Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a method of
reducing the content of pollutants which are lignin or lignin ~ ;
degradation products in the aqueous eff:Luent from forest
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industries working with cellulose conta:Lning produ~cts. The
method is primarily applicable to the treatment of chemical pulp~
mill effluent, e.g. bleached plant waste liquor from such
mills but can also be used to treat other effluents
$~ containing lignin degradation products, such as screening plant
'~ effluent, e.g. back water from su}phite screening plants~
, 10 alkaline condensates etc
In our Canadian Patent ~o. 987459 issued April 20th
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~! 1976 we describe and claim a method of reducing the content
l of lignin degradation products in the aqueous ef~luent from
forest and other industries working with cellulose containing
I5 products which comprises bringlng the effluent into contact~
with a porous and granular phenollc resln which~will~absorb~
:3~ the lignin and lignln derivatlves~from the effluent~ séparating ;~
an effluent of reduced lignin and~lignin derivative~content
and recirculatlng lt or discharging it to an outflow;~and~
eluting the resin to ;recover the lignin and llgnin;derivatives
~ for disposal.
J~ In the operation of this method on full plant`~scale,~
t~is desirable to~be~able to~maximise the num~er~of bed valumes~
of~effluent that;~can be treated~to~give~adequate~decolouratlon ;~
; 25~ ~of the~effluent~before lt ls necessary to elute the resln. ;
We~have now found~that one reason~for the falling~off in the
~l~ ability of the~resin to decolour the effluent is that the volume
of the~resin Ls~influenced by the pH of its~environmént and ~ -
;~ ; that changes in environmental~pH bring about chang~s in ~the
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~ 30 resin volume and this in turn may bring about the~formation of
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channels in the resin bed which reduces the ability o~ the
re~in to decolour the effluent. The present invention provides ; ;
a method of ~ubstantially eliminating this problem.
In one aspect of the present invention, in a method of
reducing the content of organic pollutants which are lignin
or lignin degradation products in an aqueous effluent solution ~ ~
from forest industries working with cellulose containing`
products which comprises passing the aqueous effluent solution
through a bed of a porous and granular phenolic resin which
will take up the pollutants from the effluent, said resin being ;
of a type whose volume changes with change of the pH of the
liquid phase in which the resin is located, separating an
effluent of reduced pollutant content and eluting the~resin to
remove the pollutants for disposal and regenerate the resin for i
further use, we provide the improvement which comprises
minimising volume changes inthe resin bed by batchwise addikion
of an aqueous acid solution to the resin bed so that the pH of
the li~uid phase in which the resin is located is~repeatedly
lowered during treatment o~ the effluent whereby formation of
channels in the resin bed is ubstantially eliminated. ~` ;
In another aspect of the present invention ln a method~ ;
of binding solute which is lignin or lignin degradation products ~
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dis~olved in an aqueous effluent solution, said methocl comprising~
~a) preparing a bed of a phenolic resin capable of `
binding said solute, said resin bed being a bed which changes
its volume with change of pH of the liquid phase in which the
resin is located, by passing through the resin bed an acidic
first liquid having an acid pH,
~ (b) thereafter passing through the resin becl a
second liquid having an alkaline~pH value, said second
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103856Z ; ~ ;~
liquid containing dissolved solute which becomes bound to
said resin, and
~c) eluting the bound solute from the resin bed
by passing a third liquid through the resin bed,
we provide the improvement comprising minimizing
channel formation in the resin bed and thereby increasing
the exchange capacity of said resin bed by pa3sing through the
resin bed during the time when said second liquid is in
contact therewith, on more than one occasion in a batchwise
10 manner a fourth liquid having an acid pH value which is
sufficiently different from the pH value of said second
liquid so as to lower the pH of the li~uid phase in which
the resin i~ located on each occasion a batch of fourth
liquid is passed through the resin bed.
The process of the~present invention can be used in
association with and under all of the conditions of the pr~ocess
described in our Canadian Patent ~o. 987459 issued~April 20th
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1976. Canadian Patent No. 987459 corresponds to our Swedish '
pat~nt ~o. 345085 which was open to public inspection in March
20 1~73.
One of the most polluted of the various effluents
that arise in the paper making process is the effluent arising
from a post chlorination alkali extraction stage in the
tradiional bleaching of woodpulp, this.being a very dark brown
25 liquid containing lignin degradation produots and other
organic pollutants.. The decoLouration of this effluent prior
to discharge is very important and the present inven~ion is
particularly designed to treat such effluents although it can
equally be used~in conjunction wit~ the decolouration of
30 other effluents arlsing in the paper m~king process.
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~)3856Z ` : ~
~ he resins used in the process of our Swedish
patent No 345085 are particulate phenolic anion exchange
resins having pendant groups such as DUOLITE ~ A4-F, A-6,
~ A-7, S-30 and S-37 which are marketed by Diamond Shamrock
Chemical Co. of California, U.S.A. and the same resins can
be used in the process of this invention.
It is desirable to activate the resin by treatment
with aqueous acid prior to contacting the resin with the
effluent. ~his aqueous acid may be sulphuric acid or an
aqueous solution of SO2. It is convenient to use the same
type of acidic solution to activate the resin prior to
decolouration of the effluent and to treat the resin batchwise
during the decolouration of the effluent in accordance ;~
with the present invention.
According to this invention, the resin is contacted
with the aqueous acid on two or more occasions in a ba~chwise
man~er during the decolouration of the effluent, that is to
say, after activation of the resin but before elution of
t~e resin. `;
The following Examples are given to contrast the
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ability of the resin to decolour effluent when used in accord~
ance with the present invention and when used in accordance
with the process of our Swedish patent No. 34S085.
In both Examples a column having an inside diameter
of 3.25 m, was filled with a DUOLI~E A-6, a weakly alkaline
phenolic anlon exchange resln having pendant amine groups on
the phenolic structure.
, .
EX~PLE 1
Process accordinq to Swedish patent No. 34_085
In this run, the ion exchange resin was activated ~ ;~
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with s40 kg of SO2-water, whereby the liquid phase in the
upper, activated parts of the resln bed has a pH of between
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'1 and 4 approximately. Thereafter,'a daxk coloured aqueous '
effluent from the first alkaline extraction stage of a
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bleaching plant for sulphate wood pulp haYing a capacity
of 300 tons of wood pulp per day, was passed through the ion
exchange resin. On entry, the aqueous efEluent had a pH of
around 11. During the decolouration the pH of the water
leaving'the column was kept under observation. It became apparent
that only a few bed volumes of effluent were sufficient for the
pH to be'brought down to very low values due to the formation
of channels in the ion exchange bed which caused an excess quan- '~
ity of~acid to flow out tofether with the purified water. ;
A further efect was that the purifying ability of the resin ; '~
bed declined very r~pidly. This meant that after only S to 6
bed volumes, the effluent retained an unacceptable coluur
because of the high content of~lignin degradation products
s~ill contained in the e~fluent. ~ Line ~o~ 1 in the Figure
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in the accompanying drawing shows the variation in pH of the
treated effluent during thi~ run. In all, 12 bed volumes of '
effluent were treated and only for the initial S or 6 of these
an acceptable colour reduction achieved.
EXAMPLE 2
In this run,~the same quality of the same ion
exchange resin was activated with SO2-water having the s~me
concentration as that used in Example 1. 400 kg of SO2-water
were used for this purpose. During the effluent decolouration
phase of the proce~ a further 200 kg of the 5O2-water, in
two batches each o~ 100 kg, was brought into contact with the
.
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resin bed, the pH of the treated aqueous effluent was measured,
but it was no longer possible to detect such low pH-values
.as in the first run. This indicates that no formation of
channels in the bed of ion exchange resin was occuring and
as many as 16 bed volumes of aqueous effl.uent could now be ..
treated with an acceptable degree of colour reduction, being
. obtained in each bed volumer This pH of the treated aqueous ;~
effluent in each bed volume is shown on line ~o. 2 on the .
Figure-O
Similar results to those described above were .~
achieved using sulfuric acid as the activation agent and as ..
the addltive agent during the decolouration process.
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