Ind. Eng. Chem. Res. 1988,27, 153-156
This effect becomes much more pronounced when the periodicity of constriction is increased, and as a result the thermal boundary layer resistance is further reduced and the heat-transfer coefficient gets much more enhanced. In conclusion, it may be stated here that divergingconverging geometries exhibit highly attractive features toward the augmentation of heat-transfer efficiency. They can be recommended for the improved design of heattransfer equipment such as heat exchangers, condensers, evaporators, etc. The increased cost of fabrication of such geometries should necessarily be compensated by the excellent increase in the transfer efficiency attainable at the same operating cost (since the corresponding increase in pressure drop is negligibly small). Such variable-area heat exchangers can also be specially attractive to systems incorporating low temperature differences such as the OTEC (Ocean Thermal Energy Conversion) power plants (Narayanan and Bhattacharyya, 1985). This field undoubtedly invites more elaborate work.
Nomenclature A = heat-transfer area, cm2 C, = specific heat, cal/(g.K) D = inside diameter of outer straight column = 2R, cm D1 = minimum inside diameter of constricted tube = 2R1, cm D2 = maximum inside diameter of constricted tube = 2Rz, cm De = effective diameter of the annulus = (D2- D:)/Ds, cm D, = surface diameter of constricted tube = ( 1 + cot2 a)1/2 (02 - D12)/2L, cm D, = volumetric diameter of constricted tube = [(D; - D?)/3L tan aI1I2,cm f,= friction factor for constricted geometry = (-AI’)@ Dv)/ ~ P Vm2 L h, = heat-transfer coefficient, call (cm2.s.K) K = thermal conductivity, cal/(cm.s.K) L = length of each segment of constricted tube, cm (characteristic length) Pr = Prandtl number = C,p/K Q = volumetric flow rate, cm3/s R e ’ = surface Reynolds number = 4Qp/rDep ReM = modified Reynolds number = LV,,p/p Re, = volumetric Reynolds number = 4 Q p / r ( D + Dv)p
153
rw(z) = distance from the axis to the wall of the constricted tube at any z, cm r* = dimensionless radial coordinate = r/L
T * = dimensionless fluid temperature at any point = TIT, Tb= average bulk temperature at any cross section, K T,= wall temperature of constricted tube, K To = average temperature at the entrance constriction, K (characteristic temperature) V , = average velocity based on D, = 4Q/7(D2- D:), cm/s V , = average velocity at the entrance constriction, cm/s (characteristic velocity) V,* = dimensionless radial component of fluid velocity = vr/ v o
V,* = dimensionless axial component of fluid velocity = V,/ V, z* = dimensionless axial coordinate = z/L Greek Symbols
a = angle of constriction a’ = thermal diffusivity = K / p C , a* = a’/VJ = l / ( R e M P r ) p = fluid density, g/cm3
+* = dimensionless stream function = +/ V J 2
p
= viscosity, P
Literature Cited Bird, R. B.; Stewart, W. E.; Lightfoot, E. N. Transport Phenomena; Wiley: New York, 1960. Fujita, Y.; Hasegawa, S. Bull. J S M E 1970, 13, 697. Hamel, G. Jahresber. L. Dt. Mathematiker-Vereinigung. 1916,34, 25 Jeffery, G. B. Phil. Mag. 1915, 29, 455. Klepper, 0. H. AIChE Symp. Ser. 1973, 69, 131. Millsaps, K.; Pohlhausen, K. J. Aerosol Sci. 1953,20, 187. Narayanan, C. M. ”Momentum and Heat Transfer Studies in Irregular Geometry”. PbD. Thesis, Indian Institute of Technology, Kharagpur, 1983. Narayanan, C. M.; Bhattacharyya, B. C. Proc. Annu. Sess. IIChE, 31st 1978, 24.
Narayanan, C. M.; Bhattacharyya, B. C. Reg. J . Energy Heat Mass Transfer, 1985, 7, 39. Payatakes, A. C.; Tien, C.; Turian, R. M. AIChE J . 1973, 19, 67. Sheffield, R. E.; Metzner, A. B. AIChE J . 1976, 22, 736. Received for review October 28, 1985 Accepted September 21, 1987
Dissolving Pulps from Wheat Straw by Soda-Anthraquinone Pulping Mohamed A. Abou-State,*+Ahmed M. El-Masry,$and Naglaa Y. S. Mostafat Department of Chemistry, Faculty of Science, Cairo University, Giza, A.R. Egypt, a n d Department of Chemistry, Faculty of Science, Zagazig University, A.R. Egypt
Dissolving pulps are obtained by subjecting prehydrolyzed Egyptian wheat straw to soda-anthraquinone pulping. The pulps obtained are satisfactorily bleached by the CEH sequence, while in the absence of anthraquinone an additional chlorite step should be applied to raise the degree of whiteness. A very important effect of anthraquinone takes place in the fine structure of the pulp whereby it increases the affinities toward water and alkali, lowers the crystallinity, and results in considerable improvement in the reactivity toward xanthation. Soda-anthraquinone pulps with suitable a-cellulose content can be obtained by using the appropriate concentration of acid in prehydrolysis to hydrolyze a greater amount of the lower molecular weight carbohydrates before the soda-anthraquinone pulping. Extensive studies have been carried out on the effect of anthraquinone on pulp and paper from pulpwood. The presence of anthraquinone during alkaline pulping of wood chips results in highly beneficial effects on the properties of pulp and paper obtained. It leads to better deliginifi+Cairo University. t Zagazig University.
cation (Hassan et al., 1981; Germer et al., 1983; Fossum et al., 1980; Sjoeholm and Wikbald, 1980; Ivanova et al., 1980), increased carbohydrate stabilization (Germer et al., 1983), higher yield (Hassan et al., 1981; Fossum et al., 1980; Ivanova et al., 1980; Virkola, 1981; Goel et al., 1980; Kleppe, 19811, better strength properties (Hassan et al., 1981; Germer and Caluzin, 1982; Cameron et al., 1982; Bogomolov et al., 1981; Li et al., 1984), lower alkali consumption, and decreased cooking chemical charge (Germer and Ca0 1988 American Chemical Society
154 Ind. Eng. Chem. Res., Vol. 27, No. 1, 1988
luzin, 1982; Fossum et al., 1980; Virkola, 1981; Goel et al., 1980; Boiko et al., 1980; Farrington et al., 1979). Limited amounts of studies were interested in the use of anthraquinone for the production of dissolving pulps from pulpwood. Thus,cooking of steam treated slash pine chips with soda-anthraquinone liquor gave dissolving pulp useful in the production of viscose and cellulose acetate in high quality (Baker et al., 1980). The addition of anthraquinone during prehydrolysis of wood chips or in pulping had essentially the same beneficial effect on pulp yield and acelluloe content (Kosaya et al., 1982). The increased cost of pulpwood and its scarcity in many countries have directed the attention toward the use of nonwood plant fibers for the production of different grades of pulps. However, no previous studies were carried out for the production of dissolving pulps from nonwood plant fibers by pulping in the presence of anthraquinone. The only exception is our recent investigation (Abou-State et al., 1986) in which we have found that the presence of anthraquinone during pulping of wheat straw results in a marked improvement in the reactivity toward xanthation. The pulp obtained was much more reactive than good commercial softwood viscose pulp. (This has been subject to patent application: Patent 272, Nov 5,1986 (Patent Office, A.R.E.).) In the present investigation, it was intended to find out the reason for this increased reactivity. A detailed study of the effects of anthraquinone on the bleachability, the yield, the chemical and physical properties of the pulps obtained, their fine structure, and their reactivity toward xanthation was carried out. No such studies have been done before.
Experimental Section Raw Material. The raw material used in the work was Egyptian wheat straw. It was obtained from the farms of the Faculty of Agriculture, Cairo University. Prehydrolysis, Pulping, and Bleaching. These were carried out as before (Abou-State et al., 1983). The raw material was treated with boiling water for 'Iz h at a liquor ratio of 151before prehydrolysis since this reduces the ash content, lowers the pentosans, and raises the a-cellulose as well as the degree of whiteness. It also results in a more open and accessible fine structure, as indicated by higher affinities toward water and alkali, lower crystallinity, and better reactivity toward xanthation (Mostafa, 1986). Prehydrolysis was carried out with 0.4% sulfuric acid solution (the mild conditions) and in other experiments with 1% sulfuric acid solution (the strong conditions). The duration of prehydrolysis was 6 h at a temperature of 100 "C and a liquor ratio of 151. This was followed by pulping for 5 h at 100 "C with 1.67% sodium hydroxide solution. In experiments 1 and 6, pulping was carried out by the action of sodium hydroxide alone. In the other experiments, different amounts of anthraquinone were present during pulping as indicated in Tables I and 11. In the experiments carried out in absence of anthraquinone, the CEH bleaching sequence was followed by treatment with sodium chlorite. For 100 g of pulp, 4 g of sodium chlorite and 3 mL of glacial acetic acid were added at 5% consistency and 80 "C for l1I2h. Chemical Analysis of Pulp. The ash, permanganate number, pentosans, and a-cellulose were determined according to the American Tappi Standards T 211 os-58, T 214 m-50, T 223 ts-63, and T 203 os-61 (Technical Association of the Pulp and Paper Industry, Atlanta, GA). The natural chlorine requirement of the unbleached pulp is the maximum amount of chlorine which can be absorbed by the pulp from a chlorine solution in which the remaining chlorine will be a t its minimum. It gives a measure of bleachability. The natural chlorine requirement was de-
Table I. Soda-Anthraquinone Pulping under the Mild Prehydrolysis Conditions expt 1 2 3 4 5 concn of HzSOl soln, 70 0.4 0.4 0.4 0.4 0.4 0.05 0.10 0.15 0.20 concn of AQ/100 g material liquor ratio 15:l 15:l 15:l 15:l 15:l max temp, OC 100 100 100 100 100 time at max temp, h 5 5 5 5 5 concn of NaOH soln, % 1.67 1.67 1.67 1.67 1.67 liquor ratio 15:l 15:l 15:l 15:l 15:l yield, % 24.0 27.8 27.5 27.9 27.6 ash, % 0.15 0.13 0.14 0.12 0.13 permanganate no. of unbl. pulp 14.5 13.8 13.2 9.4 11.5 3.8 4.0 nat. Clz req. of unbl. pulp, 70 5.6 5.1 4.4 a-cellulose, % 89.5 89.1 88.7 87.3 86.9 pentosans, % 8.2 9.5 9.8 10.9 11.6 D.P. 1070 913 911 845 945 degree of whiteness, % 87 90 91 92 93 W.R.V., % 99.0 116.0 104.4 102.9 120.3 L.R.V., 70 257.3 279.5 264.0 274.5 285.7 55.2 62.2 56.8 64.5 66.5 NaOH R.V., % crystallinity, % 71 61 65 69 57 reactivity ( % insol. cellulose) 58.0 15.5 32.1 35.6 10.4 Table 11. Soda-Anthraquinone Pulping under the Strong Prehydrolysis Conditions expt 6 7 8 9 1 0 concn of HzS04soln, % 1 1 1 1 1 concn of AQ/100 g material 0.05 0.10 0.15 0.20 151 15:l 15:l 15:l 15:l liquor ratio max temp, O C 100 100 100 100 100 time at max temp, h 5 5 5 5 5 concn of NaOH soln, 70 1.67 1.67 1.67 1.67 1.67 15:l 15:l 151 15:l 15:l liquor ratio yield, % 21.0 24.8 24.8 24.6 24.5 0.15 0.12 0.14 0.12 0.13 ash, % permanganate no. of unbl. pulp 14.6 10.9 10.2 9.9 12.9 nat. Clz req. of unbl. pulp, % 5.7 3.9 3.8 3.6 4.4 a-cellulose, % 92.8 91.9 91.6 90.6 90.9 pentosans, 70 4.3 5.8 5.7 5.7 5.5 D.P. 775 912 915 911 911 degree of whiteness, % 87 88 90 92 93 W.R.V., % 81.2 96.5 108.7 110.0 97.3 L.R.V., % 257.4 279.7 186.9 289.0 271.3 NaOH R.V., % 54.8 59.8 65.6 66.4 60.0 80 81 crystallinity, 70 76 82 78 reactivity ( % insol. cellulose) 41.8 42.0 17.8 15.8 30.5
termined as before (Abou-State et al., 1983). Physical Properties. The average degree of polymerization (D.P.) and the degree of whiteness were determined as before (Abou-State et al., 1983). Fine Structure of the Pulp. There are no absolute methods for measuring the fine structure of the pulp. However, some properties of cellulose give a clear comparative indication of its fine structure. The best common examples are the degree of swelling in water or in sodium hydroxide liquor. The fine structure also includes the ratio of crystalline to amorphous cellulose. In this work, the water retention value (W.R.V.) was estimated according to Jayme (1958). The liquor retention value (L.R.V.) and sodium hydroxide retention value (NaOH R.V.) were determined by allowing the pulp to swell in sodium hydroxide solution of mercerizing strength at 20 "C followed by centrifuging to eliminate the excess alkali. The centrifuged pulp was weighed, washed with distilled water to neutrality, dried to constant weight, and weighed again. The washings were titrated against standard acid. Thus, L.R.V. and NaOH R.V. were determined. The degree of crystallinity was determined according to Hessler and Power (1954). Reactivity toward Xanthation. The reactivity toward xanthation was estimated by carrying out emulsion xanthation using 50 mL of 8% sodium hydroxide solution and 1 mI, of carbon disulfide. The dissolved cellulose in
Ind. Eng. Chem. Res., Vol. 27, No. 1, 1988 155 the viscose was determined volumetrically and was subtracted from the original amount of cellulose according to the method of Fock (1959).
Results and Discussion Effect of Anthraquinone on Pulp Bleachability. When pulping was carried out in the absence of anthraquinone (experiments 1 and 6), the CEH bleaching sequence had to be followed by treatment with sodium chlorite in order to improve the degree of whiteness. However, the presence of anthraquinone during pulping (experiments 2-5 and 7-10, Tables I and 11) raised the degree of whiteness, and the CEH sequence was sufficient. Mild Prehydrolysis Conditions (Table I). In experiments 1-5, prehydrolysis was carried out with 0.4% sulfuric acid solution. In experiment 1, sodium hydroxide alone was used in pulping, while 0.05%, 0.10%, 0.15%, and 0.20% anthraquinone were present together with the hydroxide during pulping in experiments 2, 3, 4, and 5, respectively. It is clear that the presence of anthraquinone raised the yield from 24.0% to 27.5-27.9%. It lowered the permanganate number and the natural chlorine requirement of the unbleached pulp. The lowest permanganate number and natural chlorine requirement were obtained when 0.15% anthraquinone was present during pulping (experiment 4). Compared to soda pulping (experiment l ) , the presence of 0.05% anthraquinone lowered the acellulose from 89.5% to 89.1%. I t lowered the D.P. and increased the degree of whiteness. However, the most significant effect took place in the fine structure of the pulp. The presence of 0.05% anthraquinone increased the affinities toward water and alkali and lowered the crystallinity. This resulted in considerable improvement in the reactivity toward xanthation (cf. experiments 1 and 2). It is also clear from Table I that the a-cellulose decreased and at the same time the pentosan increased with an increase in the amount of anthraquinone from 0% to 0.20%. This was due to the stabilizing effect of anthraquinone on the short-chain carbohydrates. The highest affinities toward water and alkali, the lowest crystallinity, and the best reactivity toward xanthation were attained when the highest amount of anthraquinone (0.20%) was added in pulping. Strong Prehydrolysis Conditions (Table 11). It is clear from above that the only drawback of anthraquinone was due to its stabilizing effect on the short-chain carbohydrates which lowered the a-cellulose and increased the pentosans. Thus, it became of interest in the following experiments to find out the effects of anthraquinone on pulp properties after removing higher amounts of the lower molecular weight carbohydrates by carrying out prehydrolysis under the stronger conditions. It is clear from Table I1 that the presence of anthraquinone during soda pulping under the strong prehydrolysis conditions raised the yield from 21.0% to 24.5-24.8%. It also improved the degree of delignification, lowered the bleachability, and improved the degree of whiteness. The best degree of delignification and the lowest bleachability were attained when 0.15 % anthraquinone was used (experiment 9). Compared to soda pulping (experiment 6), the presence of 0.05% anthraquinone (experiment 7) lowered the a-cellulose from 92.8% to 91.9%, increased the pentosans from 4.3% to 5.8%, and increased the affinities toward water and alkali. However, it did not improve the reactivity toward xanthation, as in case of the mild prehydrolysis conditions (Table I). This was most probably due to the increase in D.P. from 775 to 912 and in crystallinity from 76% to 80%. The increase in the average degree of polymerization and in crystallinity
means better stabilization and higher protection of the a-cellulose macromolecules against degradation during the alkaline pulping. Increasing the amount of anthraquinone to 0.10% (experiment 8) resulted in a more open and accessible fine structure, as indicated by higher affinities toward water and alkali as well as better reactivity toward xanthation. Further improvements in the affinities toward water and alkali as well as in the reactivity were attained when the amount of anthraquinone was raised to 0.15% (experiment 9). However, increasing the quinone concentration to 0.20% (experiment 10) lowered the W.R.V., L.R.V., NaOH R.V., and reactivity. I t is also clear from Table I1 that the pentosan increased and the a-cellulose decreased with quinone concentration. However, all soda-anthraquinone pulps had a-cellulose and pentosan contents within permissible limits. Thus, the increase in pentosan content resulting from pulping in the presence of anthraquinone should not adversely affect the quality of regenerated cellulose. Moreover, the first step in the viscose process involves treatment with sodium hydroxide solution of mercerizing strength. This reduces the pentosan content to a great extent (Abou-State et al., 1977). It was shown that large amounts of hemicellulose could be present in several types of rayon without serious deterioration in the qualities of the filaments (Croon et al., 1968). It is worth mentioning that with the availability of large quantities of wheat straw at a reasonable price which is considerably lower than that of pulpwood, particularly in countries with limited wood resources, as well as the reduction in bleachability, the increase in yield and reactivity justify the cost of anthraquinone. An increase in yield means a decrease in the cost of production. A more reactive pulp leads to the formation of a more soluble viscose and hence better filtrability.
Conclusions In order to obtain dissolving pulps from wheat straw if pulping is carried out in the absence of anthraquinone, the CEH bleaching sequence does not lead to a suitable degree of whiteness and should be followed by chlorite bleaching. However, with alkali-anthraquinone pulping, the CEH sequence is sufficient. Under mild prehydrolysis conditions the presence of anthraquinone during soda pulping results in favorable effects on the yield, degree of delignification, bleachability, and degree of whiteness. Optimum delignification and lowest bleachability are attained with 0.15% quinone. A very important effect of anthraquinone takes place in the fine structure of the pulp, whereby the use of only 0.05% anthraquinone increases the affinities toward water and alkali, lowers the crystallinity, and results in considerable improvement in the reactivity toward xanthation. The most open and accessible fine structure and the best reactivity are attained when the highest amount of quinone (0.20%) is used. The only drawback of anthraquinone is due to its stabilizing effect on the short-chain carbohydrates which lower the a-cellulose and increase the pentosans. Soda-anthraquinone pulps with suitable a-cellulose content can be obtained by using the appropriate concentration of acid in prehydrolysis to hydrolyze a greater amount of the lower molecular weight carbohydrates before the soda-anthraquinone pulping. Registry No. Anthraquinone, 84-65-1;sulfuric acid, 7664-93-9. Literature Cited Abou-State, M. A.; Abd El-Megeid, F. F.; Nesseem, R. I. 2nd. Eng. Chem. Prod. Res. Deu. 1983, 22(3),506.
Ind. Eng. Chem. Res. 1988,27, 156-161
156
Abou-State. M. A.: El-Mastrv. A. M.: Mostafa. N. Y. S. Chem. Ind. 1986, 585. Abou-State, M. A.; Fahmy, A. M.; Safy El-Din, N. M. Polymer 1977, 18, 315. Baker, T. J.; Hamilton, J. K.; Harruff, L. G.; Wilson, J. D. Int. Dissolving Pulps Conf. [Conf. Pap.] 5th, 1980; Tappi, Atlanta, GA, pp 45-52. Bogomolov, B. D.; Gorbunova, 0. F.; Pivovarova, V. A.; Butsalenko, V. S. Khim. Dreu. 1981, 3, 27; Chem. Abstr. 1981, 95, 63963. Boiko, Y. A.; Ivanov, M. A.; Kryukov, V. M.; Kozhevnikov, P. A.; Zubkov, B. J. Tsellyul.-Bum. Karton 1980, 6, 11: Chem. Abstr. 1980,93, 74135. Cameron, D. W.; Farrington, A.; Nelson, R. F.; Raverty, W. D.; Samuel, E. L.; Vanderhoek, N. Appita 1982,35(4), 307. Croon, I.; Jonsen, H.; Olofsson, H. G. Suen. Papperstidn. 1968, 71, 40. Farrington, A,; Nelson, P. F.; Vanderhoek, N. Appita 1979, 33(3), 207. Fock, W. Papier (Darnstadt) 1959, 13, 92. Fossum, G.; Haegglund, S.; Lindqvist, B. Sven. Papperstidn. 1980, 83(15), 430. Germer, E. I.; Butko, Y. G.; Wandelt, P.; Surewicz, W. Khim. Drev. 1983,5, 38; Chem. Abstr. 1983, 99, 214367. “
I
Germer, E. I.; Caluzin, N. G. Khim. Drev. 1982,5, 31; Chem. Abstr. 1982,97, 184203. Goel, K.; Ayroud, A. M.; Branch, B. Tappi 1980, 63(8), 83. Hassan, S. H.; Marshak, A. B.; Chudakov, M. I. Khim. Drev. 1981, 1, 54; Chem. Abstr. 1981, 94, 141456. Hessler, L. E.; Power, R. E. Text. Res. J. 1954, 24, 822. Ivanova, I. S.; Gugnin, Y. A.; Luzina, L. I.; Vasilenko, L. L.; Aleksandrovich, A. N. Bum. Prom-st. 1980,11,14; Chem. Abstr. 1981, 94, 32498. Jayme, G. Tappi 1958,41, 180A. Kleppe, P. J. Pap. Puu 1981,63(4), 204, 209. Kosaya, G. S.; Prokop’eva, M. A.; Menshutkina, A. I.; Zotova, L. G.; Viktorova, T. V. Bum. Prom-st. 1982, 12, 9; Chem. Abstr. 1983, 98, 55829. Li, Z.; Yao, G.; Zhang, D.; Xue, G. Nanjing Nongxueyuan Xuebao 1984,1, 60; Chem. Abstr. 1984,101, 132766. Mostafa, N. Y. S. Thesis, Department of Chemistry, Faculty of Science, Cairo University, Giza, A.R.E., 1986. Sjoeholm, R.; Wikbald, P. Pap. Puu 1980, 62(4), 289. Virkola, N. E. Tappi 1981, 64, 51.
Received for review October 15, 1986 Accepted September 17, 1987
Production of Coal-Based Asphalt by Single- and Two-Stage Catalytic Liquefaction Christine W.Curtis,* James A. Guin, J y h Huei Kang, and A. Ray Tarrer Chemical Engineering Department, Auburn University, Auburn, Alabama 36849
Three coal liquefaction processing configurations were investigated for producing a coal-based asphalt paving binder. The requirement of high process severity to achieve specification asphalt properties resulted in unacceptably low asphalt yields for single-stage processing. A two-stage process was developed which resulted in acceptable specification grade coal-based asphalt yields of 30% based on maf coal feed. N
In the United States, highway construction and maintenance consume 25-30 X lo6 tons (22.7-27.3 metric tons) of asphalt each year. In hydrocarbon value, this consumption is approximately equivalent to 400 000 barrels (63 588 m3) per day of crude oil. Thus, the replacement of asphalt with a functionally equivalent substitute would result in a lowering of U.S. petroleum consumption. Processes to convert coal into liquid and gaseous fuels have undergone considerable investigation since 1974. It is possible that, with slight modification, some of these processes could be used to produce a product functionally equivalent to petroleum-based asphalt, i.e., coal-based asphalt. The United States has vast supplies of coal, and development of an acceptable coal-based asphalt would provide our nation a strategic advantage by reducing our dependence on imports of foreign oil for the production of asphalt, our basic road building material. In the event that coal liquefaction becomes a feasible energy alternative, a full slate of products will be produced, ranging from light ends to heavy asphaltic materials. These heavy ends must be fit into an economic scope of products, and their suitabilities for usage in the paving industry are important for fully utilizing the entire coal liquefaction product slate. Thus, the objective of this work was to develop processes by which coal can be converted to a material which is functionally equivalent to petroleum asphalt. This is a formidable objective due to the inherently different properties of coal and petroleum. Since asphalt specifications have been developed from petroleum experience, one can expect possible difficulties in producing a material
meeting these specifications from a chemically different raw material, such as coal. Coal tar pitches and oils derived from carbonization processes have been used to some extent for various road paving and coating applications as reviewed by Curtis et al. (1986). The production of most of these materials did not involve high-temperature, high-pressure, catalytic hydrogenation typical of current direct coal liquefaction technology. However, Calkins and Silver (1968) and later Hoffman (1967) did use coal liquefaction technology at high severity to produce a coal-based asphalt-type product. In general, this product had higher viscosity temperature susceptibility (VTS) and oxidative hardening rates than a corresponding petroleum asphalt. Previous work in our laboratory has shown that an asphalt binder material (asphalt cement) can be produced from coal by catalytic hydrogenation (Curtis et al., 1986; Guin et al., 1985). When modified by the addition of -3 wt % styrene-butadiene copolymer, the asphalt binder is functionally equivalent to currently used petroleum asphalts. That is, the coal-based asphalt meets current ASTM and AASHTO specifications for asphalt cements used in road construction, with the exception of the optional thin film oven test (TFOT) weight-loss specification. The purpose of the present paper is to report processing considerations regarding production of a coal-based asphalt using direct coal liquefaction technology. In this work we investigated three processing configurations for producing a coal-based asphalt, as shown in Figure 1. All process streams, e.g., mineral matter, gases,
0888-5885/88/2621-0156$01.50/0 0 1988 American Chemical Society
