IMPROVEMENTS IN THE MANUFACTURE OF PULP FROM WOODY MATTER BY CHEMICAL PROCESS
Year: 1884

page_text: "
I SYDNEY PITT of Sutton in the County of Surrey Gentleman do hereby declare
the nature of my invention for "IMPROVEMENTS IN THE MANUFACTURE OF PULP
FROM WOODY MATTER BY CHEMICAL PROCESS A communication to me from abroad
by Raoul Pierre Pictet of Geneva and Georges Louis Brélaz of Lausanne
Switzerland to be as follows:-
This Invention which relates to improvements in the manufacture of wood
pulp by chemical process is described to me by my foreign correspondents as
follows:-
In the processes at present in use for the manufacture of wood pulp by chemical
means alkaline, solutions of soda are almost invariably employed associated
with different preparations of certain acids (sulphurous acid hydro-chloric and
others).
These solutions in a somewhat concentrated state are placed in closed vessels or
boilers heated by steam. A high pressure of from 5 to 7 atmospheres is developed
resulting from the high temperature arrived at in this system of heating.
The wood cut into fragments is first placed in these strong lead lined reservoirs,
and under the influence of the boiling liquors the wood decomposes. The gums
the resins and enclosing substances dissolve and are partially destroyed undergoing
chemical decomposition, whilst the pure cellulose which is the essential element of
the ligucous fibre appears and separates from the mass.
It is necessary in order to obtain this result to raise the temperature to above
120 or even 140 degrees, without which the disaggregation is incomplete, and the
wood remains hard and unsuited to be operated on by the machines intended to
reduce it to the state of paper pulp.
The high temperature transforms in great part the gums and the resins into tar
and pitch. Carbonaceous substances which penetrate the fibre of cellulose and
render the bleaching very laborious and costly,

page_text: The washings and repeated lixiviations which then become necessary injure the
whiteness of the product and reduce the yield.
We have endeavoured to obviate these several inconveniences by the following
process.
We use a solution in water of a sulphurous acid, only this solution must be of a
strength which it is impossible to obtain in the ordinary towers, in fact it is
necessary to dissolve from a 100 to 150 grammes of gaseous sulphurous acid to a
litre of water which gives a pressure of 5 to 6 atmospheres in the boiler or closed
vessel at a temperature between 80 and 90 degrees centigrade.
This temperature allows the enclosing substances to preserve their chemical
characters without any trace of decomposition liberating carbon. On the other
hand this temperature and this pressure causes the liquid to penetrate to the centre
of the wood, completely dissolving all the organic matrix in which the cellulose is
retained. ⚫
Thus by procuring a supersaturated solution of sulphuric acid the problem of the
use of chemical manufacture of wood pulp is completely solved.
To obtain this solution we have two processes; one is as convenient as the other
and it can be commercially employed.
(1) Having a closed boiler or vessel full of wood cut into fragments and water
filling the free intervals sulphurous acid liquified under pressure is introduced into
this vessel in the proportion indicated above, that is to say of 100 to 150
kilogrammes to the 1000 litres of water.
(2) By means of a pump the gaseous sulphurous acid is directly compressed
and forced into the boiler or vessel which contains the water and the wood.
In order that the solution of sulphurous acid may enter more completely in the
interior of the wood, we consider it suitable to produce a vacuum in the boiler or
vessel before admitting the solution to it, the wood only being in the boiler or
Vessel. All the air contained in the fibres and in the pores is compelled to leave
them in consequence of the reduction of the pressure.
At this moment supersaturated sulphurous acid liquor is admitted into the
closed vessel, and these vapours immediately take the place of the air occluded in
the boiler or vessel.
The disaggregation of the wood is thus simultaneously affected throughout the
entire thickness of the woody tissue, this hastens and assures rapidity in the
operation.
When the wood is sufficiently cooked the acid solution contains a number of
different products, of which the following are the principal.
(1). A large proportion of gums resins and glucose resulting from the enclosing
substances, and from the essential oils of the wood.
.
(2) Sulphates of lime in a small proportion
(3) Almost the whole of the sulphurous acid introduced in a free state.
Successive cooking operations can be carried out in the saine quantity of liquor:
The solution is able to dissolve the gums and essences of the wood in very large
proportion before becoming saturated with these products.
It is sufficient to cause the solution obtained from one boiler or vessel where
the process is complete to pass into a second filled with fresh wood, and to
continue at once in the second boiler or vessel a like operation to that performed in
the first.
'
The moist and disaggregated wood which remains in the boiler or vessel retains
its form and exterior appearance, but on the least pressure it gives way and
divides into a multitude of cellulose elements which in their glomeration constitute
wood pulp.
Liquid is retained by capillarity in the wood and will not flow out from the
first boiler or vessel into the second; it is necessary to remove the wood from the
boiler to press it and then to utilize the liquid which flows out.

page_text: Before this operation the sulphurous acid gas which disengages itself spon-
taneously from the liquor is caused to pass into a gasometer where the
sulphurous acid gas is stored and when gas ceases to be given off, then hydraulic
pressure is applied to the material.
By evaporating the residual liquids from the hydraulic presses colophony
resins, tartaric acid, tannin & can be extracted according to the nature of the wood
treated.

page_text: او
I SYDNEY PITT of Sutton in the County of Surrey Gentleman do hereby declare
the nature of my invention for "IMPROVEMENTS IN THE MANUFACTURE OF PULP
FROM WOODY MATTER BY CHEMICAL PROCESS (A communication to me from
abroad by Raoul Pierre Pictet of Geneva and Georges Louis Brélaz of Lausanne
Switzerland) and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:-
This invention which relates to improvements in the manufacture of wood pulp
by chemical process is described to me by my foreign correspondents as follows:-
In the process at present in use for the manufacture of wood pulp by chemical
means alkaline solutions of soda are almost invariably employed associated with
different preparations of certain acids (sulphurous acid hydro chloric and others).
These solutions in a somewhat concentrated state are placed in closed vessels or
boilers heated by steam. A high pressure of from 5 to 7 atmospheres is developed
resulting from the high temperature arrived at in this system of heating.
The wood cut into fragments is first placed in these strong lead lined reservoirs,
and under the influence of the boiling liquors the wood decomposes. The gums,
the resins and incrusting substances dissolve and are partially destroyed undergoing
chemical decomposition whilst the pure cellulose which is the essential element of
the ligneous fibres appears and separates from the mass.
It is necessary in order to obtain this result to raise the temperature to above
120 or even 140 degrees without which the disaggregation is incomplete and the
wood remains hard and unsuited to be operated on by the machines intended to
reduce it to the state of paper pulp.
The high temperature transforms in great part the gums and the resins into tar
and pitch. Carbonaceous substances which penetrate the fibre of cellulose and
render the bleaching very laborious and very costly.
The washings and repeated lixiviations which then become necessary injure the
whiteness of the product and reduce the yield which from 48 to 50 per cent falls to
150 to 170 per thousand. The cost of the product is thus considerably increased
by this inevitable loss in the yield. Finally the strength of the fibre of the
cellulose is considerably reduced in consequence of the repeated action upon them
of chloride of lime.
We have endeavoured to obviate these several inconveniences by the following
process of which we will in the first place give a theoretical statement before
describing the special arrangement to which we have reduced it.
It is well known that all bodies are capable of being decomposed into their
essential elements when they are heated, organic bodies in particular pass through
a series of successive transformations due to the elevation of temperature. The
higher the temperature is raised the simpler are the products of decomposition and
the more nearly they resemble the bodies studied in inorganic chemistry. "
The hydro carbons and the same bodies oxidized and azotized have a tendency
when they are heated to yield hydrogen and carbon.

page_text: This is what immediately takes place when wood is heated to a temperature
beyond a 100 degrees Centigrade. The carbon of the resins and gums and the
incrusting substances tends to appear, it detaches itself from each organic molecule
and deposits itself on the fibres of the wood cellulose in a powder of such fineness
that the insterstices of the cells and their pores are filled and obstructed.
Carbon is insoluble and cannot be bleached, hence it is only by prolonged
chemical action that it can be got rid of.
On the other hand if a solution be found capable of dissolving and decomposing
the incrusting substances of the wood at a sufficiently low temperature for the
carbon to remain chemically associated with the other components hydrogen oxygen,
azote, there is no longer this special difficulty; the cellulose will no longer be
injured by the immoderate use of chloride of lime; the yield will be the maximum
and the quality of the product obtained will be very superior whilst costing less
than that obtained by other processes.
After numerous investigations we have arrived at this conclusion that a solution
in water of sulphurous acid fulfills completely the required conditions only this
solution must be of a strength which it is impossible to obtain in the ordinary
towers. In fact it is necessary to dissolve from a 100 to 150 grammes of gaseous
sulphurous acid to a litre of water to obtain a pressure of 5 to 6 atmospheres in the
boiler closed vessel or autoclave at a temperature between 80 and, 90 degrees
Centigrade.
This temperature allows the incrusting substances to preserve their chemical
characters without any trace of decomposition liberating carbon. On the other
hand this temperature and this pressure causes the liquid to penetrate even to the
centre of the wood completely dissolving all the organic matrix in which the
cellulose, is retained.
Thus by procuring a supersaturated solution of sulphurous acid the problem of
the use of simple and economical chemical manufacture of wood pulp is completely
solved.
To obtain this solution we have two. convenient processes which can be
commercially employed.
1 There being given a closed vessel or autoclave full of wood cut into chips and
water filling the free intervals by means of a pump free sulphurous acid gas is
forced directly into it. This sulphurous acid gas can be produced by the decom-
position of sulphuric acid gas either with sulphur or with carbon; it is stored in a
large oil gasometer. The pump at each stroke takes a definite weight of sulphurous
gas and the working of the pump is stopped as soon as the necessary quantity of
acid is passed into aqueous solution. It is necessary as far as possible to avoid loss
of the sulphurous acid so as to reduce the consumption of this gas. To recover it at
the end of each operation the gas from the autoclave (which is under pressure) is
directed into an oil gasometer from which the force pump draws it and passes it
into a second vessel full of wood and water. The small quantity of gas lost during
the operation is compensated by gas drawn from the reserve of sulphurous acid.
:
2 This second process which is more simple than the preceding in that it does
not require a force pump is the one shewn by the annexed drawing-it operates in
the following manner :-
A is a cast iron still in which sulphur or charcoal is introduced, the still is
covered by a cast iron dome B, it is heated and then a small continuous stream of
sulphuric acid is allowed to enter by the safety tube C. The sulphurous gas passes
off by the tubes D E and enters the receptacle F where water condenses. It passes
then into the drying vessel H and by the tube I passes into a system of boxes J. J.
with partitions upon which a current of water is caused to fall in small streams.
The gas is almost entirely dissolved in the first box and the small quantity which
escapes passing into the regulator K opens more or less the valve L which regulates
the delivery of water from the reservoir M proportionally to the quantity of gas
'to be dissolved.

page_text: The solution is collected in a large reservoir O of wood lined with lead-this
solution is not sufficiently concentrated to produce disaggregation, to obtain the
strength required it is conducted into a reservoir Q of copper or cast iron lined
with lead and capable of sustaining pressure. The autoclave S we will suppose it
be under pressure and the boiling terminated; the cocks TUXR are opened
and the others V. Z. P. are closed. The gas from the autoclave then passes into a
safety vessel Y where all the liquid brought over by the gas is deposited and the
gas under pressure is delivered into the solution in the reservoir Q by the tube d
perforated with holes and furnished with a valve to prevent the return of liquid
from the safety vessel. Y.
By drawing a sample one judges from the density of the solution when it has
arrived at its proper condition. The cock R is then closed and Z is opened and the
gas which remains in the autoclave or vessel passes into the boxes J. J. to form a
fresh quantity of weak solution which nearly replaces that employed in the
previous boiling.
To obtain the first supersaturated solution the autoclave is filled with a weak
solution and after having heated it it is allowed to disengage gas into that of the
reservoir Q. After this preparatory operation the wood and water are introduced
and the process just described is commenced.
The autoclave is of copper or iron lined with lead and is heated either by free
steam introduced into it or by a double bottom or chamber or by a serpentine b of
lead or copper.
To return the solution under pressure into the autoclave equilibrium is estab-
lished by putting the reservoir Q and the autoclave in communication by a pipe
when the cocks V. T. R are opened the others X. U. Z. being closed.
With this process it is possible to have always on hand a boiler or vessel full of
wood soaked in a supersaturated solution of sulphurous acid of the strength
required.
In order that the solution of sulphurous acid may enter more completely in the
interior of the wood we consider it suitable to produce a vacuum in the boiler or
vessel before admitting the solution to it. The wood only being in the boiler or
vessel. All the air contained in the fibres and in the pores is compelled to leave
them in consequence of the reduction of the pressure of gas.
At this moment supersaturated sulphurous acid liquor is admitted into the closed
vessel or autoclave and these vapours immediately take the place of the air
previously occluded.
The disaggregation of the wood is thus simultaneously effected throughout the
entire thickness of the woody tissue; this hastens and assures rapidity in the.
operation.
When the wood is sufficiently cooked the acid solution contains a number of
different products of which the following are the principal:-
(1) A large proportion of gums resins and glucose resulting from the enclosing
substances and from the essential oils of the wood.
(2) Sulphates of lime in a small proportion.
(3). Almost the whole of the sulphurous acid introduced in a free state.
Practice has shown that several successive cooking operations can be carried out
with the same quantity of liquor the solution is able to dissolve the gums and
essences of the wood in very large proportion before becoming saturated with
these products.
It is sufficient to cause the solution obtained from one boiler or vessel where the
process is complete to pass into a second filled with fresh wood and to continue
at once. in the second boiler or vessel a like operation to that performed in the
first.
The moist and disaggregated wood which remains in the boiler or vessel retains
its form and exterior appearance but on the least pressure it gives way and divides
into a multitude of cellulose elements which in their glomeration constitute wood
pulp.

page_text: Liquid is retained by capillarity in the wood and will not flow out from the first
boiler or vessel into the second; it is necessary to remove the wood from the boiler
to press it and then to utilise the liquid which flows out.
Before this operation the sulphurous acid gas which disengages itself.
spontaneously from the liquor is caused to pass into a gasometer where the
sulphurous acid gas is stored and when gas ceases to be given off hydraulic pressure
is applied to the material.
By evaporating the residual liquids from the hydraulic presses colophony, resins
tartaric acid, tannin & can be extracted according to the nature of the wood
treated. All the bye-products are capable of being worked according to the
geographical position of the works and the requirement of the market.
In each charge a fresh quantity of liquid is added of which the volume is
equivalent to the volume of liquid retained by the capillarity of the disaggregated
wood.
In fact a wood pulp factory on our system consists in its essential parts of the
following departments :-
1. A manufacture of sulphurous acid gas produced by the decomposition of
sulphuric acid by sulphur or by carbon; this gas is passed into an oil gasometer
or into the boxes where it is dissolved according to the process employed.
2. Of two autoclaves of copper or cast iron lined with lead communicated by a
system of pipes and stop cocks which permit the liquids to pass from one to the
other under the influence of the difference of interior pressure if the first process
be employed; or if one or several independent autoclaves connected by pipes to a
reservoir of supersaturated solution if the second process be employed. These
autoclaves furnished with pressure gauges and thermometers may also by these
pipes be connected to a vacuum pump and for the first [process to a force pump
supplying sulphurous acid gas.
All these connections are furnished with stop cocks suitable to the operations.
The boilers or closed vessels may be vertical or horizontal fixed or capable of
turning on their axes like ordinary lixiviating vessels.
3. Of a hydraulic press intended to press the wood when it comes out of the
boiler or vessel.
4. Of the stampers intended to effect the complete disaggregation of the fibres of
the wood and their transformation into wood pulp.
The bleaching by chloride of lime is preceded in this manufacture by the action
of sulphurous acid which diminishes very considerably the cost of this operation.
Besides bleaching is not essential for it may be done at the Paper Works quite
as well as in the Wood Pulp Factory.
The extraction of the by-products obtained from the liquids from the hydraulic
press can be effected by known processes.
It is necessary to say that we do not limit ourselves in any way to the arrange-
ment represented by the drawing considering that all arrangements realizing either
wholly or in part the essential features stated in the claiming clause fall within
the scope of the present Patent.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what
we claim is
The treatment of cellulose for the manufacture of wood pulp by the process
substantially as described above, to which one or more of the following points are
essential although it is not indispensable that all should be employed :-
(a) To prepare by any means but especially by the means described, a super-
saturated solution of sulphurous acid in water having a gaseous tension of from
5 to 6 atmospheres at a temperature below 100 degrees centigrade.
(b) Using a vacuum for mechanically removing the air contained in the wood
to facilitate the penetration of the sulphurous solution into the interior of the
immersed fibres.

page_text: (c) Employing low temperatures under 100 degrees Centigrade or thereabout
which do not decompose the matters which incrust the fibre of the wood..
(d) Re utilizing the solutions from the boilers or vessels after the operation and
recovering almost the whole of the sulphurous acid retained in the liquid. by
capillarity in the disaggregated wood.
(e) Re-utilizing the sulphurous acid gas contained in the autoclave after the
operation to make a new solution according to the system represented in the
drawing annexed.
(f) Utilizing the by-products resulting from the solution of the incrusting
matters to obtain gums resine, tannin alcohol &c.
1000
CARPMAEL & Co.,
Agents for the Applicant.