Abstract: A process for the thermal decomposition of metal sulphate mixtures at temperatures from 800.degree. to 1100.degree. C. under oxidizing conditions, in which the metal sulphate mixtures are mixed with roasting residue and reacted together with fuels in the decomposition reactor to form roasting residue and SO.sub.2 -containing gases from roasting wherein the roasting residue admixed with the sulphate mixture is the finely divided fraction of the resulting roasting residue which is separated from the stream of gas in an electrostatic gas purification apparatus and returned to the decomposition reactor.This procedure has an advantageous influence on the formation of coarse roasting residue and also significantly reduces the proportion of undecomposed, water soluble sulphates in the roasting residue.

Abstract: A process for the preparation of titanium dioxide by the sulphate process in which titanium raw materials are decomposed with sulphuric acid, the resulting titanyl sulphate is hydrolyzed, the waste acid is separated from the hydrolyzate and evaporated to a concentration of 60 to 70%, sulphuric acid is separated from the solid metal sulphates, and the sulphuric acid which has been concentrated by evaporation is used again for the decomposition of the titanium raw material, the improvement wherein the 60 to 70% sulphuric acid is concentrated to 70 to 80% H.sub.2 SO.sub.4 in a further evaporation stage and the concentration of a part of this sulphuric acid is raised to a concentration of 98 to 99% H.sub.2 SO.sub.4 by the absorption of SO.sub.3 and then used together with the remainder of the above-mentioned 70 to 80% sulphuric acid for the decomposition of titanium raw materials.

Abstract: A process for the purification of hot exhaust gases containing dust, sulphur dioxide and/or hydrogen chloride and/or hydrogen fluoride and having a water vapor partial pressure of at least 15 volume %, whereina) the hot exhaust gases are cooled to temperatures below 135.degree. C. by scrubbing with 60-75% sulphuric acid,b) the exhaust gases from a) are cooled to 60.degree.-80.degree. C. by contact with 5-20% sulphuric acid,c) the exhaust gases from b) are desulphurized in contact with moist active charcoal to form sulphuric acid,d) the sulphuric acid formed in c) is raised to a concentration of 5 to 20% H.sub.2 SO.sub.4 in contact with the hot exhaust gases,e) the 5 to 20% sulphuric acid formed in d) is evaporated to a concentration of 60 to 80% H.sub.2 SO.sub.4 by the heat obtained from cooling the exhaust gases of a) andf) prior to stage e) HCl and/or HF is removed from a mixture of 5 to 20% H.sub.2 SO.sub.4 from d) with 60 to 80% sulphuric acid.

Abstract: A process for the recovery of sulphuric acid from waste acids containing metal sulphates by evaporative concentration and separation of the metal sulphates from the suspension obtained by evaporation, the improvement wherein vapors leaving the evaporators together with droplets of sulphuric acid containing metal sulphates and solid metal sulphates are condensed by direct contact with cooled contaminated vapor condensate, cooling of this vapor condensate which is circulated as cooling medium is carried out in a flash evaporator and the vapors leaving the flash evaporator free from metal sulphates and sulphuric acid are directly or indirectly condensed by means of cooling agent.

Abstract: A process for the separation of metal sulphates from dilute sulphuric acid by evaporative concentration of the sulphuric acid to a concentration of from 55 to 75% by weight H.sub.2 SO.sub.4, cooling of the resulting solution or suspension and mechanically separating the solid metal sulphates and/or hydrogen sulphates, wherein an Fe(III) content of at least 0.01% by weight is ensured before the separation.

Abstract: A process for the removal of dust and sulphur dioxide from hot exhaust gases which have a low hydrogen halide content and the reheating of the purified exhaust gases, wherein(a) the hot exhaust gases are cooled to temperatures below 135.degree. C. by scrubbing with sulphuric acid,(b) sulphuric acid containing solids and dissolved metal sulphates is then separated from the exhaust gases from (a),(c) the exhaust gases from (b) are cooled to temperatures of 50.degree. to 70.degree. C. by scrubbing with 15 to 50% sulphuric acid,(d) and desulphurized with the formation of sulphuric acid,(e) and reheated to temperatures of 70.degree. to 90.degree. C. by scrubbing with 50 to 65% sulphuric acid while the sulphuric acid discharged from (c) is concentrated and(f) the sulphuric acid from stage (a) together with the solid particles contained therein is cooled with the pure sulphuric acid from (e) in heat exchangers.

Abstract: A process for heating up moist gases containing hydrogen halides comprising removing the hydrogen halides from the gases by partial condensation of the water vapor, separating out the condensate and heating up the resultant gas in indirect or recuperative heat exchangers.

Abstract: Cleaned flue gases normally accumulate as steam-saturated gases with temperatures of from 40.degree. to 55.degree. C. after wet cleaning processes for the removal of sulfur and/or nitrogen compounds. Before being let off through a stack, however, these gases have to be heated to at least 72.degree. C.This invention relates to a process for reheating flue gases after wet cleaning.

Abstract: A process for the preparation of sulphur dioxide by the thermal decomposition of metal sulphates in a fluidized bed reactor with sulphur-containing reducing agents and energy suppliers, characterized in that a mixture comprising the metal sulphates, the sulphur-containing reducing agents and 75 to 99% of the energy suppliers is fed into the fluidized bed reactors and the remainder of the energy suppliers is introduced separately into the fluidized layer of the fluidized bed reactor.

Abstract: In the production of nitrobenzene by subjecting benzene to nitration with a mixture of nitric acid and sulfuric acid, separating off the nitrobenzene formed, concentrating the sulfuric acid by evaporation and returning the concentrated sulfuric acid to the bezene nitration stage, the improvement which comprises concentrating sulfuric acid to a concentration of from 75 to 92% by evaporation in vacuo at temperatures in the range from 130.degree. to 195.degree. C. Thereby the energy per kg of water evaporated is drastically reduced compared to processes wherein the sulfuric acid is concentrated to a higher level, without a corresponding loss in efficiency or capacity.

Abstract: In the desulphurizing of SO.sub.2 - and hydrogen halide-containing flue gases by catalytically oxidizing the sulphur dioxide on moist active carbon at a temperature of from 45.degree. to 70.degree. C. with the formation of 3 to 20% dilute sulphuric acid, the improvement which comprises contacting the dilute sulphuric acid with the hot flue gases to be desulphurized so as to evaporate water resulting sulphuric acid of a concentration of from 60 to 85%, and removing by evaporation the hydrogen chloride and hydrogen fluoride dissolved in the dilute sulphuric acid. Advantageously evaporation is carried out in two scrubbing stages, the hydrogen chloride and hydrogen fluoride being removed, by vacuum evaporation or by stripping with air or flue gas, from a mixture of the dilute sulphuric acid from the second scrubbing stage with the concentrated sulphuric acid from the first scrubbing stage, the mixture having the H.sub.2 SO.sub.4 concentration of from 40 to 70%.

Abstract: In the production of dinitrotoluene by a two-stage reaction of toluene with nitric acid in the presence of sulphuric acid, wherein toluene is nitrated to mononitrotoluene in the first stage using spent acid from the second stage, and the mononitrotoluene is nitrated to dinitrotoluene in the second stage using concentrated spent acid from the first stage, the improvement which comprises concentrating spent acid under vacuum in an indirectly-heated evaporator and feeding mononitrotoluene into the superheated vapor of the evaporator.

Abstract: In the preparation of titanium dioxide comprising autothermically digestion a titanium-containing raw material with sulphuric acid to form a solid relatively easily soluble digestion cake containing titanyl sulphate, extracting metal sulphates from this cake by water or dilute sulphuric acid, separating the undissolved residues and, optionally after crystallization of iron sulphate heptahydrate, hydrolyzing the titanyl sulphate to produce titanium oxide hydrate, and calcining the titanium oxide hydrate to titanium dioxide, the improvement which comprises adding to the raw material a metal sulphate and effecting the autothermic decomposition with sulphuric acid of about 80 to 88% concentration. Advantageously the acid is obtained by mixing dilute acid with concentrated sulphuric acid or oleum, some of the dilute acid and metal sulphate coming from a by-product filter cake produced in the course of the process.

Abstract: A process for the recovery of sulfuric acid from waste sulfuric acid containing iron sulfate and from solid iron sulfate of high water content of crystallization which consists essentially of:A. concentrating waste sulfuric acid to an acid concentration of 25-55 weight percent, based upon the suspension, by removing water therefrom;B. mixing the concentrated acid of Step A with recycled concentrated sulfuric acid obtained from Step E to form a resultant acid mixture of acid concentration of 30-65 weight percent, based upon the suspension;C. adding said solid iron sulfate of high water content of crystallization to the acid mixture of Step B thereby obtaining iron sulfate of low water content of crystallization;D. separating the iron sulfate of low water content from the resultant sulfuric acid solution of Step C;E. concentrating the separated sulfuric acid solution of Step D to an acid concentration of 45-70 weight percent, based on salt-free acid, and recycling at least a portion thereof to Step B; andF.

Abstract: Spent sulphuric acid, either alongside or mixed with contaminated metal salts such as iron sulphate heptahydrate, is regenerated to fresh acid by countercurrent contact with gases from cleavage of the sulphate salts, such gases containing SO.sub.3 which effects build up of the acid concentration. The built up acid is evaporated in another stage to obtain pure acid. The metal sulphate solids are subjected to high temperature cleavage, generating SO.sub.3 which effects the previous concentration. Cleavage also produces some SO.sub.2 which is converted to SO.sub.3 by wet catalysis.