466573 Syngas Fermentation for Production of Bulk Chemicals: Design and Integral Sustainability Assessment of Multiple Value Chains
The five products from syngas fermentation considered in this study are: Ethanol, 2,3-butanediol, hexanoic acid, decanoic acid and nonane. They have been selected from a list of possible products for which, experimental results have shown possible technical feasibility of production. The selection was carried out among several alcohols, carboxylic acids and bio-polymers. The criteria for selection included mainly: the attractiveness on the market, ease of separation from the fermentation broth, plus published experimental achievements on titres, productivities and methods.
Conceptual process design was performed to determine possible production routes and process configurations. Several assumptions were made due to the lack of experimental results on the performance of the selected unit operations dealing with the specific conditions, which are defined by the unique characteristics of the fermentation of syngas. The main focus, on this stage of the project, was given to the design of the fermentation units, for which, thermodynamic approaches were used as to examine the stoichiometric and kinetic behaviours of the fermentations, as function of probable operation conditions, such as temperature, pressure and pH, as well as compositions of the feeds.
The ethanol production process was scaled according to existing plants that use second generation feedstocks. The processes for the other chosen products were scaled in order to be comparable with the ethanol throughput. Most of the equipment needed to execute the main unit operations were sized and priced with the assistance of computer aided design software. Sizes and costs for specific pieces of equipment such as fermentors, adsorption units and membrane-based operations were determined through conventionally accepted models and referencing to literature on techno-economic evaluations on similar processes.
Economic and environmental evaluations (life cycle assessment, LCA) were performed on the conceptually designed production processes, considering different compositions for the syngas fed to the systems and different geographical plant locations (three location were considered: i.e. the Netherlands, the United States and Brazil) as possible scenarios. The evaluation was finally strengthened through a sensitivity analysis applied on variables previously defined as important contributors to the processes’ economic and environmental performances.
At the end, 2,3-butanediol was found to be the most attractive of the five studied bulk chemicals, regarding to several criteria: its minimum selling price fell inside the range of the last-ten-years tendency on market prices, even when expecting a pay-back time of 3 years; its environmental impacts (emissions of greenhouse gases and non-renewable energy use), at the worst scenarios, were lower than its fossil and bio-based counterparts. The process showed to be robust to changes in feedstock production costs and plant geographical location. Furthermore, it showed to have room for improvement at the fermentation stage if further achievements are reached experimentally.
Ethanol and nonane’s minimum selling prices were found to be far above the higher limit of historical bio-ethanol and jet fuel prices in the market, respectively. Although their environmental performances showed to be better compared to the fossil-based counterparts, they did not perform better than other bio-based technologies. In the cases of the carboxylic acids, production costs were found to be higher than those for biofuels applications but lower than those for food additives. However in the latter case, the relatively small global market could be a limiting factor.