Process for preparing sulphuric acid from gases containing...

Details Process for preparing sulphuric acid from gases containing... Process for preparing sulphuric acid from gases containing...

1999-06-14

2003-09-30

Silverman, Stanley S. (Department: 1754)

Chemistry of inorganic compounds

Sulfur or compound thereof

Oxygen containing

C423S523000, C423S531000

Reexamination Certificate

active

06627172

ABSTRACT:

DESCRIPTION
This invention relates to a process for producing sulfuric acid from gases containing SO
3
and gaseous nitrosyl sulfuric acid by contacting with highly concentrated sulfuric acid.
BACKGROUND OF THE INVENTION
Processes for producing sulfuric acid are known. In Rompps Chemie-Lexikon, 8th edition, 1987, pages 3760 to 3764, there is described a process for producing sulfuric acid. As raw material sulfur dioxide is used, which is contacted with a catalyst and catalytically converted to SO
3
. The SO
3
discharged from the catalytic furnace is subsequently introduced into a 98% sulfuric acid, where first of all disulfuric acid (H
2
S
2
O
7
) is formed, which by adding water is converted to sulfuric acid. In this way, particularly highly concentrated sulfuric acids as well as various types of oleum can be obtained. This process, however, has the disadvantage that in the catalytic conversion of SO
2
to SO
3
, in dependence on the content of nitrogen oxide after the SO
2
production, there is also formed nitrosyl sulfuric acid, which likewise gets into the highly concentrated sulfuric acid and must be removed with a relatively great technical effort. In the DE-OS 17 92 348 there is described a process for producing sulfuric acid free from ammonia and nitrose, where it is provided to add hydrazine compounds to the sulfuric acid for the purpose of denitration. However, this is a relatively time- and cost-consuming process. The DE-195 16 303 describes a process for reducing the NO
x
content of sulfuric acid, where NO
x
is reduced with SO
2
to form N
2
, and N
2
is discharged, so that SO
2
is used for denitration. This process has the disadvantage that the nitrosyl sulfuric acid obtained in the absorption towers cannot be removed due to the high concentration of sulfuric acid.
It is the object underlying the invention to create a process for producing sulfuric acid from gases containing SO
3
and gaseous nitrosyl sulfuric acid by contacting with highly concentrated sulfuric acid, where there is no enrichment of nitrosyl sulfuric acid in the absorption towers.
SUMMARY OF THE INVENTION
The object underlying the invention is solved in that before contacting with highly concentrated sulfuric acid the gases are passed through at least one cooler and are cooled to 160 to 130° C. “Nitrosyl sulfuric acid” is understood to be the gaseous nitrosyl hydrogensulfate (NO
+
HSO
4
−
or HO
3
SONO). The concentration of the highly concentrated sulfuric acid generally lies in the range between 94 and 98%. As coolers, conventional gas coolers or heat exchangers may be used, such as shell-and-tube heat exchangers or ribbed tube-coil heat exchangers. It was surprisingly found out that the gases containing SO
3
and gaseous nitrosyl sulfuric acid can advantageously be cooled in at least one cooler, so that the nitrosyl sulfuric acid condensates out of the gases and does therefore no longer come in contact with the highly concentrated sulfuric acid in the absorption tower. The condensate containing nitrosyl sulfuric acid can advantageously be denitrated by means of the process described in DE-195 16 303.
A preferred embodiment of the invention consists in that the gases are cooled to 160 to 150° C. Advantageously, the nitrosyl sulfuric acid condensates out almost exclusively in the cooler. Since the gases containing SO
3
and gaseous nitrosyl sulfuric acid generally also contain a certain amount of steam, the gases will generally also have a content of gaseous sulfuric acid, which at lower cooler temperatures would condensate out together with the nitrosyl sulfuric acid, which is, however, not desired. But when the gases are cooled to 160 to 150° C., it is ensured that the gaseous sulfuric acid will not condensate out, but can subsequently be introduced into the absorption tower.
In accordance with a further preferred aspect of the invention it is provided that the gases are catalytically oxidized after contacting with highly concentrated sulfuric acid for the enrichment of SO
3
, are subsequently again passed through at least one cooler and are cooled to 160 to 130° C., and thereafter are again contacted with highly concentrated sulfuric acid. The advantage is that the gases which are removed from the absorption tower and contain still larger amounts of SO
2
can again be used for the production of sulfuric acid. Furthermore, the concentration of SO
2
in the pure gas is reduced.
The invention will subsequently be explained in detail and by way of example with reference to the drawing (FIG.
1
and
2
), wherein:


REFERENCES:
patent: 3525586 (1970-08-01), Drechsel et al.
patent: 3656900 (1972-04-01), Drechsel et al.
patent: 3920421 (1975-11-01), Collins
patent: 1792348 (1971-10-01), None
patent: 0191725 (1986-08-01), None

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