Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article RSM optimization of microwave pyrolysis parameters to produce OPS char with high yield and large BET surface area Manoj Tripathi a,b, ⁎ , Ashish Bhatnagar a , N.M. Mubarak c , J.N. Sahu d , P. Ganesan b a Department of Physics and Materials Science and Engineering, Jaypee Institute of Information Technology, A-10, Sector 62, Noida 201309, India b Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia c Department of Chemical Engineering, Faculty of Engineering and Science, Curtin University of Technology, 98009 Sarawak, Malaysia d South Ural State University, Chelyabinsk, Russia ARTICLE INFO Keywords: Biomass Microwave pyrolysis Optimization Process parameters RSM ABSTRACT Microwave pyrolysis is a very effective technique to convert organic waste into energy rich products. In the present work micro porous and carbonaceous OPS char was synthesized by microwave pyrolysis technique. OPS char yield and its BET surface area was investigated as a function of process parameters to make the microwave pyrolysis of OPS more efficient. Both of these quantities were found to be affected by the process parameters. With the rise in microwave power (MWP) and radiation time (RT), OPS char yield was lowered while increase N 2 flow rate (NFR) increased the OPS char yield slightly. Extreme values of either of the process parameter was seen to lower the BET surface area of OPS char. Response Surface Methodology (RSM), was used to optimize the process parameters for maximized OPS char yield and its BET surface area. Regression models for the OPS char yield and its BET surface area were also developed in this study. These regression models were having high Fischer test value & lower p-value which ensure its reliability and applicability. ANOVA analysis of the ex- perimental data provided the process parameters to achieve maximized OPS char yield (60.93%) and BET surface area (250.03 m 2 /g). The predicted results were validated and it was found that the experimental data varied only by 5.99% in yield and 6.34% in BET surface area from the predicted values. 1. Introduction Microwave pyrolysis is considered to be one of the most potential techniques in the pyrolysis process. Microwave pyrolysis reduces the issues associated with conventional pyrolysis methods like slow heating and necessity of feedstock shredding. It also improves the quality of pyrolysis products. Moreover by adopting the microwave pyrolysis technique processing time and energy can be saved significantly [1]. Microwave preheating is a very effective technique and is superior to conventional heating or chemical preheating techniques. Therefore, Microwave pyrolysis has overall higher efficiencies to process the bio- mass with higher moisture content and larger size materials then the conventional pyrolysis [2,3]. Microwave pyrolysis has an influential role in development of biomass derived char with large BET surface area. Microwave pyrolysis provides a rapid heating with almost no or very little ‘local temperature gradient’. In case of conventional heating the heating rate is not as large as that in the microwave heating and there is also a temperature gradient. The rapid heating causes an abrupt rise in local temperature and leads to sudden removal of volatile ma- terials present in biomass. Sudden removal of these volatile materials produces a void within the material which leads to large BET surface area. BET surface area of the produced char does also depend upon the properties of raw feedstock taken. Feedstock with higher volatile con- tent, when are treated with microwave radiation, will produce char with large BET surface area. Zhu et al. based on their studies on rice straw [4] & wheat straw [5] reported that for the fermentation and enzymatic hydrolysis, microwave preheating is very effective tech- nique. Pre-treatment of sugarcane biogases using the microwave ra- diation reported to improve the enzymatic hydrolysis [6]. Microwave pretreatment of different agricultural waste such as corn stover [7], palm kernel shell [8], sorghum biogases [9], empty fruit bunch [10], oil palm fiber [11], Jatropha hull [12], pulp mill sludge [13], oil palm shell [14] has been studied. These studies confirm that microwave pyrolysis is a suitable technique for the treatment of organic waste materials. Oil palm shell (OPS) is a solid waste material generated from the palm oil factories. Malaysia produces a large amount of palm shell https://doi.org/10.1016/j.fuel.2020.118184 Received 6 December 2019; Received in revised form 27 April 2020; Accepted 20 May 2020 ⁎ Corresponding author at: Department of Physics and Materials Science and Engineering, Jaypee Institute of Information Technology, A-10, Sector 62, Noida 201309 India. E-mail address: manoj.tripathi@jiit.ac.in (M. Tripathi). Fuel 277 (2020) 118184 0016-2361/ © 2020 Elsevier Ltd. All rights reserved. T