Biofuels and platform chemicals from bio-wastes by coupling thermochemical and biochemical processes – experimental studies and process modelling

Abstract

Increasing energy demand due to population growth and technological advancement, coupled with the overexploitation of fossil fuels, has pushed humanity to an irreversible point where it is essential to find more and alternative sources of energy. Biowastes can play a significant role in this regard. Two major types of technologies are available to convert waste into energy: thermochemical processes (such as pyrolysis, gasification, hydrothermal liquefaction, and hydrothermal carbonization) and biochemical processes (such as anaerobic digestion and fermentation). Among these, anaerobic digestion (AD) is already commercially established due to its low cost, low energy input, easy installation, and ability to treat a wide variety of organic matter. Another advantage of AD is its potential to be integrated with thermochemical processes both upstream and downstream, thereby enhancing energy and material recovery. In this study, Kitchen waste and grass were used as feedstock, with cow dung serving as the inoculum. Cumulative biogas production was found to be 172.5, 301.875, 248.58, 275.625 ml/g VS for cow dung, grass, kitchen waste1, kitchen waste2 respectively. Methane content of the biogas was between 69 to 80 %. The undegraded anaerobic digestate was subjected to pyrolysis and hydrothermal liquefaction (HTL). Pyrolysis was performed at three different temperatures, while HTL was conducted at 200°C with a residence time of 1 hour. A comparative study of the characteristics of the products from pyrolysis and HTL was conducted, revealing that both pyrochar and hydrochar could have better soil amending properties compared to digestate. Hydrochar was found be more effective than pyrochar in case of dye removal when Congo red was used. A comprehensive kinetic model for both AD and pyrolysis was investigated, and a process model based on this was developed using ASPEN Plus V10.