CA2116544A1 - Pulping of fibrous plant materials and recovery of resultant by-products - Google Patents

Abstract

Filtrates from the bleaching and delignification of the pulp are recycled for reuse in pulping, separation, and recovery of lignin and other by-products which results in significant energy savings and mitigation if not the elimination of pollution typically associated with bleaching. This invention also relates to products derived from the process and apparatus for carrying out the process. Lignins of various molecular weights and by-products of the pulping process are also recovered (13). The lignins are precipitated (20) in high yields and at a high rate from a black liquor (40) produced by pulping wood (100) at high temperature and pressures. As a by-product of this process a purified furfural product is recovered (71). This furfural may be recycled for use in the recovery of the low molecular weight lignin of this process.

Description

WO~3JlS2filPCT/~S93/012~6 211~5~ 1 PU~PING OF FIB~OUS PLANT MATERIALS
AND RECOVERY OF RESULT~NT BY-PRODUCTS
-:
CROSS-REFERENC~ TO RELATED APPLIC~TION

.This is a continuation-in-part of International Application Serial ~oO PCT/US92/00720 filed January 29, 1992 which corresponds to U-.S. ~pplication Serial No. 07/
649~683, filed February 1, 1991 entitled ~"PULPING OF
LIGNOCE~LULOSIC MATERIALS AN~ R COVERY OF RESULTANT BY-PRODUCT5" which is a continuation-in-part of appli~ation ;~.
Serial No. 07/232,298, filed Au~us~ 15, :1988,~ en~itled "LIGNIN RECOVERY" which is a divi~iona1 application of Serial No. 06/940,460, filed December 11, 1986t now U.S.
Patent 4,764,596 entitled "RECOVERY ~F LIGNIN", which is continuatlon-in-part of applicaltion Serial No. 06/795,069, filed November 5, 1985 entitled "PROCESS FOR LIGNIN
RECOVERY" now abandoned.

BACKGROUND OF T~E INVENTION

: This invention generally relates~to the~ ~pulping~ ;
: of ~fibrous pla~t ~materials :including~ lignoc~llulosic~
mat~erials and the:recovery of the: resultant~by-products resulting from the pulping pro~ess. Mo~re speci~ically, this invention relates~ t~ pulping of;~ ~ibrous ~ pla~nt materials in a water mi:scible organi~ solvent;~e~g.~ l:ower;~
~ aliphatic :alcohol) and~ re~overing; and ; r~cyc~ the; ~:~
:?5 o ~.?~ .t an~ ~vaA ~ L~V~ i' t~ g .
p~C,5 ~ iluios~ ;'r., Ll~7~ misell~'~se ~d ~ Pulp~r-g~-~f ~ Ci~ro~_~ p~ t~ t~er~ d~
~he re-~o~erv O~c the resuLta~ by-produ~ts:may ~e~ carrifd out in either ~onti~nlous or ~tch proc~sses.

Processes ~or treatin~ wood wl'h organic solvents, such as alcohol, to separate the w~od's lignin, hemicellulose, sugar and cell_ ose fri~ctions aFe now well : .

WV93/1~26~ P~T/US93/01256 21~6S~4 -2-known. See, for example, Kleinert et al U.S. Patent 1,856,567 and Kleinert U.S. Patent 3,585,104. Such solvent pulping processes have appeared to be attractive alternatives to conventional chemical pulping processes, such as kraft and sulfite, which suffer from relatively high equipment cost and pollution problems.

One solvent pulping process, disclosed in Diebold et al U.S. Patent 4,1~0,016, has appeared to be particularly attractive in providing highly ef~icient recQvery o~ its alcohol solvent, separation of: the cellulose: and lignin fractions of wood, and recov~ry of cellulose pulp with no apprecîable:air or water pollution or solid waste products~ This patented process has als~
provided hardwood pulps with yields, Kappa numbers, viscosities, fiber strengths and bleachability characteristics that are equaL to or better than kraft and sulfite hardwood pulps. :
However,~ the ::recovery of lignîn:and other by-products from the alcohol/water~ black~ lIquor, generated by the~solvent pu~lping pr~cess ~f Di~ebold et al U.SO Patent 4,100,016, has been r~elatively inefficient and difficult to control. Lign;in~has~been recovered from;the black liquor in this patent by:first strippin~preferably vacuum strlpping) ~alcohol ~from the ~lack liquor~and then separatin~ the lignin which~precipitates~from~the stripper ~ottoms or :tail5~ (praferab:ly~ by: thickening ~and~ then:~ ~ -centrifuging the ~settled so:lids from : the~ ~ strippe~r:
; bottoms). However, a~ portion of the lign:in~has tended to precipitate ~s ~ sticky tar ~ or gum on ~the~ internal sur~aces of the stripper, rh~r~by fouli~g the stripper a~
~-educingiits eff~ciency ~.n recover~y of ~l~ohol from the black liquo~r~ T~h~ lignin~also ha9 tended~to precipitat~
from the st~.ipper bottoms as a sticky amo~hous mass which has be~r die~icult to hand~e nd has req~_~red substantiai 35~:~ crusbing to convert the~lignin mass into a powder.

.. . .
'~,' .

WO93/15261 PCT/US93/01~S~
~116~i4~

As a result r more efficient ways have been sou~ht for removing lignin and other by-products from the black liquor produced by a solvent pulping process such as is disclosed in Diebold et al U~S. Patent 4,100,016. One method has involved precipitating lignin from the alcoholJ
water black liquor by diluting it with water. See Rydholm, "Pulping Prvcesses', pp~ 672-673, Interscience Publishers, New York (1971). However, this method has resulted in very slow settling rates of the lignin, and in some cas~s, a very stable colloidal suspension of the lignin has been formed which has been dificult to filter or centrifuge. There has been a continuing need~
therefore, for a relatively simple way of rPcoverin~
lignin and other by-products from an alcohol/water blac~
liquor in high yields and at high rates in an easy to handle and useful form. ~oreover, whlle solvent pulping processes produce hardwood pulps that are comparable in strength, brightness and cleanliness to kraft pulps produced from the same ~ood species, the resultant pulp from such pulpin~ operations contains: highe~ residual lignin in the pulp. Therefore pulps resulting~from solvent pulping processes ge~nerally have a higher residual lignin content as me~sured by the pulp kappa number, and require, among other things~ a large quantity of :bleaching~ ;~
chemicals to produce satisfac:tori:ly~ bleached: pulps~ The increased use of::large quantities of bleaching chemicals using conventional bleaching~techni~ues created a need for devising new bleaching met:hods :~and/or systems for t~he disposai or recycling of these ~chemicals. Further, 3~ s;)lver~t pulping processes produce as a by product furfur~l wh~ c~. can accumulate in the pulping solvent and interfere with d~lignification. here is therefore a~distlnct need for methl~ds,: apparatus and/or systems, which provlde ener~y efficient, environmentally att,active and 35 economically feasible ~eans for pulpin~ ~ibrous plant materials and recouering the by-products of the pulping process.

21~ fi~4 The Lora et al, U.S. Patent No. 4,764,596, addresses some of the oregoing problems. In Lora, lignin and other by-products of the pulpin~ process are recovered from a "black liquor" produced when wood or other fibrous plant materials are contacted with a water miscible organic solvent (e.y. ethanol/water solvent~ at elevated temperatures and pressures. The Lora process successfully allows for the recovery of many by-products, including most of the lignin liberated durin~ pulping. It has also been discovered through improvement.~ of the Lora patent as set forth herein that additional by-products, including lower molecular weight lignin and furfuralg ~ay be recovered while simultaneously increasing the overall ener~y efficiency of the process, reducing the consumption of solvent required throughout the system and significantly reducing or eliminating environmentally undesirable effluent.

The inventlon describ~d herein includes the ~oregoing improYements an~ additionally accelerates delignification of th~ black liquor and allows for ~the recovery of additional by-products and streams from the pulping proc~ss.~ This~ invention not only recovers furfural from the residual black liquor filtrates produced during lignin recovery but uses the furfural; to recover low molecular welght lignin by recycling it into the system. Also incvrporated herein is a ~system which not only accom~odates novel blea~hing techniques but provides for the recycling of bleachiny effluent filtrates, which 2ccelerate deli~niEica~ qn and mit ig.~t ayainst pc~ t SUI~';~RY OF THE I~VENTiO~

This inv~ntion provides for the ~ecover~ ,f lignir; and other bi~ o~ ts from pul~in~ of fi~rcus material. In accordan~e with this invention, solvents and:
fil~rates are recovered and recycled for reuse. This results in a signiicant solve~t and energy savings.

''''''' WO93~15261 5~ S 44 PCT/US93/01256 In accordance with this invention, filtrates from the bleaching and deligni~ication of the pulp of this invention are recycled for reuse in the continuous or batch pulping, ~eparation and recovery of lignin and other by-products. The reuse of the bleaching filtrates results . in accelerated delignification and ~reater op~rating efficiency. The net result is a significant energy ~avings and mitigation if not the elimination of pollution typically associated with bleaching.

In ac~ordance with this invention, lignin is recovered from a black liquor comprising a solution of lignin, hemicellulose, and a water miscible organic solvent by precipitating lignin solids by diluting the black liquor with water and acid under conditions to form a diluted residual black 1iquor including a diluted residual black liquor supernatant and precipitated lignin s~lids which are free from the formation of tarry~ lignin precipitates and~ recovering the lignin by separating the lignin solids from the diluted residual black li~uor supernatant.

In accordance with another aspect of this invention, a novel lignin is precipitated by the process o~ this invention. A preferred lignin is haracterized by: a number aver~age~molecular wei~ht of about 700 to 2S 1500 g/mol, a glass;transition temperature~of about 70 to 170C, a polydispersity of less than about 4 and a me~hc.-.~yl co~itent approximately e~ual to tha- OL naL1.~Je li?r,in ~

Ln accor~anc~ with a~cLher ~spect of this inventio~., a novel low mole~ular weight 1ignin is obt-.a~ned. ~ preferred lignin is char~t~rized by: Q '`'.C.'~
average molecular weight in the range of less than 600 9/
mol, a glass transition in the range of from about 24 to 75 C and a syringhaldehyde to vanillin ~olar ratio of W~93/1S261 PCTJUS93/01256 2116~44 -6- ' about 2~7:1 to 5.3:1 especially as it relates to hardwoods. It is expected that a more soluble lignin having a novel structure is produced.

In accordance with another aspect o~ this invention, a purified furfural product is recovered. The furfural product contains from about 95 to 98% furfural, from about 0.1 ~o 0~5% ethanol and from~about 0.1 to 2%
water. : ~ i I
Other aspects of this invehtion wil;l be apparent from a reading :of; the~remainder:of this specificationi~
including the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

~ igures 1, 11 and 12 represent:batch proce~sses for producing~cellulose pulp~from~ ibrous plant~ mate~riàls : ~ 15 by tre~ting the :fibrous~p:Lant material~s~:with~an:aq~eou~
~alcohol~solven~, and for~recovering lig~i~n~and~ othe~ ~by- :~
products from:the:~alcohol/wat~er~black liquor~

~ Figure~; 2~ is ~a~ s~chematlc~ se~ctional~view of~ an~
:example~of an~apparatus~f;or~ pr:e~cipitati~g~ ni~n:~rom the~
~: 20 alcohsl/water~ black liquor: from~the processes;o~ igures~
1, 3,:4, 9,~10,~11 and~::12.

Flgures~3 ~, 4, 9 and 10 represent a ~flow~ chart of a continuoùs~process ~or:produci,~ ce~:lulose~p~ p;~;rom ~;~c~d ~y treatir~g ~th~ wood with an aq~e~u~ ~lcohoi ~soi~t : 25~and ~o~ recove~ln~ lisnin,~an~d ot~her by-products~rom the ~ ;
Icohol/water~.ac~;:: liquor pro~ced :~.r~ the~ ~pulp~ng : ~:
process. ~ : : : :

Figure~5~i~s a schematic representation~of~crude ~ '.
~furfura1 upgrading :and purification:: by li:quid/Iiquid 30:~cross-curren~ extr~ction followed by pe:rvaporation.

:~

WO 93/1~;261 2 1 1 6 ~ 4 ~L Pcr/US93/0l2s6 ~-- .

Fi~ure 6 is a schematic representation of crude furfural upgrading and purification by liquid/liquid :~
counter-current extraction followed by pervapora~ion.

Figure 7 is a flow chart for the recovery of low molecular weight lignin.

Fi~ure 8 is a schematic representation of a continuous extractor used in the processes of Figure~ 3, ;~
4, 9 and 10.
,~:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

10The process shown in ~igure 1 initially involves pulping a batch of wood chiE)s ~r other fibrous p~ant~
materials that are loaded ~from: a hopper 1 into an extractor 2. The extractor 2 is operated in accordance ~:
wi:th~ Diebold et al U.S. Paten:~ 4,100,:016~at an elevated 15temperature (e.g., about 180 to 210C) and an elevated :-.
pressure (e.g., about 20 to 35 atmospheres) and.with a :~
: solvent compr:is;ng: about~4~0 to ;~80~ (~by volume:). of a ~:
water miscible lower aliphatlc~alcohol of l to 4 carbon~ ::
atoms (e,~., methanol, ~ethano~, ~:isopropanol~or ter~
butanol); 20 to~60% water; and if~ needed, a small~amount:
of:a :strong:water~solu~ble:acid~,~s~ch: as~ ~a mineral :acid:~
: ~ (e.g., hydrochloric~ sulfuric, phosphoric or nitrlc~ac~id) :~ :
or an org~nic acid~(e~ xali~ acid, preerably: ~ t.iC , `:
formic or pero~y acids), OL a CmaLl ~nount o~ a niner~l s~lt. Th~ solvent:;can further~comprise recover~d aic~nol~
and aicohol/water ~ rate fr~.~ t~!e ~ - ocess .

Prefer6~1 Y the fibrous plant materi~ls in the ;~
extractor 2 are preheat:ed with low pressure steam, and then, a twice- used:60% ethanol/40% water, primary solvent :
. .
from a: primary solven~ accumulator 3 contacts the fibrous ~, plant materials in the extractor 2. The primary solvent is rapidly recirculated through the extractor 2 and through a peak load (e.g., steam-heated) heat exchanger 4 to raise the temperature of the fibrous plant materials to about l90~ to 200C in a few minutes (preferably not more than about 5 minutes). Alternatively, in large scale plant operations, a time of from about 5 to 60 minutes is required. After this first pulping step is completed, the resulting extract or "black liquor" in the extractor 2 is displaced into a recovery feed accumulator 5 by a once-used 60% ethanol~40% wa~er, secondary solvent (preferably heated to from 190 to 20:0C) from a secondary solvent accumulator 6. The black liquor which contains lignin, hemicelluloses, other saccharides and extractives (e.g., resins, organic acids, phenols and tannins) fro~ the fibrous plant materials and the ethanol is recovered at a temperature of from about 180 to 210C :and under a pressure of from about 20~ to 35 atmospheres in the recovery feed accumulator 5. At the :end of the bl~ck li~uor displacement,: the sec~ndary solven:~ in the extractor ;2 is displaced into the primary:~solvent accumulator 3 by a fresh 6G% ethanol/40% water solvent (preferably heated to~190~ to 2:00C) Ç~rom a fresh solvent : accumulator 7. The fr~esh~solvent~in the~ extr~actor 2 is then drained~ into~: the secondary solvent~ accumulator 6.
Once the extractor 2 has been drained~ it~ is vented, alcohol-rich vapor~ from the~extracto~r~are condensed:in a~
water-cooled :("C~W.")~ cond:enser; 8~, and the~ resulting ethanoliwater mixture f~rom the conden~ser~8:is~recycled to tne fresh ~ lvent accumulator 7. 4fter vent.:t~, ihe extractor 2, residual~alcoho.l in the ~lilp .in ~he e~t~:~ct~r ,s .hen stipped wi;~h : low pressure~ stea~., an& the re~ul~ing~ cohcl/' .~ter vapors are~condensed ~and reco~ered ~ discussed below. After stea~; stripping, the pulp~ in 35 ~he ~xtrac:tor~2 i~s sluiced with ~ater, piped tG~ ~ ~.ol~ing tank 9 an~ pumpéd through a pulp~screen 10, The pulp can:
: then be suita~ly subjected to conventional pulp handlin~, : bleaching and paper-making procedures. Alternatively, as .

. . .

2 11 6 5 4 ~ PCT/US93/01256 shown in Figure 11, the steam stripping step can be omitted and after sluicin~ the pulp with recycled solvent to the holding tank 9, the pulp is sent through line 5 and washed in pulp washing equipment 47 (e.gO one or more pressure diffusers, drum washers bel~ washers) with recycled solvent from tank 7a which is a holding tank and with makeup alcohol from line 49. The pulp is cooled to a temperature below 80C while simultaneously additional lignin is removed and recycled through line 60 to tank 7 and the kappa number is reduced to a bleaohable g~rade. The pulp is further washed in multistage counter-current washing equipment 44 ~e.g. one or ~more~ drum washers :or belt washe~s) by water introduction through line 43 or by introduction of bleaching filtrates and cooled to~ a temperature of from about 40~ to 70C. Counter-current washing equipment 44 replaces conventional, less energy efficient, steam stripping methods and ~removes from about to about 90~ additional. alcohol from the pulp.
Alternatively as shown;~in ~Figure 1~2;~, the pulp can be washed on washing equipment 77 (e.g. one or more drum or : belt:~washers)~;with recycled~ alcohQl~:from:tank 7a while simultaneously additional~lignin is removed and recycled through line 60 to:tank 7:.~:~ The pulp is~;fur~t:her~washed on :washing equipment~77 by water;intro~duction~through:line 43 :or bleaching filtrates~and~cooled to a temperature~of ~from~
About 40 ~o 70C. After wa~shing o~ the pulp on counter~
current washing equipment~44 or:~alterna~tively on:washing equipment 77, the pulp is tr~nsfere~d to holdin~ tank 9 an~
pumped: through a~ pulp screen~ 10. The pulp can~then:be~
suitably subje~ted to c~nven~ional pulF ~handlinc~
blPaching ar,d: paper--making proced~res.

The extr~tor 2 can~be loded wi~h another batch o' ibrous plant:materials from: the hopper 1, and ~the:~
fibrous; p~nt: materials c~n be ~-~ntactèd: by the primaryr ~35 secondary and fresh solvents f:rom ~ccumulators 31 6 and 7 : - as~described~above.
~ .

:, ~:

WOg3~1~261 PCT/US93/01256 21165~ o-Alternatively, a continuous pulping process is shown in ~iqures 3, 4, 9 and 10. Initially, wood chips ~50% moisture) or other fibrous material are pre steamed in steaming bin 31 by injection of steam at atmospheric S pressure. As shown in Fi~ures 3, 4, 9 and 10 the chips are wetted and passed into metering screw 32 which can be positioned at an angle. The excess water from the steam condensates in metering screw 32 and the wet chips are ~:~
passed through a first rotary valve feeder 33, heated in line 46 by direct steam injection at a temperature of from about 270F to about 330F and at a pressure o from about 30 to about 100 psig. In another em~odiment, direct -steam injection can be acomplished in a number of ways, for example by using a steaming vesseL at a temperature of lS from about 200F to about 340F and at a pressure of ~rom a~out 30 to about 100 psig. The steaming vessel can be ~i equipped with a vent which can be connected to a heat exchanger, for example a water cooled condenser which can ~ , .
be~ u:se~ to conden5e any vapors and produce a:condensate 20 :which can be returned to solvent recovery tower 14 and recycled for reuse with: the solvent.: Lin~ 46 can be equip~ed with a steam b~rrier which helps prevent backup of alcohol-containing vapors ln~to rotary valv~e~feeder 33.
The steamed fibrous plant materials are~pass~d:~through ~:a: : `
25 second :rotary va~ve feeder 3~and are::mixed in line 45 .;~.
with a solvent from line 36 as shown in:Figures 3 and 4. `
The solvent is mixed with the~ chips;in~high~pressure : r sluice 35 or the~solvent is mixe~ with~the ch1ps~ in~ chip slui~e tank 65: as shown in ~igures 9 and 10 3G The chips are impr ~r.ated and ~ t~ cesultant slurry ~rom h~ ~ pressure sluice 35 or from c~hi:p sluice tank:65 passes thro gh line 37 and enters e~ractor:~100 at inlet 38. As sho~n~in ~igures 9 and 10,~ the slurry is pressurized ~ ~G~h multista~e centrifu~l pu~ing system 35 :67 which can :be: selected to comprise at least one centrifugaI pump or several centrifug~l pumps in series such that the slurry is pressurized to the operating WO9~/15261 2 t 1 6 ~ ~ ~ PCT/U~93/01256 pressure of extractor lO0. As the cooking mixture enters extractor lO0 at inlet 38, a liquid separat~r lOl regulates the flow of the mixture in~o extrac~or lO0.
Excess cooking mixture liquid overflows extractor lO0 at outlet 39, is recycled through line 57 and pumped back into high pressure sluic2 35. The excess cooking liquid from high pressure sluice 35 i5 pumped through line 58 and recycled back into sur~e tank 50. The cooking mixture in surge tank 50 is mixed internally throu~h line Sl. Any overflow cooking mixture from surge tank 50 is pumped through line 54 into line 37O In a preferred embodiment, a mechanical separator lOl is utilized. to accomplich :the li~uid separation as described above. Additionally, mechanical separator lOl i5 utilized to convey the slurry of fibrous plant materials into extractor lO0 in a manner which maintains the free flow of excess cooking mixture liquid~ Further, mechanical separator lOl comprises movable screens ~o allow the adjustment of the position of such screens in mechanical ~separator lOl in~ide and r lative to the top of extra tor lO0, as may be desirable, i~. view of :the fibrous materials to be pulped and the pulping conditions:in extr ct~r lO0.
Alternatively as shown in Figure 9 and lO, as the exeess coo~ing mixture liquid overflows extractor lO0 at outlet~39, it is recycled through l1ne 57. The cooking mixture liquid passes through li~uid surge tank 684 Liquid sur~e tank 68 is equipped with a Ievel indicator and controls the overflow level of the cooking mix~ure liquid. Liquid surge tank 68 can sepa~ate: any :~3 r~or~.orldersablr- ~ses from the coQking mixture m}d ca~
e~ui~p~d -~1th a ~nt wh1ch can be connected to ~ he~s eiA han~er, ~o- example a col~i water condenser. A~y e~cess vapor fro~ 1 iq;li d s~r~e tank 68 can be condens~d ~r;d recysled to solvent recovery tower 14 and recycled~eor ~,5 ~euse with the solvent. The cooking mixture pa~;3es ~ rough line 57 into chip sluice;tank 65. In one:embodiment of the invention, line 57 is equipped with a heat exchanger 69 whlch can ~perate tO reduce the temperature of the cookin~

WO93/1~61 ~CT/US93/01256 2116~44 -12-mixture to a level such that the liquid in the cooking mixture does not flash when the cooking mixture passes through pressure reduction device 70 (e~g~ a pressure reducing valve or a turbine~, or when the cooking mixture passes through chip sluice tank 65. Pressure reduction device 70 can operate to ~educe the pres~ure of the cooking mixture in line 57, namely to from 650 psi~ to about 20 to 650 psig. In a preferred embodiment, the pressure reduction device 70 operates to reduce the pressure in line 46 from an operatin~ pressure within extractor lO0 to a pressure slightly be1Ow ~he presure in line 46. When pressure reduction device 70 is a turbine, the energy which is generated can be used to operate multistage cent~ifugal pumping system 67. In a pre~erred embodiment, chip sluice tank 65 can be within the pressure range of extractor lO0, narnely of from about lS0 to 650 psig. In another preferred embodiment, chip sluice tank 65 can be at the same pressure a:s in line 46~ In another preferred embodiment, chip slllice tank :65 can be at a 20 pressure lower then the pressure in line 46~, such pressure ~eing at a level low enough such that the solvent vapors do not escape into line 46.

The ~1mpregnated chlps in extra~tor lO0 are digested and extracted with :solvent which is fed into extractor lO0 at inlets 52 and 53O Preferably, the solvent is similar to that used in the process shown in Fi~gure l.
As shown in Figures 3, 4, 9 and lO, the solvent comprises ~ppropriate ~uantities of makeup alcohol, introduced at 49, with rPcovered alcohGl from the alc(~hol :al~ y-3~ products recovery sy tem introduced at 7 ar~d line 45, and ..
with ~lco~.ol~water filtrate rom ~ovn.'er~ rLent ~ashingequip~ent 44 or wit~ alcohol/wa~er Liltrate from washing equipment 77. As shown ~ ure~ 3 and 4, the solvent con~ained . line~36 is h~e~ in pulp washing equipment 47 (e.g. one or more pressure diffusers, drum washers or belt washers) by heat exchange with the pulp leaving extractor lO0 at outlet 41 or as shown in ~igures 9 and WO93/15261 PCT/VSg3/012~?6 -13- 211~

lO, the solvent in line 36 is heated hy heat exchange with the pulp on washing equipment 77.

The type of extractor used is not critical, however i~ should be adaptable to the continuous pulping of the cooking mixture. Typical extractor dimensions depend on the required capacity of the extractor. ~or example, extractor lO0 is operated in a continuous co-cuxrent/counter current mode and at a pressure range of from a~out 150 to abc,ut 650 psig. Such ar1 extractor is comprised of se~uential reaction zones and means to add and remc,ve solvent. The latter can be:in the fc,rm of liquor extra~tion screens e~uipped with wipe~s cr other cleaning devices that prevent screen plu~ging such as steam injectors.
~".

In one particular extractor confiquration as shown in Figure 8~ the cookina ~ixture:which typically contains 5% chip~ in ~ solvent passes throù~h ~extractor lO0 and is exposed sequent:ially to six react~ion zones.
With this parti~ular ext~actor ~onfi~uration, fu~ther alcohol impregnation of the~ chips occur~s: at a constant temperature o:from about 100 to; l30C~ in:~separation zone (a) for ~about 2 to~about 20~minutes.:In separation~
; zone (~), a vapor head space is:maintained~with the: leve~l :: of the sclven~ in the ~cook1ng m1xture higher than the ?5 level of the chips. Any excess solvent is r~emoved~ through ~ outlet 39 and recycled as ~ described above. The -~ temperature o~ the:~cooking m;ixtu:re~:~chips :i~s~e~levated ~asthe cook~ q mixt~.re passes into preheating ~on~ ~b~ and i~
preheate~ to ~rGm ~bout 15C to 18GC ln ~o~t 50 minu~es.
The hea~iny o~ the cook:.ng mixture in p:e~ ating zone (~
is achieved ~y:circ~Iating ~h~ cooking olve~t ~ounter-currently through a nea changer (t~pica'ly of the t~be and she~ r,^3 ~hich 1s h~ated with s"am. The hea' - exchanger temperature is ~aintained at a level:su:ffi~ient tc cause ~he cooking mixture in preheating zone (b) to - heat to from about 150 to 180~ C. The preheated cooking WO93/15261 P~T/US~3/01256 211fi5~ 4~

mixture is further heated in primary extraction ~one ~c) to from about 160 to 205 C and subjected to digestion and extraction for about 70 minutes. The cooking mixture is heated in primary extraction zone (c) by circulating the cooking solvent co-currently through a heat exchanger a~ described above. In zone (c) , a hot ethanol/water extract or "black liquor" is produced during the digestion and extraction process. The hot black liquor which contains lignin, hemicellulose, other saccharides and extractives ~e.~.. resins, organic acids, phenols and tannins) is separated from the cooking mix:ture throu~h line 40 and subsequently treated~to recover the lignin and other by-pr~ducts of the pulping process.

The cooking mixture is further digested and extracted for about 60 minutes in secondary extraction zone (d) at a temperature o Erom about l50 to 180~. The temperature is cooled in secondary extraction zone (d) by recircu1ating the cooking solv:ent in a heat exchange~ as described above. The heat exchange~ temperature is - 20 maintained at a level;sufficie~t;to achieve the cooling of the cooking :mixture to maintain a temperature~of from about 150 to l80 C in seconda~y extraction zone (d)~.~The;
:coo~ing mixture is further ~digest~d~and extracted for about 45 minutes in tertiary extraction zone ~e) and the mix~ure is cooled to a temperature of~from about:130~to 160C by recirculating the ~cooking solvent co-currently through a heat exchanger as described:above. The cooking mixture is further cooled to from about 70 to :100C in (~o'~.n~ zo~e ~f~ for a~:out 2~ minutes ~nd ~roken up nto 30 pU.'L~ Wi~h In.Xer 102. COO.Lil19 of ~ the c~oking~ mixture ~-.
ccOlin~ ZOne ( f ) iS a~ 1eVed bY miXing the~ miYtUre W ~ ~h the 501~ent i:ntroduc~d ~t:inlet 52 in a co~nter-current fashi~l and at inlet 53 in a co-current fashion. The sQlvent mixture c~nsis , oE makeup a~ohol, recycled alcohol from the alcohol and by-product recovery and alcoho1~water filtrate from counter-current washin~

-15- 2~ 4 equipment 44 or altern~tively from washing equipment 77.
The pulp exits extractor 100 through line 41.

As shown in Figures 3 and 4, the pulp is defiberi2ed as the pulp passes through pressure reduction valve 42D Pressure reduction valve 42 is prefera~ly a blow valve. The pulp is washed in pulp washing equipment 47 ~e~g. one or more pressure diffusers, drum washers or belt washers) with recycled alcohol through line 7 and make-up alcohol through line 49 and cooled to a temperature below 80~C while simultaneously additional lignin is removed and recycled th~ough line 36 and the kappa number~ is reduced to a bleachable grade. The pulp is further washed in multistage counter-current washing e~uipment 44 by introduction of water or bleaching filtrates through line 43 and cooled to a temperature of from about 4~ to 70C.
Counter-current washing equipment 4:4 replaces conventional, less energy efficient, steam stripping .
methods and re~oves from about S0 to about:~0% additional alcohol from the~pulp. Alternative1yr a~ shown:in~:Figures 20 9 an~ 10, and in connection with certain~fibr~us plant materials~ it l5 ~elieved possible to tr:ansfer~ the pulp throu~h line 41 to a holding tank 74 which is at pressure sufficient to:~preserv2:pulp strength,~and:~where possible such :pressure lS atmospheric. The pu:l:p is ~washed on ~:~ 25 washing equipm nt 77 with recycled alcohol through line 7 ,~ and make-up ~alcohol ::rom line 49 ~and~- cooled to~ a tempera~ure below 80C~ while simul:taneously aùditional ~lignin is removed~and recycled throu~h ~L~ne~36- ~The~pulp i5 ~urther washed or. w2shing e~ul~me~t 77 ~ a~er ir.troduction t~rough line 43 or ~leA-.~hirlg filtrates and cosl~d to a temperature OL from about ~Q to 70C~

.
After washing of: the pulp on cGunter-current:
. ..
washin~ equipment 44 o~ alternativ~ly an washing equipment `-77, the~pulp i:s sent to holding tank 3 and:pumped through 35 a pu~p screen 10. The pulp can then be suitably subjected '~

W~93/15261 PCT/US93/01256 2116~ 16-to conventional pulp handling, bleaching and paper-making procedures.

In one bleaching techni~ue, the pulp now xeferred to as brownstock can be~delignifled by treating with oxygen coupled with a prior peroxy treatment using a peroxy compound such as peracetic acid or hydroqen peroxide. Filtrates thus obtained under acidic conditions can be recycled:as wash water for brown stock washi:ng.
These filtrates are intr:oduced at inlet 43,~mixed:with water and become part o the;solvent in;li:ne~36. 5ince the rate of delignification :is directly proportîonal to the acidity of the solvent, it is:believed that t:hese:~acidi~
filtrates will accelerate the rate o delignification. It is also believed that the presence in 'the filtrates of organic acids of sodlum lignate accelerates the rate of delignification~ It is believed that such acid catalyzed delignification will result::in lowering the operating temperature~and~p~ressure~in~extractor~100~ Additionally, i~ sever~l ~peroxy compound: treatments: are: used ~sequen~ially:,~counter-c~tr~rent filt~rates~can~be ~ recycled.
:~ Alt:ernatively,~ a~fter~:pH~ adjustment~ fi~l;tra~t~es: from alkaline;~xygen delignificatlon~ can~:also be :used~ For exam~pl:e, delignification~::of ~pulp~ with:~:oxygen~ can ::~be~
:~ car:ried:out by flrst mixing~a:~pulp~slurry at~;fr~om~abou~t::~9 to :l5~ consistency~ by :~weight~ of~;~pulp~s~ ds~:~wi~th~a~
solution~ of:sodium hydroxide (~caustic~and~further~mixing~
: : : at~ high shear~:;wi:th :oxygen g~as~. ~The~amount of~caus:ti~c~: ~: added can pref~erably~be~ from~ about~ 2";~to~ 8%;, ~:more~
pre~rabiy from ~bout 3 to 6% based on ~wt/wt o~oven dry ~o.d,) pulp. The:temper:a~ture~;of the reactlon~mixture~can:
preferaDIy ~ be~ b~tween: ~about~ 60C and~ lo~~c,,~: more~
: preferably ~be~ween~ a'~o~t ,'1,~C~:and 90C,~: and ~:oxyger~
pressure ln the;; bleachlng vessel can~ p~referably ~he~
: maintained~:~at:from àbout 40;t;o~llO psig, ~more::~p~e~ bly~
at ~:from ::about 80~to lOO psig for;oxygen:delignii~cation:
~and at~from about 32~ to~60 psig for deIignification~using oxidative~ extractlon.~ Tne reaction time with oxygen can ::

W093/15261 PCT/~S93/01256 -l7-2~ 5~4 preferably be from about 6 to 60 minutes, more preferably from about 40 to 50 minutes. Additional chemical agents which may be added to help preserve strength pro~ertie include 0.5~ to 1% magnesium sulfate, 005~ diethylene triamine pentaacetic acid (DTPh~, and up to 3~ sodium silicate. ~or example, peroxy treatment of pulp can be achie~ed by mixing peracetic acid with the pulp at a pH of about 2 to about 10 and in amounts of from about 0.5 to about 4% by weight of peracetic acid per wei~ht of oven dried pulp. The pulp can be of any consistency, but is preferably between about 10 and 12% by~ weight o pulp solids. ~he reaction time can preferably be from about 20 minutes to about 3 hours at a temperature of from about 40C to ~0C. Alternatively,~peroxy treatment of pulp can also be achieved by mixing hydrogen peroxide with the pulp in amounts of from about Q.5~ to about 4~ hydrogen peroxide and at a pH of from ~bout 2 and ll. The pulp can be of any consistency, but is~preferably between a~out 10~
and 12% by weight of pulp solids and the temp~ra~ure of the reaction can~be maintained at from~about 40~ and 90C.
~agnesium sul~fate;at from about:0.5% to~l.0% may be added for Vlscosity protect~on of ~the pulp, and DTPA may be added at rom about 0.05 to 0.5%: to ~pr:event :ca~aly:tic ~ decomposition: oE ~the ~:peroxide by meta~l ions such as :manganese~ copper, and iron.
: ~
As shown in Figures 1,~3,~ 4, 9,~10,:11 ~and 12, the black liquor :is flashed into a flash~tank 11 to : recover part of the ethanol. The:~flash tank~ 11 can be~ at ~.~mospk.eric pressur~ for simplicity ~f opera~ion ~r at 3¢ r duc~ pres.~ure to further cool the biack ii~oor ar.~
G~iha.nce the aloohcl recovery. The re~uc~ion~in pressure in ~nP flash tank li causes partial vap~rization OL the thanol ~:~d leaves the residual blac~ liquor in the fla:sh ::
tank with ~n eth~:lol content o~ ~bout ~0 to 45%
preferably about:3~ to 40%. The residual black liquor is cooled du~ing this step to a temperature of less than about 9~C, preferably down to about 80 to 92C, but not , WO93/15~61 PCT/US93/012~6 211654 l -18-below about 70C to avoid premature precipitation of lignin in the flash tank 11. The black liquor can be heated by steam injection or indire~t heating before flashing in flash tank ll to vaporize more ethanol, therefore decreasing the ethanol concentration of the liquor to from about 25 to ~4% and reducin~ the amount of dilution water needed for precipitation by from about 20 to 70%. Steam injection or indirect heating can also be introduced directly into flash tank ll or in any of the flash tanks that can be used in sequential series with flash tank 11. The ethanol/water vapors obtained are condensed in condenser 8 and recycled, alon~ with any makeup ethanol, water and/or acid, for use in treating subsequent batches of fibrous plant materials.
Alternatively, in the continuous process as shown in Figures 3, 4, 9 and 10, the ethanol/water vapors from flash tank 11 (or flash tanks in sequential series :with flash tank 11) can be recycled in reboiler 24, thus providing ener~y for distil:Lation in solvent ~ecovery tower 14. Solvent recover~y can be further enhanced by interfacing solvent recovery tower 1:4 with additional solvent recovery towers and reboilers ~arran~ed in sequential series with solvent recovery tower l~.

In accor~ance with this invention, lignin is ::
then separated from the residual black~liquor discharged from the f~ash:~tank ll. Thls step lS~ carried out ~by~
diluting and preferably cooling the res:idual black iiquor as it leaves the fl~sh tank 11, with water and~ acid ~to fGrm a diluted re~iduai black li~uor with: a) an~lcohol 3~ contPnt of less than about 3~ 'by volume), pre.erably ab~ut fO to 25~ particularly abou~ 12 to 21%1 w.ith~an al~ohol content o~ a.b~Jt 8% being a practical minimum for subsequently reccvering the alcohol e ono~ically; b) a temperature of less tr.an ~bout 75C, pre~ rabiy lecs than a~out 6~C, particularly about 35 to 55C, and c) a pH of:
less than about 3, preferably less than about 2.5, particularly about l~5 to 2.5. In this step, particular W~93/15261 PCT/US93/01256 l92~ 16 ~44 temperatures are not critical, although providing higher temperatures in the diluted residual black liquor will generally increase settling rates of the lignin but will yie7d a darker colored lignin and may decrease its yield.
About 75C is a maximum temperature to avoid the formation of tarry lignin precipitates, ambient temperatures (e.g., about 20C) is a practical minimum, although lower temperatures (e.g., down to about 0C) can be used if low settling rates can be tolerated. Temperatures below about 65C, particularly below 60C, provide a significantly lighter colored li~nin precipitate. Alternatively, in large scale plant operations t about 30C i~ a maximum temperature in order ~o avoid the formatio~ of tarry li~nin precipitates D Also, particular p~'s of the diluted residual black liquor are not critical in this step, but lower pH's increase the yield of pr~cipitated lignin from the diluted residual black liquor and permit the use of hi~her temperatures in the diluted residual black liquor.
However, lowering pH below about 1 provides little or no 20 additional improve~sent in yield, and for this: reason, a p~
of abou~ 1 is a ~ractical minimum although lower pH ' s can be used. At a pH of less than a~out 3, lignin wil~
precipitate rom the diluted residual black liquor in high yield and at a high rate as fine solids. These lignin solids can then be separated from the remaining diluted residu~l black liquor supernatant in a conventional manner. Preferably, the lignin solids are separated by:
allowing them to settle out as a paste of about 6 to 12%
(by weight) sollds in a conventional clarifier or settling t~.nk 12; then ~oncent~ating this paste of lignin soli~s in a conventional ~en~.ifugal separato. to form a wet cake~ Or about 30 to 40% solids; and then drying this wet cake tG
form a uniform fine, free ~lowing powder. ~lternativelyt in lar~e scale plant operations, the llgnin so'ids are preferably separated by using large scale filters (e.
belt filter and filter press, preferably drum filter~
which allows easy washing of the lignin cake.

W~93/lS261 PCT/US93/0125~
211~44 -20- ~
In diluting the residual black liquor from the flash tank 11 with the water and acid to precipitate lignin, any conven~ional water soluble acid can be utilized which will provide the diluted residual black liquor with a pH of less thah about 3.0, preferably less than about 2.50. For example, a strong mineral acid (e.g., hydrochloric, nitric, sulfuric or phosphoric acid) or a strong organic acid ~e.g., oxalic acid, preEerably acetic, formic or peroxy a~ids) can ~be used.
Alternative1y, filtrates from the bleaching step can also be used. They can be added to the water in line 43 and alternative1y, ~they can be ~added to mixing tank 20.
Additionally, oxygen deli~nification filtrates, after p~
adjustment, ~are able to precipitate lignin at a p~ above 3~0, preferably between approximately: 3.5 and approximately 4Ø
~.
Preferably, the water: and :acid ~are mixed together before they are used to:dilute~the residual black liquor. In:~this~:regard, a;particularly preferr~ed~mixt:ure o~ aci~d~and water`is:a residual b~ack: liquor supernatant that i~s derived rom a previous~batch:~of~fibrous~plant materials and:~that has been recycled~and ~used: to~ di:lute the~ residual~black~ liquo:r:f~rom the~flash~t:ank~ after~
a);~:the supernatant has been~ separated ~from ~the;::lignin : ~ : 25: solids from t;he~:~previous~ batch of~fibro~s~plant mater-lals~
n~t~he:settling ~t~ank~:12~and~the centr~ifugal ~separator~ 13 as shown in Figur~es 3:and 9,~or as~shown in F;gures :4::,~10, :and 12 in large~s-cale filter;6~3; an-d~ b) the:~ alcohol:~
oollt~n~ Oe t~e supernatant ha5~ be3n re~:ov~ered in a onventional: solven~t condenser l5 as de~crib~d~be~low~: ~The recycled resid~ : biack liquor~ supernatant or~stzipper ~ ittoms, when u;sed lor::dilutin~::the~residual black ~ quor~
: from the flash;tank~ ll, provides higher~yiel~s and faster:~ :
: settling of li~g:~nln;~solid9 precipitatin~ ~ln the~:settl:ins 35 tank 12 and centrifugal separator :13 as shown in Figures 3 and 9~
.:
:
:
';'' :`

-2l?l1&s~ l In precipitating lignin from the residual black liquor from the ~lash tank ll, the method of diluting the residual black liquor with the water and acid also is not critical, so long as there is rapid and intimate mixing o~
the residual black liquor with the acid and water. For example, the residual black liquor can be suitably diluted by adding it to the acid and water in a conventional static dispersion mixer or a mixing tank, generally 20.
The residual black liquor can also be diluted by adding it as a finely divided stream to a strea~ comprising a solution of the water and acid, for example, by means of a venturi-type device, genera~lly 20, a~ shown schematically in Figure 2. The residual black liquor~from flash tank ll in Figures l, 3, 4 , 9, lO, ll and 12 can be~pumped through a small nozzle 21 located at about the center of a pipe 22 in the venturi-type device 20 in Figure 2, and the acid and water solution can flow in the pipe 22 towards the settling tank 12. As the ~re idual black liquor is injec:ted by the nozzle 21 into the acid~and wat~er solution 20 in the pipe~ 22, the residual~ black liquor~is rapidly: :
~diluted and cooled by the acid~and water~ ln~the~ piFe~ 22`.
Lignin rapidly precipitates~ as fine solids~ from the resulting diluted residual blac~ liquor~in:~the~ pipe 22, wh1ch::solids can~be easily~collected and concentrated in::
: 25 the settling ~tank 12: :and~ centr:ifugal~separator 13.
Alternatively,~ as~ shown in;Figures 4, 10, ll and l?, the:
, residual black l~iquor exits~mixing :tank~20~ and ~enters ~a ~liquid/solid separation system con~sisting of large scale ~ilter~63 (e.g. ~elt filter,~filter press;, prefer~ably drum~
filter), and ~ryer`~6. Filtrates of alcohol and dissolved solids, incIudin~ hemicellulose, are extr~cted rrom ~ilter 63 to be dist1lled in :solvent recove:ry:: tower 14.
Pr~cipitated lignln cake is:discharged~from filter 63 and is dried to a powder-like Eorm ~in dryer 6:6. :
:
3~ : In precipitating lignin in accordance with this inventiont the yield and settling r~tes of the lignin are generally- a funct:on of: a) the wood species, b) the .

WO~3/15261 PCT/US93/01256 21~6544 -2~- ~
process conditions utilized in the extractor 2; c) the temperature, pH and solids content of (i) the residual black li~uor from the flash tank 11 and ( ii) the acid and water used to dilute it; and d) the ratio of residual S black liquor to the acid and water used to dilute it. For example, the lignin from softwoods, such as spruce, is preferably precipitated at a temperature after dilution of about 40 to 60C using an acid and water solution with a pH of about 1.5 to 2.5 and with a ratio of residual black liquor to the acid and water solution of about 0.5 to about l. ~or hardwoods such as aspen~ it is preferred to use an acid and water solut1on with a pH~of-abou:t 1.2 to 2~2 and a temperature after dilution of less~ than ~about 50C. In this regard, it is preferred to us~e a ratio of residual black liquor to the acid and water solu~ion of:
a) about Ot 2 to 0.8 if thé temperature after dilution is about 40C; and b) about 0.6 to l.0 if the temperature after d~lution is less than about 40C (e.g., down to ambient temperature). For~ hardwoo:ds, such ~as~ sweetgum, maple and oak, i:t is preferred :to use a temperatùre after dilution of about 40 to 60C, an acid and~wat:er solution with a pH of about l.5 to 2~5, and:a ratio;~o~ residual :blac~liquor to the ac~id and water~ solution~o about::0.35 to Q.7-:

~ The cla:rlf~1ed res~idual~:black llquor i~Ltrate;
from the lignln soIids~separation~step~:con~t:aln;~:alc~ohol,:
furfural, wood sugars, acetic acid :;:and~low:molecular ~e:.ig~ht: lignin:fragments :~that were not; captured~ ~1n -the ~1~ci~it.atio.. p~çcedure. As shown in~Figures:l, 3 J~ 4, l~ na _2,~t'1e ethanol content;is preferably recover~
in~ t:~'ne sol~an~-: rec ~very towe~ 14 and solvent conden;ser 1:5~
The ethanol conterl- oE~ the ~ ~supernatant ~can:~be~:;stripped (e~g., down to ab,ut 200 pp~-) in 3 convent;ion~l manner in the solvent recovery;tower 14 at atmospheric pres ure.
35 Preferably,: the ~:: tower 14 is h ated; by heating and recycling a:portion of the bottoms stream from the tower 14 in a heat exchanger 24 as sho~n in Figures l, ll and ~:~

WO93/lS261 PC~/US93/01256 -2~-12, using the low pressure steam used to strip residual ethanol from the pulp in the extractor 2. Alternatively, when additional recovery towers are used sequentially with solvent recovery tower 14, the tower 14 can be operated S under vacuum or pressurized. The e~hanol/water vapors from the tower 14 are condensed in a conventional manner in the water-cooled condenser 15 tor by heat exchange with the stripper feed) and are then recycled together with the ethanol/water mixture which condenses from the low pressure steam in the heat exchanger 24. In accordance with this invention, th~ ethanol content o~f the: -supernatant from the settling tank 12 and centrifugal separator 13, or alternatively from large scale filter :63 as shown in Figures 4 and 10, can:be suitably recovered in lS high yield in a simple manner, without lignin precipitating within the solvent recovery tower:14 and forming tarry or ~ummy deposil:s on the ~internal ~surfaces of the tower. ~ ;

The clarified :residual ~bl?ck liquor filtrates from~the lignin solids separation step t~pically:~contains from about ~0.2 to ~ 0.8% furfur~al, from about 10 to;~15%
alcoh~l~ Erom~about ~0:.5:;to 10%~ dissolved~: so:lids,: and ~water. As shown i~n:Figures~ 3,~4, :9,~10,~lL~and~12 the~
:black Liquor i~s~ed to solvent~recover:y~:~tower 14~ and~a :~ :25 ;furfuraL side draw is~ removed~which~contains~:f~rom~about`l2 to 30% furfural. Th0~furfural~sId~e;~draw~ is ta;ken:~at:~a : : plate above the fe~ed p~Late~:a~t ll~ne ~700 a~nd~compr~is~es~o~
: ~rom about 2 to:about ~ of 2-hydroxy-ethylbutanoa~e~(HEB):
on a weight basis~with ~urfural compr~is~ in~ihe~side draw. HEB ca:n b~e significantly destroyèd b~ int:roducing : into ~1~ine 700: an~acidic soLutiDn of a~mineraL acid~, for~
example sulfuric acid, hydrochloric acidl and ~the 1ike;~at a pH :of from ~about 1 :to~about 2.5 and ~or at least 5 : minut~es, pre~erabLy:~ rom~abo~t:~ to~about 120 minutes::
35;:and preferably at the operating:tempe~rature at~line 70~0~
Alternativelyr HEB can be significantly destroyed by introducing into Line 700 an alkaline sol-ution of for ~
:

2 11 65~4 -24-example sodium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, sodium bicarbonate and the like at a pH of ~rom about 8 to about 11 and for at least 5 minutes, preferably~of from about 5 to about 120 minutes at the operating temperature at line 700. The acid or alkali catalytically break down HEB into ethanol and 2-hydroxybutyric acid. The treated furfural side draw which comprises of from about 1.5 to about 3~5% 2-hydroxybutyric on a weight basis with furfural is cooled by indirect heat exchange in heat exchanger 701 to a temperature of less than about 50 C and separates in decanter 71 into a crude furfural layer which comprises from about 60 to 75~ furfural and~from about 1~5 to about 3.5~ 2-hydroxybutyric acid on a weight basis with furfural and an alcohol rich aqueous layer which is returned directly to solvent recovery tower 14. The crude furfural can be upgraded to from about 85 to 91% furfural using liquid/liquid extraction and can be further purified to from about 95 to 98~ furfural using pervaporation. Other 20 purification techni~ues include~ free~ze ~conce:n~ration, dehydration`, distilaltion and~the use ~f a desi:ccant.

The~ crude furfural; layer ~ which typically contains from ~about 60:to 75% furfural, from about 5 to 15~ ethanol, from about 0.5 to 2~:~methanol from about 7 to 15:~ water and: from ~about ~ 5; to about~;3.5~% of 2 : ~ ~hydroxybutyric a`cid :can be upqraded using ~liquid/liquid extraction. Cross:-current liquid~extraction can:~be used, and as shown in Fi~ure 5, the crude furfura:l is mixed in mixer 71 usi ng mech~nical -gi ~;;ion ~iith a solvent, preEerabl~ water. When t~ crude furfural a~n~ ~wa~r separate in set~ler 72. a ~urural ra~inat~ and an ~cohol ricll wa~.er extract are obtained~. Several ex~ractions steps ~!N:=extraction steps i~ Figure 5) can;be used with mora than one mix~ ~nd settler arranged in sequential series. However, upgrading of the crude layer can be satisfactorily achieved ~with preferably two or - three sequential :cross-current e:xtract:ions. Water and W~93/15261 2 ~ ~ 6 ~ ~ ~ PCT/USg3tO~256 crude furfural are mixed in a volume ratio of from about 1:1 to 3:2, for about 30 minutes, and at a temperature of from about 0 to 50~ C. As shown in Fi~ure 5, the alcohol extract which contains from a~out 0.5 to 6% ethanol, from about 0.2 to 1% methanol and from about 6 to 10~ furfural is returned to solvent r~covery tower 14. A furfural raffinate is obtained which contains Erom about 89 to 91%
furfural, from about 0.1 to 0.2% ethanolt and from about 4.2 to 4.6% water.

Alternatively, as shown in Fi~ure 6~ the crude furfural can be upgraded using counter-current extraction.
The crude furfural is extracted with a solvent, preferably water in counter~current extractor 73. A temperature of from about 0 to 50C is used, and the flow of crude furfural to water is about 3:2. An upgraded furfural raffinate is obtained which contains from about 85 to 90%
furfural, Erom about 0.2 to 1% ethanol and from about 4 to 7% water. An aqueous alcohol extract typically~ containing from about 1 :to 12~ ethanol, from about~.4 to 1.5%
methanol and from about 6 to 10% furfural is returned to solvent recovery tower 14.

The upgr;aded ;furfural raffinate can b~e further .;
purified to remove the water (:e.g~ ~y :dehydr~ation or ::
pervaporation~ igures 5: and 6 are illustrative of:
purification by~pervaporation. The pervaporation~sys~tem is comprised of:a cell separated~ by a membrane~:82 into two compartments 81 and 83. Membrane 82:is :prefe:rably a ;~ -hydrophyllic membrane, fer e~ mple, a pol?vlnyl alcoho membra~e. r~he upgraded furfural is fed into compartment : 30 81 and the ~ater :contained in the up~r:aded furfural is~
preferentially~ attracte~d: by rll~mbrane R~. The water~
L ravels thrcu ~h membrane 82 into compartmen:t 83~. A vacuum pressure oL ri-om about:O~B to 8 psia ~prerera~ly::from about 1 to : 2 psia) is maintained in tank 83 to:vaporize the water. A:final furfural product is obtained which contains from~about 95 to 98% furfural, from about 0.1 to , .
`~

~ 1 4 -~6-0.5% ethanol and from about O.l to 2% water and is removed from compartment 81.`

Alternatively, the crude furfural can be upgraded using conventional distillation. An upgraded S furfural distillate is obtained whi h contains Çrom about 95 to 99% furfural, from about 0.2 to l~ ethanol and from about 0.2 to 1% water. Although a high purity furfural distillate is obtained, upgrading and purification o~
furfural using liquid~liquid extraction~and pervaporation is the preferred method over a single distillatiQn since this results in an energy savings of at least two-fold and the r~sultant furfural produrt contain~ less ethanol ~nd water, The bottoms streant removed from the solvent recovery tower 14 contains: wood sugars, low mo:lecular ~w~ight lignins, ~acetlc:~:ac1d,~ ash ~a~nd :other: minor components.: A portion of~th~e bottoms:~:stream~is~preferably concentrated in a conventional ~ manne:r~ fo~ example,~in ~multiple effect evapora~ors 26~ :In this::step~ scaling or:
fouli;ng ~of th;e~evapo:rat1on:equipment is~not a ~ignif~icant ~problem becaus:;there a:re:n~;substantia:l;amounts o~ high~
molecu~ar weigh~t :~lignin~ in~ th~bottoms~stream from t~he~
~ solvent recovery tower 14.~ The ~resulting: ~syrup, :~ containing hemicell~uloses~:together wi:th~small:amounts~ of~
~: ~25~:other saccharides, ext:ractives~ and~ very low : average:~
mo:lecular weight :li~nin~ .e. r ~:lignin;with a:molecular weight of less than about~00 9/ mol), ca~n :be ~urned ~ to r~cover its fuel value, ~s~e as 2r~imal fee~ r cGnver.ed to Ot~ chemica' pro~urts. ~ Alternati~ve y,::~he~ low iO molecular weight ~i~nin can be recov~r:ed.: ~he low molecular weight llgnin corresponds~ to lig:nirl~ ~ragments ~.hat:were not~captured by ~he precipità~ic~T. ~rocess due to their low mole~ular weiyht :and~ water solu~ility and se:veral different frac~tions can be isolated. In general, low molecular weight lignin can be characterized by a: low average molecular weight fraction in the r~nge of less WO~3/15~61 PCT/US93/01256 -272 ~

than 600 g/mo~ and.a low ~lass ~ransition temperature in the range of from about 24 ~o 75 C. Another characteristict when hardwoods ~re pulped, is that th~ low molecular weight lignin is predominantly of the syringyl type, since by nitro~enzene oxidation, it yields a syringaldehyde to vani~llin molar ratio of from about 2.7:1 to about 5.3:1. This low molecular weight lignin can be used as an extender in phenolic wood adhesive systems. It can also be used in applications requiri~ng water solubility during processing le.g. fiberglass binders)`and as an intermediate for the production of syringaldehyde and other chemicals. : ~ ~

Figure 7 illustrates the :recove~y of ~low molecular weight lignin. ~ portion of the bottom streams lS removed from solvent recovery tower 14 is concentrated to a syrup 90 by multiple ~effect evaporat~or 26 containing Erom about lO to 30~ solids. Optionally, the~pH of the bottom streams is raised to;~a~pE of from: abou~ ~2.0 to a~out 6.0: by al:kaline addition before~concentra~ting the bottom streams. Upon concentr~atio~n:~of the~ bo:ttom ~streams,~
the:::low molecular:~weight :lignin~fragments form~:a ~a:rry organic phase 9~Oa~Phich contains~from about 30 tQ~: 70`~ o~
the~ low~ molecular~; weight lignin;~that:wa~s~pres~ent~in the bot;toms stream, and an aqueous fraction ~:9Ob~ This tarry 2~ organic phase~9Oa;~contai~ns: Çrom abou~t ~6~0:~;to~90~%~ low~
' molecular weight: 1 ignin~solid:s~and~ at a~t~emperature ~o~
from about: ~0 to 95C,:it has:a~viscos~lty~of~from~about: :
400 to 3000 cps~. This organi~ phase i~ separated in dec~nter 91 rom aa,ueol~s ~ract1i~ . gO'tl.: Tne ~agueous fr~ction ~Ob:containine the remaioing low ~olecular~weight igniR l~ concentrated ln evaporator~9~:to ~from about 40 t~ 65% solids,~and is~extracted with an~ or~ganic solvent . ~preferab]y l:l volume~ratio) in counter-current~ quid,' : li~ui.d~ex~raction column ~. Grganic so~lvents~ such~ a diethyl: ether:,~ cyclohexane, furan, and ~-hexanol`c~n be used, however ~u:rural~is a particularly~preferred solvent since it removes in exoess of 70~ of the low molecular ::

' WO 93/15261 PCr/US93/ûï256 ~21 1~5~4 -28-weight lignin present in the aqueous phase in a single extraction. The furfural obtained by upgrading and purification as shown in Figures 5 and 6 can also be used to extrac~ the low molecular wei~ht lignin as described 5 above . The raf f inate f rom column 93 contains ~rom about 5 to 20% low molecular weight lignin , f rom about 70 to 85%
~urfural and from about 5 to lS~ water. The raffinate is vacuum distilled in column 94. The bottoms stream from column 94 contain low molecular weight lignin and the condensate from condenser 94Q containing primariIy from about 85 to 95% furfural and from about 5 tQ 15% water is recycled to column 93. The extract from :column g3 containing from about 6 to 10~ furfu~al, from about 4 to 5% sugars and from about 50 to 80% water is stripped from furfural in column 95. The condensate from column 9S in condenser 950 is decanted in decanter 96 and the heavy layer containing from about 85 to 95% furfural and from about :5 to 15% water ~is recycled to column 93. The stripper bottoms :from column~ ~ 95 cont~ain sugar~,; mostly 20 ~xylose, which can be further used for furfural production by acid catalyzed dehydration.

A second po~rtion ;of: the bottoms stream: removed from the tower 14 is prefera:bl:y used as th:e acid and water solution for diluting~ the resid~lal~ black 1iquor ~ from ~ the 25 flash tank ll in order to precipitate lignin therefr~m.
In this regard, the second:portion of the bottoms :strearn~:
f rom the tower 14 is prefera~ly ~ cooled: to a temperature ~ of less th~i abo~t 50C, preferably about 25~c to 40C (~about ûC ;.-ein~ a practic~l r, in~.num), and its ~,~'r'r i~ ad juCted, ii.
3~ r.eces~ar~y~ r.~ ~bout l~0 to 3.0 by addin~ a stron~ water soluble acid~ to i~t~ T~en the ~ooled and acidified: second portion of the bottvms stream ~ (hereinbefore called ~ the "recyclec ~es dual black liquor s;;p~rnatant" ) -.s intimately and rapidly m-xed (e.g., in the venturi-type 35 device 20 oE ~igure 2 ) with the residual black liquor to dilute and cool the residual blaclc liquor and precipitate li~nin .

WO93/1~261 PCT/US93/01256 -29~ 6S~ ~

The very pure lignin, which precipitates as fine solids f rom the diluted residual black liquor in the settling tank 12, can be subsequently removed from the centrifugal separator 13, or alternatively from large S scale filter 63 as shown in Figures 4, 10, 11 and 12, water-washed and dried in a conventional manner (e.g., by spin flash drying) to form a fine uniform, free flowing, water insoluble powder. This li~nin can be characterized as having: a relatively low number average molecular weight of about 700 to lS00 g/mol, preferably about 900 to 1300 g/mol, more preEerably about 800 to lO00 g/mol, and a glass tran~ition temperature which is preferably about 80C to 170~C, preferably about I30~- to 150C, particularly about 80C to 120C, and more particularly about 80C to 95C although a glass transition temperature of about 70 to 150C, is also observed; a narrow molecular weight distribution, i.e., a polydispersity of less than about ~, preferably no more than about 3, particularly only about 1.5 to 2.7; and a methoxyl content approximately e~ual to the methoxyl content of native lign1n (i.e~, about 20% for hardwoods~and about 14% for softwoods). This lignin also has a softening temperature which is preferably: about 120 :to 15~C, particularly about 125 to 150C and more particularly about 130~ to l35C. These:characteristics show, inter alia, the purity and low degree of chemical modiC cation of the lignin of this invention~ This lignin can be used for example, as a~
p~.enol formaldehyde resin extender in the manuEacture of par~ cle board ~nd plywood lhis lignin can alsG ~e used 30 in the man.u~asture of moidi~g compoun~s:, u:ethane and epoxy resins, anticxid~n?st c^ntrolled--re'e~se agents and ~low control agents~

This invention and many of its attendant advantage~ will be understood from the foregoing description, and it will be apparent that various modifications and changes can be made without departing ~ 5~ -30-from the spirit and scope of the invention or sacrifici~g all of its material advantages, the processes hereinbefore described being merely preferred embodiments. For example,. the process for precipitating the lignin of this invention can alternatively be carried out by separately adding an acid and water to a solution of lignin dissolved in a water miscible organic solvent to form a dilute aqueous solut1on with a. pH of less than about:3, an organic solvent content of less than about 30~ and a temperature of less than abou~ 75C, from which diluted solution the li~nin will precipitate as uniform fine solids. In this regard, the acid can be separately added to the residual black li~uor from:the flash tank ll i~n Figure l by adding the acid to the primary s~lvent f rom lS the primary solvent accumulator 3 before the p~imary solvent is used~ in the extractor 2 for pulping fibrous ;~
plant materials to produce~ the black liquor (which becomes, after removal :of ethanol in the flash tank:~ll, -the:residual black liquor~. Also, the process:-~of this in~ention can b~ carried out~with ~a water mis~cibl* organic solvent other than:a lower a~iphatic alcohol~ (pre~ferably ; ~:~
ethanol), such: as;acetone,~:glycol~or glycerol;,~ or;~with a ; : mixture of such~:so1vent~s.~ ~Also, these ~processes~can ~be~
:carried out using any fibrous plant~;mater}al~ such~a:
bamboo, bagasse, kenaf, cereal-:straws, a~nd not:just:wood.

: ' We cl ~ m~

/ l. ~ rocess for ~ pi~g~fibro ~ lant~ ma ~ al /..n ~ ~?~te~ m cibl~ ~ anic so1ve~.~and for rec~ ~ ng / sai~ wa~2f miscib?.e or~n~c~ solven~ :lignin ~d~:o~,er;
~0 ~ pro~cts ~result ~ ~...O1 the /puip..nq of ~id fibr pla ~ mater~al c ~ iiQ~ tne ~ pa;~Of / ;~

/ w ~ ng sal ~ s plant m ~ ial;

eating said tted;fibr ~ plant ma rial;

Claims (51)

What Is Claimed Is:

1. A process for steaming fibrous plant material during the pulping of said material in a water miscible organic solvent and of feeding said material to an extractor having a top and a bottom, said process utilizing first and second steaming zones, a mixing zone and comprising the steps of continuously:
(a) adding steam to said material in said first steaming zone at atmospheric pressure to wet said material;
(b) removing excess water from said material;
(c) passing said material from said first steaming zone to said second steaming zone;
(d) adding steam to said material in said second steaming zone, said steam at a temperature of from about 200°F to about 340°F and at a pressure of from about 30 to about 100 psig;
(e) mixing said steamed material from said second steaming zone with said water miscible organic solvent in said mixing zone to impregnate said material and to produce a slurry;
(f) venting gases which comprise vapors of said water miscible organic solvent and excess of said steam wherein said solvent is recyclable for reuse in said process; and (g) pressurizing and discharging said slurry from said second mixing zone to the top of said extractor.

2. The process of claim 1 wherein step (c) further comprises passing said material to said second steaming zone from said first steaming zone through a feeder.

3. The process of claim 2 which further comprises:
(h) barring with steam the backup of alcohol-containing vapors from said second steaming zone to said feeder.

4. A process as in Claim 1 which further comprises:
(i) separating and recovering said water miscible organic solvent from said extractor, recycling said recovered water miscible organic solvent, and combining it with said water miscible organic solvent in step (f).

5. A process as in Claim 4 which further comprises:
(j) separating gases comprising condensable and noncondensable gases from said recovered water miscible organic solvent;
(k) venting and condensing said condensable gases to form a solvent; and (l) recycling said solvent for use in combination with said water miscible organic solvent in step (f).

6. A process as in Claim 5 which further comprises:
(m) depressurizing said recovered water miscible organic solvent as said water miscible organic solvent is recovered; and (n) simultaneously generating energy as said recovered water miscible organic solvent is recovered.

7. A process for recovering cellulose pulp produced during the pulping of fibrous plant material in a water miscible organic solvent comprising the steps of continuously:
(a) separating said pulp from the cooking mixture produced during the pulping said material;
(b) washing said pulp with a mixture of a solvent comprising said water miscible organic solvent and alcohol to remove the lignin in said pulp, and producing alcohol/water filtrates;
(c) cooling said washed pulp to a temperature below 80°C;
(d) washing said cooled pulp with water and further cooling said pulp to a temperature of from about 40° to 70°C, and producing bleaching filtrates; and (e) further washing said cooled pulp with water and further cooling said washed pulp to further remove said lignin and to reduce said pulp kappa number to a bleachable grade.

8. A process as in Claim 7 which further comprises:
(f) during the practice of steps (b) and (d), removing of from about 50 to 90% of said alcohol from said pulp.

9. A process as in Claim 8 which further comprises:
(g) prior to step (a), storing said pulp at a pressure such that the strength of said pulp is preserved.

10. A process as in Claim 9 which further comprises:
(h) prior to step (g), reducing said cellulose pulp kappa number.

11. A process as in Claim 10 which further comprises:
(i) combining said alcohol/water filtrates and said bleaching filtrates; and (j) recycling said combined alcohol/water and bleaching filtrates for use with said step (b) solvent mixture.

12. A process for pulping fibrous plant material with a water miscible organic solvent utilizing an extractor having a top and a bottom, first and second steaming zones, and a mixing zone, comprising the steps of continuously:
(a) adding steam to said material in said first steaming zone at atmospheric pressure to wet said material;
(b) removing excess water from said material;
(c) passing said material from said first steaming zone to said second steaming zone;
(d) adding steam to said material in said second steaming zone, said steam at a temperature of from about 200°F to about 340°F and at a pressure of from about 30 to about 100 psig;

(e) mixing said steamed material recovered from said second steaming zone in said mixing zone with said water miscible organic solvent to impregnate said material and to produce a slurry;
(f) venting gases which comprise vapors of said water miscible organic solvent and excess of said steam said solvent being recyclable for reuse;
(g) pressurizing and discharging said impregnated material from said mixing zone to the top of said extractor;
(h) extracting said impregnated material with said water miscible organic solvent to produce a cooking mixture comprising cellulose pulp and black liquor, said black liquor comprising said lignin and by-products;
(i) separating said black liquor from said cooking mixture and withdrawing said separated black liquor from said extractor; and (j) recovering said lignin, said by-products and said cellulose pulp.

13. The process of claim 12 wherein step (c) further comprises passing said material to said second steaming zone from said first steaming zone through a valve feeder.

14. The process of claim 13 which further comprises:
(k) barring with steam the backup of alcohol-containing vapors from said second steaming zone to said feeder.

15. A process as in Claim 14 wherein said black liquor is withdrawn between the top and the central portions of said extractor.

16. A process as in Claim 15 which further comprises:
(l) separating and recovering said water miscible organic solvent from said extractor, recycling said recovered water miscible organic solvent and combining it with said water miscible organic solvent in step (e).

17. A process as in Claim 16 which further comprises:
(m) separating gases comprising condensable and noncondensable gases from said recovered water miscible organic solvent;
(n) venting condensable gases and condensing said condensable gases to form a solvent; and (o) recycling said solvent for use in combination with said water miscible organic solvent in step (e).

18. A process as in Claim 17 which further comprises:
(p) depressurizing said recovered water miscible organic solvent as said water miscible organic solvent is recovered; and (q) simultaneously generating energy as said recovered water miscible organic solvent.

19. A process as in Claim 18 which further comprises:
(r) separating said pulp from said cooking mixture;

(s) washing said pulp with a mixture of a solvent comprising said water miscible organic solvent and alcohol to remove the lignin in said pulp, and producing alcohol/water filtrates;
(t) cooling said washed pulp to a temperature below 80°C;
(u) washing said cooled pulp with water and further cooling said pulp to a temperature of from about 40° to 70°C, and producing bleaching filtrates; and (v) further washing said cooled pulp with water and further cooling said washed pulp to further remove said lignin and to reduce said pulp kappa number to a bleachable grade.

20. A process as in Claim 21 which further comprises:
(w) during the practice of steps (s) and (u), removing of from about 50 to 90% of said alcohol from said pulp.

21. A process as in Claim 20 which further comprises:
(x) prior to step (o), storing said pulp at a pressure such that the strength of said pulp is preserved.

22. A process as in Claim 21 which further comprises:
(y) prior to step (u), reducing said cellulose pulp kappa number.

23. A process as in Claim 22 which further comprises:

(z) combining said alcohol/water filtrates and said bleaching filtrates; and (aa) recycling said combined alcohol/water and bleaching filtrates for use with said step (s) solvent mixture.

24. The process as in Claim 23 which further comprises:
(ab) recycling said alcohol/water filtrates for use in step (u).

25. A process as in Claim 24 which further comprises:
(ac) removing of from about 50 to 90% of the alcohol from said pulp during the performance of steps (u) and (v).

26. A process as in Claim 25 which further comprises:
(ad) before the practice of step (s), storing said pulp at a pressure such that said pulp strength is preserved.

27. An apparatus for steaming fibrous plant material during the pulping of said material in a water miscible organic solvent and of feeding said material comprising:
(a) first and second steaming zones;
(b) means for passing said material from said first steaming zone to said second steaming zone, connected thereto;

(c) a mixing zone connected to said second steaming zone;

(d) means for adding steam, connected to said first steaming zones, to said material in said first steaming zone at atmospheric pressure to wet said material;

(e) means for removing excess water from said material in said second steaming zone, connected thereto;

(f) means for adding steam, connected to said second steaming zone, to said material in said second steaming zone, wherein said steaming means (f) is operable at a temperature of form about 200°F to about 340° and at a pressure of from about 30 to about 100 psig;

(g) means for venting gases comprising vaporized solvent and excess of said steam from said first and second steaming zones, connected thereto;

(h) means for recovering said vented solvent connected to means (g);

(i) mean for mixing said steamed material, connected to said first and second steaming zone, with said water miscible organic solvent to impregnate said material and to produce a slurry; and (j) means for pressurizing and discharging said impregnated material from mixing means (i) to an extractor, said extractor having a top and a bottom.

28. An apparatus as in Claim 27 which further comprises:

(k) means for separating and recovering, connected to steaming means (f), said water miscible organic solvent from said extractor; and (l) means for recycling said recovered water miscible organic solvent, connected to said extractor.

29. An apparatus as in Claim 28 which further comprises:
(m) means for separating gases, connected to means (l), wherein said gases comprise condensable and noncondensable gases from said recovered water miscible organic solvent;
(n) means for venting said condensable gases from and connected to said separating means (m) to form a solvent; and (o) means for recycling said solvent, connected to said venting means (n), for use in combination with said water miscible organic solvent in mixing means (i).

30. An apparatus as in Claim 29 which further comprises:
(p) means for depressurizing said recovered water miscible organic solvent, connected to said recycling means (o), as said water miscible organic solvent is recovered, wherein said depressurizing means (p) generates energy.

31. An apparatus for recovering cellulose pulp produced during the pulping of fibrous plant material in a water miscible organic solvent comprising:

(a) means for separating said pulp from the cooking mixture produced during the pulping of said material;

(b) means for washing said pulp with a mixture of a solvent comprising said water miscible organic solvent and alcohol to remove the lignin in said pulp, and for producing alcohol/water filtrates, wherein said washing/producing means (b) is connected to said separating means (a);
(c) means for cooling said washed pulp, connected to washing/producing means (b), to a temperature below 80°C;
(d) means for washing said cooled pulp with water and for further cooling pulp to a temperature of from about 40° to 70°C, and for producing bleaching filtrates, wherein said washing/cooling/producing means (d) is connected to washing means (b); and (e) means for further washing said cooled pulp with water and means for further cooling said washed pulp to further remove said lignin and to reduce said pulp kappa number to a bleachable grade, wherein said washing/
cooling means (e) is connected to washing/cooling/
producing means (d).

32. An apparatus as in Claim 31 which further comprises:
(f) means for removing of from about 50 to 90%
of said alcohol from said pulp, wherein said removing means (f) is connected to means (b) and (d).

33. An apparatus as in Claim 32 which further comprises:

(g) means for storing said pulp at a pressure such that the strength of said pulp is preserved, wherein said storing means (g) is connected to means (a).

34. An apparatus as Claim 33 which further comprises:
(h) means for reducing said cellulose pulp kappa number, wherein said reducing means (h) is connected to means (g).

35. An apparatus as in Claim 34 which further comprises:
(i) means for combining said alcohol/water filtrates and said bleaching filtrates connected to means (d); and (j) means for recycling said combined alcohol/
water and bleaching filtrates for use with said means (b) solvent mixture, connected to means (b).

36. An apparatus for pulping fibrous plant material with a water miscible organic solvent comprising:
(a) first and second steaming means;
(b) means for passing said material from said first steaming means to said second steaming means, connected thereto;
(c) means for mixing said material connected to said second steaming means;
(d) means for adding steam, connected to said first steaming zone, to said material in said first steaming zone at atmospheric pressure to wet said material;

(e) means for removing excess water from said material in said second steaming zone, connected thereto;

(f) means for adding steam, connected to said second steaming zone, to said material in said second steaming zone, wherein said steaming means is operable at a temperature of form about 200°F to about 340° and at a pressure of from about 30 to about 100 psig;

(g) means for venting gases comprising vaporized solvent and excess of said steam from said first and second steaming zones, connected thereto;

(h) means for recovering said vented solvent connected to means (g);

(i) means for mixing said steamed material, connected to said first and second steaming zones, with said water miscible organic solvent to impregnate said material and to produce a slurry;

(j) means for pressurizing and discharging said impregnated material from mixing means (i) to an extracting means, wherein said extracting means extracts said impregnated material with aid water miscible organic solvent to produce a cooking mixture comprising cellulose pulp and black liquor, said black liquor comprising said lignin and by-products;

(k) means for separating said black liquor from said cooking mixture and means for withdrawing said separated black liquor from said extracting means, wherein said separating and withdrawing means are connected to said extracting means; and (l) means for recovering said lignin, said by-products and said cellulose pulp, connected to said extracting means.

37. An apparatus as in Claim 36 which further comprises:

(m) means for separating and recovering said water miscible organic solvent from said extracting means, connected thereto; and (n) means for recycling said recovered water miscible organic solvent, connected to said extracting means.

38. An apparatus as in Claim 37 which further comprises:

(o) means for separating gases, connected to means (n), wherein said gases comprise condensable and noncondensable gases from said water miscible organic solvent;

(p) means for venting said condensable gases from said recycling means (n), connected thereto, to form a solvent; and (q) means for recycling said solvent, connected to said venting means (p), for use in combination with said water miscible organic solvent in mixing means (i).

39. An apparatus as in Claim 38 which further comprises:
(r) means for depressurizing said recovered water miscible organic solvent, connected to said recycling means (n), as said water miscible organic solvent is recovered, wherein said depressurizing means (r) generates energy.

40. An apparatus as in Claim 39 which further comprises:

(s) means for separating and recovering said water miscible organic solvent from said extractor, connected thereto, recycling said recovered water miscible organic solvent and combining it with said water miscible organic solvent in said extractor.

41. An apparatus as in Claim 40 which further comprises:

(t) means for separating said pulp from said cooking mixture, wherein said separating means (t) is connected to said extracting means;

(u) means for washing said pulp with a mixture of a solvent comprising said water miscible organic solvent and alcohol to remove the lignin in said pulp, and for producing alcohol/water filtrates, wherein said washing/producing means (u) is connected to said separating means (t);

(v) means for cooling said washed pulp, connected to washing/producing means (u), to a temperature below 80°C;

(w) means for washing said cooled pulp with water, for further cooling said pulp to a temperature of from about 40° to 70°C, and for producing bleaching filtrates, where said washing/cooling/producing means (w) is connected to washing means (u); and (x) means for further washing said cooled pulp with water and for further cooling said washed pulp to further remove said lignin and to reduce said pulp kappa number to a bleachable grade, wherein said washing/cooling means (x) is connected to said washing/cooling/producing means (w).

42. An apparatus as in Claim 41 which further comprises:
(y) means for removing of from about 50 to 90%
of said alcohol from said pulp, wherein said removing means (y) is connected to means (w) and (x).

43. An apparatus as in Claim 42 which further comprises:
(z) means for storing said pulp at a pressure such that the strength of said pulp is preserved, wherein said storing means (z) is connected to means (o).

44. An apparatus as in Claim 43 which further comprises:
(aa) means for reducing said cellulose pulp kappa number, wherein said reducing means (aa) is connected to means (t).

45. The process as in claim 7 which further comprises:
(k) bleaching said pulp after step (e).

46. The process as in claim 45, in which bleaching step (k) further comprises oxygen delignifying said pulp and treating said pulp with a peroxy compound.

47. The process as in claim 19 which further comprises:
(ae) bleaching said pulp after step (v).

48. The apparatus as in claim 31 which further comprises:

(k) means for bleaching said pulp connected to washing means (e).

49. The apparatus as in claim 48 wherein said bleaching means (k) further comprises (l) means for oxygen delignifying said pulp;
and (m) means for treating said pulp with a peroxy compound.

50. The apparatus as in claim 41 which further comprises:
(ab) means for bleaching said pulp connected to washing means (x).

51. The apparatus as in claim 50 wherein said bleaching means (ab) further comprises (ac) means for oxygen delignifying said pulp;
and (ad) means for treating said pulp with a peroxy compound.