Recovery of useful chemicals from palm oil mill wastewater

¹ Rajamangala University of Technology Krungthep, Faculty of Engineering, 2, Nanglinchee Rd., Thunmahamek, Satorn, Bangkok 10120, Thailand
² King Mongkut's Institute of Technology Ladkrabang, Faculty of Engineering, 1, Chalongkrung 1, Ladkrabang, Bangkok 10520, Thailand
³ Tokyo Institute of Technology, Graduate School of Science and Engineering, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8552, Japan
⁴ Hokkaido University, Faculty of Engineering, N13W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan

^* Corresponding author: dnaranong@hotmail.com, duangkamol.na@kmitl.ac.th

Abstract

A two-step process consisting of pyrolysis of dried sludge and catalytic upgrading of pyrolysed liquid was proposed. Wastewater from a palm oil mill was separated to solid cake and liquid by filtration. The solid cake was dried and pyrolysed at 773 K. Liquid product obtained from the pyrolysis had two immiscible aqueous and oil phases (PL-A and PL-O). Identification of chemicals in PL-A and PL-O indicated that both phases contained various chemicals with unsaturated bonds, such as carboxylic acids and alcohols, however, most of the chemicals could not be identified. Catalytic upgrading of PL-A and PL-O over ZrO₂·FeO_x were separately performed using a fixed bed reactor at various conditions, T = 513-723 K and mass of catalyst to feed rate = 0.25-10 h. The main components in the liquid products of PL-A upgrading were methanol and acetone whereas they were acetone and phenol in the case of PL-O upgrading. More than 15% of carbon in raw material was deposited on the catalyst. To reduce the carbon deposition, the used catalyst was treated with air at 823 K. This simple treatment could reasonably regenerate the catalyst only for the case of PL-A catalytic upgrading.