Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser Novel confguration of supercritical water gasifcation and chemical looping for highly-efcient hydrogen production from microalgae ☆ Anissa Nurdiawati a,∗ , Ilman Nuran Zaini b , Adrian Rizqi Irhamna c , Dwiwahju Sasongko d , Muhammad Aziz e,∗ a Department of Transdisciplinary Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan b Department of Materials Science and Engineering, Royal Institute of Technology (KTH), Brinellvägen 23, 100 44, Stockholm, Sweden c Faculty of Mechanical and Aerospace Engineering, Institut Teknologi Bandung, Ganesha 10, Bandung, 40132, Indonesia d Department of Chemical Engineering, Institut Teknologi Bandung, Ganesha 10, Bandung, 40132, Indonesia e Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba Meguro-ku, Tokyo, 153-8505, Japan ARTICLE INFO Keywords: Hydrogen production Hydrogen carrier System integration Energy efciency Aspen plus ABSTRACT This study proposes a novel system to efciently produce hydrogen from microalgae, based on supercritical water gasifcation and syngas chemical looping, and its conversion to methylcyclohexane. The process consists of a gasifer, a syngas chemical looping reactor, and a methylcyclohexane synthesis reactor as the main units. Microalgae are converted to syngas in the supercritical water gasifcation reactor. Thereafter, the produced syngas is introduced into the syngas chemical looping module to produce pure hydrogen and a separated carbon dioxide stream. The hydrogen is then reacted with toluene through the hydrogenation reaction to produce methylcyclohexane as a hydrogen carrier. The heat released from the methylcyclohexane synthesis module and chemical looping combustor is utilized to sustain the thermal balance of the supercritical water gasifcation unit. The system performance is observed under diferent feed moisture contents, operating temperatures in the su- percritical water gasifcation unit, and operating pressures in the syngas chemical looping unit. A steady-state process simulation of Aspen Plus software is used for this purpose. The proposed integrated system exhibits of approximately 13.7%, 45.3%, and 59.1% for power generation efciency, hydrogen production efciency, and total energy efciency, which demonstrates an efcient process of hydrogen production. The preliminary eco- nomic assessment shows that more than half of the operating cost accounts for microalgae production. This indicates the microalgae feedstock is one of the critical cost drivers in the microalgae-to-hydrogen production system. 1. Introduction Hydrogen (H 2 ) has been regarded as one of the potential energy carriers of the future. It is considered to have a major role in reducing the world's dependence on fossil fuels and transition to a carbon-free and energy-efcient society [1] . Among the energy carriers, H 2 ofers high fexibility because it is easily converted to electricity in fuel cells [2] and characterized by a very high gravimetric energy density [3]. The higher heating value of H 2 is 142 MJ/kg, and no other energy carrier shows a higher gravimetric energy density [4]. The increasing requirements for carbon emission reduction make H 2 more attractive as a fuel because its combustion yields only H 2 O[5]. Currently, about 99% industrial production of H 2 relies on the fossil fuel feedstocks, mainly by steam reforming of natural gas [6]. However, the processing of fossil fuels for H 2 production releases signifcant amounts of CO 2 in the process which could not address the energy and environmental con- cerns. Biomass is considered as the ideal replacement of fossil fuels due to their carbon-neutral balance and abundant availability [5]. Among various biomasses, algae represent a potential alternative energy source because they display a higher growth rate than terrestrial plants [7], do not compete with food agriculture, and require no additional land use [8]. In addition, algae can absorb large amounts of waste CO 2 as a critical nutrient, thereby acting as a greenhouse gas removal agent [9]. Microalgae have received more attention compared to the other types of algae because of their simpler structures [10], faster growth rate https://doi.org/10.1016/j.rser.2019.05.054 Received 23 January 2019; Received in revised form 5 May 2019; Accepted 27 May 2019 ☆ The short version of the paper was presented at PRES 2018, Aug 25–29, Prague, entitled “Efcient hydrogen production from algae and its conversion to methylcyclohexane” (paper ID PRES18.0937). This paper is a substantial extension of the short version of the conference. ∗ Corresponding authors. E-mail addresses: nurdiawatianissa@gmail.com (A. Nurdiawati), maziz@iis.u-tokyo.ac.jp (M. Aziz). Renewable and Sustainable Energy Reviews 112 (2019) 369–381 1364-0321/ © 2019 Elsevier Ltd. All rights reserved. T