Note: Descriptions are shown in the official language in which they were submitted.
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.
WO93/15261 PCT/US93/01256
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
~,
WO93/15261 PCT/US93/01256
2116544 -8-
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
.
. . .
WO93/15261 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~
W093/15261 PCT/US93/01256
-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~
.:
:
:
';''
:`
W093/15261 PCT/US93/01256
-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
~
:
WO93/15261 PCT/US93/01256
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
, .
`~
WO93/15261 PCT/US93/01256
~ 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
WO93/15261 PCT/VS93/01256
~ 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;
