WO1996041052A1

WO1996041052A1 - Modified organosolv pulping

Info

Publication number: WO1996041052A1
Application number: PCT/US1996/009942
Authority: WO
Inventors: Jairo H. Lora; Stephen R. Winner; Gopal C. Goyal
Original assignee: Alcell Technologies Inc.
Priority date: 1995-06-07
Filing date: 1996-06-07
Publication date: 1996-12-19
Also published as: BR9609008A; JPH11507416A; EP0830475A4; CA2221619A1; NO975672D0; EP0830475A1; NO975672L; AU6270596A

Abstract

A method and apparatus for producing pulp (95) from fibrous plant materials (10). The method comprises the step of pulping (100) the fibrous material with a cooking solvent of a lower aliphatic alcohol and an additive mixture comprising at least one additive selective from the group consisting of sulfite salts, bisulfite salts and caustic.

Description

MODIFIED ORGANOSOLV PULPING

BACKGROUND OF THE INVENTION

Current environmental 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 obtained in the range of from about 12 to 20. Alternatively, in the case of organosolv pulps obtained 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 obtained 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 of kappa number and brightening without significant subsequent strength losses. For certain wood species and feedstocks, however, the conditions needed for achieving 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 of dense hardwoods such as, for example, maple, the cooking conditions resulting in kappa numbers in the range of from about 40 to 50 are relatively severe. Such cooking conditions generally can cause deterioration of pulp strength. Similarly, with softwoods such, as for example, pine or spruce, similar kappa numbers are obtained under more severe conditions than with dense hardwoods and bleachable pulps with lower pulp strength are obtained.

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 of from about 15 to about 35.

Schroeter et al. in "Possible Lignin Reactions in the Organocell 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 continuous, 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 softwood 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 delignification.

Valladares et al. in "Pulping of Sugarcane

Bagasse with a mixture of Ethanol-Water Solution in Presence of Sodium Hydroxide and Anthraquinone", Progress Report No. 15, Tappi Press, pp. 23-28 (1984) propose the addition of small quantities of sodium hy¬ droxide to a mixture of about 60% to 40% ethanol-water by weight and the addition of a small amount of anthraquinone 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 containing from 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, Anthraquinone, Methanol Pulp¬ ing", 6th ISWPC, pages 609-617 propose the use of more than 5% caustic, more than 30% sulfite and catalytic amounts of anthraquinone in a solvent with 15% methanol. The pulps produced have good physical properties such as quality, 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 sulfite 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. Chen et al. in "Pulp Characteristics and Mill Economics for a Conceptual 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 of 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 "Processing 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 containing 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 Delignification", 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 of an hour. They have obtained pulps with high kappa numbers and their product is a semichemical pulp rather than a fully bleachable chemical pulp. 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 of 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 example of 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 of from about 0.05% to about 6%. Sulfite 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 obtained with the autocatalyzed organosolv pulping process. Selectivity can be enhanced by the addition of additives such sodium hydroxide, sodium sulfite, ammonium 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 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, sulfuric, 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, flax, straw, kenaf, reed, and softwoods such as spruce and balsam fir mixtures. Bleachable pulps can be obtained with low kappa number, high pulp strength and high yields.

Improved pulping selectivity can be obtained 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 recondensation reactions which are believed to interfere with the pulp reaching a very low kappa number. Additionally, the products of sulfonation are believed to act as surfactant and as such contribute to the removal of the organosolv lignin. Furthermore, oxidation-reduction side reactions in the presence of sulfite and bisulfite additives are believed to create a catalytic effect. 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 of hemicellulose as evidenced by the higher viscosity and higher hemicellulose content of the pulp which is produced.

Generally, sulfite and bisulfite can be added as sodium, magnesium or ammonium sulfites and bisulfites salts to a wide range of fibrous plant materials such as 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 uniform pulp cooking can be obtained with lower pulp screening rejects and pulp with a lower kappa number.

For example, 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 of from about 190°C to about 200°C, from about 100°C to about 155°C for a secondary extraction and from about 100°C to about 124°C for a tertiary extraction. The pH of the cooking liquor during primary extraction is from about 5 to about 5.4. The resulting pulp obtained had a low kappa number and a high yield of delignification.

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 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 maximum 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 of jute. When used alone, the level of 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 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 maximum 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 l.

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 fibrous 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 of from about 5% to about 60% can be steamed by feeding steam 20 into the plant materials in steaming equipment 15 to a temperature of in the range from ambient to about 120°C. The materials are steamed for 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 feeder 25. The materials in feeder 25 can be pressurized to from about atmospheric to the pressure in impregnation vessel 45 or alternatively to the pressure in extractor 100.

Following feeding, the materials can be im¬ pregnated in impregnation vessel 45 with additives 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 obtained. The impregnation time is from about 1 minute to about 120 minutes and the materials are simultaneously heated to from 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 fed 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 liquor 71 and a pulp slurry 75 can be withdrawn from extractor 100. Spent liquor 71 can be processed in liquor recovery equipment 85 to yield lignin, co-products and alcohol. Pulp slurry 75 can be processed in pulp recovery equipment 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 continuous process can be practiced in accordance with Figure 2 where steaming equipment 15 can be comprised of metering screw 32, first 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 passed into metering screw 32 which can be positioned at an angle. The excess water from the steam condensates in metering screw 32 can be removed and the wet fibrous plant materials can be passed through a first rotary valve feeder 33, heated in line 46 by direct steam injection at a temperature of from about 50°C to about

130°C and at a pressure of from about 30 to about 100 psig. Line 46 can be equipped with a steam barrier which helps prevent backup of alcohol-containing vapors into rotary valve feeder 33. The steamed fibrous plant materials are passed through a second rotary valve feeder 34. The fibrous plant materials in chip sluice tank 65 can be mixed with cooking solvent 30 and recycle solvent 50 from impregnation vessel 45.

Following feeding, 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 referred to as cooking mixture can enter extractor 100 at inlet 38, a liquid separator 101 regulates the flow of the mixture into extractor 100. Excess cooking mixture liquid overflows extractor 100 at outlet 39, is recycled through line 57 and pumped back into impregnation vessel 45. In a preferred embodiment, 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 of fibrous plant materials into extractor 100 in a manner which maintains the free flow of excess cooking mixture liquid. Further, mechanical separator 101 comprises movable screens to allow the adjustment of the position of such screens in mechanical separator 101 inside and relative to the top of extractor 100, as may be desirable, in view of the fibrous materials to be pulped and the pulping conditions in extractor 100.

Alternatively, as the excess cooking mixture liquid overflows 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 overflow level of the cooking mixture liquid. Liquid surge tank 68 can separate any noncondensable gases from the cooking mixture and can be equipped with a vent which can be connected to a heat exchanger, for example a cold water condenser. Any excess vapor from liquid surge tank 68 can be condensed and recycled to solvent recovery tower 14 and recycled for reuse with the solvent. Line 57 can be equipped with a heat exchanger

69 which can operate to reduce the temperature of 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 of the cooking mixture in line 55, namely to from 650 psig to about 20 to 650 psig. In a preferred embodiment, chip sluice tank 65 can be within the pressure range of extractor 100, namely of from about 150 to 650 psig.

The impregnated fibrous plant materials can enter extractor 100 and can be digested and extracted with solvent 36 which can be fed into extractor 100 at inlets 52 and 53. Solvent 36 can comprise appropriate quantities of cooking solvent 30, with recovered alcohol from the alcohol and co-products recovery system introduced at 7 and with alcohol/water filtrate from countercurrent washing equipment 77. The solvent contained in line 36 can be heated in pulp washing equipment 77 by heat exchange with the pulp leaving extractor 100 at outlet 41.

The type of extractor used is not critical, however it should be adaptable to the continuous pulping of the cooking mixture. Typical extractor dimensions de¬ pend on the required capacity of the extractor. As shown in Figure 3, extractor 100 can be operated in a continuous cocurrent/countercurrent mode and at a pressure range of from about 150 to about 650 psig. Such an extractor is comprised of sequential reaction zones and means to add and remove solvent. The latter can be in the form of 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, further alcohol impregnation of the fibrous plant materials occurs at a constant temperature of from about 50°C to 170°C in separation zone (a) for about 2 to about 20 minutes. In separation zone (a) , a vapor head space is maintained with the level of the solvent in the cooking mixture higher than the level of the fibrous plant materials. Any excess solvent is removed through outlet 39 and recycled as described above. The temperature of the cooking mixture is elevated as the cooking mixture passes into preheating zone (b) and is preheated to from about 150° to 180°C in about 50 minutes. The heating of the cooking mixture in preheating zone (b) is achieved by circulating the cooking solvent countercurrently through a heat exchanger (typically of the tube and shell type) which is heated with steam. The heat exchanger temperature is maintained at a level sufficient to cause the cooking mixture in preheating zone (b) to heat to 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 mixture is heated in primary extraction zone (c) by circulating the cooking solvent cocurrently through a heat exchanger 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 contains lignin, hemicellulose, other saccharides and extractives (e.g. resins, organic acids, phenols and tannins) 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 of 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 for about 60 minutes in secondary extraction zone (d) at a temperature of from about 100° to 190°C. The temperature is cooled in secondary extraction zone

(d) by recirculating the cooking solvent in a heat exchanger as described above. The heat exchanger temperature is maintained at a level sufficient to achieve the cooling of the cooking mixture to maintain 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 further cooled to from about 70° to 100°C in cooling zone (f) 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 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 embodiment, oxygen delignification of pulp can be carried out by first mixing a pulp slurry at from 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 maintained at from about 40 to 110 psig, more preferably at from 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 preferably from about 40 to 50 minutes. Filtrates

110 from oxygen delignification can be subjected to treatment with SO2 gas prior to mixing with additives mixture 40. If needed, any excess water can be removed from filtrates 110 using processes known in the art.

Black liquor 71 can be obtained from extractor 100 and the lignin, co-products and alcohol can be re¬ covered in liquor recovery equipment 85 as described by Lora.

The invention may be further illustrated by the following examples. Example 1

In this example, sugarcane bagasse is cooked with additions of sodium hydroxide, sodium sulfite singly and in combination. The concentration of the cooking solvent was 60% by weight of ethanol, at 175°C and at 10:1 liquor to bagasse ratio. Conditions are sum¬ marized in Table 1. The results obtained show that higher pulping yields and pulp viscosity are obtained with the additives for a same kappa number or autocatalyzed organosolv pulping.

Table 1

__-2S^Q3

Example 2

Sugarcane bagasse was pulped in a pilot plant using the conventional autocatalyzed organosolv process and by addition of sodium hydroxide and sodium sulfite. Table 2 summarizes the results obtained in both cases. The pilot plant data confirms the results obtained at the bench level. The modified process results in higher pulp yields and lower kappa numbers than the con¬ ventional process. Furthermore it was observed that in¬ creasing the severity of cooking conditions when using additives increased the viscosity. This unexpected phenomenon is perhaps the result of the preferential removal of hemicelluloses with a molecular weight lower than cellulose as the cooking severity increases.

Table 2

Conv Conv Conv Mod Mod

NaOH (%) 3.86 3.86

Na2S03 (%) 0 2.98 2.98

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 17.0 32.2

31.9 15.0 30.9

Kappa

(after 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 diffusion bagasse

Conventional process with crushed bagasse

Example 3

Table 3 compares the properties of sugarcane bagasse pulps produced by the conventional autocatalyzed ALCELLR process and with pulping in the presence of sodium sulfite and sodium hydroxide. The data indicates that the unbleached pulps obtained by the modified process have higher tear index, breaking length and burst index than pulps obtained by the conventional process.

Process

Yield (%)

Kappa (washed)

Bulk

(cm³/g)

Tear Index 3.3 5.8 4.2-4.5 7.2 (mNm²/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 of sodium hydroxide, sodium sulfite 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 obtained show that sodium sulfite improved delignification of the pulp as measured by the kappa number.

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 of from about 0% to about 6% on a weight basis on wood. The results obtained are compared with results obtained using sodium sulfite as an additive.

Table 5 shows that the pulp obtained with about 4% sodium sulfite has a final 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 sulfite 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 for the enhanced delignification.

Table 5

Additive pH Kappa Yield (%) (%)

Na2C0 ^"

0 4 .09 43 .9 52 .42

2 5 .21 61.87 57.37 3 5.39 61.07 59

4 5.55 62.38 60.54

5 5.79 60.49 60.78

6 5.91 66.58 61.9

Na2SQ3

0 4.09 43.9 52.42

3 4.84 41.96 51.99

4 5.1 40.4 55.78

Example 6

In 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. Conditions are summarized in Table 6 and the results obtained show a higher pulp viscosity at a given kappa number.

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 obtained has a kappa number of about 31, a viscosity of about 65 cps, a Pulmac strength index of about 83 and a Kajaani weighted average fiber length of about 0.71 mm. The pulp is beaten and its physical properties were measured. The physical properties of the resulting pulp are compared with a commercial kraft pulp obtained from maple. Results in Table 7 demonstrate that the pulp has superior physical properties than unmodified organosolv pulp and that its physical properties such as breaking length are better than kraft pulp.

Tear Index 6 .1 4 . 9 6 .2

(ttiNm²/g)

Burst index 2 .95 2 .3 2 .95

(kPam²/g)

Breaking Length 5.6 4.8 5.2

(km)

Example 8

In this example, jute was pulped with sodium sulfite. Table 8 shows the results obtained 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 improved the pulp strength of both the unbleached and bleached pulps. Table 9 shows the bleaching conditions used for jute and the results show that when an additive was used, a lesser amount of bleaching chemicals can be used.

Table 8

No additive 4% N_a2S03

Alcohol 70 60

(%) (v/v)

Pulp yield 68.8 66.7

(%)

Kappa No. 35.0 18.4 -26-

Viscosity 33.2 72.5

(cps)

Unbleached

Burst index 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)

Final

Brightness 88.7 88.5

Brightness after Dl 60 65

*: pulped without additive **: pulped with additive

Example 9

In this example, additives were used to pulp seed flax whole stalks. The seed flax 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 obtained from the core without the use of additives.

Table 10

Bast Bast Cor

Pulps produced in the presence of sodium bisulfite were bleached by EQDED using conditions in Table 11. A final brightness of 83.1 and viscosity of 30.2 cps was obtained for the core. For the bast, 84.5 brightness and 32.6 cps was obtained. The strength properties obtained are shown in Table 12.

Table 12

Core Bast

CSF 214 53 (mis)

Bulk 1.33 2.04 (cm³/g)

Burst index 3.3 3.9 (kPam²/g)

Tear Index 4.5 15.1 (mNm²/g) Breaking Length 7.0 6.3

(km)

Example 10

A mixture of spruce and balsam fir was pulped using alcohol water in the presence of sodium bisulfite. Processing conditions used per batch were as follows: 30 grams of wood (oven dried basis) , 240 mL of solvent (made up of SDA-1 alcohol and water in a ratio of 60:40 v/v and taking into account the water present as moisture in the wood) and 1.2 grams of sodium bisulfite were put together in a Parr bomb (Parr Company, Moline, Illinois) and were heated to 195°C for 120 minutes. Then the cooked chips were defiberized and then washed using 50:50 alcohol:water. Pulp was obtained with a yield of 57% on oven dried wood. It had a kappa number of 73 mL/g and a viscosity of 51 cps. The kappa number could be reduced to 51 mL/g after 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) This invention and many of its attendant ad¬ vantages will be understood from the foregoing descrip¬ tion, and it will be apparent that various modifications and changes can be made without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the processes hereinbefore described being merely preferred embodiments.

Claims

C l a i m s

1. A method of producing pulp from fibrous plant materials comprising the step of pulping said plant materials with a cooking solvent comprising an aqueous solution of a lower aliphatic alcohol and an additive mixture comprising at least one additive selected from the group consisting of sulfite salts, bisulfite salts and caustic.

2. The method of claim 1 comprising the steps

Of:

(a) steaming said fibrous plant materials to heat said materials and to remove any air trapped therein;

(b) wetting said steamed material with said cooking solvent;

(c) feeding said wetted steamed material and pressurizing said wetted material;

(d) introducing said wetted steamed material into an impregnation vessel and impregnating said wetted, steamed material with said additive mixture to form a fibrous plant materials slurry; and

(e) feeding said slurry into an extractor and extracting said slurry with said cooking solvent to produce said pulp and spent liquor.

3. The method of claim 2 which further comprises the step of (f) withdrawing said pulp; and (g) recovering said pulp.

4. The method of claim 3 which further comprises the step of (h) withdrawing said spent liquor from said extractor, said spent liquor comprising lignin, co-products and said alcohol.

5. The method of claim 4 which further comprises the step of (i) recovering said lignin, said co-products and said alcohol.

6. An apparatus for pulping fibrous plant materials with a cooking solvent comprising an aqueous solution of a lower aliphatic alcohol and an additive mixture comprising at least one additive selected from the group consisting of sulfite salts, bisulfite salts and caustic, said apparatus comprising:

(a) steaming equipment to steam and heat said fibrous plant materials and to remove any air trapped therein;

(b) a feeder to pressurize said wetted material;

(c) an impregnation vessel to impregnate said wetted and steamed material with said additive mixture to form a fibrous plant materials slurry,- and

(d) an extractor to extract said slurry with said cooking solvent to produce said pulp and spent liquor comprising lignin, co-products and said alcohol.

7. The apparatus of claim 6 which further comprises (e) pulp recovery equipment to recover said pulp.

8. The apparatus of claim 7 which further comprises (f) liquor recovery equipment to recover said spent liquor, said lignin, co-products and alcohol.

9. A pulp manufactured in accordance with Claim 1.