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98-99 Project SummariesTable of Contents
Process Development and Integration

 

Enzymatic Cellulose Hydrolysis Process Development

Research Funded by: U.S. Department of Energy Office of Fuels Development through the National Renewable Energy Laboratory
Project Manager: Robert Wooley 303.384.6825, Robert_Wooley@nrel.gov
Performing Organization: National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401-3393, http://www.nrel.gov
Principal Investigator: Richard Elander, 303.384.6841, richard_elander@nrel.gov
Contract Number: N/A
Contract Period: 10/97–09/99
Contract Funding:
FY 1998: $273,000
FY 1999: $650,100
Research Funded by: U.S. Department of Energy Office of Fuels Development through the National Renewable Energy Laboratory
Project Manager: Robert Wooley 303.384.6825, Robert_Wooley@nrel.gov
Performing Organization: National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401-3393, http://www.nrel.gov
Principal Investigator: James D. McMillan, 303 384-6861, jim_mcmillan@nrel.gov
Contract Number: N/A
Contract Period: 10/98–09/99
Contract Funding:
FY 1998: $1,263,786
FY 1999: $1,291,414

Objectives:

  1. Develop and demonstrate integrated enzymatic cellulose conversion-based biomass-to-ethanol process technology that meets performance goals of the Multiyear Technical Plan for year 2000.
  2. Ultimately demonstrate the integrated process technology at scales sufficient to confirm accurate carbon mass balance closures so that the integrity of generated performance data can be verified.

Approach/Background: This effort will establish baseline performance levels for enzyme-based process technology and identify key unit operations and integration issues to focus on to further improve perform-ance and reduce the projected cost of bioethanol.The process technology that is being integrated incorporates dilute-acid biomass pretreatment, hemicellulose hydrolyzate conditioning, cellulase enzyme production, enzymatic cellulose conversion, and biomass sugar fermentation by simultaneous saccharification and cofermentation (SSCF). The model feedstock is yellow poplar hardwood sawdust. The cellulase production microorganism is the fungus Trichoderma reesei. The ethanol production microorganism is an adapted xylose-fermenting Zymomonas mobilis bacterium. Process development and integration research is guided by process engineering sensitivity analyses that identify the process variables with the largest effect on overall ethanol production cost.

In previous years we developed effective conditioning methods to partially detoxify the inhibitory yellow poplar hemicellulose hydrolyzate and we adapted a Z. mobilis strain to tolerate higher levels of the conditioned hydrolyzate. These accomplishments enabled integration of dilute-acid pretreatment and SSCF processing steps to be achieved for the first time. Integrated SSCF performance using conditioned pretreated yellow poplar was subsequently demonstrated at the bench and minipilot scales at total solids loadings of approximately 15% w/w and 20% w/w, respectively.

Process engineering analyses indicated that the most important cost factors were xylose yields in pretreatment, the productivity of cellulase enzyme production, and the cellulase loading required to achieve high cellulose conversion yields in SSCF. These analyses led to a re-emphasis of cellulase production and pretreatment work. FY 1998 efforts were directed primarily at demonstrating cellulase production using cellulosic substrates and at achieving high xylose yields in pilot scale pretreatment of yellow poplar feedstock. FY 1999 efforts extended these efforts by focusing on increasing cellulase enzyme volumetric productivity and reducing the enzyme loading required in SSCF.

Status/Accomplishments: In FY 1998 we identified improved pretreatment conditions, increased the volumetric productivity of cellu-lase production, and investigated spectroscopic methods for measuring Z. mobilis cell viability in inhibitory hydrolyzates. The major effort was devoted to pilot-scale pretreatment of yellow poplar feedstock. A reduced central composite experimental design was used to explore pretreatment performance at a residence time of 10 min and a solids loading of 20% w/w as a function of reaction temperature and acid concentration. Results showed that a temper-ature of 175oC and an acid concentration of 0.8% reliably produced pretreated yellow poplar sawdust that exhibited good bioconversion characteristics. Even with this progress, however, absolute performance levels for pretreatment and for enzyme production on cellulosic substrates and enzyme usage in SSCF remained below the year 2000 goals. It was decided to focus FY 1999 work on cellulase production and use and to postpone further efforts to optimize pretreatment.

The FY99 work effort focused on the largest showstopper process development challenges: cellulase enzyme production and cellulase enzyme use. We substantially overcame both of these key technical hurdles in FY 1999, although performance levels are still somewhat below the Multiyear Technical Plan near-term targets. In particular, we demonstrated significantly higher productivities for cellulase production by T. reesei: Average 5-day to 7-day volumetric productivities in batch production runs initiated at 5% cellulose (Solka-Floc®) were approximately 50 FPU/L-h at the best operating conditions. We also showed that lower cellulase enzyme loadings could be used to achieve high cellulose conversion yields in SSCF when the cellulase enzyme was produced using cellulose as the primary carbon source. An SSCF carried out at a total solids loading of about 15% (10% w/w insoluble pretreated solids and 5% w/v soluble biomass sugars) reached approximately 90% of theoretical cellulose conversion yield in seven days using a cellulase loading of 18 FPU/g cellulose.

The results of the FY 1999 work suggest that the Multiyear Technical Plan near-term target of obtaining greater than 80% cellulose conversion using a cellulase loading below 15 FPU/g cellulose is achievable. However, the programmatic thrust shifted towards corn stover as the year progressed, and future efforts will be directed at this widely available and underutilized biomass resource. We are in an excellent position to shift the process development effort from enzymatic cellulose hydrolysis to corn stover feedstock, based on the success achieved in FY 1999. Although working with a new feedstock presents many challenges, process development should progress more rapidly based on the knowledge we’ve gained using yellow poplar feedstock.

Publications and Presentations:

  1. McMillan, J.D., M.M. Newman, D.W. Templeton, and A. Mohagheghi.1999. Simultan-eous saccharification and cofermentation of dilute acid pretreated yellow poplar hardwood to ethanol using xylose-fermenting Zymomonas mobilis. Applied Biochemistry and Biotech-nology,77-79:649-665.
  2. McMillan, J.D., N. Dowe, A. Mohagheghi, and M.M. Newman. 2000 (in press). Assessing the efficacy of cellulase enzyme preparations under simultaneous saccharification and fermentation processing conditions. In Glycosyl Hydrolases for Biomass Conversion. Edited by M. Himmel. ACS Symposium Series 7yy. American Chemical Society, Washington, DC.
  3. Hayward, T.K., J. Hamilton, A. Tholudur, and J.D. McMillan. 1999 (in press). Improvements in titer, productivity and yield using Solka-floc for cellulase production. Applied Biochemistry and Biotechnology.
  4. Hayward, T.K., J. Hamilton, D. Templeton, E. Jennings, M. Ruth, A. Tholudur, J.D. McMillan, M. Tucker, and A. Mohagheghi. 1999. Enzyme production, growth and adaptation of T. reesei strains QM9414, L-27, RL-P37 and RUT C-30 to conditioned yellow poplar sawdust hydrolyzate. Applied Biochemistry and Biotechnology, 77-79:293-309.
  5. McMillan, J., J. Farmer, A. Mohagheghi, M. Newman, M. Ruth, D. Templeton, and R. Wooley. Sept. 1998. Demonstration of repro-ducible pretreatment and conditioning for enzymatic cellulose hydrolysis-based bioethanol production. C-level milestone report. National Renewable Energy Laboratory. Golden, CO.
  6. McMillan, J.D., T.K. Hayward, J. Hamilton, A. Tholudur, and D. Schell. April 1999. Reducing the cost of cellulase enzyme production on cellulosic substrates by demonstrating increased volumetric productivity. C-level milestone report, National Renewable Energy Laboratory. Golden, CO.
  7. McMillan, J.D., N. Dowe, A. Mohagheghi, and M. Newman. Sept 1999. Reducing the cost of saccharification and fermentation by decreasing the cellulase enzyme loading required for cellulose conversion. C-level milestone report, National Renewable Energy Laboratory internal report. Golden, CO.
  8. Templeton, D.W., J. Farmer, J. Hamilton, T.K. Hayward, R. Lyons, M. Newman, M.F. Ruth, and J.D. McMillan. 1999. Response surface analysis of pilot-scale pretreatment reactor performance for improved ethanol production. Poster presentation (by D. Templeton), Twenty-first Symposium on Biotechnology for Fuels and Chemicals, Fort Collins, CO. May 2-6 [1999].
  9. Newman, M., A. Mohagheghi, J. Hamilton, T.K .Hayward, D.W. Templeton, and J.D. McMillan, 1999. Mapping dilute acid pretreatment performance on hardwood substrates using enzymatic digestibility and biomass sugar fermentability testing. Poster presentation (by M. Newman), Twenty-first Symposium on Biotechnology for Fuels and Chemicals. Fort Collins, CO. May 2-6 [1999].
  10. Hayward, T.K., J. Hamilton, A. Tholudur, and J.D. McMillan. 1999. Improvements in titer, productivity and yield using Solka-floc for cellulase production. Poster presentation (by J. Hamilton), Twenty-first Symposium on Biotechnology for Fuels and Chemicals. Fort Collins, CO. May 2-6 [1999].
  11. Newman, M.M., N.Dowe, A.Mohagheghi, and J.D. McMillan. 1999. Decreasing the enzyme loading required for enzymatic cellulose conversion. Poster presentation (by M. Newman), Third Conference on Recent Advances in Fermentation Technology, Sarasota Springs, FL. Nov. 13-16 [1999].
  12. Tholudur, A., J .Hamilton, J.C. Sáez, K. Stanlis, and J.D. McMillan. 1999. Modeling cellulase production on purified cellulose using Trichoderma reesei L-27. Presented at the Annual Meeting of the American Institute of Chemical Engineers, Dallas, TX. Oct. 31-Nov. 5 [1999].
  13. McMillan, J.D., N. Dowe, J.D. Farmer, J. Hamilton, R. Lyons, A. Mohagheghi, M.M. Newman, J.C. Sáez, D.J. Schell, D.W. Templeton, and A. Tholudur. 1999. Develop-ment of integrated enzyme-based process technology for ethanol production from biomass. Presented at the Sixth Seminar on Enzymatic Hydrolysis of Biomass. Maringá, Paraná, Brazil. Dec. 6-10 [1999].

Summary Date: March 2000
 
 

Develop Continuous Cofermentation Process

Research Funded by: U.S. Department of Energy Office of Fuels Development through the National Renewable Energy Laboratory
Project Manager: Robert Wooley 303.384.6825, Robert_Wooley@nrel.gov
Performing Organization: University of Toronto, Toronto, Ontario, Canada M5S 1A8
Principal Investigator: H.G. Lawford, 416.978.7096, hugh.lawford@utoronto.ca
Contract Number: ACO-8-17095-01
Contract Period: 10/97–01/99
Contract Funding:
FY 1998: $30,000
FY 1999: $0

Objective: This project assessed the growth and fermentation characteristics of NREL's hard-wood hemicellulose hydrolyzate-adapted xylose-fermenting recombinant Zymomonas mobilis strain ATCC 39676 (pZB4L) under a range of operating conditions. It established the minimal levels of cost-effective nutritional supplements required to support high-yield biomass-to-ethanol fermentations. This effort is significant because of the potential to reduce overall processing cost by converting to continuous operation and using inexpensive biocatalyst nutrients.

Approach/Background: The selective pressure exerted on a microorganism within a continuous-flow bioreactor is a powerful method for improving a strain. In particular, through a process of long-term exposure to gradually increasing levels of inhibitory substances, strains can be adapted to better tolerate such substances. This technique was used by NREL’s Enzymatic Process Development researchers to adapt xylose-fermenting recombinant Zymomonas mobilis strain ATCC 39676 (pZB4L) to conditioned (overlimed) dilute-acid pretreated yellow poplar hemicellulose hydrolyzate.

This subcontract effort assessed key factors that affect growth and fermentation performance of this putatively improved strain of Z. mobilis in order to provide information for optimizing the design of a Z. mobilis-based simultaneous saccharification and cofermen-tation process. Synthetic hydrolyzate media formulated with pure sugars were used to assess growth and fermentation performance as a function of key medium composition character-istics, including (1) nutrient compo-sition, (2) total sugar concentration, (3) glucose:xylose ratio, and (4) the concentration of inhibitory acetic acid and ethanol, both individually and combined.

Status/Accomplishments: The adapted Z. mobilis strain possesses altered sugar transport characteristics and improved acetic acid tolerance as compared with the nonadapted parental strain. These characteristics are reflected in a higher xylose fermentation rate at pH 5.75. However, unadapted Z. mobilis strain CP4 (pZB5) performs better than adapted strain 39676 (pZB4L) under similar assay conditions.

In batch fermentations using high sugar loading, xylose utilization halted when ethanol concentrations reached 5.6%–6.0% w/v. In batch fermentations run at a total sugar loading of 5% w/v, the rate of xylose consumption was markedly slower when the xylose:glucose mass ratio was below 3:1.

At a constant dilution rate of 0.04 h-1 (i.e., a residence time of about 1 day) feeding corn-steep-liquor–based media containing either 4% w/v xylose + 0.8% w/v glucose or 3% w/v xylose + 1.8% w/v glucose, the volumetric ethanol productivities (QP) were 0.78 and 0.82 g/L-h, respectively. When 0.4% w/v acetic acid was added, the corresponding QP values decreased slightly to 0.67 and 0.74 g/L-h, respectively. The approximately 10%–15% reduction in QP and modest increase in residual xylose levels at pH 5.75 when 0.4% w/v acetic acid was present were independent of the sugar ratio in the medium. Moreover, at pH 5.75 the presence of 0.4% w/v acetic acid did not alter the high ethanol yield based on consumed sugars (0.48 g/g, or 94% of theoretical). However, the ethanol yield based on total input sugars decreased to 80% owing to elevated levels of residual xylose.

In continuous fermentations with the adapted strain, performance using a 1% w/v CSL-based medium was similar to that achieved using expensive yeast extract-based medium. At an estimated cost for CSL of $150/ton, the cost of nutrients using only CSL at 1% w/v is $0.113/gal ethanol. This cost can be reduced to $0.44/gal by using a medium composed of 0.25% w/v CSL supplemented with 0.12% w/v diammonium phosphate.

Publications and Presentations:

  1. Lawford, H.G. and J.D. Rousseau. 1998. Improving fermentation performance of recombinant Zymomonas in acetic acid-containing media. Applied Biochemistry and Biotechnology, 70-72:161-172.
  2. Lawford, H.G., J.D. Rousseau, A. Mohagheghi, and J.D. McMillan. 1998. Continuous culture studies of xylose-fermenting Zymomonas mobilis. Applied Biochemistry and Biotechnology, 70-72:353-367.
  3. Lawford, H.G., J.D. Rousseau, A. Mohagheghi, and J.D. McMillan. 1999. Fermentation performance characteristics of a prehydrolysate-adapted xylose-fermenting recombinant Zymomonas in batch and continuous fermentations. Applied Biochemistry and Biotechnology, 77-79:191-204.
  4. Lawford, H.G. and J.D. Rousseau. 1999. The effect of glucose on high-level xylose fer-mentations by recombinant Zymomonas in batch and fed-batch fermentations. Applied Bio-chemistry and Biotechnology, 77-79:235-49.
  5. Lawford, H.G. and , J.D. Rousseau. 1999. Final technical report. NREL subcontract ACO-8-17095-01. Reporting period Oct. 1997-Jan. 1999. National Renewable Energy Laboratory. Golden, CO.
  6. Lawford, H.G. and J.D. Rousseau. 2000 (in press). Comparative energetics of glucose and xylose metabolism in recombinant Zymomonas mobilis. Applied Biochemistry and Biotechnology.
  7. Lawford, H.G., J.D. Rousseau, A. Mohagheghi, and J.D. McMillan. 2000 (in press). Continuous fermentation studies with xylose-utilizing recombinant Zymomonas mobilis. Applied Biochemistry and Biotechnology.
  8. Lawford, H.G. and J.D. Rousseau, 1999. Final technical report. NREL subcontract ACO-8-17095-01. Reporting Period Oct. 1997–Jan. 1999. National Renewable Energy Laboratory. Golden, CO.

Summary Date: March 2000
 
 

Identification of Overliming Mechanism

Research Funded by: U.S. Department of Energy Office of Fuels Development through the National Renewable Energy Laboratory
Project Manager: Robert Wooley 303.384.6825, Robert_Wooley@nrel.gov
Performing Organization: Fralin Biotechnology Center, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0346
Principal Investigator: Richard F. Helm, 540.231.4088, helmrf@vt.edu
Contract Number:
FY 1998: XAC-4-13363-01
FY 1999: XCO-9-29049-01
Contract Period: 05/98–07/99
Contract Funding:
FY 1998: $70,000
FY 1999: $63,100

Objective: Hemicellulose hydrolyzates from dilute-acid pretreatment processes usually need to be conditioned beyond simple pH adjustment in order to be fermentable. The primary objectives of this work are to determine how overliming provides a benefit to fermentative ethanol production and to propose and test other ways to achieve this benefit. Secondary objectives are to support conditioning and process integration research at NREL (by developing methods to improve compositional analysis) and to perform routine analytical work.

Approach/Background: NREL supplies pre-treated yellow poplar hemicellulose hydrol-yzates in either treated (anion-exchanged) or untreated form. Virginia Polytechnic Institute evaluates the composition of this material and assesses its ability to be fermented by xylose-fermenting Zymomonas mobilis. Virginia Tech further evaluates the efficacy of overliming as well as other conditioning protocols in order to determine the mechanism of overliming. The goal is to use this information to devise alternative and more efficient conditioning processes.

Comparing the chemical compositions of the treated and untreated hydrolyzates provides information on what is occurring during conditioning. Efforts are therefore also directed at developing new or improved analytical separation and measurement schemes. New approaches being evaluated include derivatization followed by gas chromatography, reverse phase high performance liquid chromatography (HPLC), and HPLC-mass spectroscopy. In contrast to traditional techniques, the liquid chromatographic methods being developed require no sample concentration (e.g., freeze-drying or evaporation under reduced pressure) or extraction (solid phase or liquid–liquid), and thus they minimize or eliminate losses due to manipulating and processing the samples.

Status/Accomplishments: We have extensively evaluated the improvement in fermentation afforded by conditioning yellow poplar hemicellulose hydrolyzates using anion exchange or overliming. Results show that gas chromatography methods are not very useful for quantifying phenolic compounds, although applying a reduction–silylation protocol enables an excellent fingerprint of the major and minor monosaccharides (as their silylated alditols) to be obtained.

A liquid chromatographic method using a phenyl-type column has been developed to separate ultraviolet-absorbing compounds. Analysis of hydrolyzates conditioned according to the various conditioning protocols reveals significant differences in chromatographic fingerprints for total phenols and condensed tannins. Efforts are currently underway to determine if fingerprint compounds can be identified using HPLC-mass spectroscopy in combination with sample spiking.

Conditioning protocols beyond tradi-tional overliming are also under investigation. Studies are examining oxidative treatments using polyphenol oxidases (laccase and tyrosinase) as a potentially more effective way to eliminate toxic, water-soluble phenolics.

Publications and Presentations:

  1. Ranatunga, T.D., J. Jervis, and R.F. Helm. 1998. Identification of inhibitory components in dilute acid pretreated lignocellulosic materials, final technical status report. Reporting period May 1997-Feb. 1998. NREL subcontract XAC-5-13363-01. National Renewable Energy Laboratory. Golden, CO.
  2. Helm, R.F., J. Jervis, and T.D. Ranatunga. 1999. Identification of inhibitory components in dilute acid pretreated lignocellulosic materials, final technical report. Reporting period May 1998-June 1999 (subcontract extension period). NREL subcontract XAC-5-13363-01. National Renewable Energy Laboratory. Golden, CO.
  3. Helm, R.F., H. Leeson, and J. Jervis. 1999. Identification of overliming mechanism, bimonthly technical status report I. Reporting period July–Aug. 1999. NREL subcontract XCO-9-29049-01. National Renewable Energy Laboratory. Golden, CO.
  4. Helm, R.F., H. Leeson, and J. Jervis. 1999. Identification of overliming mechanism, bimonthly technical status report II. Reporting period Sept.–Oct. 1999. NREL subcontract XCO-9-29049-0. National Renewable Energy Laboratory. Golden, CO.
  5. Ranatunga, T.D., J. Jervis, R.F. Helm, J.D. McMillan, and R.J. Wooley. 2000 (in press). The effect of overliming on the toxicity of dilute acid pretreated lignocellulosics: The role of inorganics, uronic acids and ether-soluble organics. Enzyme Microbiology Technology.

Summary Date: March 2000
 
 

Process Development Unit Operations and Improvements

Research Funded by: U.S. Department of Energy Office of Fuels Development through the National Renewable Energy Laboratory
Project Manager: Robert Wooley 303.384.6825, Robert_Wooley@nrel.gov
Performing Organization: National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401-3393, http://www.nrel.gov
Principal Investigator: D. Schell, 303.384.6869, dan_schell@nrel.gov
Contract Number: N/A
Contract Period: 10/97–09/99
Contract Funding:
FY 1998: $694,851
FY 1999: $790,806

Objectives:The objectives of this task are to

  1. maintain and upgrade the operability of the biomass-to-ethanol Process Development Unit , and
  2. support and maintain utility systems in the pilot plant that in turn support industrial partners and internal NREL research efforts in the Alternative Fuels User Facility.

The Process Development Unit is an integrated pilot plant that includes equipment for feedstock handling, pretreatment, fermentation, solids–liquid separation, and distillation and is designed to convert 1 ton/day of biomass to ethanol.

Approach/Background:Some routine maintenance and calibration activities are needed in the pilot plant throughout the year. This work maintains the Process Development Unit in partial operational readiness for use by customers. In particular, this effort allows the Unit to be used to generate material for both NREL and industrial clients and maintains the systems required to support other Biofuels Program activities not directly associated with the Unit (e.g., the countercurrent reactor, ion-exchange equipment, and steam gun). In addition, this task plans and conducts activities that improve the operability of the pilot plant and enhances its capability to supply process performance data for customers.

Status/Accomplishments: In FY 1998, in addi-tion to normal maintenance activities, the following work was accomplished. The computer control system was upgraded and reprogrammed for better reliability and ease of use. A hydrous ammonia addition system was installed for pH control in the larger process development unit fermentors (i.e., 1500-L and 9000-L fermentors). This system was required for cellulase production, but it will also support other fermentation processes. Extraordinarily high seal failure rates were corrected by mechanical and procedural fixes. Finally, installation of a foam breaker, knockback condenser, and antifoam-addition system equipped one of the 1500-L fermentors for aerobic operation.

In FY 1999, the following activities were completed. Fermentation systems were repaired and made operational in late 1998 in anticipation of work for an industrial client (production of lignin product for the Gridley Project). Although this work was not done, the fermentors were later used in 1999 in projects for two industrial clients (BC International and Arkenol). Additionally, an antifoam system was installed in the pilot plant allowing antifoam addition to all of the 9000-L fermentors.

Also in FY 1999, two large-scale cellu-lase production runs took place in the Process Development Unit’s 1500-L and 9000-L fermentors. The goal for the 1500-L run was to produce at least 3 filter paper units (FPU)/mL on an insoluble substrate (Solka-Floc®) and measure oxygen uptake rates ). Both goals were met as the enzyme titer exceeded 3 FPU/mL (measured 4.5 FPU/mL after four days and achieved a productivity of 51 FPU/L-h) and we measured a maximum oxygen uptake rate of 22 mmol O2/L-h. Although bench-scale runs have achieved better performance, the results were still impressive for a first demonstration at this scale at NREL. Results were achieved that are similar to average bench-scale performance.

Trichoderma reesei L 27 was also successfully grown in a 9000-L fermentor on glucose, and oxygen uptake rates were measured and compared with rates derived from predictive correlations and rates suggested from bench-scale runs. The results suggest two positive outcomes. First, the measured oxygen uptake rates in the bench-scale fermentors have been very low and suggest that even higher productivities may be possible in larger fermentors that can achieve higher oxygen transfer rates. Second, this work also suggests that high oxygen uptake rates assumed for large-scale fermentors (80 mmol/L-h) may not be necessary to achieve good cellulase production. The valuable information obtained on these rates will help guide future cellulase production efforts.

Publications and Presentations:

  1. Schell, D., J. Hamilton, and A. Tholudur. 1999. Demonstrate readiness of 1500-L PDU fermentor to produce enzymes by performing a cellulase production run on Solka-Floc. Ethanol Project C-Milestone Report. National Renewable Energy Laboratory, Golden, CO.
  2. Schell, D., J. Farmer, J. Hamilton, B. Lyons, J.C. Saez, and A. Tholudur. 1999. Determine oxygen transfer rates in the PDU 9000-L fermentor using T. reesei. Ethanol Project P-Milestone Report. National Renewable Energy Laboratory, Golden, CO.
  3. Schell, D. 1999. Conduct one project to operate some or all of the PDU systems (i.e., pretreatment reactor, 9000-L fermentors or seed fermentors) for an industrial client. Ethanol Project C-Milestone Report. [Information protected by BC International CRADA]. National Renewable Energy Laboratory, Golden, CO.
  4. Farmer, J., T. Johnston, and D. Schell. 1998. Complete reprogramming of Mistic I and Mistic II. Ethanol Project P-Milestone Report. National Renewable Energy Laboratory, Golden, CO.
  5. Johnston, J., and D. Schell. 1998. Add ammonia addition capability to PDU fermentors. Ethanol Project P-Milestone Report. National Renewable Energy Laboratory, Golden, CO.
  6. Johnston, J., and D. Schell. 1998. Resolve fermentor agitator seal problems. Ethanol Project P-Milestone Report. National Renewable Energy Laboratory, Golden, CO.
  7. Schell, D., and T. Johnston. 1998. Equip one 1500-L fermentor for aerobic operation. Ethanol Project P-Milestone Report. National Renewable Energy Laboratory, Golden, CO.
  8. Schell, D., J. Farmer, E. Jennings, T. Johnston, and T. Plummer. 1998. Make PDU ready to operate as an integrate plant for Ogden lignin production work. Ethanol Project P-Milestone Report. National Renewable Energy Laboratory, Golden, CO.
  9. Johnston, T., J. Farmer, E. Jennings, B. Lyons, and D. Schell. 1999. Add antifoam addition capability to PDU 9000-L fermentors. Ethanol Project P-Milestone Report. National Renewable Energy Laboratory, Golden, CO.

Summary Date: January 2000
 
 

Process Development Unit Solids–Liquid Separations

Research Funded by: U.S. Department of Energy Office of Fuels Development through the National Renewable Energy Laboratory
Project Manager: Robert Wooley 303.384.6825, Robert_Wooley@nrel.gov
Performing Organization: National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401-3393, http://www.nrel.gov
Principal Investigator: D. Schell, 303.384.6869, dan_schell@nrel.gov
Contract Number: N/A
Contract Period: 10/97–09/98
Contract Funding:
FY 1998: $106,860

Objective: Good solids–liquid separations and recovery of dissolved wood sugars is a key step in many of the proposed biomass-to-ethanol conversion technologies. Applications include the recovery of hemicellulosic sugars from pretreated biomass, recovery of glucose produced during the hydrolysis of cellulose, and dewatering of the recovered solids. These are critical applications for which very little information is available. The objective of this work was to generation information needed to both support process engineering efforts and to identify an appropriate solids–liquid separator for the Process Development Unit.

Approach/Background: Experiments at NREL to determined sugar recoveries as a function of washwater usage for both single-stage and countercurrent washing of pretreated poplar. These experiments generated data on washing under laboratory conditions to allow better evaluation of vendor test results and to generate data on countercurrent washing, which was work not done by any of the vendors. Pretreated poplar samples were sent to solids–liquid separation vendors for evaluation of washing and separation efficacy on their equipment. Samples were sent to Dorr-Oliver (centrifuges and horizontal- and pan-type vacuum belt filters), Komline-Sanderson (rotary vacuum and pressure drum filters), and Larox (belt pressure filter).

Status/Accomplishments: Bench scale testing at NREL using vacuum filtration confirmed that countercurrent washing of the material is required to achieve adequate sugar recoveries (e.g., above 95% at 3–4 g washwater/g insoluble solids). Testing by Dorr-Oliver and Komline-Sanderson repeated much of the testing conducted at NREL but added no new information. Good sugar recoveries in the filtrate were not achieved using the Larox filter press. However, some of the cakes showed very little residual glucose, but the glucose mass closure data was poor so it was difficult to judge the validity of these results. It may be that pressing the solids into a cake reduces the ability of washing to extract the remaining sugars.

Based on tests conducted at NREL and vendor laboratories, a vacuum belt filter could be used in the Process Development Unit. Pressure filtration has not been discarded, but further investigation is needed to confirm the validity of this approach. The Larox pressure filter may offer both good sugar recoveries and dewatering in one machine.

Publications and Presentations:

  1. Schell, D.J. 1997. Determine best solid/liquid equipment to install in the PDU. Ethanol Project P-Milestone Report. National Renewable Energy Laboratory, Golden, CO.

Summary Date: January 2000
 
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