Value-Added Chemicals from Microalgae: Greener, More Economical, or Both?

Abstract

This paper addresses the sustainable design and synthesis of manufacturing processes for making algal bioproducts. We propose by far the most comprehensive superstructure capable of producing biodiesel, hydrogen, propylene glycol, glycerol-tert-butyl ether, and poly-3-hydroxybutyrate from microalgae. The major processing sections include cultivation, harvesting, lipid extraction, remnant treatment, biogas utilization, biofuel proneduction, and bioproduct manufacturing. Based on the superstructure, we integrate a cradle-to-gate life cycle analysis and techno-economic analysis with multiobjective optimization to simultaneously optimize the environmental and economic performance. We also apply a tailored global optimization algorithm to efficiently solve the problem in reasonable computation times. Results show that the most environmentally sustainable processes reduce life cycle greenhouse gas emissions per kilogram of the algal bioproducts by 5% to 63%, compared with petrochemical counterparts. In addition, the coproduction of value-added bioproducts in the algal glycerol process helps reduce the biodiesel production cost to as low as $2.79 per gasoline-gallon-equivalent. a complete superstructure which not only incorporates existing technologies for the conversion of algal biodiesel, but also takes advantage of the versatile glycerol and converts it on site to environmentally sustainable and value-added bioproducts. Process integration is an important method in sustainable process design to explore the possibilities of improving the overall process efficiency by utilizing waste streams and ultimately reduce the overall expenditure and environmental impacts of the entire process.Bioproduct manufacturing production has the potential for boosting the algal biodiesel performance by utilizing byproducts in transesterification and generating carbon dioxide feed for microalgae growth. The aim of the current work, therefore, is to explore the potential environmental and economic benefits for the production of both biodiesel and value-added bioproducts from microalgae.In order to bridge the research gap, we develop by far the most comprehensive superstructure, which is able to produce biodiesel and four types of bioproducts, including hydrogen, propylene glycol (PG), glycerol-tert-butyl ether (GE), and poly-3-hydroxybutyrate (PHB). In particular, the hydrogen can be produced by either steam reforming, autothermal reforming, or aqueous-phase reforming. The superstructure also includes a methanol synthesis process in the biogas utilization section. Additionally, we simulate the lipid extraction processes using hexane and n-butanol as extractants for data validation.Based on the proposed superstructure, a cradle-to-gate life cycle analysis (LCA) is performed to account for the life cycle greenhouse gas (GHG) emissions associated with three life cycle stages, namely feedstock acquisition, transportation, and algal biodiesel and bioproduct manufacturing. Following a life cycle optimization methodology, we further integrate the...

Life Cycle Network Modeling Framework and Solution Algorithms for Systems Analysis and Optimization of the Water-Energy Nexus

“…technologies were included in the model, as there is no straightforward way to analyze the economic and water footprint impacts of their production from a water-energy nexus perspective. This is done not to imply that production of bioproducts is not promising-Indeed, several studies cite bioproducts as key to enhancing the economic viability of biofuels processes [50][51][52]. However, this possibility is not a focus of this work.…”

Sustainable design and synthesis of energy systems

“…As opposed to other methods, this method enables systematic generation and automatic evaluation of design candidates with the best process economics and highest levels of environmental sustainability. Recently this method has been actively applied to optimally designing and synthesizing various energy systems, including hydrocarbon biorefineries [25 ,26,27,28 ,29], algal systems [30][31][32][33], polygeneration systems [34][35][36], shale gas processes [37][38][39], and network systems [40].…”

“…Examples of successfully integrated energy systems abound in recent contributions, such as the integration of shale gas processing and bioethanol dehydration [37], biodiesel and bioproduct manufacturing [33], organic Rankine cycle and utility systems [99], microalgae processing and electricity generation [100], as well as biofuel production and solarbased hydrogen conversion [101]. Much research effort has also been devoted to the integration of solar, heat, and power systems [102][103][104].…”

“…As opposed to other methods, this method enables systematic generation and automatic evaluation of design candidates with the best process economics and highest levels of environmental sustainability. Recently this method has been actively applied to optimally designing and synthesizing various energy systems, including hydrocarbon biorefineries [25 ,26,27,28 ,29], algal systems [30][31][32][33], polygeneration systems [34-36], shale gas processes [37][38][39], and network systems [40].As illustrated in Figure 1, there are three stages in sustainable design and synthesis of energy systems based on superstructure optimization: superstructure generation, optimization model development, and optimal design decision determination. The remainder of this section describes each stage in detail and presentspertinent challenges.…”

Fast optimization algorithms for large-scale mixed-integer linear fractional programming problems

“…A general form of MILFP problem is given as the following problem (P): MILFP models are widely applied to address a variety of problems, ranging from manufacturing, cyclic production, life cycle optimization, supply chain retrofit, finance, etc. [2][3][4][5][6][7][8][9][10][11][12][13]. MILFP problems are nonconvex MINLP problems and challenging to globally optimize due to its combinatorial nature and the pseudo-convexity of the objective function [14].…”