An Improvement in the Process for the Simultaneous Production of Cellulose and Oxalic Acid from Vegetable Fibrous Substances.
Year: 1891

page_text: Date of Application, 31st Jan., 1891
Complete Specification Left. 25th Sept., 1591-Accepted, 5th Dec., 1891
PROVISIONAL SPECIFICATION.
An Improvement in the Process for the Simultaneous Production of
Cellulose and Oxalic Acid from Vegetable Fibrous Substances.
I, ISAAC LIPSCHÜTZ, Dr. ph., of Grünau near Berlin, Kingdom of Prussia,
Manufacturing Chemist, do hereby declare the nature of this invention to be as
follows:-
If vegetable fibrous materials, such as wood, are treated with diluted nitric acid
at a moderate heat (about 60° Centigr.) the substances that incrustate the fibres
are dissolved and cellulose is obtained, while a portion of the cellulose is decomposed
and converted into oxalic acid.
In this process, as heretofore carried out, the nitric acid is, however, not utilized
entirely, the time required for the process is considerable, the quantity of oxalic
acid obtained is but small, it is difficult to separate the same out, and its production
is attended with losses of both oxalic and nitric acids.
The object of my invention is to render the said process practically useful for
simultaneously producing cellulose and oxalic acid, and for utilizing the whole
amount of nitric acid employed. For this purpose I add sulphuric acid to the
diluted nitric acid, and I treat the crude fibrous material with such mixture of
acids, the sulphuric acid having the effect to considerably promote the action
of the nitric acid, so that the latter, even if highly diluted, operates efficiently
until it is used up entirely. The process may be carried out at the mean
temperature of the air and no pressure is required, but, if the nitric acid is
highly diluted, it is advantageous to apply heat, the temperature being raised,
up to about 80° Centigrade, in the measure as the dilution of the acid is greater.
After one portion of fibrous material has been treated, I repeat the process with
new portions, always using the same acid mixture over again, and preferably
raising its temperature gradually, until all or nearly all nitric acid has been
consumed. If the process is carried out at the ordinary temperature of the air,
the oxalic acid commences to crystallize out when the acid mixture is becoming
short of nitric acid, and, after the disappearance of the latter, only about
1 or 2 per cent. of oxalic acid remain in solution in the residual liquid, which then
mainly consists in sulphuric acid. In case heat is applied during the process, the
liquid finally obtained is substantially sulphuric acid saturated with oxalic acid,
and from which the oxalic acid separates out with exception of the aforesaid
amount, when the liquid is cooled. The oxalic acid thus obtained contains, about
per cent. of pure acid, so that for its complete purification it only requires to be
dissolved and recrystallized once.
93
The fibrous product resulting from the process is washed with water, hoiled
with a weak alkalic solution and washed again in view of obtaining pure cellulose.
Dated the 20th day of January 1891
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.

page_text: CUMI LEIM DI DUINICALIOA
An Improvement in the Process for the Simultaneous Production of
Cellulose and Oxalic Acid from Vegetable Fibrous Substances.
1, ISAAC LIFSCHÜTZ, Dr. ph., of Grünau, near Berlin, Kingdom of Prussia,
Manufacturing 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:-
If vegetable fibrous materials, such as wood, straw, jute and the like, and which
I shall in the following call ligneous materials, are treated with diluted nitric acid
at a moderate heat (about 60° Centigr.) the substances that incrustate the fibres
of the material are dissolved and cellulose is obtained, while a portion of the
cellulose is decomposed and converted into oxalic acid. In this process, as hereto-
fore carried out, the nitric acid is, however, not utilized entirely, the time required
for the process is considerable, the quantity of oxalic acid obtained is but small, it
is difficult to separate the same out, and its production is attended with losses of
both, oxalic and nitric acids.
The object of my invention is to render the said process practically useful for
simultaneously producing cellulose and oxalic acid, and for utilizing the whole
amount of nitric acid employed. For this purpose I add sulphuric acid to the
diluted nitric acid, and I treat the crude ligneous material with such mixture of
acids, the sulphuric acid having the effect to considerably promote the action of the
nitric acid, so that the latter, even if highly diluted, operates efficiently until it is
used up entirely. The process may be carried out at the mean temperature of the
air and no pressure is required; but, if the nitric acid is highly diluted, it is
advantageous to apply heat, the temperature being raised up to about 80° Centigrade,
in the measure as the dilution of the acid is greater. After one portion of material
has been treated, I repeat the process with new portions, always using the same
acid mixture over again, and preferably raising its temperature gradually, until all
or nearly all nitric acid has been consumed. If the process is carried out at the
ordinary temperature of the air, the oxalic acid commences to crystallize out when
the acid mixture is becoming short of nitric acid, and, after the disappearance of
the latter, only about 1 or 2 per cent. of oxalic acid remain in solution in the
residual liquid, which then mainly consists in sulphuric acid. In case heat is applied
during the process, the liquid finally obtained is substantially sulphuric acid
saturated with oxalic acid, and from which the oxalic acid separates out with
exception of the aforesaid amount, when the liquid is cooled. The oxalic acid thus
obtained contains about 93 per cent. of pure acid, so that for its complete purification
it only requires to be dissolved and recrystallized once.
The fibrous product resulting from the process is washed with water, boiled
with a weak alkalic solution, and washed again in view of obtaining pure cellulose.
If, for instance, diluted nitric acid containing 10 per cent. of acid, is mixed with
one third its volume of sulphuric acid, and the mixture is caused to act, at the
mean temperature of the air, on fir-wood, the incrustating substances of the
fibres have, after about 30 hours, become soluble, so that if the material is boiled
in a weak alkalic lye, or even in water, the fibres thereof will separate from
cach other. After the removal of the converted material the acid liquid contains
sulphuric acid, the residual nitric acid, fatty acids (such as acetic acid, butyric
acid, valerianic acid, &c.) and a considerable quantity of oxalic acid. By cautious
application of heat the time required for the reaction may be considerably
shortened. A diluted nitric acid containing 25 per cent. of acid and likewise
mixed with one third its volume of sulphuric acid, gives at 40° Centigr. excellent
results in respect to cellulose and oxalic acid. The yield of the two products
varies with the amount of acid mixture and the temperature applied, more oxalic

page_text: acid (up to 30 or 35 per cent, of the wood employed) being obtaining at higher
temperatures, while at lower temperatures more cellulose is produced.
The particular influence which the sulphuric acid has in the process, appears to
consist, firstly, in this that by its dehydrating action it promotes the infiltration of
the acid mixture into the pores of the fibres and thereby accelerates the action
of the nitric acid. In the second place the sulphuric acid operates by virtue of the
same property, in a manner to concentrate the nitric acid, so as to render the latter,
even if highly diluted, capable of converting the incrustating substances and of
abundantly generating oxalic acid from the fibres.
Moreover, it is by means of the sulphuric acid that the direct production of
oxalic acid in solid state is rendered possible, inasmuch as oxalic acid is but very
little soluble in cold sulphuric acid, while nitric acid dissolves the same easily.
Now, as by repeated employment of the acid mixture with fresh material the nitric
acid may be used up entirely, the remaining liquid will readily allow the oxalic
acid to separate out, as herein before stated.
For practically carrying out my invention I proceed as follows.
Crude ligneous material, for instance fir-wood cut into small pieces, is put into
a vessel of earthenware or other suitable substance, and a cold mixture of diluted
nitric acid and sulphuric acid is poured upon the same, so that the material is
entirely immersed in the liquid. By preference one part by measure of concentrated
sulphuric acid and three parts of nitric acid having a specific gravity of from 1.15
to 118, are employed. The whole being left to repose, brown vapors are evolved
consisting in different compounds of uitrogen and oxygen (NO3, NO, NO₂), but
not containing nitrous oxide (NO) and which may therefore be regenerated so
that nitric acid is reproduced. When the evolution of vapors abates considerably
the reaction is completed, the ligneous material having at the time been converted
into an intermediate product which is not yet disaggregated, but which contains
the undissolved portion of the incrustating substances in such state of conversion
that they may easily be removed. The said product is separated from the acid
liquid and washed, first with cold and then with hot water, and subsequently it is
boiled with a weak alkalic solution (containing about per cent. of caustic alkali
or alkalic carbonate) whereby the incrustating substances are completely dissolved,
so that the fibres become disaggregated. By finally filtering and again washing
with water, pure cellulose is produced, the amount obtained from fir-wood being
about 45 per cent. of the weight of the latter.
The acid liquid separated from the intermediate product is used over again for
the treatment of new portions of ligneous material until the nitric acid has been
consumed and oxalic acid has separated out. Preferably however, each succeeding
operation is carried out at a temperature being from 5° to 10° Centigr. higher than
the preceding one. In operating in this manner with fir-wood the nitric acid is
used up before the temperature of 80° Centigr. is arrived at.
The liquid remaining
after separation therefrom of the intermediate product consists in sulphuric acid
having a strength of about 30 or 33 per cent. and highly saturated with oxalic acid.
The same is allowed to cool in view of causing the oxalic acid to crystallize out.
The acid obtained in either way is collected and purified by dissolution and
recrystallization.
The residual sulphuric acid is mixed again with nitric acid and used anew, the
oxalic acid then separating out at the end of the process consisting in the whole
amount formed during the same. A quantity of oxalic acid equal to the portion
that remains in solution, may, however, be incorporated into the sulphuric acid at
the commencement by saturating the same in cold state with the former, and,
moreover, the enrichment of the acid mixture with oxalic acid may be brought
about by restituting to the mixture, after every operation, the nitric acid consumed,
and then proceeding to use it up entirely.
It is to be observed that no nitro-compounds are formed either in the intermediate
product or in the liquid.

page_text: Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
1. The process of producing cellulose and oxalic acid, which consists in immersing
ligneous material in a mixture of nitric acid water, and sulphuric acid, separating
froin the the liquid the converted ligneous material previous to its disaggregation
repeating the operation with new portions of material until the nitric acid has been
used up, and separating from the liquid the oxalic acid which has crystallized out,
substantially as specified.
2. The process of producing cellulose and oxalic acid, which consists in immersing
ligneous material in a mixture of nitric acid water, and sulphuric acid, separating
from the liquid the converted ligneous material previous to its disaggregation,
repeating the operation with new portions of material until the nitric acid has been
used up, the temperature of the liquid being raised at every succeeding operation,
cooling the remaining liquid, and separating therefrom the oxalic acid which has
crystallized out, substantially as set forth.
Dated 1
1
ca
1001
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.