Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/04—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides
  • D21C3/06—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides sulfur dioxide; sulfurous acid; bisulfites sulfites

Definitions

• This invention relates to a new process for producing semi-chemical pulp from a wide variety of cellulose-containing raw materials including all kinds of soft woods (many of which are not now used in semi-chemical pulp processes), hard woods, annual and other plants, stem plants, and the like. More particularly, the invention relates to a novel acid bisulfite process for producing chemical pulps and especially relates to the production of semi chemical pulps in exceptionally high yields for given degrees of delignification, ofttimes from raw materials heretofore considered unsuited for the production of such pulps such as unbarked woods.
• cellulose containing plants and trees can be considered to be composed of three main components, namely, (A) cellulose, which is present substantially wholly in the form of cellulose fibers, (B) lignin and other similarly acting substances, including pectins, serving primarily as binders between the cellulosic fibers, and (C) the non-cellulosic carbohydrates, generally referred to as hemicellulose, and sometimes referred to herein as non-cellulosic hydrocarbons.
• A cellulose, which is present substantially wholly in the form of cellulose fibers
• B lignin and other similarly acting substances, including pectins, serving primarily as binders between the cellulosic fibers
• C the non-cellulosic carbohydrates, generally referred to as hemicellulose, and sometimes referred to herein as non-cellulosic hydrocarbons.
• the ingredients, other than A, B and C, are usually designated as extraneous components or extractives and are not a part of the cell walls. Such components designated as D seldom exceed 6% of the dry weight of the wood and may be as little as 1% and are not the concern of this invention. Very little is known about the real chemical and physical nature of these three main components A, B and C. In woods and like plants it is known that the fibrous cellulose A is by far the most important among the major components and is present in a greater proportion than either lignin B or hemicellulose and the like C, usually being present in a quantity of the order of 40 to 55% of the woody material.
• the hemicellulose C is usually present in a lesser quantity than the lignin B and is intimately associated with the fibrous cellulose.
• the cellulose A and the hemicellulose C and the like are together designated as the holocellulose content.
• the lignin B is the ingredient of wood and like cellulosic fibrous material which primarily serves to bind the fibers together, and although it is present as an ingredient of the fibrous proportion of the cellulosic material, it is primarily present between the fibrous ingredients in the so-called middle lamella.
• the mechanical pulp is the type of pulp which is obtained from the cellulose-containing materials by mechanical means.
• Chemical pulp is the type of pulp which is obtained from the cellulose-containing materials by chemical means, such as, by chemical extraction or conversion. When substantially all of the non-cellulosic content of the cellulose-containing raw material is removed by chemical means, leaving substantially only pure cellulose, the resulting pulp is designated as a chemical pulp.
• a semi-chemical pulp is produced when substantial quantities of the non-cellulosic hydrocarbon content of the cellulose-containing raw material is left unextracted in the chemical treatment.
• the treated raw material is sufiiciently delignified to permit a relatively easy defibration of the raw material in the form of wood chips or parts of plants as contrasted with the relatively severe treatment of mechanical pulping processes characterized by grinding or other severe abrading techniques used on logs, the whole stem of plants, or the like, by which most of the fibers are broken or damaged.
• mechanical pulping processes characterized by grinding or other severe abrading techniques used on logs, the whole stem of plants, or the like, by which most of the fibers are broken or damaged.
• a water solution of S02 when employed at a high temperature is one of the best known and most effective reactants to sulfonate and thereafter dissolve out the lignin and form chemical pulps.
• Such a pulping process is called a bisulfite or sulfite process and may take place under acid or neutral conditions, but it is most widely used under acid conditions at pHs below 2.
• an acid bisulfite process Generally speaking, acid bisulfite processes consist of the digestion of wood or other cellulose-containing fibrous raw materials in the form of chips or other small pieces, customarily designated as a comminuted material, at temperatures of to C.
• alkali bisulfites usually alkaline earth bisulfites (such as calcium bisulfite or a mixture of calcium and magnesium bisulfites, although ammonia and sodium bisulfites are also used) and an excess of sulfur dioxide.
• alkali bisulfites usually alkaline earth bisulfites (such as calcium bisulfite or a mixture of calcium and magnesium bisulfites, although ammonia and sodium bisulfites are also used) and an excess of sulfur dioxide.
• the bath or liquor is prepared by introducing the desired amount of S02 and then adding an alkali, usually an alkaline earth alkali, such as MgO or preferably CaO, to adjust the pH from about 1.1 of pure S02 solutions to the desired pH of 1.5 or 1.7.
• an alkali usually an alkaline earth alkali, such as MgO or preferably CaO
• the amount of S02 really consumed in a conventional bi- This is known as 3 sulfite process i. e., the amount of SO: chemically combined with the components of the raw materials when the digestion of the wood is carried as far as possible without undesirable burning or attack by the reactants or degradation of the cellulose A, is of the order of 120 to 130 kg.
• the amount of S02 contained in the pulping bath or liquor is usually 180' to 200 kg. or higher, say 250 kg.
• the conv'e'ritiohzil bisulfite process when referred to in this appiica'tion, refers to a process wherein the cooking step lattes place at temperatures of the order of 130 to 150 C.- and wherein digestion baths are used which have an pH of the order of 1.5 to 1.7 and contain S02 substantially in excess of the amount consumed or absorbed during the delignification process.
• the amount referred to is the amount consumed when dclignification is carried a far as practical without undesirable degradation of the cellulose A content of the cellulosic raw material. It will be understod also that the weights of the raw materials used, yields of pulp, and the like are always expressed herein in metric units and on an oven-dry basis.
• the delignification or the digestion takes place in two steps oi stages, namely, the soaking or impregnation step and the cooking step.
• the soaking step it is necessary to obtain as thorough a penetration of the cellulosic raw material a possible before raising the temperature to the cooking temperature, such as previously described, for otherwise a so-called burning reaction will take place impairing the digestion of the wood. It is desirable to obtain complete penetration as quickly as possible without burning or other degrading or carbonizing reactions taking place.
• the temperature is raised to cooking temperatures as rapidly as possi ble while avoiding burning reactions at the operating pH.
• the formed lignosulfonic acid combines with the HSOs ions but there is no cleavage of the lignin B from the woody substance by hydrolysis which only takes place during the cooking step.
• the cellulosic material After thorough penetration has taken place, the cellulosic material is subjected to cooking temperatures within the previously stated range, the particular temperature being adjusted to the nature of the raw material and the pH used. In known acid bisulfite processes, the time consumed in achieving a predetermined degree of delignification is determined by the pH and temperature used. As applied to woods, a pulp yield of the order of 40 to 50% having a lignin content of about 2 to 5% is obtained.
• Yet another object of this invention is to obtain sulfite pulp of a quality superior to that produced in like yields by known sulfite processes.
• the temperature used in this invention is correlated with the pH and the nature of the raw material so as to prevent the burning or degradation or carbonization of the cellulosic material but it is usually lower than the temperature used in known acid bisulfite processes, thereby resulting in a considerable saving in heat energy.
• the processes of this invention provide pulps in any desired yields which pulps, due to their greater degree of delignification, are superior in quality and are much more easily difibrated than known sulfite pulps produced in kindred yields. It has been surprisingly found that the process of this invention in producing a given yield of pulp consumes considerably less, not more, chemicals than does the conventional bisulfite process while at the same time providing the stated significantly greater degree of delignification.
• the amount of S02 used in the digestion bath is of the order of 60 to kg. per ton of raw materials being delignified and normally does not exceed kg. per ton.
• the pulps of this invention are much more easily defibrated, and they may be bleached with a much smaller quantity of chlorine.
• the process of this invention provides a pulp with a very large percentage of its hemicellulose C content retained, while the conventional bisulfite process has removed substantially all of the hemicellulose C.
• Such pulps differ markedly in their properties from analogous known sulfite pulps and may have entirely different utilities due to their greater strength and other properties.
• sulfite pulps can be produced by the process of this invention from unbarked soft or hard woods also and from unbarked woods of very small diameter, such as unbarked branches, by cooking them in their natural state apart from chipping in the conventional way.
• stems comprising an outer layer of bark and an inside woody part, such as cotton stalks and similar materials may be treated by the process of this invention in order to obtain unbleached or pure white bleached pulps.
• pure cortical layers such as ramie (China grass) may be cooked by the process of this invention, and, in this case, the fibers obtained may be used bleached or unbleached for textile or paper purposes.
• the amount of S02 to be employed is determined for the woody part of the material under treatment in the exposed way and for the bark or cortical layer by determining the S02 necessary to dissolve it experimentally by means of cooking the pure bark.
• the S02 consumption of pure bark may be completely diiferent from that of woody parts and the result to be obtained in this case is not only that of obtaining the cellulosic fibers contained in the bark if any but also of removing and dissolving the undesired parts of the bark or of transforming some parts into forms removable by further treatments with chlorine and alkalies.
• these undesired parts of the bark may substantially represent the totality of the bark as for instance in the case of soft woods and also in this case this bark is removable under the conditions of treatment corresponding to this process.
• Example 1 is 88 kg. S02 per ton of wood and the amount of lignin to be removed is about 220 kg.
• the cooking time will be about 7 hours.
• a pH of 2.70 in the presence of 88 kg. of S02 per ton of oven-dry wood such a speed of lignin removal requires a temperature of 135 C. for soft wood.
• the pulp is then unloaded, washed and defibrated in known ways.
• the yield of pulp is 75%.
• Chemicals used per ton of oven-dry wood are 88 kg., 502, less about 10% recovery at the end of cooking, or 80 kg.
• 40 kg. of sulfur is used per 750 kg. of oven-dry pulp or 54 kg.
• Example 2 A beech wood is employed.
• the desired yield of pulp is about 85%.
• the amount of S02 to be employed is 72.2 kg. per ton of treated wood.
• the cooking time should be 5.8 hours and the amount of lignin removed should be about 130 kg. of the about 240 kg. in a ton of Wood.
• a temperature of C. is required.
• the digester is therefore charged with 1000 kg. of wood (oven-dry basis) and with about 3500 kg. of liquor containing 72.0 kg. of S02. This liquor is usually sufiicient to cover the 1000 kg. of wood and gives a liquor with about 2.5% of S02. In order to obtain a pH of about 3 about 28 kg.
• Example 3 Same wood is used as the one used in Example 2. A 65% yield is to be obtained.
• the amount of S02 to be employed is 118 kg. per ton of wood.
• the cooking time will be 8.2 hours and the amount of lignin to be removed is about 215 kg. of the about 240 kg. in a ton of wood. It is found that such a speed of lignin removal at a pH of 3 requires a temperature of C.
• Other operations and results are analogous to those of Example 2.
• Example 4 Cotton stalks containing in total 25% lignin and about 25% bark are treated in order to obtain any easy bleachable pulp of mixed cortical and inside fibers with a yield of about 65%.
• the amount of S02 required is 120 kg.
• the cooking time is determined to be 7.6 hours. As it seems preferable by experience to use a high pH for such a peculiar raw material this is fixed at pH 4.
• Temperature at this pH for the removal speed of lignin with about the same amounts of S02 employed is known to be C. for hard woods. An experiment is made at this temperature and at 130 C. :5 C. temperatures to determine the better speed of removal in order to approach the desired results. This temperature is found to be 133l35 C.
• MgO is added in order to bring the pH to a value of 4. i
• the digester is brought to a temperature of 133135 C. in a known manner. This temperature is maintained for 7.6 hours, but not after the S02 has reached a value of 0.3%.
• Example Unbarked soft wood The wood is the same as in Example 1 but is treated with full bark, the bark repre senting 12% by weight of the treated wood. A yield of 65% is desired for the woody part of the material. With a yield of 65%, S02 needed is 90 kg.
• the pulp obtained with a yield of about 60% calculated on the unbarked wood may be bleached to pure white employing about 14% chlorine of which about 6% is used to dissolve and remove the residual parts of bark.
• Example 6 Ramie (China grass) is to be treated in order to obtain a textile fiber. It is known by analysis that this material contains 78% of cellulose fibers. With a yield of 75% or kg. S02 per ton are employed. The pH, is determined to be pH 3.3. With this material and with the determined amount of S02 a removal speed of 28 kg./hour at pH 3.3 the temperature is 120 C.
• this invention is particularly suitable for all annual plants typified by cotton stalks having non-homogeneous stems composed of lignified fibers (inner fibers of shive) and also composed of nearly delignified fibers (bast fibers) such as the straw of seed flax, the whole stem of hemp, bamboo, bagasse, kenaf, elephantine grass, ramie, and the like.
• a process for the production of a semi-chemical pulp from comminuted cellulosic raw material in the form of wood chips and small pieces of plants comprising digesting said raw material in an acid bisulfite liquor having an initial pH of 2.2 to 5.0 and containing per ton of dry raw material an amount of 502 between about 60 to 120 kg. per ton of dry raw material which is insufficient to remove all of the lignin in the raw material, said digesting taking place at cooking temperatures not substantially exceeding 137 C. and until at least a major part of the weight but not all of the lignin is removed, said liquor containing about 3.5 to 11 times as much liquid weight as dry raw material, and mechanically defibrating the digested raw material to form said pulp.
• a process for the production of a semi-chemical pulp from wood chips comprising digesting said wood chips in an acid bisulfite liquor having an initial pH of to 5.0 and containing per ton of dry chips an amount of S02 between about 60 to kg. per ton of dry chips which is insufiicient to remove all of the lignin in the chips, said digesting taking place at cooking temperatures not substantially exceeding 137 C. and until at least a major part of the weight but not all of the lignin is removed, said liquor containing about 3.5 to 11 times as much liquid by weight as dry wood, and mechanically defibrating the digested chips to form said pulp.
• a process for the production of a semi-chemical lp from wood chips comprising digesting said wood chips in an acid bisulfite liquor having an initial pH of 2.7 to 3.00 and containing per ton of dry chips an amount of S02 between about 60 to 100 kg. per ton of dry chips which is insufiicient to remove all of the lignin in the chips, said digesting taking place at cooking temperatures not substantially exceeding 137 C. and until at least a major part of the weight but not all of the lignin is removed, said liquor containing about 3.5 to 11 times as much liquid by weight as dry wood, and mechanically defibrating the digested chips to form said pulp.
• a process for the production of semi-chemical pulp from small pieces of yearly plants comprising digesting said yearly plants in an acid bisulfite liquor having an initial pH of about 3 to 4 and containing per ton of dry yearly plants an amount of S02 between about 60 and kg. per ton of dry yearly plants which is insulficient to remove all of the lignin in the plants, said digesting taking place at a cooking temperature not substantially exceeding 137 C.

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• 0
  • BE BE496841D patent/BE496841A/xx unknown
• 1950
  • 1950-07-06 FR FR1021571D patent/FR1021571A/fr not_active Expired
  • 1950-07-10 CH CH290905D patent/CH290905A/de unknown
  • 1950-07-10 GB GB17266/50A patent/GB707982A/en not_active Expired
• 1952
  • 1952-01-18 FR FR63228D patent/FR63228E/fr not_active Expired
  • 1952-03-08 US US275671A patent/US2749241A/en not_active Expired - Lifetime

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