Hydrotreating the Organic Fraction of Biomass Pyrolysis Oil to a Refinery Intermediate

The effect of the catalyst type, hydroprocessing conditions, and feed preparation on the mild hydrotreating of biomass pyrolytic lignin was examined. Pyrolytic lignin oils were produced by water separation at 1:1 and 3:1 water/oil mass ratios. Hydrotreating was performed in a semi-batch reactor at three severities using sulfided NiMo/Al₂O₃, Pd/C, and Pt/C catalysts. Over half of the carbon in the pyrolytic lignin could be converted to a low-oxygen (<5%), low-acid, volatile, hydrocarbon-miscible liquid product. This was achieved with all three catalysts at the most severe condition (400 °C and 2450 psig) and with Pt/C at somewhat less severe conditions. Nuclear magnetic resonance (NMR) analyses indicated that the remaining oxygen is largely phenolic in character. Hydrotreating of the organic fraction (pyrolytic lignin) gave oil with better properties, lower O and lower acidity, than hydrotreating of the whole oil at equivalent conditions

Production of Furfural from Process-Relevant Biomass-Derived Pentoses in a Biphasic Reaction System

Furfural is an important fuel precursor which can be converted to hydrocarbon fuels and fuel intermediates. In this work, the production of furfural by dehydration of process-relevant pentose rich corn stover hydrolyzate using a biphasic batch reaction system has been investigated. Methyl isobutyl ketone (MIBK) and toluene have been used to extract furfural and enhance overall furfural yield by limiting its degradation to humins. The effects of reaction time, temperature, and acid concentration (H₂SO₄) on pentose conversion and furfural yield were investigated. For the dehydration of 8 wt % pentose-rich corn stover hydrolyzate under optimum reaction conditions, 0.05 M H₂SO₄, 170 °C for 20 min with MIBK as the solvent, complete conversion of xylose (98–100%) and a furfural yield of 80% were obtained. Under these same conditions, except with toluene as the solvent, the furfural yield was 77%. Additionally, dehydration of process-relevant pentose rich corn stover hydrolyzate using solid acid ion-exchange resins under optimum reaction conditions has shown that Purolite CT275 is as effective as H₂SO₄ for obtaining furfural yields approaching 80% using a biphasic batch reaction system. This work has demonstrated that a biphasic reaction system can be used to process biomass-derived pentose rich sugar hydrolyzates to furfural in yields approaching 80%

Evaluation of Clean Fractionation Pretreatment for the Production of Renewable Fuels and Chemicals from Corn Stover

Organosolv fractionation processes aim to separate the primary biopolymers in lignocellulosic biomass to enable more selective deconstruction and upgrading approaches for the isolated components. Clean fractionation (CF) is a particularly effective organsolv process that was originally applied to woody feedstocks. The original CF pretreatment employed methyl isobutyl ketone (MIBK), ethanol, and water with sulfuric acid as a catalyst at temperatures ranging from 120 to 160 °C. Understanding the feasibility and applicability of organosolv processes for industrial use requires mass balances on the primary polymers in biomass, detailed understanding of the physical and chemical characteristics of the fractionated components, and viable upgrading processes for each fraction. Here, we apply two CF approaches to corn stover, one with MIBK/ethanol/water and acid and the other with MIBK/acetone/water and acid, with the aim of understanding if these fractionation methods are feasible for industrial application. We quantify the full mass balances on the resulting solid, organic, and aqueous fractions and apply multiple analytical methods to characterize the three fractions. Total mass yields of the cellulose-enriched, hemicellulose-enriched, and lignin-enriched fractions are near mass closure in most cases. For corn stover, the MIBK/acetone/water CF solvent system is more effective relative to the original CF method based on the enhanced fractionation susceptibility of the aqueous and organic phases and the lower molecular weight distribution of the lignin-enriched fractions. Overall, this work reports component mass balances for the fractionation of corn stover, providing key inputs for detailed evaluation of CF processes based on bench-scale data

High-Performance Liquid Chromatography/High-Resolution Multiple Stage Tandem Mass Spectrometry Using Negative-Ion-Mode Hydroxide-Doped Electrospray Ionization for the Characterization of Lignin Degradation Products

In the search for a replacement for fossil fuel and the valuable chemicals currently obtained from crude oil, lignocellulosic biomass has become a promising candidate as an alternative biorenewable source for crude oil. Hence, many research efforts focus on the extraction, degradation, and catalytic transformation of lignin, hemicellulose, and cellulose. Unfortunately, these processes result in the production of very complex mixtures. Further, while methods have been developed for the analysis of mixtures of oligosaccharides, this is not true for the complex mixtures generated upon degradation of lignin. For example, high-performance liquid chromatography/multiple stage tandem mass spectrometry (HPLC/MSⁿ), a tool proven to be invaluable in the analysis of complex mixtures derived from many other biopolymers, such as proteins and DNA, has not been implemented for lignin degradation products. In this study, we have developed an HPLC separation method for lignin degradation products that is amenable to negative-ion-mode electrospray ionization (ESI doped with NaOH), the best method identified thus far for ionization of lignin-related model compounds without fragmentation. The separated and ionized compounds are then analyzed by MS³ experiments to obtain detailed structural information while simultaneously performing high-resolution measurements to determine their elemental compositions in the two parts of a commercial linear quadrupole ion trap/Fourier-transform ion cyclotron resonance mass spectrometer. A lignin degradation product mixture was analyzed using this method, and molecular structures were proposed for some components. This methodology significantly improves the ability to analyze complex product mixtures that result from degraded lignin