WOOD HYDROLYSIS Raphael Katzen', Robert
S.
Aries, and Donald
F. Othmer
POLYTECHNIC INSTITUTE OF BROOKLYN, N. Y.
Production OF chemically converted products from wood and wood waste has increased For several decades, a further impetus being provided b y wartime shortages of other materials. The continuous hydrolysis OF wood and other plant fibers with dilute sulfuric acid produces lignocellulose for use in plastics. The waste liquors, in addition to the sulfuric acid, contain valuable constituents; yields, on the basis of dry wood processed, are: organic acids (as acetic), 5-6y0) furfural, 2-370; and wood sugars, 20-25s. The liquors may then b e treated under pressure at a temperature which "rehydrolyzes" the sugars to give additional organic acids and furFural. Thus, a 15-minute treatment at 100 pounds per square inch was found to increase the furfural yield by 100-14070 and the organic acids b y as much as 14%. By-products have been separated subsequently b y extraction with high-boiling solvents, such as octyl acetate, octyl alcohol, isophorone, and FurFural. Batch and countercurrent extractions indicated that isophorone is the most practical solvent tested for extracting furFural and acetic acid From dilute hydrolysis liquors. A plant process utilizing isophorone i s proposed.
the chemical process were to be applied to wood hydrolysis liquors, t'he acids would have t o be neutralized with lime before or after the recovery of furfural, and the solution evaporated to yield the salts. The organic acids can be recovered from their salts by redistillation with strong acids. This method requires the evaporation of large quantities of water; the steam cost,, added t,o the cost of alkalies and acids used, makes it uneconomical. Distillation of aqueous acet,ic acid to produce anhydrous acid is theoretically possible but expensive. Azeotropic distillation reduces costs (8, 10) which would, however, still be excessively high for these dilute solut,ions. Mains (5) claimed a recovery of 95% of furfural present in four distillations of dilute solutions, but his heat costs are high. The extraction method was decided upon as being the most, practicable to avoid the high heat requirements of a straight dist,illation process. M E T H O D OF A N A L Y S I S
ORGANIC SciDs. Total acidity was titrated. Sulfuric acid was then obt,ained by precipitation as barium sulfate, and organic acids (as acetic) were calculated by difference. Unless otherwise indicated, amounts expressed as acetic include foymic or other organic acids so determined. Solvent extracts seldom contained measurable amounts of sulfuric acid. FURFURAL. Phloroglucinol was used for quantitative precipitation of furfural. The precipitate was filtered on a Gooch crucible and dried a t 100' C. Furfural was calculated from the weight of the phloroglucide. REDUCISG SVGARS.Feliling solution was reacted with sugar solution to give a cuprous oxide precipitate. This was dissolved in ferric alum and t,it,ratedwith a st,andard permanganate solution. Sugar values as glucose were then obtained from standard conversion tables.
A
II' 1L;AIILIER paper (3) described a continuous process for
the hydrolysis of wood. Although the lignocellulose residue was the main product (for utilization in plastics), byproduct yields (organic acids as acetic, furfural, and reducing sugars) from maple sawdust were determined It was noted that increased yields of organic acids and furfural vere accompanied by a decrease in sugars with increased degree of hydrolysis. Standard continuous T, ood hydrolysis runs (50% of cellulose hydrolyzed) yield approximately 10 pounds of liquor per pound of dry wood substance (d.w.s.). *4verage liquor analyses are: organic acids (as acetic), 0.5-0.6%; furfural, 0.24.3%; reducing sugars, 2.0-2.5%,. On the basis of d.w.s., yields are: organic acids (as acetic), 5-6%; furfural, 2-391,; reducing sugar?, 20-25910. ricetic acid and furfural are the most valuable of the above byproducts. Ethyl alcohol could be produced from the hexose sugars by fermentation, but concentrations seem to be on the borderline for economic operation except under present conditions. The possibility of conversion of the pentoses into furfural, and the pentoses and hexoses into organic acids such as acetic, was investigated. This operation is feasible, as the solutions already contain sulfuric acid to act as catalyst. It is generally knonm that pentoses yield furfural by treatment with mineral acids (4, 6 , 10). The conversion of xylose to furfural by dilute sulfuric acid depends on the concentration of acid, the temperature, and the duration of the operation (2). Other norkers ( 7 ) hydrolyzed pentoses in birch wood with 0.257, hydrochloric acid or 0.5% sulfuric acid a t 6 atmospheres pressure. Other investigators (1, 18) have studied production of pentoses and methylated pentoses from rye straw, cornstalks, etc., although current production is based on oat hulls and cottonseed hulls. Three principal methods for concentrating aqueous solutions are used: chemical interaction, distillation, and extraction. If 1
REHYDROLYSIS OF BY-PRODUCT LIQUORS
~ I E T H.ISD O DEQUIPJIENT. The apparatus Tvas a specially constructed pressure vessel having a capacity of 2.8 liters. It mas made of 4-inch copper pipe, 22 inches long, capped at the bott,om, fitted with a flanged cover carrying pressure gaxe and feed connections, and tested to 250 pounds per square inch. Approximately 2 liters of liquor, obtained by continuous hydrolysis of maple sawdust, were charged into the pressure vessel. The unit was then placed on an inclined stand, and t,he liquor brought to boiling by means of gas burners. All air was displaced through the vent' by steam, the vent valve was closed, and heating was cont,inued until the desired pressure was att>ained. This was maintained until it was desired to take one of the several samples required during a run. The bomb was t,hen reversed on the stand, so that the flanged head mas down anti the feed or vent tube was connected to a water-cooled coil. Samples were removed slowly to prevent flashing. The vessel was then reversed on the stand to c o n h u e processing. D ~ T T-AKEN. A Rehydrolysis runs were made a t pressures of 50, 100, and 150 pounds per square inch; 250-cc. samples were
Present address, 1321 lrliohigan Ave , Cincinnati 8, Ohio.
442
INDUSTRIAL AND ENGINEERING CHEMISTRY
May, 1945
withdrawn a t intervals ranging from 3 to 60 minutes after operating pressure was attained. Results of these runs are listed in Table I and shown graphically in Figure 1. EFFECTOF TIME. Acetic acid in the hydrolysis liquor increased with time of rehydrolysis at all three pressures studied, b u t the curves indicate that the increment decreases with prolonged time of treatment. The furfural curves, on the other hand, show a rapid initial rise in concentration, followed by a rapid decrease. As would be anticipated, the critical time of treatment for optimum yields decreased with increased operating temperature (or pressure), EFFECT OF TEMPERATURE. The elevation of the boiling point of the dilute hydrolysis liquors due t o solute content was negligible, and values for water a t the pressures concerned could be used. Operation at a temperature equivalent t o 150 pounds per square inch gage yielded the greatest increase in organic acids, but best results for furfural were obtained a t 100 pounds gage. Since the increment in furfural yield is so much greater than that for organic acids, it is obvious t h a t the optimum temperature for formation of the former should govern. At this temperature the optimum operating time was about 15 minutes. The rates of increase and decrease of furfural are greater at higher pressures, a n indication t h a t the reactions of hydrolysis of pentosans t o furfural and of decomposition or polymerization and condensation of furfural are of the same order, and are affected in the same degree by temperature.
443
and isophorone. Furfural was also tested as a solvent for the organic acids. DISTRIBUTION COEFFICIENTS.Appropriate amounts of solvent, water, and acetic acid were shaken in a separatory funnel, both layers were titrated for acid, and the indicated terminals of tie lines were thus found. TERNARY DATA. Solubility data for the ternary diagrams of the systems solvent-water-acetic acid were determined for the solvents listed above, using pure mixtures of acetic acid and water rather than hydrolysis liquor. The diagrams and corresponding data for octyl acetate and isophorone were presented by Othmer, White, and Trueger (9); those for octyl acetate, octyl alcohol, isophorone, and furfural are shown in Figure 2 and Table 11. Tie lines, as determined from the distribution data, are shown for each ternary system. The ternary diagrams indicate desirable extraction characteristics for each of the solvents, although some shortcomings exist in each case.
EXTRACTION STUDIES
Only a few solvents meet specifications for extraction of organic acids and furfural from the dilute liquors involved, and the following were selected for trial: octyl alcohol, octyl acetate,
Table
I.
Rehydrolysis Runs
% CONC~NTRATION AT 50 LB./SQ. IN. Time, Min. Organic acids (as acetic) Furfural Reducing sugars Sulfuric acid
0 0.50 0.197 2.21 2.57
9 0.50 0.207 2.05 2.80
23 0.62 0.261 1.7 2.61
43 0.55 0.323 1.4 2.68
% CONCENTRATION AT 100 LB./SQ. IN. Time, min. Organic acids (as acetic) Furfural Reducing sugars Sulfuric acid
0 0.50 0.197 2.21 2.57
8 0.51 0.344 1.28 2.60
16 0.52 0.489 1.08 2.51
27 0.55 0.461 0.90 2.61
9% CONCEINTRATION AT 150 LB./SQ. IN. Time, min. Organic acids (as acetic) Furfural Reducing sugars Sulfuric acid
Wt. % a t 24' * 0.5O C. Octyl Acetic acetate Water acid 0.1 95.0 4.9 0.1 88.5 11.4 0.1 79.1 20.8 0.1 65.5 34.4 0.7 48.6 60.7 0.9 46.8 52.3 1.8 44.2 54.0 2.4 36.8 60.8 5.4 29.9 64.7 7.8 26.9 65.3 10.9 24.6 64.5 13.4 22.8 63.8 18.1 20.4 61.5 25.1 17.8 57.1 41.3 11.4 47.3 59.8 6.2 34.0 79.4 2.6 18.0
0 0,50 0.197 2.21 2.67
3.5 0.52 0.349 1.10 2.62
6 0.52 0.419 0.90 2.50
12 0.55 0.465 0.60 2.50
11.
Ternary
Table
Wt.% ' a t 25' Oct 1 alcoKol 0.8 1.5 5.2 9.2 11.3 21.0 25.1 29.5 33.6 36.1 38.3 43.3 50.2 56.9 63.9 89.3 77.0 80.9 82.7
* 0.5O C.
Water 62.0 55.6 42.4 36.3 32.7 25.8 23.6 21.4 19.2 18.0 16.8 14.1 11.3 9.9 7.1 4.2 0.8 0.7 0.9
Acetic acid 37.2 42.9 52.4 54.6 56.0 53.2 51.3 49.1 47.2 46.9 44.9 42.6 38.5 33.2 29.0 26.5 22.2 18.4 10,4
60
0.66 0.401 '1.1 2.67
Octyl acetate and octyl alcohol have a low mutual solubility with water, which is not increased appreciably until high concentrations of acetic acid are reached. Distribution coefficients for 46 acetic acid, as indicated by the slopes of the tie lines, are only 0.58 fair. 0.388 0.90 Isophorone is soluble to a limited extent in water, wiLh a 2.62 greater solubility of water in solvent. The distribution coefficients for acetic acid are excellent, being about 1: 1. The high mutual solubility of furfural and water is a n unde21 sirable factor, especially in view of the large proportion of water 0.57 0.361 present in the liquor. The use of furfural and octyl acetate as a 0.50 2.50 mixed solvent has been found advantageous in reducing Solubility Data this mutual soluWt. % at 24' A 0.5O C. Wt. % a t 27' * 0.5' C. bility (11) Iso-
phorone Water 7.5 65.1 13.7 58.6 19.2 50.8 23.6 41.7 24.2 45.6 25.9 42.9 30.0 38.8 30.9 37.8 31.7 37.8 39.2 30.8 48.8 23.6 56.9 19.1 66.6 14.0 89.3 13.1 71.1 12.1 77.4 10.8 86.9 7.4 90.3 5.8
Acetic acid 27.4 29.7 30.0 34.7 30.2 31.2 31.2 31.3 30.6 30.0 27.0 25.0 19.4 17.0 16.8 11.8 5.7 3.9
.
Furfural 8.3 9.9 13.2 19.0 21.6 74.8 78.6 83.5 86.2 88.4 91.0 92.5 94.0
Water 91.8 86.0 76.1 87.0 62.9 14.5 12.2 10.1 8.9 7.6 6.6 5.8 5.1
Acetic acid 0
6.1 10.7 14.0 15.8 10.7 9.2 6.4 4.9 4.0 2.5 1.7 0.9
I N D U S T R I A L A N D E N G I N E E ,RI N G C H E M I S T R Y
444
ATER
00
VOl. 37, No. 5
neither can extract efficiently batchwise more than about 85% of the organic acids; although octyl alcohol removed 90% of the furfural, isophorone removed only 50% due t o the very large reduction in the coefficient. CONTINUOUS EXTRACTION. Further studies of the efficiency of extraction of organic acids and furfural were carried out in a continuous laboratory extraction column. This unit consisted essentially of a 1-inch Pyrex tube, 4 feet long and jacketed with a 2-inch tube to permit heating. Solvent and solution were fed by small centrifugal pumps through brass spargers which could be adjusted t o vary the feed rate and droplet size of the liquid streams. Operations were controlled t o give: fixed position of the interface, fixed ratio of solvent to liquor, and controlled rate of flow of solvent and liquor. Extractions with equal solution-solvent rates of 500-2310 cc. per hour, made with octyl acetate and isophorone (Table IV), proved that only traces of sulfuric acid and no sugars were extracted by either solvent. Recovery of furfural and organic acid increased with liquor rate for both solvents, a n indication that critical flow rates were not reached. Excessive acetic acid in the raffinate from the octyl acetate extractions was probably due to hydrolysis of the solvent.
ATER 00 Table Liquor
Rate”, @c./Hr. 660 960 ACETIC ACID
A A . A A A
ao
1200 2000
Figure 2.
Ternary Solubility Diagram and Tie Lines for Four Systems of Solvent-Water-Acetic A c i d
HarcH EXTRACTION. Preliminary tests on the efficacy of the aoivents in extracting organic acids and furfural from hydrolysis liquors were carried out batchwise i n separatory funnels. Initial teats were run on synthetic mixtures of water, sulfuric acid, furfural, and acetic acid, in order to minimize possibilities of interFeience with analyses due to sugars and extraneous materials piesent in wood hydrolysis liquors. Batch extractions were then carried out on hydrolysis liquor obtained from treatment of maple sawdust in the continuous hydrolysis process. Ifter elimination of the less desirable solvents, multiple batch extractions were carried out with isophorone and octyl alcohol in four steps. A fresh batch of solvent equal in volume t o the original liquor was used in each step (Table 111). Since both solvents have rapidly decreasing coefficients for wetic acid and furfural with reduced concentration in the liquors,
Table
dolvent i)ctyl dcohol Total Isophorone
111.
Multiple c/o Extd. in Each Stage Stage Organic FurNo, acids fural 1 47.4 61.5 2 34.3 53.7 3 36.8 44.2 4 25.6 1.1 1 2 3 4
74.5 26.5 16.9 5.5
47.7
[email protected] a
Total * Insufficient material for analysl.
Batch Extractions yo Extd. oi Total Materlal K (per Stage) Organic Fur- Organic Furacids fural acids fural 47.4 61.5 0.9 1.6 18 1 20.7 0.52 1.16 12.7 7.9 0 58 0.79 5.6 0.1 0.34 0 01 83.8 90.2 74.5 47.7 2.92 0.91 7.0 3;4 0.35 0.27 3.1 0.20 0.8 85.4
0.06
61.1.
IV.
Continuous Extractions Organic Acids, Furfural, Reducing Sugars,
Component Extraot Ra5nate Extract Raffinate Extraot Raffinate Extract Raffinate
Extract Raffinate 1000 Extract Raffinate 1760 Extract Raffinate Extract 2310 Raffinate 0 So1vent:solution ratio = 600
Wt. %
Wt. %
Octyl Acetate 0.076 0.066 0.505 0.07 0.069 0.08 0.57 0 062 0.069 0.074 0.518 0.063 0.125 0 081 0.525 0.051 I
Isophorone 0.16 0.04 0.40 0.104 0.13 0.039 0.39 0.105 0.25 0.064 0.08 0.26 0.27 0.089 0.25 0.055 1: 1.
Wt. % 0 1.57 0 1.57 0
1.58 0
1.57 0 1.65 0 1.65 0
1.65
0
1.65
Sulfuric Acid, wt. % Traces 2.4 Traces 2.4 Traces 2.4 Traces 2.4 0 2.5 0 2.5 0 2.5 0 2.5
Octyl acetate was more efficient in extraction of furfural than organic acids b u t was eliminated due to excessive hydrolysis. Isophorone showed good solvent power for both components; especially notable is the fact that the efficiency of extraction of furfural was even greater than t h a t of acetic acid. This is not in agreement with the low coefficients found for furfural in the multiple batch extractions, indicating some difficulty in analysis a t low concentrations. The recoveries of 59-60% obtained in a 4foot column are promising for design considerations for a large scale extractor. CONCLUSIONS
Rehydrolysis of waste wood hydrolysis liquors yields 10-14qrb additional organic acids (as acetic) and 100-140% additional furfural, over and above the original yields obtained during the hydrolysis of the wood. Optimum conditions for obtaining these yields are 15-20 minutes of treatment at 100 pounds per square inch gage in batch operation. Correlation with operations on batch and continuous wood hydrolysis (3’) would indicate that the same result could be obtained in about 1-2 minutes a t 200 pounds per square inch gage in a continuous hydrolysis unit. The question also arises as to whether the same results could be obtained by recycling hydrolysis liquors t o accomplish rehy-
May, 1945
INDUSTRIAL A N D ENGINEERING CHEMISTRY
SOLVENT^ Figure 3. A.
E. C.
'
to the feed. The extract layer, with most of the furfural and organic acids and also a small amount of water, is then sent t o azeotropic column B for separation of furfural and water from the acids and solvent. Crude furfural is drawn off from decanter F after adjusting the reflux to column B, so as to keep down t h e acids and solvent. The crude furfural is sent t o furfural column E where it is stripped from the isophorone, preferably under vacuum. The water layer from decanter F goes to stripping column D. Acid column C is used for the separation of solvent, and organic acids. The small amount of solvent dissolved in the deacidified water discharged from the extraction column is recovered in stripping column D. The solvent is returned t o extractor A . The water layer is run t o waste. Suitable additions to this system may be employed t o recover most of the sensible heat present in the solvent or water leaving each column. The most important heat exchanger would recover the sensible heat in the solvent discharged from the base of acid column C by preheating the liquid feed to column B. These exchangers are not shown in Figure 3. The necessary pumps, as well as storage tanks, are also omitted from the diagram.
I
ACKNOWLEDGMENT
Proposed Flow Sheet for Recovery of Organic Acids and Furfural b y lsophorone
Extraction column Areotropie dehydrating column Acetic acid column
D. E.
445
Water column Furfural column
Bcknowledgment is made to the Northwood Chemical Company, Phelps, Wis., for thp support of the fellowship under whirh this work was done.
F,C. Decantera
LITERATURE CITED
drolysis (of pentosans) and hydrolysis of wood simultaneously. Initial work along this line has been promising. Recovery of the by-products from the very dilute solutions encountered may be feasible in work with isophorone. Final cost analysis must await further research on stripping of solvent from water and determination of equipment sizes and costs t o balance these values against heat economy. Figure 3 is a proposed flow sheet of a process utilizing isophorone for the solvent recovery of organic acids (as acetic) and furfural from dilute solutions obtained by the hydrolysis of wood. The dilute solution is charged into extraction column A and is met by solvent passing up through the extractor countercurrent
(1) Bott, H.G.,and Hirst, E. L., J . Chem. Soc., 1932,2621. (2) Hurd, C.,and Isenhour, L., J. Am. Chem. SOC.,54,317 (1932) (3) Katzen, R., and Othmer, D. F., IND.ENO. CHEM.,34, 344 (1942). (4) Killefer, D.,Ibid., 18, 1217 (1926). (5) Mains, G.H., Chem. & Met. Eng., 26,841 (1922). (6) Miner, C. S., and Brownlee, G., U. S. Patent 1,735,084(1929). (7) Midis, G.,and Gorokholinskaya, M., J. Chem. Ind. (U.S.S.R.), 12, 166 (1935). (8) Othmer, D.F.,Chem. & Met. Eng., 48,6-91 (1941). (9) Othmer, D.F.,White, R. E., and Trueger, E., IND. ENO.CHEM., 33, 1240 (1941). (10) Pervier, N.C.,and Gortner, R. A.,Ibid., 15, 1167 (1923). (11) Wentworth, T.O.,U. S. Patent 2,255,235(1941). (12) Zagryatzkaya, V.,J . Applied Chem. (U.S.S.R.), 9,254 (1936).
.
OXIDATION of HEXADECANE H. B. H a s , E. T.
McBee, and J.
W. Churchill'
PURDUE UNIVERSITY AND PURDUE RESEARCH F O U N D 4 T I O N , L A F A Y E l T E , IND.
Hexadecane was oxidized with air under a pressure of PO00 pounds per square inch at temperatures from 190: to 300" C. The products were analyzed for alcohols, acids, esters, and carbonyl compounds. Hydrogenation of the oxidation products gave materials containing alcohols having average molecular weights as high as 165. Conversions for the two-step process were as high as 17%. Oxidations at 300" C. were characterized b y the formation of sooty suspensions and products low in partial oxidation products.
A
LCOHOLS possessing long aliphatic chaias are commercially important in the production of detergents, synthetic waxes, insecticides, fungicides, and wetting, emulsifying, and foam-producing agents. Such alcohols are obtained industrially by catalytic hydrogenation of esters of the corresponding acids. The availability and low cost of raw materials 1 Present address, Mathieson Alkali Works, Inc., Niagara Falls, N. Y,
has stimulated interest in the production of these higher alcohols by air oxidation of hydrocarbons. Aliphatic hydrocarbons are easily oxidized. Bubbling air through hexadecane a t 110' C. and atmospheric pressure will effect dehydrogenation, carbon-carbon -fission, and the formation of alcohols, aldehydes, acids, ketones, peroxides, carbon dioxide, and water (11). The rate at which oxygen reacts with normal octane in the vapor phase at atmospheric pressure is greater than its rate of reaction y i t h 3-methylheptane, Q-ethylhexane, 2-methyl-3-ethylpentane, or 2,2,4trimethylpentane under similar experimental conditions (16). It has not been demonstrated that normal alkanes are more rapidly oxidized than their branched-chain isomers
