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
  • D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
  • D21C3/028—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes in presence of O3

Definitions

• This invention relates to a pulping process for cellulosic raw materials. More particularly, the invention is a pulping process wherein high yields of substantially pure holocellulose are obtained and wherein the ligneous and resinous materials present in the cellulosic raw material may be simultaneously recovered in a commercially valuable form.
• An object of the present invention is a process by which capitaous and resinous materials can be substantially completely removed from raw cellulosic materials.
• a further object of the invention is a process for pulping raw cellulosic materials which gives a high yield of substantially pure holocellulose
• An additional object of the invention is a pulping process in which it is possible to obtain simultaneously high yields of substantially pure holocellulose and recover the ligneous and resinous materials in a commercially valuable form;
• the present invention is a process for simultaneously pulping cellulosic raw materials and removing theimpurities therefrom which comprises digesting the cellulosic raw material in an aqueous medium maintained at a pH of from 7 to 9; said digestion being conducted at a temperature of from l25-175 C in an atmosphere of pressurized oxygen-carrying gas, said oxygen-carrying gas having, at reaction temperature, a partial oxygen pressure of at least 800 p. s. i. If pure oxygen is employed,
• the minimum pressure at reaction temperature is 800 p. s. i. If an oxygen-carrying gas such air is employed, then a pressure must be emany, Wilmington, DeL,
• a partial oxygen presp. s. i. at reaction temperathe preferred embodiment digestion is carried out at a pH of from 7 to 7.5, at a temperature of about (3., and in" an atmosphere of pure oxygen at a pressure of 1000-1100 p. s. i. alkaline reagent is sodium bicarbonate.
• the unbleached pulp from the present process' is com-- parable in strength to bleached sulfite pulps.
• the pulp obtained from the process of the invention may be bleached by conventional processes to producea pulp of superior characteristics;
• the reaction medium has been alkaline for substantially the entire cook in accordance with the invention.
• the reaction liquid must be substantially neutral at the end of the reaction so that the cock is not conducted under acid conditions for any substantial period.
• a buffering agent must,
• the preferred ed substantially above therefore, be present or a similar buffering action must be obtained by the continuous addition of an alkaline agent to maintain the pH within the necessary range.
• the salts of a strong base and a weak acid are preferred when used so that. the reaction solution has a pH of between 7 and 9.
• Such substances include sodium bicarbonate, sodium tetraborate, sodium benzoate, sodium hydrosulfide, sodium phenolate, sodium acid tellurate, and sodium monohydrogen orthophosphate.
• Alkali metal salts of the weak acids are preferred.
• Pulping can be obtained when alkaline earth metal salts and higher valence metal salts are used, but because these metals form insoluble salts with constituents of the solubilized lignin and other noncellulosic materials and because these salts remove from the resulting pulp, the use of such alkaline earth and other higher valence metals is undesirable except when certain special pulps are needed.
• gaseous and dissolved oxygen be present.
• the oxygen may be in a pure state or in physical admixture with another gas as in the case of air. Substantially pure oxygen is preferred.
• oxygen or oxygen-carrying gas should be introduced into the reaction vessel at a. pressure which will result in a partial oxygen pressure of at least 800 p. s. i. at temperature. If the necessary pressure is not employed, the reaction rate is lowered to a point where the time necessary for pulping is undesirably increased. Under these conditions, the pulp is maintained at a high temperature for such an extended period that a degraded product is obtained. Consequently, if the pressurized oxygen or oxygen-carrying gas is admitted to the digester prior to raising the temperature, the gas should have a partial oxygen pressure of about 500 p. s. i.
• the temperature of the reaction must be maintained between 125 C. and 175 C. Below 125 C., the reaction rate is too low and poor yields of degraded pulp are obtained. Above 170 C., a highly degraded pulp is obtained.
• the reaction time of the process of the invention is from about 2 to about 5 hours as compared with a minimum of about 8 hours for any known process resulting in acceptable yields of high-grade pulp.
• the reaction rate is also affected by the degree of agitation employed. Faster reaction times are obtained with increases in agitation efficiency. Satisfactory agitation may be obtained by mechanical means or by liquor circulation.
• the amount of water employed is not critical but is governed by practical considerations. Enough water must be employed, of course, to produce a workable slurry. The use of an excessive.amount above this point necessitates the use of larger reaction vessels for a given charge and complicates the recovery of the reaction products and reagents. It is preferred, therefore, that water to raw cellulosic material ratios be kept between 6:1 and 20:1.
• EXAMPLE 1 Three hundred g. (dry weight) of solvent-extracted pine stump shreds, 150 g. of sodium bicarbonate, and 6 liters of water were placed in an autoclave and oxygen was introduced until a pressure of 750 lbs. was reached. The contents are difficult to Hemicellulose (soda soluble) do of the autoclave were agitated and heated to a temperature of C. over a period of one hour. The pressure within the autoclave at 140 C. was about 1000 p. s. 1. At the end of 8 hours, during which time the contents of the autoclave were continuously agitated and maintained at 140 C., the contents of the autoclave were cooled to 70 C. The end pH of the reaction solution was 7.2. The resulting suspension was filtered. One hundred forty-eight g. (dry weight) of pulp was obtained for a yield of 49.5%. The pulp exhibited the following characteristics:
• EXAMPLE 3 Three hundred g. (dry weight) of spruce chips, g. of sodium bicarbonate, and 6 liters of water were introduced into an autoclave. The procedure of Example 1 was repeated except that the contents of the autoclave were maintained at 140 C. for 4 hours instead of 3 hours. The end pH of the reaction solution was 7.0. One hundred eighty-one g. (dry weight) of pulp was obtained for a yield of 60%. The pulp exhibited the following characteristics:
• Pentosans do Lignin do Gums and resins (alcohol-benzene extraction) percent EXAMPLE 4
• EXAMPLE 6 Fifty g. (dry weight) of aspen chips, 25 g. of sodium bicarbonate, and 500 cc. of water were charged into an autoclave and cooked for 2 hours at a temperature of 150 C. and under an oxygen pressure of 800 p. s. i. The end pH of the reaction solution was 8.90. A partially degraded but acceptable pulp was obtained in 50% yield which had an A. C. S. viscosity (5%) of 212 seconds.
• EXAMPLE 7 Three hundred g. (dry weight) of spruce chips, 150 g. of sodium bicarbonate, and 3 liters of water were charged into an autoclave and cooked with agitation for 4 hours at 120 C. and under an oxygen pressure of 1000 p. s. i. The end pH of the reaction solution was 7.4. At the end of this time, only a small amount of pulp had been produced. Longer reaction time under these conditions resulted in greater yields but with undesirable degradation of the pulp. When the tem perature was raised, increased yields of good quality pulp were obtained in normal reaction times.
• EXAMPLE 8 Fifty g. (dry weight) of spruce chips, 25 g. of sodium bicarbonate, and 500 cc. of water were charged into an autoclave and cooked for 2 hours at a temperature of 175 C. under an oxygen pressure of 1000 p. s. i. The end pH of the reaction solution was 7.7. A 37% yield of partially degraded but acceptable pulp was obtained which had an A. C. S. viscosity (5%) of '70 seconds and an a-CBIIHIOSG content of 59%. The use of a longer reaction time at 175 C. or the use of higher temperatures for the same period resulted in a highly degraded pulp.
• EXAMPLE 9 Three hundred g. (dry weight) of solvent-extracted pine stump shreds, 150 g. of sodium bicarbonate, and 3 liters of water were charged into an autoclave and cooked for 3 hours at a temperature of C. and under an oxygen pressure of 800 p. s. i. A somewhat degraded but satisfactory pulp was obtained in 55% yield which had an A. C. S. viscosity (5%) of 385 seconds).
• EXAMPLE 10 The run described in Example 9 was repeated under identical conditions except for employing an oxygen pressure at temperature of only 500 p. s. i. A 5% yield of partially degraded pulp was obtained which had an A. C. S. viscosity (5%) of 220 seconds. A much longer reaction time under these conditions increases the yield somewhat but results in a highly degraded pulp.
• EXAMPLE 1 Three hundred g. (dry weight) of spruce chips, 300 g. of sodium tetrabcrate, and 3 liters of Water were introduced into an autoclave. The procedure of Example 1 was repeated with A. C. S. viscosity (5%) sec 461 a-CEHUIOSG per cent 72 Hernicellulose (soda soluble) do 38 Pentosans do 5.9 Lignin d0 2.0
• EXAMPLE l3 Handsheets were prepared from unbleached pulps produced in accordance with the invention and compared with sheets prepared from Burgess bleached sulfite .pulps produced from similar raw materials. The sheets compared were made from pulps beaten to a comparable freeness. The sheets made from the pulp produced according to the invention were found to possess superior dry burst and tensile strengths. Their dry tear strength was somewhat lower than the dry tear strength of the sheets prepared from the Burgess bleached sulfite pulp but was relatively high for a paper having such extremely high bursting and tensile strengths. set forth in Table I. Basis weights were 40 1b.:1.0. All tests were conducted in accordance with TAPPI specifications.
• Aspen pulp prepared by the process of this invention was bleached in a three-stage process consisting of the following steps: (a) chlorination with 2.3% chlorine based on pulp weight for 0.5 hour at 24 C., (b) extraction with 0.25% sodium hydroxide at a consistency of for one hour at 96 C., (c) alkaline bleach with 1.0% chlorine (hypochlorite at pI-I 9.8) in 10% consistency for one hour at 55 C.
• the bleached pulp was a bright white and was characterized by an Exand a dominant wave length of 576.5 millimicrons with respect to Illuminant C.
• the bleached pulp was refined as follows: It was treated with 11.1% sodium hydroxide at a consistency of 10% for 2 hours at 0 C. The product had an a-cellulose content of 92.8%. The yield of this product is 29% on the aspen chips, 52% on the unbleached pulp, and 54% on the bleached pulp.
• the uses to which the solubilized materials recovered from the alkaline oxidation liquor can be put are mainly due to the greatly enhanced solubility, high acidity, and high alcoholic hydroxyl contentI
• Complete esterification with low molecular weight acids and alcohols produces low melting substances usable as plasticizers.
• Intermolecular condensation with polyhydroxy and polycarboxylic materials results in high melting resins usable in protective coating finishes of all sorts where color is not a factor.
• Y J The solubilized materials in the alkaline oxidation reaction liquor may be recovered in a number of ways.
• the resins and lignin are present in the liquor as soluble salts and are most easily recovered by partial evaporation and acidification as illustrated in Example 15.
• no definite molecular materials include softwoods, semihardwoods, hardwoods, bamboo, straw, hemp, jute, and fiax seed.

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Cited By (15)

Citations (16)

• 0
  • CA CA553349A patent/CA553349A/fr not_active Expired
• 1950
  • 1950-10-04 US US188487A patent/US2673148A/en not_active Expired - Lifetime

Patent Citations (16)

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