Year: 1887

page_text: Date of Application, 9th Apr., 1887.
Specification Accepted, 13th May, 1887.
[Communicated from abroad by RAOUL PIERRE PICTET, of Geneva, and GEORGES
LOUIS BRELAZ, of Lausanne, Switzerland, Chemists.]
I GEORGE PITT of Sutton in the County of Surrey Gentleman 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:-
The object of this invention is to reduce to an exceptional cheapness the process of
the reduction of cellulose by sulphurous acid, both as regards the process itself and as
regards the plant employed to obtain the sulphurous acid at the required strength.
The new arrangements hereinafter described are based upon the employment of
solutions, very weak at first, but gradually strengthened by recuperation which
permits of the adoption of a most simple system.
This consists in taking an ordinary sulphur distiller or a pyrites roasting furnace of
the usual make, calculating its dimensions so as to obtain the combustion of a given
weight of sulphur per hour.
The products of this combustion are nitrogen and sulphurous acid; the nitrogen is
more abundant with pyrites.
These gases are conducted into a column with shelves similar to those used in the
rectification of alcohol, having 20 to 30 shelves or even more, superposed one above
the other, pierced with holes of 5 to 10 millimetres or made with slits, of copper, lead
or even of wood, receiving from above a shower of water and from below the sulphur
vapours destined to be absorbed by the water which they meet. Waste pipes fitted
in each plate and submerged in the liquid which covers them, ensure its regular outflow,
in the usual way.
The quantity of water descending through the column is regulated by means of a
cock, so as to supply from 80 to 110 kilos of water, or thereabouts, for each kilo
of sulphur burned.
The water, in descending, becomes charged more and more with sulphurous acid,
so that at the top of the column nothing but nitrogen is disengaged, and the maximum
of absorption is thus obtained.
In consequence of the proportions of water and sulphurous acid brought together,

page_text: the solution collected at the bottom of the column never exceeds 1° Beaumé, so that
the losses of sulphurous acid are insignificant, the solution being very far from its
point of saturation at ordinary temperatures.
To secure the circulation of the gases through the column, it seems preferable to make
use of some exhausting power. For this purpose any suitable means of exhaustion
may be used, whether by pump or by ventilator, the effect being to exhaust with a
slight vacuum the gases not absorbed at the top of the column. This vacuum will be
measured simply by the sum of the heights of water covering each shelf and in a
column of 36 shelves it will be equal to about 75 centimetres of water, representing
a very slight vacuum, less than one tenth of an atmosphere.
Under these circumstances nothing will really come out but nitrogen, which can be
emptied into the atmosphere without inconvenience; but if the exhaustion should
bring traces of sulphurous acid, it would be sufficient to make the gaseous stream
pass through a lime wash which would instantly absorb all the sulphurous acid, which
it might contain.
These arrangements permit of the column being constructed of wood, in the form
of a long square case, consisting of four boards joined together at right angles; the
shelves are fitted in on ledges, like the grooves of a cup-board, and one of the
boards, unfastened for the purpose of fitting them in, is simply screwed in its place
when work is to begin. A thin sheet of lead may envelop the column, to avoid all
sulphurous exhalation and the entrance of any air. The slight vacuum in the interior
will secure the staunchness of the wood and will prevent its deformation.
Instead of exhausting the gases, they may be compressed.
In that case, it will be advisable to place the burner in a water tight sheet-iron
reservoir, which can resist a light pressure, of about 1 metre of water at most.
Bellows or any suitable compressor will compress the atmospheric air in the furnace
to feed the combustion, and the products of the combustion pass thence with their own
pressure into the column, which will be of the form above described, but of such a
nature as to offer sufficient resistance, or it may be of any other suitable form. The
nitrogen coming out at the top of the column is treated as in the previous case.
The water is fed in the same way.
The furnace is opened from time to time, to feed it with sulphur or pyrites.
The solutions of sulphurous acid, from 1° to 2° Beaumé, obtained by one or the
other of these two ways, are collected in a reservoir of large dimensions, closed in on
all sides, made of wood, or preferably of wood covered with a thin sheet of lead.
In order to bring these solutions to the degree of concentration requisite for their
disaggregating action on the wood, the following procedure is adopted.
Two digesters, of ordinary construction are made use of preferably they are of the
same dimensions and both provided with heating appliances, only one of these is
heated in the operation, while the other is not. The heating is effected by means of
direct steam circulating in the liquid, or by a coil through which circulates a current
of the vapour of water capable of raising the liquid contained in it to a sufficient
temperature to separate the sulphurous acid gas which it holds in solution.
The two digesters are filled with the solution at 1° or 20 Beaumé obtained by the
operation above described, but the heat acting on the contents of one of them drives
out the sulphurous acid gas, which is conducted by a pipe at the top to the bottom of
the other unheated digester, the liquid of which absorbs it as it ascends, while the
liberated water escapes at the bottom of the heated digester. The heated digester then
receives a fresh charge of weak liquid, which similarly gives off the gas to the
unheated digester, the liquid in which is enriched by all the sulphurous acid gas given
off by the heated one. Thus the liquid in the unheated digester will soon attain
the degree of about 10 per cent., suitable for its utilization.
This operation of recuperation being practiced in various chemical and other
operations I do not claim it so far as regards the operation itself, and I do not intend
to limit myself to the details given, nor need I enter into further particulars as to its
mode of application.. It forms part of my invention as constituting a known means
applied to a new result, viz., the perfect and economical appropriation of the weak

page_text: solution, the preparation of which I have described above, to the disaggregation of the
fibre of the wood intended for the manufacture of paper.
As soon as the gauge of the liquid contained in the unheated digester has attained
the desired degree, for its utilization, there is nothing further to do but to keep it up
by continuing the action of the heated digester by a continual supply of weak liquid.
Care should be taken to charge the unheated digester with the substance to be
treated before commencing the work of recuperation; this will enable the fibres of the
wood to become impregnated gradually with the sulphurous acid of the gradually
enriched solution, and the reduction of the cellulose is then effected by the process
described in a previous patent granted to Sydney Pitt No. 9509 in the year 1884.
When the operation is finished and the cellulose has to be taken out of the
digester in which it was contained, the functions of the two digesters are reversed,
by stopping the heating of the one hitherto heated, filling it again with weak
solution, and placing its bottom in communication with the top of the other, which
thus transmits to it all the sulphurous vapours which have accumulated therein during
the heating sufficiently to allow of the withdrawal of the treated cellulose, without any
waste and without smell. A fresh charge of pieces of wood to be treated has first
been put in, and a fresh treatment is effected by means of the vapours transmitted
firstly by the residue of the previous treatment and secondly by the passage of the
weak liquid through the digester in which such treatment took place, and in which a
sufficient heat is retained for the purpose. By these successive reversals, and this
system of recuperation, the operation can thus be performed without any incon-
venience and without loss.
The process has this great advantage over the one described in the specification
above referred to that it avoids all waste of sulphurous acid all smell in the course of
the work, as also at the end of each treatment, and it simplifies considerably the
means employed.
The accompanying drawing shows the column above described, for the preparation
of the weak solution.
A is a rectangular wooden case, placed vertically and one side of which is partly
torn away:
B is a suphur or pyrites burner. C is the pipe which conveys the
water, which falls in showers on the top of the column. D is the outlet pipe of
the gases escaping at the top of the column. E is a large reservoir sunk in the
ground, in which the weak solution accumulates, flowing the bottom of the column
to be conveyed thence to the digesters; a. a. are the internal shelves of the
column; a a¹ the waste pipes arranged between the shelves. is the pipe through
which
pass the
gases produced by the combustion of the sulphur, entering the bottom
of the column A above the lower outlet of the liquid which escapes through the pipe
into the reservoir E.
Having now particularly described and ascertained the nature of my said invention
and in what manner the same is to be performed I declare that what I claim is :-
1st. The substitution, for the strong liquid hitherto used in the process of dis-
aggregating the fibre of cellulose by sulphurous acid in solution in water; of weak
liquid destined to be subsequently enriched according to the needs of the operation.
2nd. The arrangement described and shown in the drawing for the preparation
of the weak liquid in a very economical manner.
3rd. The process of enriching the weak solution of sulphurous acid by the
operation of recuperation above described.
Dated this 9th day of March 1887