IMPROVEMENTS IN THE PURIFICATION OF GAS
Year: 1876

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, for the Invention of "IMPROVEMENTS IN
THE PURIFICATION OF GAS"-A communication from abroad by Alfied Antoine
Paulin Mallet, of Paris, France.
Sealed the 23rd February 1877, and dated the 4th September 1870.
PROVISIONAL SPECIFICATION left by the said Alexander Melville Clark at
the Office of the Commissioners of Patents on the 4th September 1876.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middle-
sex, Patent Agent.
IMPROVEMENTS IN THE PURIFICATION OF GAS."
This Invention relates to the purification of gas by the absorbtion of the frec
acids contained therein.
Illuminating gas obtained from coal still contains after passing through the con-
densers volatile ammoniacal salts, principally carbonate and hydrosulphate, as well
as free hydrosulphuric and carbonic acids. In purifying with oxide of iron the
latter absorbs the hydrosulphuric acid, whether free or combined with ammonia,
and the gas on leaving the purifiers contains carbonic acid and a certain quantity
of ammonia, generally insufficient however for converting the whole of the carbonic
acid into carbonate and a fortiori into bicarbonate of ammonia. The free carbonic
acid remaining in the gas passes either wholly or in part to the burners and impairs
the illuminating power of the gas. This excess of carbonic acid is usually removed
from the gas by means of lime.
This Invention consists in an improved process for absorbing this acid, whereby
the whole of the carbonic acid remaining in the gas after purification with oxide
of iron is transformed into sesqui-carbonate, or preferably into bicarbonate of
ammonia, both of which are soluble in water. To this end the gas after being freed
from the hydrosulphuric acid is brought into intimate contact with caustic
ammonia, in, quantity sufficient to convert the carbonic acid into sesqui-carbonate,
or preferably bicarbonate of ammonia. This ammonia may be either in a gaseous
or liquid condition, and if in a gaseous form it may be introduced into a pipe in
which gas at a higher pressure is circulating. If the ammonia be employed in it
liquid state it is introduced into a vessel or receiver and the gas made to bubble

page_text: through it. The ammonia may also be introduced in the gas in the form of spray.
In both cases the gas is passed through a series of washers or scrubbers, water or
the liquids obtained from the preceding operations being used so as to completely
dissolve the carbonate formed.
.
The quantity of ammonia it is necessary to introduce into the gas to effect the
complete transformation of the carbonic acid necessarily varies with the conditions
of the distillation and condensation, and the kind of coal, &c; it is therefore
necessary from time to time to test the amount of carbonic acid and of ammonia
contained in the gas in order to ascertain the quantity of ammonia required. The
bicarbonate thus formed may be obtained in the form of a more or less concentrated
solution, or even in a solid form, or in crystals forined in the liquor.
The bicarbonate of ammonia thus obtained is suited for various uses in the arts
and in the manufacture of chemical products, but instead of collecting the bicar-
bonate of ammonia it may at the moment of its formation be made to effect certain
chemical reactions and preparations For example, saline solutions as neutral as
possible, chlorides, sulphates, or nitrates may be placed in the second and third of
the series of wash vessels above referred to, whereupon there will be formed bi-
carbonates if solutions of soda or potash have been employed, or carbonates, which
being soluble or but slightly soluble will be deposited, hydrochlorate, sulphate, or
nitrate of ammonia remaining in the liquid. The bicarbonates or carbonates are
separated and purified by known processes.
The supernatant liquid may if necessary be again passed through the washing
apparatus. The carbonic acid contained in the gas may also be absorbed in another
manner by placing in the several washing apparatus a solution of carbonate of soda
or potash, bicarbonate being formed on the passage of the gas and deposited. I
may also place in the washing apparatus the saline solutions above indicated after
dissolving therein gaseous aminonia or adding thereto a highly concentrated
solution of ammonia
The apparatus employed in the application of these processes vary according to
the nature of the products to be obtained. If it is desired to obtain products in
solution, such as bicarbonate or carbonate of ammonia, a series of washing vessels
may be employed, through which the gas is caused to bubble, or it may be passed
through columns or scrubbers. If solid products are to be obtained washing
apparatus provided with agitators or scrapers should be employed, and in the latter
case it would be of advantage to isolate one of the washers in order to more readily
extract the precipitate formed All the above apparatus are well known in gas
making.
Instead of employing caustic ammonia in the before described operations ammonia
water may be used, deprived of the hydrosulphuric acid it may contain, or the
same water may be used desulphuretted and concentrated by distillation. The
carbonic acid contained in the gas may also be freed by the action of ammonia after
condensation The ammonia in this case combines not only with the carbonic acid,
but also with the free hydrosulphuric acid, although after a certain time the
carbonic acid partially decomposes the hydrosulphate formed and hydrosulphuric
acid is again set free. It would therefore on account of this reaction be difficult, if
not impossible, to completely purify the gas by washing with water after the inter-
vention of ammonia. This result is better obtained by passing the gas through
neutral metallic solutions, and then through at least one oxide of iron purifier in
order to ensure a thorough purification.
I may also pass the gas after condensation through neutral metallic solutions, 5
and after the absorbtion of the ammoniacal compounds it contains add to it by one
of the methods before indicated caustic ammonia in sufficient quantity to transform
the free hydrosulphuric and carbonic acid into hydrosulphate and carbonate or
bicarbonate of ammonia, which may be afterwards eliminated from the gas by
washing.
The above processes are applicable to coal gas and gases obtained from other
matters, and containing free carbonic acid The gas obtained from wood would
5

page_text: come under this category, but as it contains considerable quantities of pyroligneous
acid it is necessary that the latter be completely absorbed before the intervention
of the ammonia.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alexander Melville Clark in the Great Seal Patent Office on the 3rd
March 1877.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middle-
sex, Patent Agent. "IMPROVEMENTS IN THE PURIFICATION OF GAS." A. com-
munication from abroad by Alfred Antoine Paulin Mallet, of Paris, France.
This Invention relates to the purification of gas by the absorption of the freo acids
contained therein.
Illuminating gas obtained from coal still contains after passing through the con-
densers volatile ammoniacal salts (principally carbonate and hydrosulphate), as well
as free hydrosulphuric and carbonic acids. In purifying with oxide of iron the
latter absorbs the hydrosulphuric aad, whether free or combined with ammonia,
and the gas on leaving the purifiers contains carbonic acid and a certain quantity
of ammonia, generally insufficient however to convert the whole of the carbonic
acid into carbonate, and a fortiori, into bicarbonate of ammonia. The free carbonio
acid remaining in the gas passes either wholly or in part to the burners and impairs
the illuminating power of the gas. This excess of carbonic acid is usually removed
from the gas by means of lime.
This Invention consists in an improved process having for its object to effect the
absorption of this acid, transforming the whole of the carbonic acid remaining in the
gas after purification with oxide of iron into sesqui-carbonate, or preferably into
bicarbonate of ammonia, both of which are soluble in water. To this end the gas
after being freed from the hydrosulphuric acid is brought into intimate contact
with caustic aminonia in quantity sufficient to convert the carbonic acid into sesqui-
carbonate, or preferably bicarbonate of ammonia. This ammonia may be either in
a gaseous or liquid condition, and if in a gaseous form it may be introduced at a
higher pressure than that of the gas into a pipe in which the gas circulates. If the
ammonia be employed in a liquid state it is introduced into a receiver, and the gas
made to bubble through it The liquid ammonia may also be introduced in the gas
in the form of spray. In both cases the gas is passed through a series of washers
or through a number of scrubbers, water or the liquids obtained from preceding
operations being used in the washers or scrubbers so as to completely dissolve the
carbonate formed.
The quantity of ammonia it is necessary to introduce into the gas to effect the
complete transformation of the carbonic acid varies according to the various con-
ditions of the distillation and condensation, and the kind of coal, &c.; it is
therefore necessary from time to time to test the amount of carbonic acid and of
ammonia contained in the gas in order to ascertain the quantity of ammonia
required. The bicarbonate may be obtained in a condition of a more or less con-
centrated solution, or even in a solid form, in crystals formed in the liquor
The bicarbonate of ammonia thus obtained is suited for various uses in the arts
and in the manufacture of chemical products, but instead of collecting the bicar-
bonate of ammonia it may at the moment of its formation be used for certain
chemical reactions and preparations. For example, saline solutions (chlorides,
sulphates, or nitrates), as neutral as possible, may be placed in the second and
third of the series of wash vessels above referred to, whereupon there will be formed
bicarbonates if solutions of soda or potash have been employed, or carbonates, which
being insoluble or but slightly soluble, will be deposited, hydrochlorate, sulphate, or
nitrate of ammonia remaining in the liquid. The bicarbonates or carbonates are
separated and purified by known processes.

page_text: The supernatant liquid may if necessary be again passed through the washing
apparatus. The carbonic acid contained in the gas may also be absorbed in another
manner; thus by placing in the several wash vessels a solution of carbonate of soda
or potash on the passage of the gas bicarbonate is formed, which deposits. I may
also place in the washing apparatus 'the saline solutions above indicated after
dissolving therein gaseous ammonia, or adding thereto a highly concentrated solution
of ammonia.
The apparatus employed in the application of these processes may vary according
to the nature of the products to be obtained. If it is desired to obtain products in
solution only (for instance, bicarbonate or carbonate of ammonia) a series of washing
vessels may be employed, through which the gas is caused to bubble, or it may be
passed through columns or scrubbers. If solid products are to be obtained washing
apparatus provided with agitators or scrapers should be employed, and in this case
it would be of advantage to isolate one of the washers in order to more readily
extract the precipitate formed. All the above apparatus are however well known
in gas making.
Instead of employing caustic ammonia in the before described operations
ammoniacal water may be used deprived of the hydrosulphuric acid it may contain,
or the same water may be used desulphuretted and concentrated by distillation.
The carbonic acid contained in the gas may also be fixed by the action of ammonia
after the condensation of the gas. The ammonia in this case combines not only
with the carbonic acid, but also with the free hydrosulphuric acid, although after a
certain time the carbonic acid partially decomposes the hydrosulphate formed, and
bydrosulphuric acid is again set free. It would therefore on account of this reaction
be difficult if not impossible to completely purify the gas by washing with water
after the intervention of ammonia. This result will be more effectually attained by
passing the gas through neutral metallic solutions, and then through at least one
oxide of iron purifier in order to ensure a thorough purification
I may also pass the gas after condensation through neutral metallic solutions,
and after the absorption of the ammoniacal compounds it contains add to it by one
of the methods before indicated caustic ammonia in sufficient quantity to transform
the free hydrosulphuric and carbonic acids into hydrosulphate and carbonate or
bicarbonate of ammonia, which may afterwards be eliminated from the gas by
washing.
The above processes are applicable to coal gas and gases obtained from other
matters, and containing free carbonic acid. The gas obtained from wood comes
under this category, but as it contains a considerable quantity of pyroligneous acid
it is necessary that the latter should be completely absorbed before the ammonia is
used.
I will now describe the general arrangement of apparatus adapted for use in
carrying into practice the process above described.
The apparatus as before mentioned may consist of a series of washing vessels or
a column similar to that used in distillatory operations, but both however require
to be specially arranged in consequence of the great volatility of the agent employed
for absorbing the carbonic acid. If a series of washing apparatus at different
levels be used the gas instead of ascending is made to pass in a downward direction;
the same is also the case with the ammonia.
Figures 1 and 2 of the accompanying Drawings respectively show a vertical
section and plan of one arrangement of apparatus.
The vessel A, which is provided with a gauge glass, contains caustic ammonia.
The flow of the liquid may either be intermittent or continuous, and in the latter
case it may be rendered constant by constructing the vessel A on the principle of
Mariotte's bottle. The ammonia passes into the first washer B made of cast or sheet
iron, and of any suitable form, through which the gas is made to bubble To the
side of this vessel is attached a chamber, which communicates with the interior of
the washer B by an opening at the lower part; an ordinary syphon would also
answer the same purpose. The liquid in vessel B overflows through a pipe a into

page_text: a second washer C, into which the gas which has bubbled through vessel B also
passes. Instead of using two wash vessels only a larger number may similarly be
employed operating per descensum. The liquid overflowing from the lowest washer
and containing carbonate more or less bicarbonated- is conducted by a pipe b into a
closed reservoir E. If the liquid still contains caustic ammonia it may be again
used, either alone or with the addition of a fresh quantity of ammonia, for
the gas passing through the vessels B, C. If the gas on leaving the last washer Ĕ
still contains free ammonia it is conducted into a washer D, to which water is
supplied either intermittently or continuously. The liquid from this washer is
conducted to a special reservoir to be again utilised in the washers operating per
descensum.
washing
If it be preferred to effect the washing of the gas in a column the arrangement
shown in elevation and plan at Figures 3 and 4 may be adopted. The gas enters at
the base M of the cast-iron column S, and passes out after having successively
passed the distributors i, l, n, by bubbling through the liquid into which they dip.
The number of partitions or compartments and of distributors composing the
column may be varied. The ammonia is supplied continuously as in the former
case to a vessel A, and enters the column at about the middle of its height, and
passes down from shelf to shelf, mixing with the liquid in which the distributors
dip As the gas after contact with the ammonia carries along with it a certain
quantity of ammonia it is necessary to remove the latter by washing with water,
and the upper compartments of the column are devoted to this purpose.
Water is supplied from a tank H into the upper compartment, and descends to
the one immediately over that into which the caustic ammonia is introduced. The
water after thus passing through the upper compartments necessarily contains some
free ammonia or carbonate of ammonia, or both together, and it may if desired be
allowed to descend to the bottom of the column and mix with the liquid therein;
or it may be separately collected by opening the cock r on a syphon pipe m, by
which it is conveyed to a covered receptacle.
In using wash vessels before described the ammoniacal liquid may be made to
flow in the contrary direction to the gas, which would go per ascensum. The
ammonia would be supplied to the highest vessel, which would be surmounted by
one or more water wash vessels
In employing either system, whether washers or a column, if the gas cannot be
readily deprived by washing with pure water of the fiee ammonia or carbonate of
ainmonia it contains it may be introduced into a vessel, either made of or lined with
lead containing dilute sulphuric acid or other chemical solution.
The vessel represented at D provided with a gauge would answer for this
purpose.
Having described the nature of the Invention and the manner of performing the
same, I declare that what I claim as the Invention to be protected by the herein-
before in part recited Letters Patent is, the processes as herein specified for
purifying or depriving gas of the free acids it contains, particularly the car-
bonic acid.
In witness whereof, I, the said Alexander Melville Clark, have hereunto set
my hand and seal, this Third day of March, in the year of our Lord One
thousand night hundred and
A. M. CLARK. (L.S.)