Table II. Propylene Disproportionation by Sulfide Catalysts"
Catalyst
Temp., F.
10% MoSz .Also3 10% WS2 *A1203 5% MoSZ.SiO2 5% WSg.SiO2
300 300 1000 1000
a
Table IV. Disproportionation Catalysts on Supports Other Than Alumina, Silica, and Aluminum Phosphate"
Space Rate, Propylene WHSV Conuersion, 76
Propylene Temp., F. Conuerswn, %
1.3 1.0 9.1 18.3
2 1 2 2
Pressure. Atmospheric. Table 111. Disproportionation of Propylene by Catalyst Promoters Other ihan Molybdenum and Tungsten Compounds
Catalyst 10% TaZO6.Si02 3% TeOs.SiO2 10% Nb205.Si02 10% ResO7.Sios
Temp., F. 1000 1000 1000 400 600 900
A1203.Ti02 A1203 .Tho2
Propylene Pressure, Space Rate, Conuersion, P.S.I.G. WHSV 5% 450 450 450 0 0 0
15 20 20 2 2 2
18 20 20 4.0 0.5 3.0
Conclusions
Useful supports for disproportionation catalysts were oxides of silicon, aluminum, thorium, and zirconium; phosphates of aluminum, zirconium, titanium,. magnesium, and calcium; and mixed oxides of some of these metals. Active promoters were hexacarbonyls, oxides, and sulfides of molybdenum and tungsten; and oxides of rhenium, tantalum, and tellurium. The various combinations reported here differed somewhait in activity. Tungsten or molybdenum oxides on silica, alumina, or aluminum phosphate had the highest activities.
a
10% Moos 8% wo3
400 1000
3 2
800 1000
4 3
1000 1000
3
350 350
3 3
250 400
15 1
1
Pressure. Atmospheric. Space rate. 2 W H S V .
Literature Cited
Banks, R. L. (to Phillips Petroleum Co.), Belg. Patent 620,440 (July 31, 1961); U.S. Patent 3,261,879 (1966). Banks, R. L., Bailey, G. C., IND. ENG. CHEM. PROD. RES. DEVELOP. 3, 179 (1964). Heckelsberg, L. F. (to Phillips Petroleum Co.), Brit. Patent 1,006,049 (Sept. 9, 1963); U. S. Patent 3,365,513 (1968). Heckelsberg, L. F. (to Phillips Petroleum Go.), U.S. Patent 3,340,322 (1967). Heckelsberg, L. F., Banks, R. L., Bailey, G. C., IND. ENG.CHEM.PROD. RES. DEVELOP. 7, 29 (1968). RECEIVED for review September 30, 1968 ACCEPTED April 15, 1969 Division of Petroleum Chemistry, 155th Meeting, ACS, San Francisco, Calif., April 1968.
PRODUCTION OF LEVOGLUCOSAN BY PYROLYSIS OF CARBOHYDRATES c.
M. LAKSHMANAN,
BENJAMIN GAL-OR,
AND
H. E .
HOELSCHER
University of Pittsburgh, Pittsburgh, Pa. 15213 A lprocess involving the pyrolysis of naturally occurring carbohydrates such as starch and cellulose has industrial potential for the production of levoglucosan and levoglucosan-like material. The reaction is complex. For high conversions and good product yields, high temperature, low pressure, and a low-pressure gas, flow are necessary. A screw conveyor type of reactor has been used for continuous pyrolysis of starch. Dielectric heating is being studied as a means of overcoming poor heat transfer to the starch mass.
THEindustrial
potential of a process for the production of levoglucosan and levoglucosan-like materials by the pyrolysis of carbohydr,ates such as starch or cellulose has recently become known and appreciated. This growing interest is due to a number of factors. First, levoglucosan is potentially useful i n the chemical industries for the manufacture of plastics, surfactants, explosives, propel-
lants, and resins, and as a low cost substitute for such materials as sorbitol. Secondly, the raw material is cheap and plentiful as a by-product from various industrial processes or from agricultural surpluses. Thirdly, the process involves only pyrolysis under vacuum, with removal and separation of the products. Finally, other by-products formed in the pyrolysis process may have considerable VOL. 8 NO. 3 SEPTEMBER 1969
261
market value. Thus, a method for the production of levoglucosan and by-products by pyrolysis is of interest. Levoglucosan, 1,6-anhydro-~-~-glucopyranose, is an anhydride of glucose, which can be considered to result from the loss of water from glucose with the simultaneous formation of the 1,6 oxygen bridge. Commericial interest in levoglucosan as an intermediate in various important industrial processes arises from the three reactive hydroxyl groups. Further, levoglucosan, unlike glucose, is known to be stable in alkaline solution. It polymerizes into dimers, tetramers, hexamers, etc., under the influence of heat and catalyst (Carvalho et al., 1959; Pictet, 1918) and forms crystalline ethers (Irvin and Oldham, 1921; Ruckel and Schuerch, 1966; Zemplen et al., 1937) as well as crystalline triacetates and tribenzoates (Schwenker and Pacsu, 1957). Levoglucosan is soluble in water, slightly soluble in methanol, ethyl alcohol, acetone, etc., and insoluble in ether. I t readily sublimes in vacuum. In this paper, the complex nature of the pyrolysis reaction is indicated. Additional experimental results relating to optimum operating conditions for the pyrolysis process are presented. In particular, this work is concerned with optimum methods for heating the reaction mass and removing the gaseous products from the reaction zone.. The effect of particle size of the raw material, temperature, and pretreatments of the raw material is reported. The production of levoglucosan by the pyrolysis of starch, cellulose, and similar carbohydrate material is discussed in a limited literature. The vacuum pyrolysis of P-D-glUCOSe (Karrer, 1920), starch (Bryce and Greenwood, 1965; Pictet, 1918; Pictet and Sarasin, 1918; Pictet and Cramers, 1920; Ward, 1963; Wolff et al., 1968; Zemplen and Gerecs, 1931), and cellulose (Bryce and Greenwood, 1965; Golova et al., 1957, 1958; Pictet, 1918; Pictet and Cramers, 1920; Pictet and Sarasin, 1918; Tishchenko and Fedorishev, 1953) has been studied. Cellulose and lignocellulose have been pyrolyzed in superheated steam 01 inert gases(Carlson, 1966; Epsheim et al., 1959; Esterer, 1967a,b; Heritage and Esterer, 1967). These latter pyrolysis studies are mostly reported in the patent literature. Ward (1963) proposed a laboratory method for preparing levoglucosan from starch. Wolff et al. (1968) report on the pyrolysis of various types of starch. Cornstarch is reported to give the best levoglucosan yield (approximately 40%), while sweet potato starch gives the lowest levoglucosan yield (approximately 12%). The authors conclude that none of the differences among the starches studied, including the difference in the nature of phosphorus linkage, granular size, tendency to retrogade, and gelatinization temperature, are directly related to the yield of levoglucosan obtained. The formation of levoglucosan from cellulose or starch by pyrolysis could be represented by the following simple equation: 0
I
262
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
From this equation the theoretical yield of levoglucosan from pure cellulose or starch is loo%, but in practice the yield is below 50%. Various other products are formed during the reaction. Some by-products of interest include: 1,6-anhydro-~-~-glucofuranose, 2-furaldehyde, furan, acetaldehyde, formaldehyde, acetone, acrolein, formic acid, acetic acid, carbon monoxide, and carbon dioxide. Schwenker and Beck (1963) identified at least 37 different compounds in the products of cellulose pyrolysis, many of them occurring in very minor quantities. These by-products clearly indicate the complex nature of the pyrolysis reaction. Various mechanisms have been suggested. Irvin and Oldham (1921) suggested that acids produced during the pyrolysis of starch catalyze the hydrolysis of starch into glucose and that the p-form of glucose undergoes dehydration to form levogiucosan. Recent work of Bryce and Greenwood (1965) seemed to support this hypothesis. Parks et al. (1955) proposed that during the pyrolytic decomposition of cellulose a t elevated temperatures cellulose depolymerizes by scission of the 1-4-glycosidic linkages and this is followed by an intramolecular rearrangement of monomer units to levoglucosan, which subsequently undergoes fragmentation to form low molecular weight products. This mechanism was later supported by many workers (Berkowitz-Mattuck and Noguchi, 1963; Madorsky et al., 1958; Schwenker and Beck, 1963; Schwenker and Pacsu, 1957). Pakhamov (1957) postulated that mono- or difunctional radicals are formed by the scission of glucosidic linkages and are further degraded to volatile compounds before the formation of levoglucosan. Recently Kat0 (1967) substantiated this radical mechanism. Wolff et al. (1968) indicated a similar mechanism for the pyrolysis of starch. They suggested that the production of levoglucosan from starch is not independent only of the nature of starch component, whether linear or branched, but also of the position and configuration of the linkage between glucose units, if the degradation of starch involves momentary formation of a monomer followed by a migration of hydroxylic hydrogen and rearrangement to the stable beta configuration and levoglucosan molecule. Kilzer and Broido (1965) described the mechanism of cellulose pyrolysis in terms of two interactions. An intermediate, 1,4-anhydro-a-~-glucopyranose, is formed by the first interactions of atoms, and the second interaction involves the attack within this anhydride of its C-6 hydroxyl group on its C1 carbon atom. Displacement of the 1-4 oxygen bridge produces levoglucosan, and displacement of the 1-5 oxygen bridge yields l-6-anhydro-p-~glucofuranose. Gardiner (1966), on the other hand, suggested that during the pyrolysis of cellulose an epoxide end group is formed with a 1,2-anhydro-a-~-glucopyranose prior to the formation of levoglucosan, but there is no direct evidence for the pyrolytic formation of 1,2anhydrohexoses. However, the formation of levoglucosan may be facilitated by conformational changes in the glucopyranose units which permit reaction by a concerted displacement mechanism. The mechanism proposed by Gardiner (1966) also accounts for the formation of the levoglucosan end group and the possibility of acid catalysis. Chatterjee and Conrad (1966) proposed a mechanism for the formation of levoglucosan from cellulose via the levoglucosan end groups formed during the pyrolysis. Byrne et al. (1966) indicated a similar mechanism for the forma-
tion of anhydroglucoses and furfural and then suggested a mechanism for the formation of carbonyl compounds from cellulose. They indicated that the free radical mechanism postulated by l?akhamov (1957) may also contribute significantly to the formation of products of relatively low molecular weight. Bryce and Greenwood (1963) and Berkowitz-Mattuck and Noguchi (1963) indicated possible mechanisms for the formation of lower hydrocarbons and other gases by the decomposition of 1-6-anhydro-P-~glucofuranose and levoglucosan, respectively. Although there is insufficient evidence to accept any of the proposed mechanisms completely, these mechanisms clearly indicate the complexity of the pyrolysis reaction. The pyrolysis reaction first yields a viscous, tan-tobrown colored sirup. Quantitative analysis for levoglucosan or any of the other compounds is difficult because of the large number of compounds in the sirup. The gas chromatographic method developed recently by Sawardeker et al. (1965) is quantitative, convenient, and reasonably rapid for the estimation of levoglucosan in the sirup. It uses the trimethylsilylation technique described by Sweeley et al. (1963) for the separation and estimation of carbohydrates and related polyhydroxy compounds. The trimethyl silyl d e r h t i v e s of the glucosans in the sirup are first made and then subjected to gas chromatography at a temperature at which these derivatives are volatile and stable. This method was used throughout the present study. Experimental
Starch was the ralw material. The pyrolysis reaction was conducted in three types of reactors: a direct-heated Vycor tubular batch reactor, a direct-heated screw conveyor type continuous reactor, and a dielectrically heated Vycor tubular reactor. Materials. The starches used were either high grade commercial samples or those prepared and submitted by the U. S. Department of Agriculture, Northern Regional Research Laboratory, Peoria. For convenience in handling and to prevent loss during the introduction of material into the reaction zone, the starches received in finely powdered form were converted to lumps by suspending them in water, followed by vacuum filtration and drying of the cake to a constant weight at 110°C. The product was then sieved through standard sieves and a particular sieve fraction was used in the pyrolysis experiments. Procedure. DIRECT-HEATED VYCORTUBULAR BATCH REACTOR.The experimental set-up is shown in Figure TO V o r i a c
1. A Vycor tube, 24 inches long and 1 inch in i.d., served as the reactor. It was heated by a 750-watt tubular furnace. The feeding end of the Vycor tube was closed with a rubber stopper having a hole through which a piston rod was introduced. The other end of the tube was closed with a two-holed rubber stopper through which a thermocouple and a vapor outlet were inserted into the reactor. The product outlet was connected to two ice traps, which in turn were connected to a Drierite column and a vacuum pump. A weighed quantity of starch, usually 5.0 grams, was introduced into the feeding end of the reactor. The reactor temperature was raised to the desired level and the pressure inside was reduced to 1 to 2 mm. of Hg absolute. When the temperature and the pressure became steady, the starch lumps were introduced into the reaction zone by using the piston. Condensable products of the reaction collected as a tan sirup a t the cold exit end of the tube. The cotton pad a t that end prevented carry-over of the sirup to the connecting tubes and traps. The pressure inside the reactor increased during the reaction and then decreased to near the initial pressure a t the end of the reaction. This was taken as an indication of complete reaction. After sufficient time to remove all volatile products from the reaction zone, the reactor tube was taken out and cooled to room temperature. The carbon residue was removed, and the sirup was dissolved in methanol. The methanol solution was filtered to remove carbon particles, and the sirup was collected by distilling off the methanol solvent under vacuum. After the sirup weight was noted its levoglucosan content was estimated by gas-liquid chromatography. During the pyrolysis experiments in the direct-heated batch reactor, it was observed that the starch particles underwent several physical changes, represented diagrammatically in Figure 2 for a continuous tubular reactor configuration. As the particles moved from the feed inlet to the reaction zone, their temperature increased gradually and simultaneously the particles turned brown. At this point the particles seemed to be “softening” and sticking together. When the temperature of the particles increased further, say above 250”C., they began to swell and expanded to form a foam. At a still higher temperature, the whole mass “melted” and a vigorous effervescence occurred. Yellow to brownish yellow vapors condensed into a sticky, tan-colored sirup. A porous carbonaceous residue was left behind. These stepwise physical changes of starch particles are Coolin( W a t r r
lcr T r a p s
Drlrrltr Column
Figure 1. Direct-heated tubular reactor setup VOL. 8 N O . 3 S E P T E M B E R 1 9 6 9
263
I
I
I
FEED INLET!
HEATING ZONE
I
I
to r o f k o I
I
I
I
I
REACTlON ZONE
Vlgorous Effervorcmce
PRODUCT OUTLET
I
RalduO
I
I
I
;c.ndeMOr I
I
?O
Syrup
Figure 2. Schematic of reaction
of considerable importance in the design of a continuous reactor. Considerations of these changes led to the conclusion that a screw conveyor type reactor would be suitable for performing the pyrolysis reaction continuously. Material could be moved inside this type of reactor regardless of the physical changes described above. SCREW CONVEYOR TYPECONTINUOUS REACTOR:The screw conveyor type reactor made of stainless steel is shown in Figure 3. The clearance between the screw and the reactor wall was kept to a minimum, so that the inner wall would be scraped continuously by the screw to prevent the accumulation of carbonaceous residues. The screw was rotated using the handle, and the heating was provided by a pair of 750-watt electrical heaters. The residue receiver was heated to about 250°C. to prevent condensation of the product in it. With an adequate stuffing box seal, it was possible to obtain an absolute pressure as low as 2 mm. of Hg. The experimental procedure was almost similar to the batch reactor, except that starch particles of a particular sieve fraction were continuously fed to the reactor after the desired reactor temperature and pressure were reached. The carbonaceous residue and the sirup were treated with methanol a t the end of the experiment, and the sirup weight was estimated after recovery. The starch feeding rate was approximately 200 grams per hour. The low heat conductivity of starch and cellulose is a major problem in the development of an industrial scale pyrolysis under vacuum. The rate of heat transfer to the mass is very low. One possibility of overcoming this
apparent difficulty is to subject starch granules to a radiofrequency electric field and allow the dielectric losses in the starch to heat it. An attempt was made to study the starch pyrolysis reaction in a dielectric field. DIELECTRICALLY HEATEDVYCORTUBULAR REACTOR. The reactor setup was similar to the direct-heated Vycor tubular reactor (Figure l ) , except for the heating device. Two parallel copper electrodes were made from copper tubing of appropriately the same internal diameter as the outer diameter of the Vycor tube. The cross section was slightly less than a semicircle and the air gap between the electrode and the Vycor tube wall was negligible. The radiofrequency field was supplied to the electrodes by a 5-kw. Dynatherm, Model PS-5 generator. Temperature was measured by a thermocouple inserted into the reactor after momentarily stopping the field and connecting the thermocouple circuit to the potentiometer. A weighed quantity of lumpy starch was placed in the reactor, which was evacuated before applying the radiofrequency field. Results and Discussion
The effect of temperature, starch particle size, and pretreatment of starch on the yield of levoglucosan from the pyrolysis of starch was studied in the direct-heated Vycor tubular batch reactor. Effect of Temperature. Temperature of reaction is an important factor in a pyrolysis process, especially when many competing reactions occur. The effect of temperature on the yield of levoglucosan was determined by conducting
I Figure
264
3. Continuous reactor
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
Reeldue Rocolver
Product Rocolvor
the pyrolysis at various temperatures, fixing other variables (weight of feed, fstarch particle size, type of starch, and pressure). From Figure 4 it is clear that the formation of levoglucosan from st arch is a temperature-sensitive reaction. The maximum yield was obtained between 350" and 880" C. However, the highest fraction of levoglucosan in the sirup was obtained at approximately 350" C. Although the weight of sirup obtained at higher temperatures was almost constant, the fraction of levoglucosan in the sirup decreased with the temperature. This could be due to polymerization or decalmposition of levoglucosan into other products. At higher temperatures, the sirup obtained was dark in color and a dark brown hard mass was found immediately after the heating zone at the product exit end of the reactor. A sudden change in the reaction rate seemed to occur between 260" and 300" C. To test the reproducibility of the experimental results, five separate experiments were carried out a t 380" C. under similar conditions (Table I). The yield of levoglucosan varied between 40.6 and 38.970, hence the variations in the yield a t various temperatures were considered significant. Effect of Particle Size. Various sieve fractions of cornstarch A lumps were used to study the effect of particle size on levoglucosan yield. The pyrolysis was carried out at 380°C. and initial pressure of 2 mm. Results presented in Table I1 indicate that lump size has no effect on the yield of levoglucosan. Reaction a t 380°C. was very fast and surface area of the particle had no effect on the yield. Effect of Pretreatment and Source of Starch. Starches of different origins were pyrolyzed a t 380°C. after pretreating with water to determine the effect of starch source on the yield of levoglucosan. These starches were also treated with a 50% aqueous acetone solution to prepare comparatively quick-drying lumps without gelatinization. In the case of water-treated starch, any remaining excess water caused gelatinization upon heating. The starch
o.*l
lumps prepared by acetone treatment could be easily dried without gelatinization, and were light and porous. The experimental results are presented in Table 111. The yield of levoglucosan varied considerably with the source of starch. Wolff et al. (1968) also observed similar variations in the yield and that different samples of starch from the same source gave varying yields. A maximum yield (45.2%) of levoglucosan was obtained from waxy sorghum starch. Acetone-treated starches invariably gave the same or lower yields compared to water-treated starches. The lower yield of levoglucosan might be due to the removal of fatty material in the starch by the acetone. Levoglucosan formation by the pyrolysis of starch is thought to be acid-catalyzed (Byrne et al., 1966). Some of the starches foamed considerably during the pyrolysis. Acetone treatment had no effect on foaming. Results in Screw Conveyor Type Reactor. Some of the experimental data obtained in the screw conveyor type reactor are presented in Table IV. The yield of levoglucosan from cornstarch A a t an average temperature of about 400°C. is about 30%. This is low compared to the yield obtained from the same starch in the Vycor batch type tubular reactor (Figure 4). Hence it can be assumed that a part of the levoglucosan decomposed during the passage of product vapors through the reactor. Carbonaceous residue accumulated on the screw after prolonged reaction occasionally bound the screw in the reactor. The screw could be freed by passing a current of air into the hot reactor to burn out carbonaceous deposit. Heat transfer in a large vacuum unit of this type would be a major problem. A temperature drop of about 30" to 40°C. was observed between the wall of the reactor and the center of the screw shaft during the reaction. Maintenance of vacuum in this type of reactor could also be a problem because of wear on the packing. Results in Dielectrically Heated Vycor Tubular Reactor. The yields of levoglucosan (Table V) were invariably low compared t o the yield obtained by direct heating method.
Figure 4. Effect of temperature on yield of levoglucosan Direct-heated Vycor tubular reactor
n
Corn starch A Weight of feed. 5.0 grams
0.4 0 Y 0 0
-
0.3
260
300
340
360
420
460
500
Tom per arat urr,'~
VOL. 8 N O . 3 S E P T E M B E R 1 9 6 9
265
Table V. Yield of Levoglucosan by Dielectric Heating
Table I. Reproducibility of Results
Direct-heated Vycor tubular reactor Corn starch A 5.0 grams -8, +18 mesh 380" C. 1 to 7 mm. Hg
Reactor. Starch used. Weight of feed. Particle size. Temperature. Pressure.
Weight of Sirup, G.
Fraction of Leuogl ucosan in Sirup
of LG, 70
3.77 3.73 3.89 3.84 3.84
0.54 0.53 0.52 0.53 0.51
40.7 39.5 40.5 40.7 39.2
Yield
Table II. Effect of Particle Size
Reactor. Starch. Weight of feed. Temperature.
Particle Size Mesh -4, -8, -10, -14, -18,
Direct-heated Vycor tubular reactor Corn starch A 5.0 grams 380" C.
Pressure, Mm. Hg
Wt. of Fraction LG Sirup, G. insirup
3-5 2-3 2-3 2-4 2-5
+8 +10
+14 +18 +35
3.6 3.8 3.7 3.7 3.5
Yield of LG, % 39.7 39.9 39.4 40.2 38.0
0.55 0.52 0.53 0.54 0.55
Table 111. Yields of Levoglucosan from Various Starches and Effect of Pretreatment with Water and Acetone
Reactor. Weight of feed. Temperature. Pressure. Particle size.
Type of Starch Corn A WSY corn Corn B WSY sorghum Milo sorghum Sweet potato Tapioca AITOWroot Wheat starch
Direct-heated Vycor tubular reactor 5.0 grams 380" C. 1-6 Hg -8, +18 mesh
e.
Water-Treated Sirup wt., Fraction Yield, g. LG 7% 3.78 0.53 40.1
50% Acetone-Treated Sirup wt., Fraction Yield, g. LG % 3.88 0.50 38.8
3.82 3.54
0.39 0.53
29.8 37.5
3.58 3.56
0.31 0.51
22.2 36.3
3.77
0.60
45.2
3.47
0.59
41.0
3.75
0.45
33.8
3.70
0.37
27.4
3.80 3.53
0.54 0.43
41.0 30.4
3.88 3.24
0.54 0.32
41.9 20.7
3.49
0.40
27.9
3.18
0.34
21.6
3.00
0.56
33.6
3.11
0.49
30.5
w t . of Feed, G. 200 60 210 400 300
340-380 380-400 380-420 370-420 480-500
4-18 2-10 2- 8 2-10 3- 8
111 40 162 269 213
0.59 0.47 0.39 0.49 0.32
Yield of LG, 7%
33 31 30 32 28
~
266
Starch Type Corn A corn c Corn D Soluble
Pressure, Mm. Hg 2-34 2-32 2-28 2-30
B y Dielectric Heating LG Temp., "C. Yield, % 450 19.0 430 8.2 440 7.5 425 12.5
Direct Heating LG Yield, % 40.7 16.5 19.0 25.3
This could be due to various factors. A glow discharge was observed inside the reactor when the material was heated in this way. This discharge could be due to the ionization of residual gases and might well be causing very high localized temperature decomposing or polymerizing of levoglucosan formed. The temperature measured was certainly not the true temperature when the radiofrequency field was applied. Even though dielectric heating is a good method for uniform heating of such materials, it poses many operating problems: temperature measurement, materials of construction, sealing (if a vacuum system is needed), and inefficiencies caused by geometrical factors. In spite of these problems, dielectric heating remains an interesting and potentially attractive technique in this process and is being investigated further. Conclusion
This work indicates the industrial potential of a process involving the thermal degradation of starch and cellulose as a source of levoglucosan and, possibly, other glucosans of value. The process involves the thermal degradation of starch or cellulose in a flow system operating a t low pressure. High temperature, low pressure, and a low-pressure gas flow are all necessary for high conversions and reasonable yields of products. The product, as formed, must be removed quickly from the high temperature reaction zone. An efficient heating method is necessary, as starch and cellulose are poor conductors of heat. A kind of scraper mechanism is needed in a continuous pyrolysis reactor to remove the sticky carbonaceous residue formed. The use of a dielectric energy source has not yet proved attractive for heating the starch granules to reaction temperature. The attractive features of dielectric heating are the rapidity with which the starch can be heated and the possibility of localized heating in places filled with starch. Further work is being done to study the advantages of dielectric heating. Acknowledgment
Table IV. Yields of Levoglucosan in Screw Conveyor Type Reactor
Corn starch A; particle size, -8, +18 mesh Wt. of Fraction Temp., Pressure, Sirup, LG in c. Mm. Hg G. Sirup
Weight of feed, 5.0 grams
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
The assistance of L. Viswanathan in the chromatographic analysis for levoglucosan and the pyrolysis experiments in the dielectric field is gratefully acknowledged. Literature Cited
Berkowitz-Mattuck, J. B., Noguchi, T., J. A p p l . Polymer Sci. 7, 709 (1963). Bryce, D. J., Greenwood, C. T., Sturke 15, 359 (1963). Bryce, D. J., Greenwood, C. T., Stlirke 17, 275 (1965).
Byrne, G. A,, Gardiner, D., Holmer, F. H., J . Appl. Chem. 16, 81 (1966). Carlson, J., U. S. Patent 3,235,541 (Feb. 15, 1966); C A 64, 16122 (1966). Carvalho, J. da Silva, Prins, W., Schuerch, C., J . A m . Chem. SOC.81,16122 (1966). Chatterjee, P. K., Conrad, C. M., Textile Res. J . 36, 487 (1966). Epshtein Ya. V., Golova, 0. P., Durynina, L. I., Izu. Akad. Nauk, S S S R , Otdel. Khim. Nauk 1959, 1126; C A 54, 1330 (1960). Esterer, A. K., U. S. Patent 3,298,928 (Jan. 17, 1967); C A 66, 56886 (1967a). Esterer, A. K., U. S. Patent 3,309,356 (March 14, 1967); C A 66, 106072 (1967b). 1966 (C), 1473. Gardiner, D., J . Chem. SOC. Golova, 0. P., Pakhamov, A. M., Andrievskaya, E. A., Krylova, R. G., Llokl. Akad. Nauk, S S S R 115, 1122 (1957); C A 52,4165 (1958). Golova, 0. P., Pakhamov, A. M., Nikloaeva, I. I., Izu. Akad. Nauk, SSSA!, Otdel. Khim. Nauk 1957, 519; C A 51, 14258 (1957). Heritage, C. C., Esterer, A. K., U. S. Patent 3,309,355 (March 14, 1967); C A 66, 10607 (1967). Irvin, J. C., Oldham, J. W. H., J . Chem. SOC.119, 1744 (1921). Karrer, P., Helu. Chirn Acta 3, 258 (1920). Kato, K., Agr. Biol. Chem. (Tokyo) 31, 519, 657 (1967). Kilzer, F. J., Broido,, A., Pyrodynamics 2 , 151 (1965). Madorsky, S. L., Hart, V. E., Strauss, S., J . Res. Natl. Bur. Std. 60, 343 (1!358). Pakhamov, A. M., Im. Akad. Nauk, S S S R , Otdel. Khim. Nauk 1957, 1497; C A 52, 5811 (1958).
Parks, W. G., Esteve, R. M., Gollis, M. H., Guercia, R., Petrarca, A., Abstracts, Division of Cellulose Chemistry, 127th meeting, ACS, Cincinnati, Ohio, April 5, 1955. Pictet, A., Helu. Chim. Acta 1, 226 (1918). Pictet, A., Cramers, M., Helu. Chim. Acta 3, 640 (1920). Pictet, A., Sarasin, J., Helu. Chim. Acta 1, 87 (1918). Ruckel, E. R., Schuerch, C., J . Org. Chem. 31, 2233 (1966). Sawardeker, J. S., Sloneker, J. H., Dimler, R. J., J . Chromatog. 20, 260 (1965). Schwenker, R. F., Jr., Beck, L. R., J . Polymer Sci., Part C, No. 2, 331 (1963). Schwenker, R. F., Jr., Pacsu, E., I d . Eng. Chem., Chem. Eng. Data Ser. 2, 83 (1957). Sweeley, C. C., Bentley, R., Mikita, M., Wells, W. W., J. A m . Chem. SOC.85, 2497 (1963). Tishchenko, D. V., Fedorishev, T., Zh. Priklad. Khim. 20, 393 (1953). Ward, R. B., “Methods in Carbohydrate Chemistry,” Vol. 11, R. L. Whistler, M. L. Wolfrom, Eds., p. 394, Academic Press, New York, 1963. Wolff, I. A., Olds, D. W., Hilbert, C. E., Sturke 20, No. 5 , 150 (1968). Zemplh, G., Csuros, Z., Angyal, S., Ber. 70, 1848 (1937). Zemplh, G., Gerecs, A., Ber. 64B, 1545 (1931). RECEIVED for review November 27,1968 ACCEPTED April 29,1969 Project supported by the Agricultural Research Service, U. S. Department of Agriculture, Grant 12-14-100-8043 (71) administered by the Northern Utilization Research and Development Division, Peoria, Ill.
URETHANE PLASTICS BASED ON STARCH AND STARCH-DERIVED GLYCOSlDES F . H . O T E Y , R . P . W E S T H O F F , W . F . K W O L E K , C . 1. M E H L T R E T T E R , A N D C . E . R l S T
Northern Regional Research Laboratory, U. S . Department of Agriculture, Peoria, Ill. 61604
INCORPORATION of low-cost starch and starch derivatives into polymers provides a potential method for expanding the applications and improving the economics of certain plastics. The chem.istry, processing conditions, and increasing importance of polyurethanes make them especially promising for starch modification. Polyurethanes are generally defined as polymers produced by the addition reaction between diisocyanates and polyols:
n OCN-R-NCO
+ n HO-Ri-OH
0
II
(C--MH-R-NH-C
-+
0
II
-O-R1-0-),
The alcoholysis reaction between starch-derived glycol glycosides and castor oil gives a series of polyols with a wide range of equivalent weights suitable for preparing urethane polymers. Furthermore, when isocyanate in excess of that required for the poly01 is added, polymers are produced with terminal -NCO groups. A significant number of these -NCO groups are believed to react with hydroxyls on the surface of starch particles when a mixture of the urethane polymer and starch is subjected to heat and pressure molding. Presumably, starch particles and the urethane interact to form crosslinked structures, causing changes in properties of the plastics. On the one hand, the urethane resin contains the “soft segment” of the plastics and thus contributes to low glass transition temperatures, elasticity, elongation, and tear strength. On VOL. 8 NO. 3 S E P T E M B E R 1 9 6 9
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