Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIEL~ OF THE INVENTION
The present invention relates to the production of
organic aldehydes from waste pulping liquor. It is concern-
ed, more particularly, with a process for making syringeal-
dehyde and/or vanillin by alkaline oxidative treatment of
waste liquor from alkaline and neutral sulfite pulping
operations.
DESCRIPTION OF THE PRIOR ART
There is no commercial production of syringealde-
hyde, as far as we know. There are known methods of pre-
paring syringealdehyde by synthetic routes, e.g. through
several intermediate reactions starting from pyrogallol as
disclosed in U.S. Patent 2,516,412, or from vanillin by
selective methylation of the 5-hydroxyvanillin derivative
(J. Am. Chem. Soc. 74, 4262, 1952~. These methods how-
ever do not lend themselves to commercial use, and only
minute quantities of syringealdehyde have been available
in the trade. The potential demand for syringealdehyde,
however, has greatly increased, primarily in connection
with its usefulness for the production of 3,4,5-trimethoxy-
benzaldehyde, itself an important drug intermediate.
It is known to produce vanillin from lignin re-
s$dues obtained from the digestion of wood to cellulosic
pulps and a number of commercial processes of this type for
the production of vanillin have been in existence for many
years. All these processes, however, are based on the
processing of lignin from spent sulfite liquor in which the
lignin residue is in the form of lignosulfonate. To the
best of our knowledge, vanillin has never been produced
on a commercial scale from alkaline waste pulping liquors,
such as Kraft black liquor.
Vanillin produced by the above processes using
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an oxidative breakdown of liynin i.n spent sulfite li.quors
is often accornpanied by syringealdehyde. The quantities of
syringealdehyde thus appearing as an impurity vary from very
small in the case of lignin originating from coniferous
woods to substantial in the case of lignin from pulping de-
ciduous woods.
BRIEF DESCRIPTION OF THE INVENTION
A process for the production of syringealdehyde from a
lignin containing waste liquor of a hardwood alkaline or
neutral sulfite pulping operation comprising: forming a charge
of the waste liquor and alkali, passing oxygen containing gas
in intimate contact with the charge in a reactor to oxidize
said liquor, neutralizing the oxidized liquor, extracting the
neutralized oxidized liquor with an organic solvent thereby
to separate an organic solvent soluble fraction containing
lignin derived aldehydes and an aqueous fraction containing
residual lignin and inorganic chemicals, treating the organic
solvent soluble fraction with an aqueous solution of sodium
bisulfite to form from part of the organic solvent soluble
fraction an aqueous solution of a sodium bisulfite complex of
syringealdehyde and vanillin, separating the aqueous solution .: `
of the complex from the remainder of the organic solvent
soluble fraction, acidifying the aqueous solution to recover
a mixture of syringealdehyde and vanillin, separating syringe-
aldehyde from vanillin.
The single Figure of the drawing is a schematic re-
presentation of the sequence of steps in the present process
including the several cycles of recovery and reuse of the :
chemicals used at various stages.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The starting material in the process of the invention ..
is a waste liquor from an alkaline or neutral hardwood pulping .
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pulping operation, e.g. a Kraft black liquor, or a residualliquor from a soda cook or from a neutral sulfite semi-
chemical cook. Spent liquors from sulfite pulping
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104021~;
operations are also suitable, however such Iiquors have now
become less widely available because of the relative decline
of the sulfite process. While in the present description
reference is made particularly to conventional Kraft liquor,
it will be understood that the process may also be used with
waste liquors from modified Kraft processes, such as vapour
phase Kraft, polysulfide, etc., as well as with other waste
liquor as hereinabove stated.
In the normal operation of a Kraft mill, the black
liquor collected after separation and washing of the pulp
is concentrated by evaporation, e.g. in a multiple effect
evaporator, and the concentrated liquor is burnt in a re-
covery furnace. The combustion of the organic constituents
of the liquor provides valuable quantities of heat, e.g
for steam production, while the inorganic constituents col-
lect in the form of a smelt which is recovered and processed
back to a composition identical with that of the initial
pulping liquor. In accordance with the invention, at
least a portion of the black liquor is transferred to a
reactor in the aldehyde plant. The liquor to be processed
may be withdrawn from the stream of black liquor on the way
to recovery, or, in a particular embodiment of the inven-
tion, a portion of the cooking liquor may be withdrawn
from the digester before the end of the cook.
We have found that there is an advantage in the
latter procedure, since with exposure to elevated tempera- ~ ;
ture for an extended time the lignin in the liquor becomes
less susceptible to conversion to the desired aldehydes.
Naturally, if the latter procedure is used, only a certain
percentage of the liquor can be withdrawn from the digester
without affecting the yield or quality of the pulp, but it `
has been found that up to a third of the liquor can be
withdrawn from the digester without ill effects. The best
.
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1040Z~i
time for such withdrawal may have to be de~ernlirled lor
particular cook schedules, keeping in mind that in the early
stages of the cook the lignin will be highly reactive and
convertible to the desired aldehydes at a high yield, but
the quantity of lignin dissolved out of the wood wi]l be
relatively small, while with the passage of time the quantity
of lignin dissolved out will increase but some of the lignin
will have undergone thermolytic changes which make it less
susceptible to conversion. Since the two tendencies will
exist simultaneously, the optimum for any particular cook
schedule, species, etc., will best be found experimentally
with the help of a few simple measurements on samples of
the liquor during the cook.
For the purpose of this process it is preferred to
use the black liquor in a partly concentrated condition,
e.g. at a concentration of about 25-35% solids. Alkali,
such as caustic soda, is added to this liquor in the reactor,
so that the ratio of alkali to lignin present in the liquor
to be treated is about 0.5 - 3 parts alkali to 1 part lignin
on a weight basis. The oxidation is carried out in a known
manner by passing air through the alkaline solution at a
temperature above 100 C, preferably 140 - 180 C, under
pressure of about 50 to 150 psig. A catalyst may be used
to increase the yield of aldehyde, such catalyst consisting
essentially of a salt of a transition metal capable of
readily existing in more than one oxidation stage. Examples
of such catalyst are salts of copper, manganese, nickel,
iron and cobalt. The oxidation is continued until the yield
of syringealdehyde and vanillin has reached a maximum which
is generally indicated by a drop in the pH of the solution
or a drop in its temperature (in the absence of external
heating), or can otherwise be determined in a simple test
for aldehyde content.
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104~)Z16
As illustrlted in -the drclwing, the oxidiz~d alka-
line liquor is neutralized. This can be done, e.g., by car-
bonation in a suitable vessel, the carbonation being prefer-
ably carried out in two stages: in a f`irst stage the oxi-
dized liquor is contacted with scrubbed flue gas, e.g. in
a packed tower, until the pH of the liquor is reduced to
9-9.5; and in a second stage the partially carbonated liquor
is subjected to pressure carbonation, e.g. with C02 re-
covered in the process, under pressure, until the pH of the
solution is brought down as close to 7 as possible. Ob-
viously the neutralization can be carried out by treatment
with other acids as well, e.g. sulfuric acid. The neutralized
solution is then subjected to an extraction with an organic
solvent, e.g. benzene, toluene or the like, preferably at a
temperature up to 80 C under pressure. The residual aqueous
liquor remaining after extraction and containing residual
lignin and substantial amounts of caustic is stripped of
residues of the organic solvent and of residual C02, and
returned to the pulp mill system for recovery of alkali
values. The residual liquor may be added to the concen-
trated black liquor going to the furnace, or to the "green
liquor" in advance of the causticizing stage, depending on
circumstances existing in the mill. For example, where the
recovery furnace is already operating at capacity, it may be
preferable to add the residual liquor to the green liquor,
- .... : .. . .
but in normal circumstances it will be more advantageous to
add it to the concentrated black liquor on the way to the
furnace.
The organic extract containing the desired alde-
hyde product is concentrated, the recovered solvent being
returned for use in the extraction step, and the concen-
trated solution is treated with an aqueous solution of
sodium bisulfite to form a water-soluble sodium bisulfite
. . .- . : : . : . - , . . : ~ .
104()'~
complex of syril~geLlldellydc ~Ind va~ irl. The ('()mr)leX i !i
extracted and removed in the aqueous phase, whilc the or-
ganic phase consisting primarily of the solvent (benzerle
or toluene, or the like) is recovered, purified and return-
ed for re-use in the solvent extraction step. Ihe aqueous
extract is washed, e.g. with an alcohol, partially soluble
in water, preferably an aliphatic alcohol having a chain of
4 - 6 carbons, to remove impurities, and then acidified with
sulfuric acid to break up the complex and recover the mixture
of aldehydes. The aldehyde mixture separates as a heavy oil
which is washed, e.g. with water, to remove excess sulfuric
acid, and the washed oil is transferred to further treat-
ment or allowed to cool for storage. The wash water, to-
gether with the aqueous phase from the acidification step
(from which the S02 has been removed by heating), may berecycled, e.g. to the initial oxidized liquor, so as to
minimize losses of the valuable aldehydes.
The crude aldehyde mixture is treated to separate
the syringealdehyde from vanillin. It was found that such
separation can be carried out successfully, contrary to es-
tablished belief in the art, by fractional distillation,
provided the mixture is substantially free of acid or al-
kaline impurities. Hence the importance of the washing
steps hereinbefore described. Syringealdehyde of a purity
of 99.5% and vanillin of a purity of 99.9~ were obtained
from the distillation. The products can be further purified
by crystalization or other methods.
The process will be further described by means of
the following examples which are provided to illustrate, but
by no means to limit, the invention.
E mple 1
In a hardwood Kraft mill cook a portion of the
liquor was withdrawn after 1.25 hours of pulping and evapor-
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104~)Z16
ated to 27.7% w/v (weight per v~lumd) totcll ~olid.s, (~1' wllich
8.48% was lignin and 2.30% free alkali. An oxidation charge
was prepared consisting of 811 cu. ft. of this liquor, 80 cu.
ft. of 50% W/W (weight per weight) sodium hydroxide, 20 - 25
lbs ammonia-ted manganese sulfate and lO lbs of a defoamer,
giving a mixture containing 7.72% W/V of lignin and a ratio
of total free alkali to lignin 1.16:1. The mixture was
oxidized by passing air through it at a temperature of 140 C,
atla pressure of 70 psig, the air flow being about 15,000 cu.
ft. per hour.
Samples were taken at regular intervals and analyzed
for syringealdehyde and vanillin (S-V) by gas-liquid chromato-
graphy. The peak concentration of S+V was 0.439% W/V, reached
in 6.5 hours and representing a yield on lignin of 5.69%. The
S/V ratio was 2.04:1.
Liquor thus oxidized was treated to produce a crude - ~ -
product, consisting of a mixture of syringealdehyde and vanil- -~
lin, by the following steps: the oxidized liquor was neu-
tralized by carbonation in two stages, the neutralized liquor
was extracted by means of benzene, the organic extract was
concentrated and treated with an aqueous solution of sodium
bisulfite to form a water-soluble aldehyde-bisulfite com-
plex, the aqueous solution of the complex was separated from
the organic phase and washed with amyl alcohol, and then
treated with sulphuric acid. A heavy oil, consisting of a
mixture of syringealdehyde and vanillin, was obtained. The
oil was carefully washed with water and removed to storage.
Several samples of the crude product, of about 2
kg each, were subjected to fractional distillation in lab- -
30 oratory apparatus under a vacuum of 120 - 175 microns.
Eight consecutive cuts were taken and analyzed by gas-liquid
chromatography. In the temperature range 128 - 130C, (taken
on the vapour) after a first cut of vanillin of a purity of
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51040Z~6
98.5% and amounting to 3. of the charge, vclnillin Or ~1
purity 99.9% was collected totalling 35.1~ of the crude mix-
ture. In the temperature range 170 - 172 C syringealdehyde
was collected of a purity from 98.8% to 99.8%, totalling
36.1% of the mixture.
An intermediate fraction containing a mixture of
vanillin and syringealdehyde and amounting to 12.4% of the
charge was collected and recycled to the crude mixture for
subsequent distillation. The fraction contained between
84.3% and 87.7% syringealdehyde and the remainder vanillin.
Example 2
Waste liquor from a conventional hardwood Kraft
cook was evaporated to a total solids (TS) content of 53.7%
weight per volume (W/V) which included a lignin content of
11.8% W/V. The black liquor, water and 50% (W/W) sodium
hydroxide were mixed in proportions such that the mixture
contained 5% W/V of lignin and a ratio of added alkali to ~-
lignin of 2:1. A quantity of 1500 ml of this mixture, to
which were added 3.65 grams of the catalyst cupric sulfate
pentahydrate, was placed in a one-gallon autoclave provided
with suitable fittings for the addition and removal of
samples and for the addition of air, and also fitted with
heaters and a Cavitator stirrer operating at 1400 RPM. The
mixture was oxidized by passing air through continuously at
the rate of 7 litres per minutes, at a temperature of 165C
~- (which was reached in 1/2 hour) and at a pressure of 100 psig.
Samples were removed every 15 minutes and analyzed for
syringealdehyde and vanillin (S+V) by gas-liquid chromato-
graphy. Peak concentration of S+V in the oxidized liquor
was reached after 1.5 hours. This concentration w~`s 0.396% - -
W/V of S + V, representing a yield of S ~ V on lignin of 7.9%.
The syringealdehyde to vanillin ratio (S/V) was 2.19~
.,:
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Examples 3 - 6 104~Z16
Kraft waste liquor from a hardwood cook was pro-
cessed substantially as in Example 2, except that some of
the conditions such as temperature, pressure, lignin con-
centration, alkali ratio, etc. in the reactor were changed
from run to run. Also in some runs ammoniated manganese
sulfate in an amount of 0.6g was used as catalyst. These : -
conditions and the resulting yields of syringealdehyde and
vanillin are set out below: -
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Example 7 104QZ16
This example illustrates further the u~e ~f early
stage Kraft waste liquor, i.e. liquor removed from the
digester before the completion of the cook. Such liquor was
found to contain lignin in a form more amenable to conversion
to S+V, but the lignin is in lower concentration than in a
liquor withdrawn after completion of the cook. A sample of
lignin was taken from the digester one hour after the start
of steaming. It contained 22.7% total solids, of which 3.2%
lignin, and 1.69% free alkali as sodium hydroxide (all W/V).
The liquor was evaporated in the laboratory to 6%W/V lignin
and after mixing with alkali and water the oxidation charge
of 1500 ml contained 5% W/V of lignin, a ratio of toal
alkali to lignin of 2.53:1, and a quantity of 3.65g of -
cupric sulfate catalyst. The temperature of oxidation was
165C, the pressure 100 psig and the air flow was 7.0
litres per minute. The peak concentration of S+V, reached
in 2.5 hours, was 0.597% W/V, representing a yield on lig- -
nin of 11.94%. The S/V ratio was 2.43:1.
ExamDle 8 - 11
Early stage Kraft waste liquors, similar to the
one used in Example 7, were used for the preparation of
.. : .. .
syringealdehyde and vanillin substantially as described in -
preceding examples with variations in the initial composi-
tion of the liquor and in the conditions of the oxidation. ;
The liquors used were removed from the digester 1.25 - 1.5
hours after the start of pulping and were of the following
composition:
Example Run No. Total solids Lignin Alkali
% W/V % W/V % W/V ~
, '
8 261 24.0% 5.67% 1.09%
9 310 26.9% 5.48% 3.04%
284 23.2% 4.17%
Il 286 23.2% 4.17% 2.28%
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1040Z~6
The oxidation charge was, as before, 1500 ml and
the catalyst was either cupric sulfate pentahydrate in the
amount of 3.65g or ammoniated manganese sulfate in the
amount of 0.6g. The conditions in the reactor were:
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The invention permit~ the production of valuable
chemical compounds, notably syringealdehyde and vanillin
from kraft and similar wa~te liquor, thus providing a new
practically limitle~s ~ource for these chemical~, the de-
mand for which $~ now growing and the u~e of which as chemi-
cal intermediates becomes ever greater.
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