Advances in heterogeneous catalysis are driven by the structure–function relationships that define catalyst performance (i.e., activity, selectivity, lifetime). To understand these relationships, cooperative research is required: prediction and analysis using computational models, development of new synthetic methods to prepare specific solid-state compositions and structures, and identification of catalytically active site(s), surface-bound intermediates, and mechanistic pathways. In the application of deoxygenating and upgrading biomass pyrolysis vapors, a fundamental understanding of the factors that favor C–O bond cleavage and C–C bond formation is still needed. In this review, we focus on recent advances in heterogeneous catalysts for hydrodeoxygenation of biomass pyrolysis products. Focus is placed on studies that made use of model compounds for comparisons of catalysts and the reaction networks they promote. Applications of transition metal sulfide catalysts for deoxygenation processes are highlighted, and compared to the performances of noble metal and metal carbide, nitride, and phosphide catalysts. In general, it is found that bifunctional catalysts are required for deoxygenation in a single reactor, with bifunctionality achieved on the catalyst or in conjunction with the catalyst support. Catalysts that activate hydrogen well will be preferred for ex situ catalytic pyrolysis conditions (upgrading downstream of pyrolysis reactor prior to condensation of bio-oil, pressures near atmospheric, temperatures between 350–500 °C). Supports that limit chemisorption of large reactants (leading to blockage of catalyst sites) should be employed. Finally, the stability of the catalyst and support in high-steam and low hydrogen-to-carbon environments will be critical.
The distillation behavior of mixed alcohols was studied by use of the Advanced Distillation Curve (ADC) methodology. Crude mixed alcohols (oxygenates) were generated from syngas over a potassium-promoted cobalt–molybdenum-sulfide catalyst and assayed for major and minor products. Distillation (boiling) curves were generated for the crude mixed oxygenate products and composition channel data were collected. The crude mixed alcohols consisted primarily of methanol with significant quantities of ethanol, 1-propanol, 1-butanol, methyl acetate, and ethyl acetate. These six species constitute 93.7%–95.8% (mass/mass) of the total product. Ester, ether, and aldehyde impurities were identified, as well as thiols and organic sulfides. Considering just the alcohol products without impurities, these can be blended into gasoline at 8.5% (v/v) and meet the requirements of the Octamix waiver if an appropriate corrosion inhibitor were also included (the blend would contain 3.0%–3.4% methanol, >2.5% higher alcohols (v/v), and a total oxygen content of 3.7% (mass/mass)). Distillation targeted at 50% methanol removal increased the volume of product that could be blended to over 9% (v/v). Methanol, aldehydes, and dimethyl sulfide were the first to vaporize from the mixture, and all C4+ alcohols remained within the last 20% of the distilled volume. Other products, including ethanol, propanols, esters, and organic sulfur species distilled over a range of boiling temperatures. ADCs suggest the presence of one or more azeotropes in the distillate, consistent with a large number of known binary azeotropes between components found in the mixed oxygenate product. Enthalpies of combustion were calculated for multiple distilled fractions and ranged from 890 kJ mol–1 in the first drop of distillate to 1150 kJ mol–1 in the first drop collected after distilling 80% of the original liquid volume. This energy density is low, compared to 91-octane gasoline at 3700 and 4940 kJ mol–1 in the first drop and at 80%, respectively. Comparisons of fractional distillation of the mixed oxygenate products showed directional agreement between experiment and simulation with Aspen Plus. This study provides useful insights into mixed oxygenate products derived from a sulfided catalyst, including considerations for process recycle, product constituents and their blending, and the applicability of distillation information from process simulators.
Abstract This work 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 via indirect gasification, gas clean‐up via reforming of tars and other hydrocarbons, catalytic conversion of syngas to methanol, methanol dehydration to dimethyl ether ( DME ), and the homologation of DME over a zeolite catalyst to high‐octane gasoline‐range hydrocarbon products. The current process configuration has similarities to conventional methanol‐to‐gasoline ( MTG ) technologies, but there are key distinctions, specifically regarding the product slate, catalysts, and reactor conditions. A techno‐economic analysis is performed to investigate the production of high‐octane gasoline blendstock. The design features a processing daily capacity of 2000 tonnes (2205 short tons) of dry biomass. The process yields 271 liters of liquid fuel per dry tonne of biomass (65 gal/dry ton), for an annual fuel production rate of 178 million liters (47 MM gal) at 90% on‐stream time. The estimated total capital investment for an n th ‐plant is $438 million. The resulting minimum fuel selling price ( MFSP ) is $0.86 per liter or $3.25 per gallon in 2011 US dollars. A rigorous sensitivity analysis captures uncertainties in costs and plant performance. Sustainability metrics for the conversion process are quantified and assessed. The potential premium value of the high‐octane gasoline blendstock is examined and found to be at least as competitive as fossil‐derived blendstocks. A simple blending strategy is proposed to demonstrate the potential for blending the biomass‐derived blendstock with petroleum‐derived intermediates. Published 2015. This article is a U.S. Government work and is in the public domain in the USA . Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.
2,3,3-Trimethyl-1-butene (triptene) and other branched C6–C8 olefins, having structures characteristic of the products from the low-temperature acid-catalyzed homologation of dimethyl ether (DME), were converted to distillate-range hydrocarbons (C10–C20) with high selectivity via dimerization over a commercial ion-exchange acidic resin (Amberlyst-35) under liquid-phase stirred-batch conditions operating at ambient pressure. Triptene conversion and dimer (2,2,3,5,5,6,6-heptamethyl-3-heptene) production were monitored with time at different temperatures (60, 80, and 100 °C). The dimer production rate increased with increasing temperature; however, dimer concentration decreased with increasing temperature due to competing side reactions. Dimerization, as compared to cracking, isomerization, and oligomerization, was the dominant reaction pathway during the first hours of reaction at all temperatures. Dimerization at 100 °C achieved a conversion of 35% and a molar selectivity to the desired dimer of 71% in 2 h. In longer runs (≥16 h), the highest conversion (80%) was achieved at 100 °C whereas the maximum total C10+ production (1.83 g/batch, 52% by weight of the reactant) was achieved at 80 °C. The nucleophilicity and extent of branching of the C6–C8 olefins were found to have a strong effect on dimerization yields. The cloud point, boiling range, carbon-number distribution, and lower heating value of the dimerized product were compared to ASTM specifications for middle-distillate fuels, and the results suggest that approximately 80% of the product has potential as a jet fuel blend stock.
