May, 1930
INDUSTRIAL AND ENGINEERING CHEMISTRY
are sampled, and physical tests, including tensile strength, deflection, and bursting strength, are made. The weight and caliper are taken and a portion of the sample is tested for moisture absorption. I n addition, each type of board has certain tests n-hich are made periodically to determine its value for specific applications. Any boards which do not meet the rather rigid specifications are graded out. Furthermore, these tests, since they are made a t short intervals, afford a running check on production and any variations from the standards of operation can be immediately corrected. The moisture regain in the humidifier is carefully checked, not only by spot tests and inspections, but by weighing entire truck loads of boards to determine the moisture regain. A control of the water used in the process is very important, particularly since m‘e have a neutral water, an alkaline water, and white water which has already passed through the process and which is re-used to take advantage of its heat content and the soluble materials it contains. Correct proportions of each of these must be combined to give the optimum pH for refining and to reduce corrosion. Furthermore, the water usage must be carefully controlled to prevent overloading of the system. Since our white water is clarified and re-used, an excessive supply of fresh water will throw a burden on our clarifying units. Since the bark enters the guns with the wood, during the explosion it is completely pulverized and, together with some water-soluble portions of the wood, is in suspension in the white water. This white water was formerly discharged into a small stream near the plant which was useless for any purpose. Owing to the quantity of eflluent and its sludge, the stream turned a deep brown and was relatively unsightly, although it was no menace to public health. It was found,
497
however, that the re-use of the white water without the bark would pay for the removal of this sludge, due to the heat and the dissolved solids in the effluent. This is now being done, thus, partially a t least, solving the problem of stream pollution as well as saving money by the re-use of the white mater. Research Activities
Undoubtedly the most fascinating part of our research activities is the attempt t o follow chemically the changes which occur in the process and to investigate the possibilities of various by-products. The dream of every manufacturer of insulation board is to have many gradations of fiber length, each in its separate bin, from which he may combine a certain amount of one length with some of another, securing the optimum results so far as strength, rigidity, and density are concerned. While this is not feasible in practice, we are striving to accomplish this by systematic studies of the effect of various fiber lengths on the physical properties of the board, both by studies of the individual fiber and by semi-commercial experiments. The photomicrograph and the balopticon have greatly aided us in this study and, although definite results come slowly, we are gradually gaining an insight into the private lives of these fibers and their reactions. An entirely different line of research is the investigation of the uses of different types of machinery and modifications of our existing machines. This calls for an investigation of the design and uses of many kinds of equipment. Chippers, screens, guns, rod mills, refiners, machines, presses, and so onall come under close scrutiny and we try to be always on the alert for possible changes or modifications which will tend to improve operation or reduce cost.
Semi-Commercial Production of Xylose’,’ W. T. Schreiber, N. V. Geib, B. Wingfield, and S. F. Acree BUREAUOF STANDARDS, WASHINGTON. D. C .
BOUT two years ago the Bureau of Standards was authorized by Congress to investigate and tto develop uses for the so-called waste products from the land. “Waste products from the land” are understood to be those parts of the farmers’ crops which have no commercial value. Cottonseed kernels, before the advent of the cottonseed-oil industry, were in this category. Now there is a market for cotton fibers, linters, and seed kernels; while the bulk of the c r o p t h e leaves, burrs, hulls, roots, etc.-has no value. If it were possible then to develop uses for these products, either as such or after chemical treatment, the farmer, as well as the rest of the country, would undoubtedly profit. The Bureau divided its work on waste products from the land into three more or less correlated parts.
A
(1) The laboratory research on many of these products is being done in Washington. ( 2 ) A cooperative research with Iowa State College is being carried out on the production of wall board from cornstalks a t Ames, Iowa. (3) An experimental semi-commercial plant for the production of xylose from cottonseed-hull bran has been in operation a t the Anniston plant of the Swann Corporation for the past year. 1 Received March 27, 1930. Presented by W. T. Schreiber hefore the Division of Industrial and Engineering Chemistry a t the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 to 11, 1930. * Publication approved by the Director of the Bureau of Standards of the United States Department of Commerce.
This development has been a cooperative project of the Alabama Polytechnic Institute, the University of Alabama, the Swann Corporation, and the Bureau of Standards. It is the purpose of this paper to discuss xylose and the operations of the xylose plant a t ilnniston, Ala. Previous Work on Xylose
Xylose is a dextrorotatory five-carbon sugar. It is not new to the scientific world, although until recently it sold a t the exorbitant price of $100 per pound. This was true despite the fact that xylan, the condensation product from which it is obtained, is, next to cellulose and lignin, probably the most widely distributed organic compound found in nature. Koch (S),its discoverer, isolated xylan from wood in 1886. Since then it has been obtained from innumerable plant materials. It has been found in various grains, straws, gums, woods, parts of the corn plant, and other plant substances. Koch prepared xylose by extracting wood with a caustic solution, precipitating the xylan from the extract with alcohol, and hydrolyzing the xylan to xylose. I n 1899 Bertrand (1) showed that xylose could be prepared by direct hydrolysis of oat straw and therefore that the isolation of xylan before hydrolysis was unnecessary. Interest in xylose seemed to lapse from that time until the World War. Then, because of the greatly increased demand for acetic acid, research on xylose was resumed. The reason
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
500
leached with previous rinses and water. These rinses were then pumped to the treating tanks for processing or were used for further rinsing. The ratio by weight of liquor to bran in this type of digester was about 21/4 to 1. Results obtained in building up the extract in this digester agreed with those secured in the agitating digester. ADVANTAGES OF EACH TYPEOF DIGESTER-Each of the digesters experimented with had certain inherent advantages as well as certain disadvantages. The agitating type had the advantage of making possible the use of bran containing a considerable quantity of fines. Further, every bran particle was subjected to a thorough and identical treatment. The main disadvantage was that it required considerable handling of the bran and an increased amount of acid. Packing and channeling difficulties were encountered when bran containing a considerable quantity of fines was used in the circulating digester. For coarse bran, which contained a negligible quantity of fines, the circulating digester seemed to give greater yields and had the advantage of requiring no handling of the bran during the processing operations. OTHERDETAILSOF OPERATIONS-The details of the operations given above were based on numerous experiments and were considered to be the optimum conditions for plant opera-
Vol. 22, No. 5
used which removed most of the deleterious gums and yet left intact the greater part of the xylans. Both the hot-water treatment and the cold-acid wash contain by-products, uses for which have not been extensively investigated. The former contains gums, while the solids in the latter are largely potash salts. Processing of Extract
The treatment of the extract was the next step in the process. Considerable work was done in which the extract was treated with decolorizing carbon to remove the color and possibly gums and other impurities. The data showed that the use of carbon was unnecessary; it improved the color of the crystalline product, but the added cost did not seem warranted. The yields and reducing-sugar content of the crystalline xylose obtained from carbon-treated liquors and from untreated liquors were approximately the same. However, for recrystallization work a carbon treatment was resorted to as a very pure product was desired. The first operation of the treatment process was to neutralize the extract to a pH of 2.8 with a milk of lime slurry. It was then filtered through a plate-and-frame filter press (Figure 3) and concentrated to a specific gravity of 1.28 in a single-effect vacuum evaporator (Figure 4). This solution was again-filtered and concenFlow S h e e t for t h e M a n u f a c t u r e of Xylose f r o m Cottonseed-Hull Bran, U s i n g Circulating trated to a specific gravity of Digester 1.350 a t 45-50' C. The purpose of the intermediate filtration was to reduce the ash in the final prodand rinsing from taining 30 Ibs. of uct by removing as much calcium previous run sulfate as possible from the solution before supersaturation. At specific gravities above 1.28 filtration was slow and difficult, and 1. Digest with 530 Ibs. of water at a steam pressure of 15 Ibs. there was danger of premature 2. Wash with 330 Ibs. of cold water crystallization. 3. Circulate through the washed bran with 130 additional Ibs. of water and f L 3 Ibs. 9 02. of HzSO4 C r y s t a l l i z a t i o n was accomI 4 Wash with 330 Ibs. of cold water plished in two ways. One was to allow the supersaturated xylose 5. Digest washed bran with 145 Ibs. of rinse containing 14 Ibs. of xylose and 2 Ibs. 15 02. of H S O l at a steam pressure of 10 Ibs. sirup to stand in oak barrels. This Wash with 330 Ibs. of rinses and cold water 6. standing method of crystallization required from 15 to 35 days for completion. The other method Waste. 730 Ibs. of water, 4 to 6 Ibs. of gums, was to use a crystallizer in which it + water-soluble ash, and was possible to obtain controlled conditions of temperature and agitation. Complete crystallization was thus obtained in 30 to48 hours. The crystallizer used (Figure 5) consisted of a monel-metal shell horizontally mounted on a shaft. It was equipped with a spiral agitator driven by a motor working through a set of reducing gears, belt, and sprockets. The temperature control was obtained by running water over the outside of the shell from a water-storage t a n k . T h e method used for crystallization was to charge the crystallizer with the hot supersaturated sirup. The control water was started a t a temperature of tion. It must be remembered that the solvents used in the 50" C. and dropped 1 degree an hour. When the control pretreatments were not strictly selective, Impurities, such water reached 43' C. the liquor was seeded. From there on as gums, were only relatively more soluble than the xylans. the control water was dropped 1 degree per hour to the temThe operating details used necessarily had to assume a middle perature of tap water, about 18" C. During the entire course. In the pretreatment, for example, a pressure was period both agitator and shell were slowly revolved.
I
The yields obtaiiicd by the tn-o ir,etliods 3rc q i i i t t . diiTiwnt, Standing crystallinatiori g a w yields oE a little over 40 per cent, of the original xylose in rlie sirup on one crystallization, while first. crystallization yields froin tlie crystallizer were approximately 55 per cent. Tlie reducing-sugar content oi the crystals obtained by t,he t,wo Inutliods was in general the sanw. The analysis showed 90 to 94 per cent reducing sugar, 1 to 2 per cent ash, and the remainder niiistly inoidirre.
pcmi"rlcnt r i p i n i t.tie type and purity of the prodnct desired, tire size of the producing p h t , wllicli again is determilied by the market For tlie material, and finally on the delivered price of t,lie cott.onseed-lid1 bran. Then, too, there is the possibility of inakirig the by-products pay some of the recovery cost. I'erliaps tlie most reliable figures would be the costs of Ireat, power, and clieniicals in tlie manufacture of xylose rather than a possible production cost. Based on figures ohtaincd from operation on a 100-pound-pcr-day basis, the it.enrized cost per pound of crystalline and sirup xylose is given in Table I. 'l'ahle I
Cuafs of lfmf, Power. and Chomicalli In Manusaccure of Xvlole C.YST*LLINB
Cost per lb.
36 cents P" $0.00810 I000 Ibr. i'ower 0.7 C C l l f per 0.GQ038 kw-hour water 5 Cents per 0.W300 1000 C I I f' Sulfuric 91.075 per 0.00539 itcia 100 11,s. 1.ime 35 cents per 100 Ibe. T o i r l eust per._____ Ib. Ileal
XYLOS*
Amount
24 Ibs. steam
Siaup C U N T I I I I ~AP(~ PXOX. 50% XVLOSS Cost per lb.
Amount
SU.00420 12 lbs. steam 249w-hrs.
911 w-hrr.
0.00174
60 cu. If.
0.00166 33 cu. It
0.501 lb.
0.00298 0 . 2 7 7 Ib. D , O U O I & u.04311,
. O.Oi072
.~
Tlie operating, overhead, depreciation, arid raw-tiran costs are not included in the above cost figures.
65 der cent yielci of wliitr, crystalline xylosc oi \Try iiigli purity. Xylose rccrysta1liat:d three times from water gave a product whose rotation practically agreed with the specific rotation of 1-18 degrees given in the literature. The extracted liraii or residue remaining after tile extraction oi the xylose, oil a dry basis, reprcsentu approxinrately half oi the original weight of cottonseed-liull bran. This product consists oi a fairly u;ell washed and purified cellulose. A very good grade of carbon tias been made from this material. It may also find use as a suitable srilistitilf.e For W O ( J ~ flour in the conilensatki~iproduct ficld.
Vuring the past six years there have been exposed on the roof of the Bureau of Standards chemistq building a great variety of cxpcrirnantally prepared outsidc white paints. Invariably these have heen applied in either three coats 011 well-selected woad or in two coats on carefully cleancd metal panels. Repeatedly, straight white-lead paint has shown good durability. Likewise lead-zinc paints. provided the zinc oxide content of the pigment does not exceed 30 per cent, h a w shown good durability. On w a d panels increasing the zinc oxide content up to 50 per cent
Acknowledgment
'l'liia is to acknrnvledge the whole-hearted co6peratiun given to the dcvrlopinent, of the xylose project by the Swanii Corporatioii d Rirminglrain, Theoilore Swam and his representatives, eslxcially E. 11. Huford and J. W. Perry, Jr.; the Alabama I'olytechnic Institute and their representatives, M. A. Urail.;haw and Fred Acrec, Jr.; and the University of Ala!lama and their rt!presentative, J. 1,. Kassner. Literature Cited
has resulted in rather bad cracking and scaling of the pdint. On metal tile lead-zinc paints containing not over 30 per cent zinc oxide are more durable than straigllt white lead. Of the newex types of outside white paints on wood, the titanium-zinc paints show good durability. provided the zinc oxide content does not exceed 30 per cent. These paints stay cleaner and whiter than the lead-zinc or white-lead paints. After nearly three years of exposure, some of these paints are showing unusually good reSUI&.
