PROCEDE D'OXYDATION DE L'HYDROGENE SULFURE CONTENU DANS L'ACIDE MINERAL

PROCESS FOR OXIDIZING HYDROGEN SULFIDE CONTAINED IN MINERAL ACID

Abrégé anglais

PROCESS FOR OXIDIZING HYDROGEN SULFIDE CONTAINED IN
MINERAL ACID
ABSTRACT OF THE DISCLOSURE
Hydrogen sulfide contained in mineral acid is
oxidized. To this end, a vanadium content of at least 10
ppm is established in the mineral acid prior to adding
hydrogen peroxide.

Revendications

WE CLAIM
1. A process for oxidizing hydrogen sulfide contained in
mineral acid by means of hydrogen peroxide which com-
prises initially establishing in the mineral acid a
vanadium content of at least 10 ppm and then adding
the hydrogen peroxide.
2. The process as claimed in claim 1, wherein a vanadium
content of up to 100 ppm is established.
3. The process as claimed in claim 1, wherein a vanadium
content of up to 200 ppm is established.
4. The process as claimed in claim 1, wherein the reac-
tion mixture is allowed to stand over a period of 10
to 30 minutes.
5. The process as claimed in claim 1, wherein the mine-
ral acid is admixed with 4 to 20 mols H2O2 per mol
H2S.
6. The process as claimed in claim 5, wherein the mine-
ral acid is admixed with 5 to 10 mols H2O2 per mol
H2S.

Description

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This invention relates to a process for oxidizing hy-
drogen sulfide contained in mineral acid by means of hy-
drogen peroxide.
It has been described that hydrogen sulfide can be
reacted in a neutral or alkaline solution with hydrogen
peroxide with formation of sulfate and thiosulfate ions
(cf. KIRK-OTHMER: "Encyclopedia of Chemical Technology",
3rd edition, volume 22, 1933, page 116). It has also been
described that the oxidation behaviour of hydrogen per-
oxide with respect to hydrogen sulfide in a mineral acid,such as hydrochloric acid, sulfuric acid or phosphoric
acid, is not uniform; depending on the particular acid and
its concentration, the reaction occurs but incompletely,
at low reaction velocity or even fails to take place (cf.
"Gmelins Handbuch der Anorganischen Chemie", 8th edition,
system number 9, "Schwefe].", part 3, issue 1, 1953, page
94; VDI-Richtlinie No. 3486, sheet 1, 1979, page 3).
It is also possible for hydrogen sulfide contained in
mineral acid to be expelled by evaporating the mineral
acid or blowing out with air (cf. WINNACKER-KUCHLER:
"Chemische Technologie", volume 2, Anorganische Technolo-
gie I, 4th edition, 1982, page 219; "Ullmanns Enzyklopadie
der technischen Chemie", 4th edition, volume 18, 1979,
page 313). In this case, however vaporous matter and off
gas containing hydrogen sulfide are obtained for which it
is invariably necessary to be worked up.

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It is therefore highly desirable to have a procass
for oxidizing hydrogen sulfide contained in mineral acid
with the aid of hydrogen peroxide, permitting the hydrogen
sulfide to be oxidized quantitatively within short reac-
tion periods, independently from the concentration of themineral acid and the mineral acid to be freed from it. To
this end, the invention provides for a vanadium content of
at least 10 ppm to be established in the mineral acid
prior to admixing it with hydrogen peroxide.
Further preferred and optional features of the inven-
tion provide:
a) for a vanadium content of up to 200 ppm, preferably
of up to 100 ppm, to be established;
b) for the reaction mixture to be allowed to stand over
a period of 10 to 30 minutes;
c) for the mineral acid to be admixed with 4 to 20,
preferably 5 to 10 mols H202 per mol H2S.
In the process of this invention, sulfate ions and
elementary sulfur are obtained as the oxidation products
of the sulfide ion. Despite the fact that the sulfur is
obtained in the form of fine-particulate material, it is
possible for it to be separated from the mineral acid by
pressure or suction filtration.
The process of this invention occurs at a satisfacto-
ry velocity already at room temperature; it is however
advantageous for it to be carried out at a temperature of
from 30 - 60C.
The following Examples illustrate the invention which
is naturally not limited thereto:

~3~1t58~3
Example 1 (comparative Example)
Chemically pure phosphoric acid (40 % H3P04) contain-
ing 350 ppm sulfide was admixed at room temperature with 6
mols H202 per mol sulfide, while stirring. Stirring was
continued for a period of 20 minutes, and 21 % of the hy-
drogen sulfide contained in the phosphoric acid was found
to have been oxidized.
Example Z (invention)
The procedure of Example 1 was repeated with that mo-
dification however that a vanadium content of 10 ppm wasestablished in the phosphoric acid prior to admixing it
with H202. Aftar a reaction period of 15 minutes, the
phosphoric acid was odorless. Analysis indicateq that 100
% of the sulfide had been oxidized.
Example 3 (invention)
Wet-process phosphoric acid (40 % H3P04) containing
630 ppm sulfide and 100 ppm vanadium was admixed at 40C
with 10 mol Hz02 per mol sulfide, and the whole was
stirred for 20 minutes. After that time, 100 % of the hy-
drogen sulfide contained in the wet-process phosphoric
acid was found to have been oxidized.
Example 4 ~invention)
Wet-process phosphoric acid (70 % H3Pû4) containing
85 pprn sulfide and 30 ppm vanadium was admixed with 8 mol
H202 per mol sulfide, and the whole was stirred for 15 mi-
nutes at 60C. After that time, 100 % of the hydrogen sul-
fide contained in the phosphoric acid was found to have
been oxidized.

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Example 5 (comparative Example)
Sulfuric acid (10 % strength) containing 290 ppm sul-
fide was admixed with 10 mols H202 per mol sulfide and the
whole was stirred for 20 minutes at room temperature.
After that time, the sulfuric acid still had the distinct
smell of hydrogen sulfide; only 9 % of the hydrogen sul-
fide contained in it was found to have been oxidized.
Example 6 (invention)
The procedure of Example 5 was repeated with that mo-
dification however that a vanadium content of 100 ppm wasestablished in the sulfuric acid prior to admixing it with
H202. After a reaction period of 15 minutes, the sulfuric
acid was odorless. Analysis indicated that 100 % of the
sulfide had been oxidized.
Example 7 (comparative Example)
Hydrochloric acid (5 % strength) containing 340 ppm
sulfide was admixed with 10 mol H202 per mol sulfide and
stirred for 20 minutes at room te~lperature. After that
time, 48 % of the hydrogen sulfide contained in the hydro-
chloric acid was found to have been oxidized.
Example 8 (invention)
The procedure of Example 7 was repeated with thatmodification however that a vanadium content of 10 ppm was
established in the hydrochloric acid prior to admixing it
with H202. After stirring for 20 minutes at room tempera-
ture, 100 % of the hydrogen sulfide contained in the hy-
drochloric acid was found to have been oxidized.
The results of the above Examples are summarized in
the following Table.

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