WO1995018260A1

WO1995018260A1 - Process for delignifying virgin and post-consumer used ligno-cellulosic plant meterials for the purpose of preparing cellulosic fiber, free sugars and lignin by-products

Info

Publication number: WO1995018260A1
Application number: PCT/CA1994/000721
Authority: WO
Inventors: Venanzio Di Tullio
Original assignee: Mauvin Material and Chemical Processing Ltd
Current assignee: Mauvin Material and Chemical Processing Ltd
Priority date: 1993-12-28
Filing date: 1994-12-28
Publication date: 1995-07-06
Anticipated expiration: 1996-06-28
Also published as: AU1378695A

Abstract

A process for the preparation of free sugars, lignin, lignin by-products, and cellulose pulp using recyclable solvents which have lower critical solution temperatures.

Description

PROCESS FOR DELIGNIFYING VIRGIN AND POST-CONSUMER USED

LIGNO-CELLULOSIC PLANT MATERIALS FOR THE PURPOSE OF

PREPARING CELLULOSIC FIBER, FREE SUGARS AND

LIGNIN BY-PRODUCTS BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The Invention relates to a process for the extraction of soluble and solublllzed sugars, lignin and lignin by-products from virgin and non-delignifled post- consumer ligno-celluloslc plant materials.

The process is effective in depolymerizing, dissolving, and concentrating the greater part of the lignin and its by-products and some of the sugars.

This invention is also directed to the prepara- tion of relatively high brightness pulps which require limited bleaching. DESCRIPTION OF THE PRIOR ART

It is known that unprocessed, i.e. non- delignified ligno-celluloslc plant materials have as their major constituent components: water, lignin, mono-, di-, oligo- and polysaccharides. Lignin makes up 20-30% of the dry weight while saccharides make up 60-80%. (Smook G.A., Handbook for Pulp and Paper Technologists, page 6 (1986) ISBN 0-910898-007) . Separation of lignin from the cellulosic fiber can be accomplished by mechanical, thermal, chemical, extractive, or by a combination of the above treatments. Extractive pulping is also known as organosolv pulping. Solvents used are aliphatic and aromatic alcohols, dimethyl sulfoxide, ketones, organic acids and aliphatic esters or a combination of the above in acidic, basic, and neutral solutions (Aziz, S. and McDonough, T.J. TAPPI 70 (3) , 137 (1987) ) .

Pulp yields from hardwoods vary In the 50 percentlie range while kappa numbers of 9-30 are common.

To date most organosolv pulping processes have been carried out in the temperature range of 150-210 °C. The purpose of high temperatures is to prevent recondensa- tion of the lignin solvolysis product (Paszner, L., CHO, H.J.; TAPPI 72 (2), 135 (1989)).

High temperature solvolysis requires: (1) the use of high pressure equipment which can withstand up to 35 atmospheres of pressure, and

(2) bleaching of the resultant cellulose pulp. SUMMARY OF THE INVENTION

The present invention provides a process whereby delignlfication can be realized at much lower temperatures than previously thought possible.

According to the present invention there is provided a method of delignlfying wood or plant material, both virgin and post-consumer with a recyclable liquid composition comprising:

Sodium silicate Up to 2.5%

Sodium hydroxide Up to 2.5%

Alkyl or dialkyl glycol ether and/or diglycol ether and/or propylene glycol ether 10-40%

Hydrogen peroxide Up to 10%

Triethylamine and/or diethylmethylamine and/or dimethyl pyridine and/or methyl pyridine and/or methyl piperldine Up to 10%

Water to 100%

having a lower critical solution temperature between about 0 and about 100 °C. which method comprises heating said wood or plant material with an effective amount of said liquid composition.

The invention further provides a method of delignifying a lignin-containing plant-derived material with a recyclable liquid composition comprising water and an organic compound which can be azeotropically purified, said liquid composition having a lower critical solution temperature of between 0°C and 100°C above which lower critical solution temperature said liquid composition divides into a heavier aqueous phase and a lighter organic phase, which method comprises: treating said lignin-containing plant derived material with a lignin-removing amount of said liquid composition at a temperature between 100 °C and 210 °C for sufficient time to release lignin from said lignin-contain¬ ing plant-derived material. The operating temperature range is usually 100-

210 °C. However, above 140 °C the pulp turned a darker color so temperatures of 100-140 °C are preferred, particu¬ larly 120-130 °C. Good results have been obtained at about 127 °C. Amounts of neutralizing agents such as sodium hydroxide, potassium hydroxide or sodium silicate, if present, usually comprise up to about 2.5% by weight. If used, preferably at least about 0.003% by weight of such a neutralizing agent is employed. A particular select range is 0.25-1.0% by weight.

The method usually requires at least 20 minutes, preferably 20-30 minutes, especially 20-60 minutes.

The method can be employed upon virgin lignin- containing plant material such as wood or it can be employ- ed on recycled post-consumer fiber products which have not been delignlfled such as TMP newsprint.

Most delignlfications performed here were carried out at 127 °C and/or 22 psi pressure without concomitant recondensation of the lignin. The present invention can thus be considered an improvement over the art known process for the desacchari- fication and delignification of plant materials.

The invention can be more fully appreciated when it is shown (1) the organosolv, (a solvent system with a lower critical solution temperature or LCST, i.e. as the temperature is raised the mutual solubilities of the two solvent constituents decrease until above a certain criti¬ cal temperature a blphasic mixture is formed) is used to separate mono and disaccharides from the remainder of the polysaccharide/lignin complex (A.I. Vogel, Practical

Organic Chemistry, Third Edition (1961 impression), pl8, Longmans, London) .

(2) the organosolv, at basic pH, is used to depolymerize the saccharide-lignin complex, and further (3) the organosolv is used to dissolve low molecular weight saccharldes while depolymerizing lignin thus freeing the alpha cellulose fraction for recovery. It is known to those familiar in the art that alkoxy ethanol ethers form crown ether complexes with alkali cations, thus generating anions of enhanced chemical activity which may account for the ease of depolymerlzation (Glymes: The Grant Family of Glycol Ethers-Ferro Corporation Publication; Stephenson, R.J. Chem. Eng. Data 1993 38 134) . The present invention thus provides a mechanism by which the reaction rate of delignlfication and desac- charification of ligno-celluloslc complexes can be enhanced.

Lower critical solution temperature solvents have the further distinction of separating into blphasic mix¬ tures of disproportionate lipophilicity by raising their temperature or inorganic salt solution content to, for example, 1-2% by weight (Glycol Ethers Technical Brochure F-60617 10/89-5M (Union Carbide Chemicals and Plastics Company Inc.)).

Organosolvs which have lower critical solution temperatures have the further capability of proportioning, with bias, lipophilic material to the upper phase, and hydrophllic material to the lower phase. The ability to simultaneously raise the lipo¬ philic and hydrophllic properties of the solution by causing a biphase to form greatly enhances both the cata¬ lytic capabilities of the solution and solubility of the respective layers to lignin degradation by-products and soluble saccharides. The present invention provides a method of solu- bilizing mono and disaccharides with a recyclable liquid composition (Composition A) comprising:

alkyl or dlalkyl glycol or diglycol ether and/or propylene glycol ether 10-40% Triethyl amine and/or diethyl methyl amine and/or methyl pyridine and/or dimethyl pyridine and/or methyl piperidine 0-10%

Water Up to 100%

having a lower critical solution temperature between 0 ° and about 100 °C which method comprises treating said plant material ln a soxhelet extractor at about 100 °C or ln a pressure vessel at 100-₂₁₀ o_{c but pre}fera_bly 100-140 °C, especially 120-130 °C, particularly at 127 °C.

The present invention provides a method of rais- ing the efficacy of anionic catalysis of lignin decomposi¬ tion and acetal hydrolysis with a recyclable liquid composition (Composition B) comprising:

Sodium silicate up to 2.5%

Sodium hydroxide up to 2.5% Alkyl or dlalkyl glycol or diglycol ether and/or propylene glycol ether 10-40%

Triethyl amine and/or diethyl methyl amine and/or methyl pyridine and/or dimethyl pyridine and/or methyl piperidine 0-10% Water up to 100%

having a lower critical solution temperature of between 0 °C and about 100 °C which method comprising treating said plant material in a pressure vessel at 100-210 o_{c but pre}_ ferably at 100-140 °C, especially 120-130 °C, particularly at 127 °C.

The present invention further provides a method of sequentially extracting low molecular weight sugars, solublllzed low molecular weight sugars, lignin and depoly- erlzed lignin with a recyclable liquid composition from the ligno-cellulosic plant materials.

Among preferred features are a system which: 1) has the versatility to process a broad spectrum of ligno-celluloslc species.

2) permits separation of soluble sugars from the celluloslc mass of the plant,

3) causes the hemicellulose to become partially hydrolysed and soluble,

4) effects depolymerlzation of the lignin- cellulose complex,

5) promotes hydrolysis activity of inorganic anions, 6) results in the separation of the lignin by¬ products from the sugars and from the pulp,

7) generates fiber which requires minimal bleaching,

8) provides a process where pulp peroxide bleaching is possible during dellgnification,

9) provides a process whereby chromophoric compounds can be oxidized,

10) generates a more consistent quality level of pulp and lignin by-products in a shorter cycle time period, 11) permits partitioning of the reaction products between the two layers of the blphasic mixture,

12) is sulfur free,

13) involves a simple chemical recovery system,

14) can be operated economically at below the 100 ton/day level,

15) requires a low capital outlay, and 16) is more energy efficient. Among advantages of the invention are the following:

1) isolation of sugars which can be enzymatically or chemically converted into by-products,

2) partial conversion of cellulose to monosaccharides,

3) rupture of llgnin-cellulose bonds and depolymerlzation of the lignin at low temperatures and pressures,

4) separation of pulp cellulose which requires little or no bleaching in paper production,

5) isolation of alkyl aromatic derivatives as raw material chemicals, 6) isolation of bleached lignin by-products,

7) delignlfication being effected in a smaller space at a lower cost,

8) use of solvents having low flammability ratings, and 9) use of low cost solvents.

DESCRIPTION OF THE DRAWING

The drawing which illustrates aspects and embodi¬ ments of the invention is:

FIGURE 1 is a schematic of events in a particular embodiment directed to explaining isolation of the products . DESCRIPTION OF SPECIFIC EMBODIMENTS

In a preferred embodiment of the process of the invention, a mixture of lipophllic compound which exhibits a lower critical solution temperature in water is used for extraction of free mono- and disaccharides.

Another embodiment of the invention relates to the use of solutions which have a lower critical solution temperature i.e. three levels of lipophilicity can be incorporated into one solution by changing the temperature and/or salt concentration and/or solvent concentrations. The single phase composition employed must be capable of generating an aqueous and an organic phase above the lower critical solution temperature i.e. showing decreasing mutual solubility with an increase in tempera- ture (e.g. as shown with water-glycol ethers by Stephenson R.M.; J.Chem.Eng.Data 1993, 38, 134-138).

Below the lower critical solution temperature the composition comprises one phase; above it it comprises two p^hases. The _crιtical temperature is between 0 °C and about 100 °C preferably below 50 °C.

The composition is used for delignlfication of ligno-cellulosic materials, depolymerlzation of the freed lignin, and hydrolysis of the lower molecular weight sugars. The composition is further used above the lower critical solution temperature to separate the blphasic layers, one rich in lipophillc and the other rich ln hydro¬ phllic components.

Compositions of the invention include Compositions A and B as described above.

Composition A is the same as composition B but does not contain sodium silicate and hydroxide. It is a subset of composition B which is neutral ln pH and free of salts. A specific composition of interest is:

20% butoxy ethanol

2.5% sodium hydroxide

2.5% sodium silicate

Balance water (all by weight).

For economy the process is preferably carried out at as low a temperature and pressure as is compatible with the process. 1 . Ext ract ion of Free Sugars

In the process of the invention the extraction from a mixture of 50% maple, 35% birch and 15% poplar ground wood, of free sugars such as glucose, mannose, galactose, xylose and arabinose is made possible. Mono-, di- and oligosaccharides are recovered. Hemicellulose can be made extractable.

A 20% concentration of butoxyethanol by weight in water at temperatures of 100-210 °C, but preferably 127 °C or about 22 psi gives a 2-3% cumulative yield of free sugars based on the dry weight of the fiber.

When sodium hydroxide or sodium silicate are used lignin, oligo and polysaccharldes are depolymerized.

2. Extraction of Depolymerized Lignin By-Products Contact of the mixed ground wood fiber with solu¬ tions of 20% butoxyethanol in water, causes very little lignin to be extracted at a temperature of 127 °C.

Addition of 5% by weight of Inorganic alkali agents such as sodium hydroxide and sodium silicate to the solution i.e. formation of composition B, causes the ligno- celluloslc bonds to rupture and the free lignin to depoly- erize. Depolymerized lignin oils can be recovered.

In treating mixed groundwood fiber it is desir¬ able to carry out the extraction at elevated temperatures of 100-210 °C, but preferably at 127 °C for 1 to 2 hours.

In cases where extraction was Incomplete we found treatment with a second charge of fresh solvent was of advantage.

The method of the invention allows for isolation of lignin and/or depolymerized lignin by-products, without substantial condensation of lignin on cellulose fiber.

Upon completion of the extraction, the biphasic solvent mixture was split into the upper and lower layers. Lignin and lignin by-products and sugars are collected in the upper and lower phases (layers) respectively. After extraction of lignin a low-lignin cellulose can be obtained. The darker upper layer was neutralized with concentrated hydrochloric acid and concentrated at reduced pressure. Distillation of the mother liquor at 1 mm pressure gave three oil fractions and a solid lignin residue.

In a preferred embodiment chromophoric groups ln isolated pulp or extracted oil can be oxidized with an oxidizing agent .

The explanation of the utility of the composi- tions, which explanation should not be taken as limiting, appears to be as follows.

The presence of sodium hydroxide and sodium silicate can neutralize acids, and make organic salts which are calcium based more soluble by exchanging the calcium ion for sodium. Generally, sodium silicate increases the wetting power of the solution. Potassium hydroxide can be expected to work as an alternate to sodium hydroxide. Cellulose

The fibrous Insoluble residue separated from the liquid was cellulose. Not all lignin had been removed since kappa numbers of 20-30 were obtained. The yield of cellulose was above 60%.

A solvent which has a lower critical solution temperature (LCST) (against water) of 0 to 100 °C, prefer- ably between 12 and 50 °C, and having the ability to dis¬ solve organic compounds is an essential constituent of the mixture. Some examples of such solvents are found in the table below. The numbers in brackets are the lower criti¬ cal solution temperatures. A range is given when a mixture of isomers is involved.

Dimethyl pyridine, (-3 to 34 °C), 3-methyl pyri¬ dine (49 °C), butoxy ethanol (49 °C), isobutoxy ethanol (24 °C), hexamethyleneimine (67 °C), methyl diethyla ine (49 °C), triethylamine (12-18 °C), 2 and 3 methyl piperl- dine (79 and 57 °C), 1,2 propylene glycol-1-propylether (34 °C) and 1,2 propylene glycol -2-propylether (43 °C) . (A.W. Francis, Critical Solution Temperatures, Advances in Chemistry Series #31 1961:American Chemical Society.) - (Note:Dimethyl pyridine is made of three isomers. Depend- ing on the mixture used the LCST can range from -3 to

+34 °C). Applicant's range of 0 to 100 °C fits the water component .

For purposes of simplicity and example we used butoxy ethanol as the LCST solvent. The reason for using a LCST solvent is in order to take advantage of its capability to selectively change the solubilities of the solution by either increasing salt concentration or temperature. A further reason is to partition the extracted materials between the two layers formed thus using this phenomenon for partial isolation of the extractants and for purification of the solvent. Salt concen ration and/or temperature can be used to temporarily generate a two phase system in order to solubilize specific organic compounds. Upon isolation of the extraction, the two phase system can be reverted to one phase at will.

Under normal conditions the wood or plant materi¬ al is extracted using an LCST solvent. The solvent is next separated from the pulp, and the solution turned into a two phase system. Water is azeotroped from the upper organic phase and the solvent azeotroped from the lower aqueous phase, the organic phase (if butoxyethanol) normally carry¬ ing the extracts (usually coloured) has a concentration of about 60:40 butoxy ethanol:water while the aqueous phase is 10:90 respectively. Suffice it to say, other methods of solvent purification including selective absorption on silica or alumina and carbon black as well as distillation are well known to the art. It is not within the scope of the present invention to describe the various methods of ^'purification. Figure 1 shows that the process of the invention can be carried out as several steps and the extraction composition can be changed from step to step depending upon the nature of the fibrous plant material employed and the nature and mix of desired end-products.

The embodiment shown in Figure 1 shows that the fibrous plant material is preferably prepared e.g. by chipping, shredding or forming shavings. The prepared plant material is then treated (step 2.0) with composition A (which lacks neutralizing agents). Soluble sugar and lignin can then be removed (step 2.1). Further extraction using composition B (step 3.0) leads to lignin and lignin by-products and sugar which can be Isolated from the fiber and from each other using the mutual insolubility of the LCST liquid composition compo¬ nents (step 3.1) above the LCST. Further extraction using composition B ln the presence of a bleaching agent such as hydrogen peroxide (step 3.0.1) leads to bleached lignin and bleached lignin by-products and sugar which can be isolated from the fiber and from each other using the mutual Insolubility of the LCST liquid composition components (step 3.0.2) above the LCST. Insoluble cellulose fiber is then collected (step 4.0) .

A single extraction or multiple extractions can be made depending upon the starting materials and end- products desired. The optional bleaching step can be integrated as shown or can be carried out separately.

A further advantage of the invention is that bleaching by hydrogen peroxide (preferably 3-35% strength) is possible by introducing the bleaching agent into the solution with no known detrimental effects to its efficacy. Hypochlorite (e.g. 1-5% strength) or similar composite bleach can be used in place of hydrogen peroxide. Elemental oxygen, usually at low pressure is a further alternative bleaching agent. Example

The following example was carried out by solvent extracting lOOg of microwave dried maple : birch : poplar shavings (50:35:15) with 1.75 liters of the variant of composition B. The mixture was heated to 127 °C for 1 hour. A fresh charge was added and the wood fiber reheated for another hour. The wood fiber was then refined in an osterizer for 2 minutes (liquify). The pulp was next washed with 2 charges of water. At each charge the pulp fiber was further refined in the osterizer for 2 minutes. The consistency was then raised to 50%, i.e. by means of ricer, and dried in a microwave oven (low). The fiber was dried at 110 °C for 4 hours before being weighed. A yield of 64.2% was obtained. The slightly yellow unbleached fiber had a kappa number of 24 and an ISO brightness of 67. The upper layer of the LCST solution was neutralized with concentrated hydrochloric acid, and reduced in volume on a rotatory evaporator under vacuum. Salt which precipitated was separated from the oil layer. Distillation at 1.5 mm pressure of the remaining "88 ml of oil gave the following fractions: FRACTION b.P. RANGE mis. COMMENT

1 22 2 clear

2 62-65 20 clear

3 70-115 10 light yellow

4 118-135 4 yellow

5 235-138 5 dark yellow

6 138 5 dark brown

7 175 2 brown

8 20 residue

Analysis by gc-ms showed the initial fractions to be water and butoxy ethanol; the middle fractions to be C-9 and C-10 derivatives; and the residue to be lignin and decomposed lignin. Free lignin (non depolymerized) has been extracted by a mixture of butoxy ethanol:water which have no alkali salts present at temperatures as low as 100 °C. The solvents employed are thus recovered, purified and reused.

Claims

CLAIMS :

1. A method of delignlfying wood or plant material, both virgin and post-consumer with a recyclable liquid composition comprising: Sodium silicate Up to 2.5%

Sodium hydroxide Up to 2.5%

Alkyl or dlalkyl glycol ether and/or diglycol ether and/or propylene glycol ether 10-40% Hydrogen peroxide Up to 10%

Triethylamine and/or dlethylmethylamine and/or dimethyl pyridine and/or methyl pyridine and/or methyl piperidine Up to 10% Water to 100%

having a lower critical solution temperature between about 0 and about 100 °C. which method comprises heating said wood or plant material with an effective amount of said llguid composition to release lignin from said wood or plant material.

2. A process according to Claim 1 wherein said composition comprises

Alkyl or dlalkyl glycol ether and/or diglycol ether and/or propylene glycol ether 10-40%

Hydrogen peroxide Up to 10%

Triethylamine and/or dlethylmethylamine and/or dimethyl pyridine and/or methyl pyridine and/or methyl piperidine Up to 10% Water to 100% having a lower critical solution temperature between about 0 and about 100 °C and recovered and Isolated lignin is substantially non-depolymerized.

3. A method according to Claim 1 wherein said lignin is isolated.

4. A method according to Claim 1 wherein said liquid composition comprises sodium hydroxide or sodium silicate and low molecular weight depolymerized lignin oils are recovered.

5. A method according to claim 1 which additionally comprises oxidizing chromophoric groups in isolated pulp or extracted oil with an oxidizing agent.

6. A method according to Claim 1 wherein sodium hydroxide or sodium silicate are present and lignin, oligo- and polysaccharides are depolymerized.

7. A method according to Claim 1 wherein mono-, di- and oligosaccharides are recovered.

8. A method according to Claim 1 wherein lignin and lignin by-products and sugars are collected in the upper and lower phases respectively.

9. A method according to Claim 1 wherein hemlcellu- lose Is made extractable.

10. A method according to Claim 1 wherein lignin is extracted and a low lignin content cellulose results.

11. A method according to claim 5 wherein said pulp is bleached.

12. A method according to Claim 1 wherein the extraction occurs at a low temperature and pressure.

13. A method of delignlfying a lignin-containing plant-derived material with a recyclable liguid composition comprising water and an organic compound which can be azeotropically purified, said liquid composition having a lower critical solution temperature of between 0°C and 100°C above which lower critical solution temperature said liquid composition divides into a heavier aqueous phase and a lighter organic phase, which method comprises: treating said lignin-containing plant derived material with a lignin-removing amount of said liquid composition at a temperature between 100°C and 210°C for sufficient time to release lignin from said lignin- containing plant-derived material.