Assessing Feedstocks and Catalysts for Production of Bio-Oils from Hydrothermal Liquefaction

A bench-scale hydrothermal liquefaction (HTL) process was utilized to convert several readily available biomass feedstocks into bio-oils that could potentially be converted to renewable liquid fuels. Bio-oils produced from dairy manure, poultry litter, pine sawdust, tallow seeds, switchgrass, peanuts, and vegetable oil were compared based on heating values and product yields. Catalysts tested in the HTL process were sodium carbonate (Na2CO3), potassium carbonate (K2CO3), and sodium hydroxide (NaOH). Operating parameters included 350 degrees C processing temperature with a corresponding pressure of similar to 20.5 MPa. Carbon monoxide was used as the process gas with an initial pressure of 2.1 MPa for all trials. Quantification of oils was achieved by using an acetone and ethyl ether extraction. Bio-oils from acetone soluble fractions (ASF) showed the highest heating values ranging from 31.1 to 35.4 MJ kg(-1). The effect of the catalysts on ASF was not clearly evident from these studies, although sodium carbonate catalyst appeared to improve conversion efficiency, measured by overall energy value, at 1-2 g catalyst quantities. The feedstock study indicated that the highest energy recovery of 70.8 % was possible from dairy manure. GC-MS results indicated that oily feedstocks produced fewer compounds, while feedstocks that have high lingocellulosic contents produced significantly higher number of compounds at relatively lower concentrations. Results indicated that high oil content was not necessary for effective energy conversion in the HTL process; therefore, from an economic perspective, feedstocks with high lipid concentrations do not offer major advantages over low-value (economic) cellulosic or waste feedstocks.