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Home , Hydrolysis, Sulfuric acid

TWO-STAGE, DILUTE SULFURIC OF HARDWOOD FOR PRODUCTION

John F. Harris, B.S. Chemical Engineer

Andrew J. Baker, B.S. Chemical Engineer

John I. Zerbe, Ph.D. Program Manager

Energy Research, Development, and Application Forest Products , Forest Service, USDA Madison, Wisconsin53705

ABSTRACT

The Forest Products Laboratory has developed fundamental kinetic relationships for the hydrolysis of lignocellulose dating back to World War II. Recent work at the Laboratory has provided additional informa­ tion on hydrolysis of red oak by a two-stage process at higher tempera­ tures with lower liquid-to-solid ratios. The complications of working with mixtures of and (6 percent of oak) are such that effective fractionation is necessary. This is best accomplished by prehydrolysis using dilute . Dilute is also currently the best method for conversion of the residual prehydro­ lyzed lignocellulose to . The course and yield of reactions are well predicted by kinetics data, but more attention needs to be given to the effects of ash constituents on the catalyst acid and the rever­ sion reaction, and in reducing the -to-wood ratio in hydrolysis. The purity of the generated by the two-stage process is considerably better than that obtained by the previous percolation process, but this advantage is offset somewhat by the higher yields of the percolation process. Projections on the economics of the two-stage process, although better than for processes based on prior technology, are still considered high risk.

1151 TWO-STAGE, DILUTE SULFURIC ACID HYDROLYSIS OF HARDWOOD FOR ETHANOL PRODUCTION

INTRODUCTION

Interest in wood hydrolysis dates to 1819 when Braconnot dis­ covered that could be dissolved in concentrated acid solutions and converted to . Glucose, the principal sugar pro­ duced, could then be quite readily fermented to ethanol. Other carbo­ in wood can also be hydrolyzed to sugars. Next to glucose, xylose is the most important sugar from hardwoods. is obtained from softwoods in significant amounts, and and arabinose may also be produced.

This is a synopsis of a large report (6) soon to be released by the Forest Products Laboratory (FPL). The original report was devel­ oped in cooperation with the Tennessee Valley Authority (TVA). The report presents information on a two-stage, dilute acid hydrolysis process and its application to the production of ethanol from hard­ woods. The process, in its simplest outline, is shown in Figure 1. Wood chips, impregnated with a dilute sulfuric acid and drained of all interstitial liquid, are charged to the first stage. Here they are heated with direct , resulting in the hydrolysis of most of the , and then discharged to washers. After being washed free of the material solubilized in the first stage, the lignocellulose is reimpregnated with acid and charged to the second stage. As with the first stage, the liquid content of the second-stage charge is kept to a minimum. Conditions here are sufficient to hydro­ lyze the resistant cellulose. The resulting mixture is discharged to washers where the glucose solution is separated from the lignin residue.

This process was selected for investigation because it was thought that: 1) The separate stages for hydrolyzing the hemicelluloses and cellulose would result in high yields and high-purity products. 2) The energy consumption would be minimized since much of the liquid is removed before each of the hydrolysis steps. 3) The resulting sugar solutions would be more concentrated. 4) The information available on the use of dilute sulfuric acid as a hydrolysis medium would be a great advantage if the process were to be carried rapidly to commercial operation, which was the underlying motivation for the work.

Some development work on a similar process was carried out in Sweden during World War II and a short description of the results presented at a United Nations conference in 1952 (2). Although the results were encouraging, the process was clearly considered to be a wartime expedient, and work was discontinued when the war ended. No attempt had been made to deal with effluents, to complete the design, or to optimize the process. The wood used was spruce (Piceaexcelsa ), whereas the present study deals with hardwoods--southern red oak (Quercus falcata Michx.) in particular.

The large amount of fundamental data available from previous re­ search at FPL (Madison) shaped the approach taken in this research. Existing information was believed sufficient to permit a fairly accurate design of the process; that is, the more important components

1152 Figure 1.--Two-Stage hydrolysis process could be modeled and brought into a harmonious whole. Our purpose was to recommend processing conditions pertaining to each unit, and to estimate yields, energy requirements, and other pertinent process information. Additional experimental work was planned to validate or modify the assumptions and data used in modeling. The project spawned several related fundamental studies not essential to the current process design. They include investigations of xylose , cellulose hydrolysis, sugar degradation, and deacetylation kinetics. We plan to continue these studies and release the results through technical journals.

PREHYDROLYSIS (FIRST STAGE)

The studies on the first-stage hydrolysis or prehydrolysis were intended to simulate, as nearly as possible, the performance of a continuous digester with direct-steam heating. Successful modeling of the system would allow prediction of yields as a function of time as shown in Figure 2. This figure shows the removal of xylose from the wood and the amount of solubilized xylose and produced. It applies to a particular sample of wood being reacted at a specific set of hydrolysis conditions. These curves are for 9-mmsouthern red oak chips reacting in a sulfuric acid solution at pH 1.7 and having a liquid-to-solid ratio of 1.35 when charged to the reactor. After charging to the digester, they are heated to 170°C with direct steam.

It was found that complete modeling of the system was not possible. The difficulty lies in predicting the rate of removal of the xylan from the wood. The lower curve of Figure 2 must be experi­ mentally determined for particular wood samples at each set of hydrolysis conditions. Continuing research on the kinetics of hemi­ cellulose hydrolysis will undoubtedly remove this restriction, but at present it is not possible to estimate the removal curve with suffi­ cient accuracy for process calculations. However, having established the removal curve, the yields of xylose and furfural can be predicted satisfactorily.

Figure 3 shows experimental data for the removal of xylan and yield of total xylose in solution (for southern red oak chips con­

tacted with a 1.45 percent H2SO4 and reacted at 170°C). The lower curve through the xylan yield data is the empirical functional relationship:

bt ct Xylan Yield = a e - + (100 - a)e-

where a, b, and c are constants determined from the experimental data.

As noted previously, it is necessary to determine this relation­ ship experimentally for each substrate and each particular set of hydrolysis conditions. However, once having established the rate of xylan hydrolysis, it is possible to predict the soluble xylose yield. This is the upper curve in Figure 3, which is seen to agree satisfac­ torily with the experimentally determined points. Since the xylose in solution is simply the difference between xylose released to the solu­ tion and the xylose loss, one need only know the amount of xylose

1154 1155 Figure 3.--Xylanremoval and soluble xylose yields versus hydrolysis time. Experimental values compared to predicted southern red oak chips (9 mm), 170oC, pH - 1.7, direct steam heating.

1156 destroyed during the hydrolysis to construct the upper curve. Root (13) studied the kinetics of xylose in aqueous H2SO4 solu­ tions, and his data were used in this calculation. However, the calculation is quite involved because of the difficulty of determining the acidity of the hydrolyzing solution.

The acidity is dependent on the and amount of the acid solution used, the neutralizing capacity of the wood, and the move­ ment of solution during heating. These complicated relationships have been discussed in detail in other publications (7,15). It was found that, at the low liquid-to-solid ratios employed in this work, the neutralizing effect of the substrate was significant; in some instances as much as 50 percent of the applied acid was neutralized. It was determined that not all of the inorganic cations present in the wood were solubilized, and further, that they were released slowly as hydrolysis proceeded. The water content of the hydrolyzing solution is determined by the amount of water charged with the chips, the amount of steam condensed in heating the chips, and the subsequent movement of the solution. It was found that, on heating with direct steam, chips lost solution from the interior while steam was condensing on the surface. All of the aforementioned factors must be considered to determine the actual acidity of the hydrolyzing solution, which is then used to calculate the xylose yield in solution, the upper curve of Figure 3.

Furfural yields were also estimated using Root's data. From this information it was determined that at the conditions of prehydrolysis they should be nearly solely dependent on the amount of xylose decom­ posed and independent of the particular conditions of hydrolysis employed. Figure 4 compares the experimental values for a large number of runs with that predicted. The wide scatter in the data is believed due to the difficulties and differences of the experimental method.

To summarize: It was determined that complete modeling of the first-stage hydrolysis was not possible, that it was necessary to determine, for each substrate and set of hydrolysis conditions, the xylan removal- time relationship.

On the basis of this experimental data the yields of soluble xylose and furfural could be satisfactorily predicted.

The neutralizing capacity of the substrate and the movement of liquid during heatup were important elements entering into the calcu­ lation of yields.

SACCHARIFICATION (SECOND-STAGE)

The model used for the second-stage hydrolysis or saccharifica­ tion step was considerably more complex than those previously used (14). At low liquid-to-solid ratios, such as considered in this process, it is necessary to include the following elements in the model:

1. Properties of the substrate

(a) Neutralizing capacity

1157 Figure 4.--Experimental and calculated furfural yields versus xylose reacted southern red oak chips (9 m), 170°C, direct steam heating.

1158 (b) Proportion of easily hydrolyzable cellulose (c) Amount and rate of hydrolysis of the difficultly hydrolyzable material.

2. Acidity of the system, which is dependent on:

(a) Neutralizing capacity of the lignocellulose. (b) Quantity and concentration of applied solution. (c) Properties of the acid employed. With sulfuric acid it is necessary to consider the degree of dissociation of the secondary

3. Rate of destruction of the hydrolysis products which is dependent on:

(a) Temperature. (b) Acidity or [H+]. (c) Concentration of glucose which determines the extent of reversion.

A simplified illustration of the model used is shown in Figure 5. Prior information on the rate of resistant cellulose hydrolysis (9,14) and the rate of glucose destruction (11) were available, but it was necessary to obtain new information on the reversion reactions. These data have been reported (12) and the method of incorporating it into the model is the subject of a paper being prepared.

At hydrolysis conditions which produce solutions containing in excess of 10 percent glucose the reversion phenomenon is very impor­ tant. Glucose combined as oligomeric material is partially protected from degradation and thus these reactions must be considered in yield predictions. However, more importantly, reversion results in much of the glucose being present not as free glucose but as dimers, oligomers, and anhydrosugars which are unavailable to the used in fermentation. The amount of glucose combined as reversion products ranges from 10 to 20 percent of the total glucose (i.e., including the combined material) in solution.

The success of the model for predicting yields is shown in Figure 6 where it is compared with experimental values. Also shown is a curve derived from the pervious model used (14). The data in Figure 6 are gathered using small glass ampoules (5 mm OD). The substrate was the lignocellulose residue obtained from the first-stage hydrolysis.

In addition to reversion material, the glucose solution from the second-stage hydrolysis contains large amounts of soluble decomposition products. Many of these are toxic to the Saccharomyces yeast used in the ethanol fermentation, and it is desirable to know the complete composition of the hydrolyzate to evaluate its value as a fermentation substrate. Using kinetic data (11) available on the yields of solids, hydroxymethylfurfural, , and total , the above cellulose hydrolysis model was expanded so that this information is supplied. For a particular substrate reacted at a specific set of conditions, the complete composition of the hydrolyzate as a function of time may be calculated. The components of the solution include free glucose, glucose oligomers, levoglucosan, hydroxymethylfurfural,

1159 Figure 5.--Model for cellusose saccharification. 1161 levulinic acid, and, from a balance, the amount of unaccounted soluble material. Information such as that in Figure 7 is readily calculated. The varying composition of the inorganic impurities is apparent from this figure. Notice that early in the hydrolysis HMF is the major impurity but subsequently levulinic and formic acids predominate. At the usual conditions of hydrolysis, maximum glucose yield occurs at the time where the amounts of HMF and LA are equal. The total amount of organic impurities is very large under any practical conditions of hydrolysis amounting to more than 25 percent of the free glucose present.

Prior studies of the fermentability of wood sugars (4) indicate that solutions such as these can be successfully fermented although they may need pretreatment similar to that described by Harris and Beglinger (5). No work was done on the fermentation of the second- stage hydrolyzate but studies evaluating xylose as a substrate for ethanol production were carried out. Previous work by Leonard and Hajny (10) indicated that ethanol yields of 30 to 35 percent could be obtained from xylose when fermented with the fungus Fusarium lini but rates were extremely low. Studies at FPL (8), TVA (1), and the other (3, 16) have resulted in significant progress being made along this line, and there seems to be a good possibility of a process being developed; however, the time required for commercialization eliminates it from our consideration.

PROCESS DESIGN AND EVALUATION

Based on our experimental work, a logical design for a two-stage hydrolysis process operating on hardwoods is shown in Figure 8. The major products are molasses and ethanol with byproduct furfural and acetic acid. Molasses marketed as an animal feed appears to be the preferred way of utilizing the prehydrolyzate. Other possibilities are ethanol, single-cell , and furfural. However, there is no commercial technology available for ethanol production and there are serious problems in marketing single-cell protein and large quantities of furfural. The acetic acid and furfural, both of which are unavoid­ ably produced in the process, are recovered to negate their polluting effects. The large quantities of unfermentable material produced in the second-stage hydrolysis also presents a large pollution problem. This is handled by concentrating and burning the slops.

The yield of ethanol, as indicated in Figure 8, is 8.7 percent based on processed wood or 7.3 percent based on the total wood charged to the plant which includes the additional wood needed for energy production. This yield is equivalent to 114 liters of 95 percent ethanol from 1,000 kg of processed wood. The major product is molasses, produced in 39.8 percent yield based on total wood. Furfural and acetic acid are minor products, but the furfural would contribute significantly to the economic viability of the process.

The heat requirement for the process shown in Figure 8 is about 50 percent greater than the heat available from the lignin residue. The additional energy is supplied from bark and additional fuelwood. In evaluating the process as an energy producer, we might consider the net gain in energy as liquid fuel. The energy content of the liquid fuel required to deliver the wood to the plant is 3 to 5 percent of

1162 Figure 7.--Calculated yields of the dehydration products, hydroxymethylfurfural, levulinic and formic acids during cellulose saccharification. Southern red oak prehydrolysis

residue, 220°C, 0.8 percent H2SO4.

1163 Figure 8.--Production of ethanol by two-stage hydrolysis of southern red oak. the energy content of the delivered material, and energy is also required to supply the acid and other process materials, as well as the materials for construction and maintenance of the plant. In com­ parison, the maximum energy content of the liquid fuel is about 11 percent of the heating value of the incoming wood. Thus, there is probably at least a doubling of the liquid fuel energy output compared to input. Another way to view the energy production is to consider the efficiency of conversion of the energy consumed in the process. The total products--ethanol, furfural, molasses, and acetic acid--have a total heating value of 40.7 percent of the incoming wood; the ethanol alone, 11.1 percent. Thus, based on the energy consumed (59.3 percent), the energy yield of the ethanol is 18.7 percent.

The economic problems associated with this process are very similar to those of any dilute-acid wood conversion process. The general comments given here could equally apply to all dilute-acid saccharification processes. The suggestions are restricted to possi­ bilities for improving the process illustrated in Figure 8. Such improvements could be expected to do no more than raise the process status to where it might be a marginally competitive source of ethanol. It is unlikely that major gains could be made without changing the basic process steps.

If one examines the economic contribution from each of the carbo­ fractions-- and cellulose--the problems associated with each are found to be quite different. The yield from the hemi­ cellulose fraction is quite high; more than 80 percent of the potential xylose is recovered. The major shortcoming of hemicellulose utiliza­ tion is the very low value of the product. The molasses contains 70 percent of the carbon of the marketable products from the process but accounts for only 25 percent of the total product value. Attaining higher value products from the hemicellulose could significantly im­ prove the economic outlook for the process. The energy and acid consumed in the prehydrolysis, although significant, probably could not be substantially reduced. The situation regarding the utilization of the cellulose fraction is quite different. Only 44 percent of the glucose available from the prehydrolysis residue is converted to ethanol. Some loss occurs in washing and fermenting, but the principal problem is the low conversion of cellulose to monomeric glucose in the hydrolysis reaction. High impurity loads, primarily the result of low glucose yields, are also a serious deficiency. The cellulose hydrolysis also consumes large quantities of high-pressure, expensive steam.

The income from the hemicellulose fraction could be increased by producing more furfural. In Figure 8 the furfural contributes about 16 percent to the total product value. The level of production indi­ cated was set by prolonging past maximum xylose yield to the maximum summative yield of xylose and furfural. Although furfural is generated at decreasing efficiency, probably twice as much could be produced by the same procedure by simply extending the time of pre­ hydrolysis. This would result in some loss in molasses and a small decrease in ethanol production. The net effect would be favorable, with total product value increasing by about 10 percent.

Furfural could also be considered as the principal product of the hemicellulose; all of the xylose might be utilized for furfural

1165 production. This would require processing of the xylose solution after separating it from the lignocellulose residue. However, serious marketing problems arise, even with the production from a single plant. An 800-tonne/day unit would produce approximately 35 million pounds of furfural annually, which would seriously impact on the market. Current U.S. consumption is on the order of 150 million pounds/year.

Perhaps the most promising means of improving the utilization of the hemicellulose rests on the success of current research regarding the fermentation of xylose to ethanol. The ethanol potential of the hemicellulose sugars is slightly more than the estimate of that from the cellulose sugars. Thus, ethanol production could theoretically be doubled. Since this additional ethanol would be produced at the expense of the molasses, the economic outlook would not improve propor­ tionately. The higher valued ethanol would approximately double the income from the hemicelluloses and increase the gross product value from the process by 25 percent. Other fermentation products from xylose such as butanediol and itaconic acid could be considered, but these do not seem to have the optimistic potential of ethanol.

In the second-stage hydrolysate, a large quantity of potential glucose is present as reversion material. This is a mixture consisting primarily of [1,6]-linked oligomers of glucose that are not fermented by the yeast. It can be made available for fermentation by hydrolyzing it to the monomer. To do this, two process possibilities exist. The oligomers could be treated enzymatically during the fermentation, or the fermentation bottoms could be recycled to the cellulose hydrolyzer. Unfortunately, both of these options are hampered by the presence of the impurities in solution. Conversion of the reversion material to , by either method, can only be realized if the impurities are removed.

There are other incentives to remove the degradation products from the second-stage hydrolysate. The major compounds--hydroxymethyl­ furfural, levulinic acid, and formic acid--are present in substantial quantities even when attempts are made to minimize their production. Their removal and recovery would contribute directly to the economic viability of the process, but this would also make indirect contribu­ tions. As already pointed out, their removal would open up the possibility of recovering the reversion products. In addition, the efficiency of the alcohol fermentation would be enhanced, and the pollution load from the process would be decreased.

Unlike the impurities of the prehydrolysis which can be recovered as marketable products by known processing methods, those of the second-stage are not currently marketed, and there is little informa­ tion regarding means for their recovery. This is an area for research that offers considerable promise for process improvement. Information on the yields of various nonglucose products of acid-catalyzed saccharification and on possible schemes for their recovery is needed.

Much work remains to make the process technically feasible. Suitable equipment must be developed for the reactors of both stages and construction materials selected for these harsh environments. Reliable machinery must also be designed for many of the ancillary process steps.

1166 REFERENCES CITED

1. Beck, M. J. and Strickland, R. C. Effects of conditions of dilute acid hydrolysis of hardwood on the efficiency of biocon­ version to ethanol: Summary of the Southern Biomass Energy Research Conference; 1983 October 18-20; University of Alabama, Tuscaloosa, Ala.

2. Cederquist, K. N. "Some remarks on wood hydrolyzation" In: The production and use of power alcohol in Asia and the Far East: Report of Seminar; 1952 October 23-November 6; Lucknow, India. New York: United Nations 193-197 (1954).

3. Gong, C., Ladisch, M. R., Tsao, G. T. "Production of ethanol from wood hemicellulose hydrolyzates by a xylose-fermenting yeast mutant, Candida Sp XF 217". Biotechnol. Lett., 3(11):657-662 (1981).

4. Hajny, G. J. "Biological utilization of wood for production of chemicals and feedstuffs." USDA Forest Serv. Res. Pap. FPL 385. Madison, WI: Forest Products Laboratory (1981) 64 p.

5. Harris, E. E. and Beglinger, E. "Madison wood sugar process," Ind. Eng. Chem., 38(9):890-895 (1946).

6. Harris, J. F., A. J. Baker, A. H. Conner, and others, "Two-stage, dilute sulfuric acid hydrolysis of wood," USDA Forest Serv. Res. Pap. FPL . Madison, WI: Forest Products Laboratory (1984) (in press).

7. Harris, J. F., R. W. Scott, E. L. Springer, and T. H. Wegner, "Factors influencing dilute sulfuric acid prehydrolysis of southern red oak wood," Progress in Biomass Conversion 5: (1984) (in press).

8. Jeffries, T. W. "Utilization of xylose by bacteria, , and fungi," Adv. Biochem. Eng. Biotechnol. 27, 1-32 (1983).

9. Kirby, A. M., Jr., "Kinetics of consecutive reactions involved in wood saccharification, Masters Thesis (ChemicalEngineering), Madison, WI: University of Wisconsin (1948).

10. Leonard, R. H. and G. J. Hajny, "Fermentation of wood sugars to ethyl alcohol, Ind. Eng. Chem. 37(4), 390-395 (1945).

11. McKibbins, S. W., J. F. Harris, J. F. Saeman, and W. K. Neill, "Kinetics of the acid-catalyzed conversion of glucose to 5-hydroxymethyl-2-furaldehyde and levulinic acid," Forest Prod. J., 12(1), 17-23 (1962).

12. Minor, J. L., "Nonfermentable glucose-containing products formed from glucose under cellulose hydrolysis conditions," J. Appl. Polym. Sci.; Applied Polym. Symp., 37, 617-629 (1983).

1167 13. Root, D. F., J. F. Saeman, J. F. Harris, W. K. Neill, "Kinetics of the acid catalyzed conversion of xylose to furfural,'' Forest Prod. J., 9(5), 158-164 (1959).

14. Saeman, J. F., "Kinetics of wood saccharification," Ind. Eng. Chem., 37(1), 43-52 (1945).

15. Scott, R. W., T. H. Wegner, and J. F. Harris, "Dilute sulfuric acid prehydrolysis of southern red oak chips by direct steam heating," J. Wood Chem. Tech., 3(3):245-260 (1983).

16. Suihko, M. L. and T. M. Enari. "Theproduction of ethanol from D-Glucose and D-xylose by different Fusarium strains," Biotechnol. Lett., 3(12), 723-728 (1981).

DISCUSSION

Klass I think one of the problems with acid hydrolysis of wood has always been that the sugar yields are only half of the theory. Except in a few rare cases, I believe a few techniques such as Dr. Rugg's at New York University, have been developed to increase yields to around 75% of theory.

Zerbe I doubt that he got that high. I thought the yield was about30-35%.

K. Jones, Is any equipment being developed �or commercialization of EG&G Idaho thisprocess?

Zerbe TVA is getting some equipment to operate the prehydrolysis processcontinuously.

Jones How do you reach high pressure in the second stage?

Zerbe A sealed reactor is pressurized with steam to about 300 psi, and then the pressure is released. There is some pulping equipment that looks like it would be adaptable to thisprocess.

R. Busche, I have been in touch with Dr. Rugg, and I think he's got a duPont goodprocess. His whole scheme is based upon twin screw extrusion, which very adequately controls the time element. He's getting about 50% yields on alpha-cellulose, and about 80% on hemicellulose. So the total weight average yield is then about 58-60%.

Klass Weight percent of the dry wood as sugars?

Rusche Yes.

Zerbe With soft woods, you could certainly get a fair amount from thehemicellulose.

M. Godsay, I think the and paper equipment should be very International adequate because prehvdrolysis is being done in pulp Paper manufacture. I don't see any reason for not using the same type of equipment for hydrolysis. Regarding the use of xylose from hemicelluloses for ethanol, BEC has come up with processes in which they separate hemicelluloses to

1168 make ethanol, and the cellulose is used for pulp and paper manufacture. Also, I don't think the equipment for Rugg's process is commercially available.

Klass I believe the twin screw extruder is commercial equipment.

Godsay It is, but I don't know if it would be used for this particularapplication.

Klass Perkin Baker manufactures the twin screw extruder.

J. Dodd, Kendall Fye at the University of Pennsylvania is using a EG&G Idaho pretreatment for acid hydrolysis and that's why his yields are so much higher than those you quoted. He found that if he bleached the material ahead of time, he was able to achieve much higher yields.

Zerbe Higher than 50%?

Dodd He reported 72% at one point on one particular run.

S. Newman, If you've got equations which relate hydrolysis and Bechtel yields, what do you get when you solve them for the optimum?

Zerbe You should be able to get a lot more, hut the problem is that as the cellulose is converted to glucose sugar, it doesn't remain as glucose. Some of it is converted to and much is decomposed if it isn't removed as it's formed, you lose a lot of it.

Newman What I was thinking of is a paper by A. D. Little in which the equations of Saeman, which are somewhat different from yours, were solved for batch, cocurrent, and countercurrent operations. Without going into any details as to how countercurrent operations are achieved, at very high temperature, very short residence time, and countercurrent operations, yields are excellent.

Zerbe At shorter residence times, the better the yields should be.

Newan Not only that, in countercurrent operations, the effluent wood is washed with the incoming acid and you don't have the problem of getting the residual sugars off the solid. It's taken care of automatically, and very short residence times can be achieved.

Zerbe I haven't seen the A. D. Little paper, but that sounds very interesting.

Godsay How difficult is it to separate lignin from the solution?

Zerbe The people at our laboratory say that it's no problem. The hydrolysate is washed off, and the lignin remains.

Klass Is it dispersed like a colloid?

Zerbe It's a solid precipitate.

E. Palmer, You didn't mention the work that's been done in New New Zealand Zealand. That's excusable because it's all on soft woods and not hard woods, but starting from the same point, the Madison process of the World War II, Tichtner and Goohar(?)

1169 went through the same exercise of developing the kinetics for hydrolysis and prehydrolysis. If I remember correctly, they did it for both sulfuric acid and hydrolysis. This work was developed on a larger scale at The Forest Research Institute in New Zealand in a batch plant. Another plant has been built by a commercial firm morerecently. It's only a small plant although they're claiming it's running on a commercial basis.

Klass A hydrochloric acid percolation process has been reported which removed the glucose as soon as it was formed and washed it off similar to the technique Stan just mentioned. I recall that the yields were higher than those of the sulfuric acid process.

W. Smith, One of our faculty members has been working on a novel U. of Florida approach to acid hydrolysis using the anhydride trioxide, and he is getting 80% yields from the process. The status of it right now is that a patent for the process has just been assured, and NASA has fabricated a laboratory-scalepilot plant for testing the process.

Harris, John F.; Baker, Andrew J.; Zerbe, John I. Two-stage, dilute sulfuric acid hydrolysis of hardwood for ethanol production. In: Energy from biomass and wastes VIII: Symposium Papers; 1984 January 30-February 3; Lake Buena Vista, FL. Chicago, IL: Institute of Technology; 1984: 1151-1170.

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