Correspondence to: Yogendra Shastri, Indian Institute of Technology Bombay - Department of Chemical Engineering Room 311, Department of Chemical Engineering IIT Bombay Powai, Mumbai, Maharashtra 400076 India. E-mail: yshastri@iitb.ac.in © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd 1 Modeling and Analysis Introduction T he species of microalgae is one of the most promis- ing resources of renewable energy. Te di ferent constituents of microalgae cell can be used as raw materials to yield various fuels. For instance, biodiesel and ethanol can be produced from cellular lipid and carbo- Optimization of integrated microalgal biorefinery producing fuel and value-added products Soumyajit Sen Gupta, Yogendra Shastri , Sharad Bhartiya, Department of Chemical Engineering, Indian Institute of Technology Bombay, Mumbai, India Received March 30, 2017; revised June 21, 2017; accepted July 24, 2017 View online at Wiley Online Library (wileyonlinelibrary.com); DOI: 10.1002/bbb.1805; Biofuels, Bioprod. Bioref. (2017) Abstract: An integrated microalgal biorefinery is desirable from an economic standpoint but challeng- ing to synthesize, due to diversity of options. This work uses a model-based optimization approach to address this challenge in a systematic manner. A superstructure of the integrated biorefinery is devel- oped where biodiesel is considered as the main product, while polar lipid, protein, and carbohydrate are also processed to various value-added compounds. Mass balances, equipment capacity limita- tions, and cost functions corresponding to these processes constitute the constraints of the optimiza- tion problem. The decision variables include the process synthesis as well as process scheduling and operations-related decisions. A Mixed Integer Linear Programming (MILP) model was developed to minimize the net annualized life cycle cost (ALCC) of the biorefinery. For a scenario of 30 Mg/d pro- duction target of biodiesel, with no intermediate storage between the stages, the superstructure yielded an optimal biodiesel production cost of US$8.53/L and reduced sugar was selected as a co- product. Several cases were analyzed in terms of the decision making of the process on the upstream and downstream levels, as well as variations in scheduling strategies. Co-cultivation of the phototro- phic and heterotrophic strains resulted in net ALCC of US$7.66/L, which was 10.2% less than the base case. Batch scheduling with various strategies were also investigated and the case with infinite intermediate storage coupled with debottlenecking reduced the net ALCC by 25% to US$6.4/L. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd Supporting information may be found in the online version of this article. Keywords: superstructure; optimization; MILP; microalgae; integrated biorefinery hydrate, respectively. Other cellular components such as pigment and protein are potential precursors of di ferent pharmaceutical and nutritious products. 1,2 Several strains of microalgae have been found to grow with high produc- tivity levels on marginal land with limited water usage. 3 Tese promising characteristics notwithstanding, micro- algae-based biorefneries have not yet been commercialized