JPS6328157B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention involves treating lignocellulose with a solvent mixture consisting of water, a lower aliphatic alcohol having 3 carbon atoms and less, and a dissolved proton-forming salt catalyst under conditions of elevated temperatures in the range of 130 to 210°C to form plant cell walls. The present invention relates to a novel method for producing fibrous chemical pulp by preferably and at least partially depolymerizing and dissolving lignin and hemicellulose. This method is particularly successful in producing pulps with low Kuppar or Rohe numbers and high fiber strength while keeping the cellulose in its natural undegraded state. Importantly, the present invention is equally effective on both gymnosperm and angiosperm wood species and lignocellulosic agricultural residues when carefully digested under the conditions described above. In today's energy and chemical shortages, emphasis should be placed on the efficiency of cooking and the integrity of chemical recovery. This new pulping method is effective in lignin removal to allow short cooking times, and at the same time is gentle enough to allow near-grind fiber yields and quantitative recovery of dissolved by-products. The delignification must be as complete as possible to avoid loss of fiber bond strength and to reduce the amount of bleach required when fully bleached paper quality is required. Furthermore, it is a requirement for a good pulping process that the fiber release be as complete as possible. The delignification must thus be extended both to the fiber junction layer (middle lamellae) consisting of the lignin-carbohydrate matrix and to the cell wall matrix containing lignin and hemicellulose in various proportions. This effective delignification leads to low sieving rejection and requires little if any mechanical manipulation of the cooking chips for complete disintegration, which saves process energy as well as preserves fiber strength. In conventional methods of hydrolyzing wood in aqueous or aqueous-organic solvent mixtures containing unbuffered, unmild acid catalysts at temperatures of e.g. and extensive degradation of the cellulose occurs upon it before the hemicellulose component dissolves.
Even when relatively weak acids, such as organic dicarboxylic acids, are used as catalysts, the fibers as liberated have a degree of cellulose polymerization below that found in the natural state, and thus paper made from this pulp Sheets lack the high tear strength, burst strength and failure length desirable for industrial applications. While the known process has the advantage of a very short cooking time and produces soluble lignin and dissolved sugars with significant values, the known process produces significantly higher amounts of soluble lignin and dissolved sugars with a very short cooking time. However, the following objectives are not achieved: leaving almost the entire polyglucan fraction and maintaining the original content of cellulose fibers even when the lignin content of the pulp is reduced below an acceptable value. The purpose of liberating cellulose fibers to ensure that strength is maintained is not achieved. Another object of the invention is to produce high yield, low residue lignin content pulp to improve fiber bonding and structure in paper webs and to reduce the amount of bleaching agent required when fully bleached grades are made. It is in. Another desirable objective is to avoid damage to cellulose by acids. To achieve this objective, the present invention uses certain water-miscible organic solvents. This solvent ensures delignification properties and does not attack carbohydrates. Another major improvement of the present invention is to generate a weakly acidic solution in aqueous alcohol, which contributes to the production of acidic protons in the system through cation exchange with the functional groups of lignin and protects the cellulose from attack by highly acidic protons. resulting from a selection of inexpensive and mild salt catalysts with unique properties that This substantially reduced acidity further eliminates the need to provide highly acid-resistant cooking hardware. Another object of the invention is to provide a pulping process that is essentially free of water and air contamination. Further objects of the invention will become apparent in the following description of this method. Aqueous solvent pulping methods are known, for example, in U.S. Pat.
No. 3,585,184 and most recently in US Pat. No. 4,100,016. The present invention is generally carried out with water at a temperature of from 130 to 210°C, preferably from 170 to 200°C, and particularly preferably from 195 to 200°C, for a period of from 15 to about 90 minutes.
methanol, in a ratio of 80, or 80 to 20% mixture;
a solvent made from ethanol or a mixture thereof and selected from chlorides, sulfates or nitrates of metal magnesium, calcium or barium;
A method consisting essentially in treating a lignocellulosic feedstock with a solvent mixture containing from 0.005 to 1.0 mol/liter of metal salts soluble in water and alcohol, at least four times the weight of the lignocellulose to be pulped. Its use overcomes the major deficiencies of these and other known chemical pulping methods. When lignocellulose, which is generally difficult to delignify, is treated with a salt with a low catalytic effect, such as magnesium sulfate, the degree of delignification can be greatly increased by adding a small amount of mineral acid; The polydispersity of the recovered cellulose is not substantially adversely affected. This strong acid is present in the solution at a concentration of 0.0005-0.008N, that is, a treatment solution containing a salt catalyst and a strong acid at the above concentration is used. Preferred strong acids are those of the type that correspond to the anions in the salt catalyst. The above method is a unique method that exhibits an excellent delignification effect, and in this case, cellulosic fibers with a high degree of polymerization and a high glucan content can be recovered. The method is characterized in that the salt is a chloride or sulfate of magnesium or calcium at a mole/liter concentration of 0.02 to 0.05 mol/liter, the volume ratio of water to methanol in the solvent mixture is about 30:70, and
It is particularly effective when cooking at a temperature of 200°C.
When softwoods such as spruce are digested using this novel method, they retain significant amounts of hemicellulose, yet have a lower residual lignin content and a higher degree of polymerization (DP) than most pulps obtained by the kraft process.
A pulp with: Katsupar number 33, 0.5 is obtained.
tuppy viscosity of g, 20 centipoise, or degree of polymerization
Cooking time may be only 30 to 45 minutes to yield 1320. By simply slurrying in water, the cooked chips are separated into individual fibers and the resulting pulp ranges from 50% GE of cooking brightness to the desired starting brightness of 80% and as low as starting brightness, typically 35%GE
It can be easily bleached to a higher brightness than kraft spruce pulp with comparable residual lignin content. Currently used pulping processes further suffer from the drawback that by-product recovery greatly precludes cooking chemical recovery, making this effort economically unattractive. Furthermore, in the Kraft process, for example, dissolved sugars are converted primarily to saccharate, which has only limited utility as an industrial chemical. Similarly, in order to obtain the degree of solubility necessary to separate low lignin-containing fibers, lignin is converted to sulfur derivatives, which converts the otherwise partially soluble lignin into one that can only be dispersed in alkalis. In contrast to the difficulties described above with respect to byproduct recovery from lignocellulose digestion, the present method leaves behind a relatively concentrated aqueous sugar solution that dissolves as it is normally separated during cooking solvent recovery by flash evaporation. Lignin and sugars may be recovered, and separately, solvent-soluble lignin is produced as a powdery precipitate. Separation of lignin from sugars occurs by centrifugation or simple filtration. The recovered sugar solution was found to be rich in xylene and other hemicelluloses with relatively low yields of glucans. Most of the saccharides occur as dimers and low molecular weight oligomers, which can be easily degraded to simpler sugars by secondary hydrolysis in near quantitative yields. The fact that the sugars occur as low molecular weight polymers protects them from dehydration during high temperature cooking and allows higher dissolved sugar recovery. Following removal of the solvent, the precipitated lignin retains its solvent solubility, a property highly desirable when intended for chemical processing. The molecular weight of this solvent-soluble lignin is determined by gel permeation chromatography and high pressure liquid chromatography and falls between 300 and 12,000 with a calculated average molecular weight of 3,000. The lignin thus obtained was redissolved in acetone and
The acetone solution can be easily purified by filtration to remove water or insoluble matter and repeated reprecipitation into water or a nonpolar solvent such as diethyl ether, benzene, and n-hexane. Other solvents such as dichloromethane can also be used as precipitants, while tetrahydroxyfuran, dimethyl sulfoxide, furfural, methyl cellosolve, dioxane ethanol and acrylonitrile are excellent solvents for lignin. The most attractive energy-saving technique for the recovery of precipitated lignin is by spray drying from an acetone solution under a temperature of 65 °C. The lignin thus obtained is usually light colored and in the form of a free-flowing powder. Thoroughly cooked chips are easily separated into free fibers upon slurrying them into a good lignin solvent that removes most of the lignin from the fibers. A simple wash with hot methanol-water or acetone is usually sufficient to remove clumps of dissolved lignin lodged within the fibers. Subsequent washing with water has no negative effect on the bleaching properties of the fibers. It is another characteristic of the fibers produced in this way that the normally desired freeness of paper pulp can be obtained with virtually no energy during the beating process. The original freeness of 750 obtained with spruce pulp is
Slightly in PFI beater to obtain freeness of 300
4000 revolutions is sufficient, whereas for kraft pulp with the same initial freeness, the same freeness, typically
Requires 7000 to 9000 revolutions by 300. The invention will be explained in further detail in the following examples and description of a preferred mode of carrying out the above method. EXAMPLES Delignification and cellulose polydegradation studies were carried out using CaCl ₂ at a concentration of 0.16 mol/liter in a 30:70 mixture of methanol, ethanol or n-propanol and water. Approximately 20cm in height and 8cm in diameter
The digestion was carried out in a laboratory scale stainless steel pressure vessel with dimensions of . Air-dried wood chips of spruce species at 8% moisture content with 100 g of pre-prepared cooking solution.
I put it in batches of 10g into the digester. The sealed bomb was heated to 200° C. in an oil bath and kept at cooking temperature for the scheduled time. Cooking times were selected to produce free pulp after slurrying the cooked chips in 500 ml of acetone and stirring the solution below 800 rpm. At the end of this digestion the vessel was cooled and the liquid was decanted. The pulp was washed with acetone followed by water and air dried until constant weight was obtained. Samples were saved for Kuppar number and viscosity measurements, at which time the final moisture content of the residual pulp was determined to allow calculation of pulp yield. The TAPPI standard test method was used for all analyses. All test data from this series of cooks is summarized in Table 1. This data clearly shows the excellent selectivity of methanol as a delignifying agent as indicated by the high viscosity of the separated cellulosic pulp.

Table of Examples: Under otherwise constant cooking conditions, this process shows a high tolerance to large variations in the molar concentrations of the metal salts used. In general, hardwoods can be cooked at lower salt concentrations of any of the preferred salt catalysts than softwoods; e.g.
Cooking poplar wood with calcium or magnesium chlorides or nitrates takes less than 30 minutes at a salt concentration of 0.025 to 0.10 mol/liter, whereas the same concentration of magnesium sulfate requires 45 minutes. Softwoods such as spruce generally contain 0.05 to 0.20 mol/
Improved fiber separation is obtained at concentrations that require higher salt concentrations of liters and in certain cases reach 0.5 moles/liter or more. Preferred salts are magnesium and calcium chlorides, which are well tolerated and at least as low as possible for fermentation processes in which an aqueous sugar residue is provided to convert the sugars into ethyl alcohol, yeast or other fermentable products. has the cost advantage of Magnesium sulfate has limited solubility in alcohol and therefore the salt concentration that can be put into solution is often limited. More cooking time than would be considered satisfactory is required to compensate for the lower salt concentration of MgSO ₄ . The table shows a constant wood:liquid ratio of 1:10 at 200°C.
When digested in aqueous methanol, one hardwood,
Representative data on pulp yield and properties are shown for poplar and one softwood, spruce (water:
methanol ratio is 30:70).

Table: In the table, the values for the degree of polymerization are obtained by using TAPPI standard viscosity measurements and the nomogram published in Rydholm, page 1120. EXAMPLES Further cooking was carried out with wood and liquid charge as described in the previous examples. This liquid consisted of a 30:70 mixture of water and methanol containing 2 moles/liter of CaCl ₂ as catalyst. Cooking times and temperatures were varied as recorded in the table.

【table】

[Table] Hemlock Pinus 0.10 200 30 54 35
20.5 1340

Claims (1)

[Claims] 1. Lignocellulose with water, 1 to 4 volumes per volume of water of a low molecular weight aliphatic alcohol having 3 or fewer carbon atoms, and certain metal salts and optionally small amounts of acid-reactive 130 to 230 for a time not longer than 2 hours with a mixture containing the substance
℃, at least 4 parts by weight of cooking liquor are added to 1 part by weight of the lignocellulosic material, the cellulose fibers liberated thereby are separated from the liquor, and the alcohol is evaporated from the salts. In the process of decomposing lignocellulose, the chloride or sulfate of magnesium, calcium or barium as a metal salt, or magnesium sulfate, is added to the aqueous alcohol used as the cooking liquor in order to obtain lignin and sugar from the remaining liquor. , or a soluble mixture thereof, and optionally a strong mineral acid as acid-reactive substance, provided that the soluble mixture is still maintained. 2. The method according to claim 1, characterized in that methanol is used as the low molecular weight alcohol. 3. Process according to claim 1, characterized in that hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid is used as the strong mineral acid. 4. Using as cooking liquor an aqueous alcohol having a concentration of metal salts between 0.001 and 1.0 mol/liter and, if strong mineral acids are used, a concentration of strong mineral acids between 0.0005 and 0.008 normal. A method according to claim 1, characterized in that: 5. Alcohol is removed by distillation from the solution of lignocellulose decomposition products remaining after separation of cellulose fibers by a known flash evaporation method, and lignin precipitated as a powder is separated from the remaining aqueous residue by filtration or centrifugation. The method according to claim 1, wherein: