NZ204262A - Kraft and alkaline pulping processes using synergistic composition to enhance pulp yield - Google Patents

Description

204262 Priority Date(s): JL- C S-2- Complete Specification Filed: /.7". £*. ?.? Class: P.?. s8 OCT 1986 " Publication Date: ...r: P.O. Journal, No: ...

SUBSTITUTION OF APPLICANT UNDER SECTION 24 Ce-ft*V£lA=rioM • NEW ZEALAND PATENTS ACT, 1953 No: Date: COMPLETE SPECIFICATION IMPROVED PULPING PROCESS & COMPOSITION FOR ACHIEVEMENT OF SAME ^T^ftE&KH>ftPER--e0MPANY, a corporation incorporated under the laws of the State of New York, United States of America, of 237 Park Avenue, New York, N.Y. 10017, United States of America, hereby declare the invention for which we pray that a -patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: (followed by page -la-) 2 042 6 2 IMPROVED PULPING PROCESS AND COMPOSITION FOR ACHIEVEMENT OF SAME This invention relates to alkaline pulping and in particular 5 to the use of additives in alkaline pulpinq to increase pulp yield.

Alkaline pulping includes processes of pulp manufacture in which plant materials containing cellulose fibers are treated with aqueous alkaline solutions. Since the most common alkaline pulping process is the sulfate or kraft process in which the wood is treated 10 at temperatures above 160° C with a solution containing sodium sulfide and sodium hydroxide, the preferred embodiment of this invention will be set forth with resDect to the kraft process, although it has application to any form of alkaline pulping.

In the conventional kraft pulping process, lignocellulosic 15 materials, such as wood chips, are treated in a digester with a fresh cooking liquor (white liquor) consisting of an aqueous solution of sodium hydroxide and sodium sulfide under a certain set of conditions of temperature, pressure and time. Upon completion of the cooking schedule, the resulting pulp is washed to remove spent 20 chemicals and dissolved wood substance. The washed pulp is screened and/or refined to remove or disperse undercooked material. The pulp is stored until drawn as required for the direct manufacture of paper products, or may be subjected to conventional bleaching treatment for the manufacture of bleached qrades of paper. 25 The spent liquor from the pulping process is referred to as weak black liquor, which contains degraded and dissolved wood constituents and inorganic salts. This liquor is further processed to recover chemicals and energy. A portion of the black liquor may be used to adjust the volume and concentration of the cooking liquor. 204262 The objective of the pulping process is to chemically degrade and dissolve the lignin matrix, while preserving the carbohydrate fraction. Lignin is a high molecular weight polymer which gives wood its structural rigidity by holding the cellulose fibers together. During the course of delignification in kraft pulping, other components of the fibrous raw material are dissolved to a degree determined by the process conditions. Ideally, pulping should be conducted in a way which dissolves lignin selectively, with no dissolution or degradation of cellulose or other carbohydrate materials. There is no process which achieves this total objective.

A number of chemical additives and modifications of the pulping liquor composition have been used in the art which achieve some degree of pulp yield enhancement. In any discussion of pulp yield improvement, it should be remembered that the objective is to increase the yield of components other than lignin. It is entirely possible and common practice to increase yield by terminating the pulping reactions at an earlier stage, thus retaining more of the starting material including lignin. Yield improvement via this method involves a trade-off between yield and product quality. In practice, for any end product, there is a limiting residual lignin content above which product quality becomes unacceptable.

Among the additives and modifications in the art which have achieved higher yield at equal lignin content are polysulfide, hydrogen sulfide pretreatment, and a number of other agents which stop the "peeling reaction" by which carbohydrates are degraded and dissolved. Much interest has been generated by the discovery that anthraquinone, added to a kraft pulping solution, accelerates the dissolution of lignin and suppresses the dissolution of carbohydrates. This discovery is found in U. S. Patent No. 4,012,280. It is believed that anthraquinone functions as a catalyst, cycling between a form which accelerates the delignification process and a form which stabilizes the carbohydrates from alkaline degradation. While the use of anthraquinone in alkaline pulping represents an improvement in the efficiency of pulping by providing for a yield enhancement per given lignin content, anthraquinone does not provide for complete carbohydrate protection. 204262 U. S. Patent Nos. 4,115,186 and 4,080,248 disclose that molecular oxygen and a quantity of a divalent or monvalent metal salt, especially calcium hydroxide in the former case and sodium carbonate in the latter instance, will bleach pulp and improve 5 the overall pulping operation.

While the aforementioned patents do not specifically teach pulp yield enhancement by the addition of calcium salts and an oxidizing agent, U. S. Patent Nos. 3,695,994 and 3,384,533 teach that input of molecular oxygen and concurrent addition of calcium 0 chloride will act to increase pulp yields in a calcium deprived wood pulp manufacturing system where the need for a stabilizing agent exists.

Recently a paper was presented at a scientific convention in Europe attended by research people from the paper and pulp 5 manufacturing industry which underscores the unexpected and quite beneficial nature of the present discovery. (Johnson, Eckert and Mark -- Factors Influencing Performance of Quinone Promoters in Alkaline Delignification of Douglas Fir -- Stockholm, Sweden, International Symposium on Wood and Pulping Chemistry - The '0 Ekman Days, June 1981). In the text of this publication (Figure and commentary thereon) the authors discuss complexes of 1-hydroxy-anthraquinone with copper, cobalt, nickel and magnesium. These complexes were prepared by Johnson et al. in a stated effort to enhance the catalytic activity of the 1-hydroxyanthraquinone in 5 alkaline pulping. The conclusion expressed in their report was that such complexes showed no improvement over the use of 1-hydroxyanthraquinone alone, which in itself is relatively ineffective as a pulping catalyst.

Hence, at a point in time contemporaneous to our disclosure 0 of a new composition for enhancement of the yield of pulp derived from lignocellulosic material the art attests to the fact that analogs of the composition of the invention are shown not to function in the enhancement of pulp yields achieved by the present invention. This sart is actually leading those skilled in the art away from our dis-;5 covery of the unexpected and beneficial effects obtained by the use of certain metal salts with anthraquinone. 204262.

With the aforesaid background in mind, we will now describe in general terms and in specific detail the objects and purposes of our research effort as well as how: it was conducted and the unexpected and beneficial improvement in pulp manufacture which resulted therefrom.

- N r > *2 1 MAR 1986 "Is It is the principal object Of our invention to provide a new and unique pulpina catalyst composition whose chief attribute is the unexpected enhancement in yield of puId from the raw material.

It is a very specific object of the present invention to provide a new and unique catalyst composition of anthraquinone and a divalent metal cation selected from the group of calcium, barium, magnesium, strontium and zinc.

An ancillary object of the invention is to provide a new and improved process of manufacture of paper pulp from a plurality of available raw materials, and most particularly from pine wood chips, in a manner which permits the use of presently available plant facilities without major modification.

More specifically, the process of this invention comprises treating lignocellulosic material in a digester with an alkaline pulping liquor containing anthraquinone, a metallic salt selected from the group consisting of calcium, barium, strontium, magnesium and zinc, and spent pulping liquor diverted from the outflow of the digester.

These and other related objects will become clear upon review of the following specification of the invention and of the several specific examples of embodiments of the invention and the data and results and conclusions derived therefrom.

Several figures of drawina will be employed to further illustrate the process modification which has led to the improved result. Reference will be made to these figures during the course of the general presentation of the basic concept of the invention which will key into the working examples of the new process.

Figs. 1 and 2 are graphs showing the effect of calcium hydroxide addition on the kappa-yield relationship of the kraft pulping process with anthraquinone; 204262 Figs. 3 and 4 are graphs showing the effect of kraft black liquor fill back on the magnitude of yield increase obtained from kraft/anthraquinone and kraft/anthraquinone/calcium hydroxide pulping; Fig. 5 is a graph showing the effect of calcium hydroxide 5 addition on the kappa-yield relationship of the soda pulping process with anthraquinone; Figs. 6 and 7 are graphs showing the effect of employing metal cations other than calcium with anthraquinone in alkaline pulping; and Fig. 8 is a graph showing the effect of employing metal cations in alkaline pulping without anthraquinone.

I The present invention concerns itself with the discovery that the yield-enhancing ability of anthraquinone in alkaline pulping 15 can be increased by the simultaneous addition of a divalent metal salt which enhances the effectiveness of anthraquinone in preserving carbohydrates during alkaline pulping and thus provides for an increase in pulp fiber yield by several percentage points. By comparison to the conventional kraft pulping system, the combined effect of 20 anthraquinone and a divalent metal salt results in significant pulp yield increases. Since the addition of a divalent metal salt alone „ to a kraft cooking liquor has little to no effect on pulp yields, the invention calls for the combined use of the anthraquinone catalyst with the divalent metal salt.

The amounts of the various components used in the composition of this invention are not narrowly critical and can range, for example, between about .01 and 1.5 percent by weight, based on the lignocellulosic material treated, of anthraquinone, between about .01 and 10.0 percent by weight, based on the lignocellulosic material treated, of a metallic salt selected from the group consisting of calcium, barium, /SqI!£ strontium, magnesium and zinc/, and up to 50 percent by volume of the spent pulping liquor diverted from the outflow of the digester. There is no upper limit to the quantity of anthraquinone or metallic 204262 salt, but as a practical matter the point of diminishing returns is reached when the indicated limits are exceeded. In respect of the lower limits, there should be sufficient anthraquinone and metallic salt to provide an increase in yield sufficient to warrant the use of 5 these additives.

Preferably, calcium hydroxide is the divalent metal salt and the amount of the anthraquinone catalyst and the divalent metal salt employed is generally in the range of 0.05 - 0.15% on wood (oven-dried basis) for the anthraquinone and within 0.1 - 0.5% on O.D. wood for the calcium salt. The relative amounts of these additives may be varied to some degree without detracting from the additional benefit in yield obtained through the combined use of these additives, although the magnitude of the yield increase will vary. For optimum results, black liquor fillback, i.e., spent pulping liquor diverted 15 from the outflow of the digester, is employed with the additives. An additional but small yield enhancement is obtained when black liquor fillback is practiced and this result is attributable to the increased solubility of the calcium salt during the early stages of the pulping schedule. Black liquor fillback is a normal practice for 20 mills employing batch digesters and is used to the extent of 10-50% by volume of the total cooking liquor to obtain the desired liquor to wood ratio without adding additional water. Thus, when employing the additives called for in this invention, black liquor fillback provides the added benefit of solubilizing the metal salt.

The nature of the divalent metal cation applied with the anthraquinone is apparently critical, as evidenced by the finding that other metal cations were either not as effective or completely noneffective relative to calcium in enhancing the yields obtained when anthraquinone was employed. For example, the monovalent lithium 30 cation and the trivalent aluminum and boron cations showed no improvement in the pulp yield over use of anthraquinone alone, while other divalent metals showed yield enhancing properties. Barium, zinc and, to a much lesser extent, magnesium and strontium were effective in enhancing pulp yields when applied with anthraquinone to the kraft cook-35 ing liquor. Of the metal cations evaluated, calcium was most effective when comparison is based on an equimolar addition of the metal cation. 204262 It is anticipated that quinones other than anthraquinone, such as tetrahydro-anthraquinone, that function like anthraquinone in promoting the delignification of lignocellulose, would also be further enhanced in their ability to catalyze the stabilization of carbohy-5 drates during alkaline pulping by the simultaneous addition of the calcium metal cation. Compounds which function in an equivalent manner like anthraquinone include those which oxidize the carbohydrates and reduce lignin intermediates formed during pulping and thereby prevent the lignin intermediates from condensing during pulping. Such 10 compounds include cyclic keto compounds as disclosed in U. S. Patent No. 4,012,280. The source for enhancement of anthraquinone by the divalent metal and its versatility for use with similar quinones is believed to be related to the ability of calcium to catalyze the rearrangement of dicarbonyl sugars into alkali-stable aldonic acids. 15 It has been demonstrated in the literature that the alpha-dicarbonyl sugar, glucosone, when treated with Ca (OHis converted primarily to mannonic acid, while treatment with NaOH gives preferentially arabin-onic and erythronic acids which are not as stable as mannonic acid in an alkaline medium. (Lindberg, B. and Theander, 0. Acta Chem Scand 20 22 (1968) p. 1782). In the case of anthraquinone catalyzed yield increases, it is believed that, as part of a cyclic mechanism, anthraquinone catalyzes the oxidation of the reducing end-groups of carbohydrates to form dicarbonyl sugar intermediates which then, in the presence of alkali, will rearrange to form a series of aldonic acfds. 25 The formation of these acid end-groups stabilizes the carbohydrates from degradation that would otherwise occur. These acids, which vary in stability during the pulping process, can break down and re-expose the carbohydrates toward alkaline degradation. The ability of calcium, and apparently other divalent metal cations, to react with these 30 dicarbonyl sugar intermediates to preferentially give the more alkali-stable acids, is thus believed to be the cause of the yield enhancement. Therefore, yield increases catalyzed by quinones, other than anthraquinone, which would proceed through similar chemical pathways, should be similarly enhanced by the presence of calcium.

It should therefore be noted that while the emphasis of this invention rests with the combined use of anthraquinone and calcium hydroxide, the scope of this invention includes: 2042 (1) The use of anthraquinone with calcium hydroxide but including calcium salts such as CaCl2- (2) The use of anthraquinone with other divalent metal cations including zinc, barium, strontium and magnesi um. (3) The use of the metal cation from the above list with a qui none, other than anthraquinone, which in itself will show yield-enhancina DroDerties.

The tabulated data in the following Table 1 illustrates the relation between pulp yield and kappa number under the kraft and soda pulping processes. The data is keyed to the several examples set forth hereinbelow as well as to the related curves on puld yield improvement illustrated in the drawings. The data illustrates the reaction conditions for several pilot plant runs related to varied reaction conditions within either the kraft or soda process of pulping both unmodified or modified in the manner of the present invention. The process conditions for each run relates to a pulp yield vs. kappa number and can be compared to a control where the additive quinone-Dromoter combination sought to be patented was employed.

Those runs marked "kraft" in Figure 1 and Example 1 were, for instance, the control runs. In a similar manner the runs marked "Kraft/Ca" and "Kraft/AQ" were control runs where each of the components of the novel composition claimed was singly employed.

The value in the tabulation marked "Kraft/AQ/Ca" represents the process runs of the invention and the improved pulp yield conditions. 204262 C sC CD c irs •e c c ^ c C- ^ O- K c c c «e e> %r> C w» e-«c *c C "5 c w o 0 IN >■; c — ^ »e ^ ^ «- &■ %c •r» *»•^ tr\ «} ^ n p> r-> c c *- ^ »N © CC fr- l-> <£ ^ *v © « »r»r^«© fTlc^^rw K ( %C ^ r> M ». M K e e *» *•» >£ n n c c o ^ C pi N «J C ^ ^ ^ ^ tr\ »r\ *r> »r> n c C c ^ ^ ^ ^ c c c ^ ^ c e k c *► < J? *zr- fe -to *1 9i u; t •• c ftS — CI. "'■sl* — to n | — qj^I e ^ *.• o «— TI ^ ffc = £| C c »r .r «s «e •r- E ©©CCCCCC O c C fc^> — c e e e c e c c ^ c c c c c ©fee **. V *r> © e c < c «e c c c *c « 4 c c «e <e c c •? *r c •? <r «t < «* *r «e «e < «e *;*?«: c i. •c C c u a ^ r »*> c> e c- © — c c — — ~4 <M 01 J —< K k. w C «; t ft b w b ^ k w W «* *W Sp c © © — -« c © — — — — — (vfvfvftNKrvrv i I I l l I i < « * K •* U u. <<<<<<<< «nc«ftf, e« <t ^ r e «e ^ c e» r- © © © © c c c — — — — f* fv *v ew I I \ I I I i »- t- t- t- t- *» *-~ - * 5 U k <«»*«*••« u> u u> u u> u> u W W W S„ o ©■ © & © © & <<<<<<< « n ft s • c e b l» b W W w tf tt K K K K * ** rv 0 X 0 #v c t 1 c H 9 e ri c o N • c e 1 c t c K fcTt wa K « X c U • W © i *■> «■ ( e K k. © r K N < u Cook Type Cook ' 2321 K/Arj/c.i++ 2 37.2 K/Af)/ C.1++* Fig 2 2323 K/M)/Cn++ Ex. 2 2331 K/AQ/C.-H+ 2332 K/AQ/CA++ 2333 K/AQ/Cn-W- 23«2 K/AQ Fig 231A K/AQ 2 2315 K/AQ EX . L 2316 K/AQ 2317 K/AQ/OL f 2310 K/AQ/M.

Fig 4 2319 K/AQ/OL Ex. 3 2320 Km ft 2336 Kraft Fig 2 23'.1 Kraft EX. 2 2 3ft 0 Kraft 2392 T.iblc I - cont'd fulplnfi 0.1 tn Illustrated In F)j>tirc Mi nutes Temp *F Time tip/ft t Z AA 3'-ft 60/ 30 3ftft 60/'• 5 y< ft 60/35 1.5 v> ft 60/2 5 3ft ft 60/20 3ft ft 60/30 3ft ft 60/22 3ft ft 60/25 Jhlt 60/35 3ft ft 60/ft5 3ft ft 60/20 y>t> 60/25 .6 3ft ft 60/20 .6 3ft ft 60/25 .6 3 f.r, 60/30 17 3 ft ft 60/ftO 17 3ft ft 60/30 17 3 ft ft 60/23 17 f shown in Fig. 4 of Drawing as Kraft/AO points on curve 2 *- Example 2 1iPJPi % Yield Z ReJccts 7. Ash 77.6 55.2 .ft 1.00 63.3 52.91 .53 1.88 66.7 53.18 1ft. 1 1.00 05.2 56.8 .5 1.90 9ft. 6 59.6 39.2 2 .02 77.7 56.32 19.5 90 90.0 50.2 3ft. 3 00.9 55.16 21.7 1.09 72. 2 53.30 .3 0.99 6ft. 2 52.06 9.9 0.77 91.3 57.61 '.2.6 1.31 75.9 56.96 19.0 1.11 05.7 56.03 32.2 1.26 79.9 5ft. 95 22 1.01 00.2 53.90 .3 0.97 6ft. 3 51.0 6.63 0.06 79.5 53.96 19.9 1.60 91 56.0ft .5 1.09 N) showing lack of eEfect of fillback o 4* N) O Is) X 5 ^ ^ « X >>>>>> O O O O iO o o n n o o n u u u ci a tttttt 9 3 3 CI 3 9 c- c- c- c- r- c- w 1 x H* td U) ^ ^ ,-x .t ^ X >>>>>>> o o o o o o o o ci o n <■» n o 'J i) O ^ 4 tt )> ttttttt w i x >— N4 M M N> Nl M N u u g u u u u O a -j o u u u u u u U» <«» U» <—» 1 u u 3 -* •* *3 C* S\ O T* c* 3* o o o o o 9 o a 9 9 9 9 9 "■*S.

*■** *■*«» -X* h- iNi LJ fSJ rsi Ui rs» SJ U» c» <w o o W* N) o 9 v» W* »w* 9 *3 r» .9 i ^ = c P ^ n- p— 3 A" 3 C9 9 n n o r+ 3 V W V ^ V« ^ 3> |J1 ui ^ ^ wi w« u* \ CI X 31 3 T3 v-» fl) u> O M3 >J CS "W Iji CJ V* O I- ^ UJ -J Lrt ^ CJ -s* o o ^ OS ^ ^ a s> ^ «w V" a* U M U ^ U1 V< m Ui wt Q 4 £> U ^ N N ^ 9 U O < fi* O* i* ' ui t/ ^ ui </i C9 <4 9 U M Ui <4 fs» 08 U O > O 33 -g £+<*/•>& $• ^ k* *-««-» IS* *» P- *— C» O ^ V* O CD U M U* ^ C» -LL- Z9ZP0Z O»ok Type Cook t Temp *F S/AQ/Ca+-HIL 2375 366 S/A(J/C.i W-M, 2396 366 S/AQ/Ca++/0L Fig 4 2397 3'.ft s/Aq/ca-w-nt Ex 5 2390 3'.'.

S/AQ/CaWOL 2399 366 S/AQ/Ca++/0l. 2600 3'>'.

S/AQ/Ca++/nb 2605 366 S/AQ 2601 366 S/AQ 2'<07 366 S/AQ Fig 4 2603 3'i'i s/Aq Ex 5 2600 366 S/AQ 26 17. 366 Soda 2 '■ 0 7 366 Soda Soda Fig 4 Ex 5 2609 2613 3'<6 366 T.il»Jc T. - cont'd fulplnp, Data Illustrated In rip.urr 5 Minutes Time up/.it 2 AV\ 60/30 17.6 60/60 17.6 60/6 5 17.6 60/50 17.6 60/55 17.6 60/60 17.6 60/70 17.6 60/60 17 60/70 17 60/60 17 60/50 17 60/36 17 60/150 17 60/100 17 60/100 17 Example 4 Kapjra %Yleld Z Rejects 92.7 57, ,96 29.6 00 ' 56 .6 .7 02.9 55. ,53 .3 79.3 '-. ,69 16.63 76.6 53. ,6 12.96 72.1 52, .75 .1 63.6 51, .21 7.90 75.1 52, .06 .0 69.9 50, .96 .3 91.7 56.4 27.6 03.9 <- .39 .19 100 56, .96 31.7 70 69, .1 105.5 51. .52 .97 9 6 52, .07 13.08 NJ O fO & N> Table I - cont'd Pulping Data Illustrated tn Figures 6,7 ,8 _ Exampleg 5 and 6 Cook Type K/AQ/Hg^/BI. pig. 6 K/AQ/Mg /BL. Ex. 5 K/AQ/Zn£*/BL Same K/AQ/Zn /BL K/AQ/Sr^/Bl, K/AQ/Sr^/BL K/Ca4^ K/Ca4^ K/Ca-^ K/Zn++ K/Bn"H' K/AQ/B+++/BL K/Aq/B"w't"/BL K/AQ/AL+++/nL K/AQ/AL^/BL K/AQ/LI+/BL K/AQ/U+/BL K/L1+ K/AQ/Ca^/BL K/Aq/Ca++/BL K/AQ/Ca^/BL K/AQ/Cn^/BL K/AQ/Ca^/BL K/AQ/Ca+^/BL K/AQ/Ba^/BL Fi9 6 K/AQ/Ba'^/BL Ex* 5' Same Fig 8 Ex. 6 Same Fig 7 Ex 5 Fig 8 Ex. 6 K = Kraft S = Soda CooV ff Temp °F Minutes, Timc/Up/At 7. AA Kappa ?Yleld 7. Relects 7. Ash 2m 344 60/30 .6 73.4 54. ,1 16.6 1.09 2363 344 60/30 .6 75.6 54. ,79 18.4 1.07 2339 344 60/30 .6 76.5 55, .98 .9 1.89 2340 344 60/30 .6 78.5 55. .91 22.3 1 10 2368 • 344 60/30 .6 70.3 53, ,73 13.6 1,8? 2369 344 60/30 .6 62.3 52. .3 .68 1.59 2347 344 60/30 17 87.2 55.6 22.8 1.60 2383 344 60/40 17 72.4 53.3 .4 1.52 2384 344 60/35 17 74.4 53. .08 .78 1.57 2345 344 60/30 17 93.7 56, ,1 27.2 1.66 2366 344 60/30 17 80.4 55, ,2 .4 2.20 2359 344 60/30 t5.6 73.8 53, ,84 17.71 1.04 2360 344 60/30 .6 77.8 54, ,98 18.6 1.11 2414 344 60/25 17 74.8 54, .35 21.0 1.1 2415 344 60/20 17 88.9 57, .33 29.8 1.55 2361 344 60/30 .6 74.1 53.45 19. 1 11 2362 344 60/27 .6 72.2 53, ,87 .5 1.06 2363 344 60/30 17 74.6 53, ,06 14.93 0.93 2324 344 60/45 .6 53.3 52. ,28 7.1 2.01 2325 344 60/25 .6 74 56. ,04 18.3 2.01 2326 344 60/35 .6 61.8 53, ,36 .4 1.85 2327 344 60/20 .6 70.7 54. ,86 14.9 1.84 2328 364 60/17 .6 95.5 59. ,6 40.5 2.21 2330 344 60/20 .6 88.7 58. ,2 33.4 2.26 2337 344 60/30 .6 63.7 54, , I 11.8 3.16 2338 344 60/27 .6 75.2 56, ,1 18.1 3.06 AQ = Anthraquinone BL = Black liquor fillback Ca = Calcium AA = Active Alkali CO I K» o ■fSfc M O h»> 20426Z EXAMPLE 1 EFFECT OF A CATALYST COMPOSITION OF ANTHRAQUINONE AND A CALCIUM OXIDE PROMOTER ON A KRAFT PULPING PROCESS To illustrate the enhanced effect of the new catalyst combination on the operation of a kraft pulping process, a trial run was made on a pilot plant digester employing the new method.

This Example will serve to illustrate the best or preferred mode of operation of our new process of pulping. 17000 wet grams of Southern pine wood chips having a moisture content of approximately 4'8% by weight i 3 charged to a 2-1/2 ft tumbling digester. The wood chips had been screened and thoroughly blended. Chips greater than 1-1/8" and less than 3/16" were rejected. To the digester is added: a) 33.3 liters of conventional kraft white liquor having an active alkali concentration Of 42.9 gpl with a 29% by weight sulfidity; b) 3.5 liters of kraft black liquor, obtained after soap skimming, and having a solids content Of 25? by weight and a composition of approximately 5.3 gplt NaOH a Na^O and 10.7 opl Na^S as Na^Ojc) 8.73 q anthraquinone;and d) 61 a lime (CaO). The anthraquinone is added to the digester charged with wood chips followed by the mixture of lime in black liquor and then white liquor. Taking into account the wood moisture, the total volume of liquor is 45 liters corresponding to a liquor- to-wood ratio of 5.2.

The digester is heated to a temperature of 344°f in 60 minutes and held at that temperature for a predetermined length of time (10-70 minutes) depending upon the target kappa number. Upon completion of the cooking cycle, the wood chips are pressure-blown into a "blow tank" then washed.

Pulp yields from this procedure were 2-3 percentage points greater than that obtained from kraft cooks which employed no additives, and 1-1.5 percentage points greater than kraft cooks where anthraquinone was added as the sole additive.

Ouite unexDectedlv, the addition of the anthraouinone-cal-cium oxide combination does what each of the individual components actinq bv itself is unable to accomplish. The addition of calcium 1 hydroxide or calcium oxide to the white pulping liquor do ,7 204262 increase pulp yield to any significant degree, nor does the increase in pulp yield achieved by use of a known anthraquinone catalyst alone reach the synergistic point achieved by the combination. The addition of the mixture appears to inhibit the formation of arabinonic and erythronic acid end groups and induce the formation of mannonic acid end groups. Mannonic acid is considerably more alkali stable and is believed to retard "peeling" or alkali degradation of the carbohydrates during the cook and hence increase pulp yield.

Example 2 EFFECT OF CALCIUM HYDROXIDE ADDITION ON THE KAPPA-YIELD RELATIONSHIP OF THE KRAFT PULPING PROCESS WITH ANTHRAQUINONE The effect of calcium hydroxide as a pulping additive on the kappa/yield relationship of kraft and kraft/anthraquinone pulping processes is illustrated in Figures 1 and 2. The application of anthraquinone was 0.1% by weight on O.D. wood and the amount of calcium hydroxide added was 0.5" by weight on O.D. wood as Ca++. pulping was carried out in a 2-1/2 ft^ pilot plant digester using about 37-40 lbs. wood chips with a moisture content of 50% W/W. The data presented in Figures 1 and 2 represents the pulpina results obtained from two separate Southern pine wood samples. The pulpina conditions employed and the results obtained are presented in Table 1.

For both cases, the yield-enhancing ability of small levels of calcium hydroxide is clearly demonstrated. Pulp yield increases of 2-3 percentage points over the kappa range of 50-100 are obtained relative to kraft pulping, while yield increases of 1-1.5 percentage points are obtained when anthraquinone alone is applied.

From a comparison of the results obtained from the pulping of the two separate wood samples, it is noted that the total net yield increase obtained per given lignin content differed somewhat.

Such differences in final yield obtained among separate wood samples in alkaline pulping are quite common and any differences in the net yield increase obtained is attributed to inherent differences in wood chemistry. It should be noted that the yield increases obtained from anthraquinone addition alone also differed slightly between the 204262 two separate studies, as did the kraft pulp yields when comparison is made at a given kappa number.

EXAMPLE 3 EFFECT OF KRAFT BLACK LIQUOR FILLBACK ON THE MAGNITUDE OF YIELD INCREASE OBTAINED FROM KRAFT/AQ AND KRAFT AQ/Ca PULPING Using the same pulping conditions as in the preceding example, pulping experiments were carried out using the additives with and without black liquor fillback. For cooks with black liquor fillback, the amount of black liquor employed was 7% v/v of the total cooking liquor. The black liquor was of a 25%' by weight solids content and was obtained from a kraft pulping process. The black liquor was soap-skimmed prior to use in these studies.

The results of this study, as illustrated in Figures 3 and 4, show that while black liquor fillback had no effect on the kraft/ anthraquinone system, which is consistent with literature findings, kraft black liquor did-have an apparent effect on the pulp yields obtained from the kraft/AQ/Ca system.

While this additional benefit may be due to the increased solubility of the calcium cation through formation of organo-calcium complexes (phenolics, acids, sugars, etc.), it could be that by introducina black liauor into the Dilot plant diaester small amounts of pol.ysulfide were formed which can have an impact on pulp yields.

The purpose of this illustration is to demonstrate that for optimum benefits to be derived from the combined use of anthraquinone and calcium hydroxide, black liquor fillback is to be employed.

EXAMPLE 4 EFFECT OF CALCIUM HYDROXIDE ADDITION ON THE KAPPA/YIELD RELATIONSHIP OF THE SODA PULPING PROCESS WITH ANTHRAQUINONE Proceeding in the manner described in the preceding examples, pulping studies were carried out in which the combined use of anthraquinone and calcium hydroxide was tested for an alkaline pulping process other than the kraft process and compared to results 2042 obtained when anthraquinone alone is applied and when no additive is applied. The results of this study are illustrated in Figure 5. For optimum results, a soda black liquor was employed as fillback. These results demonstrate that the benefits derived from 5 the combined use of both additives are applicable for an alkaline pulping process other than kraft.

EXAMPLE 5 THE EFFECT OF EMPLOYING METAL CATIONS OTHER THAN CALCIUM WITH ANTHRAQUINONE IN ALKA- LINE PULPING To determine whether metal cations other than calcium would function in a similar manner with anthraquinone or whether calcium is unique in its ability to synergistically enhance AQ-catalyzed yield increases, pulping studies were extended to the 15 evaluation of other divalent metal cations as well as to monovalent and trivalent metals.

The procedure followed was similar to that of the several preceding examples with the amount of metal cation being kept constant. A comparison of the various metals was made on an 20 equimolar basis.

Among the metals evaluated were: magnesium in the form of magnesium oxide, barium as barium hydroxide, zinc as zinc carbonate, strontium as strontium hydroxide, boron as boric acid, lithium as lithium chloride and aluminum as aluminum hydroxide. Calcium as cal-25 cium oxide was included for the control comparison, as was anthraquinone with no metal salt addition. A kraft black liquor was employed as fillback.

The effect of the various divalent metal compounds on the kraft/ AQ kappa-yield relationship is illustrated in Figure 6 and the effect 30 of the mono- and trivalent metals is illustrated in Figure 7. For these figures, pulp yields were corrected for ash content so as to remove the possibility of including any ash deposition on the pulp in assessing the final yield obtained. 204262 These results reveal that although calcium was not unique in its ability to synergistically enhance the AQ catalyzed yield increases, calcium was most effective when compared to other metals on an equimolar basis. Barium and zinc v/ere found to be 5 effective, as were magnesium and strontium but to a much lesser extent. The monovalent lithium cation and the trivalent boron and aluminum cations were not effective, thus illustrating that the nature of the cation employed is critical.

EXAMPLE 6 THE EFFECT OF EMPLOYING METAL CATIONS IN ALKALINE PULPING WITHOUT ANTHRAQUINONE To demonstrate that this invention calls for the combined use of the divalent metal with the anthraquinone, and does not include the use of the metal alone, the following example illustrates 15 that the addition of the metal alone to an alkaline pulping process has little to no effect on pulp yields per given lignin content.

Again, as an extension to the experimental procedure practiced in the preceding examples, pulping was carried out in which various metal cations were employed in the kraft process 20 but without the simultaneous addition of anthraquinone. As in the preceding example, pulp yields were corrected for ash content.

The results of this study, as illustrated in Figure 8, reveal that the addition of only the metal had no significant effect on pulp yields obtained per given lignin content. These results, 25 when coupled with the yield increase obtained when anthraquinone is present, demonstrates the ability of the metal cation, particularly calcium, to synergistically enhance AQ-catalyzed yield increases.

While the precedinq description serves to illustrate the present invention its definition of its scope may be obtained onl.y 30 by reference to the several appended claims. 204263 <

Claims (13)

WHAT WE CLAIM IS:

1. In a single-stage kraft pulping process wherein lignocellulosic material is digested in a digester to produce pulp by a kraft pulping liquor and without the addition of an oxygen-containing gas, the improvement which comprises adding to the pulping liquor to increase pulp yield a synergistic composition consisting essentially of a. between .01 and 1.5 percent by weight, based on the lignocellulosic material, of anthraquinone, and b. between .01 and 10.0 percent by weight, based on the lignocellulosic material , of a divalent metal salt selected from the group consisting of calcium, barium, strontium and magnesium^.

2. In a single-stage kraft pulping process wherein lignocellulosic material is digested in a digester to produce pulp by a kraft pulping liquor and by up to 50 percent by volume of the total liquor, of spent liquor diverted from the outflow of the d-itstci1, and without the addition of an oxygen-containinq gas, the improvement which comprises adding to the pulping and spent liquors to increase pulp yield a synergistic composition consisting essentially of: a. between .01 and 1.5 percent by weight, based on the lignocellulosic material , of anthraquinone, and b. between .01 andlO.O percent by weight, based on the lignocellulosic material, of a divalent metal salt selected from the, group consisting of calcium, barium, strontium and magnesiuny^-l^ 20*262 - 20 -

3. The process of Claim 1 in which the divalent metal salt is calcium hydroxide.

4. The process of Claim 2 in which the divalent metal salt is calcium hydroxide.

5. In a single-stage alkaline pulping process wherein lignocellulosic material is digested in a digester to produce pulp by an alkaline pulping liquor and without the addition of an oxygen-containing gas, the improvement which comprises adding to the pulping liquor to increase pulp yield a synergistic composition consisting essentially of: a. between .01 and 1.5 percent by weight, based on the lignocellulosic material, of anthraquinone, and b. between .01 and 10.0 percent by weight, based on the lignocellulosic material, of a calcium salt.

6. In a single-stage alkaline pulping process wherein lignocellulosic material is digested in a digester to produce pulp by an alkaline i pulping liquor and by up to 50 percent by volume of'the total liquor, of spent dialer liquor diverted from the outflow of. the di^oter, and without the addition of i ; an oxygen-containing gas, the improvement which comprises adding to the pulping and spent liquors to increase pulp yield a synergistic composition consisting essentially of: a. between .01 and 1.5 percent by weight, based on the lignocellulosic material, of anthraquinone, and ! b. between .01 and 10.0 percent by weight, based on the 1ignocellyier— sic material, of a calcium salt. ,' V o 13 MAY 1966^ 204262 - 21

7. The process of Claim 5 in which the calcium salt is calcium hydroxide.

8. The process of Claim 6 in which the calcium salt is calcium hydroxide.

9. In a single-stage kraft pulping process wherein lignocellulosic material is digested in a digester to produce pulp by a\ kraft pulping liquor and without the addition of an oxygen-containing gas, the improvement which comprises adding to the pulping liquor to increase pulp yield a synergistic composition consisting essentially of: a. between .01 and 1.5 percent by weight, based on the lignocellulosic material, of anthraquinone, and b. between .01 and 10.0 percent by weight, based on the lignocellulosic material, of a calcium salt.

10. In a single-stage kraft pulping process wherein lignocellulosic material is digested in a digester to produce pulp by a kraft . pulping liquor and by up to 50 percent by volume of-the total liquor, of spent- liquor diverted from the outflow of the diqester, and without the addition of an oxygen-containing gas, the improvement which comprises adding to the pulping and spent liquors to increase pulp yield a synergistic composition consisting essentially of:- a. between .01 and 1.5 percent by weight, based on the lignocellulosic material, of anthraquinone, and b. between .01 and 10.0 percent by weight, based on the lignocellulosic material, of a calcium salt - 22 - 204262

11. The process of any one of claims 3, 4, 7 or 8, in which the quantity of anthraquinone is between .05 and .15 percent by weight, based on the lignocellulosic material, and the quantity of calcium hydroxide is between .1 and .5 percent by weight, based on the lignocellulosic materi al.

12. The process of either of claims 4 or 8 in which the quantity of anthraquinone is between .05 and .15 percent by weight, based on the lignocellulosic material, the quantity of calcium hydroxide is between .1 and .5 percent by weight, based on the lignocellulosic material, and the quantity of spent liquor is between 10 and 50 percent by volume of the total pulping liquor.

13. A process as claimed in any one of claims 1 to 12 when performed substantially as hereinbefore described with reference to the accompanying drawings and/or any example herein. AGENTS FOR THE APPLICANTS