Improvements in the Purification of Coal Gas and in Obtaining Products therefrom.
Year: 1892

page_text: Date of Application, 29th Mar., 1892
Complete Specification Left, 20th Jan., 1893-Accepted, 4th Mar., 1893
PROVISIONAL SPECIFICATION.
Improvements in the Purification of Coal Gas and in Obtaining
Products therefrom.
We WILLIAM BELTON of the Gas Works Shrewsbury in the County of Salop
Civil Engineer, and GEORGE EDWARD DAVIS and ALFRED ROLAND DAVIS
both of 32 Blackfriars Street, Manchester in the County of Lancaster, Chemical
Engineers do hereby declare the nature of this invention to be as follows:-
Our invention consists in the method of washing the crude coal gas with a
solution of carbonate of soda, or of caustic soda, or a mixture of the two, in such
a manner that the impurities consisting chiefly of carbonic acid ammonia,
sulphuretted hydrogen and other sulphur compounds are removed from the gas in
such a form that the resulting compounds may be readily utilized.
Instead of employing water alone in the scrubbers as, is now generally the case
we employ a solution of carbonate of soda or of caustic soda as aforesaid or a
mixture of the two, of any convenient strength, but preferably we employ a
solution of carbonate of soda (soda-ash of commerce) of about 10° on Twaddell's
hydrometer. The liquid employed is brought into contact with the gas, both being
brought to as low a temperature as is practicable, as, the lower the temperature,
the more easily are the impurities absorbed.
The operation of arresting the impurities with the aforesaid solutions cau be
carried out in any of the washers or scrubbers at present in use where water only
is employed, and it is advantageous to employ the washers or scrubbers in a series.
of two or more, the solution being used systematically in them so that when
removed from the earlier scrubbers or washers the solution may be saturated as near-
as may be with the impurities.
The aforesaid solution charged with impurities from the crude gas can be purified
for use over again by heating it with a current of steam or in any other known
manner, the carbonic acid sulphuretted hydrogen and ammonia are evolved and the
acids of the fixed ammonia combine with the soda-base present in the liquor, the
ammonia being liberated in loose combination with carbonic acid; but the liquor is
best purified, by heating it in a still of the column form now largely employed for
the manufacture of sulphate of ammonia and the gases issuing from the still may
be passed through diluted sulphuric acid or through diluted nitric or hydrochloric
acids to retain the ammonia, thus separating it from the carbonic acid & sulphuretted
hydrogen, the latter of which may be utilized in any known manner.
As the process aforesaid is a circular one, the purifying agent being used over
& over again until exhausted, it is necessary to keep up & renew the activity of
the solution, which is apt to become weaker by the gradual accumulation of water
in the process and by the exchange of the acids of the fixed ammonia for the
carbonic acid originally combined with the soda. The activity of the solution is
kept up by evaporating the surplus water, and by adding from time to time
sufficient soda-ash or caustic soda to replace that neutralized by the fixed acids of
the ammonia.
The ammoniacal liquor from the hydraulic main may be advantageously mixed
with the washer or scrubber liquor aforesaid before heating in the still for
purification as already described, but in such case, the whole of the water so added
will have to be evaporated as surplus water.
After the liquor has been purified of its gaseous contents in the still as already
described, and the surplus water evaporated a portion is to be used over again,
after cooling, in the washers or scrubbers, while another portion is regularly treated
for the elimination of the fixed impurities such as carbolates, hyposulphites,

page_text: sulphocarbonates, sulphocyanides & other compounds. This we find is best effected
by reserving at intervals a quantity of liquor running from the still, evaporating it
to crystallizing strength & setting aside to crystallize. Fairly pure crystals of
carbonate of soda are obtained which are to be collected and dissolved in water to
the proper strength for use over again. The mother liquors from these crystals
contain the bulk of the impurities which may be sold or worked up for the
preparation of carbonates, hyposulphites, sulphocyanides, cyanides and other salts.
Dated this 28th day of March 1892.
COMPLETE SPECIFICATION.
Improvements in the Purification of Coal Gas and in Obtaining
Products therefrom.
We, WILLIAM BELTON, Civil Engineer, of the Gas Works, Shrewsbury, and
GEORGE EDWARD DAVIS and ALFRED ROLAND DAVIS, Consulting Chemical
Engineers, both of 32, Blackfriars Street, Manchester, 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:-
Our invention relates to the method of washing crude coal gas with a solution
of carbonate of soda or of caustic soda, or a mixture of the two, or their
equivalents, in such a manner that the impurities consisting chiefly of carbonic
acid, ammonia, sulphuretted hydrogen, and other sulphur compounds may be
removed and readily utilized.
Instead of employing water alone in the scrubbers, as is now generally the case,
we employ a solution of carbonate of soda, or caustic soda as aforesaid, or a
mixture of the two or equivalents of any convenient strength but preferably we
employ a solution of carbonate of soda (soda ash of commerce) of about 10° on
Twaddell's hydrometer. The liquid employed is brought into contact with the gas,
both being brought to as low a temperature as is practicable, as the lower the
temperature the more easily are the impurities absorbed by the liquid.
The operation of arresting the impurities with the aforesaid solutions can be
carried out in any of the washers or scrubbers at present in use where water only
is employed, and it is advantageous to employ the washers or scrubbers in a series
of two or more, the solution being used systematically in them, so that when
removed from the earlier scrubbers or washers the solution may be saturated as
near as may be with the impurities.
The aforesaid solution charged with impurities from the crude gas can be
purified for use over again by heating it with a current of steam, preferentially live
steam, or in any other known manner, the carbonic acid, sulphuretted hydrogen
and ammonia are evolved, and the acids of the fixed ammonia combine with the
alkali base preseut in the liquor, the ammonia being liberated in loose combination
with carbonic acid; but the liquor is best purified by heating in a still of the
column form now largely employed for the manufacture of sulphate of ammonia,
and the gases issuing from the still may be passed through diluted sulphuric acid
or nitric acid or hydrochloric acid to retain the ammonia, thus separating it from

page_text: the carbonic acid and sulphuretted hydrogen, the latter of which may be utilized
in any known manner, such for instance as that described in the Specification of
Harrison Blair No. 313 Feb. 18th 1858.
As the process aforesaid of arresting the impurities of crude coal gas is a circular
one, the purifying agent being used over and over again, it is necessary to keep up
and renew the activity of the solution, which is apt to become weakened or
exhausted by the gradual accumulation of water in the process and by the exchange
of the acids of the fixed ammonia for the carbonic acid originally combined with
the soda. The activity of the solution is kept up by evaporating the surplus water,
and by adding from time to time sufficient soda ash or caustic soda to replace that
neutralized by the fixed acids of the ammonia.
The ammoniacal liquor from the hydraulic main may be advantageously mixed
with the washer or scrubber liquor aforesaid before heating in the still for purifica-
tion as already described, but in such case the whole of the water so added will
have to be evaporated and dissipated.
After the liquor has been purified of its gaseous contents in the still as already
described and the surplus water evaporated, a portion of the residue is to be cooled
for use over again after cooling in the washers or scrubbers, while another portion
is regularly treated for the elimination of the fixed impurities such as carbolates,
hyposulphites, sulphocyanides, sulpho-carbonates and other compounds, by the
process of evaporation and fishing.
We also find this may be effected by reserving at intervals a quantity of the
liquor running from the still evaporating it down to crystallizing strength and
setting aside to cystallize. Fairly pure cystals of carbonate of soda are obtained
which may be then collected and dissolved in water to the proper strength for use
over again.
The mother liquors from these crystals contain the bulk of the
impurities which may be sold or worked up for the preparation of carbolates, hypo-
sulphites, sulphocyanides, cyanides and other salts. If, however, there is but little
carbonate of soda remaining in the nearly exhausted liquor, the impurities aforesaid,
will either crystallize or be fished out by the foregoing treatment and the small
quantity of carbonate of soda will be found in the mother liquor which can there-
fore be used over again.
When it is preferred to use a mixture of carbonate of soda, and caustic soda, as
already described as the solution for washing the crude coal gas, the said solution
is to be kept to the proper state of causticity by the addition of quicklime or of
hydrate of lime to the solution. This we prefer to do by adding the lime to the
solution in the form of milk of lime, at a point in the still aforesaid, where all the
volatile ammonia has been disengaged, though it would be equally efficacious, but
probably not so economical, if the lime were added either previously or subsequently
to the stilling operation. The addition of lime to the solution will cause a
precipitation of carbonate of lime which must be allowed to settle and be removed
before the solution can be employed again.
In the foregoing description we have referred to the use of soda in the form of
carbonate of soda or caustic soda, as it is the agent which, having regard to
economy, will, we have found, be most advantageous for effecting our object. It
must however be noted that the known equivalents for soda and in particular forms
of potass may be employed where expense is not an obstacle, as the like chemical
results would be obtained and the object of our invention would be thereby effected
by like means and in like manner as above described.
We have found that the foregoing processes do not wholly remove the sulphur
existing as bisulphide of carbon; if therefore it is desirable to remove this impurity,
the gas should be further passed through foul lime purifiers in the manner now
usually practised and well understood, or through purifiers or washers, charged
with solutions or mixtures of the various sulphides or polysulphides or sulphydrates
of the alkalies or alkaline earths to combine with or remove the bisulphide of
carbon.

page_text: Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. The method of washing and purifying coal gas and similar gaseous mixtures
with solutions of carbonate of soda, or caustic soda, or a mixture of the two or
their equivalents substantially as is described herein.
2. The purification of the solutions charged with impurities, by treating them in
the manner substantially as is described herein, for use over again.
3. The production of crude or pure alkaline carbolates, hyposulphites, cyanides
and sulphocyanides from the solutions herein described substantially as is described
herein.
4. The production of sulphur from the gases issuing from the still in which the
impure liquor is purified as herein described.
Dated the 20th day of January 1893.
G. F. REDFERN & Co.,
4, South Street, Finsbury, Loudon, Agents for the Applicants.