Conversion of secondary pulp and paper sludge to glucose by hydrothermal treatment

Abstract

Secondary pulp and paper sludge is typical residue supplied from water treatment process of paper industry. The main components of secondary pulp/paper sludge are cellulose, hemicellulose, lignin and calcium carbonate (CaCO₃). The cellulose and hemicellulose could be converted to glucose by hydrothermal treatment. In this work hydrothermal treatment of the secondary sludge has been conducted in a stainless-steel tubular batch reactor. It was found that dried powder of secondary pulp/paper sludge with nominal size of lower 595, 595 - 841, over 841 µm contains different amount of CaCO₃. Effect of temperature, holding time, particles sizes, CaCO₃ and Acid catalyst (CH₃COOH) on the glucose and 5-HMF yields has been examined under designated conditions of 220-260 ºC, holding time 0-40 min, In every experiments, heating rate is set constant at 10 ºC/min. Identification and quantification of glucose and 5-HMF in the aqueous phase is performed with high-performance liquid chromatography (HPLC). Content of total organic carbon in liquid products is determined by total organic carbon analyzer (TOC), while concentration of Ca2+ ion could be quantified by using an Inductively coupled plasma spectroscopy (ICP). Fresh feed of pulp and residual solid is subjected to the scanning electron microscopy (SEM). Plausible reaction pathway of cellulose would be proposed and discussed. The highest glucose yield could be obtained from secondary sludge at 220 °C and 20 min of holding time. It was found that CaCO₃ must be separated before hydrothermal treatment to gain higher cellulose conversion.