CA1094264A

CA1094264A - Delignification of lignocellulosic material with a soda liquor containing a cyclic keto compound and a nitro aromatic compound

Info

Publication number: CA1094264A
Application number: CA291,265A
Authority: CA
Inventors: Harry H. Holton; Gordon H. Segall
Original assignee: Canadian Industries Ltd
Current assignee: PPG Architectural Coatings Canada Inc
Priority date: 1976-12-14
Filing date: 1977-11-18
Publication date: 1981-01-27
Also published as: AU504177B2; NZ185812A; FR2374464B1; BR7708249A; FI773771A; ZA777226B; JPS5374102A; DE2755769A1; AU3087577A; ES465038A1; FR2374464A1; JPS5345402B2; SE7714129L; NO774265L

Abstract

ABSTRACT OF THE DISCLOSURE
Delignification of lignocellulosic material such as wood, straw, bagasse, etc., with a soda pulping liquor containing as additives, a cyclic keto compound such as anthraquinone and a nitro aromatic compound such as nitrobenzene.

Description

1094Zfi4 CIL 563 This invention relates to a process for the de-lignification of lignocellulosic material such as wood, straw, bagasse, etc.
The processing of lignocellulosic material to produce cellulose suitable for the manufacture of paper products involves the removal of lignin and other non-cellulosic components such as gums. Reagents that attack lignin without affecting appreciably the cellulose compo-nent are preferred for this purpose. In the sulphate or kraft process, lignocellulosic material is cooked with a mixture of sodium hydroxide and sodium sulphide. In the soda process the cooking is carried out with sodium hydroxide alone. In Canadian Patent ~o. 895,756 issued on March 21, 1972 to H. E. Worster and M. F. Pudek there is described a two-stage soda-oxygen pulping process comprising a first stage sodium hydroxide digestion, followed by defiberiza-tion of the product of the sodium hydroxide digestion, and a second stage digestion with sodium hydroxide in the pre-sence of excess oxygen. This process produces pulp in yield comparable to the yield of a conventional kraft process.
Although these processes are effective in the removal of lignin from lignocellulosic material such as wood, the cel-lulose component of the material is attacked also to a certain degree, resulting in a lowering of yields and de-gradation of the product.
The contribution to air pollution of volatile mercaptans and hydrogen sulphide is a serious disadvantage of the kraft process. The soda process is superior in this respect; however, the soda process is unsuitable for pulping coniferous woods because of long cooking times and low yieLds 109~264 Even in the case of hardwoods, yielcls are inferior to those achieved using the kraft process. A recent pub-lication (B. Bach and G. Fiehn, Zellstoff Papier 21, No. 1,3-7, January 1972) and a related East German Patent No. 98,549 of June 20, 1973 disclose the use of anthra-quinone-2-monosulphonic acid (AMS) as a means of improving yields in the soda process. More recently, (United States Patent No. 3,888,727) this additive was employed in the first stage of a soda-oxygen process, resulting in yields superior to those of a conventional kraft process; the - pulp possessed strength properties comparable to kraft.
Unfortunately, the soda-AMS pulping process does not eliminate the odour problem, since sulphur derived from the additive is converted to sulphide in the pulping che-micals recovery systems and thence to mercaptans or hydrogen sulphide during the next cooking cycle. The econo-mic advantages resulting from higher yields are largely offset by the relatively high cost of AMS. Other deriva-I tives previously evaluated in soda cooking (Bach and Fiehn, above), not containing sulphur, were substantially less effective than AMS.
In United States Patent No. 4012280 issued on March 15, 1977, it is proposed to use, instead of AMS
as an additive in the soda process, a sulphur-free cyclic keto compound such as, among others r naphthoquinone, anthraquinone, anthrone r phenanthrenequinone and the alkyl r alkoxy and amino derivatives of said quinones. Compared to AMS r these quinone additives have the very great advantages that they do not contribute to pollution and that for a given concentration and under ~`~

~09 ~2~,4 comparable pulping conditions, they are more effective.
The Pulp and Paper Research Institute of Canada has reported Sv. Pappers 71(23) 857-863 (1968)l the effects of several nitro-aromatic compounds in accelerating and improving the yields from the soda pulping of soft-wood. While not the most effective, nitrobenzene is iden-tified in this publication as the only additive of com-mercial significance. Large amounts of nitrobenzene are used (1-10%) resulting in yields equivalent to that of the kraft process. However, the process is not felt to be commercially practicable due to severe deficiencies in cooking time and poor strength properties when compared to the kraft process.
It has now been found that lignocellulosic material can be delignified in higher yield than hereto-fore attained by a process which comprises a digestion with a soda pulping liquor in the presence of a sulphur-free cyclic keto compound together with a sulphur-free nitro aromatic compound. Optionally, the digestion with the soda pulping liquor may be followed by a second stage digestion in alkaline medium with oxygen or an oxygen-containing gas under pressure. Compared to the above prior processes wherein a cyclic keto compound or an aromatic nitro compound is used alone as an additive, the novel process provides a pulp in a much higher yield at a given kappa number with a comparable rate of delignification and comparable strength properties. When used in combina-tion with cyclic keto compound, as in the novel process of this invention, small amounts of nitroaromatic compounds have been found to exert negligible negative effects on 109426~ CIL 563 pulp prope ties (viscosity) and key paper making para-meters whereas when used alone, they are not commercially practicable as is indicated in the above publication of The Pulp and Paper Research Institute of Canada.
Thus the main object of the invention is to provide a soda pulping process for the efficient digestion of softwood Another object is to provide a soda pulping process that gives an increased yield of cellulosic pulp as compared to that of the kraft process A further object is to provide a pulping process that has a low pollution potential Additional objects will appear hereinafter.
The process of the invention comprises the steps of 1) treating lignocellulosic material in a closed reaction vessel with a pulping liquor containing alkali metal base and, as additives, from 0.001% to 10.0% by weight, based on the lignocellulosic material, of a cyclic keto compound selected from the group consisting of naphthoquinone, anthraquinone, anthrone, phenanthrenequinone, the alkyl, alkoxy and amino derivatives of said quinones, 6,11-dioxo-lH-anthra 1,2-c -pyrazole, anthraquinone-1,2-naphthacridone, .
7,12-dioxo-7,12-dihydroanthra 1,2-b pyrazine, 1,2-benz-anthraquinone and 10-methylene anthrone, and from 0 01%to 10.0% by weight, based on the lignocellulosic material, of a nitro aromatic compound selected from the group con-sisting of mono- and di-nitrobenzenes and the amino, carboxy,hydroxy and methyl derivatives of said nitro-benzenes, the trea.ment taking place at a maximum tempera-ture in the range of 150C to 200C for a period of 0 5 - 480 minutes, and ~.~942fi4 CIL 563

2) displacing the pulping liquor from the lignocellulosic material with water or an aqueous liquor inert to the ligno-cellulosic material to obtain delignified lignocellulosic material.
The delignified lignocellulosic material pro-duced by the above two steps may be used without further treatment or may be subjected to conventional bleaching steps.
Optionally, the delignified lignocellulosic material may be subjected to the following additional treatment steps:

3) treatment of the delignified lignocellulosic material in aqueous suspension at a consistency of 2% to 40% by weight for 0.5 to 60 minutes at 20C, to 90C. with 2% to 20% by weight of an alkali metal base, and

4) treatment of the alkaline material in aqueous medium at a consistency of from 3% to 40% by weight with oxygen or an oxygen-containing gas for 0.5 to 120 minutes at a temperature of 80C. to 150C. and a partial pressure of oxygen of 20 to 200 pounds per square inch.
When the lignocellulosic material employed is wood, this is first converted into the form of chips.
This step will not be required when the lignocellulosic material is of fibrous form.
The lignocellulosic material may be refined between steps (1) and (2) or between steps (2) and (3).
Refining can be carried out with known equipment such as a single disc or double disc refiner, The process of this invention can be used to de-lignify either coniferous or deciduous species of wood.

lQ94Z~4 CIL 563 By coniferous is meant species such as pine, spruce and balsam fir. sy deciduous is meant species such as birch, aspen, eastern cottonwood, maple, beech and oak. When employed with a high density deciduous wood such as birch it is preferable to employ a longer time to reach maximum cooking temperature in the first step. Even then, however, the overall cooking time is still greatly reduced in com-parison with that of the conventionalsoda process. It is also preferable, in the case of high density deciduous wood, thatthe alkali base added in the optional third step be so added while the pulp is at a low consistency, e.g. 2% to 6%.
The soda liquor employed in the first step of the process contains from 8% to 20% by weight of alkali metal base expressed as percent effective alkali, based on the weight of the lignocellulosic material, and normally also contains alkali metal carbonate.
Since the first step treatment of the process is carried out in a closed reaction vessel at a temperature in the range of from 150C. to 200C. in the presence of water, the reaction will take place under supra atmospheric pres-sure.
As mentioned above, the cyclic keto compounds which are suitable for use as additives in the process of the invention in combination with the nitro aromatic compounds are selected from the group consisting of naphthoquinone, anthraquinone, anthrone and phenanthrenequinone, the alkyl, alkoxy and amino derivatives of these quinones, 6,11-dioxo-lH-anthra 1,2-c pyrazole, anthraquinone-1,2-naphthacridone, 7,12-dioxo-7,12-dihydroanthra 1,2-b pyrazine, 1,2-benzanthra-quinone and 10-methylene anthrone~ Among the alkyl derivatives which ~094264 CIL 563 may be mentioned are any of the above quinones substituted with one or two alkyl groups containing from 1 to 4, preferably 1 to 2, carbon atoms. Among the alkoxy deri-vatives which are suitable for use as additives are any of the above quinones which are substituted with at least one alkoxy group having 1 to 4, preferably one, carbon atoms.
Preferred among the above additives are anthrone, anthra-quinone and the derivatives of anthraquinone. Most preferred because they can be easily and economically prepared and areparticularly efficient are l-methyl anthraquinone, 2-methyl anthraquinone, 2-ethyl anthraquinone, 2,6-dimethyl anthraquinone, 2,7-dimethyl anthraquinone, 2,3-dimethyl anthraquinone, l-methoxy anthraquinone and 2-amino anthra-quinone. The additive is employed in proportions of from 0 001% to 10.0%, preferably 0.01% to 1.0%, by weight based on the lignocellulosic material.
As is also mentioned above, the nitro aromatic compounds which are suitable for use as additives in the process of the invention in combination with the cyclic keto compounds are selected from the group consisting of mono- and di-nitrobenzenes and the amino, carboxy, hydroxy and methyl derivatives of said nitrobenzenes. Examples of these compounds are nitrobenzene, 2-nitroaniline, 4-nitro-aniline, 4-nitrobenzoic acid, 4-nitrobenzaldehyde, 2-nitro-resorcinol, 4-nitrostyrene, 2-nitrotoluene, 4-nitrotoluene, 1,2-dinitrobenzene, 1,3-dinitrobenzene, 1,4-dinitrobenzene, 2,4-dinitrotoluene, 3,5-dinitrobenzoic acid, 4,5-dinitro-o-cresol and 2,4-dinitroresorcinol. Among the above com-pounds, nitrobenzene is particularly preferred because, as it will be demonstrated hereinafter, it shows maximum 10942~4 CIL 563 benefits in the production of pulps of high kappa number.
The nitro aromatic compound is emp:Loyed in proportions of from 0 O~Oto 10.0%, preferably 0. l~/o to 2 0%, by weight based on the lignocellulosic material.
It is understood that all the combinations of ad-ditives formed from any one of the above defined cyclic keto compounds with any one the above defined nitro aromatic compounds are suitabls for use in the process of the inven-tion. Preferred, however, are the combinations comprised of nitrobenzene with any one of the cyclic keto compounds selected from anthraquinone, l-methyL anthraquinone, 2-methyl anthraquinone, 2-ethyl anthraquinone, 2,6-dimethyl anthraquinone, 2,7-dimethylanthraquinone, 2,3-dimethyl anthraquinone, l-methoxy anthraquinone and 2-amino anthra-quinone. Certain combinations of the above nitro aromatic compounds and cyclic keto compounds are especially preferred becau~e of the economical advantage presented by their mutual involvement in the synthesis of the cyclic keto com-pounds. As example of such combinations is that consisting of nitrobenzene and anthraquinone, which is thus a particu-larly preferred combination.
After the first step treatment with pulping liquor, the resulting pulp yield will be 40% to 70%, by weight, based on the lignocellulosic material. The kappa number of the material at completion of the first step will lie in the range 10 to 150 for coniferous woods and in the range 5 to 100 for deciduous woods.
The partially delignified material resulting from the first treatment step is discharged from the pulping vessel and the spent liquor displaced by fresh water or 42fi4 optionally by an aqueous liquor inert to lignocellulosic material such as the spent liquor Erom the alkaline oxygen treatment step or "white water" from a later stage of a papermaking process.
Optionally, the delignified lignocellulosic material may then be subjected to an alkaline oxygen treat-ment, To the material is added alkali metal base, The alkali metal base may be provided in the form of pulping liquor such as used in the first step of the process, This liquor therefore may contain carbonate in addition to alkali metal base, Preferably, there is also added 0,1% to 1,0%, by weight of the pulp, of a magnesium salt such as magnesi-um chloride or magnesium sulphate calculated as magnesium ion, The magnesium salt may be added directly as the salt or as a complex formed with the spent liquor from the alka-line oxygen treatment step, The alkaline treated material is then fed into an oxygen treatment vessel, The material is then treated with oxygen or an oxygen-containing gas under a partial pressure of oxygen of from 20 to 200 pounds per square inch, The product of the oxygen treatment is separated from the spent liquor and washed with water, It will have a residual lignin content of 1% to 6%, preferably 1,5% to 4,5%, of the weight of the original cellulosic material corresponding to a yield of 80~/o to 98% by weight, The alkali metal base employed as reagent in the process of this invention may be sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate.
The material resulting from step (2) may be bleached by any conventional bleaching process. A conventional g 10~4Z~4 CIL 563 sequence comprising chlorination, alXaline extraction, chlorine dioxide treatment, alkaline extraction, chlorine dioxide treatment (C-E-D-E-D) when applied to the material resulting from step (2), will provide a product having a brightness of approximately 85-90 units (~lrepho) The material resulting from step (4) may be bleached by the sequence chlorination, alkaline extraction, chlorine dioxide treatment (C-E-D) or any other conventional sequence. When applied to the material resulting from step (4), the se-quence C-E-D will provide a product having a brightness of approximately 85-90 units (Elrepho) The process of this invention has the advantage that the absence of sulphur-containing reagents results in lessened pollution potential as compared to the process of East German Patent No, 98,549. The process also provides a pulp in much higher yield at a given kappa number, than has been heretofore attainable by any of the prior art pulping processes mentioned hereinabove.
The invention is illustrated by the following examples but its scope is not limited to the embodiment shown therein.
In the Examples, the brightness, kappa number and viscosity determinations were carried out by the following methods, Brightness TAPPI Method T217m, 218m Kappa Number TAPPI Method T-236 M-60 Viscosity TAPPI Method T-230 SU-65 In all the following Examples, pulping was carried out in stainless steel pressure vessels of either one of the following two types; (1) a se' of three such vessels each containing a rotatable horizontal basket, and (2) an ~0942fi4 CIL 563 assembly of eight such vessels (hereinafter called the microdigester assembly) each of which is itself horizont-ally rotatable. Large size samples of chips of 300, 600 or 2400 grams (oven dried weight) were pulped in any one of the three vessels of the first type while small size samples of 75 grams were pulped eight at a time in the second type of vessels, i.e. in the microdigester assembly The chips were dried to approximately 90% consistency divided into appropriate portions in consideration of the number and size of the pulping runs to be carried out and stored at 4C. Exact amounts of chips of accurately known consist-ency were weighed out and soaked 24 hours in water prior to pulping. Soaked chips were placed inside the pressure vessel and optionally pre-steamed for 10 minutes. Pulp-ing liquor and dilution water were then added in the amounts required to give the desired effective alkali and to obtain a liquor to wood ratio of 4:1. Indirect electrical heating was used in both types of vessels. In the case of the microdigester assembly water under pressure was employed as a heat transfer medium. Heating was controlled to line-arly raise the temperature to a preset maximum in a given time and to maintain it within + 2C of said maximum to the end of the cooking period.
After completion of the cooking, the pressure was released and the pulp together with the used cooking liquor was transferred to a mixer such as a Cowles dis-solver, diluted to 2% consistency and stirred for 5 minutes to simulate the blow down of pulp that occurs in commercial scale digesters. The pulp was then washed twice by di-lution to 2% consistency with water and filtered and pressed ~94~4 CIL 563 to 25% consistency. The pulp was then crumbed in aHobart mixer, weighed and samples were taken for yield, kappa number and viscosity measurements, 63 samples of chips from a variety of wood species were subjected to pulping treatment employing soda pulping liquor containing combinations of cyclic keto compounds and nitro aromatic compounds according to the invention as additives, or soda pulping liquor containing either cyclic keto compounds or nitro aromatic compounds as additives. Cooking with pulping liquor was carried out using the digester and procedure described immediately above. The characteristics of the 63 pulping runs and the results obtained are shown in TABLE I.

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__ 1094Z~ CIL 563 3 samples of chips from black spruce were subjected to soda pulping treatment using the same digester and pro-cedure as in Example 1. In runs 1 and 2 the soda pulping liquor contained as additives nitrobenzene together with either anthraquinone or 2-methyl anthraquinone while in run 3, the liquor contained 2-methyl anthraquinone as the only additive. The characteristics of the three pulping runs are shown in TABLE II.
The cellulosic pulpsresulting from each of the 3 runs were then subjected to a conventional bleaching sequ-ence C-E-D-E-D in which C means chlorine, E means caustic extraction and D means chlorine dioxide. The details of the bleaching are given in TABLE III. The physical properties of breaking length, burst factor, tear factor, bulk and elonga-tion were then measured in all the runs. The details of these measurements are given in TABLE IV.
The physical properties of the pulps were determined on material processed by P.F.I. mill to freeness levels of 300 and 500 Canadian Standard Freeness (C.S.F.). Handsheets were prepared in accordance with TAPPI Method T-220-M-60.
The physical properties were determined by the following methods: -Breaking length TAPPI T-220 M-60 Burst factor TAPPI T-220 M-60 Tear factor TAPPI T-220 M-60 Bulk TAPPI T-220 M-60 Elongation TAPPI T-220 M-60 _ 20 -~a ~ - l ~ ~ ~
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. ~.. .. ....... _ ZO ..... ,_ 1094Zfi4 Two samples of black spruce chips (B,S,) were subjected to pulping treatment using the same digester and procedure as in Example 1, In run 1 a soda liquor was used containing no additive while in run 2 a soda liquor was also used but containing anthraquinone and nitrobenzene as addi-tives, The characteristics and pulping results of the 2 pulping runs are shown in TABLE V, The two runs were then subjected to alkaline oxygen treatment, In this treatment, the pulp at a consist-ency of 35% by weight was treated with sodium hydroxide.
Then at a consistency of 26% by weight, the alkaline pulp was treated in a pressure vessel with oxygen at a pressure of 90 pounds per square inch, In the two runs, Mg++ was added to the sodium hydroxide in the amount of 0,2% on pulp, The characteristics and results of the oxygen pulping stage are shown in TABLE VI, In the two runs, the pulps were refined prior to measurement of kappa number and further treatment, Refining was done in one pass through a laboratory Sprout-Waldren refiner at 0.005 inch clearance, 1.0~4Z~9~

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_____________ SODA OXYGE~ PULP I~G
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NaOH Yield Yield Run% on Temp. Time Kappa% on % on Viscosity l!;lo. pulp C. min. ~o. pulpwood ~ cps 1 6.6 120 30~ 27.1 91.0 48.9 1 9,4 2l 6.5 120 30 32,7 91.8 55,5 13.4

Claims

WHAT WE CLAIM IS:

1. A process for the delignifcation of ligno-cellulosic material comprising the steps of:
(1) treating the lignocellulosic material in closed vessel with a pulping liquor containing alkali metal base and, as additives, from 0.001% to 10.0% by weight, based on the lignocellulosic material, of a cyclic keto compound selected from the group consisting of naphtho-quinone, anthraquinone, anthrone, phenanthrenequinone, the alkyl, alkoxy and amino derivatives of said quinones, 6,11-dioxo-1H-anthra 1,2-c pyrazole, anthraquinone-1, 2-naphthacridone, 7,12-dioxo-7,12-dihydroanthra 1,2-b pyrazine, 1,2-benzanthraquinone and 10-methylene anthrone, and from 0.01% to 10.0% by weight, based on the lignocellulosic material, of a nitro aromatic compound selected from the group consisting of mono-and di-nitrobenzenes and the amino, carboxy, hydroxy and methyl derivatives of said nitrobenzene, the treat-ment taking place at a maximum temperature in the range of 150°C. to 200°C. for a period of 0.5 to 480 minutes, and (2) displacing the pulping liquor from the ligno-cellulosic material with water or an aqueous liquor inert to the lignocellulosic material to obtain de-lignified lignocellulosic material

2. A process as claimed in Claim 1 wherein the alkyl quinone derivatives are quinones substituted with one or two alkyl groups each having 1 to 4 carbon atoms and the alkoxy quinone derivatives are quinones substituted with at least one alkoxy group containing 1 to 4 carbon atoms.

3. A process as claimed in Claim 1 wherein the cyclic keto compound is anthraquinone.

4. A process as claimed in claim 2 wherein the nitro aromatic compound is selected from the group consisting of nitrobenzene, 2-nitroaniline, 4-nitroaniline, 4-nitro-benzoic acid, 4-nitrobenzaldehyde, 2-nitroresorcinol, 4-nitrostyrene, 2-nitrotoluene, 4-nitrotoluene, 1,2-dinitro-benzene, 1,3-dinitrobenzene, 1,4-dinitrobenzene, 2,4-dinitro-toluene, 3,5-dinitrobenzoic acid, 4,6-dinitro-o-cresol and 2,4-dinitrorecorsinol.

5. A process as claimed in Claim 1 wherein the nitro aromatic compound is nitrobenzene and the cyclic keto compound is selected from the group consisting of 1-methyl anthraquinone, 2-methyl anthraquinone, 2-ethyl anthraquinone, 2,6-dimethyl anthraquinone, 2,7-dimethylanthraquinone, 1-methoxy anthraquinone and 2-amino anthraquinone.

6. A process as claimed in Claim 1 wherein the cyclic keto compound is anthraquinone and the nitro aromatic compound is nitrobenzene.

7. A process as claimed in Claim 1 wherein the pulping liquor contains from 0.01% to 1.0% by weight based on lignocellulosic material, of the cyclic keto compound and from 0.10% to 2.0% by weight based on the lignocellulosic material, of the nitro aromatic compound.

8. A process as claimed in Claim 1 wherein the delignified lignocellulosic material is subjected to the following additional steps:
(3) treatment of the delignified lignocellulosic material in an aqueous suspension at a consistency of from 2% to 40% by weight for from 0.5 to 60 minutes at from 20°C. to 90°C. with from 2% to 20% by weight of an alkali metal base and (4) treatment of the alkali treated material in an aqueous medium at a consistency of from 3%
to 40% by weight with oxygen or an oxygen-containing gas for from 0.5 to 120 minutes at a temperature of from 80°C, to 150°C. and a partial pressure of oxygen of from 20 to 200 pounds per square inch.

9. A process as claimed in Claim 1 wherein the delignified lignocellulosic material is subjected to con-ventional bleaching,

10. A process as claimed in Claim 8 wherein the delignified lignocellulosic material is subjected to con-ventional bleaching.