Ind. Eng. Chem. Res. 1997, 36, 5063-5067
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Rapid and Selective Conversion of Glucose to Erythrose in Supercritical Water Bernard M. Kabyemela,* Tadafumi Adschiri, Roberto M. Malaluan, and Kunio Arai Department of Chemical Engineering, Tohoku University, Aza, Aoba, Aramaki, Aoba-ku, Sendai, Japan
Hiroshi Ohzeki Analytical Research & Computer Science Center, Asahi Chemical Industry Company, Ltd., 2-1 Samejima, Fuji-city, Shizuoka, 416 Japan
We here report a continuous method in which glucose is converted by reaction with supercritical water at 400 °C and 30 MPa, to erythrose in as high as 50 wt %. This method is noncatalytic and operates continuously with a reaction residence time of as low as 0.11 s. Erythrose is stable under these conditions and its selectivity changes only slightly from about 50 to 45 wt % over the range of glucose conversion from 50 to 90 wt %. This method has an advantage over other conventional methods in that it is rapid and continuous and results in comparative high yields of erythrose. Furthermore, the use of toxic chemicals is reduced and product separation is facilitated. Introduction Erythrose has a high potential in food, polymers, fine chemicals, and pharmaceutical industries. Erythrose can be reduced by hydrogenation over a platinum catalyst to yield erythritol (Sonogashira and Nakagawa, 1972), which is quite important in food applications (Roper and Goossens, 1993) as it is toothfriendly, has no side effects, is safe for diabetics, and has a low calorific value (0.3 kcal/g). The condensation products obtained by the N-acetylneuraminic acid adolase reaction with erythrose are side-chain-modified sialic acids of biological interest (Fitz et al., 1995). The original method for preparing D-erythrose is referred to in the review of the methods of carbohydrate chemistry by Whistler et al. (1962) who degraded D-arabinose oxime through the acetylated aldononitrile. Improvements to this method have been formulated (Hockett and Maynard, 1939), but the more direct route giving high D-erythrose yield has been proposed which involves the oxidation of glucose by using lead tetraacetate (Whistler et al., 1962) (eq 1). D-glucose
2Pb(OCOCH3)4
98 H3O+
di-O-formyl-D-erythrose 98 D-erythrose (1) However, this method (Whistler et al., 1962) still involves a series of complicated treatments: first, mixing with glacial acetic acid and cooling, followed by lead tetraacetate addition. The mixture is then treated with oxalic acid and filtered and the filtrate concentrated with the residual triturated with ethyl acetate. It is then extracted twice and dried. Ethyl acetate is then evaporated, and the colorless liquid remaining (mainly di-O-formyl-D-erythrose) is dissolved in sulfuric acid and stored for 5 h. The hydrolyzate is neutralized and regenerated with sodium hydrogen carbonate, and the resin is filtered and washed. The filtrate contains about 75 wt % D-erythrose which amounts to about 50 wt % yield from glucose. This method is used for lab scale †
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production of erythrose and would be difficult for mass production. Our method which we propose here is simple: just heat up the glucose aqueous solution to the supercritical state without any catalyst and quench the reaction after a reaction time of 80 ms. Nevertheless the selectivity of erythrose equals that of the conventional one. The hydrothermal decomposition of glucose with the acid catalyst in subcritical water has been under study by a number of researchers (Smith et al., 1982; Theander and Nelson, 1988; Dadach and Kaliaguine, 1993). A study of the products has shown the major product to be 5-(hydroxymethyl)-2-furaldehyde (5-HMF) (Wolfrom et al., 1948; Theander and Nelson, 1988) for temperatures between 100 and 200 °C. Also a number of research studies (Bonn and Bobleter, 1983; Holgate et al., 1995) have been reported for the hydrothermal decomposition of glucose without catalyst in the temperature range of 150-300 °C. Reaction conditions of 240 °C and residence times of about 1.3 min have shown the products to be mainly fructose, glyceraldehyde, dihydroxyacetone, glycolaldehyde, methylglyoxal, 5-HMF, and furfural. At higher temperatures of 600 °C and residence times of 6 s (Holgate et al., 1995), the products of glucose hydrolysis have been mainly gases such as hydrogen, carbon dioxide, carbon monoxide, and methane, with liquid products such as acetic acid, acetaldehyde, and 5-HMF. Erythrose has not been detected in these previous studies in hydrothermal conditions. The difference in conditions of our method (Kabyemela et al., 1997) from the previous studies are (i) the temperature range of 380-400 °C as compared to other studies at 150-300 °C (Bonn and Bobleter, 1983) or 600 °C (Holgate et al., 1995) and (ii) the very short residence time in our case. The objective of this paper is to demonstrate that erythrose is produced selectively by the decomposition of glucose in supercritical water at extremely short residence times. Experimental Section Materials. The source of the chemicals used as feed and during the calibration of the HPLC are as follows. © 1997 American Chemical Society
5064 Ind. Eng. Chem. Res., Vol. 36, No. 12, 1997
Figure 1.
Glucose (99+%), fructose (99+%), glyceraldehyde (97+%), erythrose (60%), pyruvaldehyde (40%), and dihydroxyacetone (99+%) were obtained from Wako Pure Chemicals Industries Limited (Osaka). 1,6 Anhydroglucose (99+%) was obtained from Tokyo Chemical (Tokyo). Glycolaldehyde (91%) was obtained from Aldrich Chemical Co. Inc. (Tokyo). Apparatus and Procedure. The experimental apparatus used was the continuous flow-type reactor shown in Figure 1. An aqueous solution of glucose of about 0.6 wt % was fed to the reactor at a feed rate of 5 mL/min by high-pressure pumps (GL Science Co., model PUS-3). Preheated water was fed from another line at a feed rate of 20 mL/min and mixed with the aqueous solution at the mixing point just before entering the reactor. The concentration of glucose entering the reactor is therefore 0.12 wt %. At the mixing point, the aqueous solution was rapidly heated up to its reaction temperature and the reaction was initiated. The tem-
perature was measured after the mixing point by a chromel-alumel thermocouple to assure that the reaction temperature was reached. The reactor was made of stainless steel, having an internal diameter of 0.077 cm. The entire reactor was submerged in a hot metal salt bath (KNO3, KNO2; Shin Nippo Kagaku Co.) set at the reaction temperature. At the exit of the reactor, cooling water was injected into the line at 14 mL/min while at the same time the reacting mixture was cooled externally by a cooling water jacket to terminate the reaction. The flowrates of the feed solutions and the density of water are known, and therefore the residence time of the solution in the reactor can be accurately determined. The residence time was varied by changing the reactor length and therefore the reactor volume. Pressure of the system was controlled at the sampling point using a back-pressure regulator (Tescom, Model 26-1721-24). The liquid sample was also analyzed for total organic carbon (TOC) using a TOC analyzer
Ind. Eng. Chem. Res., Vol. 36, No. 12, 1997 5065
Figure 2.
(Shimadzu Model 5000). The experimental conditions reported in this work are at 400 °C and 30 MPa with a residence time of up to 0.12 s and glucose concentrations of about 0.12 wt %. Further details on the operation of the experimental apparatus are available elsewhere (Kabyemela et al., 1997). Products Identification and Analysis. The sampled products were analyzed by injecting into a high-performance liquid chromatograph (HPLC) where they were separated by an Ionpak KS 802 (Shodex) column operated at 80 °C with a 1 mL/min flow of water solvent. The detectors used were the ultraviolet (UV) (Thermoseparations Products, Model Spectra 100) detector set at 290 nm and a refractive index (RI) (ERC, Model 7515A) detector. To check for the peak shifts during analysis resulting from many compounds eluting during close retention times, we frequently added 1 mL of solution of the standard of the product species to 10 mL of the sample solution. The relative increase in the specific peak corresponding to the added amount of the suspected product species and was taken as proof of its existence in the product sample. TOC analysis of the liquid products showed a 95-100% carbon balance, and so no attempt was made to analyze gaseous products. The results from the HPLC analysis are shown in Figure 2. Further details on the HPLC analytical procedure are available elsewhere (Kabyemela et al., 1997). The samples were also analyzed by 1H-NMR. The sample was first freeze-dried to increase the concentrations of the various products. The sample was then fractionated using the HPLC column mentioned above to trap specific products like erythrose, which eludes at about 10.5 min. The fractionated sample was then mixed with deuterium oxide (D2O) in a weight ratio of 1:9 in a micro sampling tube which has an internal diameter of 4.2 mm up to a level of 1 cm. 1H-NMR spectra were recorded at room temperature on the Japan Electron Optics Laboratory JNMA500 spectrometer operating at 500 MHz. This provided additional confirmation for the existence of erythrose in the products sample. Figure 3a-c shows the 1H-NMR spectrum of pure glyceraldehyde, pure erythrose, and the fractionated sample at 10.5 min, containing glyceraldehyde and erythrose, respectively. The peaks position and shapes at 3.68, 3.75, 3.85, and 4.95 ppm which are characteristic in the glyceraldehyde sample (Figure 3a) are also observed in the fractionated sample (Figure 3c). Similarly, for erythrose, the peaks at 3.8, 3.9, 4.05,
Figure 3.
4.1, 4.2, 4.3, 4.35, 4.45, 5.1, and 5.25 ppm have similar shapes in both the pure sample (Figure 3b) and the fractionated sample in Figure 3c. The >90% duplication
5066 Ind. Eng. Chem. Res., Vol. 36, No. 12, 1997
Figure 4.
of the peaks from the pure sample to the fractionated sample confirms the peaks obtained by HPLC analysis. Also, the existence of glycolaldehyde were detected by the 1H-NMR results. 1H-NMR spectra closely fitting that of pure glycolaldehyde was obtained from a fractionation sample which eludes at the same retention time as pyruvaldehyde. Results and Discussion As shown in Figure 2, the products of glucose decomposition detected and quantified by HPLC using the RI detector were erythrose, fructose, dihydroxyacetone, glyceraldehyde, 1,6-anhydroglucose, and 5-(hydroxymethyl)furfural. Some product peaks were detected by the UV/RI detectors but could not be quantified. These are such as formaldehyde, formic acid, and acetic acid which elude at similar retention time in the HPLC. Their existence was further clarified by the pH of the sample solution which was found to be about 3-4, and they are also known to be formed in the hydrothermolysis of glucose (Baugh and McCarty, 1988). Figure 4 shows a theoretically possible mechanism which may lead to the formation of erythrose and glycolaldehyde. After ring opening, glucose may undergo a reverse aldol condensation reaction as shown to form erythrose and glycolaldehyde or dihydroxyacetone and glyceraldehyde (Gibbs, 1950; Speck, 1958). Other products are isomerization to form fructose and dehydration to form 1,6anhydroglucose. The results from our experiments at 400 °C and 30 MPa are shown in Figures 5, 6, and 7. The product carbon balance in terms of carbon weight ratio obtained are shown in Figure 5. The erythrose yield increases with increasing residence time and shows 40% yield at residence times of about 0.11 s. On the other hand, the yield of fructose, glyceraldehyde, dihydroxyacetone, 1,6-anhydroglucose, and 5-(hydroxy-
Figure 5.
methyl)furfural are not high, the sum of which are about 20%. The total carbon yield shown in Figure 5 corresponds to that calculated from the species which were detected and quantified by the HPLC analysis. Deficient total carbon yield of these detected species at longer residence times (∼15%) is perhaps due to the formation of acids which were detected by the HPLC and glycolaldehyde which was detected by 1H-NMR but could not be quantified. Figure 6 shows the product selectivity versus glucose conversion. This Figure shows that the glucose selective conversion to erythrose decreases slightly from 50 to 45 wt % over a conversion range of 40% up to 90 wt % for glucose. The high selectivity for erythrose indicates that erythrose is rather refractory and decomposes at low rates under these conditions. This high selectivity and stability of erythrose under this condition clearly indicates the advantage of this method. The mole ratio selectivity of each erythrose and fructose per mole of glucose reacted is shown in Figure 7. The selectivity of erythrose is around 0.7 mol/mol of glucose reacted. Also,
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Acknowledgment The authors gratefully acknowledge support by a grant-in-aid for Scientific Research in the Priority Area Supercritical Fluids No. 04238103 from the Ministry of Education, Science and Culture. This work was also sponsored by New Energy and Industrial Technology Development Organization (NEDO)/Research Institute of Innovative Technology for the Earth (RITE). One of us (B.M.K.) is grateful for the support of a Monbusho Scholarship. Literature Cited Figure 6.
Figure 7.
the high selectivity at zero conversion level if the present data is extrapolated suggests as per Delplot analysis (Bhore et al., 1990) that erythrose is directly produced from glucose. The selectivity of fructose which is formed from the epimerization of glucose was around 25-30% at a 0.5 glucose conversion level. This result suggests that the bond cleavage to form erythrose (70%) and ring opening to epimerization to form fructose (25%) are the main glucose conversion pathways as shown in Figure 4. This trend in the product distribution and the high yield of erythrose differs completely from that of the acid hydrolysis of glucose which forms mainly dehydration products such as 5-HMF. The absence of an acid catalyst and the high-temperature conditions may favor the bond cleavage, leading to the formation of erythrose as shown in Figure 4. We think this is a novel method of producing erythrose because, on comparison with the conventional method, it does not require any catalyst, and apart from being quite rapid and continuous, it results in high yields of erythrose. However, for industrial upgrade, higher concentrations may be used; assuming that the yield remains the same as in this study, the end products will contain mainly glucose, fructose, and erythrose. Separation of these products may be achieved by first fermenting the mixture where glucose and fructose will form ethanol, while erythrose which is not fermented by yeast (Windholz et al., 1983) will remain unchanged. Subsequent distillation will then separate the erythrose from ethanol. However in the course of attaining commercial production we expect more problems to arise which could not be envisaged as a result of our work.
Baugh, K. D.; McCarty, P. L. Thermochemical Pretreatment of Lignocellulose to Enhance Methane Fermentation: 1. Monosaccharide and Furfurals Hydrothermal Decomposition and Product Formation Rates. Biotechnol. Bioeng. 1988, 31, 50. Bhore, N. A.; Klein, M. T.; Bischoff, K. B. The Deplot Technique: A New Method for Reaction Pathway Analysis. Ind. Eng. Chem. Res. 1990, 29, 313. Bonn, G.; Bobleter, O. Determination of the Hydrothermal Degradation Products of D-(U-14C) Glucose and D-(U-14C) Fructose by TLC. J. Radioanal. Chem. 1983, 79, 171. Dadach, Z.; Kaliaguine, S. Acid Hydrolysis of cellulose, Part 1: Experimental Kinetic Analysis. Can. J. Chem. Eng. 1993, 71, 880. Fitz, W.; Schwark, J.; Wong, C. Aldotetroses and C(3)-Modified Aldohexoses as Substrates for N-Acetylneuraminic Acid Aldolase: A Model for the Explanation of the Normal and the Inversed Stereoselectivity. J. Org. Chem. 1995, 60, 3663. Gibbs, M. On the Mechanism of the Chemical Formation of Lactic Acid from Glucose Studied with C14 Labelled Glucose. J. Am. Chem. Soc. 1950, 72, 3964. Hockett, R. C.; Maynard, C. W., Jr. The Chemistry of Tetrose Sugars. IV. The Structure of Methyl-D-erythroside. The Mutarotation of D-Arabinose Oxime. J. Am. Chem. Soc. 1939, 61, 2111. Holgate, H. R.; Meyer, J. C.; Tester, J. W. Glucose Hydrolysis and Oxidation in Supercritical Water. AIChE J. 1995, 41, 637. Kabyemela, B. M.; Adschiri, T.; Malaluan, R. M.; Arai, K. Kinetics of Glucose Epimerization and Decomposition in Subcritical and Supercritical Water. Ind. Eng. Chem. Res. 1997, 36, 1552. Roper, H.; Goossens, J.; Erythritol, A New Raw Material for Food and Non-food Applications Starch 1993, 45, 400. Smith, P. C.; Grethlein, H. E.; Converse, A. O. Glucose Decomposition at High Temperature, Mild Acid and Short Residence Times. Sol. Energy 1982, 28, 41. Sonogashira, K.; Nakagawa, M. Total Syntheses of Carbohydrates. II. DL-Erythrose and DL-Threose. Bull. Chem. Soc. Jpn. 1972, 45, 2616. Speck, J. C., Jr. The Lobry de Bruyn-Alberda van Ekenstein Transformation. Adv. Carbohydr. Chem. 1953, 13, 63. Theander, O.; Nelson, D. A. In Advances in Carbohydrate Chemistry and Biochemistry; Tipson, R. S., Horton, D., Eds.; Academic Press: New York, 1988; p 273. Whistler, R. L.; Wolfrom, M. A.; BeMiller, J. N.; Shafizadeh, F. Methods in Carbohydrate Research; Academic Press: New York, 1962. Windholz, M.; Budavari, S.; Blumetti, R. F.; Otterbein, E. S. The Merck Index; Merck & Co., Inc.: Rahway, NJ, 1983. Wolfrom, M. L.; Schuetz, R. D.; Cavalieri, L. F. Chemical Interactions of Amino Compounds and Sugars. III. The Conversion of D-glucose to 5-(Hydroxymethyl)-2-furaldehyde. J. Am. Chem. Soc. 1948, 70, 514.
Received for review June 16, 1997 Revised manuscript received September 10, 1997 Accepted September 11, 1997X IE9704354
Abstract published in Advance ACS Abstracts, November 1, 1997. X
