An Improved Process and Apparatus for the Removal of Sulphuretted Hydrogen from Gases or Gaseous Mixtures.
Year: 1896

page_text: Date of Application, 6th July, 1896
Complete Specification Left, 18th Mar., 1897-Accepted, 15th May, 1897
An Improved Process and Apparatus for the Removal of Sulphuretted
Hydrogen from Gases or Gaseous Mixtures.
I, Dr. HUGO STRACHE, of 4 Pointengasse, Vienna XVII, in the Austrian
Empire, Lecturer at the K. K. Technischen Hochschule, do hereby declare the
nature of this invention to be as follows:-
The method generally adopted for the removal of sulphuretted hydrogen from
gases (such as illuminating gas, water-gas or the like) by means of hydrated oxide
of iron (Laming's material, bog-iron-ore or the like) by the dry process, involves
a considerable amount of labour on account of the changing of the filling or
charge of the purifier and the necessary regeneration of the material, and neces-
sitates, more especially in large plants, the use of large and costly apparatus
(purifiers) which occupy a large amount of space; moreover, the changing of the
purifier-charge causes a loss of gas and consequent nuisance to the neighbourhood
by the unpleasant smell.
The present invention is designed to effect the removal of the sulphuretted
hydrogen by a wet process in scrubbers or similar gas vessels or chambers with
continuous motion.
The action of concentrated nitric acid on sulphuretted hydrogen is known; it.
decomposes it with the formation of sulphuric acid and nitrogen trioxide (N,O3),
together with small quantities of ammonia, nitrogen and sulphur, according to the
equation:
(1) 4 HNO3 + H₂ = H₂
The nitrogen trioxide combines partly with the water to form nitrous acid
according to the equation:
==
(3) N2O3 NO₂+ NO.
If it be desired to remove the sulphuretted hydrogen in this way, for every
34 parts by weight of sulphuretted bydrogen, 252 parts by weight of concentrated
nitric acid are required, which is a very large quantity, and the gases after
treatment contain nitrogen tetroxide and nitric oxide (NO).
Taking into consideration that nitrogen tetroxide (NO) dissolves in water with
the formation of nitric acid (HNOs) and nitrous acid (HNO,) according to the
equation
(4)
2 NO, + H₂O HNO3 + 3 HNO,,
that moreover nitrous acid in aqueous solution is easily decomposed into nitric
acid and nitric oxide according to the equation :
=
(5) 3 HNO, HNO, + 2 NO + H,O;
[Price 8d.]

page_text: further, that nitric acid in dilute solution sets free sulphur (S) from sulphuretted
hydrogen (H2S) with the formation of nitrous acid according to the equation:
although this decomposition is not complete and undecomposed sulphuretted
hydrogen always remains in the gas, whilst it is completely removed by concen-
trated nitric acid according to equation (1), it will be seen that, by the following
process, as favourable a utilization of the nitric acid will be obtained as according
to equation (1) alone.
Three scrubbers or similar vessels Nos. I, II and III preferably arranged one
above another, No: III being the uppermost, are filled with suitable pieces of acid-
resisting, solid material of large surface (such as pieces of glass, earthenware,
pumice or the like).
The gas to be purified enters the lowermost scrubber No. I and is there freed
from the greater part of the sulphuretted hydrogen as hereinafter described,
and passes with the undecomposed residue of sulphuretted hydrogen into
scrubber No. II..
Into this scrubber, concentrated nitric acid drops from above and removes the
remainder of the sulphuretted hydrogen according to equation (1). The sulphuric
acid formed and the aqueous solution of nitrous acid flow into the scrubber No. I.
The purified gas, mixed with the nitrogen tetroxide and nitric oxide produced,
passes into the scrubber No. III.
Water flows into the scrubber No. III from above and dissolves the nitrogen
tetroxide out of the gas and forms nitric acid and nitrous acid according to
equation (4). The purified gas, mixed with nitric oxide, passes out of the
apparatus, whilst the aqueous solution of nitric acid and nitrous acid passes into
the scrubber No. I through a direct communicating pipe or conduit and on the
way mixes with the nitrous acid from No. II.
In this manner an aqueous liquid passes into the scrubber No. I, which liquid
contains some sulphuric acid, nitric acid and nitrous acid. The last-named
decomposes into nitric acid and nitric oxide gas according to equation (5), this
passes away through Nos. II and III with the gas, while the aqueous solution in
No. I now contains principally nitric acid together with sulphuric acid and a very
small quantity of undecomposed nitrous acid. This nitric acid, according to
equation (6) effects the decomposition of the greater part of the sulphuretted
hydrogen with the separation of sulphur, so that in No. II, as above stated, only
a very small quantity of undecomposed sulphuretted hydrogen is left, therefore
also not much sulphuric acid is formed therein. The nitrous acid formed in
No. 1 according to equation (6) decomposes again immediately according to
equation (5) into nitric acid and nitric oxide gas, so that, by the continuous com-
bined operation of reactions (5) and (6), it is gradually transformed entirely into
nitric oxide gas. A small quantity of undecomposed nitrous acid runs away from
the waste or liquid outlet-pipe of scrubber No. I with water and a little sulphuric
The final result of this reaction can be shown, as regards its essential point, by
the combined equation:
acid.
2 HNO 3 HS NO SHO
-
according to which 102 parts by weight of sulphuretted hydrogen are converted
into sulphur and nitric oxide by 128. parts by weight of nitric acid, therefore the
utilization is considerably more favourable than when concentrated nitric acid is
used alone. The purified gas passing away at the gas-outlet of scrubber No. III
is, however, mixed with nitric oxide gas. This can be absorbed by water after a

page_text: suitable quantity of air or oxygen has been added thereto, according to the
following equations :
the nitric oxide with oxygen and water being converted
It is, however, more advantageous to add the requisite quantity of air or oxygen
to the gas before it enters the scrubber No. I, since the nitrous acid formed in
No. 1 is then continually reconverted into nitric acid, according to the equation:
(9) HNO, & O = HNO,
so that here the nitrous acid or nitric acid acts as an oxygen-carrier and so the
smallest quantity can decompose a very large (theoretically, an infinitely large)
quantity of sulphuretted hydrogen with separation of sulphur.
At the same time the added quantity of air can be so proportioned that not the
slightest amount of nitric oxide passes out at the gas-outlet, but it is all returned
to No. I in the form of nitrogen tetroxide or nitric acid.
The consumption of nitric acid will then depend only upon the small quantity
used for forming sulphuric acid and upon the small quantity of undecomposed
nitrous acid which runs away as above mentioned.
The sulphur separated in No. 1 partly settles on the filling material and can be
obtained therefrom directly as pure sulphur by melting it off after drying. Another
part of the sulphur is deposited from the discharged fluid in the form of porous
lumps and in this case can be removed therefrom directly.
The removal of sulphuretted hydrogen from gases can also be effected so that a
small part of the gas is allowed to pass through concentrated nitric acid, and the
nitric oxide produced according to equation (1) mixes with the main portion of
the gas with or without the addition of air or oxygen. The purification of the gas
is, however, in this case, not so rapid and complete as when the whole quantity of
gas passes through or in contact with the concentrated nitric acid, whereby the
escape of undecomposed sulphuretted hydrogen is entirely prevented.
Dated this 6th day of July 1896.
D. YOUNG & Co.,
11 & 12 Southampton Buildings, London, W.C.,
Agents for the Applicant.
An Improved Process and Apparatus for the Removal of Sulphuretted
Hydrogen from Gases or Gaseous Mixtures.
I, Dr. HUGO STRACHE, of 4 Pointengasse, Vienna XVII, in the Austrian
Empire, Lecturer at the K. K. Technischen Hochschule, do hereby declare the
nature of this invention and in what manner the same is to be performed, to be
particularly described and ascertained in and by the following statement :-
The method generally adopted for the removal of sulphuretted hydrogen from
gases (such as illuminating gas, water-gas or the like) by means of hydrated oxide
of iron (Laming's material, bog-iron-ore or the like) by the dry process, involves
a considerable amount of labour on account of the changing of the filling or charge
of the purifier and the necessary regeneration of the material, and necessitates,

page_text: more especially in large plants, the use of large and costly apparatus (purifiers)
which occupy a large amount of space; moreover, the changing of the purifier-
charge causes a loss of gas and consequently a nuisance to the neighbourhood by
the unpleasant smell.
The present invention is designed to effect the removal of the sulphuretted
hydrogen by a wet process in scrubbers or similar gas vessels or chambers with
continuous motion.
The action of concentrated nitric acid on sulphuretted 'hydrogen is known; it
decomposes it with the formation of sulphuric acid and nitrogen trioxide (N,O3),
together with small quantities of ammonia, nitrogen and sulphur, according to the
equation:
(1) 4 HNO3 + H2S = H₂SO +2 N₂O3 + 2 H₂O.
The nitrogen trioxide
(1)
4 HNO3 + H2S = H₂SO + 2 N₂O3 + 2 H₂O.
The nitrogen trioxide nembines partly with the water to form mitto
according to the equation
If it be desired to remove the sulphuretted hydrogen in this way, for every
34 parts by weight of sulphuretted hydrogen, 252 parts by weight of concentrated
nitric acid are required, which is a very large quantity, and the gases after treatment
contain nitrogen tetroxide and nitric oxide (NO).
Taking into consideration that nitrogen tetroxide (NO2) dissolves in water with
the formation of nitric acid (HNO3) and nitrous acid (HNO2) according to the
equation:
that moreover nitrous acid in aqueous solution is easily decomposed into nitric acid
and nitric oxide according to the equation:
ΠΙ
HNO3 + H2S =HNO2 + H2O + S
although this decomposition is not complete and undecomposed sulphuretted hydrogen
always remains in the gas, whilst it is completely removed by concentrated nitric
acid according to equation (1), it will be seen that, by the following process, as
favourable a utilization of the nitric acid will be obtained as according to
equation (1) alone.
Three scrubbers or similar vessels Nos. I, II and III (shown diagrammatically
in the drawing) are filled with suitable pieces of acid-resisting solid material of
large surface (such as pieces of glass, earthenware, pumice or the like).
The gas to be purified enters the lowermost scrubber I, and is there freed from
the greater part of the sulphuretted hydrogen as hereinafter described, and passes
with the undecomposed residue of sulphuretted hydrogen into scrubber No. II.
Into this scrubber concentrated nitric acid drops from above (from a) and removes
the remainder of the sulphuretted. hydrogen according to equation (1). The
sulpburic acid formed and the aqueous solution of nitrous acid flow via b into the
scrubber No. 1. The purified gas, mixed with the nitrogen tetroxide and nitric
oxide produced, passes into the scrubber No. III at c..

page_text: so that here the nitrous acid or nitric acid acts as an oxygen-carrier and so the
smallest quantity can decompose a very large (theoretically, an infinitely large)
quantity of sulphuretted hydrogen with separation of sulphur.
At the same time the added quantity of air can be so proportioned that not the
slightest amount of nitric oxide passes out at the gas outlet e, but it is all returned
to No. I in the form of nitrogen tetroxide or nitric acid.
The consumption of nitric acid will then depend only upon the small quantity
used for forming sulphuric acid and upon the small quantity of undecomposed
nitrous acid which runs away at 9 as above mentioned.
The sulphur separated in No. 1 partly settles on the filling material and can be
obtained therefrom directly as pure sulphur by melting it off after drying.

page_text: Another part of the sulphur is deposited from the discharged fluid in the form of
porous lumps and in this case can be removed therefrom directly.
The removal of sulphuretted hydrogen from gases can also be effected so that a
small part of the gas is allowed to pass through concentrated nitric acid and the
nitric oxide produced according to equation (1) mixes with the main portion of the
gas with or without the addition of air or oxygen. The purification of the gas is,
however, in this case, not so rapid and complete as when the whole quantity of gas
passes through or in contact with the concentrated nitric acid, whereby the escape
of undecomposed sulphuretted hydrogen is entirely prevented.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The removal of sulphuretted hydrogen from gases or gaseous mixtures, such
as lighting gas, water-gas, or the like, by a process in which the said gases are
treated with nitric acid, nitrous acid or oxides of nitrogen, with or without the
addition of air or oxygen.
2. A process such as is hereinbefore described, in which the gas or gaseous
mixture to be purified, with or without the admixture of air or oxygen, is first
freed from the principal part of the sulphuretted hydrogen by dilute nitric or
nitrous acid, and then from the remainder of the sulphuretted hydrogen by
concentrated nitric acid, and is subsequently washed with water to remove the
nitrogen tetroxide therefrom.
3. An apparatus for the treatment of gases or gaseous mixtures as herein before
described, consisting of three vessels I, II and III, so connected and arranged that
the gas or gaseous mixture to be purified, with or without the addition of air or
oxygen, will pass successively through them from the first up to the third, whilst
concentrated nitric acid will flow into the vessel II and water into the vessel III,
and the liquid (containing dilute nitric aud nitrous acids) running off from the
vessels II and III will be conducted into the vessel I, substantially as, and for the
purposes, herein before described.
Deted the 18th day of March 1907
D. YOUNG & Co.,
11 & 12 Southampton Buildings, London, W.C.,
Agents for the Applicant.