Note: Descriptions are shown in the official language in which they were submitted.
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MODIFIED ORGANOSOLV PULPING
~ BACKGROUND OF 1~ INVENTION
Current envir~nm~nt~l concerns dictate the
production of pulp with a low kappa number with a re-
sulting decrease in the amount of bleaching chemicals
used to bleach the pulp. In the case of kraft hardwood
pulps, kappa numbers are obt~in~ in the range of from
about 12 to 20. Alternatively, in the case of organosolv
pulps obt~;n~ with an autocatalyzed organosolv pulping
process such as the ALCELLR process as described in Lora
et al. in U.S. Patent No. 4,764,596 or Diebold et al.
in U.S. Patent No. 4,100,016, kappa numbers are obt~;n~
typically in the range of from about 20 to 30 with
pulping of mixtures of North American hardwoods of about
50~ maple, 35~ birch and 15~ poplar. Generally,
organosolv pulps have superior bleachability due, among
other reasons, to the structure of residual lignin and
the low metal content of the pulp which results in a
highly selective response to alkaline extraction and/or
oxygen delignification and other bleaching chemicals.
This results in a reduction o~ kappa number and
brightening without significant subsequent strength
losses. For certain wood species and feedstocks,
however, the conditions needed for achievlng bleachable
level kappa numbers may lead to a decrease in strength.
As a result even though selective delignification and
brightening are performed, the pulp strength properties
of the final bleached product may be lower than optimum.
In the case of autocatalyzed organosolv
pulping o~ dense hardwoods such as, for example, maple,
the cooking conditions resulting in kappa numbers in the
range of ~rom about 40 to 50 are relatively severe. Such
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cooking conditions generally can cause deterioration of
pulp strength. Similarly, with softwoods such, as ~or
~mr~e, pine or spruce, similar kappa numbers are
obt~; n~ under more severe conditions than with dense
hardwoods and bleachable pulps with lower pulp strength
are obt~; n~,
When for example sugarcane bagasse is pulped
using autocatalyzed organosolv pulping, pulping can be
stopped at a kappa number above 50 to prevent fiber
degradation. Pulping is then followed by alkaline
extraction in order for the kappa number to reach a
bleachable level at a kappa number o~ from about 15 to
about 35.
Schroeter et al. in "Possible Lignin Reactions
in the Organoceil Pulping Process", Tappi Journal, pages
197-200, 1991 propose a two stage organosolv pulping
process in which the first stage is an acid stage and in
excess of 20~ caustic by weight on wood is added in the
second stage. This two stage organosolv pulping process
was found to be impractical in cont;n~lous, industrial
scale operations. (Tappi Pulping Conference
Proceedings, Orlando, Florida, November 1991).
Marton et al. in PCT Int. App. No. WO 82
01,568 propose the use of ethanol in alkaline pulping at
20~ NaOH by weight on wood, thus producing soi~twood
pulps with improved properties as compared with pulps
produced using soda or alcohol pulping separately.
These ethanol pulps were poor compared with softwood
kraft pulps in terms of strength and deligni~ication.
Valladares et al. in "Pulping of Sugarcane
Bagasse with a mixture of Ethanol-Water Solution in
Presence of Sodium Hydroxide and Anthra~; none",
Progress Report No. 15, Tappi Press, pp. 23-28 (1984)
_
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propose the addition of small quantities of sodium hy-
droxide to a mixture o~ about 60~ to 40~ ethanol-water
by weight and the addition of a small amount of
anthra~l;n~n~ using sugarcane bagasse as raw material.
Ahmed et al. in "Steam Explosion Cooking of
Aspen Pretreated with Methanol-Water/Alkaline Water",
Forest Product Symposium, 1989 San Francisco 1989/1990
Chicago propose the use of steam explosion pulping
process including the pretreatment of aspen chips with
methanol-water/alkaline water solution cont~;ning ~rom
about 0~ to 8~ sodium hydroxide. High kappa number pulps
are produced that resemble chemithermomechanical pulps
and are not fully bleachable.
Patt et al. in "Lignin and Carbohydrate Reac-
tions in Alkaline Sulfite, Anthra~l;non~, Methanol Pulp-
ing", 6th ISWPC, pages 609-617 propose the use of more
than 5~ caustic, more than 30~ sulfite and catalytic
amounts of anthra~l;n~ in a solvent with 15~ methanol.
The pulps produced have good physical properties such as
~uality, yield and bleachability. However, the
multitude of chemicals used necessitates the use of
elaborate processes for chemical and solvent recovery.
Bublitz et al. in "The role of Methanol in a
Methanol Acid Sulfite Pulping Process", Pulping Confer-
ence, pp. 423-427, 1983, propose the addition of
methanol to an acid sul~ite pulping process. The total
pulping time is reduced from 5 to 6 hours to 1 hour or
less. The wood carbohydrates are less degraded which re-
sults in high pulp yields of about 60~ to about 65~.
The fiber strength obtained was lower than that of kraft
pulps. Furthermore, very high levels of -SO2 were
consumed in the process.
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Chen et al. in "Pulp Characteristics and Mill
Economics for a Conc~ptual SO2-Ethanol-Water Mill~
Solvent Pulping Conference, pages 663-671, 1990, propose
the use of an alkali pretreatment of wood prior to the
SO2-ethanol-water pulping. The pretreatment process was
a vacuum impregnation of wood chips in aqueous ethanol
with the presence o~ sodium hydroxide. The two-stage
organosolv process produced softwood pulps with about 6~
to about 10~ higher yield than kraft and single-stage
organosolv pulps. The pretreatment process also caused a
reduction of kappa number by around 6 units as compared
to the single-stage organosolv pulping. The pulps have
lower strength than kraft pulps, particularly in regard
to tear strength.
Primakov et al. in IlProcessing of Liquors
after Pulping with Water-Alcohol Solutions", Khim. Drev.
(4) 23-5, 1982 propose the cooking of birchwood with SO2
in a 1:1 saturated alcohol-water mixture cont~in;ng 40
to 75~ spent sulfite liquor with a Kappa number of 20.8
to 25 and a breaking length of 4900 m to 5500 m The
addition of spent liquor reduces the consumption of
alcohol in cooking.
Sakai in "Organosolv Deligni~ication", Shipa
Gikyo Shi, Vol. 48, No. 8, pp. 11-20 (1994) discloses
the addition of bisulfite to the isopropyl alcohol-water
solvent system. Large amounts of additive are used, for
example 18~ magnesium bisulfite, at 165~C for cooking
times o~ an hour. They have obtained pulps with high
kappa numbers and their product is a semichemical pulp
rather than a ~ully bleachable chemical pulp.
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SUMMARY ON THE INVENTION
It is an object of this invention to provide
for a process for manufacturing pulp by pulping with a
cooking solvent comprising an aqueous solution o~ a
lower aliphatic alcohol and one or more additive. The
additive is added in such small amounts that separate
procesess for the recovery or regeneration of the
additives are not required. One e~ample o~ such
additives are bisulfite salts added with maple and mixed
hardwoods in a range of from about 0.05~ to about 6~.
Another example are sulfite salts added to maple and
mixed hardwoods in a range o~ ~rom about 0.05~ to about
6~. Sul~ite salts can be added singly to bagasse and
jute in a range of from about 2~ to about 4~ or in
combination with sodium hydroxide which can be added in
a range of from about 1.3~ to 4~.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1, 2 and 3 are flow diagrams of the
process of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention provides for a process of
improving the selectivity of delignification and
increasing the rate of delignification beyond that which
is obt~; n~ with the autocatalyzed organosolv pulping
process. Selectivity can be ~nh~nced by the addition of
additives such sodium hydroxide, sodium sulfite,
;um and magnesium bisulfite, and sodium bisulfite
to the cooking solvent. The cooking solvent can be
~ comprised of from about 30~ to about 92~ (by weight) of
a water miscible lower aliphatic alcohol of 1 to 4
carbon atoms (e.g., methanol, ethanol, isopropanol or
tert-butanol) and from about 8 to about 70~ water. The
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cooking solvent can be further comprised of recovered
alcohol and alcohol/water filtrate from the process and
if needed, a small amount of a strong water soluble
acid, such as a mineral acid (e.g., hydrochloric,
sul~uric, phosphoric or nitric acid) or an organic acid
(e.g., oxalic acid, preferably acetic, formic or peroxy
acids), or a small amount of a mineral salt. The
resulting cooking liquor can be used to pulp a wide
range of raw materials such as for example sugarcane
bagasse, sugarcane rind chips, hardwood such as maple,
birch, poplar, oak, ash, basswood as single species or
in combination, jute, ~lax, straw, kenaf, reed, and
so~twoods such as spruce and balsam ~ir mixtures.
Ble~h~hle pulps can be obtained with low kappa number,
high pulp strength and high yields.
Improved pulping selectivity can be obt~;n~
with the additives of the invention. We believe that
bisulfite additive may be causing partial sulfonation of
the lignin present in the feedstock. Generally,
sulfonation can block re~nn~n~ation reactions which are
believed to interfere with the pulp reaching a very low
kappa number. Additionally, the products o~ sulfonation
are believed to act as surfactant and as such
contribute to the ~ l~vdl of the organosolv lignin.
Furthermore, oxidation-reduction side reactions in the
presence o~ sulfite and bisul~ite additives are believed
to create a catalytic ef~ect. Generally, additives such
as sulfite can cause the pH to rise with the net result
that hydrolysis of the cellulose fraction can occur at a
lower acidity and a higher retention o~ hemicellulose as
evidenced by the higher viscosity and higher
hemicellulose content of the pulp which is produced.
Generally, sul~ite and bisulfite can be added
as sodium, magnesium or ~mmnn;um sulfites and bisulfites
salts to a wide range of fibrous plant materials such as
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softwoods, maple, flax, wheat straw and a mixture of
hardwoods. Caustic can also be added singly or in
combination with any of the sulfite or bisulfite salts.
The fibrous plant materials can be pulped in accordance
with Diebold or as shown in Figure 1. With the addition
of additives to the cooking solvent, more uni~orm pulp
cooking can be obt~in~ with lower pulp screening
rejects and pulp with a lower kappa number.
For P~m~le, bisulfite salts can be added to
maple and mixed hardwoods, sugarcane residues such as
sugarcane bagasse at a level of from about 0.05~ to
about 6~ by weight on fibrous plant materials.
Bisulfites can be added to the cooking solvent
comprising alcohol and water in a weight percent of from
about 30~ to about 92~, preferably from about 40~ to
about 55~. The fibrous plant materials can be pulped as
taught by Diebold or using the process shown in Figure
1. With the Diebold process, primary extraction times
can be of from about 45 minutes to about 210 minutes
and at a temperature o~ ~rom about 190~C to about 200~C,
from about 100~C to about 155~C for a secondary
extraction and ~rom about 100~C to about 124~C for a
tertiary extraction. The pH of the cooking li~uor during
primary extraction is from about 5 to about 5.4. The
resulting pulp obt~lne~ had a low kappa number and a
high yield of deligni~ication.
In another preferred embodiment, sulfite addi-
tives can be used in the pulping of jute, flax, reed,
sugarcane residues, wheat straw, maple and mixed
hardwoods. When maple and mixed hardwoods are pulped,
the level of sulfite used is from about 0.05~ to about
6~ on a weight basis on feedstock. The fibrous plant
materials can be pulped as taught by Diebold or using
the process shown in Figure 1. With the Diebold
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process, the sulfite can be added to the cooking solvent
described above at the primary extraction stage. The
duration of the primary extraction is from about 60
minutes to about 180 minutes and at a temperature of
from about 175~C to about 204~C. The pH of the cooking
liquor during extraction is from about 4.4 to about 6.3.
In another preferred embodiment, sulfite addi-
tives alone or in combination with NaOH can be used in
the pulping of bagasse. When used alone, the level of
sulfite is from about 2~ to about 4~ on a weight basis
on bagasse. When used alone, the level of caustic is
from about 1.3~ to about 2.6~ on a weight basis on
bagasse. Sulfite and caustic can be used in combination.
When the two additives are used in combination, the
level of sulfite is from about 2~ to about 4~ and the
level of caustic is from about 1.3~ to about 4~ and the
level of each additive can be adjusted such that the pH
of the cooking liquor during the preheating step is in
the alkaline range. The pH reaches a level of from about
6 to about 8 as the cooking liquor temperature reaches
its m~ ml~m and becomes slightly acidic as the primary
extraction progresses. The fibrous plant materials can
be pulped as taught by Diebold or using the process
shown in Figure 1.
Alternatively, sulfite additives alone or in
combination with caustic can be used in the pulping o~
jute. When used alone, the level o~ sulfite is from
about 2~ to about 4~ on a weight basis on jute. When
used alone, the level of caustic is from about 1.3~ to
about 2.6~ on a weight basis on jute. Sulfite and
caustic can be used in combination. When the two
additives are used in combination, the level of sul~ite
is from about 2~ to about 4~ and the level of caustic is
from about 1.3~ to about 4~ and the level of each
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_g _
additive can be adjusted such that the pH of the cooking
liquor during the preheating step is in the alkaline
range. The pH re~ches a level of from about 6 to about 8
as the cooking liquor temperature reaches its m~; mllm
and becomes slightly acidic as the primary extraction
progresses. The fibrous plant materials can be pulped as
taught by Diebold or using the process shown in Figure
1.
In another preferred embodiment, caustic can
be used in the pulping of sugarcane residues, maple and
mixed hardwoods in a range of from about 1.3~ to 2.6~.
The ~ibrous plant materials can be pulped as taught by
Diebold or using the process shown in Figure 1. With the
Diebold process, the pH reaches a level of from about 5
to about 7.
The process of this invention is schematically
shown in Figure 1. Fibrous plant materials 10 having a
moisture level o~ from about 5~ to about 60~ can be
steamed by ~eeding steam 20 into the plant materials in
steaming equipment 15 to a temperature o~ in the range
~rom ambient to about 120~C. The materials are steamed
~or from about 0.5 minute to about 120 minutes to heat
the materials and to remove any air which may be trapped
therein.
Following steaming, the steamed materials are
wetted with cooking solvent 30 described above and in-
troduced in ~eeder 25. The materials in feeder 25 can be
pressurized to ~rom about atmospheric to the pressure in
impregnation vessel 45 or alternatively to the pressure
in extractor 100.
Following ~eeding, the materials can be im-
pregnated in impregnation vessel 45 with additives
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mixture 40. Additives mixture 40 can comprise cooking
solvent 30 and any of the additives mentioned above
mixed therein at the appropriate concentration level
depending on the fibrous plant material being pulped. A
slurry can be obt~;ne~. The impregnation time is from
about 1 minute to about 120 minutes and the materials
are simultaneously heated to ~rom about 50~C to about
170~C. During the impregnation time, the slurry can be
pressurized to the pressure in extractor 100.
The fibrous plant materials slurry from im-
pregnation vessel 45 can be ~ed into extractor 100 and
the slurry which typically comprises from about 5~ to
about 20~ solids is pulped for from about 45 minutes to
about 6 hours. The temperature in extractor 100 is from
about the temperature in impregnation vessel 45 to about
205~C.
During pulping, a stream of spent li~uor 71
and a pulp slurry 75 can be withdrawn from extractor
100. Spent liquor 71 can be processed in liquor recovery
e~lipmPnt 85 to yield lignin, co-products and alcohol.
Pulp slurry 75 can be processed in pulp recovery
e~l;pmPnt 95 to yield pulp and alcohol.
The invention can be applied to both batch and
continuous cooks. In the case of batch cooks, the
steaming and feeding steps described above can be
practiced in accordance with Diebold. A c~nt; nllOUS
process can be practiced in accordance with Figure 2
where steaming e~uipment 15 can be comprised o~ metering
screw 32, ~irst rotary valve feeder 33, second rotary
valve feeder 34 and chip sluice tank 65. In one
embodiment, the fibrous plant materials can be pre-
steamed in steaming bin 31 by injection of steam at
atmospheric pressure. The plant materials are wetted and
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--11--
passed into metering screw 32 which can be positioned at
an angle. The excess water ~rom the steam con~n.~ates in
metering screw 32 can be L~.luved and the wet ~ibrous
plant materials can be passed through a ~irst rotary
valve feeder 33, heated in line 46 by direct steam
injection at a temperature o~ from about 50~C to about
130~C and at a pressure o~ ~rom about 30 to about 100
psig. Line 46 can be equipped with a steam barrier which
helps prevent backup o~ alcohol-cont~;n;ng vapors into
rotary valve ~eeder 33. The steamed ~ibrous plant
materials are passed through a second rotary valve
~eeder 34. The ~ibrous plant materials in chip sluice
tank 65 can be mixed with cooking solvent 30 and recycle
solvent 50 from impregnation vessel 45.
Following ~eeding, additive mixture 40 can be
added and the fibrous plant materials can be impregnated
in impregnation vessel 45. The slurry can be pressurized
in impregnation vessel 45 to the operating pressure of
extractor 100. The slurry now re~erred to as cooking
mixture can enter extractor 100 at inlet 38, a liquid
separator 101 regulates the ~low o~ the mixture into
extractor 100. Excess cooking mixture liquid over~lows
extractor 100 at outlet 39, is recycled through line 57
and pumped back into impregnation vessel 45. In a
pre~erred embo~;m~nt, a mechanical separator 101 is uti-
lized to accomplish the liquid separation as described
above. Additionally, mechanical separator 101 is
utilized to convey the slurry o~ ~ibrous plant materials
into extractor 100 in a m~nn~ which maintains the ~ree
~low o~ excess cooking mixture liquid. Further,
mechanical separator 101 comprises movable screens to
allow the adjustment o~ the position o~ such screens in
mechanical separator 101 inside and relative to the top
o~ extractor 100, as may be desirable, in view o~ the
,
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~ibrous materials to be pulped and the pulping
conditions in extractor 100.
Alternatively, as the excess cooking mixture
liquid over~lows extractor 100 at outlet 39, it is re-
cycled through line 57. The cooking mixture liquid
passes through liquid surge tank 68. Liquid surge tank
68 is equipped with a level indicator and controls the
over~low level o~ the cooking mixture liquid. Liquid
surge tank 68 can separate any noncon~n~able gases ~rom
the cooking mixture and can be equipped with a vent
which can be connected to a heat exchanger, ~or example
a cold water cnn~n.~er. Any excess vapor ~rom liquid
surge tank 68 can be con~n~ed and recycled to solvent
recovery tower 14 and recycled ~or reuse with the
solvent. Line 57 can be equipped with a heat exchanger
69 which can operate to reduce the temperature o~ the
cooking 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). The cooking
mixture can be recycled through impregnation vessel 45
and pressure reduction device 70 can operate to reduce
the pressure o~ the cooking mixture in line 55, namely
to ~rom 650 psig to about 20 to 650 psig. In a pre~erred
embodiment, chip sluice tank 65 can be within the
pressure range o~ extractor 100, namely o~ ~rom about
150 to 650 psig.
The impregnated ~ibrous plant materials can
enter extractor 100 and can be digested and extracted
with solvent 36 which can be ~ed into extractor 100 at
inlets 52 and 53. Solvent 36 can comprise appropriate
quantities o~ cooking solvent 30, with recovered alcohol
~rom the alcohol and co-products recovery system
introduced at 7 and with alcohol/water ~iltrate from
countercurrent washing equipment 77. The solvent
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cont~;ne~l in line 36 can be heated in pulp W~h; ng
equipment 77 by heat ~h~nge with the pulp leaving
extractor 100 at outlet 41.
The type o~ extractor used is not critical,
however it should be adaptable to the continuous pulping
of the cooking mixture. Typical extractor ~;m~n~ions de-
pend on the required capacity o~ the extractor. As shown
in Figure 3, extractor 100 can be operated in a
continuous cocurrent/countercurrent mode and at a
pressure range o~ ~rom about 150 to about 650 psig. Such
an extractor is comprised o~ sequential reaction zones
and means to add and remove solvent. The latter can be
in the ~orm o~ liquor extraction screens equipped with
wipers or other cleaning devices that prevent screen
plugging such as steam injectors. The cooking mixture
passes through extractor 100 and is exposed
sequentially to six reaction zones. With this particular
extractor configuration, ~urther alcohol impregnation o~
the ~ibrous plant materials occurs at a constant
temperature o~ ~rom about 50~C to 170~C in separation
zone (a) ~or about 2 to about 20 minutes. In separation
zone (a), a vapor head space is maint~;n~ with the
level o~ the solvent in the cooking mixture higher than
the level of the ~ibrous plant materials. Any excess
solvent is L~lll~v~d through outlet 39 and recycled as
described above. The temperature o~ the cooking mixture
is elevated as the cooking mixture passes into
preheating zone (b) and is preheated to ~rom about 150~
to 180~C in about 50 minutes. The heating o~ the cooking
mixture in preheating zone (b) is achieved by
circulating the cooking solvent countercurrently through
a heat ~h~nger (typically of the tube and shell type)
which is heated with steam. The heat ~h~nger
temperature is m~;nt~;ned at a level su~icient to cause
the cooking mixture in preheating zone (b) to heat to
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from about 150~ to 180~ C. The preheated cooking mixture
is further heated in primary extraction zone (c) to from
about 175~C to 205~C and subjected to digestion and
extraction for about 70 minutes to about 180 minutes.
The cooking m; ~tllre is heated in primary extraction zone
(c) by circulating the cooking solvent cocurrently
through a heat P~h~nger as 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 cont~; n~ lignin,
hemicellulose, other saccharides and extractives (e.g.
resins, organic acids, phenols and tAnn;n.~) and the
spent additive can be separated from the cooking mixture
through line 71 and subsequently treated to recover the
lignin and other co-products o~ the pulping process. In
general, the level of additive used in the process is
low enough such that there is no need for separate
recovery and regeneration steps to recover the additive.
The cooking mixture is further digested and
extracted ~or about 60 minutes in secondary extraction
zone (d) at a temperature o~ from about 100~ to 190~C.
The temperature is cooled in secondary extraction zone
(d) by recirculating the cooking solvent in a heat
P~h~nger as described above. The heat p~h~nger
temperature is maintained at a level sufficient to
achieve the cooling of the cooking mixture to m~;nt~;n a
temperature of from about 100~ to 155~ C in secondary
extraction zone (d). The cooking mixture is further
digested and extracted for about 45 minutes in tertiary
extraction zone (e) and the mixture is cooled to a
temperature of from about 100~C to 125~C by recirculating
the cooking solvent cocurrently through a heat exchanger
as described above. The cooking mixture is ~urther
cooled to from a~out 70~ to 100~C in cooling zone (f)
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for about 22 minutes and broken up into pulp with mixer
102. Cooling of the cooking mixture in cooling zone (f)
is achieved by mixing the mixture with the solvent
introduced at inlet 52 in a countercurrent fashion and
at inlet 53 in a cocurrent fashion. The solvent mixture
consists of makeup alcohol, recycled alcohol from the
alcohol and co-product recovery and alcohol/water
filtrate from washing equipment 77. The pulp exits
extractor 100 through line 41 and is processed through
pulp recovery equipment 95 which can be comprised
holding tank 74, washing equipment 77, holding tank 9
and pulp screen 10.
As shown in Figure 2, the pulp can be trans-
ferred to holding tank 74 which is at pressure
sufficient to preserve pulp strength, and where possible
such pressure is atmospheric. The pulp can be washed on
washing equipment 77 with recycled alcohol through line
7 with cooking solvent 30 and cooled to a temperature
below 80~C while simultaneously additional lignin is
removed and recycled through line 36. The pulp can be
further washed on washing equipment 77 by water
introduction through line 35 and cooled to a temperature
of from about 40~ to 70~C.
After washing of the pulp, the pulp can be
sent to holding tank 9 and pumped through a pulp screen
10. The pulp can then be suitably subjected to
conventional pulp handling, bleaching and papermaking
procedures.
In one bleaching technique, the pulp now re-
ferred to as brownstock can be delignified by treating
in an oxygen delignification step or an alkaline
extraction step. Filtrates 110 thus obtained can be
recycled into the additives mixture 40 and mixed with
~ ~ - ~
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-
cooking solvent 30. In this way, the sodium which is
typically present in filtrate 110 can be combined with
sulfur dioxide to form sodium bisulfite and/or sodium
sulfite and can thus be used in pulping. In one
embo~;m~n~, oxygen delignification of pulp can be
carried out by first mixing a pulp slurry at ~rom about
9 to 15~ consistency by weight of pulp solids with a
solution of sodium hydroxide (caustic) and further
mixing at high shear with oxygen gas. The amount of
caustic added can preferably be from about 2 to 8~, more
preferably from about 3 to 6~ based on (~) w/w of oven
dry (o.d.) pulp. The temperature of the reaction
mixture can be between about 60~C and 110~C, more
preferably between about 70~C and 90~C, and oxygen
pressure in the bleaching vessel can preferably be
maint~;ne~ at from about 40 to 110 psig, more preferably
at ~rom about 80 to 100 psig for oxygen delignification
and at from about 32 to 60 psig for delignification
using oxidative extraction. The reaction time with
oxygen can preferably be from about 6 to 60 minutes,
more pre~erably from about 40 to 50 minutes. Filtrates
110 ~rom oxygen delignification can be subjected to
treatment with S02 gas prior to mixing with additives
mixture 40. If ne~ , any excess water can be removed
from filtrates 110 using processes known in the art.
Black liquor 71 can be obtained ~rom extractor
100 and the lignin, co-products and alcohol can be re-
covered in li~uor recovery equipment 85 as described by
Lora.
The invention may be further illustrated by
the following examples.
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Example 1
In this example, sugarcane bagasse is cooked
with additions o~ sodium hydroxide, sodium sul~ite
singly and in combination. The concentration o~ the
cooking solvent was 60~ by weight o~ ethanol, at 175~C
and at I0:1 liquor to bagasse ratio. Conditions are sum-
marized in Table 1. The results obt~;ne~ show that
higher pulping yields and pulp viscosity are obt~ne~
with the additives ~or a same kappa number or
autocatalyzed organosolv pulping.
Table 1
Additive Time E~ Yield Kappa Viscosity Kappa
(~) (hr) (extracted)
None 0.75 4.57 66.9 74.2 25.1 ---
None 1 4.44 61.36 82.4 22.9 ---
None 1.75 4.25 55.14 58.7 17.4 ---
NaOH
1.3 4 5.34 73.23 69.05 28.38 39.4
2.6 4 6.13 71.5 38.58 37.13 27.13
Na~SO3
2 2 4.92 72.96 79.66 29.55 36
2 4 4.68 66.15 61.16 26.39 23.67
4 3 5.15 69.98 53.41 27.15 22.06
NaOH/Na~SO3
1.3/2 3 5.61 71.39 52.69 --- 32.56
2.6/2 3 6.23 70.2 32.83 --- 28.34
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Example 2
Sugarcane bagasse was pulped in a pilot plant
using the conventional autocatalyzed organosolv process
and by addition of sodium hydroxide and sodium sul~ite.
Table 2 summarizes the results obt~;ne~l in both cases.
The pilot plant data con~irms the results obt~;ne~ at
the bench level. The modi~ied process results in higher
pulp yields and lower kappa numbers than the con-
ventional process. Furthermore it was observed that in-
creasing the severity o~ cooking conditions when using
additives increased the viscosity. This unexpected
phPnomPnon is perhaps the result o~ the pre~erential
Vdl 0~ hemicelluloses with a molecular weight lower
than cellulose as the cooking severity increases.
Table 2
Conv Conv Conv Mod Mod
* * ** * *
NaOH (~) 0 0 0 3.86 3.86
Na2SO3 (~) 0 0 0 2.98 2.98
20 Primary
(120 min) 185~C 180~C 193~C 193~C 193~C
Secondary
(30 min) 160~C 150~C 180~C 150~C 150~C
Tertiary
(30 min) 160~C 120~C 180~C 100~C 100~C
Yield (~)
(cooked) 59. 4 62. 5 55.2 77.6 76
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Kappa
(w/o wash)41.2 73.0 34.6 17.0 32.2
Kappa
(washed) 39.8 63.9 31.9 15.0 30.9
Kappa
(a~ter E) 26.1 35.1 --- 15.3 26.9
Viscosity 24.6 31.4 32.4 33.0 59.2
*: Conventional or modified process with di~fusion
bagasse
**: Conventional process with crushed bagasse
m~l e 3
Table 3 compares the properties o~ sugarcane
bagasse pulps produced by the conventional autocatalyzed
ALCELLR process and with pulping in the presence o~
sodium sul~ite and sodium hydroxide. The data indicates
that the unbleached pulps obt~; nP~ by the modi~ied
process have higher tear index, breaking length and
burst index than pulps obtained by the conventional
process.
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Table 3
Raw Material Di~usion Baqasse Crushed Bagasse
Process Conv Mod Conv Mod
Yield (~) 59.4 77.7 60-70 76
Kappa (washed) 39.8 17 40-80 30.9
Bulk 1.5 1.77 1.8-1.9 1.70
(cm3/g) ~
.
Tear Index 3.3 5.8 4.2-4.5 7.2
(rr~m2 /g)
Burst Index 3.3 4.1 2.-2.5 2.9
(KPam2/g)
Breaking
Length (Km) 6.4 7.1 3.9-4.6 5.7
Revs. (300 CSF) 1000 1900 1400-2500 3400
Example 4
In this example, maple is cooked with
additions o~ sodium hydroxide, sodium sul~ite singly and
in combination. The temperature was 195~C and the liquor
to wood ratio was 8:1. Conditions are summarized in
Table 4. The results obt~;n~ show that sodium sul~ite
improved deligni~ication o~ the pulp as measured by the
kappa number.
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Table 4
Alc/H20 Time pH Yield Kappa Viscosity
(hr)
No additives
70:30 1.5 4.41 55.97 74.75 ---
60:40 1.0 4.51 54.88 73.46 51.36
60:40 2.0 4.1 53.52 43.27 15.81
60:40 2.5 4.09 52.42 43.9 12.96
50:50 1.5 3.86 54.26 56.49 14.43
50:50 2.5 3.91 49.45 31.53 5.4
40:60 1.5 3.69 51.66 62.53 6.38
Na~S03 (~)
70:30 2 1 4.88 65.53 75.21 ---
70:30 2 2 4.96 63.06 61.62 ---
70:30 2 3 5 55.74 49.54 ---
70:30 4 1.5 5.45 62.2 68.24 ---
70:30 4 2 5.52 59.86 62.82 ---
60:40 2 1 4.59 57.95 63.6 69.85
60:40 2 2 4.68 57.14 49.93 48.36
60:40 2 3 4.71 53.23 43.63 33.58
60:40 3 1 4.79 54.17 64.37 53.52
60:40 3 2 4.84 53.15 45.81 54.99
60:40 3 3 4.88 50.82 38.45 37.41
60:40 4 1 5.35 58.3 60.46 69.01
60:40 4 2 5.11 56.15 45.69 54.11
60:40 4 3 5.1 51.84 36.05 38
60:40 6 1 5.72 61.53 59.2 ---
50:50 4 1.5 4.71 55.12 49.76 45.76
50:50 4 2.5 4.87 49.01 33.29 23.99
40:60 4 1.5 4.37 53.42 51.26 28.11
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NaOH (~)
60:40 1.3 1 5.19 64.84 60.94 ---
60:40 2.6 1 5.52 65.31 66.97 ---
Example 5
In this example, maple is cooked with sodium
carbonate as an additive to a 60: 40 ethanol/water
cooking liquor and in an 8:1 cooking liquor to wood
ratio. The temperature is about 195~C and the cooking
time is about 2.5 hours. Sodium carbonate is added as
an additive o~ ~rom about 0~ to about 6~ on a weight
basis on wood. The results obt~;n~ are compared with
results obt~;ne~ using sodium sul~ite as an additive.
Table 5 shows that the pulp obt~;n~ with
about 4~ sodium sul~ite has a i~inal pH in the same range
as the pulp obtained using about 2~ sodium carbonate as
the additive. Yields are in the same range for both
pulps, and the pulp obtained using sodium sul~ite has a
kappa number about 20 units lower than the pulp obtained
using sodium carbonate. Results in Table 5 show that in
this case, the presence of~ additive rather than any pH
adjustment caused by the additive is responsible ~or the
enhanced deligni~ication.
Table 5
Additive ~ Kappa Yield
(~) (~) .,
Na2Co3
0 4.09 43.9 52.42
2 5.21 61.87 57.37
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3 5.39 61.07 59
4 5.55 62.38 60.54
5.79 60.49 60.78
6 5.91 66.58 61.9
Na~SO~
0 4.09 43.9 52.42
3 4.84 41.96 51.99
4 5.1 40.4 55.78
Example 6
10In this example, mixed hardwoods comprising
about 50~ maple, about 35~ birch and about 15~ poplar
are pulped with about 4~ sodium sulfite as an additive
to a 60:40 alcohol/water cooking liquor and a liquor to
wood ratio of 8:1. The temperature is about 195~C.
15Conditions are summarized in Table 6 and the results
obtained show a higher pulp viscosity at a given kappa
number.
Table 6
Time E~ Kappa Viscosity
(min) (cps)
No Additive
4.29 58.63 46.49
4.2 44.6 36.79
4.23 46.62 31.77
4.14 41.68 36.65
120 4.16 37.64 25.97
150 3.99 35.22 18.9
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Na~SO~ (4~)
5.1 46.52 60.44
5.06 47.29 47.03
120 5.14 35.62 41.73
150 5.07 30.87 41.73
180 5.05 25.57 32.62
Example 7
In this example, maple is pulped with about 4~
sodium sulfite as an additive to a 60:40 ethanol/water
cooking liquor and a liquor to wood ratio of about 8:1.
The temperature is about 195~C and the cooking time is
about 3 hours. The pulp obt~; n~ has a kappa number o:E
about 31, a viscosity of about 65 cps, a Pulmac strength
index o:E about 83 and a Kajaani weighted average ~iber
length o~ about 0. 71 mm. The pulp is beaten and its
physical properties were measured. The physical
properties o~ the resulting pulp are compared with a
commercial kraft pulp obt~ nP~ ~rom maple. Results in
Table 7 ~l~mnn~trate that the pulp has superior physical
properties than unmodified organosolv pulp and that its
physical properties such as breaking length are better
than kra~t pulp.
Table 7
Alcohol/ Alcohol Kraft
Sulfite
PFI mill revolutions 4300 4000 2500
Bulk, mL/g 1. 45 1.42 .46
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Tear Index 6.1 4.9 6 .2
(mNm2 /g)
Burst index 2.95 2.3 2.95
(kPam2/g)
Breaking Length 5. 6 4.8 5.2
(km)
Example 8
In this ~mrle, jute was pulped with sodium
sulfite. Table 8 shows the results obt~;nP~ when pulping
jute in alcohol/water with and without sodium sulfite
present at 195~C. As can be observed the presence of
the additive resulted in higher viscosity and lower
kappa numbers, i.e. improved selectivity is achieved.
Table 8 also shows the strength properties of bleached
and unbleached jute pulps at 300 CSF. The use of
additives significantly ilLL~oved the pulp strength o~
both the unbleached and bleached pulps. Table 9 shows
the bleaching conditions used ~or jute and the results
show that when an additive was used, a lesser amount o~
bleaching chemicals can be used.
Table 8
No additive 4~ N~2S03
Alcohol 70 60
(~) (v/v)
,,
Pulp yield 68.8 66.7
(~)
Kappa No. 35.0 18.4
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Viscosity 33.2 72.5
(cps)
Unbleached
Burst index 2 5.5
(kPam2/g)
Tear Index 5.8 19.4
(mNm2 /g)
Breaking Length 4.2 7.9
(km)
Bleached
Burst index 1.7 5. 2
(kPam2/g)
Tear Index 6.7 18.0
(mNm2/g)
Breaking Length 3.8 7.2
(km)
Table 9
Stage Consistencv Time Temp Charge (~)
(~) (hr) (~C) * **
E (NaOH) 10 0.5 70 3 3
D1 (Cl02) 12 3 70 2.88 1.93
E (NaOH) 12 2 70 2 1.8
D2 (Cl02) 12 3 70 0.8 0.8
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Final
Brightness 88. 7 88.5
I
Brightness
after D1 60 65
*: pulped without additive
**: pulped with additive
Example 9
In this example, additives were used to pulp
seed flax whole stalks. The seed ~lax whole stalks were
separated into core and bast fractions by grinding in a
blender in a dry state. As a result of this grinding and
of the centrifugal forces due to the blender action, the
core and bast fractions were separated, with the core
forming a lower layer and the bast a top layer. The
conditions used for pulping and the results obtained for
bast and core fractions are presented in Table 10 The
data shows that high selectivity (high viscosity, low
kappa number) for core and bast pulping was achieved
when sodium bisulfite is used. No acceptable pulp could
be obt~;ne~ ~rom the core without the use of additives.
Table 10
Bast Bast Core
Sodium Bisulfite (~) 0 3 3
Temperature (~C) 195 195 185
~ 25 Time (min) 60 30 120
Ethanol:Water 60:40 60:40 40:60
Yield (~) 64 69 46
Kappa No. 63 30 64
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Pulps produced in the presence o~ sodium
bisul~ite were bleached by EoDED using conditions in
Table 11. A ~inal bri~htness o~ 83 1 and viscosity o~
30.2 cps was obt~;n~ ~or the core. For the bast, 84.5
brightn~Fs and 32.6 cps was obt~;n~. The strength
properties obt~; n~ are shown in Table 12.
Table 11
Stage Temp Consistency Time Char~e (~)
(~C) (~) (min) Core Bast
Eo 70 12 30 3 3
D1 70 12 180 5.9 5 9
E 70 12 120 2 2
D2 70 12 180 1. 2 1.2
Table 12
Core Bast
CSF 214 53
(mls)
Bulk 1.33 2.04
(cm3/g)
Burst index 3.3 3 9
(kPam2 /g)
Tear Index 4 5 15.1
(mNm2 /g)
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Breaking Length 7.0 6.3
(km)
Example 10
A mixture o~ spruce and balsam ~ir was pulped
using alcohol water in the presence o~ sodium bisul~ite.
Processing conditions used per batch were as follows: 30
grams of wood (oven dried basis), 240 mL o~ solvent
(made up o~ SDA-1 alcohol and water in a ratio o~ 60:40
v/v and taking into account the water present as
moisture in the wood) and 1.2 grams o~ sodium bisul~ite
were put together in a Parr bomb (Parr Company, Moline,
Illinois) and were heated to 195~C i~or 120 minutes.
Then the cooked chips were de~iberized and then washed
using 50:50 alcohol:water. Pulp was obt~neA with a
yield o~ 57~ on oven dried wood. It had a kappa number
o:E 73 mL/g and a viscosity o~ 51 cps. The kappa number
could be reduced to 51 mL/g a~ter a 2 hour alkali
extraction at 70~C using 4~ NaOH on pulp and a 10
consistency. At 532 CSF the pulp had the properties
reported in Table 13.
Table 13
Bulk 1.45
(cm3/g)
Burst index 6.9
(kPam2/g)
Tear Index 13. 5
(mNm2/g)
Breaking Length 9.8
(km)
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This invention and many o~ its attendant ad-
vantages will be understood ~rom the foregoing descrip-
tion, and it will be apparent that various modi~ications
and changes can be made without departing ~rom the
spirit and scope of the invention or sacri~icing all o~
its material advantages, the processes herein~e~ore
described being merely pre~erred embo~;m~nts.
