IMPROVEMENTS IN AND RELATING TO THE PURIFICATION OF COAL-GAS, AND THE RECOVERY OF CARBONATE OF PROVISIONAL SPATION SODA AS A BYE-PRODUCT THEREFROM
Year: 1881

page_text: LETTERS PATENT to Carl Friedrich Claus, of Mark Lane, in the City of
London, Chemist, for an Invention of "IMPROVEMENTS IN AND RELATING
TO THE PURIFICATION OF COAL-GAS, AND THE RECOVERY OF CARBONATE OF
PROVISIONAL SPECIFICATION left by the said Carl Friedrich Claus at the
Office of the Commissioners of Patents on the 30th June 1881.
CARL FRIEDRICH CLAUS, of Mark Lane, in the City of London, Chemist.
"IMPROVEMENTS IN AND RELATING TO THE PURIFICATION OF COAL-GAS, AND THE
RECOVERY OF CARBONATE OF SODA AS A BYE-PRODUCT THEREFROM."
In the Specifications of former Letters Patent, dated 20th January, A.D. 1877,
No. 272, and 16th June, A.D. 1877, No. 2362, a process is described whereby the
carbonic acid and a portion of the sulphide of hydrogen are removed from coal-gas
by admitting gaseous ammonia into the coal-gas as it passes from the retorts to the
washers or scrubbers. In these washers or scrubbers (which may be of any suitable
kind) the products of combination are absorbed into the liquid, which is formed by
showering water down the last scrubber and pumping it, when arrived at the
bottom, to the top of the next adjacent scrubber; from the bottom of this to the
top of the next scrubber, and so forth, until it reaches the first scrubber. To
the strong liquor thus obtained it was proposed to add chloride of sodium, and to
pump carbonic acid, derived from the calcination of bicarbonate of soda obtained in a
subsequent operation, into the mixture of chloride of sodium and gas-liquor. It
was stated that by this operation a precipitate of bicarbonate of soda was formed
and a solution of chloride of ammonium.
+
After driving out the volatile compounds of ammonia still remaining in the
chloride of ammonium liquor by means of heat, it was proposed to put this liquor
into a still, and to add lime to the same and then heat the mixture, whereby
gaseous ammonia was reproduced, which was to serve for the purification of further
quantities of gas.

page_text: By the said process, as described, the whole of the carbonic acid and sulphide
of hydrogen are however not removed, therefore I have devised the following
improvements which form the subject of my present Invention.
When it is desired to remove the whole of the carbonic acid and sulphide of
hydrogen by means of gaseous ammonia, it is necessary that sufficient gaseous
ammonia should be introduced into the crude coal-gas to take up these impurities.
The ammonia may be added in a continuous operation before or after the gas passes
through the condensers, or it may be introduced at two stages, first, in quantity
sufficient to combine with the carbonic acid, and afterwards, when the impure
carbonate of aminonia so formed has been removed, in quantity sufficient to combine
with the sulphide of hydrogen and convert it into sulphide of ammonium.
For instance, suppose there are in coal-gas as it leaves the retorts to every one
chemical equivalent of ammonia four equivalents of carbonic acid and three
equivalents of sulphide of hydrogen. This one equivalent of ammonia is not
sufficient to take up these seven equivalents of impurities, therefore in commencing
my process it will be necessary to add six additional equivalents of ammonia, which
during the continuance of the process are repeatedly recovered and reproduced in
the state of gaseous ammonia.
For this purpose the ammonia will have to be seven times converted into chloride
of ammonium. By the action of lime upon the latter seven equivalents of ammonia
may be generated, but to produce these seven equivalents of chloride of ammonium
seven equivalents of carbonic acid are required. The gas as above supposed
however only contains four equivalents of this, and in order to supply the other
three equivalents I, according to my present improvement, treat the gas-liquor
resulting from this process of purification (and which accordingly would contain
four equivalents of carbonate of ammonia and three equivalents of sulphide of
ammonium) with carbonic acid obtained from extraneous sources, such, for example,
as fuel gases (free from oxygen or sulphurous acid). The sulphide of ammonium
may be treated thus either when it is unmixed or when mixed with the carbonate
of ammonia. By this treatment I convert the three equivalents of sulphide of ammo-
nium into carbonate of sesqui-carbonate of ammonia, and by adding the necessary
quantity of chloride of sodium, and forcing through the mixture pure carbonic
acid, obtained by calcining bicarbonate of soda (thus producing carbonate of soda),
I obtain seven equivalents of bicarbonate of soda and seven equivalents of chloride of
ammonium, as required to yield the full quantity of gaseous ammonia. Instead of
forcing carbonic acid through the sulphide of ammonium alone, or a mixture of the
carbonate and sulphide of ammonium, I may force the carbonic acid through after
the addition of chloride of sodium to the above sulphide or carbonate and sulphide
of ammonium, and afterwards complete the precipitation by pure carbonic acid-as
above mentioned.
My Invention further consists in improved means for producing the ammonia in
a gaseous state.
It is of the greatest importance that the ammonia admitted into
the coal gas for the purpose of this mode of purification should be in a truly gaseous
form; in order that it may mix with the coal-gas without being condensed or
converted into liquid ammonia before combining with the impurities of the coal
gas, and thus withdrawing itself from contact with the said gas, but on the
contrary will form an intimate mixture of the ammoniacal gas with the coal gas,
and a consequent combination with the impurities, previous to its condensation or
absorption into the liquors or water it meets with in its passage through the gas
conduit and scrubbers. To ensure this result the decomposition of the chloride of
ammonium by means of lime is effected by having a number of stills or vessels in
communication with one another, into which stills burnt lime is placed in quantities
greatly in excess of that required for the liquor passing through them at the time,
or the lime and liquor may be previously mixed in proper proportions. Heat is
applied to the first of these vessels, and the steam and ammonia evolved in the
same pass out at the top and down into the liquor of the second vessel, out of this
into the third vessel, and so on through the series of vessels, the chloride of

page_text: ammonium liquor or mixed liquor and lime running at the same time through these
vessels in the opposite direction. The inflow and outflow of the liquor are so
arranged that the liquor running away from the still or vessel which is heated is
free from ammonia, whilst the contents of the one or more stills farthest away
from the said heated still are cold, and so super-saturated with ammoniacal gas that
they can take up no more, and that therefore the ammoniacal vapors passing
through them leave only their water behind, whilst the gaseous ammonia passes
out as a dry gas.
To further prevent condensation or conversion of the gaseous ammonia into
liquid ammonia I prefer to admit the gaseous ammonia for the purpose of
purification into the coal gas after the latter has passed the condensers, that is to
say, after it has by cooling down lost most of the water which results from the
distillation of coal. The water from the condensers may be used in the scrubbers
or washers.
My further improvements in the purification of coal-gas, which are applicable
for all processes wherein gaseous ammonia is used as a purifying agent, in whatever
manner such gaseous ammonia may have been obtained, consist in so arranging the
supply of gaseous ammonia to the crude coal gas for the purpose of its purification
that the quantity of ammonia shall not be greatly in excess of that theoretically
required to take up the impurities of the gas. I thus avoid the difficulty which
would arise from an excess or surplus of ammonia, which is liable to be carried
away by the coal gas as an impurity in the same, and is difficult to remove by
washing, except with such large quantities of water as would seriously deteriorate
the illuminating power of the gas.
This object is accomplished by storing large quantities of chloride of ammonium
liquor, or other liquor from which the supply of gaseous ammonia is to be derived,
ascertaining its percentage of ammonia and regulating the flow of the liquid through
the vessels or stills by suitable adjustable measuring contrivances, so that the
quantity of gaseous ammonia evolved from the stills shall be equivalent to that
required for the purification of the gas as it passes from the retorts. Any
self-acting or self-regulating mechanical contrivance which would admit the
gaseous ammonia into the coal gas in proper proportions will answer for this
purpose.
As a further improvement in this process in order to ensure the proper mixture
of the gaseous ammonia with the coal-gas, and to afford time and opportunity for
the impurities of the gas to combine with the ammonia before coming in contact
with liquid, I employ large mixing chambers, through which the coal-gas passes
with the ammonia. These chambers should be large enough to hold the quantity
of gas produced in the retorts during two or three or more minutes. In these
chambers part of the carbonate and sulphide of ammonium is deposited, thus
diminishing the quantity of water required for washing. Moreover I make the
scrubbers of a capacity of one, two, or three times the ordinary capacity to
decrese the rush or velocity of the gas through the same, thus causing a quiet flow
and expansion of the same, during which the carbonate and sulphide of ammonium
formed have an opportunity of being absorbed into the water trickling down the
scrubbers.
By the above described improvements I am able to ensure a result which is
essential in the purification of coal gas by ammonia, namely, that the quantity of
water used for washing out the ammoniacal products of the purification in the
scrubbers shall not materially exceed the absolute quantity now used in the
ordinary process of purification by lime and oxide of iron.
Another part of my said Invention consists in the employment of chloride of
calcium to absorb the ammonia and thereby prevent its passing forward with the
coal-gas. When this chloride of calcium has become charged with ammonia I
heat the said chloride in closed vessels to drive off the ammonia, which may be
used again for the purification of coal-gas.
I may also use chloride of calcium for the absorption of the whole of the

page_text: ammonia and of all the ammoniacal compounds formed in any process for the
purification of coal-gas in which ammonia is used as a purifying agent.
The chloride of calcium may be applied also in the ordinary process of
purification by lime and oxide of iron for the purpose of arresting the
ammoniacal gas and compounds, and may when saturated be heated, as above
described, to drive off and utilize the ammoniacal compounds.
One other obstacle to the effectual purification of coal gas by ammonia and the
proper absorption or condensation in water of the products thereof, or for the
proper retention of any excess of ammonia, has been the want of a porous
material for filling the scrubbers, possessing sufficient capillary action for the
absorption of the solution and the proper passage of the said solution downwards
through its pores to the bottom of the scrubbers.
The materials hitherto used for this purpose, that is to say, coke, gravel,
broken bricks, sawdust, spent tan, wooden gurdles, and the like, have little or no
capillary action, but mere act by means of the surface they expose to the gas or
liquor; but I use pieces of bricks of a particular kind not hitherto used for the
purpose, namely, ganister or Dinas bricks, or pieces of material of which such
bricks are made, for filling the scrubbers. Where these materials are not easily
obtainable I produce substitutes by mixing plastic clay with a quantity of sawdust,
coal, coke, or charcoal dust, or vegetable or animal fibre, such as cotton or wool,
or infusorial silica, and form the same into pieces of any convenient shape and
burn them,

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
.
by the said Carl Friedrich Claus in the Great Seal Patent Office on the
30th December 1881.
CARL FRIEDRICH CLAUS, of Mark Lane, in the City of London, Chemist.
"IMPROVEMENTS IN AND RELATING TO THE PURIFICATION OF COAL-GAS, AND THE
RECOVERY OF CARBONATE OF SODA AS A BYE-PRODUCT THEREFROM."
In the Specifications of former Letters Patent, dated 20th January, A.D. 1877,
No. 272, and 16th June, A.D. 1877, No. 2362, a process is described whereby the
carbonic acid and a portion of the sulphide of hydrogen are removed from coal-
gas by admitting gaseous ammonia into the coal-gas as it passes from the retorts
to the washers or scrubbers. In these washers or scrubbers (which may be of any
suitable kind) the products of combination are absorbed into the liquid, which is
formed by showering water down the last scrubber and pumping it when arrived
at the bottom to the top of the next adjacent scrubber, from the bottom of this to
to the top of the next scrubber, and so forth, until it reaches the first scrubber.
To the strong liquor thus obtained it was proposed to add chloride of sodium, and
to pump carbonic acid derived from the calcination of bicarbonate of soda obtained
in a subsequent operation, into the mixture of chloride of sodium and gas-liquor.
It was stated that by this operation a precipitate of bicarbonate of soda was
formed and a solution of chloride of ammonium obtained.
After driving out the volatile compounds of ammonia still remaining in the
chloride of ammonium liquor by means of heat, it was proposed to put this liquor
into a still and to add lime to the same, and then heat the mixture, whereby
gaseous ammonia was reproduced which was to serve for the purification of further
quantities of gas.
By the said process as described, the sulphide of hydrogen is not entirely
removed, and I have devised certain improvements on the previous process which
form the subject of my present Invention.
When it is desired to remove the whole of the carbonic acid and sulphide of
hydrogen by means of gaseous ammonia, it is necessary that sufficient gaseous
ammonia should be introduced into the crude coal-gas to take up these impurities.
The ammonia may be added in a continuous operation before or after the gas passes
through the condensers, or it may be introduced at two stages, first, in quantity
sufficient to combine with the carbonic acid and afterwards when the impure
carbonate of ammonia so formed has been removed in quantity sufficient to
combine with the sulphide of hydrogen and convert it into sulphide of ammonium.
For instance, suppose there are in coal-gas as it leaves the retorts, to every one
chemical equivalent of ammonia four equivalents of carbonic acid and three
equivalents of sulphide of hydrogen. This one equivalent of ammonia is not
sufficient to take up these seven equivalents of impurities, therefore in commencing
my process it will be necessary to add six additional equivalents of ammonia,
which during the continuance of the process are repeatedly recovered and
reproduced in the state of gaseous ammonia.
For this purpose seven times the single equivalent of ammonia above referred to
will have to be converted into chloride of ammonium. By the action of lime upon
this chloride of ammonium seven equivalents of ammonia may be generated, but
to produce seven equivalents of chloride of ammonium, seven equivalents of carbonic
acid are required. The gas as above supposed however only contains four
equivalents of this, and in order to supply the other three equivalents, I, according
to my present improvement, treat the gas-liquor resulting from, this process. of

page_text: purification (and which accordingly would contain four equivalents of carbonate
of ammonia and three equivalents of sulphide of ammonium) with carbonic acid
obtained from extraneous sources, such for example as fuel gases (free from
oxygen or sulphurous acid), or the gases from a lime kiln. The sulphide of
ammonium may be treated thus either when it is unmixed or when mixed with the
carbonate of ammonia. By this treatment I convert the three equivalents of
sulphide of ammonium into "carbonate or sesqui-carbonate or bicarbonate of
ammonia, and by adding the necessary quantity of chloride of sodium and forcing
through the mixture pure carbonic acid obtained by calcining bicarbonate of soda
(thus producing carbonate of soda), I obtain seven equivalents of bicarbonate of
soda and seven equivalents of chloride of ammonium, as required, to yield the full
quantity of gaseous ammonia. Instead of forcing carbonic acid through the
sulphide of ammonium alone or a mixture of the carbonate and sulphide of
ammonium, I may force the carbonic acid through after the addition of chloride of
sodium to the above sulphide or carbonate and sulphide of ammonium, and after-
wards complete the precipitation by pure carbonic acid, as above mentioned.
My Invention also partly consists in improved means for producing the
ammonia in a gaseous state. It is of the greatest importance that the ammonia
admitted into the coal-gas for the purpose of this mode of purification should be in
a truly gaseous forin, in order that it may mix with the coal-gas without being
condensed or converted into liquid ammonia before combining with the impurities
of the coal-gas, and thus withdrawing itself from contact with the said gas. In
the state of gas it will on the contrary form an intimate mixture with the coal-
gas and a consequent combination with the impurities previous to its condensation
or absorption into the liquors or water it meets within its passage through the
gas-conduit and scrubbers. To ensure this result the decomposition of the chloride
of ammonium by means of lime is effected by having a number of stills or vessels
in communication with one another, into which stills burnt lime is placed in
quantities greatly in excess of that required for the liquor passing through them
at the time, or the lime and liquor may be previously mixed in proper proportions.
Heat is applied to the first of these vessels and the steam and ammonia evolved in
the same pass out at the top and down into the liquor of the second vessel, out of
this into the third vessel, and so on through the series of vessels, the chloride of
ammonium liquor or mixed liquor and lime running at the same time through these
vessels in the opposite direction. The inflow and outflow of the liquor are so
arranged that the liquor running away from the still or vessel which is heated is
free from ammonia, whilst the contents of the one or more stills farthest from the
said heated still are cold, and so super-saturated with ammoniacal gas that they
can take up no more, and that therefore the ammoniacal vapors passing through
them leave only their water behind whilst the gaseous ammonia passes out as a
practically dry gas. One or more vessels, which may be termed stills or condensers,
furthest from the said heated still are arranged to be cooled by a water-jacket or
coils of pipes through which cold water flows, so that the contents of the same may
be kept cool enough to prevent escape of aqueous vapor.
To further prevent condensation (or conversion of the gaseous ammonia into
liquid ammonia, I prefer to admit the gaseous ammonia for the purpose of
purification into the coal-gas after the latter has passed through the condensers,
that is to say, after it has by cooling down lost most of the water which results
from the distillation of coal. The water from the condensers may be used in the
scrubbers or washers.
A further improvement in the purification of coal-gas which is applicable for
all processes wherein gaseous ammonia is used as a purifying agent, in whatever
manner such gaseous ammonia may have been obtained, consists in so arranging the
supply of gaseous ammonia to the crude coal-gas for the purpose of its purification,
that the quantity of ammonia shall not be materially in excess of that theoretically.
required to take up the impurities of the gas. I thus avoid the difficulty which
would arise from an excess or surplus of ammonia, which is liable. to be carried

page_text: away by the coal-gas as an impurity in the same, and is difficult to remove by
washing, except with such large quantities of water as would seriously deteriorate
the illuminating power of the gas.
This object is accomplished by storing large quantities of chloride of ammonium
liquor or other liquor from which the supply of gaseous ammonia is to be derived,
ascertaining its percentage of ammonia, and regulating the flow of the liquid
through the vessels or stills by suitable adjustable measuring contrivances, so that
the quantity of gaseous ammonia evolved from the stills shall be equivalent to that
required for the purification of the gas as it passes from the retorts. Any self-
acting or self-regulating mechanical contrivance which would admit the gaseous
ammonia into the coal-gas in proper proportions will answer for this purpose.
As a further improvement in this process, in order to ensure the proper mixture
of the gaseous ammonia with the coal-gas, and to afford sufficient time and
opportunity for the impurities of the gas to combine with the ammonia before
coming in contact with the liquid, I employ large mixing chambers through which
the coal-gas passes with the ammonia. These chambers should be large enough to
hold the quantity of gas produced in the retorts during two, three, or more
minutes. In these chambers part of the carbonate and sulphide of ammonium
is deposited, thus diminishing the quantity of water required for washing. More-
over I prefer to make the scrubbers of a capacity considerably greater than is usual
to decrease the rush or velocity of the gas through the same, thus causing a quiet
flow and expansion of the gas, during which the carbonate and sulphide of
ammonium formed have an opportunity of being absorbed into the water trickling
down the scrubbers.
By the above described improvements I am able to ensure a result which
is essential in the purification of coal-gas by ammonia, namely, that the quantity of
water used for washing out the ammoniacal products of the purification in the
scrubbers shall not materially exceed the absolute quantity now used in conjunction -
with the ordinary process of purification by lime and oxide of iron.
Chloride of calcium may be employed to absorb the excess of gaseous ammonia,
and thereby prevent its passing forward with the coal-gas. When chloride of
calcium has been so employed and has become charged with ammonia, I according
to this part of my Invention heat the said chloride in closed vessels to drive off the
ammonia, which may be used again for the purification of the coal-gas.
I am aware that prior to my Invention chloride of calcium has been proposed for
the purpose of purifying coal-gas from ammonia, and that it has been proposed to
extract the chloride of ammonium thus formed by water in order that it might be
utilized; I consider novel however my suggestion of heating the chloride of calcium
(after it has served for the absorption of the ammonia in coal-gas) in closed vessels
to obtain the ammonia as such for further use.
Having thus fully described my said Invention and the manner of performing
the same, I wish it understood that I claim,-
First. Employing in the above described process and for the purpose specified
carbonic acid from extraneous sources sufficient to produce a quantity of
bicarbonate of soda and ammonia respectively chemically equivalent to the acid
impurities in the coal-gas which is to be purified by ammonia, as described.
Second. The distillation of the chloride of ammonium with lime for the
production of anhydrous gaseous ammonia for the purpose of purifying coal-gas
of its acid impurities according to the process herein above specified.
Third. In the purification of coal-gas by gaseous ammonia, the regulation of the
supply of the ammonia in such a manner that it shall not be greatly in excess of
the chemical equivalent of the acid impurities of the coal gas.
Fourth. In the purification of coal-gas by gaseous ammonia, the employment of
mixing chambers of large dimensions, as above specified, through which the coal-gas
passes together with the ammonia.
Fifth. The heating in closed vessels of chloride of calcium (which has been used

page_text: for the absorption of ammonia from coal-gas) for the purpose of expelling the
ammonia from the chloride of calcium in a fit condition for further use.
In witness whereof, J, the said Carl Friedrich Claus, have hereunto set my
hand and seal, this Thirtieth day of December, in the year of our Lord
One thousand eight hundred and eighty one.
Witness,
HENRY H. LAKE,
8, Southampton Buildings,
London.
C. F. CLAUS. (L.S.)