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United States Patent, C "ice 1 Patented Dec. ‘25, 1962 2.. the cellulosic material‘ (preimpregnation) nor-the‘, air or oxygen in the pores of the material, nor the mechanical treatment before or during the digestion is responsibleffor 3,070,484 PROCESS FOR THE PRODUCTION OF PULPS FROM LIGNIN-CONTAINING CELLULOSE MATERIAL 3,070,484 the‘ main drop in the average’ D.P.' of the‘celliilose: I have found that the primary cause of the degradationiof the cellulose is the oxygen content of the gas'space-above . 'Anton Rudolf Wacek, Graz, Austria, assignorstoKim b'erly-Ciark Corporation, Neenah, Wis., a corporation oféDelaware‘ the digestion liquor. Speci?cally, I have foundthat-when N0 Drawing. Filed Sept. 2, 1959, Ser. No. 837,596 Claims priority, application Austria Sept. 5, 1958, 7 Claims. (Cl. 162-23) wood chips are digested with bisul?te in the usual manner the digestion liquor always becomes dark or even black‘on 10 This" invention relates to-a process for the production of pulps. from lignin-containing cellulose material. by chemical or semi-chemical digestion of such material and has as. its principal object the reduction of the degrada tion which normally accompanies such processes. 15 In .conventional chemical digestion processes more or rapid heating regardless of'wh'ether 'the‘chip's have been previously impregnated or not if the chips corne'into con tact with the‘ oxygen-containing igasatmosphervintthe cookeror autoclave. By contrast, when the airpre’se'nt the cooker or’ autoclave is * replaced by inertv gas, such for example as nitrogen or-carbon'dioxide, the cellulosic‘ma terial can be heated in a few minutes to the di‘ge'stion'te'm pcrature, evenwithout preimpregnationof the material lesssevere degradation ofthe celluloseoccurs, as is evi dent- by, the reduction in the original value for the molecu and withoutthe liquor turning black.‘ ' ' v‘ lar weight or the average degree of polymerisation (D.P,.) I have further found thatlpro'vided the chips oriother of the cellulose, In general, the molecular weight or 20 ‘lignin containing‘ cellulosic materialare treated With5th'e digestingv liquor while avoidingall contact of'th'e cellu losic material with oxygenécontainingga-s, the liquor does average D.P.‘ of the cellulose drops to about one ?fth of the orginal value. It has previously been assumed that this degradation is due to too long a cooking treatment, not" turn black and'further the degree of'degradation of the cellulose is considerablyreduced. Thus-thechipsor to the air present in the pores of the cellulosic material ‘being digested and/or to mechanical wear and tear on the cellulose. - other material may be so‘ treated that throughout’ the digestion they are wholly immersed'in the "liquor. " - Many attempts have been made to eliminate‘ or reduce Further, if the atmosphere above the digestion liquor, the degradation which occurs during digestion but With instead of beingpure nitrogen or pure carbon dioxide, con out any substantial degree of success. Thus, for example, tains up to about 2% (the value varies somewhat with experimenters have tried to accelerate the penetration- of 30 the nature of the cellulosic material) of oxygen the same the cooking liquor intothje comminutcd cellulosic vmate effect, namely avoiding blackening and avoiding severe rial, particularly in the case of wood chips, by increasing degradation of the cellulose, is obtained. Increase in the or decreasing the pressure used;.by the use vof changing- . oxygencontent- of the inert gas to 5% brings about a pressurev and'evacuation; by the use ofdiffcrent tempera: tures, as well as» by vaporization (see for example Das Papier, 11, .page 14, (1957); Norwegian Patent No. 54,053; Finnish Patent-No‘; 17,002; and US; Patent No. 12,072,776). 'It has alsoibeen proposed to digest the mate. slight.v browning, of. the} material, while an increase to about 10% causes blackening of the cooking liquor and darkening of the cellulosic material. 35 According to the'present invention, therefore, pulps are produced frOInJligniH-cOntaining cellulosic materials rialwith causticvsoda of various concentrations'in an by digestingnthem with a" cooking liquor while preventing atmosphere of hydrogen, using for example a=preimpreg 40 contactof thecellulosic' material with external gas con— taining more than 5% of oxygen. The term “external In other nation process (Austrian Patent No. 72,881). known processes preirnpre’gnation of the material is _ef-' V‘fected at a- reduced pressure (US. Patent No. 1,025,336‘) :\or is elfected under pressure before the material has gas” ‘is used'in this speci?cation to connote gas in con tact with the outside‘of the cellulosic material and/or in contact with the} cooking liquor and is used to exclude reached a temperature above 110° C (US. Patent No. 1,790,260). ~According-to a still further process, the crude material is‘ subjected. to the action of'the‘ digesting agents after pre-treatment with anaerobic bacteria under pressure (German Patent 235,852), or wood and other the gas contained in the pores of the material since I have determined that the presence of oxygen in the pores of the cellulosic material'exercises no signi?cant effect on ?brous plant materials in a comminutcd state; are sur 50 rounded with gas, e.g. carbon dioxide, hydrochloric, acid. gas or sulfur dioxide, for the.v purpose of dissolving out lignin and similar incrustations and are. then. shaken. the darkening of the cellulose, the blackening of the cooking liquor or the degradation of the cellulose. While steps may be taken as described above to ensure that thewwooduor, other. cellulosic .material remains com pletely immersed in the cookingliquorv throughout the with concentrated sulfuric acid at room temperature and digestion process, it is preferableaccording to the present inventiontto till the remainder of the digestor with inert without pressure (German Patent No. 441,392). The gas. Thesul?te process is’customarily'used to obtain the whitest cellulose and-to obtain the highest quality of cellulose; Accordingly, the process ofith'e present inven tain a greater through-put of the cookers or disintegrators. . tion is particularly valuable in relation to the sul?te di In- addition,» the- degrading eifect of the digestion’ was 60 gesting process. It may, however, equally well be used in acribed to the-action of the air remaining-in the pore the alkali process or in-the sulfate process, it being under spaces'of the cellulosic material and it'Was-hoped by pre stood that the latter twocprocessesv even with the present impregnation to eliminate this air. These attempts, as has invention willnot give'such high-quality cellulose as the objectlof-these processes was, on the'one hand, to obtain a' betterwirnpregnation of the material and, on the-other hand, to shorten the actual digestionprocess soas to'ob previously been stated, have not been'outstandingly suc sul?te process. The invention further includes both the cessful particularly when thecellulosic material is sub 65 customary sul?te process using bisul?te with free sulfur jected'before'or during-the chemical action of the digest; dioxide and‘also the s'o-called"“'neutral sul?te" process. ing agent to'mechanical treatment such as transport of’ As is usual‘ when employing an acid sul?te process thematerial or‘agitation'or mechanical comminution dur-' ' ' ing the cooking (see “Cellulose Chemie,” 16, page 4 " (19735‘), andDasPapier, 10,- page'4" (l'956)‘). ‘ ' ' ' l have found that neither the extent of impregnation of . 7.0. any suitable soluble bisul?te may be used together with free sulfur dioxide, for example bisul?tes of the alkali or alkaline earth metal's'or ammonia, eg. sodium, potas sium, ammonium, calcium and magnesium bisul?tes. 8,070,484 4 ‘J1 The ratio of total S02 to combined S02 may be adjusted of the use of sawdust as a raw material. 'as is usual in the art. it is generally necessary to stir or agitate during the di Using sawdust I have'further determined that given the conditions of the present invention the cellulosic material may be disintegrated or comminuted either before or during the gestion process. Normally a sul?te digestion process operates at a temperature of about 130-140“ C. or in the case of re ‘digestion process without seriously degrading the cellu quiring highly puri?ed pulps at a temperature up to 150° , C. Higher temperatures are not possible in conven~ tional processes because of the severe degradation and loss of cellulose which occur. Using the process of the ing additional celluiosic material gradually forced through 10 present invention it is possible to cook at temperatures up to about 200° C. with consequent reduction in the the pad of chips or other cellulose. ’ ‘lose. Further, the invention can be used in a continu ous digestion process wherein the cellulosic material is pressed against a sieve or strainer and the liquor carry cooking time. Funthermore, since according to the pres ent invention preimpregnation of the cooking liquors Following on the digestion process of the invention wherein contact of the cellulosic material with oxygen is ‘rigorously excluded, I ?nd it advisable to exclude oxy gen in any process of transferring of the cellulosic mate rial from one piece of apparatus to another. Again, in .de?bering the’ pulp or otherwise treating the pulp while in contact with the liquor at fairly high temperature, ‘it is advisable to exclude air or oxygen. Again this may ,be achieved by ensuring that the cellulosic material is continuously submerged in the liquor or alternatively is unnecessary, or at least produces little or no advan tage, such preimpregnation may be omitted, again with resultant shortening of the total processing time. The following examples illustrate the invention but vdo not limit it in any way. In the examples where grind ing is carried out during the digestion a milling auto clave of the type shown in FIGURE 1 on page 5 of the article in Das Papier, vol. 10 (1956), was used. 'the cellulosic material may be blanketed with inert gas. Where in the examples preimpregnation is used the method is that customarily used in the art, namely evacu ation of the autoclave containing the cellulosic material By the process of the present invention good quality cellulose of high D.P. may be obtained. e.g. in the case of processes not using mechanical disintegration, D.P.’s followed by sucking in the cooking liquor, the process of 1200 or above and in the case of processes using me— being repeated as many times as required. The DR of the products was determined by the Kraemer method jchanical disintegration D.P.’s of 900 and above. Inas much as using the process of the present invention, pre (Industrial and Engineering Chemistry, vol. 30, page vious comminution of the cellulosic material does not entail any severe drop of the D.P., the invention permits 30 1200 (1938)) and lignin was determined by the Tappi Table 1 Gas above liquor ______________________ .. Trial number __________________________ __ Oxygen 56 56a Nitrogen 56b Mean 55 55a 1550 Mean value D.P ___________________________________ ._ Not measurable value 1, 264 1, 252 1, 269 1, 262 Lignin content (in percent) ____________ ._ 33. 5 35 34 34. 8 0. 6 0 3. 2 l. 2 Yield (in percent) _____________________ -. 60 62 63 61- 6 50.8 49. 5 52 50. 8 Very Very Very De?bering properties __________________ .. Does not de?ber good good good Appearance of material and spent liquor. Black White Fiber structure _________________ _. ..... -. Destroyed Maintained pH (of spent liquor) ___________________ -_ 0.7 0.7 0.8 0.7 1.8 1.9 1.8 r 1.8 Table 2 Gas above liquor ________________ -_ Trial number ____________________ .. Nitrogen ‘ 53 53a 53b Carbon dioxide Mean 54 54a 54b value Oxygen Mean 52 52a value Mean Value D .P _____ __, _____________________ __ 1, 053 1, 028 1, 070 1l 050 949 ‘380 919 949 425 641 533 Llgnin content (in percent). ...... __-l 14. 8 13. 6 10.8 13. 1 11. 3 12. 6 11. 1 11. 6 25. 6 29. 8 27. 7 Yield (in percent) ............... _. 60 63. 3 62 62 64. 1 (i1. 9 61. 9 62. 7 83 88 85 De?bering properties ............ .. Appearance ofjmaterlal __________ __ Very good Yellowish-white Fibre structure _______ __. ________ __ pH (of spent liquor) ............. _- Very good Yellowish-white Maintained 1.8 \ 1.3 I 1.8 Pulveruleut Brown powder Maintained 1.8 1. 6' 1. 4 1. 5 Destroyed 1. 5 1. 2 0. s 1.0 3,07%),484 6 5. method. In all. cases whole vknot-free wood was used in the form- of chips“ Table.3 _ . Gas above liquor... In‘cooker space: Oxygen Incooker space: Nitrogen EXAMPLE,’ ,I .In the pores: Nitrogen Inthe pores: Oxygen. 5 This ‘example illustrates digestion using different gases above the digestionliquor without “grinding during di- Tmlnumber """ “ 1 58 ' 58a" gestion. D.P ______________ _- Notmeasurable ‘ The wood chips were previously impregnated with 1, 996 ‘ sodium bisul?te liquor containing 50 grams per litre of 10 L. . . p , , igmn content (1n total S02 and 10 grams per-litre of combined 50;. The percent) ________ __ ' 36.5. ratio of chips to liquor was 1:7. After preimpregnation of the chips in‘ they autoclave and bringing the liquor up Yield (in percent)-~ a . 573 _ ‘$332.. ' 1, 942 I 1%?3‘; ' 57 35.2 35.6 I 3.7 _ 62-4, 1, 969 ‘ 63 62-7 10.9 7.3 . 60' 57 ' 53-9 to'1 level, the autoclave w-asclosed and the temperature 15 brought ‘as rapidly as possible .to' 150° C. The cooking time was .10 'hours.= Digging Prop‘ gl‘ggbggt Theresults were obtained as shown Very g°°d - ‘in Table ‘1- ‘ Appearance of .7 Black‘ White Destroyed . Maintained. material ________ 1. EXAMPLE‘ II 20 7 Fiber structure._._. 7 Further trials were carried out using the conditions 4 of Example I withv the exception that grinding was carried PH(0fSDel1t1iqu0r)- 0-'7 out continuously throughout themdigestion process and 0-7 0~7 1-7 . I 1-8 L75 _ - the cooking time was 5 hours. The results obtained are 25 These trials demonstrate conclusively that the presence of Shown in Table; 2; oxygen in‘ the pores" exercises'no substantial‘ degrading Comparison'of the results‘ obtained in Examples I and 11 using. nitrogen as the inert gas-above the digestion liquor a?ion on the cellulose While_the' Presence oflyoxygen in the space'apov? the coQkmg hquor reduces the DR to a shows that simultaneous grinding reduces the DR some- value at whlch 1t caimot what and‘also considerably'reduces the time takenin 30 . . g . . . . The- results‘ °bt‘?m?d.m ital“ 57 and-‘57a-of pliable may be compared w1th the results obtained in trials 55, digestion. 'In all-cases using inert gas the DP. 1s mamtamed at a commerclany acceptable value- 55a and. 55b‘ of Table ,1 inExample. I’ The On1y.di?er._ ence between‘ the conditions in the two sets‘ of trials‘is that in Table 1 preimpregnation is used whilst in Table 3 EXAMPLE III This example'illu'strates the negligible'etfect of 'gas in the pores of. the wood chips. ‘It compares the digestion under oxygen of 'wood‘ch‘ips containing nitrogen in the pores with the digestion under nitrogen of wood chips containing oxygenvinthe pores. Theairin the metsPred- . -. 3 35 there is no preirnpregnation. It-will be seen that'very short extension of the cooking time of the trials of Table 3 gives equivalent results .tothoseobtained in Tablel.v This Very Short increase in Cooking time is more than Offset by the time used for impregnation in Example 1 ‘10 EXAMPLE 1V, ores in the . former case wasdisplaced by repeated evacuation. in the _ , . . . . Thls examp1e ‘demonstrates ‘that much'hlgher cooknfg autoclave-l and ?lling with nitrogen. In each case the temperatures may be usedzm the PI-esent pr-ocess- than-m . g . _ , . _ conventional processes. The. conditions are 1dent1cal with (fooking 11ml"? was the same as .111 Example'l’ tne'wok' 45 thoseused -in.Examplet-1 (using nitrogen-above the cook mg ume“wa_s 10 hours; th? cookmgr'temperature150° Cing liquor) with theiexception of the cooking temperature and the ratio'of wood chips' to cooking liquor was 1:7. The chipYWeTe' not Preimpreghatedi withithe Cooking which; wasv 200*? C_I andthe cookingtime whichvaried from 11/2 to; 21/1; hours. The results obtained areas liquor.‘ Ther'esults arevas follows: .follows:. I Table 4 Digestion time in hours _____ __ Trial nuniber ............... _. 1% 74 74a 74b 1% 740 Mean so I Llgnin content (in percent)..- 21.8 Yield (in percent) __________ .- 70.5 809. Mean 73 value D.P ________________________ -- 1,062 1,059’ 1, 032 1, 033 1.0116 20.7 20.4 75' 2. value j 956 955 955 2%. 73a 73b- 73c. 73d. Mean/78.. 78a. 778a ~78i .72 Mean ’ ' 859 955 920 value 74 73.4 60.3 62.5 6114 v62 ' 997 ‘899 ', 626‘ 493 526 '405 19.2 v20.5 16.8 14. 5.. ,15;6 iGA' 16 16.3 16.3 16.9 74 _ 16.4 4 5.2 _ 5 value 653 532 ‘ 52a 4:9 :?il 59 62.5 62.5 ‘58v 6028 46:5 45.8 46.5 45.5 48.8‘ De?bering properties _______ -. Fair Very good Very good Already cornminuted Appearance of material _____ ._ White White Yellowish-white Bright yellow Fibre structure _____________ _ _ Maintained Maintained Maintained Destroyed pH(oispe11tliquor) ________ ._ 1.7 1.8 1.6 1.7 1.7 1.6 1.8 1.7 1.5 1.6 1.7 1.6 1.5 1.6 1.4 1.5 1.6 1.5 1.7 46.6 1.5 8,070,484 7 8 Comparison of these results with those obtained in Example III (Table 3), using nitrogen above the liquor, shows that at 200° C. approximately the same yield is taneously subjecting the cellulosic material to mechanical disintegration and to digestion with an acid sul?te cook ing liquor without previous impregnation with said liquor, obtained in 1% to 2 hours as is obtained after 10 hours under an atmosphere which consists, in addition to con at 150° C., while the lignin contents of the products do 5 stituents evaporated from the liquor itself, of inert gas not differ greatly. Extension of the cooking time to 21/2 hours reduces the D1’. considerably at this temperature. containing not more than 5% of oxygen, in a closed digest-or and under the autogenous pressure developed in the digestor at the digesting temperature. 3. A process for the production of pulp from lignin Accordingly, at 200° C. digestion times of 1%to 2 hours or a period not greatly in excess of 2 hours may be used. Trials were further carried out using above the diges- 10 containing cellulosic material, which comprises simul tion liquor nitrogen containing 2%, 5% and 10% of taneously subjecting the cellulosic material to mechanical oxygen. The reaction conditions were 200” C., together disintegration and to digestion with an acid sul?te cook _with mechanical treatment throughout the digestion, i.e. ing liquor at a temperature between 150° and 200° C., the conditions were as severe as possible. With 2% of without previous impregnation with said liquor, under an oxygen in the nitrogen gas the color of the product and 15 atmosphere which consists, in addition to constituents of the spent liquor was very similar to the case when evaporated from the liquor itself, of inert gas containing nitrogen alone was used above the reaction liquor. Using not more than 5% of oxygen. 5% of oxygen in the gas, there was a slight browning of 4. A process for the production of pulps from lignin the material while with 10% of oxygen in the gas the containing cellulosic material, which consists in simul cooking liquor blackened considerably and in addition 20 taneously subjecting the cellulosic material to mechan the material itself darkened. These trials demonstrate that at above 5% of oxygen in the inert gas there is a tendency to darken both in the liquor and in the material itself. ical disintegration and to digestion with an acid sul?te cooking liquor without previous impregnation with said liquor, under an atmosphere which consists, in addition to constituents evaporated from the liquor itself, of inert EXAMPLE V 25 gas containing not more than 2% of oxygen. 5. A process for the production of pulps from lignin This example demonstrates that if the chips are wholly containing cellulosic material, which consists in simul submerged in the liquor throughout the digestion process taneously subjecting the cellulosic material to mechan then results are obtained very similar to those using distintegration and to digestion with an acid sul?te normal digestion conditions but having nitrogen or other 30 ical cook-ing liquor without previous impregnation with said inert gas above the liquor. The cooking liquor and other liquor, under an atmosphere which consists, in addition conditions were the same as those in Example 11 with to constituents evaporated from the liquor itself, of sub the exception that trials were carried out both with and stantially pure nitrogen. without simultaneous grinding, and to ensure complete 6. A process for the production of pulps from lignin submersion of the chips the ratio of chips to liquor was 35 containing cellulosic material, which consists in simul 1:21. The results obtained were as follows: taneously subjecting the cellulosic material to mechanical Table 5 disintegration and to digestion with an acid sul?te cook ing liquor without previous impregnation with said liquor, With _ grf?gd' _ under an atmosphere which consists, in addition to con Wlthwt grindmg 40 stituents evaporated from the liquor itself, of carbon dioxide. Trial number _____ __ M 30 3 4 6 5,, Mean 7. A process for the production of pulps from lignin value D-P -------------- -- 1,186 1,950 2,040 2,053 1,955 containing cellulosic material, which consists in simul 45 taneously subjecting the cellulosic material to mechanical 2,009 ' Lignm content (in disintegration and to digestion with an acid sul?te cook ing liquor containing a bisul?te whose cation is selected percent) -------- -- 10 13-7 14 14-5 13'9 14 from the group consisting of sodium, potassium, ammo Yie1d(inpercent)___ 59_@ 69 70 71 70 70 nium, calcium, and magnesium and which contains free De?bering very Fair Fair Fair Fair Appearance of White properties good ' 50 sulphur dioxide, thedigestion being carried out without previous impregnahon with said hquor and under an atmosphere which consists, in addition to constituents Yellowish-white evaporated from the liquor itself, of inert gas containing material not more than 5% of oxygen. Flber structure.--" M_ain- Maintained tamed _ . I claim: , , _ . . 55 - ' . . 1. A process for the production of pulps from lignincontaining cellulosic material, which consists in simul- 60 _ ' References Cited in the ?le of this patent ~ UNITED 1,587,631 1,903,962 STATES PATENTS Clark _______________ __ June 8, 1926 Dreyfus _____________ __ Apr. 18, 1933 taneously subjecting the cellulosic material to mechan ical disintegration and to digestion with an acid sul?te _ FOREIGN PATENTS cooking liquor without previous impregnation with said 201,259 Germany ------------- -- Jan- 5, 1907 liquor, under an atmosphere which consists, in addition . to constituents evaporated from the liquor itself, of inert _ OTHER REFERENCES gas containing not more than 5% of oxygen. 55> Scheller: The In?uence of Elementary and Active Oxy 2. A process for the production of pulps from ligningen on Cellulose on the Basis of Viscosity Measurements, containing cellulosic material, which consists in simul- TAPPI Series XXV, pages 551-555, June 1942.