AN IMPROVED PROCESS FOR THE PURIFICATION OF COAL GAS."
Year: 1881

page_text: LETTERS PATENT to Carl Friedrich Claus, of Mark Lane, in the City of
London, Chemist, for an Invention of "AN IMPROVED PROCESS FOR THE
PURIFICATION OF COAL GAS."
PROVISIONAL SPECIFICATION left by the said Carl Friedrich Claus at the
Office of the Commissioners of Patents on the 28th June 1881.
CARL FRIEDRICH CLAUS, of Mark Lane, in the City of London, Chemist.
IMPROVED PROCESS FOR THE PURIFICATION OF COAL GAS."
<< AN
It has been attempted by various processes to remove carbonic acid and
sulphuretted hydrogen from coal gas by means of caustic ammonia, but none of
these has accomplished the removal of the whole of these two impurities. These
processes have moreover been accompanied with special disadvantages. By reason
of certain defects in the process and the arrangements of the plant or apparatus,
larger quantities of caustic ammonia than were necessary to take up the said
impurities were introduced into the gas without however removing the impurities;
the excess of ammonia was carried away by and contaminated the coal gas, and its
removal by washing was impracticable except with an injuriously large quantity
of water, such as would greatly impair the illuminating power of the gas.
A further disadvantage consequent upon the necessitated use of excessive quantities
of ammonia and water to wash the same out of the gas again was the formation of
such weak gas liquor, as would render the reproduction of the caustic ammonia a
matter of great difficulty.
In the Specification of Hill's Patent, No. 1369, A.D. 1868, there is described a
process for driving off from gas liquor part of the carbonic acid and sulphide of
hydrogen (which are combined in the liquor with ammonia), by treating the said
liquor and leaving a liquid consisting partly of caustic ammonia.
In the Speci-
fication of the Letters Patent, No. 510, A.D. 1870, the same inventor describes a
process whereby the purified liquor may be concentrated by distillation, and the
ammoniacal vapours may be driven into coal gas for the purpose of purifying
the same from more or less of the carbonic acid and sulphur, and cyanogen
compounds. It is stated in the Specification of the last named Letters Patent

page_text: "
that the ammoniacal vapours may be condensed into liquid ammonia by being
passed through closed pipes cooled externally by cold liquids, thus showing that
the ammonia passes off from the liquid accompanied with a considerable quantity
of water before it passes into the coal gas for the purpose of purifying the same.
Now I have found by experiment that aqueous vapors of ammonia are unsuitable
for the purification of coal gas, but that the anhydrous or uncondensible gaseous
ammonia is effectual for purifying coal gas, without necessitating the use of such
an excessive quantity of ammonia as would require for its ultimate removal
quantities of water injurious to the illuminating power of the gas, and by my
improvements I effect the practically complete removal of the carbonic acid and
sulphide of hydrogen from the coal gas.
These improvements are as follows, that is to say, the ammonia is admitted into
the coal gas in the anhydrous or uncondensible gaseous form, in order that it may
mix with the coal gas without being condensed, and thus withdrawn from contact
with and action upon the coal gas before combining with the impurities of the
latter; but on the contrary an intimate mixture of the ammoniacal gas with the
coal gas (and a consequent combination with the impurities) takes place previous
to its condensation or absorption into the liquors or water it meets with on its
passage to the scrubbers.
After the gas liquors have been "purified" by the
process described in the said Specification of Hill, No. 1369, A.D. 1868 they are
distilled. In my process I distill them in like manner, but with the essential
difference however that I first cool the liquor before admitting it to the series of
. stills. The result is that the ammoniacal vapours evolved from the heated still
in passing through the intermediate stills become gradually cooler and cooler, so
that when they reach the last and coldest still the ammoniacal gas enters the same
unaccompanied by aqueous vapors, and super-saturate the said still with gaseous
ammonia to that extent that they can take up no more ammonia, and are therefore
compelled to allow it to escape in an anhydrous condition.

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
28th December 1881.
CARL FRIEDRICH CLAUS, of Mark Lane, in the City of London, Chemist.
IMPROVED PROCESS FOR THE PURIFICATION OF COAL GAS."
"AN
Various processes have been employed in attempts to remove carbonic acid
and sulphuretted hydrogen from coal gas by means of caustic ammonia, but none
of such processes has accomplished the removal of the whole of these two
impurities. These processes have moreover been accompanied with special
disadvantages, by reason of certain defects in the process and arrangements of
the plant or apparatus larger quantities of caustic ammonia than were necessary
to take up the said impurities where introduced into the gas without removing
the impurities, the excess of ammonia was carried away by and contaminated the
coal gas, and its removal by washing was impracticable, except with an injuriously
large quantity of water, such as would greatly impair the illuminating power of
the gas. A further disadvantage consequent upon the necessitated use of excessive
quantities of ammonia and water to wash the same out of the gas again was the
formation of such weak gas liquor, as would render the reproduction of the caustic
ammonia a matter of great difficulty.
In the Specification of Hill's Patent, No. 1369, A.D. 1868, there is described a
process for driving off from gas liquor part of the carbonic acid and sulphide of
hydrogen which are combined in the liquor with ammonia by heating the said
liquor and leaving a liquid consisting partly of caustic ammonia. In the Specifi-
cation of other Letters Patent No. 510, A.D. 1870, the same inventor describes a
process whereby the purified liquor may be concentrated by distillation, and the
ammoniacal vapours may be driven into coal gas for the purpose of purifying the
same from more or less of the carbonic gas and sulphur, and cyanogen compounds.
It is stated in the Specification of the last named Letters Patent that the
ammoniacal vapours may be condensed into liquid ammonia by being passed
through closed pipes cooled externally, by cold liquids, thus shewing that the
ammonia passes off from the liquid accompanied with a considerable quantity of
water before it passes into the coal gas for the purpose of purifying the same.
In beating or distilling the purified gas liquor until all of the ammonia and
volatile ammoniacal compounds are expelled from the same, from thirty to fifty per
cent. (30 to 50%) of the water in which they have been dissolved is volatilised
along with them.
This quantity of water is sufficient to form by cooling and condensation from
the ammoniacal vapours driven off from the still a perfect and comparatively
dilute solution of caustic ammonia, carbonate of ammonia, and sulphide of
ammonium.
Now I have found by experiment that aqueous vapours of ammonia are
unsuitable for the purification of coal gas, but that anhydrous or uncondensable
gaseous ammonia is effectual for purifying such gas, that is to say, if the ammonia
before it enters the coal gas is in a truly gaseous state it mixes readily with the
coal gas and takes up all of its impurities without being condensed into liquid.
Moreover no excess of ammonia is required beyond the chemical equivalent of the
acid impurities of the gas, and by these means. the necessity for using such
excessive quantities of water for the ultimate removal of the excess of ammonia
is prevented. On the other hand, if aqueous ammoniacal vapour is admitted into
the coal gas for the removal of its impurities, this vapour speedily condenses into
liquid, and thus its aminonia is withdrawn from intimate contact with the gas,
thereby necessitating the use of a large excess of ammonia and excessive quantities
of water for its subsequent removal.
By my improvements I effect a practically complete removal of the carbonie

page_text: acid and sulphide of hydrogen from the coal gas. According to the said improve-
ments the ammonia is admitted into the coal gas in its anhydrous or uncondensible
gaseous condition so that it may mix with the coal gas without being condensed,
and may combine with the impurities of the gas previous to its condensation or
absorption into the liquors during its passage through the scrubbers.
To obtain the gaseous ammonia for the purpose of my Invention from liquors
which have been purified according to the process described in the said Specifi-
cation of Hill, No. 1369, A.D. 1868, I also distil the ammonia, but in a manner
essentially different from that proposed in Hill's Specification, No. 510, A.D. 1870,
that is to say, instead of allowing the vapours as they issue from the still to pass
into the coal gas, conduct the vapours as they issue from the still through a
series of condensing vessels arranged somewhat according to the principle of the
apparatus termed the "Woolf's bottle," that is to say, the vapours as they issue
from the still pass through a pipe, preferably perforated, into the bottom of the
first condenser, and by another pipe from the top of the first condenser into the
bottom of the second, and so on, into such a number of condensers as may be found
necessary to obtain the desired result. Purified liquor enters the last condenser,
and by an over-flow pipe passes into the next adjacent one, and so on, through the
whole series of condensers in the direction opposite to that in which the vapours
travel until it enters the still.
The Woolf's bottles which I employ may consist of a number of iron boilers or
tanks, or a series of scrubbers or apparatus, such as that known as a Coffey's still.
When the liquor enters the still and is heated in the same it parts, as above stated,
with its ammonia and ammoniacal compounds, and with about one third to one
half (to) of the volume of the water in the gas liquor in the form of vapour.
This vapour when condensed in the condensers enriches in proportion to its
quantity the contents of the same in ammonia until a point of saturation is reached,
at which no more ammonia can be absorbed or retained. The ammonia will
consequently pass in a gaseous form accompanied by some carbonate and sulphide
of ammonium vapours out of the last condenser practically free from aqueous
vapour, provided the temperature in the condensers has been kept sufficiently low
to permit the condensation of the aqueous vapour to provide for regulating the
temperature in the condensers sufficiently to allow the requisite condensation to
take place; they are fitted externally or internally with water coolers, such as
pipes or jackets, through which cold water circulates. The ammonia escaping
from the last or one of the last of these condensers, being principally gaseous,
caustic ammonia can now be admitted into the coal gas for the purpose of purifi-
cation, in quantities regulated according to the chemical equivalents of the acid
impurities passing at the time without employing an excess of ammonia. The
products of the combination are removed in the scrubbers by contact with gas
liquor or water, and, the resulting liquid is used over again, as will be understood
from the foregoing description.
Having thus fully described my said Invention and the manner of performing
the same, I wish it understood that I claim,-
The purification of coal gas by the above described process comprising the
obtaining of anhydrous gaseous ammonia or ammoniacal gas from purified gas
liquor, and the admixture of the said anhydrous ammonia or ammoniacal gas with
the coal gas, substantially in the manner specified.
In witness whereof, I, the said Carl Friedrich Claus, have hereunto set my
hand and seal, this Twenty-eighth day of December, in the year of our Lord
One thousand eight hundred and eighty one.