CA1309562C - Chemimechanical pulping process employing sodium carbonate and sodium sulphite - Google Patents
Chemimechanical pulping process employing sodium carbonate and sodium sulphiteInfo
- Publication number
- CA1309562C CA1309562C CA 608736 CA608736A CA1309562C CA 1309562 C CA1309562 C CA 1309562C CA 608736 CA608736 CA 608736 CA 608736 A CA608736 A CA 608736A CA 1309562 C CA1309562 C CA 1309562C
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- Prior art keywords
- sulphite
- sodium
- high yield
- wood
- sodium carbonate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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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
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention relates to a high yield chemimechanical pulping process for producing pulp from wood chips or sawdust or other lignocellulosic materials which comprises treating said lignocellulosic material with an aqueoussolution of mixture of sodium sulphite and sodium carbonate or sodium bisulphiteand sodium carbonate, sulphonating the treated material in a liquid phase or vapour phase cooking, and subsequently subjecting the resulting sulphonated material tomechanical defibration.
The present invention relates to a high yield chemimechanical pulping process for producing pulp from wood chips or sawdust or other lignocellulosic materials which comprises treating said lignocellulosic material with an aqueoussolution of mixture of sodium sulphite and sodium carbonate or sodium bisulphiteand sodium carbonate, sulphonating the treated material in a liquid phase or vapour phase cooking, and subsequently subjecting the resulting sulphonated material tomechanical defibration.
Description
1309~2 CHEMIMECHANICAL PULPING PROCESS EMPLOYING
SODIUM CARBONATE AND SODIUM SULPHll'E
Back~round of the invention The present invention relates to a process for the production of a high yield, high strength chemimechanical (CMP3 pulp from wood or other lignocellulosic materials. More particularly, this invention relates to a chemi-mechanical pulping process employing sodium carbonate and sodium sulphite in the cooking liquor to chemically soften the wood chips or other lignocellulosic materials prior to mechanical defibration.
In recent years there has been increased use of high yield chemimechanical pulps in the manufacture of papers and, particularly, printing papers. These pulps have relatively high strength as compared to the pure mechanical pulps such as groundwood pulps and refimer pulps.
Traditionally newsprint is manufactured from a furnish consisting of about three parts mechanical pulp, such as g~oundwood or refiner pulp and one part chemical pulp. Groundwood, manufactured by pressing logs against a revolving abrasive stone, is obtained in yields approaching 100%, whereas the refiner pulps, such as the refiner mechanical pulp (RMP~ and thermomechanical pulp (TMP~ are obtained by refining wood chips or other lignocellulosic materials in a disc refiner, under atmospheric or elevated pressure, respectively. The RMP and TMP are obtained in yields of 95% or more. Pollution problems associated with the manufacture of mechanical pulps are minimal. HoweveF, the mechanical pulp ~lbers, containing almost all the lignin present in the wood, are relatively stiff and produce papers of comparatively low strength because of their poor interfiber bonding capacity. The lignin, concentrated in the intercellular layer known as the rruddle lamella, cements the cellulose fibers to each other.
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1309a62 The main pulpose of chemical pulping processes, such as sulphate (kraft) or sulphite pulping, is to dissolve the middle lamella so that the wood structure breaks down into individual fibers without the use of substantial mechanical action.
This is accomplished by cooking the wood chips at high chemical concentrations S and high ternperatures (about 120C to 180 C~ for a prolonged period of time (up to 5 hours or rnore) and results in low yields based on the dry chips because a substantial amount of the wood, particularly lignin, is removed. The chemical pulp component is usually manufactured by either the kraft or sulphite process in yields ranging from 45% to 65%.
Chemical pulps have many advantages due to their cleanliness, high strength, and ease of bleaching, but they are expensive, make heavy demands on the mill's wood resources, and entail formidable pollution problems. The presenttrend in newsprint manufacture, therefore, is towards reduction in the use of chemical pulps.
The semichemical and chemimechanical pulping processes fall midway between the chemical and mechanical processes in these respects.
The increasing world-wide demands for pulp, paper and other forest products and the decreasing availability of fiber are creating an increasing need for the use of higher yield pulps. The present invention produces a high yield pulp that can replace some types of chemical or semichemical pulp in many products.
One attempt which has been made tO improve the yield of sulphite pulps, which is relevant from the standpoint of the present invention, involves pre-treating the chips with an alkaline solution for a period of time. Exarnples of such sulphite pulping processes are described in U.S. patent 3,177,110 to Ogait and U.S.
patent 3,354,030 to Williams et al. However, these processes remain essentially chemical pulping processes which rely upon the removal of most of the lignin from the wood and do not provide high overall yields. For example, the yields il-lustrated in the Ogait patent only range from about 55 to 65%. By contrast, the major portion of the lignin is retained in CMP and (~TMP processes due to ~le 1~09~2 use of much milder conditions in the chemical treatments.
It is known that the ~eatment of wood chips with relatively small amounts of sulphite and bisulphite, at near neutral pH, and under relatively rnild cooking conditions ~100 C - 150 C, for 2-25 minutes) produces a softening effect on the chips which makes them easier to de~lber and generally produces a cleanerand better draining pulp than can be produced by mechanical means alone. See Uschmann U.S. patent 3,607,618; Aitken et al. U.S. patent 3,013,934; and Asplundet al. U.S. patent 3,558,428.
However, the pulps produced by such processes, while being superior to conventional mechanical pulps in terms of cleanliness and drainage properties, do not have sufficiently good physical properties to justify their increased cost of production relative to the conventional mechanical pulps.
Better properties can be achieved by cooking under more severe conditions such as increased temperatures in the 160 C - 240 C range, but the strength improvement is always accompanied by a loss in yield. Instead of yieldsof over 90%, the yields are reduced to about 70-85%. See the above patents and Richardson U.S. patent 2,962,412; Zimmerman U.S. patent 1,821,198; Cederquist U.S. patent 3,078,208; Asplund et al. U.S. patent 3,44~,699; Von Hamzburg U.S.
patent 2,949,395; Olson U.S. patent 3,003,909; and Rasch et al. U.S. patent 2,847,304.
Mild sulphite treatments have been used in chernirnechanical pulping processes to chemically soften the wood fibers and thereby facilitate mechanicaldefibration. It is known that sul~onation renders lignin more hydrophillic or less hydrophobic so that the fibers swell in the sulphite liquor and the chips becomeeasier to defibraee. These chernimechanical processes produce higher yields thanchemical or semi-chemical processes, but the pulp strength is not as good.
Typically they are also more effective with softwoods than hardwoods.
U.S. patent ~,116,758 to Ford et al. describes a process which is specially suited to softwood pulps whereby wood chips are softened prior to defibration by 1309~62 sulfonating the lignin with-out substantially removing it from the wood. This istypically accomplished by maintaining the wood chips in a solution containing 50-180 g/L sodium sulphite at 100 - 140 C for approximately 30 - 60 minutes without an alkaline pre-treatment and is followed by disc refining.
U.S. patent 3,016,324 to Textor also discloses a chemi-mechanical pulping process wherein wood chips may be impregnated with sodium sulphite liquor by squeezing the chips in a screwpress and spraying the chips emerging from the press with sulphite liquor and then defibrated.
Chemimechanical pulping processes in which the chips are impregnated with aLkaline liquors are also known.
One proposed mechanism by which the use of alkali, such as caustic soda or sodium hydroxide, increases the strength of mechanical pulps is by increasingthe number of acidic groups in the wood. ~See publication of Katz et al. "A
Mechanism for the Alkali Strengthening of Mechanical Pulps", TAPPI, Vol. S4, No. 7, pp. 97-100, July, 1981). The counter-ions of these acidic groups are saidto draw additional water into the cell wall and the accompanying swelling and plasticization enhance the ability of the fibers to bond and the overall strength o the pulp improves.
U.S. patents 3,479,249; 3,617,435; and 4,795,574 to Kalisch describe a semi-chemical sulphite pulping process which is accomplished by impregnating wood chips with sodium hydroxide or sodium carbonate and, thereafter, cooking the chips in an aqueous solution of sulphur dioxide for 2 to 3 hours. In the latter treatment, the sodium hydroxide or sodium carbonate in the chips reacts with sulphur dioxide to produce bisulphite in the chips which reacts with the lignin to solubilize it in a known manner. A~ter cooking, the chips are defibrated by passing them through a disc refiner. The yields reported in the patent are about75% or less.
U.S. patent 4,486,267 to Prusas discloses a high yield chemither-momechanical (CTMP) process wherein hardwood chips are subjected to a two-stage chemical treatment prior to defibration, the first consisting of chip impregnation and reaction with an aL~aline liquor followed by a second stage treatment with sulphite and/or bisulphite. This process produces high strength hardwood pulps, but the pulp brightness (22 - 40%) and yields (79 - 85%) are greatly reduced.
U.S. patent 4,187,141 to Ahrel describes a process for producing bleached chemimechanical pulp wherein screwpressed wood chips are subjected to a two-stage impregnation with an alkaline peroxide solution, in which the impregnated chips are introduced into a pressure vessel and ground in a disc refiner. This process provides a pulp having high brightness but relatively low strength.
While sodium hydroxide has been used in the production of chemimechanical and chemithermomechanical pulps in the past to improve pulp strength, it has not maintained high b~ightness and high yield. It is ~nown thatsodium hydroxide darkens the pulp and solubilizes the hemicelluloses in known manners. We have now made the surprising discovery that both the pulp yield and brightness can be increased by replacing the sodium hydroxide by sodium carbonate in the sulphite cooking of chips carried out prior to refining.
It has been found that, as the reaction in chemical treatment of chips proceeds, the pH of the medium drops, probably as a result of hydrolysis of acetyl groups on the chip. If the pH drops below 3, there is risk of damaging the fibrethrough hydrolytic action with consequent loss of strength. Wood fiber which hasbeen subjected to mechanical action, such as refining, is particularly susceptible to acidic degradation. It is therefore a common industrial practice to add aLkali, such as sodium hydroxide or sodium carbonate to the cooking li~uor as a buffer. It iswell known that sodium hydroxide solubilizes hemicelluloses, resulting in yield loss.
Sodium carbonate has been used in semichemical pulping experiments, such as the neutral sulphite semichemical ~NSSC) processes. Conflicting results of the influences of sodium carbonate on pulping ha7/e been reported. See the 1309~62 following publications: Upadhyaya et al., "Studies on Neutral Sulphite Semichemical Pulping of Cajanus cajan", ABCP Congr. Anual l9th (Sao Paulo), Nov. 24-28, 1986, pp. 177-188; ~Ialhotra et al., "Neutral Sulphite Sernichemical(NSSC) High-Yield Pulps from Eucalyptus globulus", Holzforsch. Holzverwert.
Vol. 33, No. 3, pp. 51-52, 1981; Cameron et al., "Response of Pines and Eucalyptus to NSSC-AQ Pulping", SPCI Internatl. Symp. Wood & Pulping Chem.
Preprints, Vol. 2, 64-71 (June 9-12, 1981); Janci et al., "Production of Semiehemieal Pulp Using Green Liquor from NSSC Chemieal Recovery ~ystem", Papir Celluloza Vol. 34, No. 10, pp. 289-292 (1979); and Keller, "Is Caustic Soda Suitable for Buffering NSSC Digestions?", Southern Pulp Paper Mfr. Vol. 32, No.
5, pp. 32, 34, 36 (May, 1969).
It has now been surprisingly found that physical properties of sulphite chemimeehanieal pulps ean be significantly improved and their yields can be maintained near 90% level, by an addition of sodium carbonate to the sulphite liquor.
In aecordance with the present invention, there is provided a process of produeing ehemimechanieal pulps which eomprises cooking the ehips with aqueous sodium sulphite solution containing suf~leient sodium earbonate. The eooking is effeeted at an elevated temperature for a time suffieient to eause reaetion with the ehip and increase the swelling or the flexibility of the fibers but for a time insufficient to eause substantial dissolution of wood components, such as ligninand hemicellulose from the ehip and insuffieient to result in a pulp yield belowabout 85%.
The improvement in strength properties aehieved by the present invention permits use of the resultant pulps as either replacement or reinforcement eomponent for the low yield, high eost chernieal pulps in papers, partieularly the printing grades.
The proeedure of the present invention may be carried out on any types of wood chips or other lignocellulosic materials, and the improvement in physieal ~309562 properties is achieved on each of these materials.
It is, accordingly, an object of the present invention to provide a high yield chemimechanical pulping process for producing high strength pulp from wood chips and other lignocellulosic materials.
It is also object of the invention to provide a two-stage process of producing high yield chemimechanical pulp from wood chips whereby the chips are impregnated with an aqueous solution of sulphite and sodium carbonate followed by either liquid phase or vapour phase cooking and thereafter defibrating the chips by a disc re~mer to provide a pulp having excellent strength charac-teristics.
Other objects will be apparent to those skilled in the art from the present description.
1~ Genera! Descri~tion of the invention The process of the invention is an improved two-stage process for producing high yield chemimechanical pulps from wood or other lignocellulosic material, whereby in the first stage, the wood or other lignocellulosic material is subjected to treatment with an aqueous solution of sulphite and sodium carbonate, wherein sufficient sulphite is present to provide an amount of at least about 3% by weight, based on weight of wood or other lignocellulosic materials and wherein sufficient sodium carbonate is present to provide an amount to maintain a pH of the liquor of about 7 to 1(), the cooking being at a temperature of between 100 C
and 200 C for between about 2 and 120 minutes, without reducing the pulp yield 2~ to below about 85%; and whereby in the second stage, the resulting treated wood or other lignocellulosic material is subjected to mechanical defibration.
In the first stage of chemical treatment of the process of the present invention, the cooking of the chemically trcated wood or other lignocellulosic material may be carried out either in liquid phase or vapour phase.
~309~2 In liquid phase cooking, the chemically treated wood or other lignocellulosic material is cooked in a heated sulphite/carbonate solution under the specified conditions, prior to being subjected to mechanical defibration.
Cooking of the chemically treated wood or other lignocellulose material may also be carried out in vapour phase, whereby the wood or other lignocellulosic material is first impregnated with a sulphite-carbonate solution by means of steeping or press impregnation of wood or other lignocellulosic material and whereby the impregnated wood or other lignocellulosic material is subjected to steam cooking, and thereafter to mechanical defibration.
In a preferred embodiment of the invention, the amount of sulphite used is in the range of 10 and 25% by weight based on weight of wood, although lower concentrations down to about 1 % may be used with reduced bene~lcial effect. Similarly improvements are observed with sulphite charges up to about 50%
by weight of the wood, but the additional cost is not justified by the small additional improvement. Generally, therefore, a sulphite charge of between about1% and about 50% by weight, preferably between 10% and about 25% by weight based on weight of wood is used.
The sodium carbonate charge may range from about 2% to about 25% by weight of wood or other lignocellulosic material, preferably between 5 and 10%~
although lower concentrations down to about 1% may be used with reduced beneficial effect. Similarly improvements in pulp properties are observed with sodium carbonate charges up to about 30% by weight of the wood, but the additional cost is not justified by the substantial loss in yield.
It is preferred to carry out the impregnativn of wood with a liquor-to-wood ratio ranging from about 4 to about 6, preferably around 5. Lower ratios may not permit uniform impregnation of wood, but higher ratios increase energy costs as in liquid phase cooking, and decrease reaction rate because of dilution of the reactants, necessitating longer reaction times.
1~03 ~2 The time and temperature of reaction may be vaned over a wide range.
The essential requirements are that the reaction must be allowed to effect an increase in physical properties and must not be allowed to proceed far enough toyield substantial dissolution of lignin and hemicellulose, as it would decrease substantially pulp yield and increase pollution problems. Practically, the application of our invention is restricted to pulp yield in excess of about 85% by weight based on starting wood chip. The minimum reaction time to yield beneficial results is about 2 rninutes at 200 C, with longer times being used at lower temperatures.
In the practice of the invention, ~he wood or other lignocellulosic material is exposed to a minimum degree of cooking corresponding to 2 minutes at 200 C, and a maximum degree of cooking corresponding to a pulp yield of about ~5% by weight.
The pulps made from this invention may be used in such products as newsprint, coated papers, hook papers, sanitary tissues, corrugating medium, linerboard, paper towelling, diaper fluff, miLk carton board, etc.
Specific DescriPtion of the Invention In order to disclose more clearly the nature of the present invention, the following examples illustrating the invention are given. It should be understood, however, that this is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claims.
This example compares the effec~ of sodium carbonate to that of sodium hy~roxide in alkaline sulphite treatment of black spruce.
Pulps were prepared using a 300-mL reactor provided with live steam, a 1309~62 4-L Waring blender and a PFI mill. Black spruce chips were impregnated with a solution containing sodium sulphite, or sodium sulphite/sodium hydroxide, or sodium sulphite/sodium carbonate, under vacuum at ambient temperature for 16 hours. The liquor concentration was 100 g/L, which contained 100, 90, 80, and 70g of sodium sulphite, the balance was made up of either sodium hydroxide or sodium carbonate. A liquor-to-wood ratio of 5 was used. The impregnated chips were drained and steamed at 190 C for 9 minutes.
The cooked chips were first defibrated in a Waring blender for 2 minutes at 3% consistency, and then refined in a PFI mill at 10% consistency to yield several freeness levels. Physical properties were measured on handsheets prepared from the unscreened pulps after the removal of latency. The properties are shownin Tables lA to lG below.
It can be seen from the results of Tables lA to 1(3 that using of sodium carbonate instead of sodium hydroxide in sulphite pulping can maintain a pulp yield near 90% or above 86%, while improving substantially the physical properties, particularly the breaking length and burst index. Using sodium carbonate causes only a relatively small drop in pulp brightness, while using ofsodium hydroxide can bring about substantial loss in both pulp yield and brightness.
This example illustrates the effect of addition of sodium carbonate to the sulphite liquor and the effect of co~king time on pulp properties.
A mixture of softwood chips (2-4 mm thick) containing approximately 70% black spruce and 30% balsam fir were impregnated wi~h sulphite liquor containing about 0, 9, 17, and 33% of sodium carbonate. A liquor-to-wood ratio of 5 was used. The impregnation of chips was carried out under vacuum, a~ ambient 1309~62 temperature for 16-18 hours. The impregnated chips were drained and steamed at 180 C for 7, 10 and 13 minutes.
The cooked chips were first defibrated in a Waring blender for 2 minutes at 3% consistency and then refined in a PFI mill at 10% consistency to obtain various degrees of freeness. Physical properties were measured on handsheets prepared from the unscreened pulps after the removal of latency. The properties are shown in Tables 2A to 2D.
It can be seen from the results of Tables 2A to 2D that the addition of sodium carbonate can maintain the pulp yield in the neighbourhood of 90%, depending on the cooking tirnes. Meanwhile the physical properties of handsheet are improved particularly those of the pulp produced with 7-minute cooking time.It appears that the advantage of sodium carbonate decreases slighdy when the cooking time was prolonged beyond 7 minutes.
This example compares the influences of sodium hydroxide and sodium carbonate in sulphite pulping of softwoods, at semi-industrial scale.
Softwood chips containing approximately 85% black spruce and 15%
balsam fir were cooked in a liquor at 170 C for 20 minutes. The concentration of the liquor was 50 g/L, in which sodium sulphite represented 45, 40 and 35 g, andthe balance was made up with either sodium hydroxide or sodium carbonate. In other words, the sodium hydroxide or sodium carbonate represented, respectively,10, 20 and 30% of the total chemical applied. Ihe liquor-to-wood ratio used was 6. After cooking, the chips were washed and refined, under atmospheric pressure,using a Sunds De~lbrator 300CD re~mer. Physical properties were measured on handsheets pr~pared from the unscreened pulps after the removal of latency. The properties are presented in Tables 3A to 3F.
It can seen from the results in Tables 3A to 3F, that there is a substantial gain, from about 3 to about 13 percentage points, in pulp yield by using sodium carbonate instead of sodium hydroxide. It also can be noted that sodium carbonate did noe darkened the pulp as much as sodium hydroxide. The freeness of the carbonate pulps as shown in Tables 3D, 3E and 3F was quite high because much less specific refining energy was applied in comparison with the caustic pulps as indicated in Tables 3A, 3B and 3C. In spite of their high freeness, the carbonate pulps yielded properties which were comparable to those of the caustic pulps.
This example compares the effect of sodium carbonate to that of sodium hydroxide in sodium sulphite cooking of hardwood.
Trembling aspen chips were cooked in three different liquors; the first contained 100% sodium sulphite, the second 90% sodium sulphite and 10% sodium hydroxide,and the third contained 90% sodium sulphite and 10% sodium carbonate.
The concentration of the liquor was 100 g/L. A liquor-to-wood ratio of 6 was used. In each pulping liquor, the chips were cooked at 150~ C and at three different retention times, that is 8, 13 and 18 minutes in order to produce pulps at different degrees of pulp yield.
The cooked chips were first defibrated in a Waring blender for 2 rninutes at 3% consistency, and then refined in a PFI mill at 10% consistency tO obtain various levels of freeness.
It can be seen from Figure 1 that partial replacement of sodium sulphite by sodium carbonate resulted in considerable increase in pulp yield about 4%
points when compared with sulphite pulps. On the other hand, the replacement of sodium sulphite by sodium hydroxide reduced the pulp yield by about 2% points.
Figure 2 indicates that the tensile strength of handsheet was improved by 130~g2 the presence of sodium carbonate in the cool~ing liquor. Sodium hydroxide was also effective in improving the fiber bonding strength but it caused impor~nt yield loss. In fact the tensile strength of sulphite-carbonate pulps was quite comparable to that of sulphite-caustic pulps, but the pulp yield of the former was much higher than that of the latter, which is a significant advantage. It was also observed that using sodium carbonate maintained a high pulp brightness of about 55% (56% for sulphite pulps, 45% for sulphite-caustic pulps). The tearing resistance of aspenpulps are shown in Figure 3 which indicates the advantages of sulphite-carbonatepulps which had high tear index at high yield levels.
The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excludin~ any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claims.
1 309~62 TABLE lA
CHEMICAL COMPOSITION: 100 g Na2SO3 per liter Pulp Yield: 89.5%
Properties Freeness, mL 520 408 306 220 176 Density, g/cm3 0.39 0.41 0.45 0.47 0.48 Breaking Length, km S.l 5.8 6.2 6.5 6.6 Burst Index, kPa.m2/g2.7 3.0 3.3 3.6 3.9 Tear Index, mN.mVg 7.6 7.2 6.6 6.4 6.2 Brightness, % 46 45 45 46 46 Opacity, % 94 94 94 93 93 Light Scat. Coef. m2/kg 37 38 36 37 36 Light Abs. Coef., cm2/g 48 47 41 42 45 TABLE lB
CHEMICAL COMPOSITIONo 90 g Na2SO3 + 10 g NaOH per liter Pulp Yield: 81.5%
Properties Freeness, mL 546 412 312 274 148 Density, g/cm2 0.47 0.50 0.S2 0.54 0.56 Breaking Length, km 6.6 7.2 7.6 7.8 8.4 Burst Index, kPa.m2/g4.0 4.4 4.9 S.l 5.6 Tear Index, mN.mVg 8.4 7.4 7.2 7.0 6.5 Brightness, % 33 33 33 33 33 Opacity, % 97 96 96 96 96 Light Scat. Cbef., m2/kg 33 32 33 33 34 Light Abs. Coef., cmVg 83 82 82 83 81 1 309~62 TABLE lC
CHEMICAL COMPOSITION: 80 g Na2SO3 + 20 g NaOH per liter Pulp Yield: 79.4%
Properties Freeness, mL 540 392 266 196 Density, g/cm3 0.50 0.52 0.55 0.56 Breaking Length, km 7.7 7.9 8.4 8.8 Burst Index, kPa.m2/g4.8 5.2 5.8 6.1 Tear Index, mN.m2/g 8.6 8.0 7.9 7.4 Brightness, % 29 30 30 29 Opacity, % 97 97 97 97 Light Scat. Coef., m2/kg 32 32 33 33 Light Abs. Coef., cm2/g 105 102 104 104 TABLE lD
CHEMICAL COMPOSITION: 70 g Na~SO3 ~ 30 g NaOH per liter Pulp Yield: 79.4%
ProDerties Freeness, mL 533 380 240 160 Density, g/cm3 0.48 0.54 0.56 0.57 Breaking Length, km 7.8 8.3 8.7 9.2 Burst Index, kPa.m2/g4.7 5.6 5.8 6.2 Tear Index, mN.mVg 8.8 8.1 7.5 7.3 Brightness, % 28 27 27 27 Opacity, % 98 98 98 98 Light Scat. Coef., m2/kg 33 31 32 33 Light Abs., Coef., cm2/g 122 120 124 124 lS
1309~2 TABLE lE
CHEMICAL COMPOSmON: 90 g Na~SO3 + 10 g Na2CO3 Pulp Yield: 89.1%
Properties Freeness, mL 387 290 280 230 174 Density, g/cm3 0.47 0.49 0.49 0.50 0.52 Breaking Length, km 7.2 7.6 7.7 7.8 8.1 Burst Index, kPa.m2/g4.0 4.4 4.5 4.7 4.9 Tear Index, mN.m2/g 7.2 6.9 6.9 6.8 6.4 Brightness, % 41 41 41 41 39 Opacity, % 94 94 94 94 94 Light Scat. Coef., m2/kg 35 34 34 34 31 Light Abs. Coef., cm2/g 56 52 51 52 57 TABLE lF
CHEMICAL COMPOSlTION: 80 g Na2SO3 + 20 g Na~C03 per liter Pulp Yield: 86.9%
Properties Freeness, mL 430 356 266 187 Density, g/~m3 0.51 0.52 0.54 0.56 Breaking Length, km 7.4 8.1 8.3 8.4 Burst Index, kPa.m2/g 4.4 4.9 5.1 5.4 Tear Index, mN.mVg 7.2 7.0 7.S~ 6.9 Brightness, % 36 36 35 35 Opacity, % 95 95 95 95 Light Scat. Coef., m2/kg 33 32 32 31 Light Abs., Coef., cmVg 68 68 71 67 .
130~2 TABLE lG
CHEMICAL COMPOSITION: 70 g Na2SO3 + 30 g Na2CO3 per liter Pulp Yield: 86.5%
Properties Freeness, mL 420 316 236 172 Density, g/cm3 0.49 0.51 0.52 0.54 Breaking Length, km 6.9 7.4 7.9 7.9 Burst Index, kPa.m2/g 4.0 4.5 4.7 4.8 Tear Index, mN.m2/g 7.2 6.9 6.7 6.6 Brightness, % 36 36 35 35 Opacity, % 95 95 95 96 Light Scat. Coef., m2/kg 33 33 33 34 Light Scat. Abs., cm2/g 69 69 68 71 CHEMICAL COMPOSlTION: 100 g Na2SO3 per liter P~o~erties Cookin Time, min Pulp Yield, % 92.9 91.6 89.6 Freeness, rnL 280 190 140 340 230 170 350 260 190 Density, g/cm3 0.45 0.45 0.49 0.46 0.51 0.55 0.52 0.54 0.56 Breaking Length, km6.2 6.4 6.7 6.3 7.3 8.0 7.5 7.9 8.2 13urst Index, lcPa.mVg 3.3 3.3 3.7 3.6 4.3 4.5 4.6 4.6 4.8 Tear Index, mN. m2/g 7.0 6.8 6.4 7.5 6.7 6.1 7.1 6.8 6.7 Brightness, % 51 51 51 49 49 48 46 46 46 Opacity, % 90 90 90 90 89 89 90 90 90 L. Scat. Coef., m2/~g 34 35 35 32 32 31 31 30 30 L Abs. Coef., cm2/g33 33 31 33 34 33 38 38 38 13~93~2 CHEMICAL COMPOSITION: 100 g Na2SO3 + 10 g Na2CO3 per liter Properhes Cookin Time~ min Pulp Yield, % 92.4 89.6 88.2 Freeness, mL 280 200 150 340 240 190 300 220 160 Density, g/cm3 0.46 0.46 0.46 0.45 0.47 0.47 0.44 0.48 0.48 Breaking Length, k}n 6.9 7.4 7.6 7.1 7.6 7.7 7.1 7.6 7.9 Burst Index, kPa.m2/g 3.9 4.0 4.1 4.0 4.2 4.4 4.1 4.3 4.4 Tear Index, mN. m2/g 7.4 6.8 6.6 8.1 7.2 7.0 7.8 7.5 6.7 Brightness, % 45 45 44 45 44 44 44 44 44 Opacity, % 91 90 90 90 90 89 90 90 90 L. Scat. Coef., m2/kg 32 32 32 31 31 31 31 30 30 L Abs. Coef., cm2/g38 37 37 35 37 36 37 39 38 -TABLE ~2C
CHE~MICAL COMPOSITION: 100 g Na2SO3 + 20 g Na2CO3 per liter Properties Cookin~ Time. min Pulp Yield, % 92 89 88 Freeness, mL 280 210 140 420 280 180 420 280 180 Density, g/cm3 o~so 0.52 0.53 0.48 0.49 0.53 0.46 0.47 0.48 Breaking Length, km8.0 8.1 8.5 7.4 7.9 8.5 7.1 7.7 8.1 Burst Index, kPa.m2/g 4.5 5.0 5.3 4.5 4.9 5.1 4.2 4.6 4.6 Tear Index, mN. m2/g 7.5 7.0 6.4 7.7 7.3 6.6 8.3 7.4 6.8 Brightness, % 41 40 40 40 39 40 40 40 39 Opacity, % 91 91 90 91 91 91 91 91 91 L. Scat. Coef., m2/kg 31 30 29 30 29 29 30 30 29 L Abs. Coef., cm2lg41 42 43 45 46 47 44 44 46 130~ 2 CHEMICAL COMPOSITION: 100 g Na2SO3 ~ 30 g Na2CO3 per liter Properties Cookin~ Time min Pulp Yield, % 89.5 87.5 87.3 Freeness, mL 378 264 188 376 256 182300 200126 Density, g/cm3 0.48 0.500.53 0.45 0.47 0-490.52 0.530.55 Breaking Length, km 7.0 7.8 8.0 7.1 7.4 7.87.9 8.79.1 Burst Index, kPa.m2/g4.1 4.3 4.6 3.9 4.2 4.45.3 5.25.4 Tear Index, mN. m2/g 7.8 7.5 6.9 7.6 7.1 7.07.9 7.47.1 Brightness, % 38 38 37 39 38 38 37 36 36 Opacity, % 93 93 93 93 93 92 93 93 93 L. Scat. Coef., m2/kg32 32 31 32 31 30 30 29 29 L Abs. Coef., cm2/g 54 54 56 53 54 52 57 61 59 CHEMICAL COMPOSITION: 45 g Na2SO3 + 5 g NaOH per liter Pulp Yield: 87.1%
Properties Specific Energy, m~cg 8.9 9.8 10.5 14.6 Freeness, mL 613 502 413 147 BuL~c, cm3/g 2.53 2.54 - 2.26 2.02 Brightness, % 39 39 39 38 Opacity, % 98 97 96 95 Porosity, mL/min 3464 2527 1213 69 Brealcing Length, km 4.4 4.6 5.4 6.7 Stretch, % 2.12 2.39 2.63 3.17 Burst Index, kPa.m2/g 2.4 2.8 3.4 4.2 Tear Index, rnN.mVg 11.6 11.2 10.9 9.8 ~30~2 CHEMICAL COMPOSITION: 40 g Na2SO3 + 10 g NaOH per liter -Pulp Yield: 80.9%
Properties Specific Energy, mJ~g 12.1 12.6 13.3 13.7 Freeness, mL 254 136 88 62 Bulk, cm3/g 2.12 1.99 1.89 1.79 Brightness, % 34 34 34 34 Opacity, % 98 98 98 98 Porosity, rnIlmin166 61 24 16 Breaking Length, km5.8 6.4 6.6 6.7 Stretch, % 3.10 3.30 3.24 3.22 Burst Index, kPa.mVg 3-9 4-3 4-5 4-4 Tear Index, mN.m2/g9.5 9.2 7.8 7.5 CHEMICAL COMPOSITION: 35 g Na2SO3 + 15 g NaOH per liter Pulp Yield: 74.8%
Properties Speci~lc Energy, mJ~g 12.9 13.2 14.0 14.5 Freeness, mL 251 207 105 59 Bulk, cm3/g 2.17 2.08 2.02 1.93 Brightness, % 32 32 32 32 Opacity, % 99 99 99 99 Porosity, mL/min 201 111 46 17 Brealdng Length, km5.4 5.7 6.2 6.7 Stretch, % 2.98 3.27 3.49 3.58 Burst Index, kPa.m2/g 3.4 3.7 4.3 4.8 Tear Index, mN.m2/g11.410.8 9.0 8.8 ~ 3 ~ 2 TAI~LE 3D
CHEMICAL COMPOSITION: 45 g Na2SO3 + 5 g Na2CO3 per liter Pulp Yield: 89.9%
Properties Specific Energy, mJ/kg 5.2 5.3 6.2 6.4 Freeness, rnL 695 670 521 470 Bulk, cm3/g 3.53 3.38 3.04 2.64 Brightness, % 45 45 45 45 Opacity, % 94 94 94 94 Porosity, mL/min4696 4212 2424 582 Breaking Length, km4.0 4.2 5.0 5.2 Stretch, % 1.89 1.96 2.36 2.37 Burst Index, kPa.m2/g 2.2 2.5 2.9 2.8 Tear Index, mN.m2/g14.814.1 10.6 9.2 CHEMICAL COMPOSlTION: 40 g Na2SO3 + 10 g Na2CO3 per liter Pulp Yield: 88.8%
Properties Specific Energy, mJ~cg 6.2 7.7 7.7 7.8 Freeness, mL 485 475 470 457 Bulk, cm3/g 309 2.95 2.55 2.32 Brightness, % 41 41 41 41 Opacity, % 95 95 95 95 Porosity, mL/min4224 3352 2224 446 Breaking Length, km4.6 5.2 5.5 5.7 Stre~ch, % 2.14 2.30 2.43 2.51 Burst Index, kPa.m2/g 2.7 3.0 3.3 3.4 Tear Index, mN.m2/g14.113.1 12.3 10.1 13095~2 CHEMI(:AL COMPOSITION: 35 g Na2SO3 + 15 g Na2CO3 per liter Pulp Yield: 88~6%
Properties Speci~lc Energy, mJlkg 6.7 6.9 7.0 9.3 Freeness, mL 490 480 475 403 Bulk, cm3/g 2.82 2.74 2.50 2.15 Brightness, % 38 38 38 38 Opacity, % 96 96 96 96 Porosity, mL/min3680 3052 1520 277 Breaking Length, km4.9 5.2 5.7 6.5 Stretch, % 2.27 2.42 2.55 2.7g Burst Index, kPa.m2/g 2.9 3.1 3.5 4.0 Tear Index, mN.m2/g15.212.7 12.0 9.1
SODIUM CARBONATE AND SODIUM SULPHll'E
Back~round of the invention The present invention relates to a process for the production of a high yield, high strength chemimechanical (CMP3 pulp from wood or other lignocellulosic materials. More particularly, this invention relates to a chemi-mechanical pulping process employing sodium carbonate and sodium sulphite in the cooking liquor to chemically soften the wood chips or other lignocellulosic materials prior to mechanical defibration.
In recent years there has been increased use of high yield chemimechanical pulps in the manufacture of papers and, particularly, printing papers. These pulps have relatively high strength as compared to the pure mechanical pulps such as groundwood pulps and refimer pulps.
Traditionally newsprint is manufactured from a furnish consisting of about three parts mechanical pulp, such as g~oundwood or refiner pulp and one part chemical pulp. Groundwood, manufactured by pressing logs against a revolving abrasive stone, is obtained in yields approaching 100%, whereas the refiner pulps, such as the refiner mechanical pulp (RMP~ and thermomechanical pulp (TMP~ are obtained by refining wood chips or other lignocellulosic materials in a disc refiner, under atmospheric or elevated pressure, respectively. The RMP and TMP are obtained in yields of 95% or more. Pollution problems associated with the manufacture of mechanical pulps are minimal. HoweveF, the mechanical pulp ~lbers, containing almost all the lignin present in the wood, are relatively stiff and produce papers of comparatively low strength because of their poor interfiber bonding capacity. The lignin, concentrated in the intercellular layer known as the rruddle lamella, cements the cellulose fibers to each other.
$~
1309a62 The main pulpose of chemical pulping processes, such as sulphate (kraft) or sulphite pulping, is to dissolve the middle lamella so that the wood structure breaks down into individual fibers without the use of substantial mechanical action.
This is accomplished by cooking the wood chips at high chemical concentrations S and high ternperatures (about 120C to 180 C~ for a prolonged period of time (up to 5 hours or rnore) and results in low yields based on the dry chips because a substantial amount of the wood, particularly lignin, is removed. The chemical pulp component is usually manufactured by either the kraft or sulphite process in yields ranging from 45% to 65%.
Chemical pulps have many advantages due to their cleanliness, high strength, and ease of bleaching, but they are expensive, make heavy demands on the mill's wood resources, and entail formidable pollution problems. The presenttrend in newsprint manufacture, therefore, is towards reduction in the use of chemical pulps.
The semichemical and chemimechanical pulping processes fall midway between the chemical and mechanical processes in these respects.
The increasing world-wide demands for pulp, paper and other forest products and the decreasing availability of fiber are creating an increasing need for the use of higher yield pulps. The present invention produces a high yield pulp that can replace some types of chemical or semichemical pulp in many products.
One attempt which has been made tO improve the yield of sulphite pulps, which is relevant from the standpoint of the present invention, involves pre-treating the chips with an alkaline solution for a period of time. Exarnples of such sulphite pulping processes are described in U.S. patent 3,177,110 to Ogait and U.S.
patent 3,354,030 to Williams et al. However, these processes remain essentially chemical pulping processes which rely upon the removal of most of the lignin from the wood and do not provide high overall yields. For example, the yields il-lustrated in the Ogait patent only range from about 55 to 65%. By contrast, the major portion of the lignin is retained in CMP and (~TMP processes due to ~le 1~09~2 use of much milder conditions in the chemical treatments.
It is known that the ~eatment of wood chips with relatively small amounts of sulphite and bisulphite, at near neutral pH, and under relatively rnild cooking conditions ~100 C - 150 C, for 2-25 minutes) produces a softening effect on the chips which makes them easier to de~lber and generally produces a cleanerand better draining pulp than can be produced by mechanical means alone. See Uschmann U.S. patent 3,607,618; Aitken et al. U.S. patent 3,013,934; and Asplundet al. U.S. patent 3,558,428.
However, the pulps produced by such processes, while being superior to conventional mechanical pulps in terms of cleanliness and drainage properties, do not have sufficiently good physical properties to justify their increased cost of production relative to the conventional mechanical pulps.
Better properties can be achieved by cooking under more severe conditions such as increased temperatures in the 160 C - 240 C range, but the strength improvement is always accompanied by a loss in yield. Instead of yieldsof over 90%, the yields are reduced to about 70-85%. See the above patents and Richardson U.S. patent 2,962,412; Zimmerman U.S. patent 1,821,198; Cederquist U.S. patent 3,078,208; Asplund et al. U.S. patent 3,44~,699; Von Hamzburg U.S.
patent 2,949,395; Olson U.S. patent 3,003,909; and Rasch et al. U.S. patent 2,847,304.
Mild sulphite treatments have been used in chernirnechanical pulping processes to chemically soften the wood fibers and thereby facilitate mechanicaldefibration. It is known that sul~onation renders lignin more hydrophillic or less hydrophobic so that the fibers swell in the sulphite liquor and the chips becomeeasier to defibraee. These chernimechanical processes produce higher yields thanchemical or semi-chemical processes, but the pulp strength is not as good.
Typically they are also more effective with softwoods than hardwoods.
U.S. patent ~,116,758 to Ford et al. describes a process which is specially suited to softwood pulps whereby wood chips are softened prior to defibration by 1309~62 sulfonating the lignin with-out substantially removing it from the wood. This istypically accomplished by maintaining the wood chips in a solution containing 50-180 g/L sodium sulphite at 100 - 140 C for approximately 30 - 60 minutes without an alkaline pre-treatment and is followed by disc refining.
U.S. patent 3,016,324 to Textor also discloses a chemi-mechanical pulping process wherein wood chips may be impregnated with sodium sulphite liquor by squeezing the chips in a screwpress and spraying the chips emerging from the press with sulphite liquor and then defibrated.
Chemimechanical pulping processes in which the chips are impregnated with aLkaline liquors are also known.
One proposed mechanism by which the use of alkali, such as caustic soda or sodium hydroxide, increases the strength of mechanical pulps is by increasingthe number of acidic groups in the wood. ~See publication of Katz et al. "A
Mechanism for the Alkali Strengthening of Mechanical Pulps", TAPPI, Vol. S4, No. 7, pp. 97-100, July, 1981). The counter-ions of these acidic groups are saidto draw additional water into the cell wall and the accompanying swelling and plasticization enhance the ability of the fibers to bond and the overall strength o the pulp improves.
U.S. patents 3,479,249; 3,617,435; and 4,795,574 to Kalisch describe a semi-chemical sulphite pulping process which is accomplished by impregnating wood chips with sodium hydroxide or sodium carbonate and, thereafter, cooking the chips in an aqueous solution of sulphur dioxide for 2 to 3 hours. In the latter treatment, the sodium hydroxide or sodium carbonate in the chips reacts with sulphur dioxide to produce bisulphite in the chips which reacts with the lignin to solubilize it in a known manner. A~ter cooking, the chips are defibrated by passing them through a disc refiner. The yields reported in the patent are about75% or less.
U.S. patent 4,486,267 to Prusas discloses a high yield chemither-momechanical (CTMP) process wherein hardwood chips are subjected to a two-stage chemical treatment prior to defibration, the first consisting of chip impregnation and reaction with an aL~aline liquor followed by a second stage treatment with sulphite and/or bisulphite. This process produces high strength hardwood pulps, but the pulp brightness (22 - 40%) and yields (79 - 85%) are greatly reduced.
U.S. patent 4,187,141 to Ahrel describes a process for producing bleached chemimechanical pulp wherein screwpressed wood chips are subjected to a two-stage impregnation with an alkaline peroxide solution, in which the impregnated chips are introduced into a pressure vessel and ground in a disc refiner. This process provides a pulp having high brightness but relatively low strength.
While sodium hydroxide has been used in the production of chemimechanical and chemithermomechanical pulps in the past to improve pulp strength, it has not maintained high b~ightness and high yield. It is ~nown thatsodium hydroxide darkens the pulp and solubilizes the hemicelluloses in known manners. We have now made the surprising discovery that both the pulp yield and brightness can be increased by replacing the sodium hydroxide by sodium carbonate in the sulphite cooking of chips carried out prior to refining.
It has been found that, as the reaction in chemical treatment of chips proceeds, the pH of the medium drops, probably as a result of hydrolysis of acetyl groups on the chip. If the pH drops below 3, there is risk of damaging the fibrethrough hydrolytic action with consequent loss of strength. Wood fiber which hasbeen subjected to mechanical action, such as refining, is particularly susceptible to acidic degradation. It is therefore a common industrial practice to add aLkali, such as sodium hydroxide or sodium carbonate to the cooking li~uor as a buffer. It iswell known that sodium hydroxide solubilizes hemicelluloses, resulting in yield loss.
Sodium carbonate has been used in semichemical pulping experiments, such as the neutral sulphite semichemical ~NSSC) processes. Conflicting results of the influences of sodium carbonate on pulping ha7/e been reported. See the 1309~62 following publications: Upadhyaya et al., "Studies on Neutral Sulphite Semichemical Pulping of Cajanus cajan", ABCP Congr. Anual l9th (Sao Paulo), Nov. 24-28, 1986, pp. 177-188; ~Ialhotra et al., "Neutral Sulphite Sernichemical(NSSC) High-Yield Pulps from Eucalyptus globulus", Holzforsch. Holzverwert.
Vol. 33, No. 3, pp. 51-52, 1981; Cameron et al., "Response of Pines and Eucalyptus to NSSC-AQ Pulping", SPCI Internatl. Symp. Wood & Pulping Chem.
Preprints, Vol. 2, 64-71 (June 9-12, 1981); Janci et al., "Production of Semiehemieal Pulp Using Green Liquor from NSSC Chemieal Recovery ~ystem", Papir Celluloza Vol. 34, No. 10, pp. 289-292 (1979); and Keller, "Is Caustic Soda Suitable for Buffering NSSC Digestions?", Southern Pulp Paper Mfr. Vol. 32, No.
5, pp. 32, 34, 36 (May, 1969).
It has now been surprisingly found that physical properties of sulphite chemimeehanieal pulps ean be significantly improved and their yields can be maintained near 90% level, by an addition of sodium carbonate to the sulphite liquor.
In aecordance with the present invention, there is provided a process of produeing ehemimechanieal pulps which eomprises cooking the ehips with aqueous sodium sulphite solution containing suf~leient sodium earbonate. The eooking is effeeted at an elevated temperature for a time suffieient to eause reaetion with the ehip and increase the swelling or the flexibility of the fibers but for a time insufficient to eause substantial dissolution of wood components, such as ligninand hemicellulose from the ehip and insuffieient to result in a pulp yield belowabout 85%.
The improvement in strength properties aehieved by the present invention permits use of the resultant pulps as either replacement or reinforcement eomponent for the low yield, high eost chernieal pulps in papers, partieularly the printing grades.
The proeedure of the present invention may be carried out on any types of wood chips or other lignocellulosic materials, and the improvement in physieal ~309562 properties is achieved on each of these materials.
It is, accordingly, an object of the present invention to provide a high yield chemimechanical pulping process for producing high strength pulp from wood chips and other lignocellulosic materials.
It is also object of the invention to provide a two-stage process of producing high yield chemimechanical pulp from wood chips whereby the chips are impregnated with an aqueous solution of sulphite and sodium carbonate followed by either liquid phase or vapour phase cooking and thereafter defibrating the chips by a disc re~mer to provide a pulp having excellent strength charac-teristics.
Other objects will be apparent to those skilled in the art from the present description.
1~ Genera! Descri~tion of the invention The process of the invention is an improved two-stage process for producing high yield chemimechanical pulps from wood or other lignocellulosic material, whereby in the first stage, the wood or other lignocellulosic material is subjected to treatment with an aqueous solution of sulphite and sodium carbonate, wherein sufficient sulphite is present to provide an amount of at least about 3% by weight, based on weight of wood or other lignocellulosic materials and wherein sufficient sodium carbonate is present to provide an amount to maintain a pH of the liquor of about 7 to 1(), the cooking being at a temperature of between 100 C
and 200 C for between about 2 and 120 minutes, without reducing the pulp yield 2~ to below about 85%; and whereby in the second stage, the resulting treated wood or other lignocellulosic material is subjected to mechanical defibration.
In the first stage of chemical treatment of the process of the present invention, the cooking of the chemically trcated wood or other lignocellulosic material may be carried out either in liquid phase or vapour phase.
~309~2 In liquid phase cooking, the chemically treated wood or other lignocellulosic material is cooked in a heated sulphite/carbonate solution under the specified conditions, prior to being subjected to mechanical defibration.
Cooking of the chemically treated wood or other lignocellulose material may also be carried out in vapour phase, whereby the wood or other lignocellulosic material is first impregnated with a sulphite-carbonate solution by means of steeping or press impregnation of wood or other lignocellulosic material and whereby the impregnated wood or other lignocellulosic material is subjected to steam cooking, and thereafter to mechanical defibration.
In a preferred embodiment of the invention, the amount of sulphite used is in the range of 10 and 25% by weight based on weight of wood, although lower concentrations down to about 1 % may be used with reduced bene~lcial effect. Similarly improvements are observed with sulphite charges up to about 50%
by weight of the wood, but the additional cost is not justified by the small additional improvement. Generally, therefore, a sulphite charge of between about1% and about 50% by weight, preferably between 10% and about 25% by weight based on weight of wood is used.
The sodium carbonate charge may range from about 2% to about 25% by weight of wood or other lignocellulosic material, preferably between 5 and 10%~
although lower concentrations down to about 1% may be used with reduced beneficial effect. Similarly improvements in pulp properties are observed with sodium carbonate charges up to about 30% by weight of the wood, but the additional cost is not justified by the substantial loss in yield.
It is preferred to carry out the impregnativn of wood with a liquor-to-wood ratio ranging from about 4 to about 6, preferably around 5. Lower ratios may not permit uniform impregnation of wood, but higher ratios increase energy costs as in liquid phase cooking, and decrease reaction rate because of dilution of the reactants, necessitating longer reaction times.
1~03 ~2 The time and temperature of reaction may be vaned over a wide range.
The essential requirements are that the reaction must be allowed to effect an increase in physical properties and must not be allowed to proceed far enough toyield substantial dissolution of lignin and hemicellulose, as it would decrease substantially pulp yield and increase pollution problems. Practically, the application of our invention is restricted to pulp yield in excess of about 85% by weight based on starting wood chip. The minimum reaction time to yield beneficial results is about 2 rninutes at 200 C, with longer times being used at lower temperatures.
In the practice of the invention, ~he wood or other lignocellulosic material is exposed to a minimum degree of cooking corresponding to 2 minutes at 200 C, and a maximum degree of cooking corresponding to a pulp yield of about ~5% by weight.
The pulps made from this invention may be used in such products as newsprint, coated papers, hook papers, sanitary tissues, corrugating medium, linerboard, paper towelling, diaper fluff, miLk carton board, etc.
Specific DescriPtion of the Invention In order to disclose more clearly the nature of the present invention, the following examples illustrating the invention are given. It should be understood, however, that this is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claims.
This example compares the effec~ of sodium carbonate to that of sodium hy~roxide in alkaline sulphite treatment of black spruce.
Pulps were prepared using a 300-mL reactor provided with live steam, a 1309~62 4-L Waring blender and a PFI mill. Black spruce chips were impregnated with a solution containing sodium sulphite, or sodium sulphite/sodium hydroxide, or sodium sulphite/sodium carbonate, under vacuum at ambient temperature for 16 hours. The liquor concentration was 100 g/L, which contained 100, 90, 80, and 70g of sodium sulphite, the balance was made up of either sodium hydroxide or sodium carbonate. A liquor-to-wood ratio of 5 was used. The impregnated chips were drained and steamed at 190 C for 9 minutes.
The cooked chips were first defibrated in a Waring blender for 2 minutes at 3% consistency, and then refined in a PFI mill at 10% consistency to yield several freeness levels. Physical properties were measured on handsheets prepared from the unscreened pulps after the removal of latency. The properties are shownin Tables lA to lG below.
It can be seen from the results of Tables lA to 1(3 that using of sodium carbonate instead of sodium hydroxide in sulphite pulping can maintain a pulp yield near 90% or above 86%, while improving substantially the physical properties, particularly the breaking length and burst index. Using sodium carbonate causes only a relatively small drop in pulp brightness, while using ofsodium hydroxide can bring about substantial loss in both pulp yield and brightness.
This example illustrates the effect of addition of sodium carbonate to the sulphite liquor and the effect of co~king time on pulp properties.
A mixture of softwood chips (2-4 mm thick) containing approximately 70% black spruce and 30% balsam fir were impregnated wi~h sulphite liquor containing about 0, 9, 17, and 33% of sodium carbonate. A liquor-to-wood ratio of 5 was used. The impregnation of chips was carried out under vacuum, a~ ambient 1309~62 temperature for 16-18 hours. The impregnated chips were drained and steamed at 180 C for 7, 10 and 13 minutes.
The cooked chips were first defibrated in a Waring blender for 2 minutes at 3% consistency and then refined in a PFI mill at 10% consistency to obtain various degrees of freeness. Physical properties were measured on handsheets prepared from the unscreened pulps after the removal of latency. The properties are shown in Tables 2A to 2D.
It can be seen from the results of Tables 2A to 2D that the addition of sodium carbonate can maintain the pulp yield in the neighbourhood of 90%, depending on the cooking tirnes. Meanwhile the physical properties of handsheet are improved particularly those of the pulp produced with 7-minute cooking time.It appears that the advantage of sodium carbonate decreases slighdy when the cooking time was prolonged beyond 7 minutes.
This example compares the influences of sodium hydroxide and sodium carbonate in sulphite pulping of softwoods, at semi-industrial scale.
Softwood chips containing approximately 85% black spruce and 15%
balsam fir were cooked in a liquor at 170 C for 20 minutes. The concentration of the liquor was 50 g/L, in which sodium sulphite represented 45, 40 and 35 g, andthe balance was made up with either sodium hydroxide or sodium carbonate. In other words, the sodium hydroxide or sodium carbonate represented, respectively,10, 20 and 30% of the total chemical applied. Ihe liquor-to-wood ratio used was 6. After cooking, the chips were washed and refined, under atmospheric pressure,using a Sunds De~lbrator 300CD re~mer. Physical properties were measured on handsheets pr~pared from the unscreened pulps after the removal of latency. The properties are presented in Tables 3A to 3F.
It can seen from the results in Tables 3A to 3F, that there is a substantial gain, from about 3 to about 13 percentage points, in pulp yield by using sodium carbonate instead of sodium hydroxide. It also can be noted that sodium carbonate did noe darkened the pulp as much as sodium hydroxide. The freeness of the carbonate pulps as shown in Tables 3D, 3E and 3F was quite high because much less specific refining energy was applied in comparison with the caustic pulps as indicated in Tables 3A, 3B and 3C. In spite of their high freeness, the carbonate pulps yielded properties which were comparable to those of the caustic pulps.
This example compares the effect of sodium carbonate to that of sodium hydroxide in sodium sulphite cooking of hardwood.
Trembling aspen chips were cooked in three different liquors; the first contained 100% sodium sulphite, the second 90% sodium sulphite and 10% sodium hydroxide,and the third contained 90% sodium sulphite and 10% sodium carbonate.
The concentration of the liquor was 100 g/L. A liquor-to-wood ratio of 6 was used. In each pulping liquor, the chips were cooked at 150~ C and at three different retention times, that is 8, 13 and 18 minutes in order to produce pulps at different degrees of pulp yield.
The cooked chips were first defibrated in a Waring blender for 2 rninutes at 3% consistency, and then refined in a PFI mill at 10% consistency tO obtain various levels of freeness.
It can be seen from Figure 1 that partial replacement of sodium sulphite by sodium carbonate resulted in considerable increase in pulp yield about 4%
points when compared with sulphite pulps. On the other hand, the replacement of sodium sulphite by sodium hydroxide reduced the pulp yield by about 2% points.
Figure 2 indicates that the tensile strength of handsheet was improved by 130~g2 the presence of sodium carbonate in the cool~ing liquor. Sodium hydroxide was also effective in improving the fiber bonding strength but it caused impor~nt yield loss. In fact the tensile strength of sulphite-carbonate pulps was quite comparable to that of sulphite-caustic pulps, but the pulp yield of the former was much higher than that of the latter, which is a significant advantage. It was also observed that using sodium carbonate maintained a high pulp brightness of about 55% (56% for sulphite pulps, 45% for sulphite-caustic pulps). The tearing resistance of aspenpulps are shown in Figure 3 which indicates the advantages of sulphite-carbonatepulps which had high tear index at high yield levels.
The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excludin~ any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claims.
1 309~62 TABLE lA
CHEMICAL COMPOSITION: 100 g Na2SO3 per liter Pulp Yield: 89.5%
Properties Freeness, mL 520 408 306 220 176 Density, g/cm3 0.39 0.41 0.45 0.47 0.48 Breaking Length, km S.l 5.8 6.2 6.5 6.6 Burst Index, kPa.m2/g2.7 3.0 3.3 3.6 3.9 Tear Index, mN.mVg 7.6 7.2 6.6 6.4 6.2 Brightness, % 46 45 45 46 46 Opacity, % 94 94 94 93 93 Light Scat. Coef. m2/kg 37 38 36 37 36 Light Abs. Coef., cm2/g 48 47 41 42 45 TABLE lB
CHEMICAL COMPOSITIONo 90 g Na2SO3 + 10 g NaOH per liter Pulp Yield: 81.5%
Properties Freeness, mL 546 412 312 274 148 Density, g/cm2 0.47 0.50 0.S2 0.54 0.56 Breaking Length, km 6.6 7.2 7.6 7.8 8.4 Burst Index, kPa.m2/g4.0 4.4 4.9 S.l 5.6 Tear Index, mN.mVg 8.4 7.4 7.2 7.0 6.5 Brightness, % 33 33 33 33 33 Opacity, % 97 96 96 96 96 Light Scat. Cbef., m2/kg 33 32 33 33 34 Light Abs. Coef., cmVg 83 82 82 83 81 1 309~62 TABLE lC
CHEMICAL COMPOSITION: 80 g Na2SO3 + 20 g NaOH per liter Pulp Yield: 79.4%
Properties Freeness, mL 540 392 266 196 Density, g/cm3 0.50 0.52 0.55 0.56 Breaking Length, km 7.7 7.9 8.4 8.8 Burst Index, kPa.m2/g4.8 5.2 5.8 6.1 Tear Index, mN.m2/g 8.6 8.0 7.9 7.4 Brightness, % 29 30 30 29 Opacity, % 97 97 97 97 Light Scat. Coef., m2/kg 32 32 33 33 Light Abs. Coef., cm2/g 105 102 104 104 TABLE lD
CHEMICAL COMPOSITION: 70 g Na~SO3 ~ 30 g NaOH per liter Pulp Yield: 79.4%
ProDerties Freeness, mL 533 380 240 160 Density, g/cm3 0.48 0.54 0.56 0.57 Breaking Length, km 7.8 8.3 8.7 9.2 Burst Index, kPa.m2/g4.7 5.6 5.8 6.2 Tear Index, mN.mVg 8.8 8.1 7.5 7.3 Brightness, % 28 27 27 27 Opacity, % 98 98 98 98 Light Scat. Coef., m2/kg 33 31 32 33 Light Abs., Coef., cm2/g 122 120 124 124 lS
1309~2 TABLE lE
CHEMICAL COMPOSmON: 90 g Na~SO3 + 10 g Na2CO3 Pulp Yield: 89.1%
Properties Freeness, mL 387 290 280 230 174 Density, g/cm3 0.47 0.49 0.49 0.50 0.52 Breaking Length, km 7.2 7.6 7.7 7.8 8.1 Burst Index, kPa.m2/g4.0 4.4 4.5 4.7 4.9 Tear Index, mN.m2/g 7.2 6.9 6.9 6.8 6.4 Brightness, % 41 41 41 41 39 Opacity, % 94 94 94 94 94 Light Scat. Coef., m2/kg 35 34 34 34 31 Light Abs. Coef., cm2/g 56 52 51 52 57 TABLE lF
CHEMICAL COMPOSlTION: 80 g Na2SO3 + 20 g Na~C03 per liter Pulp Yield: 86.9%
Properties Freeness, mL 430 356 266 187 Density, g/~m3 0.51 0.52 0.54 0.56 Breaking Length, km 7.4 8.1 8.3 8.4 Burst Index, kPa.m2/g 4.4 4.9 5.1 5.4 Tear Index, mN.mVg 7.2 7.0 7.S~ 6.9 Brightness, % 36 36 35 35 Opacity, % 95 95 95 95 Light Scat. Coef., m2/kg 33 32 32 31 Light Abs., Coef., cmVg 68 68 71 67 .
130~2 TABLE lG
CHEMICAL COMPOSITION: 70 g Na2SO3 + 30 g Na2CO3 per liter Pulp Yield: 86.5%
Properties Freeness, mL 420 316 236 172 Density, g/cm3 0.49 0.51 0.52 0.54 Breaking Length, km 6.9 7.4 7.9 7.9 Burst Index, kPa.m2/g 4.0 4.5 4.7 4.8 Tear Index, mN.m2/g 7.2 6.9 6.7 6.6 Brightness, % 36 36 35 35 Opacity, % 95 95 95 96 Light Scat. Coef., m2/kg 33 33 33 34 Light Scat. Abs., cm2/g 69 69 68 71 CHEMICAL COMPOSlTION: 100 g Na2SO3 per liter P~o~erties Cookin Time, min Pulp Yield, % 92.9 91.6 89.6 Freeness, rnL 280 190 140 340 230 170 350 260 190 Density, g/cm3 0.45 0.45 0.49 0.46 0.51 0.55 0.52 0.54 0.56 Breaking Length, km6.2 6.4 6.7 6.3 7.3 8.0 7.5 7.9 8.2 13urst Index, lcPa.mVg 3.3 3.3 3.7 3.6 4.3 4.5 4.6 4.6 4.8 Tear Index, mN. m2/g 7.0 6.8 6.4 7.5 6.7 6.1 7.1 6.8 6.7 Brightness, % 51 51 51 49 49 48 46 46 46 Opacity, % 90 90 90 90 89 89 90 90 90 L. Scat. Coef., m2/~g 34 35 35 32 32 31 31 30 30 L Abs. Coef., cm2/g33 33 31 33 34 33 38 38 38 13~93~2 CHEMICAL COMPOSITION: 100 g Na2SO3 + 10 g Na2CO3 per liter Properhes Cookin Time~ min Pulp Yield, % 92.4 89.6 88.2 Freeness, mL 280 200 150 340 240 190 300 220 160 Density, g/cm3 0.46 0.46 0.46 0.45 0.47 0.47 0.44 0.48 0.48 Breaking Length, k}n 6.9 7.4 7.6 7.1 7.6 7.7 7.1 7.6 7.9 Burst Index, kPa.m2/g 3.9 4.0 4.1 4.0 4.2 4.4 4.1 4.3 4.4 Tear Index, mN. m2/g 7.4 6.8 6.6 8.1 7.2 7.0 7.8 7.5 6.7 Brightness, % 45 45 44 45 44 44 44 44 44 Opacity, % 91 90 90 90 90 89 90 90 90 L. Scat. Coef., m2/kg 32 32 32 31 31 31 31 30 30 L Abs. Coef., cm2/g38 37 37 35 37 36 37 39 38 -TABLE ~2C
CHE~MICAL COMPOSITION: 100 g Na2SO3 + 20 g Na2CO3 per liter Properties Cookin~ Time. min Pulp Yield, % 92 89 88 Freeness, mL 280 210 140 420 280 180 420 280 180 Density, g/cm3 o~so 0.52 0.53 0.48 0.49 0.53 0.46 0.47 0.48 Breaking Length, km8.0 8.1 8.5 7.4 7.9 8.5 7.1 7.7 8.1 Burst Index, kPa.m2/g 4.5 5.0 5.3 4.5 4.9 5.1 4.2 4.6 4.6 Tear Index, mN. m2/g 7.5 7.0 6.4 7.7 7.3 6.6 8.3 7.4 6.8 Brightness, % 41 40 40 40 39 40 40 40 39 Opacity, % 91 91 90 91 91 91 91 91 91 L. Scat. Coef., m2/kg 31 30 29 30 29 29 30 30 29 L Abs. Coef., cm2lg41 42 43 45 46 47 44 44 46 130~ 2 CHEMICAL COMPOSITION: 100 g Na2SO3 ~ 30 g Na2CO3 per liter Properties Cookin~ Time min Pulp Yield, % 89.5 87.5 87.3 Freeness, mL 378 264 188 376 256 182300 200126 Density, g/cm3 0.48 0.500.53 0.45 0.47 0-490.52 0.530.55 Breaking Length, km 7.0 7.8 8.0 7.1 7.4 7.87.9 8.79.1 Burst Index, kPa.m2/g4.1 4.3 4.6 3.9 4.2 4.45.3 5.25.4 Tear Index, mN. m2/g 7.8 7.5 6.9 7.6 7.1 7.07.9 7.47.1 Brightness, % 38 38 37 39 38 38 37 36 36 Opacity, % 93 93 93 93 93 92 93 93 93 L. Scat. Coef., m2/kg32 32 31 32 31 30 30 29 29 L Abs. Coef., cm2/g 54 54 56 53 54 52 57 61 59 CHEMICAL COMPOSITION: 45 g Na2SO3 + 5 g NaOH per liter Pulp Yield: 87.1%
Properties Specific Energy, m~cg 8.9 9.8 10.5 14.6 Freeness, mL 613 502 413 147 BuL~c, cm3/g 2.53 2.54 - 2.26 2.02 Brightness, % 39 39 39 38 Opacity, % 98 97 96 95 Porosity, mL/min 3464 2527 1213 69 Brealcing Length, km 4.4 4.6 5.4 6.7 Stretch, % 2.12 2.39 2.63 3.17 Burst Index, kPa.m2/g 2.4 2.8 3.4 4.2 Tear Index, rnN.mVg 11.6 11.2 10.9 9.8 ~30~2 CHEMICAL COMPOSITION: 40 g Na2SO3 + 10 g NaOH per liter -Pulp Yield: 80.9%
Properties Specific Energy, mJ~g 12.1 12.6 13.3 13.7 Freeness, mL 254 136 88 62 Bulk, cm3/g 2.12 1.99 1.89 1.79 Brightness, % 34 34 34 34 Opacity, % 98 98 98 98 Porosity, rnIlmin166 61 24 16 Breaking Length, km5.8 6.4 6.6 6.7 Stretch, % 3.10 3.30 3.24 3.22 Burst Index, kPa.mVg 3-9 4-3 4-5 4-4 Tear Index, mN.m2/g9.5 9.2 7.8 7.5 CHEMICAL COMPOSITION: 35 g Na2SO3 + 15 g NaOH per liter Pulp Yield: 74.8%
Properties Speci~lc Energy, mJ~g 12.9 13.2 14.0 14.5 Freeness, mL 251 207 105 59 Bulk, cm3/g 2.17 2.08 2.02 1.93 Brightness, % 32 32 32 32 Opacity, % 99 99 99 99 Porosity, mL/min 201 111 46 17 Brealdng Length, km5.4 5.7 6.2 6.7 Stretch, % 2.98 3.27 3.49 3.58 Burst Index, kPa.m2/g 3.4 3.7 4.3 4.8 Tear Index, mN.m2/g11.410.8 9.0 8.8 ~ 3 ~ 2 TAI~LE 3D
CHEMICAL COMPOSITION: 45 g Na2SO3 + 5 g Na2CO3 per liter Pulp Yield: 89.9%
Properties Specific Energy, mJ/kg 5.2 5.3 6.2 6.4 Freeness, rnL 695 670 521 470 Bulk, cm3/g 3.53 3.38 3.04 2.64 Brightness, % 45 45 45 45 Opacity, % 94 94 94 94 Porosity, mL/min4696 4212 2424 582 Breaking Length, km4.0 4.2 5.0 5.2 Stretch, % 1.89 1.96 2.36 2.37 Burst Index, kPa.m2/g 2.2 2.5 2.9 2.8 Tear Index, mN.m2/g14.814.1 10.6 9.2 CHEMICAL COMPOSlTION: 40 g Na2SO3 + 10 g Na2CO3 per liter Pulp Yield: 88.8%
Properties Specific Energy, mJ~cg 6.2 7.7 7.7 7.8 Freeness, mL 485 475 470 457 Bulk, cm3/g 309 2.95 2.55 2.32 Brightness, % 41 41 41 41 Opacity, % 95 95 95 95 Porosity, mL/min4224 3352 2224 446 Breaking Length, km4.6 5.2 5.5 5.7 Stre~ch, % 2.14 2.30 2.43 2.51 Burst Index, kPa.m2/g 2.7 3.0 3.3 3.4 Tear Index, mN.m2/g14.113.1 12.3 10.1 13095~2 CHEMI(:AL COMPOSITION: 35 g Na2SO3 + 15 g Na2CO3 per liter Pulp Yield: 88~6%
Properties Speci~lc Energy, mJlkg 6.7 6.9 7.0 9.3 Freeness, mL 490 480 475 403 Bulk, cm3/g 2.82 2.74 2.50 2.15 Brightness, % 38 38 38 38 Opacity, % 96 96 96 96 Porosity, mL/min3680 3052 1520 277 Breaking Length, km4.9 5.2 5.7 6.5 Stretch, % 2.27 2.42 2.55 2.7g Burst Index, kPa.m2/g 2.9 3.1 3.5 4.0 Tear Index, mN.m2/g15.212.7 12.0 9.1
Claims (12)
1. A high yield chemimechanical pulping process for producing pulp from woody lignocellulosic material, which process comprises sulphonating said woody lignocellulosic material with sulphite or bisulphite aqueous solution containing at least 1% of sodium carbonate wherein the amount of sulphite and bisulphite in said aqueous solution is between 5 g and 150 g per liter by weight calculated as sodium sulphite at a temperature of between about 100° C and 200° C
for a period of between 2 and 120 minutes, said aqueous solution having a pH of about 6 at end of said sulphonation, without reducing the yield of pulp below about 85% by weight, and subsequently subjecting the resulting sulfonated woody lignocellulosic material to mechanical defibration.
for a period of between 2 and 120 minutes, said aqueous solution having a pH of about 6 at end of said sulphonation, without reducing the yield of pulp below about 85% by weight, and subsequently subjecting the resulting sulfonated woody lignocellulosic material to mechanical defibration.
2. A high yield chemimechanical process according to Claim 1, wherein the amount of sulphite or bisulphite employed is between 5% and 50% by weight of wood.
3. A high yield chemimechanical process according to Claim 1, wherein the amount of sodium carbonate employed is between about 1% and 10% by weight of wood.
4. A high yield chemimechanical process according to Claim 1, wherein the aqueous solution of sulphite or bisulphite is of sodium sulphite or sodium bisulphite.
5. A high yield chemimechanical process according to Claim 1, wherein the aqueous solution of a mixture of sulphite and carbonate or bisulphite and carbonate is of sodium sulphite and sodium carbonate or sodium bisulphite and sodium carbonate.
6. A high yield chemimechanical process according to Claim 1, wherein said pH is between about 7 and 10.
7. A high yield chemimechanical process according to Claim 1, wherein said temperature is between about 100° C and 200° C.
8. A high yield chemimechanical process according to Claim 1, wherein said period of treatment with said aqueous solution is between about 2 and 120 minutes.
9. A high yield chemimechanical process according to Claim 1, wherein the woody lignocellulosic material is wood chips.
10. A high yield chemimechanical process according to Claim 1, wherein the said woody lignocellulosic material is sawdust.
11. A high yield chemimechanical process according to Claim 1, wherein said sulphonating is performed in liquid phase heating.
12. A high yield chemimechanical process according to Claim 1, wherein said sulphonating is performed in vapour phase heating.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 608736 CA1309562C (en) | 1989-08-18 | 1989-08-18 | Chemimechanical pulping process employing sodium carbonate and sodium sulphite |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 608736 CA1309562C (en) | 1989-08-18 | 1989-08-18 | Chemimechanical pulping process employing sodium carbonate and sodium sulphite |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1309562C true CA1309562C (en) | 1992-11-03 |
Family
ID=4140468
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 608736 Expired CA1309562C (en) | 1989-08-18 | 1989-08-18 | Chemimechanical pulping process employing sodium carbonate and sodium sulphite |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1309562C (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10000889B2 (en) | 2007-06-12 | 2018-06-19 | Westrock Mwv, Llc | High yield and enhanced performance fiber |
| US10060075B2 (en) | 2007-06-12 | 2018-08-28 | Westrock Mwv, Llc | Fiber blend having high yield and enhanced pulp performance and method for making same |
-
1989
- 1989-08-18 CA CA 608736 patent/CA1309562C/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10000889B2 (en) | 2007-06-12 | 2018-06-19 | Westrock Mwv, Llc | High yield and enhanced performance fiber |
| US10060075B2 (en) | 2007-06-12 | 2018-08-28 | Westrock Mwv, Llc | Fiber blend having high yield and enhanced pulp performance and method for making same |
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