not as active as catalase, demonstrates superior resistance to the effects of peroxide at high concentrations and deactivates slowly enough to be considered for long term usage. The kinetics of the system appear to be first order over the range of variables studied, but corrections for the rate constant are required due to particle size or feed buffer ions. An activation energy of about 8600 cal/mol is probably satisfactory for particle sizes of the present study, but should be used with 'caution for other particle sizes.
Altomare, R. E., Greenfield, P. F , Kittrell, J. R.. Biotechno/, Bioeng., accepted for publication (1974a). Altomare, R . E . , Kohler, J.. Greenfield, P. F., Kittrell, J. R . , Biotechno/. Bioeng., accepted for publication (1974b) Rosell, J. M.. Can. Dairy I c e Cream J . , 40, 50 (1961) Roundy, 2. D . , J . Dairy Sci.. 41, 1460 (1958). Rovito. 6.J . , Kittrell, J. R . , Biotechnol. Bioeng., 15, 143 (1973) Scott, D . , U.S. Patent 2,758,934 (Aug 14, 1956) Scott, D , Hammer. F . , fnzym., 22, 229 (1960) Smith, J. M.. ' Chemical Engineering Kinetics," 2nd ed. McGraw-Hill, New York, N.Y., 1970 Traher. A D . , Kittrell, J. R.. Biotechno/. Bioeng.. 16, 413 (1974). Whitaker. J. R , ' Principles of Enzymoiogy for the Food Sciences," Marcel Dekker, New York. N. y . , 1972
Literature Cited Receiced for reuzew J u n e 12, 1974 Accepted D e c e m b e r 9, 1974
Altomare. R . E., M.S. Thesis, Department of Chemical Engineering, University of Massachusetts, Amherst, Mass.. 1974.
Levulinic Acid from Sucrose Using Acidic Ion-Exchange Resins Richard A. Schraufnagel and Howard F. Rase" Department of Chemical Engineering, The University of Texas, Austin, Texas 78772
The production of levulinic acid and 5-hydroxymethylfurfural was studied using highly acidic ion-exchange resins as catalysts and sucrose as a convenient soluble polysaccharide. Four commercial resins were compared at 100°C. Resin pore size had a major effect on selectivity. Ion-exchange resins are attractive for this process because of the selectivity possible by pore-size control and the reusable character of any solid catalyst. Higher temperature resins, however, are needed to take advantage of faster rates possible with modest temperature increases.
Processes developed in the 1920's to 1940's for producing useful chemicals from farm products proved in most cases to be uneconomical because low cost natural gas and oil assured the success of a rapidly growing petrochemical industry. Recent events, however, have dramatized the need for replenishable raw materials such as farm products or, more particularly, waste materials from such products as alternate sources of industrial chemicals and polymers. It would seem desirable therefore, to reexamine older studies in this area with the view of adapting newer techniques and materials to producing useful products. One such product, levulinic acid (4-oxopentanoic acid, CH3COCH2CH2COOH), has been known since 1840 to result from the reaction of carbohydrates with mineral acid (Mulder. 1840). It has great potential as a chemical intermediate in producing various pharmaceuticals, pesticides, and plasticizers. A solution of its sodium salt is a less corrosive permanent anti-freeze than ethylene glycol (Aries and Copulsky, 1949), and levulinic acid itself is used as a dye mordant in the textile industry. Most of its extensive possible uses, which have been documented by Leonard (1956) and Morton (1947) have not been developed because of low yields of existing processes and, until recently, lower costs of petroleum derived intermediates. The many new, highly efficient, and rugged ion-exchange resins now marketed offer possibilities for more effective and economical means for converting carbohydrates to levulinic acid. In order to assess such possibilities sucrose was used as a convenient soluble polysaccharide for evaluating four commercial ion-exchange resins described in Table I as catalysts in producing levulinic acid and an intermediate product, 5-hydroxymethylfur40
Ind. E n g . Chem., Prod. Res. Dev., Vol. 1 4 , No. 1. 1975
fural (5-HMF), which has potential use as a raw material for adipic acid manufacture (Aries and Copulsky, 1949). Because of its major importance in foods and concomitant price volatility, sucrose would not be a logical raw material source, but it serves as a useful model compound since it hydrolyses into the well-known monosaccharides, glucose and fructose. Previous Work Early work on levulinic acid involved studying different carbohydrate sources including glucose, fructose, lactose, sucrose, starch, cellulose from wood pulp, and chitin (Wiggins, 1948). Yields in these studies, performed at atmospheric pressure, were usually less than 25%. In later studies by McKibbins (1962) autoclaves were used to increase reaction temperature to 160-200°C and thereby increase yields. The effects of acid concentration and type were also studied. Commercial production using an autoclave began in the United States in 1940 by A . E. Staley Co. using dextrose as feed and HC1 as the acid (Meyer, 1945). Four additional patents exist (Redmon, 1956; Dunlop, 1957; Carlson, 1962; Sassenrath, 1966). The process by Redmon employs an ion-exchange catalyst. The advantages of an ion-exchange process are : (1) little humin (or solid waste) byproduct, (2) reaction temperature can be low, and (3) the catalyst can be readily separated from the reacted mixture, and regenerated. The patent by Dunlop (1957) describes an atmospheric pressure process for producing levulinic acid from any hexose-yielding substance ranging from sucrose to cellulosic wastes such as corn cobs, bagasse, grain hulls, and wood products.
Table I. Physical Properties of Ion-Exchange Resins
Designation A
Trade name
C
4.5- 4.9
....
35
30-35
3 80
150
Amberlyst 15
3446
4.40
0.193
55
36
265
100
Amberlyst
sw 720740
3.60
1.90
540
50
51
100
SW -0161
3.50
0.716
120
40
175
100
XN-1010
D
Porosity vol 4;
Max recomAv pore mended diameter, operating A temp, "C
MM-12042PG-H
Dowex MSC - 1H
B
Lot no.
Calcd wt Wt capacity Internal capacity of on internal surface dry resin surface area, mequiv g-1 mequiv g-' m2 g-'
Amber lv st XN-1005
Herndon (1950) prepared an engineering study on the production of levulinic acid from sucrose. Even though the cost data are about 25 years old, areas that have to be considered to improve the economic picture are well documented. Cheap feedstocks are needed, such as pulp or crop wastes. The reaction conditions must be such that high yields are produced with a minimum amount of heat input. More efficient ways should be found to extract and purify the product. The acid catalyst should be easily separated from the solution. For this latter reason ion-exchange resins would improve the potential of the process. Mechanistic and kinetic studies have been reported by Anet (1962). Feather and Harris (1973), McKibbins, et al. (1962), Moye (1964), and Wiggins (1949). There appears to be general agreement that the carbohydrate is first hydrolyzed by the acid catalyst to form glucose and fructose. These sugars then react by parallel and apparently firstorder mechanisms to produce the intermediate product 5-hydroxymethylfurfural (5-HMF) which then is further degraded by the acid catalyst to levulinic acid and formic acid. Small amounts of solid products from a side reaction have been found experimentally, but the formation of these products is not completely understood. Some intermediates other than 5-HMF have been postulated. Experimental Procedure and Equipment The activity of the four acidic ion-exchange resins, physical properties for which are summarized in Table I, were compared using a 500-ml 3-neck flask with a reflux condenser as a batch reactor operating at atmospheric pressure and heated isothermally at 100°C by an oil bath. In order to avoid breakage of the resin, 200 ml of water was slowly added to 25 g of dry resin. A pH in the range of 2 in the bulk liquid was attained by this procedure. After heating the solution to 100°C, 40 g of sucrose was dissolved giving an initial sucrose concentration of 0.52 mol/ 1. Samples (0.5 ml) were taken from the well-stirred solution a t 1-2-hr intervals using an Oxford Sampler. The samples were put into glass vials, quenched in an ice bath, and then analyzed for levulinic acid and 5-hydroxymethylfurfural using gas chromatography. A sample of 4-8 pl was injected into a Perkin-Elmer Model 154D vapor fractometer with a 2-m column, packed with Teflon and containing polypropylene glycol 1500. The column was operated isothermally at 200°C with a pressure of 15 psig. Levulinic acid and 5-HMF were eluted within 15 min. A typical chromatogram exhibited a water peak followed by a peak superimposed on the tail of the water peak at about 3 min, levulinic acid at 6-7 min, and 5
HMF at 10-12 min. Occasionally a minor peak was found just after the levulinic acid peak. No additional peaks were eluted even though the chromatograph was initially run for 30 min. When freshly acidified solutions of sucrose, glucose, or fructose were injected into the column some reaction occurred to produce 5-HMF causing an error of 10-15% in the determination of this compound. No interference was found to occur with the other peaks except a larger amount of noise and more baseline drift was apparent with sugar present than without. Attempts were made to determine the identity of the unknown peak occurring a t 3 min. Samples of furfuraldehyde and formic acid did not give peaks corresponding to peak A. It was postulated that this peak was due to either an unidentified intermediate or side-reaction product. Feather and Harris (1973) also postulate intermediates that were not isolated. A reasonable approximation of the molar concentration of the unknown peak could be made using the same calibration curve as that for levulinic acid and 5-HMF. Solutions of product could be analyzed to within 5 1 0 % for levulinic acid. This error was greater than the 1-270 random error found when solutions containing no sucrose were analyzed due to some decomposition of the sugar affecting the performance of the column. Another source of experimental error was found when the time-zero sample did not give zero concentration of product. This was caused by rapid initial reaction of the sugar during its dissolution and inversion in the ion-exchange-water system a t 100°C. The random and zero-offset errors were small enough to make valid comparisons between the reactivity of the four resins. The results are plotted in Figures 1 and 2 with the spread of data indicated at each point based on two or more individual runs each analyzed in triplicate. Experimental Results Concentration of Products us. Time. The production of 5 hydroxymethyl furfural and levulinic acid from sucrose was affected by the type of highly acidic ion-exchange resin used even though the average bulk solution pH was between 1.65 and 1.95 in all cases. Figure 1 shows the molar concentration of levulinic acid produced by each resin as a function of time for an initial sucrose molar concentration of 0.52 molil. The greatest production is achieved with resin A, 0.25 mol/l. at 24 hr. Resin B has physical properties similar to resin A and, hence, gives a similar conversion curve. Only about 0.16 mol/l. of levulinic acid is produced using resin C. and 0.09 mol/l. of acid is produced a t 24 hr with resin D. The plot of conInd. Eng. Chem.. Prod. Res. Dev.. Vol. 14, N o . 1 , 1975
41
Table 11. Yield of Levulinic Acid for the Four Catalyst Resins at 100" C Resin
Time. h r
% Yield of levulinic acid
A
9 24
12.5 24 .O
B
9 24
12.5 23 .O
C
9 24
9.5 15.5
D
9 24
4 .O 9 .o
Figure 1. Comparison of levulinic acid concentration produced by several acidic ion-exchange resins.
Table 111. Time for a Given Selectivity toward Levulinic Acid to be Achieved for Each Resin Reaction time. h r Resin
505
A 7.5 B 7 C 3.5 D 16.5 a Moles of levulinic acid
Selectivity'' 705 12.5 12 8 224 X 100% /total
83q
24 24 12 >>24
moles soluble product.
TIME (hours)
Figure 2. Comparison of 5-hydroxymethylfurfural concentrations produced by several acidic ion-exchange resins.
centration us. time is linear except when the concentration of levulinic acid reaches approximately 0.14 mol/l. where a slight deceleration of the reaction occurs as equilibrium is approached. Figure 2 is a plot of concentration of 5-hydroxymethylfurfural us time. The concentration reaches a maximum value and then decays to zero as is typical for an intermediate product. Initially the reaction is quite fast. As the sucrose dissolves in solution, large amounts of 5-HMF form almost immediately with the major conversion to 5-HMF occurring in less than 3 hr. Resins A and B achieve the greatest conversion of 5-HMF. With resin D the concentration of 5-HMF is constant for the first 12 hr, meaning it is produced as fast as it is reacted. Resin C produces the least amount of 5-HMF. and after 12 hr the 5-HMF disappeared from the solution. After 24 hr 5-HMF is present in only resin A solutions. Yield and Selectivity. Because of the complex nature of this reaction system, yields and selectivities for the two major products are of major interest. These may be defined as follows for both levulinic acid (LA) and 5-hydroxymethylfurfural(5-HMF) selectivity =
moles of LA or 5 - H M F or 2(moles s u c r o s e converted)
moles of LA o r 5 - H M F moles of soluble product Soluble products are defined as all the products detected by the gc analysis. The insoluble product produced by side reactions is neglected. -
42
yield =
moles of LA o r 5 - H M F 2(moles s u c r o s e initially charged)
-
concentration of LA o r 5 - H M F Z(initia1 concentration of s u c r o s e )
Ind. Eng. Chem., Prod. Res. Dev., Vol. 14. No. 1, 1975
Yield is related to the product of selectivity and fractional conversion (moles of sucrose converted per mole of sucrose charged). High yield is thus the result of good selectivity and conversion. In Tables I1 and I11 yields and selectivities at several times are compared. The three reactive resins achieve the apparent equilibrium selectivity of 83%. Evaluation of Catalyst Performance. Under the conditions tested resins A and B are most active and produce the highest yields of levulinic acid but resin C has the highest inherent selectivity as judged by conditions removed from equilibrium. Because of its high selectivity, yields could be greatly improved by increasing the ratio of resin C t o reactant. Resin D exhibited both poor yields and selectivities. Pore Size and Selectivity. Since the overall reaction involves a series scheme in which an intermediate, 5HMF, reacts further to produce levulinic acid, one might expect an effect of pore size on selectivity as suggested by Wheeler (1951). A large pore resin will allow the intermediate, 5-HMF. to diffuse out more rapidly so that there will be less chance for it to form levulinic acid and a greater chance for 5-HMF to appear in the product. By contrast a small-pore resin will inhibit the egress of the intermediate and provide a greater opportunity for conversion to levulinic acid. There are no doubt intrinsic selectivity differences between the several resins, but the trend with pore size is significant as shown in Figures 3 and 4. Selectivities for both products are given as a function of normalized time which corrects for differences in the apparent activities of the resins. It is clear that the intermediate, 5-HMF, is favored by larger pores and levulinic acid by smaller pores. Comparison of Results with Previous Work. The mechanism of levulinic acid formation is still not completely understood, but it has been found that the monosaccharides, fructose and glucose, can break down bs a series of apparent first-order reactions to produce 5-HMF and levulinic acid (McKibbins, 1962).
90
I
/I
10r'LResIn~~
1
,
,
O 0
0
I0
5
0
i k, kg /kr
:
/
h, 1
L
I5 20 25 -TIME,, h o u r s
R a t i o ota;parent z e r o - o r d e r 'ate constant for Resin 3 to 'hot f o r lesin being considered
IC:
5
I K~
!k
r
5 ,
I5
20
1 k r I x TIME,
25
30
L
4 6 8 TIME i hours)
1
9
Figure 3. Comparison of levulinic acid produced with sucrose and fructose as reactant with resin C . Initial concentration: 0.5 mol/l.
30
Figure 3. Selectivity toward levulinic acid for each resin as a function of normalized time.
0
2
I
I
35
hours
of apparent z e r o o r d e r r a t e c o n s t a n t l o r R e s n D t o t h a t lor Rot10
resin being Coisldered
Figure 1. Selectivity toward 5hydroxymethylfurfural for each resin as a function of normalized time.
Rate data for production of levulinic acid from sucrose and from fructose using ion-exchange resin C (Figure 5) show that the reactions of both glucose and fructose are the controlling steps and that the rate for fructose is 50 times that for glucose a t 100°C. Based on homogeneous rate data (McKibbins, 1962), the glucose rate increases 70 times by increasing the temperature from 100 to 140°C. If high-temperature ion-exchange resins are developed, this higher temperature would be attractive since most waste carbohydrates would hydrolyze into glucose units. It should be noted, however, that levulinic acid may also be produced directly from a polysaccharide. Referring to Figures 1 and 5 it is seen that there is an offset at time zero which cannot be explained by an overall zero- or firstorder rate. The sample a t time zero was taken after all the sucrose was dissolved in the acid reaction system, several minutes after addition was started. Since no levulinic acid is formed initially with only fructose present (Figure 5), and the rate of formation from glucose is low at this temperature, it appears that levulinic acid can be formed by another means when a polysaccharide is present. When polysaccharides dissolve in acid solutions, they
will break down into their monosaccharide components. Thus sucrose will undergo an inversion process to form glucose and fructose. Reed and Dranoff (1964) studied sucrose inversion using an acidic ion-exchange resin and found the reaction to be first order and inversely proportional to the particle diameter. Extrapolating their data to 100°C, a first-order rate constant of 0.33 min-1 is found or the reaction will be 99% complete in about 13 min, which is considerably beyond the initial sampling time. It seems that during the process of inversion, polysaccharides can form an intermediate structure that readily reacts to give levulinic acid. The offset was different for each of the resins which would seem logical as geometry could play a vital role in this reaction. Even though the rate of reaction of glucose is slow at l W C , higher polysaccharides could still react at this temperature to form levulinic acid because of this inversion process. Earlier work using mineral acids by Wiggins (1949) and McKibbins (1962) indicate higher reaction rates at the higher temperatures used (160-220°C). Similar yields were obtained in shorter times than in the present study. Slightly higher temperature and increased reactant concentration, however, would make the resin process more attractive particularly when the possibility of manipulating selectivity through pore size is considered. Only resin A, however, can be used at a higher temperature than that employed for the comparative study. Conclusions Although it is possible to produce levulinic acid at moderate temperatures (100°C) using ion-exchange resins in the acid form, the rates are low. High selectivity is favored by small pores and further work on developing resins of this type which can be used above 100°C for extended periods is indicated. Waste sources of hexoses such as sawdust, corncobs, grain hulls, and bagasse may prove to be economical feed materials in areas of the country where large quantities are readily available in centralized locations such as grain or corn processing plants. The recent introduction of a commercial process for isomerizing glucose to fructose (Schnyder and Logan, 1974) adds the possibility of converting glucose to more reactive fructose for subsequent reaction using ion exchange. Acknowledgment
W. C. Bauman of Dow Chemical Company and Robert Albright of Rohm and Haas Company supplied resin samples and physical property data. Ind. Eng. Chem., Prod. Res. Dev., Vol. 14, No. 1 , 1975
43
Literature Cited Anet. E. F., Chem. Ind., No. 6, 262 (Feb 10, 1962). Aries, R.. Copulsky, W., "The Commercial Potential of Levulinic Acid and Related Products from Sucrose," Sugar Research Foundation, Inc., Report, New York. N. Y . , 1949. Carlson, L. J., U. S. Patent 3,065,263, (Nov 20, 1962). Duniop, A P., U . S. Patent 2,813,900 (Nov 19, 1957). Feather, M S.. Harris, J. F . , in Advan. Carbohydrate Chem., 28, 212 (1973). Herndon, L. K., "Engineering Study of Preparation of Levulinic Acid from Sucrose,' Sugar Research Foundation, Inc., Member Report No. 21, New York, N . Y . . 1950. Leonard. R , l n d Eng. Chem.. 48 (8) 1331 (1956). McKibbins, S.. Harris, J., Saeman. J.. Neill. W., Forest Products J., 17 (Jan 19621 Meyer. W.:U. S. Patent 2,382,572 (Aug 14, 1945). Morton, A. A,, "Levulinic Acid as a Source of Heterocyclic Compounds,"
Sugar Research Foundation, Inc., Scientific Report No. 8, New York. N . Y.,1947. Moye, C. J.. Rev. Pure Appl. Chem.. 14, ( 4 ) , 161 (1964) Mulder. J. C. J. Prakt. Chem., 21, 219 (1840) Redmon, Bryan, U S. Patent 2,738,367 (Mar 13, 1956). Reed, E. W., Dranoff. J. S., lnd. Eng. Chem., Fundam., 3 ( 4 ) , 304 (1964) Sassenrath, C. P., U . S. Patent 3,258.481 (June 28, 1966) Schnyder. B. J., Logan, R. M . , "Commercial Application of Immobilized Glucose Isomerase." 77th National Meeting, American Institute of Chemical Engineers, Pittsburgh, Pa., June 2-5, 1974. Wheeler, A.,Advan. Catal., 3, 317 (1951). Wiggins, L. F.. Advan. Carbohydrate Chem., 4, 293 (1949) Wiggins. L. F.. "The Preparation of Levulinic Acid from Sugar." Sugar Research Foundation, Inc., Report, New York, N. Y..1948.
Receioed /nor reuieu May 22, 1974 Accepted Xovember 11, 1974
Frictional Properties of Adsorbed Halogenated Carboxylic Acids-Potential
as
Coupling Agents Robert C. Bowers,r Elaine G. Shafrin, and William A. Zisman Laboratory for Chemical P h w c s Naval Research Laboratory. Washingtcn D C 20375
T h e adhesive and cohesive strengths of adsorbed monomolecular layers of potential coupling agents were studied by measuring t h e coefficients of friction for solutions of a series of carboxylic acids which contained either a terminal CI, Br, or I atom or a p-chlorophenyl group. Acids w e r e chosen because of their ability to adsorb on many solid surfaces. T h e selection of t h e terminal substituent on each acid was dictated by considerations of wettability, hydrophobicity, and thermal and oxidative stability. Boundary friction of t h e adsorbed acids was nearly independent of t h e specific outer terminal group. Since it is these terminal groups which determine t h e ease of spreading, it is therefore possible to design n e w coupling agsnts which have a high surface energy b u t low friction and good adhesion properties. Chlorophenylalkyl-substituted dicarboxylic acids were more effective lubricants than t h e corresponding mono- or tricarboxylic acids for glass sliding on glass.
Introduction
In the manufacture of reinforced plastics, current practice is to increase composite strength and water resistance by precoating the reinforcing fibers or particles with a thin film of molecules called a "coupling agent." The function of this film is to improve the wetting of the fiber by the molten plastic and hence increase the adhesion between them. The internal cohesive strength of the coupling film must be sufficient to prevent failure within the film, and its adhesion to the fiber must be adequate to prevent failure a t the film-fiber interface. One method of determining the combined adhesional and cohesional strengths of potential coupling agents is to measure their coefficients of kinetic friction ( b k ) under boundary lubricating conditions. Under these conditions, lubrication is independent of fluid viscosity and is determined by the degree to which adsorbed lubricant films can prevent direct contact between the sliding solids. It is generally accepted that these adsorbed films are only a monomolecular layer (see for example the standard texts by Bowden and Tabor (1950) and by Godfrey (1968)). An effective boundary lubricant usually consists of amphipathic molecules dissolved in a nonpolar base fluid. Because of their polarity and structure, the additive molecules preferentially adsorb on the surface and orient themselves nearly perpendicular to the surfaces with the 44
Ind. Eng.
Chem., Prod. Res. Dev., Vol. 14, No. 1, 1975
nonpolar ends projecting outward. The effectiveness of the adsorbed film formed by these molecules in inhibiting contact between two sliding solids depends upon the strength and rate of adsorption and upon the strength of the cohesive forces among the adsorbed molecules (Levine and Zisman, 1957a). Adhesive forces will be greater for chemical adsorption than for physical adsorption. Cohesive forces will increase with packing density and with the chain length of the film molecules. With boundary lubrication there is always some contact between the sliding solids through the adsorbed film. Since the force required to shear the solid junctions formed by contacting asperities of the sliding solids is large compared to the force required to shear the zone formed between the adsorbed monolayers on each sliding surface, a low coefficient of friction is indicative of the degree of prevention of solidsolid contact or of the strengths of the adhesive and cohesive forces of the adsorbed film (Levine and Zisman, 1957b). Advances in understanding the mechanism of adhesion (Zisman, 1963, 1965, 1969) have led to the recognition of the importance of obtaining as complete and spontaneous initial spreading of the liquid adhesive over the solid adherend as possible. This condition is an important precursor to forming strong joints. Investigations of the surface properties of solids demonstrated that organic resins could be made to wet solids coated with an adsorbed coupling
