Note: Descriptions are shown in the official language in which they were submitted.
56~i~
This invention rela-tes to a process for
reducing the eoncentration of resins and related organic
substances in wood. More particularl~, it concerns
a solvent vapor extraction of pitch-forming constituents
from pulpwood used in making paper.
Resinous and resin-forming substances in
pulpwood may eonsti-tute a con~iderable problem in
; the papermaking process because of the formation and ~ -;
accumulation of pitch. This problem is partieularly
acute in the case of softwoods, such a~ certain species
of pine and fir which eontain relatively high propor-
tions of these materials, which in this ease consi.st
essentiall~ of fatty and resin aeids, flavanoids,
sterols and steryl esters, and di- and -trig1ycerides
; 15 of the acid3 named. Specialized pulping processes
have been developed to handle these resinous woods,
but it would be desirable to have availakle a praetical
means to reduee the amount of resins and resin-orming
substances before pulping and thus simplify the proeess~
It is possible to remove these resinous
materials from wood by subjeeting the wood ehips to
eonventional extraetion with a hot li~uid organic
solvent. However, the extractea chips are then satur~-
ated with extracting liquid and the removal and
.
recovery of the very considerable amount of s~lvent
involved becomes a formidable problem.
It has now been found that the defects of the
prior art described ahove have been~substantially over-
eome by the present invention, whieh is a process for
reducing ~he concentration of solvent-extractable organic
.
.
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substances in softwood pulpwood of high resin content
which comprises contacting said wood with the vapor of
a halogentated hydrocarbon having a boiling point of
lO0-150C., at about said boiling point.
The process is particularly eEfective for
treating softwood pulpwood of high resin content before
the pulping process, using perchloroethylene as the
extracting vapor.
The present invention is essentially an
adaptation of the well~known technique for cleaning
metal parts in a solvent vapor degreasing apparatus
to the reductio~ of the resinous and resin-forming
components of wood below the point where these substances
caus~ significant problems in wood-modifying processes
such as sulfite pulping. Vapor degreasing apparatus
consists basically of a refluxing chamber or sump contain-
ing liquid solvent, means for boiling the solvent so as
to form a solvent vapor zone in the upper portion of the
apparatus above the sump, condensing means near the top
of the chamber, and means for holding articles to be
cleaned in the vapor zone. During the cleaning process,
solvent vapor condenses on the articles in ~he vapor
zone, dissolving grease or oily residues, and this
liquid drips back into the boiling solvent below, thereby
effectively cleaning and rinsing the dirty article.
In the present adaptation of that process
to the removal of resin and resin-forming substances
from wood, the hot solvent vapor similarly forms a
solution of these substances and as they are thus
gradually removed from the wood along with most of
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the water present, the wood becomes increasingl~ per-
meable to the vapor 50 that the solvent action affects
all of the wood and is not merely a surface effect.
The extracted resinous materials accumulate in the
solvent sump and so are readily recoverable. The
action of the hot solvent vapor on the wood is particu-
larly effective in removing water which is very rapidly
reduced to a minimal residue during the extraction
process.
The solvents preferred for use in the present
process are those having boiling points within the
preferred temperature range o the processl that is,
about 100C-150C. For practical reasons, halogenated
hydrocarbons are the solvents of choice, particularly
chlorinated hydrocarbons such as 1,1,2-trichlo~oethane,
perchloroeth~lene, chlorobenzene, 1,3-dichloropropane,
and 1,1,2,2-tetrachloroethane. of these, a chlorinated
aliphatic hydrocarbon such as perchloroethylene is
particularly preferred. Halogenated hydrocarbons with
lower hoiling points such as rnethylene chloride, ethylene
dichloride, and l,1,1-trichloroethane are also operable
in the process and may give about as good results as the
preferred higher boiling compounds when the wood being
treated has a lo~ to moderate resin and pitch content.
This process is primarily of utility as a
precursor to a pulping operation wherein wood chips
in bundles or baskets of me~al mesh are first extracted
to reduce their resinous content. The process can also
be used to advantage in o-ther wood-modifying or treating
procedures where a high resin content is undesirable,
for example/ in making particle hoard.
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The fastest and most effective method for
r~noving resin and resin-forming compounds from wood
is, of course, by conventional extraction with hot
li~uid solvent. This method is ordinaril~ impractical
to use for the puxposa, however, because of the large
amount of solvent re~uired and, particularly, the
difficulty of avoiding ver~ high losses of solvent
because the wood comes from the extraction soaked
through with li~uid solvent. In the present process,
the treated wood from the process contains essentially
only solvent vapor. This much smaller proportion of
solvent can be recovered by any OL se~7eral known methods,
for example, by flushing with a stream of warm air and
adsorption of the solvent vapor ~rom the effluent air
by charcoal or by adsorbent polymer beads.
Example
Ex erimental Procedure
P - - --.
Woods:
Jack pine and black spruce were chosen as
two pulpwoods representing high and low levels, respec-
tively, of solvent-extractable substances and conse-
quently more and less pitch-forming prohlem~ in sulfi'ce
pulping. Logs of both were cut and stored for two
weeks at about ~C, then reduced to chips at a pulp mill
so as to be representative of fxesh mill chips. Some
of the chips were seasoned by storage at that temperature
for six months.
Moisture Determination:
The wood chips were cuc to an avera~e size
of about 6 x 25 ~n and weighed samples were freéze-dried
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or ~8 hours. The weight loss was taken as the moisture
content of the wood.
Solvent-Extractable Content:
: Samples of dried wood chips were ground to
a fine powder in the presence of solid carbon dio~ide
by a blender and 5-g. portions were extxacted for 18
- hours with 200 ml. o~ acetone. The organic material :~:
thereby extracted was considered to be the total extract-
able organic content.
Solvent Vapor Extraction:
Six shallow stainless steel ~esh baskets
each containing about 25 g. of wood ships were secured
within the vapor zone of a conventional solvent vapor
metal degreasing apparatus of the type pxeviou~ly
described. Single baskets were removed at Ei~teen-
minute intervals and the extracted chips were cut into
smaller pieces ~or moisture content determination and
measurement of residual solvent-extractables as described
; above. Solvent retained in the vapor ext~acted chips
was measured as the solvent la~er in the condensed
ef1uent from the freeze drying procedure.
The weight percentages of solvent-extractable
organics remaining in the wood chips at each stage of
, the vapor extraction process are listed in Tables I
and II. The results in Table I are those obtained
using perchloroeth~lene as the solvent, Table II which
is included for comparison shows the results obtained
using l,l,l-trichloroethane.
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Table I
~Perchloroethylene)
Wt. % Extractables ~dry basis~
Fresh Seasoned
Time, jack jack Fresh Seasoned
Minutes pine pine spruce spruce
0 3.9 4.7 1.5 102
3.5 4.0 1.2 1.3
- - 1.2 1.3
3-3 4~0 - 1.1
2.8 2.3
1.7 1.8 1
Table II
richloroethane)
~t. ~ Extractables (dry basis)
Fresh Seasoned
Time, jack jack Fresh Seasoned
Minutes pine pine spruce _spruce
0 3.9 4.7 1.5 1.2
3.8 3.9 1.3 0.9
3.8 3.5 1.2 0.8
3.4 2.7 1.1 0.8
_ _ _ _
3.1 2~5 1.3 0.8
It is evident that the higher boiling perchloro-
ethylene provided suhstantially more effective vapor extrac-
tion in the wood of high solvent-extractable content. In
the case of the wood with relatively low extractable organic
content, comparable results were ohtained with the -two
solvents. Similar extraction tests made with meth~lene
18,255 F -6-
~561~0
chloride showed somewhat less effective extraction of
jack pine wood whereas the results with spruce were
comparable to those found with the other two solvents.
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