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The goal of this project is to obtain the necessary scientific and technological data to evaluate the economics and markets for converting lignin into valuable fuel additives. Lignin is present (15-30 wt%) in all lignocellulosic biomass and any bioethanol production process will have lignin as a residue. Lignin can be combusted to provide heat and/or power for the ethanol process; however, increasing the value of this residue by converting it to higher value fuel additives can significantly enhance the competitiveness of bioethanol technology.
A team involving personnel from NREL, the University of Utah (U of U), and Sandia National Laboratories (SNL) is working to develop a process for making fuel additives from lignin. Current specifications for gasoline define the properties of the targeted products. Valuable additives are hydrocarbons or oxygenates that have a high octane number (>100), and are compatible with the gasoline boiling point and Reid vapor pressure (RVP) parameters.
Figure 1: Conversion Processes to Produce Fuel Additives from Lignin
Professor J.S. Shabtai, from the U of U, is studying the fundamentals of lignin depolymerization and hydrotreating. Dr. J.E. Miller at SNL is also studying lignin depolymerization. NREL (Dr. D.K. Johnson) is supplying lignin feedstocks and chemically characterizing the feedstocks and products generated by the other two groups. Dr. E. Chornet at NREL is coordinating the work of the team.
The first step to converting lignin into a product compatible with the transportation fuel market is to decrease its molecular weight. Currently, base catalyzed depolymerization (BCD) of lignin is the process being studied to achieve this.
Systematic studies have been performed at the U of U on the BCD step using stirred autoclaves. The effects of reaction time, temperature, pressure, base type, base concentration, and the solvent used have been examined. High yields of depolymerized lignin (60%-80%) are obtained at moderate temperatures and short reaction times. The depolymerization reaction is currently being scaled up in a flow reactor capable of processing 150 g of lignin per hour.
SNL has been studying the kinetic and reaction chemistry of lignin depolymerization and has also been developing a solid base catalyst system utilizing rapidly heated batch microreactors. SNL researchers have replicated results from the U of U showing that high yields of depolymerized lignin can be obtained.
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Further processing of depolymerized lignin (the BCD product) is necessary before the product is suitable for fuel applications. The product must be either partially or completely deoxygenated depending on whether an oxygenate or hydrocarbon product is the final target.
In one approach, the BCD step is followed by upgrading via hydroprocessing (HPR), involving catalytic hydrodeoxygenation (HDO), and then hydrocracking (HCR). The BCD product is thus converted into a mixture of aromatic hydrocarbons. Depolymerized lignin samples hydroprocessed at the U of U produced mixtures of aromatic and naphthenic hydrocarbons that could be used as fuel additives. Analyses of these hydrocarbon samples, performed at NREL, indicate that they are predominately (~65%) made up of aromatic hydrocarbons. Estimates indicate that the octane of these products is in the 100-110 range. Production of hydrocarbon products is being scaled up so that enough is available for fuel property testing. A sample of depolymerized lignin made at SNL was hydroprocessed under the conditions normally used at the U of U and found to yield a product that was very similar to that made by the U of U.
In a second approach, selective hydrotreating (HT) is applied in which oxygen-containing functional groups are preserved while C-C bonds are cleaved to increase the yield of monomeric phenols. The HT step is followed by etherification to yield aromatic ethers that should perform at least as well as current commercial oxygenated fuel additives.
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At NREL (K. Ibsen) a conceptual design of the process was constructed, at a scale of 600 tons per day, to convert lignin from a bioethanol plant (enzyme process) into a high-octane hydrocarbon fuel additive. From this, the production cost of the fuel additive was estimated at about $1.06/gallon. Assumed design performance included 100% solubilization of the lignin in the SSF residue at a lignin concentration of 8%, a soluble base concentration of 1% or less in the lignin depolymerization step, and an overall yield of hydrocarbon product in the gasoline boiling range at 70% of theoretical yield (equivalent to about 50% on a mass basis). Extraction of the depolymerized lignin intermediate must also be performed with a low-cost solvent. Current research is aimed at meeting these performance targets.
A consultant (J.E. Sinor and Associates) familiar with the fuels market has estimated the value of a lignin derived high octane gasoline additive. The value of an octane enhancing gasoline additive has been estimated to be in the range of 0.7 - 1.4 cents per octane gallon. Based on the Annual Energy Outlook projection of $20-$25/barrel for crude oil in 2010, the spot price for gasoline should be about $0.80/gallon. The value of a high-octane (R + M/2 = 110) hydrocarbon fuel additive should then be in the range of $0.97-$1.14 per gallon using these assumptions. Thus if performance targets can be met or slightly exceeded it should be possible to use the lignin from a bioethanol plant to enhance the competitiveness of biomass-to-ethanol conversion.
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- Shabtai, J., et al., U.S. Patent No. 5,959,167 (1999). Process for Conversion of Lignin to Reformulated Hydrocarbon Gasoline.
- Shabtai, J., et al., U.S. Patent Appl. 09/376,864(1999). Process for Conversion of Lignin to Reformulated Partially Oxygenated Gasoline.
- Shabtai J. S.; Zmierczak, W; Chornet, E.; Johnson, D.K. (1999) "Conversion of Lignin. 2. Production of High-Octane Fuel Additives." ACS Div. Fuel Chem. Preprints (44);pp. 267-272.
- Shabtai J.: Zmierczak, W; Kadangode. S.; Chornet, E.; Johnson, D.K. (1999). "Lignin Conversion to High-Octane Fuel Additives." Proceedings of the Fourth Biomass Conference of the Americas, Oakland, CA.; pp. 811-818.
- Miller, J.E.; Evans, L.; Littlewolf, A.; Trudell, D.E. (1999). "Batch Microreactor Studies of Lignin and Lignin Model Compound Depolymerization by Bases in Alcohol Solvents." Fuel (78); pp. 1363-1366.
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- Search the Bioenergy Topical Search
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