CA1061511A - Method of treatment of wood pulp for greater efficiency in wood utilization - Google Patents

Abstract

METHOD OF TREATMENT OF WOOD PULP
FOR GREATER EFFICIENCY IN WOOD UTILIZATION
Abstract Of The Disclosure The addition of certain surfactant polyoxyethylene polyoxypropylene block copolymers in the sulfate pulping process results in increased yields of pulp.

Description

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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~

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- 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.

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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~

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"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~
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`~ 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.
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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 .

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:~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 ;

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~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~

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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. ~

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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

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- ;

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. 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~

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Run Additive ~0 Yield ~ Increase in Yield 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

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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~

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 .:

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Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for the preparation of pulpwood by the digestion of wood chips in an aqueous alkaline liquor in which the total active alkali consists substantially of sodium sulfide and sodium hydroxide at a maximum temperature of 400° F., the improvement which comprises carrying out the digestion in the presence of a digester additive whose structure corresponds to the formula wherein R is the nucleus of a reactive hydrogen compound, x has a value of 2 to 6, m has a value such that the oxypropylene chain has a molecular weight from about 900 to 25,000, and n has a value such that the weight of oxyethylene groups consti-tutes from about 10 to 90 weight percent of the mixture.

2. The process according to claim 1 wherein the total active alkali ranges from about 15 to 22 percent of the oven-dried weight of wood chips.

3. The process according to claim 1 wherein the Liquor-to-wood ratio is from about 3/1 to 5/1.

4. The process according to claim 1 wherein the concentration of additive ranges from about 0.1 to 0.5 percent of the oven dry weight of wood chips.

5. The process according to claim 1 wherein the nucleus of the digester additive is ethylene glycol.