The invention relates to a process for concentrating diluted sulfuric acid (10) which may comprise at least one nitroaromatic compound and/or nitric acid as impurities, comprising: (a) feeding the diluted sulfuric acid (10) into a first stage (1) in which low boilers are removed by evaporation and/or stripping to obtain a first concentrated sulfuric acid (12); (b) optionally feeding the first concentrated sulfuric acid (12) into a second evaporation stage (2) to obtain a second concentrated sulfuric acid (14); (c) feeding the second concentrated sulfuric (14) acid into a third evaporation stage (3) if step (b) is carried out, or feeding the first concentrated sulfuric acid (12) into the third evaporation stage (3) if step (b) is not carried out, to obtain concentrated sulfuric acid (16) as product, wherein an oxidizing agent (17) and/or a precursor of an oxidizing agent is fed into the third evaporation stage (3).

The invention relates to a process for concentrating diluted sulfuric acid (10) which may comprise at least one nitroaromatic compound and/or nitric acid as impurities, comprising: (a) feeding the diluted sulfuric acid (10) into a first stage (1) in which low boilers are removed by evaporation and/or stripping to obtain a first concentrated sulfuric acid (12); (b) optionally feeding the first concentrated sulfuric acid (12) into a second evaporation stage (2) to obtain a second concentrated sulfuric acid (14); (c) feeding the second concentrated sulfuric (14) acid into a third evaporation stage (3) if step (b) is carried out, or feeding the first concentrated sulfuric acid (12) into the third evaporation stage (3) if step (b) is not carried out, to obtain concentrated sulfuric acid (16) as product, wherein an oxidizing agent (17) and/or a precursor of an oxidizing agent is fed into the third evaporation stage (3).

The present invention concerns a process for the reduction of content of carboxylic acids and derivatives thereof in oleum, disulfuric acid or concentrated sulfuric acid. The invention further concerns a process for the manufacture of carboxylic acid anhydrides comprising the process for the reduction of content of carboxylic acids and derivatives thereof from oleum, disulfuric acid or concentrated sulfuric acid.

Sulfur trioxide is produced from a feed stream comprising sulfur-containing compounds and dissolved metals, such as alkali metals, in a plant comprising an incineration furnace, a waste heat boiler, a dilution air heater, a dust removal absorber and an SO.sub.2 converter. The plant may further comprise a sulfuric acid condenser for the production of sulfuric acid.

Sulfur trioxide is produced from a feed stream comprising sulfur-containing compounds and dissolved metals, such as alkali metals, in a plant comprising an incineration furnace, a waste heat boiler, a dilution air heater, a dust removal absorber and an SO.sub.2 converter. The plant may further comprise a sulfuric acid condenser for the production of sulfuric acid.

In a process for increasing the sulfuric acid concentration of 90-98 wt % sulfuric acid, comprising stripping water from the sulfuric acid by contacting it with hot stripping media in a sulfuric acid concentrator column to increase the concentration of the acid leaving the column, the concentration of the acid is increased further by recycling a fraction of the acid, which is leaving the column, through an acid recirculation loop back to the inlet of the column, and the acid is optionally heated during its passage through the acid recirculation loop.

In a process for increasing the sulfuric acid concentration of 90-98 wt % sulfuric acid, comprising stripping water from the sulfuric acid by contacting it with hot stripping media in a sulfuric acid concentrator column to increase the concentration of the acid leaving the column, the concentration of the acid is increased further by recycling a fraction of the acid, which is leaving the column, through an acid recirculation loop back to the inlet of the column, and the acid is optionally heated during its passage through the acid recirculation loop.

A method for manufacturing high purity sulfuric acid is provided. A mixed solution subsequently undergoes a first preheating step, a second preheating step, a distilling step and an evaporating step to remove peroxide, water, oxygen and insoluble impurities, so as to obtain the first gas containing sulfur trioxide, sulfuric acid and hydrogen oxide. And then, the sulfur trioxide is absorbed by a sulfuric acid solution, thereby forming the high purity sulfuric acid.

A method for manufacturing high purity sulfuric acid is provided. A mixed solution subsequently undergoes a first preheating step, a second preheating step, a distilling step and an evaporating step to remove peroxide, water, oxygen and insoluble impurities, so as to obtain the first gas containing sulfur trioxide, sulfuric acid and hydrogen oxide. And then, the sulfur trioxide is absorbed by a sulfuric acid solution, thereby forming the high purity sulfuric acid.

Sulfur trioxide is produced from a feed stream comprising sulfur-containing compounds and dissolved metals, such as alkali metals, in a plant comprising an incineration furnace, a waste heat boiler, a dilution air heater, a dust removal absorber and an SO.sub.2 converter. The plant may further comprise a sulfuric acid condenser for the production of sulfuric acid.