Ind. Eng. Cham. Prod. Res. Dev. 1982, 21, 309-314
tion during descent conditions. In any event, the de-icing capability of EGME-treated fuel makes its addition attractive, even for descent conditions.
On several occasions, after carburetor ice was allowed to form in the carburetor of one or both engines while using stock fuel, the fuel supply was switched to a tank containing EGME-treated fuel. In every case power was immediately regained. Thus EGME-treated fuel would also serve as a de-icing agent. On five occasions, carburetor ice was encountered with both engines operating on stock fuel, but with different mixture settings. As discussed earlier, Diblin (1971) and Coles et al. (1949) do not agree of the effect of the fuel/air mixture. While the experimental samples size is small, the engine with the rich mixture lost power 39% faster (on the average) than did the engine with the lean mixture. The complete flight test report is available (Newman, 1979).
Acknowledgment This work was sponsored by the Federal Aviation Administration under Contract DOT-FA78WA-4165.
Literature Cited AVCO-Lycomlng “Operator’s Manual: AVCO-Lycomlng 0-320, 10-320, AIO320, and LIO-320 Series Aircraft Engines"; AVCO-Lycomlng Publication 60297-16, 2nd ed.; Division of AVCO Corporation: Williamsport, PA, March 1973. Canadian Ministry of Transport Aviation Safety Letter 1976, Issue 6. Coles, W. D. “Investigation of Icing Characteristics of Light Airplane Engine Induction Systems"; National Advisory Committee for Aeronautics Report TN-1970, Washington, DC, Oct 1949. Coles, W. D.; Rollln, V. G.; Mulhoiland, D. R. "Icing Protection Requirements for Reciprocating Engine Induction Systems"; National Advisory Committee for Aeronatlcs Report TR-982, Washington, DC, June 1949. Diblin, J. Flying July 1971, 89(1), 82-83. Gardner, L; Moon, G. “Aircraft Carburettor Icing Studies”; National Research Council of Canada Report DME-LR-536, Ottawa, Ont., July 1970. Houston Chemical Company, "Procedure for Determining Concentration of Prist Fuel Additive (PFA-55MB) In Fuel by Freezing Point Method”; Houston Chemical Co.: Houston, ca. 1977. Newman, R. L. "Carburetor Ice: A Review”; Crew Systems Report TR-7719, Nov 1977; available from National Technical Information Services as Report N80-23280. Newman, R. L. “Flight Test Results of the Use of Ethylene Glycol Monomethyl Ether (EGME) as an Anti-Carburetor-Icing Fuel Additive”; Federal Aviation Administration Report AWS-79-1, Washington, DC, July 1979. Piper Aircraft Corporation “Owner’s Handbook for Operation and Maintenance of the Piper Apache Model PA-23 Airplane"; Piper Aircraft Publication: Lockhaven, PA (no date). Saunders, P., Canadian Ministry of Transport, private communication, 1977.
Conclusions
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309
The incorporation of 0.15 vol % of EGME into aviation gasoline greatly reduces the formation of carburetor ice during cruise power flight. Both the extent of conditions favorable to ice formation and the maximum severity of ice formation are reduced. The use of EGME should prevent virtually all cruise or climb caburetor ice accidents for pilots not flying in clouds. Since over 60% of carburetor ice accidents occur during these portions of flight (Newman, 1977), this reduction would be no small benefit. There do appear to be certain environmental conditions which make the use of EGME less favorable during descents. Certain dew point/temperature combinations may produce slightly more ice with EGME added to the fuel than without. These conditions need to be examined further before drawing any conclusions regarding the effectiveness of EGME in preventing carburetor ice forma-
Received for review December 3, 1980 Revised manuscript received October 26, 1981 Accepted February 23,1982
Process for Chemical Separation of the Three Main Components of Lignocellulosic Biomass Emmanuel G. Kouklos* School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907
George N. Valkanas School of Chemical Engineering, National Technical University of Athens, Athens, Greece
The combination of acid prehydrolysis with chemical delignification is examined as a potential method for the chemical fractionation of lignocellulosic biomass. Experiments with wheat straw show that hemicellulose can be quantitatively separated by prehydrolysis; however, the structure of the residue is substantially modified. Delignification of this residue with the conventional, alkaline methods (soda, kraft) leads to significant losses of polysaccharides and a degraded cellulose. The efficiency of the separation can be Increased by an unconventional delignification, such as chlorination by chlorine gas. In this case, the sugar losses are minimal and further degradation of cellulose during delignification can be avoided, while lignin is quantitatively recovered from the pulping liquors.
Introduction Biomass utilization has recently become the object of considerable investigations in the areas of chemical and
energy engineering. Lignocellulose conversion is of particular interest, since the major available forms of biomass, namely agricultural residues and wood, are predominantly lignocellulosic. The properties of lignocellulosic structure have been associated with a series of technical and economic problems that can only be solved by multi-stage processes, involving the separation of hemicellulose, cel-
* School of Chemical Engineering, National Technical University of Athens, 42 28th Octobriou Street, Athens 147, Greece.
0196-4321782/1221 -0309$01.25/0
©
1982 American Chemical Society
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 2, 1982
lulose, and lignin (Millet et al., 1975; Karlivan, 1978), or in other cases carbohydrates and lignin. Several such processes have been proposed. According to the oldest one, a two-stage acid hydrolysis is used to separate the polysaccharides as sugars, while lignin remains in the residue (Dunning and Lathrop, 1945; Harris, 1949). The most significant constraints to acid hydrolysis are due to the crystallinity of cellulose and presence of lignin. Therefore, the problem of selecting the best pretreatment becomes critical (Lipinsky, 1979). In the Tsao-Purdue process the crystallinity of cellulose is destroyed by appropriate solvents (Ladish et al., 1978; Hsu et al., 1980). The Iotech process makes use of an explosive depressur-
ization to disrupt the lignocellulosic structure (Marchessault, 1978; Yu and Miller, 1980). Other processes involve one or more extractions with organic solvents in order to separate the three main components of the plant-cell wall (Lora and Wayman, 1978; Myerly et al., 1981). Conventional chemical pulping, although very effective in removing lignin, shows low efficiency in separating the components of lignocellulose. Delignification is accompanied by extensive hydrolysis of hemicellulose, followed by sugar degradation. At the same time, the structure of cellulose in the pulp is essentially preserved. Addition of a prehydrolysis step before pulping could help in two ways: (1) the separation of hemicellulose at an earlier stage could increase the overall efficiency of the process; (2) the effect of acid pretreatment, combined with those of delignification, could improve the control on the quality of cellulose, especially regarding further processing. According to the literature, prehydrolysis has been mainly employed in the production of dissolving pulps from hardwoods and agricultural residues (Richter, 1955; Wenzl, 1970). However, only rarely in the past has this application involved the utilization of the sugars, mostly pentoses, or their degradation products, mainly furfural, produced from the first stage (Jayme, 1948; Koukios, 1975; Economides, 1977). Today, the few pulp mills that still practice prehydrolysis simply add the sugars of the prehydrolyzate to the pulping wastes in order to recover their heat value (Wayman, 1973). Obviously, the potential of the prehydrolysis-pulping process, in the perspective of a “biomass refining” industry (Myerly et al., 1981), requires a new evaluation. The object of this paper is the experimental investigation of this potential in the cases of the conventional, alkaline delignification, and an unconventional one using chlorine as the delignifying agent.
Experimental Section Materials. Wheat straw, the lignocellulosic material
used in this work, is a typical agricultural residue with the additional advantage of having been the object of numerous experimental investigations (Koukios, 1975). The straw used in these experiments contained, on a moisture-free basis, 69.7% carbohydrates, 27.0% pentosans and 42.7% hexosans, 13.6% lignin, 7.5% ash, 3.9% soluble material in benzene-alcohol (2:1), and 5.0% other organic
extractives. The -cellulose content was 41.1%. The material was chopped in 0.5-2 cm lengths. Procedures. Prehydrolysis was carried out in an electrically heated, 5-L autoclave made of stainless steel and equipped with an internal coil for fast cooling at the end of each run. The heat-up time was 20 to 40 min depending on the final temperature. Sulfuric and hydrochloric acid were used as catalysts at concentrations 0.01-1% (w/w), and solution-to-straw ratios 5:1-40:1 (w/w). The temperature range investigated was 100-180 °C, while the time at that temperature varied between 0 and 180 min.
1. Dissolved components in a typical prehydrolysis. The the time scale separates the heat-up time from the time at maximum temperature. Solution-to-straw ratio, 40:1.
Figure zero on
The residue from prehydrolysis was delignified according to the soda (NaOH) and Kraft (NaOH + Na2S) methods in laboratory digesters of 1, and 5 L, respectively. A 7:1 solution-to-dry residue ratio (w/w) was used in all cases. The heat-up time was 30 min in the partial delignification experiments and 90 min in the other cases. Delignification with chlorine gas followed two stages. First, the residue containing 65 ± 5% water (w/w) was chlorinated at room temperature. This stage was carried out in glass flasks of 3 L, externally cooled with water. Then, the chlorinated lignocellulose was thoroughly washed with water to remove the HC1 formed during chlorination. Finally, an alkaline extraction was adopted to dissolve the chlorolignins. A 1-2% (w/w) aqueous solution of NaOH was used at 30-60 °C and a solution-to-dry pulp ratio of 10:1 (w/w). Lignin was precipitated from the alkaline pulping liquors at room temperature and pH 1.0-1.5, by using concentrated H2S04 (Theophilatou, 1978). Analyses. The raw material, the residues from prehydrolysis, the pulps, and the spent liquors from delignification were analyzed according to the following TAPPI Standard Methods (1979): T12 (extractives), T203 (cellulose), T204 (alcohol-benzene solubility), T211 (ash), T222 (lignin), T223 (pentosans), T220 (mechanical properties), T230 (viscosity), T236 (kappa number), and T650 (black liquor). The carbohydrate content of all lignocellulosic materials was calculated as 100 (non-sugars %), where the term “non-sugars” (or noncarbohydrates) refers to the sum of lignin, ash, and noncarbohydrate extractives. The hexosan content was indirectly determined by difference, based on the separate determinations of the pentosan and carbohydrate contents. The amount of reducing sugars on the prehydrolysate was determined according to the Schoorl-Regenbogen method, which has been recently found especially suitable for this case (Economides, 1977). The yields of dissolved components, residues, and pulps, and the consumption of chemicals throughout this paper, unless otherwise stated, are based on moisture-free, untreated straw. All sugars are reported as their polysaccharide equivalent. -
Results and Discussion Hemicellulose Hydrolysis. The composition of the
material separated by a typical prehydrolysis is presented in Figure 1. Sugar hydrolysis is accompanied by removal of significant amounts of noncarbohydrates. On the other hand, as indicated by the yield of reducing sugars, a part of the sugars are present in the prehydrolysate as oligo-
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 2, 1982
Figure 2. Relationships between the components of a typical prehydrolysate (see Figure 1).
Figure
3.
Extent of pentosan separation by prehydrolysis
Figure
4.
311
Statistical correlation between the yields of dissolved
sugars and lignocellulosic residue.
(see
Figure 1).
saccharides. A post-hyrolysis of the sugar solution is needed to convert these oligosaccharides to monosaccharides. Figure 2 suggests a first qualitative analysis of the typical course of prehydrolysis. In an early phase, corresponding to the first few minutes of the heating, hemicellulose and noncarbohydrates (water-soluble extractives and inorganics) are dissolved at a ratio of ca. 3:1. The sugars are mostly oligosaccharides; e.g., an average degree of polymerization (D.P.) of 5 is observed after 10 min (ca. 80 °C). In the second phase the relative rate of removal of the non-sugars increases, while the oligosaccharides are gradually hydrolyzed to monosaccharides; in Figure 2 the average D.P. drops below 2 before the maximum temperature has been reached. In the last phase of prehydrolysis degradation of monosaccharides becomes dominant, and the removal of the non-sugars has practically come to an end. Combining this analysis with the data presented in Figure 3, we can see that it is possible to keep sugar degradation at a minimum, and at the same time dissolve 95% or more of the pentosans at a relatively moderate temperature. At this point, which is extremely important for the utilization of the highly pentosanic agricultural residues, the acid prehydrolysis examined here has been found superior compared with the water or steam pretreatments, or the low temperature acid one (Bernardin 1958, Mitra 1959, Locus 1960).
Figure
5. Effects
Table I.
of prehydrolysis
50
residue (see Figure 1).
Effects of Prehydrolysis on Hemicellulose total sugars dissolved, %
residue, % av° 60 70 80
on
max6
34.3 25.9 17.4 8.9
0 From Figure 4. for 24 points.
37.2 28.8 20.6 12.8 6
comments
extensive degradation
optimal separation
extensive separation limited hydrolysis
Estimated at 95% confidence level
Effects on Residue. The statistical correlation presented in Figure 4 shows that the extent of hemicellulose hydrolysis is strongly related to the yield of residue. This relationship is valid for residue yields between 50 and 707c and for the experimental conditions of this work. Some practical resulte of this correlation, extrapolated to include yields up to 807c, are summarized in Table I. The gradual modification in the composition of the residue is shown in Figure 5. The major effects of prehydrolysis are (1) the dramatic decrease in the fraction of noncellulosic polysaccharides (70-75% in this particular example), (2) the also extensive decrease in the combined fractions of the noncarbohydrate components (30-507c), and (3) the relative resistance of «-cellulose, especially in the early phase of hydrolysis (10-307o decrease according to Figure 5). Unfortunately, there are no simple correlations between the yield of residue and the various structural effects of
312
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 2, 1982
Table II.
Effects of Prehydrolysis
on
157 °C, 0.25% 0 min
extractives,® %
lignin,d residue,
% %
lignin
6.3
Lignin0,6 h2so4
20 min 40 min
13.7 66.5
7.4 8.7 56.5
NS
S
7.5 8.4
52.5 VS
157 °C, 0.50% 0
min
4.0 10.8 59.5 S
h2so4 167 °C, 0.125% h2so4 177 °C, 0.125% h2so4 0 min 20 min 40 min 0 min 20 min 40 min
20 min 40 min
8.4 7.6 53.5 VS
4.9 12.3 67.5 NS
7.7 7.0
51.5 VS
6.5 9.5 57.0
7.3 8.6
6.1 9.6
54.0 VS
S
6.1 8.4 51.5 VS
58.0 S
5.4 8.2
48.5 VS
condensation®
6 Solution-to-straw ratio 40:1, heat-up time 30-40 min. c Total Percentages based on moisture-free, untreated straw. extractives in benzene-alcohol (2:1), alcohol, and water. d Determined in the extractive-free material. ® Based on the amount of chlorine consumed on delignification; NS non significant, S significant, VS very significant. 0
=
=
=
prehydrolysis on lignocellulose. Therefore, a separate analysis for each component of the residue becomes necessary.
Lignin. The data from an experimental study at moderate-to-high temperatures are given in Table II. Because of the strong interrelationships between the quantitative determination of lignin and this of the various extractives (Brauns, 1952; Brauns and Brauns, 1960), the effects of prehydrolysis on these fractions must be examined together. Analysis of the data in Table II shows that, in the early phase of prehydrolysis, corresponding approximately to the heat-up time, the extractives are extensively (60-70% including the inorganics) dissolved in the aqueous solution. At the same time lignin remains practically unchanged. The next phase is characterized by a decrease in the lignin fraction and an increase in extractable material. As it has been already proposed (Aronovsky and Gortner, 1930), this phenomenon can be related to a structural change of lignin, i.e., depolymerization. A mass balance of the combined fractions indicates that lignin and/or its oligomers are further degraded to water-soluble products. In a late phase, a new decrease of the extractives may occur, along with an almost constant lignin content. This suggests that lignin has obtained a stable form, while degradation of the solvent-extractable part continues. This structural stability of lignin has been attributed to internal condensation (Wayman and Lora, 1978). When prehydrolysis is followed by delignification of the residue, a condensed lignin requires more intensive conditions (this property has been used to measure condensation in Table II); this, in turn, leads to undesirable loss of carbohydrates in the pulping wastes. Polysaccharides. As shown in Figure 5, the total amounts of polysaccharides in the residue gradually drops below the original «-cellulose content (the fraction of high-molecular-weight carbohydrates of biomass). Therefore, at high degrees of prehydrolysis, the noncellulosic carbohydrates of the residue consist mainly of products from hydrolytic degradation of cellulose. The ratio of this low-D.P. fraction to the total polysaccharides in a residue can thus measure the effects of the acid pretreatment
on
cellulose.
Figure 6 presents the values of this ratio for the more interesting cases of extensive-to-optimal separation of hemicellulose (cf. Tables I and II). Despite the substantial removal of sugars, the ratio remains remarkably constant, indicating that «-cellulose is also hydrolyzed at a significant rate. An increase in acid concentration (from 0.25 to 0.50% in Figure 6) favors cellulose degradation, while an increase in temperature (from 167 to 177 °C) favors further hydrolysis of low-molecular-weight polysaccharides. Based on these observations, one can easily understand the variations of the average D.P. of the polysaccharides in a residue (Table III). Low-temperature, low-acid pretreatments cause negligible degradation, associated with
Figure
6.
Effects of prehyrolysis
on
the composition of poly-
saccharides in the residue. Solution-to-straw ratio, 40:1.
Table III.
Effects of Prehydrolysis
prehydrolysis 60 min at 130 °C with 0.01% HC16 10 min at 130 °C with 0.20% HC1 60 min at 130 °C with 0.10% HC1 60 min at 130 °C with 0.20% HC1 10 min at 170 °C with 0.10% HC1 10 min at 170 °C with 0.20% HC1 60 min at 170 °C with 0.01% HC1 60 min at 170 °C with 0.20% HC1
on
residue, 90.2
Cellulose %
(D.P.)av° 880
85.8
780
85.7
830
84.5
800
79.0
770
74.3
700
69.1
810
64.6
680
0 Average D.P. of holocellulose in residue (in glucose units). 6 Solution-to-straw ratio 10:1 (runs with 0.01% and 0.10%) and 5:1 (runs with 0.20%).
minimal separation of hemicellulose. Any attempt to improve separation by increasing only the acid concentration causes a significant drop of D.P.; however, extensive removal of sugars, as measured by the yield of residue (of Figure 4), can be achieved with a minimal degradation of the remaining polysaccharides. The same does not seem possible for an optimal separation of hemicellulose (residue yields below 65%). Alkaline Delignification. Partial delignification of biomass has been found to improve its potential for biochemical processing (Millet et al., 1975). Data from such an application of the soda method are presented in Figures 7 and 8. It is obvious that, despite the extensive removal of hemicellulose during prehydrolysis, alkaline delignifi-
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 2, 1982
313
Conventional Delignification of Prehydrolyzed Biomass Table IV.
temperature, °C time, min HC1 % in solution0 total sugars, %b residue, %
Prehydrolysis 145 145 10
150 10
10
0.12 9.0 82.5
0.25
0.17 19.8 69.5
29.7 61.5
Delignification temperature, °C time, min active alkali, %
sulfidity,
%
dissolved sugars, % screened pulp, % kappa number
Partial delignification of prehydrolyzed biomass. Conditions of prehydrolysis are given in Table IV.
Figure
7.
170 60
160 120
160 120
13 25
11
32
10 32
16
44.0 12.5
breaking length, kmc burst index, MN/kgc tear index, Nm2/kgc
8.2 5.2 6.2
14 35.0
11
30.5 12.8 2.3 1.4 2.7
13.2 4.8 3.1 5.4
0 Solution-to-straw ratio 10:1. 6 Determined after posthydrolysis at 120 °C for 20 min, with additional HC1 1 g/L. c Pulp beaten to 45° S.R.; handsheet, made at 70
g/m2.
Table V. Delignification of Prehydrolyzed Biomass by Chlorination
residue,
Prehydrolysis0 82.5
%
Chlorination 40 temperature, °C 60 time, min 19 Cl2, consumed, %b max.
69.5
61.5
42 60
90
17
17
30 60 4.5
51
Extraction
Figure
8.
Selectivity of partial delignification
(see
Figure 7).
temperature, °C time, min NaOH, consumed, %b
60 60
6.2
30 60 5.8
dissolved sugars, % screened pulp, % kappa number breaking length, km burst index, MN/kgc tear index, Nm2/kgc
8.0 53.5
2.0
1.5
49.5
42.0
12 6.8 4.1 5.8
12
b
12
7.6 5.0 5.7
4.0 2.0 2.4
See Table IV. Based on untreated straw. Pulp beaten to 45° S.R.; handsheets made at 70 g/m2. c
reveals a gradual degradation of cellulosic fibers, due to the combined effects of acid prehydrolysis and alkaline delignification. On the other hand, because of prehydrolysis, a significant economy in the amount of alkali needed for delignification is possible (cf. the two deligni-
fication
9. Complete delignification of prehydrolyzed biomass. Conditions of prehydrolysis are given in Table IV.
Figure
cation of the residue leads to significant carbohydrate losses. Moreover, sugar losses tend to increase at higher degrees of delignification, where more than 20% of the polysaccharides in the residue are dissolved along with lignin. Complete delignification, even by a high-sulfidity kraft treatment, is also associated with considerable losses of carbohydrates (Figure 9 and Table IV). At the same time, the examination of the mechanical properties of the pulp
curves in Figure 9). The results from the conventional, alkaline delignification of prehydrolyzed biomass can be explained based on the effects of prehydrolysis on the polysaccharides and the lignin of the residue (Figure 6, and Tables II and III); a lower D.P. has been found to enhance alkali solubility and further degradation of cellulose (Binger and Norman, 1957). Lignin condensation is only significant in the case of optimal hemicellulose separation (Table II), but in this case its effects are by far counterbalanced by those of the polysaccharides, as indicated by the consumption of alkali. Chlorination. Chlorine gas is a well-known delignifying agent; however, chlorination of untreated biomass has been found to present particular problems, mainly because of the presence of hemicellulose (Müller and Stalder, 1937). Therefore, the use of chlorination has been limited to the last stages of conventional delignification (bleaching). Nevertheless, according to the data presented in Table V, prehydrolyzed straw can be easily delignified by chlori-
314
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 2, 1982
Figure 10. Effects of chlorine supply on delignification of prehydrolyzed biomass by chlorination. Conditions of prehydrolysis are given in Table IV. Table VI.
Lignin in Pulping Liquors lignin
total solids,
in total solids,
process0
g/L
%
kraft prehydrolysiskraft prehydrolysischlorination
27.0 21.6
37.4 54.3
10.1 8.2
19.5
83.5
11.4
lignin precipitated,6 % on
straw
Yield of residue from prehydrolysis 69.5%; pulping to 6 Alkali- and thiolignin from kappa number of ca. 15. kraft delignification, and chlorolignin from chlorination. 0
a
nation, following the separation of only a small part of hemicellulose in prehydrolysis. No other chemical or mechanical pretreatment is necessary, while the time of chlorination and the consumption of Cl2 and NaOH are within reasonable limits (Koukios, 1975). The loss of carbohydrates is minimal, especially in the case of extensive-to-optimal prehydrolysis. Finally, the structure of cellulose is preserved to a greater extent, compared to the alkaline processes; degradation becomes significant only after 2/3 of the hemicellulose has been removed in prehydrolysis. The major variable in this example of unconventional delignification is chlorine supply (Figure 10). By controlling this variable, one can produce cellulosic pulps with a desired lignin content and an insignificant loss of carbohydrates. At the same time, the fractionation of the initial polysaccharides to a sugar solution, and a, partially or totally, delignified pulp can be controlled through the main variables of prehydrolysis. Furthermore, as shown in Table VI, lignin can be recovered as chlorolignin from the spent liquors of the alkaline extraction, thus raising the overall separation efficiency to ca. 90% (combined hemicellulose, cellulose, and lignin, recovery based on the extractive- and ash-free untreated straw). As in the case of conventional delignification, no significant problems due to lignin condensation were observed.
Conclusions Acid prehydrolysis is a very efficient pretreatment for biomass fractionation. More than 95% of hemicellulose and can be recovered as an aqueous solution of monooligosaccharides, along with significant amounts of noncarbohydrate materials. This pretreatment can also con-
siderably affect the structure and properties of the lignocellulosic residue, especially after an extensive removal of hemicellulose. Lignin and cellulose are both degraded to low-molecular-weight products that gradually become water soluble. At higher degrees of hydrolysis, the structure of the residue is characterized by excessive condensation of lignin and depolymerization of cellulose. Alkaline delignification of prehydrolyzed biomass is associated by significant losses of low-molecular-weight carbohydrates that reduce the yield of the cellulosic pulp. At the same time, the subsequent applications of an acid and an alkaline treatment result in substantially degraded cellulose fibers. On the contrary, solubilization of lignin is facilitated by prehydrolysis. Obviously, full utilization of the potential of acid pretreatment can be achieved only through development of unconventional delignification methods. Chlorination is proved to be such a method, since it delignifies the prehydrolyzed biomass with minimal loss of carbohydrates, and by limiting further degradation of the fiber structure. Therefore, the quantitative and qualitative aspect of polysaccharide fractionation can be controlled via prehydrolysis, while the separation of lignin can be controlled by adjusting the chlorine supply.
Acknowledgment The authors wish to thank Dr. D. G. Economides for his help on sugar analysis. The financial assistance of Purdue University, where E.G.K. is a visiting faculty member on a leave of absence from N.T.U. Athens, is kindly acknowledged.
Literature Cited Aronovsky, S. I.; Gortner, R. A. Ind. Eng. Chem. 1930, 22, 264. Bernardln, L. J. Tappl 1958, 41, 491. Binger, . P.; Norman, A. G. Tappl 1957, 40, 755. Brauns, F. E. “The Chemistry of Lignin": Academic Press: New York, 1952. Brauns, F. E.; Brauns, D. E. “The Chemistry of Lignin"; Supplement Volume; Academic Press: New York, 1960. Dunning, J. W.; Lathrop, E. C. Ind. Eng. Chem. 1945, 37, 24. Economides, D. G. Dr. Eng. Dissertation, National Technical University of Athens, Athens, Greece, 1977. Harris, E. E. Adv. Carbohydr. Chem. 1949, 4, 153. Hsu, T. A.; Ladlsh, M. R.; Tsao, G. T. CHEMTECH 1980, 10, 315. Jayme, G. The Ind. Chem. Jan 1948, 30. Karllvan, V. P. In "World Conference of Future Sources of Organic Raw Materials"; St. Pierre, L. E., Ed.; Multlsclence Publ. Ltd.: Montreal, 1978; Abstr. D-1. Koukios, E. G. Dr. Eng. Dissertation, National Technical University of Athens, A
fhflho
1Q7C
Ladlsh, M.'r.; Ladlsh, C. M.; Tsao, G. T. Science 1978, 201, 743. Liplnsky, E. S. Adv. Chem. Ser. 1979, No. 181, 1. Locus, A. H. Tappi 1960, 43, 11. Lora, J. H.; Wayman, M. Tappi 1978, 81, 47. Marchessault, R. H. In “Word Conference of Future Sources of Organic Raw Materials"; St. Pierre, L. E., Ed.; Multlsclence Publ. Ltd.: Montreal, 1978; Abstr. D-10. Millet, M. A.; Baker, A. J.; Setter, L. D. Biotechnol. Bloeng. Symp. 1975, 5,
Mitra, D. N. Tappl 1959, 42, 366. Müller, O. A.; Stalder, F. Papier Fabr, 1937, 1/2, 8. Myerly, R. C. et al. CHEMTECH 1981, 11, 186. Richter, G. A. Tappi 1955, 38, 129. T.A.P.P.I. "Official Methods, Provisional Test Methods, and Useful Test Methods"; Atlanta, Ga., 1979. Theofllatou, S. Dipl. Eng. Thesis, National Technical University of Athens, Athens, Greece, 1978. Wayman, M. "Guide for Planning Pulp and Paper Enterprises"; F.A.O.: Rome, 1973. Wayman, M.; Lora, J. H. Tappi 1978, 61, 55. Wenzl, H. F. J. "Chemical Technology of Wood"; Academic Press: New York, 1970. Yu, J.; Miller, S. F. Ind. Eng. Chem. Prod. Res. Dev. 1980, 19, 237.
Received for review May 18, 1981 Revised manuscript received September 11, 1981 Accepted October 18, 1981
Paper presented at the 181st National Meeting of the American Chemical Society, Atlanta, GA, Mar 30, 1981; Cellulose, Paper, and Textile Division.
