TANNIN EXTRACT from WESTERN HEMLOCK BARK El
ECAUSE our principal domestic source of tannin is being depleted by chestnut blight, there is need for the develop ment of new domestic sources. Importation supplies B large part of the vegetable tanning materials required by this country (3). The potential market for domestically produced tannin is large, however, and among the sources being considered currently is the bark of the western hemlock (Tsuaa Irclerophyllo). Ita importsnee as B potential source of B satisfactory tannin msterial "88 discussed by Smoot and Frey (a). Peeling in the woods produces ideal bark, but high cost of collection due to the difficulty in handling the large logs in the western hemlock area has hindered this practice. Large quantities of waste bark are available 8 s s by-product in the manufaoture of wood pulp. The movement and concentration of hemlock logs used in manufseture of pulp m e shown diagrammatically in Figure 1. The mechanical barkers used to peel the logs remove B woodbark mixture containing as high as e573 ofwood. Sueh mixtures would give tannin entracts of very low purity; iurthermore, no feasible method has been developed for separating the bark from the wood. Hydraulic barkers, recently installed a t several pulp mills in the Pacific Northwest, remove B wood-bark mixture containing between 85 and So% of bark and the bark is in relatively large pieces, which could be manually separated from the wood. The savine! in wood resulting from the use of hydraulic barkers is expected to result in their replacing mechanical barkers in pulp manufacturing plants. Hemlock 1 0 ~used s for the manufacture of pulp are, in general, floated to the mills and remain in the water for various lengths of time. While in the water, the bark loses the more soluble tsnnina s beby leaching. hloreover, the bark of logs floated in ~ e water c o m e ~impregnsted with salts. These $NO fsetora introduce dif-
fioultien that would not be encountered in the production of tar,nin extract from bark peeled in the woods. The investigations reported here have dealt with the properties of extracts prepared from the bark ofsaltwater-floated logs and also that offresh-water-floated logs, a horn-mgle hydraulic preas used to prepare the bark for leaehing, and a chemical method for solubilizing the tannin extract prepared from the bsrk of floated logs. PREPARATION AND LEACHING
Prepared bark was leached by the multiplebatch method (3, pages 3304). The strongest liquor was withdrawn from fresh bark, and wster was introduced only on the nearly spent bark. Only enough liquid was used in the lesches to Cover the bark. Liquor was withdrawn from fresh bark twice for evaporation; ths third liquor withdrawn was advanced for me on fresh bark. Five leeches were used for premed bark and seven for other types of preparation. In the preparstion of bark three procedures were used. Bark from salt-wster-flosted logs was passed through hoggere produeing pieces up to 2 inches in dismeter. This material was rinsed twice with cold fresh wster (about 55" F.), covered, and immediately drained. These rinses removed from B third to B half of the salt present, some of the mud, and a little of the tannin. A higher percentage of salt was removed from bark having the lower salt content. Bark prepared in this manner is difficult to leach;
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F l g u m l . Movement and Concsntration of Western Hemlock Logs Used for Pulp Manufacture In Western Washlngton 8nd Oregon; 0 Shows Location of Pulp Mllls.
December, 1944
INDUSTRIAL AND ENGINEERING CHEMISTRY
An lmpmved proses6 is suggested for t h e preparation of tannin extract from t h e bark of floated western hemlock logs collected a t pulping centers in t h e Pacific Northwest. A horn-angle hydraulic press was used t o prepare the moist bark for extraction. Bark pressed In t h i s manner required only 4 hours for leeching, and t h e material d i d n o t pack or channel in t h e experimental leaching vats: it would probably leach well in continuous countercurrent-type equipment. Solubilization, found neEesMry t o reduce t h e high content of insolubles in t h e t a n n i n extracts, we8 acwmplished by the setion of sodium bisulfite., b The photosraph on page 1146 shows a log boom a t Everett, Waah., w i t h aconveyorcarrying logs t o t h e hydraulic barker.
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6 days st 175-185" F. are required to bring it to apparent exhaustion, wit,h about 2.5% of the tannin still in the bark, regardless of the initini content. After rinsing, the bark contains 13.5 to 68~mmoistuienndyieldrliquorseontainingonly 1.2 to 1.5% tntal solids. Solid extracts were not prepared from these dilute solutions. These observntions clearly indicntcd that B finer division of bark was necessary to shorten the loaching timo and obtain a more concentrated liquor. To prepere a more finely divided material, & hammer mill IR duccd the bark topiecesranaing up to '/sinch indiameter. About haif of the salt w.w removed by tu-" cold-water rinses, but sppreciablc amounts of t.he more soluble tannin were lost. Thia material could be leached to about 2.5% tannin content in 40 to 48 hours at 175" to 185" F. Tho liquors contained about 2.0% of total solids, and solid extracts were prepared by lowpressure evsporation (Table 1, bark and wood No. 1). Analyses of bark and extract were made by official methods of the A.O.A.C. ( 1 ) . Propsirstion of floated bark in B manner that reduced both salt and rater content, without materially sffeetinq the tannin content, snd also permitted rapid leaching was accomplished with a horn-angle hydraulic press. With this press i t was possible to obtain feed acceptance and continuit.y of feed with pressures great enough to disrupt the Euid-containing ceils of hemlock bwk. (The investigations reported here involved t,he use of only one press; no effort has been made to determine the suitability of other presses.) Pieces of bark from tho hydraulic barker (up to 1 foot wide and 2 feet long) were rinsed twice with cold fresh water toremovemud and salt from the surface and then pressed. Pressing redu'eed the bark from the original thickness of ' h inch to l / t h inch, the water
E. F. POTTER, IC. T. WILLIAMS, T. 1.S W E N S O N , A N D 1. C. F E U S T E L W P T Z R N REOIDNAL R I B L A R C H LABORATORY. U. 8. DEPARTMENT OF AORICULTURE. ALBANY. CALlF.
Mechanism for Holding and Turning Hemlock Log Whll. Water Jet Removes Bark
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TABLE I.
INDUSTRIAL AND ENGINEERING CHEMISTRY
TANNIN EXTRACTS PREPARED FROM WESTERN HEMLOCK BARK SALT-WATER-FLOATED LOOS(CALCULATED ON MOISTURE-FREB BASIS)
ANALYSES OF
TAKEN FROM
InsolNonubles, tannin, Tannin,
Extract Pre aration Prepared from: ofBark % % 6.1 45.2 Bark & wood No. 1 Hammer mill 4.0 Bark & wood No. 2 Roller press 39.3 5.8 32.1 Bark & wood No. 3 Same 2.2 26.8 Bark No. 1 Same Bark No. 2 Same 5.7 25.7 Bark No. 3 Same 1.5 28.0 Woods-peeled barkb OroundC 6.9 30.1 % of tannin/% of sol. solids) X 100 purity. ncluded for comparison. ,e Ground in a Wiley-type mill to pass a 3-mm. sieve.
%
purity4
48.7 56.7 62.1 71.0 68.6 70.5 63.0
51.9 59.1 65.9 72.6 72.7 71.6 67.7
NaCl,
Ash
9.9 4.1 4.5 4.5 2.3 2.8 0.3
15.2 8.3 8.1 7.4 8.1 5.6 2.2
%
%'
Insol. in Mixt. of l5 &G* 85 G. Water, % 31 38 4.3 19 40 33 8
Vol. 36, No. 12
ture. T h e amount of insoluble material differed but little from t h a t in the first mixture. This process was repeated twice, but the insoluble material persisted. TREATMENT O F EXTRACTS W I T H SODIUM BISULFITE
Since physical methods of preparing extracts with a low content of insolubles had failed, chemical methods were tried. The insoluble material was readily dissolved by the addition of sodium hydroxide, but when TABLE 11. ANALYSESOF COMPARAB~E SAMPLES OF PRESSED AND UNPRESSED the p H was lowered with lactic or acetic acid, WESTERN HEMLOCK BARKPROM SEA-WATER-FLOATED Loas (CALCULATED ON MOISTURE-FREE BASIS) reprecipitation occurred immediately. TreatTotal Sol. Insolu- NonSol. ment of solutions of ordinary quebracho exSolids, Solide, bles, tannins, Tannin, NaCl Ash, % % tract, containing a high percentage of insolu% % % % Preparation % Purityo 0.47 1.26 bles, with 5% of its weight of sodium bisulfite Pressed No. 1) 18.8 17.6 1.2 7.3 10.3 68.5 Preesed, Not pre'seed No.' 2b No* for 24 hours a t 180' F. changes its physical : : Not pressed No. 2 18.7 16.5 2.2 6.6 9.9 60.0 1.53 2.28 characteristics; the sulfited quebracho becomes Pressed No.*3 b 20.4 18.2 2.2 6.5 11.7 64.3 0.48 1.17 1 33 2.17 more readily soluble, and the tannin is taken up Not pr&sed, No. 3 21.6 18.8 2 7 7.4 11.4 60.6 by skins with more avidity (9). An extract a (% tannin/% sol. solids) X 100 purity. 6 T h e values are calculated on the dry wei ht of the bark before, pressing. The amount of prepared from salbwater-floated bark wh8 water expejled and its solids content were usel to make the calculations. Values calculated on mixed with six times its own weight of water the dry weight of the pressed bark would be somewhat higher. and 5% of its weight of sodium bisulfite. It was then heated o n a steam bath for 16 hours with occasional shaking. At the end of content from 65% t o about 35%, and the salt content to about that time 99% of the material was soluble. Prior to sulfiting, 26% of the original amount. The pressed bark did not pack or only 60% of this extract could be dissolved in six times it9 weight of water. channel while being leached. It could be leached t o about 2.5% tannin content (dry weight basis) in 4 hours at a temperature of During subsequent leaching experiments, sulfitina was applied 140" to 150" F. The liquors contained 2.5 t o 3.0% total solids. to liquors as they came from the leaches. The liquors were cooled Testa were also made to determine the effectof pressing on the and filtered to remove pieces of bark and coagulated gums. The content of extractable material in the bark. Slabs of rinsed bark amount of total solids present was determined by volume and barkometer measurements. The sulfiting process consisted of were cut into fourths, and alternate quarters were used t o make addition o f a n amount of sodium bisulfite equivalent to 6% of two samples of each slab. One sample was pressed, and the other was dried and ground to pass a 3-mm. screen. Portions of the total solids, followed by heating for 4 hours. Lesser amounts of sodium bisulfite were tried, but 6% was. necessary to obtain t h e samples were analyzed and the results are given in Table 11. solubilization in liquors containing about ,370 of total solids. T h e Pressing lowered t h e salt and soluble ash contents of the bark materiallv. More tannin was extracted from the Dressed than temDerature was usuallv 180' F.. b u t boiling did not affect the from the ground bark. quality of the extract. Sulfiting was carried out prior to evaporaExtra& from bark prepared with the hammer mill and the hor n - a n g l e hydraulic press BARKUSEDTO PREPARE EACHEXTRACT AND TABLE111. ANALYSESOF TANNINEXTRACTS, were evaporated under reSPENT BARK(CALCULATED ON MOISTURE-FREE BASIS) duced pressure at temperatures Insol. in Total Sol. Insolu- NonMixt. of 15 G . below 130' F. The analyses Solids, Solids, bles tannins, Tannin, Ash, NaCl. Ext. & 85 G . of some of these extracts are Materials % % %' % c/o Puritya % % PH Water, % shown in Table I. The exSulfited ext. from bark & woodb 100.0 97.8 2.2 32.3 65.6 67.0 10.8 3 . 3 .8
