(401d) Integrated Designs of Micro-Algae Biorefineries Using a Fixed Selection of Halophytic Algae

Biorefineries typically refer to lignocellulosic feedstock as they are available from agricultural activities, residues, waste organics or forestry supplies. There is much less attention to water substrates from micro-algae and macro-algae systems that feature alternative paths to products, involve competitive chemistries and require co-production of chemicals to remain feasible. A notable case relates to halophytic Dunaliella cultures capable to convert CO₂into a multitude of products. One needs to select Dunaliella for its extraordinary tolerance to salt stress establishing it as one of the few organisms that can survive in extreme environments.

The paper discusses the development of an integrated process that addresses the co-production of glycerol, b-carotene and proteins using a multitude of solvents and scoping to reduce energy consumption. The reference case refers to an industrial pilot set up to operate with the use of ethanol as solvent and produces 3.5 tones biomass per year. The cultivation of Dunaliella takes place in the cultivation pond (0.5 Ha) and after harvesting, osmotic shock is induced to the cells resulting in the accumulation of glycerol and β-carotene. Their extraction is achieved by breaking up the cell walls with the use of ethanol in a high concentration. The mixture of ethanol/water/glycerol is distilled for ethanol recycling and refinement of glycerol, while β-carotene is extracted from the remaining mixture by using hexane as solvent. The energy intensive separation of the ethanol/water/glycerol mixture raises questions regarding the sustainability of the process.

The paper discusses implications as the process develops from a single-product plant to a multi-product process with co-production of specialties and the valorization of by-products. The analysis reviews economic benefits as well as the impact of process integration in securing the viability of the incentive. Process integration is applied to target efficiency scoping reviewing thermal integration, and the use of alternative separation schemes including azeotropic distillation. The work uses a supertask model to review thermally coupled columns including prefractionators, Petlyuk columns, side strippers and side Rectifiers featuring sloppy splits, and side draws. The work concludes that, even though single-product processes are not economically viable (with or without integration), the multi-product process can benefit dramatically from process integration (38% reduction in energy use) and can yield a sustainable and profitable process.