 g/cm3; heat capacity 1.62 J/g (K. H2SO4 mixes with H2O and SO3 in any ratio, forming compounds:
H2SO4×4H2O (melting temperature - 28.36 C),
H2SO4×3H2O (melting temperature - 36.31 C),
H2SO4×2H2O (melting temperature - 39.60 C),
H2SO4×H2O (melting temperature - 8.48 C),
When aqueous solutions of carbon dioxide containing up to 70% H2SO4 are heated and boiled, only water vapor is released into the vapor phase. Above more concentrated solutions, carbon dioxide vapors also appear. A solution of 98.3% H2SO4 (azeotropic mixture) is completely distilled at boiling (336.5 0C). Sulfuric acid containing over 98.3% H2SO4 releases SO3 vapor when heated.
Chemical properties of dilute sulfuric acid and the interaction of sulfuric acid solutions with active metals.
The process is especially active with alkali and alkaline earth metals. In 1808 English chemist Humphry Davy observed how the metal barium he first obtained sank in concentrated sulfuric acid and then floated up, surrounded by bubbles of the released gas.
Potassium and sodium react explosively with dilute sulfuric acid. Even when cooled to -50 C, the hydrogen released ignites. Only near the freezing temperature of the acid (for 30% H2sO4 it is below -70) does the reaction stop.
We conducted studies of the interaction of dilute sulfuric acid with lithium and calcium.
2Li + H2 SO4 = Li2SO4 + H2
Li 0 - 1 e → Li+ *2 reducing agent
2H + + 2e → H2 0 oxidizing agent
Ca + H2 SO4 = CaSO4 + H2
Ca 0 - 2 e → Ca 2+ reducing agent
2H + + 2e → H2 0 oxidizing agent
When sulfuric acid interacts with active metals, the reaction product is hydrogen.
b\ Reactions of dilute sulfuric acid with metals of intermediate activity
When sulfuric acid reacts with medium-active metals, the reaction products are hydrogen and hydrogen sulfide.
Zn + H2SO4 = ZnSO4 + H2
2H+ + 2e → H2 oxidizing agent
4Zn + 5H2SO4 = 4ZnSO4 + H2S + 4H2O
Zn0 - 2e → Zn 2+ reducing agent
SO4 2- +8e +8H+→S 2-+4H2O oxidizing agent
Dilute sulfuric acid does not react with lead, even when heated.
c\ Reactions of dilute sulfuric acid with aluminum and iron
When sulfuric acid interacts with aluminum and iron, the reaction products are hydrogen and hydrogen sulfide.
2Al+3 H2 SO4 =Al2(SO4)3+3H2
Al0 – 3e →Al+3 *2 reducing agent
2H+ + 2e → H2 *3 oxidizing agent
8Al+15 H2 SO4 =4 Al2(SO4)3+3H2 S +12H2O
S+6 +8e →S-2 *3 oxidizing agent
2Fe+ 3H2SO4 = Fe2(SO4)3 +3 H2
Fe0 -3e →Fe+3 *2 reducing agent
2H+ + 2e → H2 *3 oxidizing agent g\ Reactions of dilute sulfuric acid with low-active metals
Dilute (50%) sulfuric acid does not react with metals located in the voltage series after hydrogen.
Chemical properties of concentrated sulfuric acid and sodium reacts more slowly with concentrated sulfuric acid than with water. But the reaction with potassium will still end in an explosion. Among other products, these reactions produce sulfides of these metals.
8Na + 4H2 SO4 (k) = 2S + 6Na2S + 4H2O
Na 0 - 1 e → Na+ *8 reducing agent
S+6 +8e →S-2 *1 oxidizing agent b\ Reactions of concentrated sulfuric acid with medium activity metals
When concentrated sulfuric acid reacted with medium-active metals, the reaction products were sulfur, hydrogen sulfide and sulfur dioxide.
Zn + 2H2 SO4 = ZnSO4 + H2O + SO2
Zn 0 - 2 e → Zn+ 2 reducing agent
S+6 + 2 e → S+4 oxidizing agent
4Zn + 5H2 SO4 = 4ZnSO4 + 4H2O + H2S
Zn 0 - 2 e → Zn+ 2 *4 reducing agent
S+6 + 8 e → S-2 *1 oxidizing agent
3Zn + 4H2 SO4 = 3ZnSO4 +4 H2O + S
Zn 0 - 2 e → Zn+ 2 *3reductant
S+6 + 6 e → S0 *1oxidizing agent in\ Reactions of concentrated sulfuric acid with aluminum and iron
In the cold, concentrated sulfuric acid passivates many metals, including Pb, Cr, Ni, steel, and cast iron.
When the reaction mixture is heated, a chemical reaction occurs.
8Fe+15 H2 SO4 =4 Fe2(SO4)3+3H2 S +12H2O
Al0 – 3e →Al+3 *8 reducing agent
S+6 +8e →S-2 *3 oxidizing agent g\ Reactions of concentrated sulfuric acid with low-active metals
Can concentrated sulfuric acid react with metals in the voltage series after hydrogen? Sulfur has an oxidation state of +6 in sulfuric acid, suggesting that sulfuric acid is an oxidizing agent due to the sulfate ion.
Cu + 2H2 SO4 = CuSO4 + H2O + SO2
Cu 0 - 2 e → Cu+ 2 reducing agent
S+6 + 2 e → S+4 oxidizing agent
When concentrated sulfuric acid reacts with low-active metals, sulfur dioxide is released.
5. Reactions of concentrated sulfuric acid with non-metals
S + 2H2SO4 = 2H2O + 3SO2
S 0 - 4 e → S+4 reducing agent
S +6 + 2 e → S+4 *2 oxidizing agent
2P + 5H2 SO4 = 2H3PO4 + 5SO2 + 2H2O
P 0+ 2H2 O -5 e → PO4 2- +4 H+ *2 reducing agent
SO4 2- +4H+ +2e →SO2 + 2H2O *5 oxidizing agent
6. Reactions of concentrated sulfuric acid with organic substances
Can conc. Does sulfuric acid interact with organic substances?
Conc. sulfuric acid exhibits water-removing properties. This property can be used in a chemical process to dry various products, such as gases.
It oxidizes sucrose, which produces volatile gases carbon dioxide and sulfur dioxide, so the mass swells and rises. In addition, it can char the cellulose.
C12H22O11 + H2 SO4 = 13 H2O + 2SO2 + 11C + CO2
Sulfuric acid removes chemically bound water from organic compounds containing hydroxyl groups - OH. Dehydration of ethyl alcohol in the presence of concentrated sulfuric acid leads to the production of ethylene or a mixture of esters.
C2H5OH H2 SO4 → CH2=CH2 + H2O
2C2H5OH H2 SO4 → C2H5O C2H5 + H2O
2C2H5OH + H2SO4 → C2H5OSO3H + H2O
1. Sulfuric acid reacts with most metals, but depending on its concentration and the position of the metal in the voltage series, the rate and products of the reaction can vary significantly.
2. The degree of oxidation of the reaction product depends on the activity of the metal; the more active the metal that reacts with concentrated sulfuric acid, the lower the degree of oxidation of the sulfur reduction product.
3. The properties of concentrated sulfuric acid differ significantly from the properties of its solutions.
4. Concentrated sulfuric acid is a strong oxidizing agent.
The oxidizing agent in concentrated sulfuric acid is the sulfate ion, and in its solutions it is the hydrogen proton.
Conclusion
As a result of working on the project: we conducted a series of independent laboratory studies and experimentally found out what reaction products are possible when sulfuric acid interacts with various substances under certain conditions.
We studied the special properties of concentrated sulfuric acid; established the concept of oxidizing agent and reducing agent.
Got the opportunity to improve and develop experimental skills.
INTRODUCTION
PHYSIO-CHEMICAL TECHNOLOGIES OF SULFURIC ACID
KINETICS AND MECHANISM OF THE PROCESS
1 Equilibrium degree of conversion
2 Reaction rate of S02 to S03
3 Oxidation of S02 on a catalyst in a fluidized bed
SULFURIC ACID TECHNOLOGY
1 Raw materials for technology
2 Technological scheme for the production of sulfuric acid and its description
3 Waste in sulfuric acid technology and methods of their disposal
4 Maximum permissible concentrations of gases, vapors and dust in the production of sulfuric acid
MAIN EQUIPMENT DESIGN
1 Oleum absorber
2 Monohydrate absorber
3 Technological characteristics of absorbers
TECHNICAL AND ECONOMIC INDICATORS OF TECHNOLOGY
REFERENCES
INTRODUCTION
Sulfuric acid is one of the main products of the chemical industry. It is used in various sectors of the national economy, since it has a set of special properties that facilitate its technological use. Sulfuric acid does not smoke, has no color or odor, is in a liquid state at ordinary temperatures, and does not corrode ferrous metals in concentrated form. At the same time, sulfuric acid is a strong mineral acid, forms numerous stable salts and is cheap.
The chemical composition of sulfuric acid is expressed by the formula H2SO4.
In technology, sulfuric acid refers to any mixture of sulfur oxide and water. If there is more than 1 mole of water per 1 mole of SO3, then the mixtures are aqueous solutions of sulfuric acid, and if less, they are solutions of sulfuric anhydride in sulfuric acid (oleum) or fuming sulfuric acid.
Among mineral acids, sulfuric acid ranks first in terms of production and consumption. Its global production has more than tripled over the past 25 years and currently amounts to more than 160 million tons per year.
Sulfuric acid is used for the production of fertilizers - superphosphate, ammophos, ammonium sulfate, etc. Its consumption is significant in the purification of petroleum products, as well as in non-ferrous metallurgy, when pickling metals. Particularly pure sulfuric acid is used in the production of dyes, varnishes, paints, medicinal substances, some plastics, chemical fibers, many pesticides, explosives, ethers, alcohols, etc.
Concentrated sulfuric acid is a strong oxidizing agent. Oxidizes HI and partially HBr to free halogens, carbon to CO2, S to SO2, oxidizes many metals. Redox reactions involving H2SO4 usually require heating. Often the reduction product is SO2:
S + 2 H2SO4 = 3SO2+ 2H2O (1)+ 2 H2SO4 = 2SO2 + CO2 + 2H2O (2)S + H2SO4= SO2+ 2H2O + S (3)
Strong reducing agents convert H2SO4 into S or H2S.
Concentrated sulfuric acid, when heated, reacts with almost all metals (excluding Au, Pt, Be, Bi, Fe, Mg, Co, Ru, Rh, Os, Ir), for example:
Cu + 2 H2SO4 = CuSO4 + SO2 + 2H2O (4)
Sulfuric acid forms salts - sulfates (Na2SO4) and hydrosulfates (NaHSO4). Insoluble salts - PbSO4, CaSO4, BaSO4, etc.:
H2SO4+ BaCl2 = BaSO4 + 2HCl (5)
Cold sulfuric acid passivates iron, so it is transported in iron containers. Anhydrous sulfuric acid dissolves SO3 well and reacts with it, forming pyrosulfuric acid, obtained by the reaction:
H2SO4+ SO3=H2S2O7 (6)
Solutions of SO3 in sulfuric acid are called oleum. They form two compounds: H2SO4 SO3 and H2SO4 2SO3
According to the standards, a distinction is made between technical and battery sulfuric acids.
Technical sulfuric acid GOST 2184-77
Technical sulfuric acid is developed for the production of fertilizers, artificial fiber, caprolactam, titanium dioxide, ethyl alcohol, aniline dyes and a number of other industries. According to GOST 2184-77, the following types of technical sulfuric acid are distinguished:
· contact (improved and technical);
· oleum (improved and technical);
· tower;
· regenerated.
According to physical and chemical indicators, it is necessary that sulfuric acid meets the following standards:
Indicator name |
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|
Contact |
Tower |
Regenerated |
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improved |
technical |
improved |
technical |
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|
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1.Mass fraction of monohydrate (H2SO4), % |
not less than 92.5 |
not standardized |
not less than 75 |
at least 91 |
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2. Mass fraction of free sulfuric anhydride (SO3), % not more than |
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3. Mass fraction of iron (Fe), %, no more |
not standardized |
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4. Mass fraction of residue after calcination, %, no more |
not standardized |
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5. Mass fraction of nitrogen oxides (N2O3), %, no more |
not standardized |
not standardized |
|||||
6. Mass fraction of nitro compounds, %, no more |
not standardized |
||||||
7. Mass fraction of arsenic (As), %, no more |
not standardized |
not standardized |
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8. Mass fraction of chloride compounds (Cl), %, no more |
not standardized |
||||||
9. Mass fraction of lead (Pb), %, no more |
not standardized |
not standardized |
|||||
10.Transparency |
transparent without dilution |
not standardized |
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11.Color, cm3 of reference solution, no more |
not standardized |
Battery sulfuric acid GOST 667-73
Concentrated battery sulfuric acid is specialized as an electrolyte for filling lead batteries after diluting it with distilled water. According to physical and chemical indicators, it is necessary that battery sulfuric acid meets the standards specified in the table.
Indicator name |
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Top grade |
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1. Mass fraction of monohydrate (H2SO4),% |
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2. Mass fraction of iron (Fe), %, no more |
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3. Mass fraction of residue after calcination, %, no more |
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4. Mass fraction of nitrogen oxides (N2O3), %, no more |
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5. Mass fraction of arsenic (As), %, no more |
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6. Mass fraction of chloride compounds (Cl), %, no more |
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7. Mass fraction of manganese (Mn), %, no more |
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8. Mass fraction of the sum of heavy metals in terms of lead (Pb), %, no more |
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9. Mass fraction of copper (Cu), %, no more |
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10. Mass fraction of substances reducing KMnO4, cm3 of solution with (1/5 KMnO4) = 0.01 mol/dm3, no more |
This paper examines the most important task of workers in the sulfuric acid industry, which is to further improve production through the use of best practices. introduction of progressive techniques and methods of work, as well as in the development of fundamentally new methods for the production of sulfuric acid based on the latest achievements of science and technology.
sulfuric acid absorber
1.
PHYSICAL AND CHEMICAL BASICS OF SULFURIC ACID TECHNOLOGY
In modern sulfuric acid production, the starting materials are sulfur dioxide (sulfur dioxide), oxygen and water, the interaction between them proceeds according to the overall stoichiometric equation:
SO2 +1/2O2 +nH2O H2SO4+(n-1)H2O+Q (7)
This process is carried out in two ways - nitrous and contact.
The nitrous method of oxidation of SO2 to SO3 occurs mainly in the liquid phase and is based on the transfer of oxygen using nitrogen oxides. Nitrogen oxides, oxidizing SO2 to SO3, are reduced to NO, which is again oxidized by oxygen in the gas mixture in both the liquid and gas phases.
The essence of the nitrose method is that the roasting gas, after cleaning it from dust, is treated with sulfuric acid, in which nitrogen oxides are dissolved, the so-called nitrose. Sulfur dioxide is absorbed by nitrose and then oxidized by nitrogen oxides by the reaction
SO2 + N2O3 + H2O = H2SO4 + 2NO (8)
The resulting NO is poorly soluble in nitrose and is therefore released from it, and then partially oxidized by oxygen in the gas phase to NO2 dioxide. The mixture of nitrogen oxides NO and NO2 is reabsorbed by sulfuric acid, etc. The nitrogen oxides are essentially not consumed in the nitrous process and are returned to the production cycle. However, due to their incomplete absorption by sulfuric acid, they are partially carried away by the exhaust gases; this amounts to irreversible losses of oxides.
The processing of SO2 into sulfuric acid using the nitrose method is carried out in production towers - cylindrical tanks (15 m or more in height) filled with a packing of clay rings. “Nitrose” is sprayed from above towards the gas clot - dilute sulfuric acid containing nitrosyl sulfuric acid NOOSO3H, obtained by the reaction:
O3 + 2 H2SO4 = 2 NOOSO3H + H2O (9)
Oxidation of SO2 by nitrogen oxides occurs in solution after its absorption by nitrose. Nitrose is hydrolyzed by water:
H + H2O = H2SO4 + HNO2 (10)
Sulfur dioxide entering the towers forms sulfurous acid with water:
H2O = H2SO3 (11)
The interaction of HNO2 and H2SO3 leads to the production of sulfuric acid:
2 HNO2 + H2SO3 = H2SO4 + 2 NO + H2O (12)
The released NO is converted in the oxidation tower into N2O3 (more precisely, into the consistency of NO + NO2). From there, the gases enter absorption towers, where sulfuric acid is supplied to meet them from above. Nitrose appears, which is pumped into production towers. In this way, the continuity of production and the cycle of nitrogen oxides is ensured. Their inevitable losses with exhaust gases are compensated by the addition of HNO3.
Sulfuric acid produced by the nitrous method has an insufficiently high concentration and contains harmful impurities (for example, As). Its creation is accompanied by the release of nitrogen oxides into the atmosphere (“fox tail”, named after the color of NO2).
At the bottom of the towers, 76% sulfuric acid accumulates, naturally, in greater quantities than was spent on preparing nitrose (after all, “newborn” sulfuric acid is added).
The disadvantage of the tower method is that the acquired acid has a concentration of only 76% (at a higher concentration, the hydrolysis of nitrosyl sulfuric acid is poor). Concentrating sulfuric acid by evaporation presents an additional difficulty. The advantage of this method is that the impurities in SO2 do not affect the progress of the process, so the initial SO2 can be freed from dust, i.e. mechanical contamination.
Previously, the nitrous process was carried out in lead chambers, which is why it was called the chamber method. Currently, this method, as it is low-productive, is not used. Instead, they use the tower method, in which all the main and intermediate SO2 processing processes take place not in chambers, but in towers filled with packing and irrigated with sulfuric acid.
Contact method. The discovery by Phillips in England in 1831 of the possibility of SO2 oxidation with oxygen on the surface of a solid platinum catalyst became widely used only in the 70s of the 19th century. Such late development is explained, firstly, by the fact that the platinum catalyst quickly lost its activity; and, secondly, by the fact that at that time there were no consumers of oleum.
In the 70s, thanks to the work of Knitch, the reason for the decrease in platinum activity was established: the presence of arsenic in sulfur dioxide during the firing of pyrites; He also found a method for purifying roasting gas from catalyst poison.
Currently, most of the world's sulfuric acid is produced by the contact method. The growth in the production of sulfuric acid by the contact method is determined by a higher technical level, due to the need for pure and concentrated acid, the possibility of automating the process, as well as reducing the content of sulfur oxides in exhaust gases to maximum permissible concentrations (MPC). The contact process for producing sulfuric acid in the world is carried out by two methods:
· single contact (SC) method with the degree of oxidation of S02 in S03 equal to 97.5-98%, and the emission of exhaust gases containing SO2 and SO3 into the atmosphere above the maximum permissible concentration (MPC), which required additional costs for construction in such purification separation systems;
· method of double contact (DC) and double absorption (DA). In DK - DA systems, the degree of oxidation of SO2 to SO3 is 99.7-99.8%, which corresponds to achieving the maximum permissible concentration of SO2 and SO3 in the exhaust gases.
The production of sulfuric acid by the contact method using the DC system consists of the following stages:
) preparation of raw materials;
) production of sulfur dioxide
4FeS2 + 11O2 →2Fe2O3 + 8SO2 + 3415 Q (t = 800°C) (13)
or 3FeS2 + 8O2 →Fe3O4 + 6SO2 + Q (14)
or burning sulfur S + O2 → SO2 (15)
)
gas purification;
) oxidation of sulfur dioxide
2SO2 + O2 ↔2SO3 + Q (400-500°C, cat. V2O5) (16)
) SO3 absorption
H2O → H2SO4 + Q (17)
) exhaust gas purification.
When producing sulfuric acid using the DK - DA system, the sixth stage is absent.
I liked the contact method of sulfuric acid technology, as the most effective (a high degree of conversion is achieved) and more favorable from an environmental point of view (emissions comply with MAC and MPE standards.)
KINETICS AND MECHANISM OF THE PROCESS
Process chemistry:
· burning sulfur
oxidation of SO2 to SO3
SO3 absorption
The most important task in the production of sulfuric acid is to increase the degree of conversion of SO2 to SO3. In addition to increasing the productivity of sulfuric acid, fulfilling this task also allows us to solve environmental problems - to reduce emissions of the harmful component SO2 into the environment.
Increasing the degree of SO2 conversion can be achieved in different ways. The most common of them is the creation of double contact circuits.
In the production of sulfuric acid by the contact method, the oxidation of SO2 according to the reaction SO2+1/2O2↔SO3+Q occurs in the presence of a catalyst. Various metals, their alloys and oxides, some salts, silicates and many other substances have the ability to accelerate the oxidation of SO2. Each catalyst provides a certain, characteristic degree of conversion. In factory conditions, it is more profitable to use catalysts with the help of which the highest degree of conversion is achieved, since the residual amount of unoxidized SO2 is not captured in the absorption compartment, but is removed into the atmosphere along with the exhaust gases.
For a long time, platinum was considered the best catalyst for this process, which was applied in a finely crushed state to fibrous asbestos, silica gel or magnesium sulfate. However, platinum, although it has the highest catalytic activity, is very expensive. In addition, its activity is greatly reduced in the presence of very small amounts of arsenic, selenium, chlorine and other impurities in the gas. Therefore, the use of a platinum catalyst led to the complexity of the equipment due to the need for thorough gas purification and increased the cost of the finished product.
Among non-platinum catalysts, the vanadium catalyst (based on vanadium pentoxide V2O5) has the greatest catalytic activity; it is cheaper and less sensitive to impurities than a platinum catalyst.
In the production of sulfuric acid, contact masses based on vanadium (V) oxide of the BAV and SVD brands, named after the initial letters of the elements included in their composition, are used as a catalyst.
BAS (barium, aluminum, vanadium) composition:
There are other inventions of catalysts. The invention relates to catalysts for the oxidation of sulfur dioxide and can be used in the production of sulfuric acid when processing gas mixtures with normal and high content of sulfur dioxide.
A known catalyst for the oxidation of sulfur dioxide consists of vanadium pentoxide with the addition of alkaline promoters of sodium, potassium, rubidium and (or) cesium compounds on a diatomite carrier containing SiO2, CaO. The mixture of alkaline promoters in terms of oxides contains, wt. Na2O 5-30; Rb2O and (or) Cs2O 15-35; K2O 8-35.
Catalyst activity at 485oC 90.2-91% at 420oC 57.8-59.7% when tested under the following conditions: V 4000 h-1, sulfur dioxide content in the initial gas mixture 7 vol. the rest is air. Mechanical crushing strength 1-2 MPa
The oxidation reaction of S02 is exothermic; its thermal effect, like any chemical reaction, depends on temperature.
In the range of 400-700°C, the thermal effect of the oxidation reaction (in kJ/mol) can be calculated with sufficient accuracy for technical calculations using the formula
Q= 10 142 - 9.26T or 24205 - 2.21T (in kcal/mol) (18)
where T is temperature, K.
The oxidation reaction of S02 to S03 is reversible. The equilibrium constant of this reaction (in Pa-0.5) is described by the equation
where Pso2, Pso3, Po2 are the equilibrium partial pressures of SO2, SO3 and O2, Pa. The value of Kp depends on temperature:
Table 1. Dependence of the equilibrium constant on temperature
390 400 425 450 475 500 |
1,801 1,410 0,768 0,437 0,258 0,159 |
525 575 600 625 650 |
0,100 0,044 0,030 0,021 0,015 |
Kp values in the range 390-650 °C can be calculated using the formula
(20)
or more precisely
2.1 Equilibrium conversion rate
The degree of S02 conversion achieved on the catalyst depends on its activity, gas composition, duration of contact of the gas with the catalyst, pressure, etc. For a gas of a given composition, the theoretically possible, i.e., equilibrium degree of conversion depends on temperature and is expressed by the equation:
(22)
where Pso2, Pso3 are the equilibrium partial pressures of SO2 and SO3.
Substituting the ratio Pso3/ Pso2 from equation (23) into equation (6-5), we obtain:
(24)
If we denote P as the total gas pressure (in Pa), a as the initial content of S02 in the gas mixture (volume %), b as the initial oxygen content in the gas mixture (volume %), then equation (6-6) will take the form:
(25)
The determination of the equilibrium degree of transformation using this equation is carried out by the method of successive approximations. The expected value of xp is substituted into the right side of the equation and calculations are carried out. If the found value differs from the previously accepted one, the calculation is repeated.
With decreasing temperature and increasing gas pressure, the value of xp increases. This is due to the fact that the oxidation reaction proceeds with the release of heat and a decrease in the total number of molecules. Below are the values of xp at various temperatures and a pressure of 0.1 MPa for a gas containing 7% S02, 11% 02 and 82% N2:
Table 2. Dependence of the degree of conversion on temperature
390 400 410 420 430 440 450 460 |
99,4 99,2 99,0 98,7 98,4 98,0 97,5 96,9 |
470 480 490 500 510 520 530 540 |
96,2 95,4 64,5 93,4 92,1 90,7 89,2 87,4 |
550 560 570 580 590 650 700 1000 |
85,5 82,5 80,1 77,6 75,0 58,5 43,6 5,0 |
The equilibrium degree of conversion depends on the ratio of SO2 and O2 in the gas, which in turn depends on the type of raw material being fired and the amount of air supplied. The more air is introduced, the less SO2 and more 02 are contained in the gas mixture and, therefore, the higher the equilibrium degree of conversion.
Table 3. Dependence of the equilibrium degree of conversion on pressure
Хр* 100 at pressure (in MPa) |
||||||
|
||||||
400 450 500 550 600 |
99,2 97,5 93,4 85,5 73,4 |
99,6 98,9 96,9 92,9 85.8 |
99,7 99,2 97,8 94,9 89,5 |
99,9 99,5 98,6 96,7 93,3 |
99,9 99,6 99,0 97,7 95,0 |
99,9 99,7 99,3 93,3 96,4 |
Table 4. Dependence of the equilibrium degree of chr conversion on the composition of the gas mixture (at 475 °C and pressure 0.1 MPa)
|
|
|||||
|
18,4 16,72 15,28 13,86 12,43 |
97,1 97,0 96,8 96,5 96,2 |
11,0 9,58 8,15 6,72 |
95,8 95,2 94,3 92,3 |
2.2 Reaction rate of S02 to S03
In production conditions, the rate of S02 oxidation is of significant importance.
The rate of the oxidation process of S02 to S03 on a vanadium catalyst (in a fixed bed) is expressed by the equation
(26)
where x is the degree of conversion, fractions of unity; τ - contact time, s; a is the initial concentration of SOa, fractions of a unit; xp - equilibrium degree of conversion, fraction; b - initial oxygen concentration, fraction; T-temperature, K; P - total pressure, Pa; Kr - equilibrium constant [equation (6-4)], Pa-0.5; k is the reaction rate constant, s-1-Pa-1:
(28)
k0 - coefficient; E-activation energy, J/mol;
The activation energy of the reaction of oxidation of sulfur oxide (IV) with oxygen into sulfur oxide (VI) is very high. Therefore, in the absence of a catalyst, the oxidation reaction practically does not occur even at high temperatures. The use of a catalyst allows one to reduce the activation energy and increase the oxidation rate.
3 Oxidation of S02 on a catalyst in a fluidized bed
In a fluidized bed, very intense mixing of gas with catalyst particles occurs, as a result of which the temperature and composition of the gas are almost the same throughout the entire volume of the catalyst. In this case, the rate of external diffusion of S02 and O2 to the catalyst surface increases significantly.
The hydraulic resistance of a fluidized bed does not depend on the grain size, therefore, for the catalytic oxidation of S02 in a fluidized bed, very small spherical granules (radius 0.5-2 mm) are used, which ensures almost complete use of the internal surface of the catalyst.
The kinetics of the oxidation of sulfur dioxide in a suspended catalyst layer is largely determined by hydrodynamic factors, since in addition to intense radial and axial mixing, gas leakage in the form of bubbles is possible. It is very difficult to take all factors into account. However, pilot and industrial tests show that full mixing conditions are achieved in large diameter reactors. Therefore, the rate of S02 oxidation in this case can be assumed to be the same at all points of the fluidized bed and, therefore, the calculation equation (6-19) can be presented as follows:
(29)
Where x is the degree of conversion at the gas outlet from the fluidized bed (it is the same throughout the entire catalyst layer)
The dependence of Chp on temperature, pressure and sulfur (IV) oxide content in the roasting gas is shown in Fig. 1.
Rice. 1. Dependence of the equilibrium degree of conversion of sulfur oxide (IV) into sulfur oxide (VI) on temperature (A), pressure (B) and the content of sulfur oxide (IV) in the gas (C).
For gas obtained by roasting pyrites and burning sulfur in air, achieving a conversion degree of more than 98% is impractical, since this is associated with a sharp increase in the amount of catalyst. Meanwhile, with the high productivity of sulfuric acid plants (currently under construction) and a conversion degree of 98%, the sanitary standard for S02 content in the atmosphere can only be achieved if a very high (and therefore expensive) pipe for exhaust gases is constructed or additional sanitary cleaning of the exhaust gases is carried out from S02- For example, with an installation capacity of 5000 t/day, the amount of SO2 emitted into the atmosphere (at one point) is 100 t/day (in terms of H2S04).
To increase the final degree of SO2 conversion, double contacting (DC) is used. Its essence lies in the fact that the oxidation of S02 (contacting) is carried out in two stages; at the first stage, a conversion rate of 90% is ensured. Then S03 is separated from the reaction mixture, after which the second stage of contacting is carried out, in which w = 95% of the remaining S02 is achieved; the overall conversion rate is 99.5%.
The oxidation reaction of S02 is reversible, so the overall rate of the process W is expressed as:
where , are the rates of forward and reverse reactions; , - rate constants of forward and reverse reactions; CSO2, CO2, CSO3 - concentrations in gas SO2, O2, SO3; l,m,n is the order of the corresponding reaction.
From equation (30) it follows that if SO3 is removed from the reaction mixture after the first stage of contacting, then before the second stage CSO3 = 0 and r2 = 0. Consequently, the speed of the process increases. In this case, the final degree of conversion is expressed by the equation
(31)
where x1, x2, xn are the degrees of transformation at the first, second (from what remains after the first stage) and at the final stages, shares.
Thus, xn = 0.9+ (1-0.9)0.95 = 0.995.
The contradiction between the kinetics and thermodynamics of the oxidation process of sulfur (IV) oxide is quite successfully removed by the design and temperature conditions of the contact apparatus. This is achieved by dividing the process into stages, each of which meets the optimal conditions of the contacting process.
Table 5. Degree of conversion at each stage of the contact apparatus
3 SULFURIC ACID TECHNOLOGY
3.1 Raw materials for technology
The starting reagents for producing sulfuric acid can be elemental sulfur and sulfur-containing compounds, from which either sulfur or sulfur dioxide can be obtained. Such compounds are iron sulfides, sulfides of non-ferrous metals (copper, zinc, etc.), hydrogen sulfide and a number of other sulfur compounds.
Traditionally, the main sources of raw materials are sulfur and iron (sulfur) pyrites. Gradually, the share of pyrites as a source of raw materials is decreasing, which is associated with high transport costs for its transportation (in addition to sulfur, it contains a very large share of other components), and with the inability to get rid of waste - cinder. A significant place in the raw material balance of sulfuric acid production is occupied by non-ferrous metallurgy waste gases containing sulfur dioxide.
To protect the environment, measures are being taken around the world to use industrial waste containing sulfur. Significantly more sulfur dioxide is emitted into the atmosphere with the exhaust gases of thermal power plants and metallurgical plants than is used for the production of sulfuric acid. For example, in the 1980s, global sulfur consumption was approximately 65 million tons/year, and 50 million tons were lost, with waste gases (in terms of sulfur) of almost 100 million tons. At the same time, due to the low concentration of SO2, in such waste gases gases, their processing is not yet always feasible.
Iron pyrite
Natural iron pyrite is a complex rock consisting of iron sulfide FeS2, sulfides of other metals (copper, zinc, lead, nickel, cobalt, etc.), metal carbonates and waste rock. On the territory of the Russian Federation there are deposits of pyrite, in the Urals and the Caucasus, where it is mined in mines in the form of ordinary pyrite.
The process of preparing ordinary pyrite for production aims to extract valuable non-ferrous metals from it and increase the concentration of iron disulfide. Increasing the iron disulfide content in the raw material by flotation of pyrites, as well as enriching the air with oxygen, increases the driving force of the firing process.
In terms of physical and chemical parameters, flotation sulfur pyrites must comply with the standards specified in Table 6.
Table 6
Name of indicators |
Standards for brands |
||||
|
|||||
1. Appearance |
Bulk powder Foreign inclusions are not allowed (pieces of rock, ore, wood, concrete, metal, etc.) |
||||
3. Total content of lead and zinc, %, no more |
Not standardized |
||||
7. Mass fraction of chlorine, %, no more |
Sulfur is found in nature in the form of metal sulfides and metal sulfates; it is part of coal, oil, natural and associated gases. About 50% of mined sulfur is used to produce sulfuric acid.
Elemental sulfur can be obtained from sulfur ores or from gases containing hydrogen sulfide or sulfur oxide SO2. In accordance with this, a distinction is made between native sulfur and gaseous (lumpy) sulfur.
The thermal method for obtaining sulfur from native ores involves smelting it using steam and purifying the raw sulfur by distillation. The production of gas sulfur from hydrogen sulfide, extracted during the purification of combustible and process gases, is based on the process of incomplete oxidation over a solid catalyst:
H2S + O2 = 2H2O + S2 (32)
Significant quantities of sulfur can be obtained from copper smelting products containing various sulfur compounds. In this case, during the smelting process, reactions occur that lead to the formation of elemental sulfur:
2FeS2 = 2FeS + S2 (33)+ C = S + CO2 (34)
According to physical and chemical indicators, technical sulfur must comply with the standards specified in Table 7
Table 7
Indicator name |
|||||
|
|||||
1. Mass fraction of sulfur, %, not less |
|||||
2. Mass fraction of ash, %. no more |
|||||
3. Mass fraction of organic substances, %, no more |
|||||
4. Mass fraction of acids in terms of sulfuric acid, %, no more |
|||||
5. Mass fraction of arsenic, %, no more |
|||||
6. Mass fraction of selenium, %, no more |
|||||
7. Mass fraction of water, %, no more |
|||||
8. Mechanical contamination (paper, wood, sand, etc.) |
Not allowed |
3.2 Technological scheme for the production of sulfuric acid and its description
The largest number of sulfuric acid production plants use sulfur as a raw material. Sulfur is reduced as a by-product of the processing of natural gas and some other industrial gases (generator gas, oil refining gas). Such gases always contain some amount of sulfur compounds. Burning natural gas that is not purified from sulfur will lead to environmental pollution with sulfur oxides. Therefore, sulfur compounds are usually first removed in the form of hydrogen sulfide, which is then partially burned to SO2, after which a mixture of hydrogen sulfide and sulfur dioxide reacts on a bauxite layer at 270-300 ºC, turning as a result of this interaction into S and H2O. The sulfur obtained in this way is called “gas”. In addition to “gas”, native sulfur can be used as a raw material.
Sulfur as a raw material for the production of sulfuric acid has a number of advantages. Firstly, unlike sulfur pyrite, it contains almost no impurities that could represent catalytic poisons at the stage of contact oxidation of sulfur dioxide, for example, arsenic compounds. Secondly, when burning it, no solid or other waste is generated that would require storage or the search for methods for their further processing (when firing pyrite, 1 ton of initial pyrite produces almost the same amount of solid waste - cinder). Thirdly, sulfur is much cheaper to transport than pyrite, since it is a concentrated raw material.
Let's consider a “short” scheme for producing sulfuric acid from sulfur using the DCDA method (Fig. 2).
Rice. 2. Scheme for the production of sulfuric acid from sulfur using the double contact and double absorption method:
Sulfur burning furnace; 2 - waste heat boiler; 3 - economizer 4 - starting furnace: 5. 6 - heat exchangers of the starting furnace. 7 - contact apparatus: 8 - heat exchangers 9 - drying tower. 10, 11 - first and second monohydrate absorbers. 12 - acid collectors: 13 - exhaust pipe.
Molten sulfur is passed through mesh filters to remove possible mechanical impurities (sulfur melts at a temperature slightly above 100 ºС, so this method of purification is the simplest) and sent to furnace 1, into which air, previously dried with production sulfuric acid, is supplied as an oxidizing agent. in the drying tower 9. The roasting gas leaving the furnace is cooled in the recovery boiler 2 from 1100-1200 ºС to 440-450 ºС and is sent at this temperature, equal to the ignition temperature of industrial catalysts based on vanadium pentoxide, to the first layer of the shelf-contact apparatus 7 .
The temperature regime necessary to bring the operating line of the process closer to the line of optimal temperatures is regulated by passing streams of partially reacted calcining gas through heat exchangers 8, where it is cooled by heated gas streams after absorption (or dried air). After the third stage of contacting, the roasting gas is cooled in heat exchangers 8 and sent to an intermediate monohydrate absorber 10, irrigated with sulfuric acid circulating through the acid collector 12 with a concentration close to 98.3%. After extraction of sulfur trioxide in the absorber 10 and the resulting deviation from the almost achieved equilibrium, the gas is again heated to the ignition temperature in the heat exchangers 8 and sent to the fourth contacting stage.
In this scheme, to cool the gas after the fourth stage and additionally mix the equilibrium, part of the dried air is added to it. The gases reacted in the contact apparatus are passed through an economizer 3 for cooling and sent to the final 11 monohydrate absorber 11, from which gases not containing sulfur oxides are emitted through the exhaust pipe 13 into the atmosphere.
To start the installation (bringing it to a given technological, in particular temperature, mode), a starting furnace 4 and starting furnace heat exchangers 5 and 6 are provided. These devices are turned off after the installation is brought into operating mode.
3 Waste in sulfuric acid technology and methods of their disposal
During the production of sulfuric acid, significant amounts of sulfur oxides are released into the atmospheric air due to leaky equipment and incomplete conversion of sulfur dioxide into sulfuric anhydride. For example, with single contacting, the degree of conversion of SO2 into SO3 reaches 98% and the content of sulfur dioxide in the exhaust gases exceeds the permissible emission standards into the atmosphere by 5 or more times. Therefore, special waste gas purification plants are provided for such systems. The production of sulfuric acid by the double contacting method provides a conversion of up to 99.8%, while SO2 emissions into the atmosphere are reduced by 2 - 3 times compared to single-stage contacting and no additional gas purification is required. System productivity increases by 20-25%, and the raw material utilization rate increases.
Fugitive emissions of sulfuric acid azrosols from oleum plants range from 0.5 to 5 kg/t of finished product.
To purify exhaust gases from sulfuric acid production, the most widely used ammonia methods are: ammonia-sulfate with the production of commercial ammonium sulfate or its solutions and ammonia-cyclic with the production of 100% sulfur dioxide and commercial ammonium bisulfite. These methods of gas purification make it possible to utilize sulfur dioxide and at the same time obtain valuable products. Thus, the production of sulfuric acid is gradually becoming waste-free. Currently, air pollutants are usually captured using one of the following methods:
· Process modification to prevent or minimize the formation of a contaminant product.
· Installation of new, more efficient devices.
· Electric precipitators, cyclones, washing towers, etc.
· Use of chemical or physical processes, such as adsorption, absorption, afterburning, double contact, catalytic neutralization, etc.
· Design solutions such as double rather than single valves and closed valve systems that capture emissions.
· The design of the installation must ensure reliable and safe operation of the devices, the possibility of inspection and cleaning, washing, purging and repair, as well as carrying out the necessary tests.
· Pipelines, cylinders, tanks are painted in colors corresponding to their contents and provided with an inscription with the name of the substance being stored or transported. To monitor the sulfuric acid production process, automatic control means are installed.
When sulfur dioxide is produced from sulfur pyrite, pyrite cinder is formed. Pyrite cinders consist mainly of iron (40-63%) with small admixtures of sulfur (1-2%), copper (0.33-0.47%), zinc (0.42-1.35%), lead ( 0.32-0.58%), precious (10-20 g/t) and other metals.
The gas leaving the kiln is contaminated with cinder dust and other impurities. The concentration of dust in sulfur dioxide, depending on the design of the furnaces, the quality and degree of grinding of the raw materials, ranges from 1 to 200 g/m3. The volume of roasting gases is hundreds of thousands of cubic meters per day. Before processing, these gases are purified in cyclones and dry (agar) electrostatic precipitators to a residual dust content of about 0.1 g/m3. Furnace gases are subjected to additional purification by sequential washing with cooled 60-75% (in hollow towers) and 25-40% (in packed towers) sulfuric acid, trapping the resulting mist in wet electrostatic precipitators. The process of additional purification of furnace gases from dust is accompanied by the formation of sludge that accumulates in the washing department equipment and wet electrostatic precipitators.
Thus, solid waste from the production of sulfuric acid from sulfur pyrites are pyrite cinders, dust from cyclones and dry electrostatic precipitators, sludge from washing towers collected in settling tanks, collectors and acid refrigerators, and sludge from wet electrostatic precipitators.
When firing sulfur pyrite, waste pyrite cinders make up ~70% of the mass of pyrite. For 1 ton of acid produced, the yield of cinder in the best case is 0.55 tons. Since the raw material for the production of sulfuric acid, along with sulfur pyrite mined specifically for this purpose, is waste generated during the enrichment of sulfide ores by the flotation method and waste generated during enrichment hard coals, then three types of pyrite cinders are distinguished (cinders from pyrites, cinders from flotation tailings of sulfide ore enrichment, carbonaceous cinders), which differ significantly from each other both in chemical composition and in physical characteristics. Cinders of the first two types are distinguished by a significant content of copper, zinc, silver, gold and other metals.
Recycling of pyrite cinders is possible in several directions: for the extraction of non-ferrous metals and the production of iron and steel, in the cement and glass industries, in agriculture, etc.
4 Maximum permissible concentrations of gases, vapors and dust in the production of sulfuric acid
Substances |
In the air of the working area of industrial premises, mg/m3 |
In the atmospheric air of populated areas |
|
|
|
maximum single dose, mg/m3 |
average daily, mg/m3 |
Mineral and plant dust, free of SiO2 and toxic substances |
|||
Arsenic and arsenous anhydrides |
|||
Arsenic hydrogen |
|||
Nitrogen oxides (in terms of N2O3) |
|||
Carbon monoxide |
|||
Dust of cement, clay, minerals and their mixtures, not containing free SiO2 |
|||
Vanadium pentoxide dust |
|||
Mercury metal |
|||
Lead and its inorganic compounds |
|||
Selenium amorphous |
|||
Selenous anhydride |
|||
Sulfuric acid, sulfuric anhydride |
|||
Sulfur dioxide |
|||
Hydrogen sulfide |
|||
Phosphorus hydrogen |
|||
Hydrogen fluoride |
|||
Hydrogen chloride and hydrochloric acid (in terms of HC1) |
MAIN EQUIPMENT DESIGN
In absorbers, sulfuric acid extracts only sulfur trioxide from the gas mixture; the rest of the gas, after passing through the absorbers, is removed into the atmosphere. Typically, SO3 is absorbed in two series-connected absorbers: in the first - oleum and in the second - monohydrate.
The main indicator of the operation of the absorption department is the completeness of SO3 absorption; at the optimal mode of the monohydrate absorber, the exhaust gases are almost transparent, they contain only traces of sulfuric acid. When the acid concentration irrigating the monohydrate absorber is less than or more than 98.3% H2 SO4, fog is formed and the exhaust gases become visible. In a monohydrate absorber, fog also forms at high gas humidity. Typically, 0.01% water vapor remains in the gas after drying towers. Since the gas after the contact apparatus contains a large amount of SO3, when the gas is cooled, water vapor is completely converted into H2SO4 vapor, the concentration of which is also 0.01%, or 0.437 g/m3.
Sulfuric acid vapor condenses on the surface of the absorber nozzle. At a very low temperature of the irrigating acid or at high gas humidity (the content of sulfuric acid in the gas is more than 0.437 g/m3), part of the sulfuric acid vapor condenses in the volume to form fog, which is not deposited in the absorbers and is released into the atmosphere.
When producing commercial products in the form of technical contact acid, it is usually removed from drying towers. To do this, in one of the drying towers, an acid concentration is maintained that meets the standard requirements for contact technical sulfuric acid, and as it accumulates, it is transferred from the collection to the warehouse. In such cases, significantly more heat is generated in the absorption section (where dilution occurs) than in oleum release, since the monohydrate has to be diluted with water.
1
Oleum absorber
Rice. 3 Design of oleum absorber
Steel shell; 2 - hatches; 3 - guard on the lid; 4 - pipe for supplying acid; 5 - pressure tank; 6 - rod for hanging slabs; 7 - steel plate with cups for distributing acid; 8 - nozzle (from the bottom of the row of rings 150x150, 120X120, 100x100, 80X80 mm, from the top there are 143 rows of rings 50x50 mm); 9 - grate; 10 - stand (steel pipe); 11 - steel mesh with acid-resistant coating: 12 - bottom (acid-resistant brick); 13 - support beams; 14 - gas box.
In old factories, the absorber walls are lined with acid-resistant bricks, and the grate is mounted from andesite or other acid-resistant slabs. In new contact plants, the steel walls of the oleum absorber are not lined, and the grate is assembled from steel beams.
To distribute acid evenly over the absorber nozzle, various devices and devices are used - steel plates into which steel or porcelain tubes are inserted, distribution chutes, sprayers, etc. At new contact plants, steel acid distributors are installed, similar in design to devices for distributing drying acid. Since even to produce all products in the form of oleum, only 1/3 of the sulfur trioxide must be absorbed in the oleum absorber, the contact surface of the gas with the irrigating oleum in it can be small, as a result of which oleum absorbers without a nozzle are installed in some plants. The necessary contact surface between gas and liquid is created by spraying oleum.
The size of the oleum absorber and the amount of oleum supplied for irrigation depends on the performance of the sulfuric acid system. Typically, 1 t/h of product requires a packing surface in the absorber from 600 to 1000 m2 with a gas velocity in the packing of up to 1 m/s and an irrigation density of 10-12 m3/m2 of the cross-section of the oleum absorber.
2 Monohydrate absorber
The monohydrate absorber is irrigated with 98.3% sulfuric acid. In the absorber, the acid absorbs SO3 and its concentration increases. In the monohydrate collector, the acid is diluted with water or drying acid to the initial concentration and again supplied through the refrigerator to irrigate the monohydrate absorber; Irrigation density is about 20m3/(m2*h).
Rice. 4 Design of monohydrate absorber
Steel shell: 2 - acid-resistant brick; 3 - asbestos; 4 - hatches; 5 - rods for hanging the plate; 6 - pressure tank; 7 - acid supply pipe; 8 - guard on the lid; 9 - cover; 10 - acid distributor on the stove; 11 - viewing window; 12 - nozzle (from below there are two rows of rings 150 X 150. 120x 120. 100x100 80X 80mm, above 144 rows of rings 60X 50 mm, on top of rings 80X80 mm in bulk); 13 - gas box; 14 - steel support beam; 15 - support structure with brick arches; 16 - brick grate.
In some installations, the oleum absorber is connected to the monohydrate absorber in a shunt. In this case, the gas after the anhydride cooler is divided into two streams, one of which is sent directly to the monohydrate absorber, and the second first enters the oleum absorber, and from it to the monohydrate one. This scheme allows the oleum absorber to be put into operation only in cases where it is necessary to release oleum.
A different design of the absorption tower is proposed, which includes (Fig. 5): a housing lined with acid-resistant brick (1), a tangentially made inlet pipe for introducing a gas or air mixture (2), a cylindrical gas distribution grid lined with acid-resistant brick (3), which has through channels of different lengths for the passage of gas at each level. On the gas distribution grid, a cylindrical body of the same diameter is lined with acid-resistant brick (4). The tower body is filled with a nozzle (5) and equipped with an acid distribution device (6).
The absorption tower works as follows:
The gas mixture or air enters through the tangentially made inlet pipe (2) into the annular space between the housing (1) and the internal cylindrical housing lined with acid-resistant bricks (4) on the gas distribution grid (3), is distributed along the entire perimeter of the annular space and flows evenly through the gas channels of the gas distribution grid to the nozzle of the absorption tower (5), on which heat and mass transfer processes occur. The nozzle is irrigated with concentrated sulfuric acid through acid distribution devices (6)
For system power
The schemes of absorption departments at factories differ little from each other, and the technological regimes used are also similar. Below are approximate standards for the technological regime of the absorption department at one of the contact plants:
Temperature at the absorber outlet, °C, not more than oleum................................................... ........................................................ ................. 60
monohydrate........................................................ ........................................... 60
Concentration of irrigating acid in the absorber
in oleum, % SO3 (free).................................................. ...........................20±1
in monohydrate, % H2SO4.................................... ............... 98.6±0.2
Degree of absorption, %, not less............................................... ............ 99.95
3 Technological characteristics of absorbers
Plant productivity, t/h
H2S04 ………………………………………………………………………………….10
Degree of conversion x……………………………………………………0.98 Completeness of SO3 absorption
in the oleum absorber y………………………………………………………….0.5
total z………………………………………………………………..0.9995
Concentration
oleum irrigating the oleum absorber Co, % SO3(free) ...20
monohydrate cm, % H2SO4……………………………98
drying acid Sp, % H2SO4 ………………………93
Roasting gas consumption, m3/h………………………………………………………. 26820
including:
so2……………………………………………………………………………… 2350
O2 ……………………………………………………………………………….2220
N2 …………………………………………………………………………………... 21460
H2O vapors………………………………………………………...……660
SO3…………………………………………………………………………………130
Barometric pressure P, Pa……………………………..1.01*105
Vacuum in front of the drying tower Pp, Pa………………………,9*103
Gas temperature at the inlet to the drying tower, °C………………….32
Water vapor pressure in this gas РН2O, Pa……………….4.75*103
TECHNICAL AND ECONOMIC INDICATORS OF SULFURIC ACID TECHNOLOGY
The cost of sulfuric acid significantly depends on the type of raw material being processed, since the cost of sulfur in different raw materials is not the same. For example, the cost of 1 ton of sulfur in pyrites is 2 times lower than in natural sulfur; the cost of sulfur in waste gases from the metallurgical industry is not taken into account at all.
The influence of the type of raw material on the cost is also reflected in the fact that the technological scheme and its hardware design are different when working with different raw materials. Thus, when using natural sulfur, there is no need for gas washing, and when burning hydrogen sulfide, gas washing and drying are not required, which reduces the cost of processing raw materials. The cost of sulfuric acid also depends on many other factors: the distance of the sulfuric acid plant from sources of raw materials, the cost of water, electricity, etc.
With an increase in the productivity of the sulfuric acid system, the cost of production decreases, since this reduces depreciation costs, increases labor productivity, reduces the cost of maintaining equipment, etc. The cost of sulfuric acid also decreases with an increase in the intensity of the equipment.
An important indicator of the sulfuric acid production process is the cost of processing raw materials, which includes all costs except the cost of raw materials. The cost of processing is continuously decreasing as the technological scheme of production is improved, its hardware design is improved, consumption coefficients are reduced, system productivity is increased, etc. The cost of processing is the main indicator characterizing the technical equipment and organization of production.
Table 8. Average consumption coefficients in the production of contact sulfuric acid depending on the type of raw material used (per 1 kg of H2S04)
Table 9. Consumption coefficients for the production of 1 ton of sulfuric acid from pure sulfur using the DK-DA method
CONCLUSIONS
This abstract examined the physical and chemical properties of sulfuric acid. The main areas of its application have been studied. Existing methods for producing acid are given. It has been revealed that the most effective method for producing sulfuric acid is the method of double contact and double absorption. The necessary reference data is provided. When producing roasting gas by burning sulfur, there is no need to remove impurities, unlike burning iron pyrites. At this time, the development of effective catalysts for the production of sulfur trioxide with a maximum degree of conversion continues, as well as the development of installations for the production of oleum in order to prevent emissions that do not comply with MPC and MPE standards. On the other hand, regardless of the type of sulfur-containing raw material, it is advisable to use acid production waste in other industries (for example, pyrite cinders in metallurgy). As reserves of sulfur and pyrite are depleted, obtaining raw materials for acid from waste gases also solves an environmental problem. Thus, sulfuric acid technology strives for waste-free production.
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