Process Design and Economics for the Conversion of Lignocellulosic Biomass to Hydrocarbons via Indirect Liquefaction. Thermochemical Research Pathway to High-Octane Gasoline Blendstock Through Methanol/Dimethyl Ether Intermediates [report]

Eric C. D. Tan, Michael Talmadge, Abhijit Dutta, Jesse Hensley, Josh Schaidle, Mary Biddy, David Humbird, Lesley J. Snowden-Swan, Jeff Ross, Danielle Sexton, Raymond Yap, John Lukas
2015 unpublished
This report was developed as part of the U.S. Department of Energy's Bioenergy Technologies Office's (BETO's) efforts to enable the development of technologies for the production of infrastructure-compatible, cost-competitive liquid hydrocarbon fuels from lignocellulosic biomass feedstocks. The research funded by BETO is designed to advance the state of technology of biomass feedstock supply and logistics, conversion, and overall system sustainability. It is expected that these research
more » ... ents will be made within the 2022 timeframe. As part of their involvement in this research and development effort, the National Renewable Energy Laboratory and the Pacific Northwest National Laboratory investigate the economics of conversion pathways through the development of conceptual biorefinery process models and techno-economic analysis models. This report describes in detail one potential conversion process for the production of high-octane gasoline blendstock via indirect liquefaction of biomass. The processing steps of this pathway include the conversion of biomass to synthesis gas or syngas via indirect gasification, gas cleanup, catalytic conversion of syngas to methanol intermediate, methanol dehydration to dimethyl ether (DME), and catalytic conversion of DME to high-octane, gasoline-range hydrocarbon blendstock product. The conversion process configuration leverages technologies previously advanced by research funded by BETO and demonstrated in 2012 with the production of mixed alcohols from biomass. Biomass-derived syngas cleanup via reforming of tars and other hydrocarbons is one of the key technology advancements realized as part of this prior research and 2012 demonstrations. The process described in this report evaluates a new technology area for the downstream utilization of clean biomass-derived syngas for the production of high-octane hydrocarbon products through methanol and DME intermediates. In this process, methanol undergoes dehydration to DME, which is subsequently converted via homologation reactions to high-octane, gasoline-range hydrocarbon products. The process configuration presented in this design report possesses similarities to methanol-togasoline (MTG) technologies such as the process licensed by ExxonMobil Research and Engineering. However, the technology presented herein differs from conventional MTG processes with respect to the quality of hydrocarbons produced and the severity of process conditions. The conventional MTG process generates a product mix with high concentrations of aromatic hydrocarbon compounds. The product mixture possesses an average octane number ((RON+MON)/2) of approximately 87 and yield of gasoline blendstock is limited by production of light hydrocarbon coproducts and coke formation. In contrast, the chemistry proposed herein and supported by preliminary experimental results produces a gasoline blendstock with high concentration of iso-paraffinic compounds with an expected average octane number of >93 and low concentrations of aromatics. Additionally, coke formation has not been observed during initial experiments, although some coke formation is expected with extended on-stream operations. The reduced coking potential can result in higher yields and improved carbon utilization. With biomass feedstock being the single most expensive component of the process, higher yields per ton of biomass can make a significant positive impact on the process economics. With respect to the process conditions, the hydrocarbon synthesis reactor in the ExxonMobil MTG process operates in the 650°F-950°F range and is limited by reactor configuration. MTG reactor operations must be controlled to limit per-pass conversions to prevent runaway in a fixed-bed, shell and tube reactor, or a reactor system must be designed to iv This report is available at no cost from the National Renewable Energy Laboratory (NREL) at utilize a fluidized bed reactor for efficient heat management to allow high single-pass conversions. Conversely, the hydrocarbon synthesis reactor conditions for the design presented here are less severe, operating in the temperature range of 350°F-450°F. In addition, the reactor system can operate at higher per-pass conversions using multiple fixed-bed reactors with interbed cooling. By operating at lower temperature, coke formation is significantly reduced. Thus, catalyst bed regeneration can be less frequent, which results in the potential to reduce capital and operating costs. The conceptual design presented here considers the economics of high-octane gasoline blendstock production, under the assumption of achieving the described product selectivities and conversions through near-term research efforts. The design features a processing capacity of 2,205 U.S. tons (2,000 metric tonnes) of dry biomass per day and a gasoline yield of 64.9 gallons per dry U.S. ton of feedstock. The gasoline selling price corresponding to this design (2022 target) is $3.25 per gallon of blendstock (or $3.41/gallon of gasoline equivalent) in 2011 dollars, assuming a 30-year plant life and 40% equity financing with a 10% internal rate of return and the remaining 60% debt financed at 8% interest. A summary of the techno-economic analysis results for this pathway is presented in the following table. v
doi:10.2172/1215006 fatcat:s4qplheconbm3eqnnyvmiytlka