Solvent Liquefaction

The influence of alkali and alkaline earth metals and the role of acid pretreatments in production of sugars from switchgrass based on solvent liquefaction

Xianglan Bai, Robert C. Brown, Jie FuBrent H. Shanks, and Matthew Kieffer, Energy and Fuels

CHART]Yields of monomeric sugars from solvent liquefaction Yields of monomeric sugars from solvent liquefaction of AI switchgrass vs reaction time for different solvents: (a) levoglucosan; (b) glucose; (c) xylose; (d) sum of levoglucosan, glucose, and xylose (mass loading = 5%, temperature = 300 °C).

This study investigated the influence of alkali and alkaline earth metals (AAEM) and the role of acid pretreatments in the production of sugars during solvent liquefaction of lignocellulosic biomass using 1,4-dioxane and water as solvents. The present study found that removal of AAEM by acid washing/water rinsing did not enhance sugar production during solvent liquefaction of pretreated switchgrass nearly to the extent observed for fast pyrolysis nor did it inhibit lignin decomposition, suggesting that AAEM play less of a role in determining product yields in solvent liquefaction. On the other hand, acid infusion greatly enhanced the yields of sugars during solvent liquefaction, presumably because the strong acid catalytically promoted both the depolymerization and the dehydration of polysaccharides. The main monomeric sugars formed were levoglucosan, glucose, and xylose. Levoglucosan was the predominant sugar when 1,4-dioxane was the solvent, whereas glucose was the major sugar when water was the solvent. When 1,4-dioxane and water were cosolvents, partial hydrolysis of levoglucosan to glucose was observed. The maximum yield of the total sugars (19.8 wt %) from AI switchgrass occurred when 9:1 mixtures of 1,4-dioxane and water were used as cosolvents. In addition, the sugars were more stable in the 1,4-dioxane and water mixture compared to water alone.

Pilot-Scale Continuous Solvent Liquefaction of Biomass

Iowa State University and Chevron Technology Ventures (CTV) are collaborating to demonstrate solvent liquefaction as a pathway to produce low cost drop-in hydrocarbon transportation fuels. A 1 kg/hr continuous liquefaction unit built by Catchlight Energy, a joint venture between Chevron and Weyerhaeuser, has been redesigned and rebuilt at ISU to demonstrate continuous production of stable bio-oil from forest biomass. A liquid cut will also be recovered and directly recycled for use as a solvent in the liquefaction reaction. This unit will also demonstrate continuous solids removal.

The bio-oil will be hydroprocessed to refinery compatible biocrude and fuel blendstocks. Optimal hydroprocessing conditions will be developed by CTV. Continuous production and recovery of bio-oil and solvent, direct solvent recycle, solids removal and hydroprocessing of resulting bio-oil are critical in demonstrating the commercial viability of solvent liquefaction for the production of drop-in hydrocarbon transportation fuels. The results of the pilot plant and hydroprocessing tests will be used to conduct a techno-economic analysis and develop a preliminary process design for a demonstration plant.


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