Note: Descriptions are shown in the official language in which they were submitted.
6~ 5~
yDd _ The Invention
~ 1. Field Of The Invention
- The present invention relates to preparation of
pulpwood using the sulfate pulping process. More specifically,
~ the present invention relates to improvements in yield of pulp
-` per ton of wood digested by the use of certain polyoxyethylene
: polyoxypropylene digester additives.
~: 2. Prior Art
The cellulosic and non-cellulosic carbohydrate~
.- 10 fibers present in wood are held together to form a semi-plastic
s~lid by llgnin~ ~ complex polymer composed~o hydroxyphenyl-
propane units.~ This complex polymer binds the wood fiber
: partially by an amalgamation between~the fiber walls, by~an
absorption within the fiber walls and~partialLy, it~is~believed,
by`chemical bonding between the celiolose and the lignin.
DelLgnified, or~partially delignified,~cellulose fibers~are
required for the~production of~certain papers and pulp pr.oducts.
In:~the sulfate process for~the~preparation of pulpwood, a ; ~ ;~
saluti~on~of sodium:hydroxidé~and~sodium sulfide is used to ::-
20~ degrade tbe~ gn~ins~to:obtain-~the;se~cellulose fibers.~:~To
degra~de~these~materiàls, moderately high temperature~s:~and~
p~èssures are~employed~to expedi~te~the:penet~ation:and~diffusion~ .
of~th ~:~sodium~sulfLde~and hydroxyl:lons into:the wood~struc~
ur~ :As~far~as:we:know,~:thé~use:of~additive~ to:~i:ncrease this~
~ ~ 6~
- penetration result1ng in increased yields has not been success-
` ful. At the present rate of production, wood supplies are
being rapidly depleted in spite oE industry efforts to
encourage reforestation on private lands, and to practice
- tree planting and controlled cutting on its own lands. Other
forms of wood salvage such as the use of barked and chipped
sawmill waste, slabs, edgings and plywood cores have been
- followed up to obtain raw materials. Even the ut;lization of
.
sawmiIl sawdust has been employed. It is quite evident that
any improvements in yieLd would be welcomed by the pulp and ~;
paper industry.
One of the major advantages of the sulfate pulping
process is its ability to pulp both coniferous and deciduous
., .
wood ln greater variety than other~processes. Among the
coniferous species which can be pulped are the Western-red
cedar, Cypress, B31sam fir, Noble fir, White fir, Douglas fir,
; .
Canadian and Western Hemlock, Larch, Loblolly p;ne, Pondeross
pine,~White pine and~Redwood, and of the spruce spec;es
~ ~Engelman, Sitka~ and;White. The deciduous specie8 which can
-~20 ~ be~used are: Ash, Basswood,~Beechg Birch~ Che~tnut, ElmJ Gum,
- ~Red~and Sugar Maple, Northern,;~Post and White Oak, Swee~gum
` the~Big Leaf and Quaking Poplars, and the ~u~ip trees.
~L~6~51~L
Summa~y Of The Invention
It has now been discovered that the addition of
minimal amounts of certain surfactant polyoxyethylene polyoxy-
- propy~ene digester additives to the sulfate liquor results in
an increased yield of pulp per ton of wood used, with no
corresponding loss of pulp brightness, tensile and bursting
strength.
Descr_~tion Of The Preferred Embodiment
The wood chips which are to be pulped are charged to
the pulping basket on an oven-dry wood basis. The moisture
content of the wood must be determined as it is desirable to
maintain the liquor-to-wood ratio within certain ranges. The
., .
; ~ liquor-to-wood ratio can vary fro~ about 2/1 to about 6/l, ~
preferably Erom about 3/l to~about 5/l. The moisture content ~ -
of the wood can contribute as~much as 50 percent of~the water
present in the cooking liquor. ~ Knowing the mois~ure content
of the wood chips) the cooking liquor is prepared by ~dis~solving ;
the~ required amounts~of sodium hydroxide (NaOH) and ~odium
sul~fide (Na2S)~in water The percentage of total active alksli
-20~ to be~used depends~on the ~species~of wood to be pulped snd on
th~deg~ree~o~deli~gnification of~the wood desired, i.e.,~whether
a~"board"~grade of~pulp~with modera~te deligni~ication or~
~ ~ 61 51~
"bleaching" ~rade of pulp with as much delignification as
possible is being made. This concentration generally varies
from about 12 percent to about 25 percent total active alkali,
preferably Erom about 15 percent to about 22 percent. Total
active alkali is expressed as percent sodium oxide (Na20~ based
on the oven dry weight of the wood charged to the digester.
This Na20 represents both the amount of NaOH and Na2S to be
used. The Na2S used will furnish about 15 percent to about
25 percent of the total Na20~ while the remainder will be
furnished by the NaOH. In actual plant practiceJ some of the
pulping liquor may be recirculated so that the total Na20
content may include salts such as sodium carbonate, sodîum
~ hydrosulfide, sodiu~ sulfate and sodium thiosulfate. This i~
,, .
`~ due to the addition of some black liquor to fresh~y prepared
~:
eooking liquor. The black~liquor is that liquor which is
obtalned from a previous pulping run and may constitute from
~about 10 percent to about 50~percent of the cooking liquor
; added to a fresh charge of wood chips.
. ~ ~
Also o~ interest is;the sulfide content of the~cook- ;
~20 ing liquor. This is usually expres3ed as Sulphidity which is
.
;; the pe~rcentsge ra~tio~of NaaS,;e~pressed as Na20, ~o the total
c c:Lv~ a lhs li .
: ~ ~
,
, . .
: :
:~6~S~l
The digester additive is best added to the cooking
liquor before it is circulated through the wood chips. After
the sulfate cooking liquor has circulated ~hrough the wood
chips for about five minutes, the air in the digester is purged
and steam is allowed to enter the cligester to its maximum
pressure which may range from 125 to 150 psig. The temperature
may range rom ~bout 250 F. to about 400 F., preferably from
about 300 F. to about 375 F. This temperature and pressure
are maintained from about 0.5 hour to about 6 hours, preferably ;,
from about 0.5 hour to about ~ hours.
At the end of the required time at the specific . . .
j temperature and pressure, the digester is blo~n to the blow
~tank, the weak black liquor drained~ and the puip is then
coarse screened and washed by such processes as are well
known to those skilled in the art. ~ ~
The surfactant additives contemplated for use in the
subject lnvention are essentially those disclosed by D. R, `~
Jackson et al in U. S. 3,036,118 issued on May 2~ 1962.
These are surface active ~agènts obtained by condensing ethylene
20~ oxide with a low molecular~welght reactive hydro~en compound
forming~ a polyoxyethyl~ene polyol and then~ further condensing
this polyol with propylene oxide. The structural formula of
,, ,.. ,, ,.. `. . ~, ..... , .,, . .. , .. ., ., ... ~ ., ' . ' '. .
~ 5
these surfactants corresponds to
r
R ~C2H40)n(C3HffO)~ H
wherein R is ~he nucleus of a reactive hydrogen compound,
x has a value of 2 to 6) m has a value such that the oxy-
propylene chain has a molecular weight from about 900 to
25,000, preferably from 900 to 5, OOOJ and n has a value such
that the weight of oxyethylene groups constitutes from about
10 to 90 weight percent, preferably 10 to 60 weight percent,
of the mixture. The concentration of surfactant may v~ry
from about 0005 percent to 1.0 percent, preferably from about
0.1 percent to 0.5 percent, based on the weight of oven dry
wood.
The above~sur~actants are prepared by the reaction
of propylene oxide with an ethylene oxide condensate of a~
reactîve hydrogen~compound. The~reactive hydrogen compound ~;
~must be a relatively Low~molecular~weight, water-soluble eom~
pound~having at~least ~wo and pre~erably not more than æix : ; -:
reactive~hydrogen atoms. One clasæof such compounds is the ~
; low~molecular weight, aliphatic, polyhydric alcohols such as -
~20~ eLhylene~glycol,~propylene~glycol,~2,3-butylene glycol,~ 3-
butylene~glycol,~1,5-pentanedial,~1,6-hexanediol, glycerol,
trimethylalpropané, sorbital,~suc~rase and;the like. Other
classes ~that~can be~used~are~;alkylamLnes,~a~lkylene polyamines,
6~ 51~
cyclic amines, amides and polycarboxylic acids. These
surfactants and their method of preparation are adequately
described i,n the aforementioned patent, U~ S. ~,036,118.
The surfactants employed in the following examples
are defined &~ follows:
Nonionic No, 1 is a polyoxypropylene adduct of a
polyoxyethylene glycol wherein the polyoxypropylene chain has
a molecular weight of about 1700 and the oxyethylene content
is about 15 percent by weight of the mixture. -, ,'
Nonionic No. 2 is a poLyoxypropylene adduct of a
polyoxyethylene glycol wherein the polyoxypropylene chain
- has a moLecular weight of about 2200 and the oxyethylene
content is about 25 percent by weight o~ the mixture.
Nonionic No. ~ is a polyoxypropyiene adduct of a
.
polyoxyethylene glycol wherein the polyoxypropylene chain has ' '
a;molecular weight of about 2500 and the oxyethylene content , ~-''
is about 25 percent by weight of the mixture.
Nonionic No. 4 is a polyoxypropylene adduct of a
polyoxyethylene glycol wherein the polyoxypropylene shain has ,~
~20 a moleeular weight of about lOOO~and the oxyethylene content is
.
about 55 percent by weight of the~mixture.
The following examples are pres,ented to illustrate
the~invention.~ The resul~ were obtained with a l~boratory ;
8- -
: ~ : : . '.. . '
:::
;, , ~ ~ : ' '''
!~. , ...'' .. .
. . '' ''. :'' . . . .
:, ': ' " '; , . ', :: '' ' , .; ' ', ', . .~, .: . .
~6~l511
digester. The laboratory digester is known to correlate
well with actual plant operations. The procedure employed
was as follows:
This la~oratory di~ester consists of a jacketed shell
constructed of ~16 stainless steel with a tight fitting
gasketed lid, secured by a lug bolt and nut system. The system
is pressure proof to 30G lbs./in. 2 gage (Static Test) and the
jacket is also proof to the same pressures. The wood chip
charge is contained in a stainless steel wire mesh basket ;
(18-20 mesh). The digester is piped to allow clrculation of ;~
cooking liquor at~the start of and at intervals during a cook.
Circulation of the liquor at cooking pressure9 is accomplished
by a positive displacement pump of ~he rotary eccentric type.
The circulation of the cooking liquor is from top to bottom of ~ -
the digester.
The heating of the diges~ter~and charge is;accompiished
by the use of live steam (maxlmum pressure available~l40 lbs./in.
gage). The steam supply pa~ses to~a~pressure regulator.~and
then~to the digester jacket (_nd~rect heating) or directly to
~20~ ~ the digester charge in the sheli (direct heating).
;; The~digester~is eqùipped with a~condenser to condense
~he~v~l-tlle ~l~d ou~ b~r~d Oe w k~ d ~L-a~
~ ~ 6~
system for removal of the black liquor at the end of the
cook.
The digester was steamed to the maxim~ presisure
required by incrementally increasing the pressure. At the
end of 60 minutes the pressure reached 100-150 psig. The
cooking cycle times ranged from 0.5 to 3.0 hours. At the end
of the cycle, the pressure was relieved rapidly by opening the
gas off valve and discharging the volatile malodorous by-
products through a condenser. The black liquor was discharged
to the sewer under slight pressure. The dige~ter lid was
removed when atmospheric pressure was reached and the charge ~ -
was washed with an amount of water five to six times the
volum~ of the charge. The pulp wa~ defibered at low consistency
with a high-speed propeller agitator, screened through a 0.010
inch cut plate, collected and dewatered by centri~uging u~lng
a 100 mesh wire ~creen belt.~ The yield wa~ calculated on an
oven dry basis. ~
**~ ****** ~ : .
'~: ~ ,: '
.,:
.
.
.. ..
~06~Sll
:
EXAMPLE I
Wood: Loblolly Pine Chips
Total Active Alkali, percent 16.5
Sulphidity 26.0
Liquor-to-Wood Ratio 3/1
Maximum Pressure, p~;ig. 130
Temperature, F. 350
Additive~ percent~
based on oven-dried chips 0.2
Run Additive% Yield ~ Increa~e in Yield
51-9
2 -- 48.6
,. .
3 ~~ 49.6 ~ :
~ ~.
4 -- 50.5
:
-- 49.1 : :
6 -- 48.5 ~ ~ ~
7 ~ 49. 7
,
Ave. ~ 4~9-7
8 ~ Nonionic No.-~ sa. 6
20~ ~;; 9 ; Nonionic No. 3~ 55.7
10~ Nonlonic~No.~:3 ~ 5~.2
Ave.~ :Nonionic~:No~ ; 56.~8~ 14.
Nonionic~No.; 2~ 53.7
12 :: Nonionic No.` 2:` ~ 5
13 ~ onion:ic~No.~:2 52:.~0:~
14 ::~ Nonionic No.::2:;~ 52.0 ~
Ave.~ Noni~nic~No.~ 2~ 52.~9:~ : 6.4- ;
~6~Sl~L
. EXAMPLE: II
- Wood: Loblolly Pine Chips
; To~al Active Alkali, percent 21.25
Sulphidity, percent 26
Liquor-to-Wood Ratio 3/l
Maximum Pressure, psig.130
Temperature~ F. ~50
Additive, percent,
: based on oven-dried chips 0.2
Run_ Additive ~~o Yield %~ncrease in_ield
-- 45.6 ~ -
. .
. 16 ~~ 1~7~l :
. 17 __ 47j1 . :~
18 ~~ 47.0
Ave. -- ~ 46.5
19 NonLonic No. 3 51^3
1 20 NonionLc No. 3 -- 51.4
i ~ 21 ~ Nonionic ~o. .3 ~ ~ 5- T:
::22~: Nonionic;No.: 3~ 50~8
2~A~e,:~: No~ionic No. 3~ ~51~ 12~0
EXAMP E III:
Wood~:~Mixed~S~o~twood~ from ~
South Dakota : : :
To~tal;Active~Alkali,: percent:~ 21.5
Sulphidîty, perc~en~t~ : 26~0
:Liquor-to_Wood~:Ratio ~: ; 3/l
M~ mum~Pressure~:~psig~ 30~
Temperature, ~:~F:.~ : 350:~: . : :
;~3~0 ~ba~ed on~:oven:-dried~chips; ~ :0.2~
-
106~S~
Run Additive ~0 Yield ~ Increase in Yield
23 - 39- 9
2~ -- 39. 4
__ 38. ~i
26 - - :39 - 2
27 -- 38. 6
28 -- ~0.6
29 -- ~;9,~ :
Ave. -~ 39. 2 --
30Nonionic No. ~i 41. 8
31Nonionic No. ~5 41. 0
, ~
32Nonionic No. 3 40. 7
. ~ 33Nonionic No. 3 42. 4
Avonionic No. 3 4L.5 ~ 5.9
34 ~ Nonionic No~. ~1 42. 9: ~ :
35 ~ Nonionic No. 1 ~ ~43~. 6;
36 ~ Nonionic~No. 1 :41.7
37 ~ Nonionic~No. 1 ~ ~42~. 2
Ave.~ Nonionlc N~ 42. 5 ~ ~ 8. 4
20 ~ EXAMPLE~IV
;Wood: Mi~éd Northern Hardwood ` ~ -
To~tal Acti~e~lka1i,~ percent 15
n~ Sulphidity, perc~ent ~
Li~quor-~to Wood~Ratio~ 5/1
Maximum Préssure,~p~ig. 96
Additive~,~ percent,~
based dn ov-n-dried cbip~ 0.2
5~ ~
Run Additive _ ~ Yield
1 ~~ 47-
' 2Nonionic No. 4 49.0
3Nonionic No,. 1 51~,2
4Nonionic NOD 2 51. 2
EXAMPLE V
' Wood: Mixed Southern Hardwood
. Chips
Total Active Alkali, percent 21.~ ,
" 10 Sulphidity, percent 26.0 ''
Liquor-to-Wood Ratio 5/1 ,,
, Maximum Pressure, psig.1.10
Additive, percent,
, based on oven-dried chips 0.2 ~ ,
Run , Additive __~ Yield
43.:4~ .,"
2 Nonionic No. 146.7 :
3 ~ Nonionic~No.: 3;46.1'
; The effect~of conce:ntration of the nonionic ~ :
;20 surfactants is ~tabulated ~in Example VI, below. ::The cooking~
conditions employed:~:were as ~fo:llows~
W o o d ~ o b~ l o l l y ; P i n é ~
: Rescreened~Ghips
Total:Activ;e :A~lkali,':percent:21.5:
; :,`:Sulphidity, percen,t:~ 26.0 : : :
Liquor-to-Wood Ratio~' : 3/L :
,~a:ximum`~Pressure,~psig~ 130: ;
Maximum Tempera:ture,:~~F.~ 350~
51
Run_ Additive ~ ield ~ crease in Yield
1 - 46.2
: 2 -- 44.~
3 -- 46.1
4 -- 43.2
__ 44.8
6 -- 45.0
Ave. 5
7 Nonionic No. L 0.2 49.2
8 Nonionic No. 1 0.2 48.3
9 Nonionic No. 1 0.2 47.8
' 10 Nonionic No. 1 0.2 47.8
Ave. Nonionic No. 1 0.2 48.2
11 Nonionic No. 1 0.3 51.4
12 Nonionic No. 1 0.3 5~.2
:13 Nonionic No. l 0.3 48.0
14~ Nonionic~No. 1 ~ 0.3 ~9.6
Ave.: Nonionic No. I 0.3 ~50.0 11.1
15 Nonionie No. l 0.4 46.4
~ ~16 Nonionic No. 1 0.4 46.7
17 Nonionic No.: l 0.~4~48.4
; 18;: ~Nonionic~No. 1 ~0.4 ~ 47.8
ve:.~ Nonionic No. 1~ 0.4~ 47.~
onei~ued)
~.~6~5~L
RunAdditive % ~ Yield ~ Increase in Yield
19Nonionic No. 2 0.2 49.7
20Nonionic No. 2 0.2 48.8
Ave.Nonionic No. 2 0.2 49.2 19-3
21Nonionic No. 2 0.3 5}.0
22Nonionic No. 2 0.3 50.7
Ave.Nonionic No. 2 0.3 51.8 15.1
23Nonionic No. 2 0.4 52-5
24Nonionic No. 2 0.4 52.9
Ave.Nonionie No. 2 0.4 52-7 17.1
25Nonionic No. 3 0.2 47-7
26Nonionic No. 3 0.2 48.~
Ave.Nonionic No. 3 0.2 48.0 6-7
27Nonionic~ No. 3 0.3 50.9
28Nonionic No. 3 0.3 49.6
Ave. Nonionic No. 3 0.~ 50.2 lL.5
29Nonionic No. 3 0.4 ~ 50.0
:
30 ~Nonionic No. 3 0.4~ 48.0
~Ave.Nonionic No. 3 0.4 ~9.3 9.5
.
~ 20~The burst ~nd tear factor~ and the brea~ing leng~h
.
~were determined at a 500 Canadian Standard Freene~s. Theise
:
~~ physLcal propert:ies~were determined according to the standard
Sl~
metllods o~ the Technical Associat:ion of the Pulp and Paper
Industry (TAPPI). The TAPPI standards employed were T404~,
T403m and T414m. Table I below indicates that the changes
in these pulp properties as reflected by the percentage
change in burst factorg tear factor and breaking length were
essentially insignificant. The sheets were prepared accord-
ing to TAPPI standards T205 and T220.
Table I
. Percent Percenta~e Chan~
Percent Increase Burst Tear Breaking
Additive Additive in Yield Fa~ctor Factor ~@~h__
Nonionic No. 1 0.2 7-3 ~6 -8 +11
Nonionic No. 1 0.~ l1.2 ~7 -7 ~7
Nonionic No. 2 0.2 906 +10 -10 ~19
Nonionic NQ. 2 O. ~ 15. 4 ~14 -10 +12
: :
: Nonionic No. 3 0.2 6.7 -15 ~8 _9
:
~ ~ Nonionic No. ~ 0.~: 11.2 -8~4 ~2 .:
~- ,
: . .
:: :
.: ~: : ~: : :
:
7-
