CS195660B2 - Process for preparing sulphuric acid especially for the production of phosphorous fertilizers - Google Patents

Abstract

Prodn. of H2SO4, esp. for phosphate fertiliser prodn., comprises passing a mixt. contg. SO2, O2 and opt. other neutral gases through an aq. soln. contg. ferrous and feric cpds. as catalysts, at Fe2; Fe3+ mole ratio 0.005-0.1 and elevated temp. The flow of gas causes intense mixing. The soln. can opt. contain H2SO4. Used for making relatively dilute acid from SO2-contg. off gases of various industrial processes, including those contg. very little SO2. The catalyst gives high reaction rates and yields. The Fe present in the acid produced prevents clumping of fertiliser granules and also provides a valuable trace nutrient.

Description

The invention relates to a process for the production of sulfuric acid, in particular for the production of phosphorous fertilizers.

In all known sulfuric acid recovery processes, sulfur dioxide is used as a semi-product.

Further processing into sulfur trioxide requires catalysts as oxidants. Accordingly, the most important issue in the production of sulfuric acid is the choice of a low-cost, stable catalyst poison, providing high production yields and technical speed over the range of sulfur dioxide concentrations used, etc.

In addition to the nitrogen monoxides used in the tower process, finely divided platinum, ferric oxide, vanadium, chromium-strontium and other catalysts are known catalysts used in the production of sulfuric acid by the high temperature catalytic process.

With good results, they are used on an industrial scale, with the sulfuric acid produced by the tower system having a concentration of about 80% and the acid produced by the catalytic process which is generally world-wide. has a concentration of 98%. However, there is a great need for weakly concentrated sulfuric acid in industry. This need is largely met by diluting the high concentration of sulfuric acid produced in the factory with water, but this requires the use of additional corrosion protection equipment from dilute aqueous sulfuric acid solutions.

Prior art processes for the preparation of a slightly concentrated, 30% non-permeable sulfuric acid concentration, for example, result from the reaction of gases containing sulfur dioxide and oxygen with an aqueous solution of fine clay minerals and 5% iron (II) sulfate catalyst. have not found widespread use, since production according to this process due to very slow oxidation requires the use of expensive large equipment. This method, according to research Bretšnajdra (Przemysl Čhemiczny No. 6, 37, 1958) can accelerate by increasing the gas-liquid contact area, i.e. by conducting the oxidation of sulfur dioxide in the dynamic foam layer, wherein the amount of ferrous sulfate used as catalyst for this reaction is relatively large, and moreover, the process places high demands on the purity of the sulfur dioxide-containing gases if sufficient profitability is to be achieved.

It has been shown that the process for the production of acid 195680

r.ov.é. by intensive flow of gas mixtures containing sulfur dioxide, oxygen and optionally other neutral gases through the catalyst-containing aqueous solution can become economical in view of the high process speed and the high reaction yield of said sulfur dioxide by accurately determining the quality and quantity of catalysts used. This rate can also be achieved in the presence of impurities in the gaseous mixture supplied with sulfur dioxide and oxygen.

The aforementioned disadvantages are overcome by the sulfuric acid production process, particularly for the production of phosphorous fertilizers, by the intensive flow of sulfur dioxide mixed with oxygen and optionally other neutral gases, an aqueous catalyst solution optionally containing sulfuric acid, at elevated temperature according to the invention. characterized in that ferric iron compounds are used as the catalyst for the oxidation of sulfur dioxide in a molar ratio of Fe ⁺² : Fe ^{+3 in the} range of 0.005 - -0.1.

According to the invention, sulphates and sulphites, carbonates, hydroxides and other iron compounds which are soluble under reaction conditions, in particular sulphates, are used as ferrous iron compounds.

The process is carried out at a constant gas flow rate of 0.8-4.5 m / s, at a temperature of 40-85 ° C, either periodically or continuously.

Sulfur dioxide can pass from waste gases of chemical, energy, petrochemical and metallurgical production mixed with other gases. In addition to sulfur dioxide and oxygen, this mixture may also contain neutral gases such as N 2, SO 3, CO, CO 2, CO 2, H 2 O and others. . '

The use of sulfuric acid produced by the process according to the invention is of particular importance in those branches of industry in which concentrated sulfuric acid is not required. This saves a substantial part of the important raw material.

The sulfuric acid produced by the process of the invention can be used either alone or for diluting concentrated sulfuric acid.

The sulfuric acid produced by the process according to the invention finds particular use in the production of phosphorous hydrocarbons because of its content of trace amounts of iron ions originating from the catalyst used.

As is known, the water-insoluble calcium phosphates contained in minerals, such as apatite and phosphite, are treated with sulfuric acid at an average concentration of 62-70%, thereby converting the insoluble phosphates into a plant-assimilable form. In the production of phosphorous fertilizers, before starting the production process, the raw minerals are first ground finely, for example in a ball mill, and then mixed in a mixer with sulfuric acid, the concentration of which is adjusted by diluting the concentrated sulfuric acid with water; .

It has been shown that by replacing the water by diluting the concentrated sulfuric acid with the sulfuric acid produced by the process according to the invention, the quality of the phosphorus fertilizer is substantially improved.

The addition of iron ions, introduced together with the sulfuric acid solution, counteracts the lumps of fertilizer granules and is a valuable microelement for plants.

A further advantage of the process for the production of sulfuric acid according to the invention is that it is possible to use the gas 4 with a very low concentration of sulfur dioxide, which would otherwise not be used in other known processes for the production of sulfuric acid; economic.

In this context, the unreacted plants leaving the gases after the sulfuric acid production by the process according to the invention have a substantially lower concentration of sulfur dioxide than the waste gases from, for example, absorption columns, a contact process for the production of sulfuric acid. This is of great importance for protection: the environment. .

The process according to the invention is explained in more detail in the examples below.

- ': ^r · ^J i Example <<>'

Above 13.1 liters of aqueous solution containing

1.5% sulfuric acid and 1.4% of iron as ferrous sulfate and ferric at a ratio of Fe ⁺² Fe ⁺³ 0.04 at 73 ° C at a constant speed of 185 EGM passed through a mixture containing 0.58% SO2, 3 16% O2. 6% CO2, 0.1% CO and 85.15% N2. When the sulfuric acid concentration rises to

5.5 percent, which corresponds to the production of 0.76 kg of sulfuric acid.

Example 2

Tanks with an initial solution of 1.5 m ³ to 0.6% of Fe as sulfate in a ratio of Fe + 2 _Fe + 3 _e 9.03 at 83 ° C, constant rate of 8800 Nm ³ / h 0 lead-containing gases, 36% SO2, 9.8% O2, 0.04% SO3, 9% H2O vapor and 80.80% N2. The solution is continuously fed into the tank at a rate of 1000 l / h and removed from the tank. The yield is 1100 kilograms of 14.5% sulfuric acid with 0.6% iron per hour.

Example 3

In a multistage absorber operating at 80 ° C, 10 tonnes of 8% sulfuric acid with an iron content of 0.38% were produced in 5 hours using the gas mixture as in Example 1 and a catalyst with a ratio of Fe ⁺² : Fe ⁺³ 0.1 . The resulting acid is diluted with concentrated sulfuric acid and then treated with Morokko phosphorous containing 34.5% phosphorus pentoxide, first ground in a manner known per se to a grain size corresponding to 20% of the residual 195860 kcal on a sieve of 1600 ок / cm ² . 82.5 tons of dust superphosphate, 2.25 tons of dust superphosphate from the absorber-derived acid are obtained, thereby increasing production by 2.8% / s while saving an equivalent amount of concentrated sulfuric acid, the so-called monohydrate.

SUBJECT

Claims (1)

SUBJECT A process for the production of sulfuric acid, in particular for the production of phosphorous fertilizers, by an intensive flow of sulfur dioxide mixed with oxygen and optionally other neutral gases, an aqueous catalyst solution optionally containing sulfuric acid at elevated temperature, characterized in that iron is used as catalyst. ferric compounds having a molar ratio of Fe ⁺² : Fe ⁺³ in the range of 0.005 to 0.1. Sevsrógrafia, n. P., Žávod 7, Most