SULFITE PULPING OF ENGELMANN SPRUCE July 1942 UNITED STATES DEPARTMENT Of AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin SULFITE PULPING OF ENGELMANN SPRUCE By E. L. KELLER, Junior Chemist and J. N. McGOVERN, Associate Technologist ABSTRACT Sulfite pulps covering a range of bleach requirements from 8 to 2k percent standard bleach powder were prepared from Engelmann spruce ( Picea engelmannii ) using standard pulping conditions. The pulps showed norrr.al vari- ations with degree of pulping. Increasing the maximum temperature, acid concentration and pressure resulted in a reduction in pulping time from 9*25 to 6.75 hours at a slight expense of yield and pulp strengths. The Engelmann spruce pulp was produced in higher yield than a sample of white spruce ( Picea glauc a) pulp made under the same conditions and having the same bleach re- quirement. Although the strength values of the Engelmann spruce pulps were higher than those of this particular sample of white spruce pulp, they were not appreciably higher than those generally obtained from white =>pruce. INTRODUCTION Results from sulfite pulping experiments conducted at the Forest Service pulp and paper laboratory in Washington, D« C, some 35 years ago (J5. 6) and from additional experiments made at the Forest Products Laboratory about 25 years ago (7) indicated that Engelmann spruce yields a sulfite pulp equal in practically every respect to that from the eastern spruces. Until recently the use of Engelmann spruce has been limited largely to one mill located in the Inland Empire. In 1939. however, Wisconsin pulp mills began importing Engelmajin spruce, and it has been estimated that the I9UI shipments will amount to about UO, 000, 000 board feet (approximately 80,000 cords) (2). Engelmann spruce grow* in the mountain ranges in the western parts of the United States and Canada, extending from the Yukon to the Mexican border (1) . In the Northern Rocky Mountain region it is found in extensive quantities along with other species. It is estimated (U) that there are 11,000,000 cords of mature Engelmann spruce, 13 , 700 t 000~cords of grand (white) fir and 2,100,000 cords of western hemlock in northwestern Montana and R1U08 northern Idaho. The possibilities of developing a pulp industry to utilize this supply have been recently described in a report (U) from the Northern Rocky Mountain Forest and Range Experiment Station at Missoula, Montana. At the request of the Station a brief study of the sulfite pulping characteristics of Engelnann spruce was undertaken to bring up to date the information obtained earlier on this species. The present study included (1) preparation of pulps covering a range of bleach requirement under standard conditions and evaluation of these pulps. (?) a few experiments to produce pulps in a shortened cooking time, and (3) a comparison of the Sigelnann spruce with a white spruce pulp made under similar pulping conditions. EXPERIMENTAL PART Three Engelmann spruce trees cut into U-foot lengths supplied by the Northern Rocky Mountain Forest and Range Experiment Station were evaluated by the standard methods of the Forest Products Laboratory. Their physical and chemical characteristics have been reported by Per ^nd Schafer (3)« Eleven bolts representative of the entire shipment were chosen for the pulping experi- ments and converted to 5/&-i n ch chips. The average physical and chemical properties of this small lot are given in table 1. Several bolts from a white spruce shipment from northern Michigan were also chipped for pulping experi- ments; the properties of these bolts are included for comparison vith the Engelmann spruce. The digestions were made in a i. 5- cubic-foot alloy-clad autoclave fitted with a steam jacket for indirect heating. The wood charge averaged about 13 pounds on a moisture-free basis. The Engelmann spruce chips had a dryness of 86.5 percent and the white spruce 8U.6 percent. The cooking liquor, which was made up as usual by bubbling sulfur dioxide from a cylinder into a suspension of calcium hydroxide in a tank, was charged in the amount of 7*5 gallons. Two sets of digestion conditions were used, one being more or less standard and the other aimed at a shortened cooking time. These conditions were as follows: Standard Shortened time conditions condit i ons Cooking acid: Total sulfur dioxide (percent) 6.5 7.0 Combined sulfur dioxide (percent) 1.25 ' 1« 2 5 Liquor-wood ratio (gallons per 100 pounds of moisture-free wood) 58. k 56.7 Temperature schedule: Time to 110° C. (hours) 2 2 Maximum temperature (°C.) 135 1U5 Time from 110° C. to maximum temperature (hours) 2 2 Time at maximum temperature (hours) 3.5 to 6.5 2.75 Total time (hours) 7.5 to 10. 5 6.75 Maximum pressure (pounds per square inch).... 85 90 Indirect steam only used. -2- The cooked chips were broken up with a stirrer and run through a snail flat screen fitted with a 12-cut plate. The pulp yields and amounts of screenings are given in table 2. These results, as ^ell as the other data in table 2, are the averages of two or more check digestions in each instance, except for number 335* The bleach requirements reported in table 2 are average results of tests made on the respective pulps by the single-stage hypochlorite method, the standard T-APPI permanganate method, end the Roe method, expressed as percent standard bleaching powder. Processing of the pulps for strength evaluation was done in a valley test beater. Strength values of the pulps at freeness levels of 800 and 550 cc. (Schopper-Riegler) and chemical analyses of the pulps are given in table 2. DISCUSSION OF RESULTS The Wood Engelmann spruce wood is described a.s generally light in color, rith the heartwood only slightly darker than the sepwocd and with a tinge of red (1) . In density it is the lightest of the spruces, having an average weight per cubic foot of 23 pounds air dry. Its fiber length is usually given as J>.0 mm. The average density of the present shipment was 22.2 and that of the bolts used for chipping 22.3 pounds per cubic foot on an oven-dry basis, or slightly above the average for the species. The trees had a rapid growth and were fairly young for Engelmann spruce. Because of the large diameter, unusu- al straightness , and thin bark, the racked cord had an unusually high volume of wood, 96.7 cubic feet. This offset the low density and gave the same weight of dry peeled wood per cord as average white spruce. It should be recognized, however, that the charge of Engelmann spruce chips per unit of digester space will be less than a charge of a denser wood. The chemical analysis of the Engelmann spruce chips used for the pulping experiments, as criven in table 1, showed them to have lignin, cellulose, an<* pentosan contents normal for spruces. The materials soluble in alcohol-benzene and ether, on the other hand, were low in the Engelmann spruce. The physical and chemical characteristics of the Engelmann spruce were almost identical with those of the white spruce used for comparison, as shown in table 1. This particular lot of white spruce, however, was rapid growing and below average in density, and contained relatively small amounts of extractives. R1U0S -3- Sulfite Pulping Experiments Degree of Pulping Series Using the standard pulping conditions, a series of digestions wps made with Engelnann spruce in which the tine at the maximum temperature was varied from 3.5 to 6.5 hours, and the total time from 7-5 to 10. 5 hours. The yields and chemical and physical properties of the pulps thus produced are given in table 2. The effect of the variation of the digestion time on the pulping results are clearly shown for most of the variables by the curves in figure 1 plotted from the data in table 2. These curves and the unplotted data in table 2 show the following trends: An increase in the digestion time from 7*5 to 10. 5 hours resulted in a decrease in pulp bleach requirement from 23 • 5 to 7«8 percent. The bleach- requirement-digestion time relation deviated slightly from a linear relation as shown in figure 1. The pulps produced in the longest time had approximately 2.5 percent higher total and alpha, cellulose and 1 percent lower lignin con- tents than those produced in the shortest time. The cellulose content in- creased more or less linearly with time, whereas the lignin contents showed little change in pulp digestion longer than 8 hours. The pentosan data were indecisive. The over-all decrease in total yield with digestion time was 2.8 percent. The yield-time relation in figure 1 also deviates from a straight line relationship, the curve showing a break toward higher yields for times shorter than 8.5 hours. Part of this deviation was due to the screenings (data in table 2) which were very low except for the shortest digestion. The relatively high screenings in the latter case may indicate that the region of the def ibering point is being approached and that shorter digestion to produce harder pulps may result in still more screenings. The variations in the strength properties of the pulps with di- gestion time were not large although the data were somewhat erratic, the general trend was toward a decrea.se in strength values with increasing di- gestion tine, as shown by the curves in figure 1 and the data in table 2. Several of the strength characteristics appeared to pass through a maximum; these included the tearing strength at a freeness value of 550 cc. , the tensile strength at 800 cc. , and the folding endurance at both freeness values. The relations between the bleach reouirements of the pulps and their properties are also of interest. Using the data in table 2, the pulp yields and physical and chemical properties have been plotted against the respective bleach requirements in order to show these relations graphically (•■fig. 2). These curves "'show- the fallowing trends: An increase in bleach requirement resulted in an increase in pulp yield, although the increase was greater for bleach requirement values above 15 percent than below this value. -U- R1U08 The strength properties also increased with bleach requirement, al- though the changes above a bleach requirement value of 15 percent were very small. The tearing strength values for a freeness level of 500 cc. and the tensile strength values at a freeness of 800 cc. appeared to pass through a maximum at bleach requirement values in the range of l6 to IS percent. The total and alpha cellulose contents of the pulp decreased prac- tically linearly with increase in bleach requirement. The lignin contents of the pulps having bleach requirements lower than 15 percent were the same, but an increase with bleach requirement was shown above 15 percent. The pentosan values were indeterminate. Effect of Shortened Time A reduction in cooking time to 6.75 hours, accomplished by increasing the maximum temperature, the total sulfur dioxide content of the cooking acid, and the maximum pressure over that employed for the standard conditions gave a medium bleaching pulp. The yield and properties of the pulp thus made are compared in table 3 with the properties of an equal bleaching pulp produced under the standard conditions. The latter values were obtained by interpo- lation of the bleach properties curves in figures 2 and 3 and the data in table 2 at a bleach requirement value of 13 percent. The higher temperature and acid concentration caused a drop in yield from h%.8 to percent. The strength properties for the lower-yield pulp were slightly inferior to those for the higher-yield pulp. The former, however, showed greater purification than the latter as far as their total and alpha cellulose and pentosan contents were concerned. Since the shortened cooking time would correspond to an increase in output per digester of about one-third, it would merit consideration when the maximum pulp production is desired. Comparison of Engelmann with TThite Spruce SvJfito Pulp A white spruce pulp was prepared using the standard pulping con- ditions for comparison with Engelmann spruce. The data are given in table U. The figures for Engelmann spruce were again obtained by interpolation of the curves in figures 2 and 3 and the data in table 2 at the desired bleach requirement. The white spruce pulp was produced in 0.3 hour shorter time, but it was inferior to the Engelmann spruce pulp in practically every respect. The white spruce yield was less, Us.2 compared with US.9 percent, and all of its strength properties were appreciably lower than those of the Engelmann spruce pulp, as shown in table U. The two pulps did not differ greatly in their chemical analyses although the white spruce had a slightly higher alpha cellu- lose content. The Engelmann spruce pulp was considered to have normal character- istics for spruce pulps, whereas this particular white spruce pulp was below average in its strength properties. PJ.U08 -5- LITERATURE CITED (1) Betts, H. S. U. S. Dept. Agr., Forest Service. American Woods. Engelnann Spruce (August I9UI). (2) Pacific Pulp and Paper Industry 15 (2):36 (February 1941). (3) Pet?, J. C. , and Schafer, E. R. Forest Products Laboratory mimeographed report. Project 1163-7, problem D-192 (October 8, 1941). (4) Rapraeger, E. F. Northern Rocky Mountain Forest and Range Experiment Station, Missoula, Mont. Station Paper No. 4 (March 1941). (5) Surface, H. E. U. S. Dept. Agr. , Forest Service. Forest Products Laboratory, Madison, Wis. Project L-73t 1 an(1 - 2 (October 20, 1911). (6) Sutermeister , E. U. S. Dept. Agr., Forest Service Laboratory Experiments, Washington, D. C. Project No. 73 (December 1909) • (7) Wells, S. D. , and Rue, J. D. U. S. Dept. Agr. Dept. Bull. 1U85 (1927). R1U08 -6- Table 1.— Average v glues for physical and chcr.ical characterletlca of jtagelmann and white spru c :o roods ( Shipments PI509 and P1571, respectively ) Characteristics : Wood species < 1 . Engelr.ann spruce White spruce Physical Properties Density (o.d. weight per green volur.e) - pounds per cubic foot i : 22.3 - I 21.1 Growth rate - rings per inch 15.3 : 1U.2 Age - years : 68 : 55 Diameter - inches : 8.9 _ f ! 7.6 Heprtwood - percent Cher.ical Analyses : Lignin - percent : 28.3 28.3 Cellulose - percent : 59.5 : 60.2 Alpha cellulose - percent ; t U2.7 : : U3.2 Total pentosans - percent J 13.5 I : 12.3 Solubility in: : Alcohol benzene - percent : 1.5 i 2.0 Ether - percent } .6 ! 1.0 1 percent NaOH - percent : g.g 8.8 Hot water - percent : 1-7 1 2.0 Ash - percent ! .15 : : .3 Pentosans in cellulose - percent i 10. h : 9.9 R1U0S CO o. a CO 0) CO >» s ct) H a) o x; o a e H a] a) co O o ♦» El C ■ IS 3 c bo O H a! co 4) C* co u co ho c ■H a CD CD fci O Ji X) 4> C -d . 03 a «H CD M S O o +* o 4> X» o kn LfN KN KN m 3 VO o CT> ON r-t o\ ^ m 4 • • • • LfN vO LfN vO LfN J- on on i*— r*« r— r-s ON o vo kn in m ON ON ON CVJ ON VO VO VO VO • • • • O H u ' o •d c ca kn H CVJ Sh O O s* I o •P co d) *-> u a> •u aj v XI s 2 a> 3 r-t > ■p D u ■p a kn cvj O CVJ ON J* ON c\J 1 i i & o o LfN O XN O eo in KN kn CVJ I v> KN KN KN to LTV aS CD • <-> CO CO hO CD c e ■H CD *-> CD D U CD Cm CQ a o' • •h ai ■p • OJi CO CO CO b0 CD a C «-t CD 4_> (0 CO (L. t, Cm 3 CQ CD "I 3 Z CO J 1 o 3 1 o c ■rH H 1 o H 1 o I &o 1 o 1 o L£> LfN ! o w 1 -TV O | • 1 o 1 O 1 1 o • 1 o o 1 to a • 1 o a fas I o b0 • a ca I o a CD i m ■ Li CO 1 LfN +j « It CO CD V c O CD CO* o r-l o o CM co to O to lO o 3 ■o o m m r— rH CVJ H vO r~- O in J* «0 m n evi cvj m X) a 3 o «o J* ON a VO 60 r — • • • U s o a) a a> h ca 3 h 3 XV LfN o VO a KN O M CVJ • • • rH H rH n 9 o D « u c s CVJ ON 60 m r«-N KN 60 in 3 i 60 fN KN J- 60 ON KN J- VO o o 60 in i i KN KN 80 Occ / » ~. ( » 801 >ee.f REEN ESS__ o J 55( » i 80 < — 1 \ T r X «> < < j » 7 5 9/0 DI6ESTI0N TIME(HOURS) 7 8 9 /0 DI6E5TI0N TIME (HOURS) FIG. I RELATIONS BETWEEN DIGESTION TIME AND PROPERTIES OF EN 6ELMANN SPRUCE SULPHITE PULPS. 1 19 !4-2005 F UNIVERSITY OF FLORIDA 3 1262 08925 4816 o o r O • 800 C C. FR FfA/£. « • ' ' • 7000 o 800 c c. FR FJ_N£ 55 , o o 55 Occ • 1 F*££A//-tc • • cqCENESS ■ SlEFf J£SS / 1 9 / • • 6J 6.0 55 BLEACH REQUIREMENT (PERCENT) BLEACH REQUIREMENT (PERCENT) FIG. 2 RELATIONS BETWEEN BLEACH REQUIREMENT AND YIELD AND PROPERTIES OF EN6ELMANN SPRUCE SULPHITE PULPS. Z K U-200 7 5