(408g) Two-Stage Hydrothermal Liquefaction of Food Waste for Biofuel Synthesis

Every year, around 1.3 billion tons of food waste is produced globally. Turning this waste into biofuel not only helps manage it but also provides a renewable alternative to the limited and harmful fossil fuels. However, because food waste has high moisture content, it's not suitable for thermochemical methods like pyrolysis and gasification. Instead, hydrothermal liquefaction (HTL) is used, which involves mixing carbon-rich waste with water at high temperatures and pressures. This process breaks down large molecules into smaller hydrocarbons, resulting in a crude oil-like liquid called biocrude. HTL is a promising method for converting this vast amount of biogenic waste into valuable products. However, one major challenge in commercializing HTL technology is the high cost of manufacturing and operating large-scale high-pressure, high-temperature reactors. A cost-effective solution to this problem is to reduce the volume of feedstock for HTL by performing it in two stages. This study aimed to conduct HTL of simulated food waste in two stages and compare the products and their characteristics with those from single-stage HTL. The first stage (HTL-1) was carried out at three different temperatures: 160°C, 180°C, and 200°C. The wet solids obtained from each temperature were then subjected to the second stage (HTL-2) at three different temperatures: 300°C, 325°C, and 350°C. The highest biocrude yields (around 58 wt%) were achieved using HTL-1 at 160°C followed by HTL-2 at 350°C. In the biocrude, diesel was the most abundant fraction, which increased by about 10 wt% for the two-stage HTL biocrude compared to single-stage biocrude. Amides were the most abundant group of compounds in both single-stage and two-stage biocrude. The results demonstrate that two-stage HTL not only addresses the reactor cost issue but also produces products with better distribution and quality.