cting Cellulose from Wood.
Year: 1884

page_text: Extracting Cellulose from Wood.
I ALFRED ALBUTT of the General Patent Office, No 4, South Street, Finsbury,
in the County of Middlesex, Mechanical Draughtsman, do hereby declare the
nature of the said invention for "AN IMPROVED PROCESS OF PREPARING A LYE
FOR AND METHOD OF EXTRACTING CELLULOSE FROM WOOD," to be as follows:-
This invention relates to an improved process whereby a very rich lye is
obtained for the purpose of extracting cellulose from wood.
As is well known what is known as Mitscherlich's process of extracting cellulose
from wood consists in boiling the subdivided wood with a lye containing
persulphite of calcium.
According to this invention, persulphite of magnesium is employed instead of
persulphite of calcium. As the sulphurous acid is a very important constituent
part of the lye, and as in consequence of the different atomic weights of calcium
and magnesium, 100 parts by weight of persulphite of calcium contain 31'6 parts
only of the said acid, while 100 parts of the magnesium salt contain as many as
344 parts of sulphurous acid, far better results are obtained by the use of this
latter salt.
Pure magnesium salt lye would be of a density of 20° B, but as in practice the
lye is prepared by the medium of magnesite or dolomite which contain great
quantities of carbonate of line, and as the persulphite of calcium formed is less
soluble than that of magnesium, the density of the lyes practically obtained is
from 10° to 20° B.
To prepare the lye, a tower or turret is filled with rather large pieces of porous
maguesite or dolomite, to which pieces of calc-tuf may be added, and then a stream
of water is allowed to flow slowly down through the tower, while sulphurous acid
is caused to enter the tower from below. The sulphurous acid is obtained by the
combustion of sulphur, and while the process of boiling the wood with the lye is
going on, the said acid is driven out by heat from the remaining liquid and
conveyed to the tower.

page_text: 133
Extracting Cellulose from Wood.
I ALFRED ALBUTT of the General Patent Office, N° 4, South Street, Finsbury,
in the county of Middlesex, Mechanical Draughtsman, do hereby declare the
nature of the said invention for "AN IMPROVED PROCESS OF PREPARING A LYE
FOR AND METHOD OF EXTRACTING CELLULOSE FROM WOOD
"and in what manner
the same is to be performed to be particularly described and ascertained in and
by the following statement:—
The object of the present invention is a new process of preparing a concentrated
lye to serve as a means for extracting cellulose from wood, by boiling the wood
with the said lye.
This concentrated lye is a mixture of solutions of bisulphite (persulphite) of
magnesium and of calcium. To prepare the lye a tower or turret is filled with
suitably sized pieces of magnesite or dolomite, which should be as porous as
possible, (calcined or not) and mixed with pieces of calc-tuf; a stream of water is
caused to flow down the tower, a stream of gazeous sulphurous acid, obtained by
the combustion of sulphur or of pyrites being caused to pass up the tower from
the bottom. As soon as the operation of boiling the wood is commenced the
gazeous sulphurous acid, which issues during the operation, is also conducted into
the tower, as hereinafter described.
When the tower is filled with pure oxyde of magnesium, the lye obtained will
have a density of 20° Beaumé, but magnesite being always more or less mixed
with lime and the dolomite being composed of about 54 per cent of carbonate of
lime and 46 per cent of carbonate of magnesium, the density of the lye, especially
when calc-tuf has been added, will be only from 10° to 20° Beaumé, owing to the
bisulphite (persulphite) of calcium being less soluble. The said density and
richness of the lye is nevertheless very considerable as compared with the lyes
which have generally hitherto been prepared for the same purpose.
For the extraction of the cellulose the roughly disintegrated wood is placed in a
boiler lined with stones, cement or lead, and provided with heating pipes, as well.
as with admission pipes and exit-pipes for steam and for the liquids. The wood
having been thoroughly acted upon by the steam, the prepared lye is introduced
into the boiler and the mass is then heated for a time (varying according to
circumstances) up to about 150° Centigrade. By this treatment the component
elements of the wood, which envelop and penetrate the cellulose are dissolved and
the cellulose remains in the liquid in the shape of a soft mass. The heating of the
contents of the boiler is then continued so long as the vapours given off (and which
are reconducted into the tower) show the presence of sulphurous acid, which can
be easily ascertained by the peculiar odour of these vapours.
The described operation having been terminated, the cellulose is removed from
the liquid which contains salts of magnesia and lime, gum, acetic acid etc, which
substances may be extracted from the said liquid, or, if preferred, the liquid can as
it is, be employed for tanning.

page_text: As compared with the known process of treating wood by bisulphite (persulphite)
of calcium, the improved process possesses the following important advantages:
1. The lye can be brought to the degree of concentration required for any given
operation at any temperature whatever.
2. It allows of preparing lyes of any desired strength, within the above
mentioned limits.
3. The lye prepared according to the described process and having a certain
density as compared with lyes prepared according to the known processes by means
of bisulphite of calcium, and having the same degree of density, contains a greater
per centage of sulphurous acid which, as has been proved by the experiments of
M Mitscherlich, is the effective element of the lye. This favorable result of the
improved process is owing to the difference between the atomic weights of calcium
and magnesium. In consequence of this difference bisulphite of magnesium
(Mg H, (S.O) 2) contains 34-4 per cent by weight of sulphurous acid whilst
bisulphite of calcium (Ca H, (SO) 2) contains only 31.6 per cent by weight of the
said acid.
4. When cellulose has been prepared by means of a calcium-lye, the paper
produced very frequently shews gypsum stains. This cannot occur when magnesium-
lye is employed, according to the improved process. When paper prepared
according to this invention shows stains, they can easily be removed by washing
with diluted muriatic acid.
5. The improved process allows of the application of highly concentrated lyes,
the duration of the heating of the mass can therefore be diminished, the action of
concentrated lyes being much more energetic.
6. The process is less costly as in a given space of time and with a given
expenditure of work the improved process allows of greater quantities of cellulose
being produced than by the processes hitherto in use.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed 1 declare that what
I claim is
1. The described process of preparing a concentrated lye for the extraction of
cellulose from wood, such process consisting in causing water to slowly descend a
tower filled with suitably sized pieces of inagnesite or dolomite (calcined or not)
with or without the addition of calc-tuf and in simultaneously introducing into
the said tower from below a current of gazeous sulphurous acid, substantially as
described.
.
2. The described process for extracting cellulose from wood, the said process
consisting in heating at about a temperature of 150° Centrigrade desintegrated
wood in a solution of bisulphite (persulphite) of magnesium and of bisulphite of
calcium, the said solution having a density of from 10° to 20° Beaumé, sub-
stantially as described.