Product identification and distribution from hydrothermal conversion of walnut shells

Agricultural byproducts are a major source of biomass for biofuel/bioenergy conversion. The southeastern U.S. produces a great amount of nutshells from pecan, walnut, and peanut processing. In this study, walnut shells were selected as a representative agricultural byproduct, and a hydrothermal process catalyzed by both bases and acid was applied to convert the walnut shells into liquefied organic compounds. Conversion rate, major organic products, and their distribution were measured under different concentration of bases (0-1.0 M) and reaction temperature (200-300 degrees C, corresponding to a pressure range of 1.5-8.6 MPa). An increase in base concentration (KOH and Na2CO3) or reaction temperature generally resulted in higher conversation rates and was more favorable to the generation of organic compounds of lower molecular weights. HCl as a catalyst promoted the generation of levulinic acid, but the conversion rates were very low. Major compounds from hydrothermal process catalyzed by bases were phenol derivatives. Small amounts of cyclopenten derivatives and C12-18 fatty acids were detected. The effects of reaction conditions on the distribution of products were characterized by the relative abundance of each compound group categorized based on the GC retention time.