Improved Process for Producing Pure Carbonic Acid Gas.
Year: 1892

page_text: Date of Application, 3rd June, 1892-Accepted, 8th Oct., 1892
COMPLETE SPECIFICATION.
Improved Process for Producing Pure Carbonic Acid Gas.
I, EDUARD LUHMANN of Andernach on the Rhine, Kingdom of Prussia,
German Empire, Chemist 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:-
My invention relates to an improved process for producing carbonic acid gas
in a pure condition, and is characterized by the employment of the phosphates of
an alkali.
The method as hitherto used for producing carbonic acid gas from substances
forming or giving off carbonic acid either by decomposition or by combustion con-
sists in causing the carbonic acid arising therefrom to be absorbed by a soda lye or
carbonate of soda, thus forming bicarbonate of soda, and in heating the lye sub-
sequently, thereby expelling the carbonic acid gas, which is conveyed to a gasometer
in order to be liquefied.
This method however of forming bicarbonate and carbonate of soda is very
costly, on account of the prolonged boiling required for the complete decomposition
of the bicarbonate; a great amount of heat being thereby consumed in this usual
process.
I have ascertained that a very convenient substitute for alkali lye and carbonate
of alkali is found in the phosphates of alkali, and more particularly in the
phosphate of soda.
When carbonic acid proceeding from a coke furnace, or natural springs, or
evolved in the course of chemical processes, is led into a solution of phosphate of
soda in cold water biphosphate of soda is formed, besides bicarbonate of soda, and
this mixture of biphosphate and bicarbonate of soda is completely re-converted into
phosphate of soda by the application of a moderate heat, somewhat below boiling
point.
Thus it will be obvious that phosphate of soda affords an excellent means for
absorbing pure carbonic acid from impure gaseous mixtures and for liberating
again this carbonic acid gas in an easy manner by the application of heat.
:
As an example, I will state the proportions in which the phosphate of soda may
be used 10 lbs. of phosphate of soda (Na,HPO) are dissolved in 100 lbs. of
water, I then lead into the cold solution the impure carbonic acid gas (proceeding
from any source), care being taken that the temperature of this said gas is as
low as possible. An absorption of the carbonic acid (CO2) then takes place, and
the chemical process is represented by the equation:
NaHPO, + CO, + HgO = NaH,PO,+ NaHCO..
1t will be seen that biphosphate of soda (NaH,PO) and bicarbonate of soda
(NaHCO3) are formed thereby. When the chemical action is complete, the mixed
solution of biphosphate and bicarbonate of soda resulting therefrom is heated by
means of a steam-coil (not perforated), the temperature employed being 212° F.
as a maximum, by the application of which said heat pure carbonic acid is
obtained, which is hereafter collected in a casometer.
NaH,PO + NaHCO3 = Na,HPO + CO2 + H₂O ;
4
4
45 that is to say, the solution has returned to its initial state, and, when cooled, may
be used again for the absorption of impure carbonic acid gas, as described.
I wish it to be understood that (although I by preference employ phosphate

page_text: of soda) I do not confine myself to the employment of this salt, as I may also use
phosphate of potash, or pyrophosphates and the like.
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 :-
The method of obtaining pure carbonic acid gas, consisting in introducing the
gases containing carbonic acid into a solution of a phosphate of alkali, (and more
particularly of phosphate of soda,) and in hereafter liberating the absorbed
carbonic acid gas by heating the mixed solution resulting therefrom, for the
purpose as described.
Dated this 3rd day of June 1809
EDUARD LUHMANN,
By Geo. H. Rayner,
37, Chancery Lane, London, W.C., Agent for the Applicant.