In an industrial crystallization process, crystal shape strongly influences end-product quality and functionality as well as downstream processing. Additionally, nucleation events, solvent effects and polymorph selection play critical roles in both the design and operation of a crystallization plant and the patentability of the product and process. Therefore, investigation of these issues with respect to a priori prediction is and will continue to be an important avenue of research.In this review, we discuss the state-of-the-art in modeling crystallization processes over a range of length scales relevant to nucleation through process design. We also identify opportunities for continued research and specific areas where significant advancements are needed.

Increasing demand for renewable feedstock‐based biofuels is driving the interest and rapid development of processes to produce fuels and chemicals from biomass‐generated syngas. Biomass is gasified to produce syngas that can be converted via thermochemical routes to fuels and chemicals such as alcohols, olefins, and fuel grade hydrocarbons. An alternate route to produce liquid products from syngas is through gas fermentation, a hybrid thermochemical/ biochemical process. Biomass gasification, thermochemical syngas conversion routes, and gas fermentation are described including a comparison for converting biomass to ethanol via thecurrent thermochemical route versus gas fermentation. © 2012 American Institute of Chemical Engineers Environ Prog, 2012

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A simple classification procedure for determining optimal steady-state operating policies for plants with recycle has recently been developed by Griffin et al. to cover complex process chemistries. (Griffin, D. W.; Mellichamp, D. A.; Doherty, M. F. AIChE J. 2008, 54, 2597). This procedure classifies a process chemistry into one of two groups of operating policies based solely on the reaction kinetics. The optimal operating policy for a bounded chemistry is to operate the reactor completely full for all production rates while a nonbounded chemistry may have a variable reactor volume subject to system constraints. The current work focuses on process chemistries with reversible reactions and demonstrates that the optimal operating policy can change depending on which reaction(s) is(are) reversible and the magnitude of the equilibrium constant(s). Process chemistries with a reversible desired reaction also exhibit multiple steady-states, but only one of the steady-states corresponds to feasible operating conditions.

in Wiley InterScience (www.interscience.wiley.com).A simple and fast procedure is developed for determining optimal steady state operating policies for chemical plants with recycle. This article improves upon the previous findings by Griffin et al. (Ind Eng Chem Res. 2006;45:8056-8062) and now provides a more general classification procedure for process chemistries that have reversible reactions or reactions of unequal overall order or both. Selectivity vs. conversion relationships are indirectly determined herein, requiring only the reaction orders of reaction species. The effect of these relationships allows process chemistries to be classified into two equivalence classes: bounded and nonbounded. This classification has important implications for the optimal operation and plantwide control structure of a flexible plant with spare equipment capacity. For instance, using the classification procedure and decision tree developed in this article, it can be determined quickly whether or not it is economically optimal to operate the reactor at the holdup constraint under all operating conditions (bounded) or away from the constraint with a variable holdup operating policy (nonbounded).

Gas fermentation has emerged as a technologically and economically attractive option for producing renewable fuels and chemicals from carbon monoxide (CO) rich waste streams. LanzaTech has developed a proprietary strain of the gas fermentating acetogen Clostridium autoethanogenum as a microbial platform for synthesizing ethanol, 2,3-butanediol, and other chemicals. Bubble column reactor technology is being developed for the large-scale production, motivating the investigation of multiphase reactor hydrodynamics. In this study, we combined hydrodynamics with a genome-scale reconstruction of C. autoethanogenum metabolism and multiphase convection-dispersion equations to compare the performance of bubble column reactors with and without liquid recycle. For both reactor configurations, hydrodynamics was predicted to diminish bubble column performance with respect to CO conversion, biomass production, and ethanol production when compared with bubble column models in which the gas phase was modeled as ideal plug flow plus axial dispersion. Liquid recycle was predicted to be advantageous by increasing CO conversion, biomass production, and ethanol and 2,3-butanediol production compared with the non-recycle reactor configuration. Parametric studies performed for the liquid recycle configuration with two-phase hydrodynamics showed that increased CO feed flow rates (more gas supply), smaller CO gas bubbles (more gasliquid mass transfer), and shorter column heights (more gas per volume of liquid per time) favored ethanol production over acetate production. Our computational results demonstrate the power of combining cellular metabolic models and two-phase hydrodynamics for simulating and optimizing gas fermentation reactors.

A simple methodology for determining optimal steady-state operating policies for plants with recycle has been developed by Ward et al. (Ward, J. D.; Mellichamp, D. A.; Doherty, M. F. Ind. Eng. Chem. Res. 2004, 43, 3957). Heuristics were developed to classify irreversible process chemistries into two groups, bounded and nonbounded. This classification has important implications for how to design a control system and operate a chemical plant that contains excess equipment capacity. In this paper, formal rules are developed and presented for classifying a common special case of process chemistries that have multiple undesired irreversible reactions with equal overall reaction order. This new classification procedure is essential for determining the optimal steady-state operating policy for process chemistries of multiple parallel or series/parallel reactions.