Catalytic hydrotreating of biomass liquefaction products to produce hydrocarbon fuels: Interim report

Abstract

This report provides interim results of bench-scale testing of catalytic hydrotreatment of both high pressure and pyrolyzate biomass liquefaction products. The goal of this research is to define appropriate operating conditions and catalysts for upgrading biomass liquefaction products to hydrocarbon fuels. Elucidation of the chemistry involved in the processing is a significant portion of the effort.The results in this report represent the progress during the past four years in this ongoing research project. Successful catalytic hydrotreatment of biomass liquefaction product to a hydrocarbon fuel has been accomplished using typical petroleum hydrotreating catalysts and conditions. The phenolic and polyphenolic wood-derived oil is hydrodeoxygenated and hydrocracked to a gasoline-range hydrocarbon. The product is a mixture of cyclic and aromatic hydrocarbon which is expected to be useful as a high-octane blending agent for gasoline.The experimentation was performed in both batch-fed and continuous-fed reactor systems. Commercially-available, heterogeneous catalysts were used throughout the research. Processing conditions ranged from 250 0 to 400 0 C at pressures of approximately 2000 psig. Experimental feedstocks and products were analyzed by elemental analysis, distillation, density and viscosity determination, gas chromatography/mass spectrometry and spectrometry methods including infrared and nuclear magnetic resonance.Among the findings derived from this experimental research, the following appear most important.• Experiments employing model compounds suggest that alkyl phenolics and naphthols follow similar reaction pathways and have similar kinetics under hydrotreating conditions. A methoxyl substituent on the phenolic ring is thermally unstable and leads to condensation reactions as opposed to hydrogenation reactions. • Of the catalysts tested, cobalt-molybdenum in the sulfided form has the best combination of high hydrodeoxygenation activity with the least tendency to saturate the aromatic systems, thus producing the largest amount of high octane gasoline components.iii• High-pressure liquefaction biomass-derived oil can be directly hydrotreated to a gasoline range hydrocarbon in high yields, but biomassderived pyrolysis oil cannot be converted to gasoline in high yields under the same conditions. • Biomass-derived pyrolysis oil can be directly hydrotreated to a gasoline range hydrocarbon in high yields following a low-temperature catalytic treatment. This treatment partially hydrotreats and partially decarboxy1ates the pyro1yzate so that its thermal stability is sufficiently increased to allow higher temperature catalytic treatment.

A Review of Hydrothermal Liquefaction Bio-Crude Properties and Prospects for Upgrading to Transportation Fuels

“…This process aims to stabilise the bio-oil and reduce reactive oxygen sites that can produce char [72]. In several studies, mild hydrogenation resulted in higher thermal stability and reduced char formation [91] due to hydrogenation of aldehydes and ketones in the initial step [72]. It can then be inferred that lower coking has decreased catalyst inactivity and resulted in a higher oil yield [87].…”

“…Furthermore, a study by Elliot and Baker [91] observed that HTL bio-oil can be directly subjected to HDO, unlike pyrolysis bio-oils which need to undergo low temperature treatment. This posits that mild hydrogenation prior to a more severe hydrogenation is an option for HTL bio-crude that has properties similar to pyrolysis bio-oil, such as high oxygen content and high amounts of carbonyl-containing groups.…”

“…An early study by the Pacific Northwest National Laboratory [91] investigated catalytic hydrotreatment of HTL bio-crude by using model chemicals, bio-crude distillates, and whole bio-crude. The study concluded that sulphided CoMo and Ni catalysts are the most effective for HDO since these two catalysts have high specificity, compared to other metallic catalysts tested.…”

“…Several HDO studies observed that products from processes that use sulphided catalysts have some amount of sulphur [91,97]. To prevent adding sulphur into the HDO product, the use of noble metal catalysts can be an alternative to the more conventional catalysts already discussed.…”

Liquid Fuels by Low-Severity Hydrotreating of Biocrude

“…A low-temperature catalytic hydroprocessing has been identified as an important first step in the overall process [1]. But low-temperature catalytic hydroprocessing alone does not yield a useful fuel oil product from the biocrude [2] [3] [4] [5]. The product is a viscous black tar which is more thermally stable and can even be distilled; but it still contains high levels of chemically combined oxygen and dissolved water.…”