Thermodynamics, Design, Simulation and Benchmarking of Biofuel Processes

In recent years the conversion of non-food based feedstocks into fuels has attracted considerable attention. The production of bioethanol from corn and sugar cane is a well-established process; however, the conversion of lignocellulosic (wood based) biomass into liquid fuels requires the development of advance theologies. Among these is ethanol from syngas fermentation, the process is referred to as indirect fermentation as it utilizes gaseous components (mainly H₂ and CO₂) derived from biomass gasification.

A general overview of the available commercial processes is presented in the first chapter. So far, only three companies: INEOS Bio, Coskata and LanzaTech have reported the operation of pilot or full scale facilities for ethanol production.

In chapter 3 is discussed the development of a thermodynamic model parameter base for the solubility of syngas components in water, ethanol and acetic acid, which is valid from low to moderate pressures. The results show that the UNIQUAC equation, coupled with an appropriate equation of state, is able to represent the binaries in the range of temperatures and pressures from 0 to 310 °C and from 1 to 400 bar, respectively. The model parameterization is further applied, with a more pragmatic approach, to the study of VLE and LLE data for systems that are of relevance for the separation and recovery of the liquid products of the fermentation.

Chapter 4 is dedicated to the process simulation and benchmarking of the available separation technologies for the recovery of alcohol and the acid downstream of the syngas fermentation. The simulation results show that the larger differences in terms of energy savings between the methods of the separation considered are most evident for low products concentrations in the feed.

Chapter 5 gives an outline on mass transfer correlations available in literature with a focus on gases-liquid dispersions. The sections provide a coherent classification of the existing equations that may be of use for the selection of the most appropriate model to be implemented in CFD simulation studies, or for the processing of experimental data relevant to gas-liquid contactors. The second part of the chapter discusses the effects of strong electrolytes on the coalescence properties of aqueous solutions since coalescence inhibition is the most cost-effective method for improving the mass transfer from the gas to the liquid phase, especially for the stirred tank and bubble column fermenters.
The last chapter 6 concerns the experimental characterization of a pilot-scale bubble column for non-coalescing conditions. High mass transfer rates and low operational and maintenance costs are the primary merits of these systems. While coalescence might be the major drawback of bubble columns, it can be virtually eliminated with the use of suitable surface active components. Bubbles size distribution, mass transfer performance, and specific interfacial area are investigated in detail for different operating conditions.
Conclusion and future work are presented in chapter 7.