There is an immediate need to drastically reduce the emissions associated with global fossil fuel consumption in order to limit climate change. However, carbon-based materials, chemicals, and transportation fuels are predominantly made from fossil sources and currently there is no alternative source available to adequately displace them. Gas-fermenting microorganisms that fix carbon dioxide (CO2) and carbon monoxide (CO) can break this dependence as they are capable of converting gaseous carbon to fuels and chemicals. As such, the technology can utilize a wide range of feedstocks including gasified organic matter of any sort (e.g., municipal solid waste, industrial waste, biomass, and agricultural waste residues) or industrial off-gases (e.g., from steel mills or processing plants). Gas fermentation has matured to the point that large-scale production of ethanol from gas has been demonstrated by two companies. This review gives an overview of the gas fermentation process, focusing specifically on anaerobic acetogens. Applications of synthetic biology and coupling gas fermentation to additional processes are discussed in detail. Both of these strategies, demonstrated at bench-scale, have abundant potential to rapidly expand the commercial product spectrum of gas fermentation and further improve efficiencies and yields.

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Gas Fermentation—A Flexible Platform for Commercial Scale Production of Low-Carbon-Fuels and Chemicals from Waste and Renewable Feedstocks

Enhanced bioethanol dehydration by extractive and azeotropic distillation in dividing-wall columns

Throughout history, distillation has been the most widespread separation method. However, despite its simplicity and flexibility, distillation still remains very energy inefficient. Novel distillation concepts based on process intensification, can deliver major benefits, not just in terms of significantly lower energy use, but also in reducing capital investment and improving eco-efficiency. While very likely to remain the separation technology of choice for the next decades, there is no doubt that distillation technology needs to make radical changes in order to meet the demands of the energy-conscious modern society. This article aims to show that in spite of its long age, distillation technology is still young and full of breakthrough opportunities. Moreover, it provides a broad overview of the recent developments in distillation based on process intensification principles, for example heat pump assisted distillation (e.g. vapor compression or compression–resorption), heat-integrated distillation column, membrane distillation, HiGee distillation, cyclic distillation, thermally coupled distillation systems (Petlyuk), dividing-wall column, and reactive distillation. These developments as well as the future perspectives of distillation are discussed in the context of changes towards a more energy efficient and sustainable chemical process industry. Several key examples are also included to illustrate the astonishing potential of these new distillation concepts to significantly reduce the capital and operating cost at industrial scale. © 2013 Society of Chemical Industry

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Distillation technology - still young and full of breakthrough opportunities

Innovative single step bioethanol dehydration in an extractive dividing-wall column

The purification of bioethanol fuel involves an energy-intensive separation process to concentrate the diluted streams obtained in the fermentation stage and to overcome the azeotropic behavior of the ethanol-water mixture The conventional separation sequence employs three distillation columns that carry out several tasks, penalized by high-energy requirements: preconcentration of ethanol, extractive distillation, and solvent recovery To solve this problem, we propose here a novel heat-pump-assisted extractive distillation process taking place in a dividing-wall column (DWC) In this configuration, the ethanol top vapor stream of the extractive DWC is recompressed from atmospheric pressure to over 31 bar (thus to a higher temperature) and used to drive the side reboiler of the DWC, which is responsible for the water vaporization For a fair comparison with the previously reported studies, we consider here a mixture of 10 wt % ethanol (100 ktpy plant capacity) that is concentrated and dehydrated using ethylene glycol as mass-separating agent Rigorous process simulations of the proposed vapor recompression (VRC) heat-pump-assisted extractive DWC were carried out in AspenTech Aspen Plus The results show that the specific energy requirements drop from 207 kWh/kg (classic sequence) to only 124 kWh/kg ethanol (VRC-assisted extractive DWC); thus, energy savings of over 40% are possible Considering the requirements for a compressor and use of electricity in the case of the heat-pump-assisted alternative, it is possible to reduce the total annual cost by approximately 24%, despite the 29% increase of the capital expenditures, for the novel process as compared to the optimized conventional separation process

Novel Heat-Pump-Assisted Extractive Distillation for Bioethanol Purification

This article is a survey of the present-day methods of dehydration of ethanol resulting from fermentation processes. The existing separation techniques for water-ethanol mixtures of various compositions are compared, and the conditions under which each particular technique is preferable are formulated.

Bioethanol dehydration: State of the art

Densities and excess Volumes of Binary and Ternary Mixtures of N, N-Dimethyl sulfoxide, N,N-Dimethylacetamide, and N-Methyl-2-pyrrolidone at T = (293.15, 313.15)K and Atmospheric Pressure

The processes of extractive distillation and heteroazeotropic distillation of mixtures containing water and a high-boiling component (propionic acid, acetic acid, 1-methoxy-2-propanol) are compared. Entrainers declared in the literature as effective agents for these processes were selected as separating agents. A distillation process simulation in AspenPlus V.11.0 is made. Parametric optimization is carried out and the column operation parameters (number of stages, feed stage, reflux ratio) that meet the minimum energy consumptions and ensure the production of marketable substances are determined. It is shown that the process of heteroazeotropic distillation is more energy-efficient compared to extractive distillation by more than 50%, due to the introduction of an entrainer that lowers the boiling point of process. In addition, in some cases (acetic acid + water with vinyl acetate, propionic acid + water with hexane, cyclohexane, cyclohexanol), one of the columns in the separation flowsheet can be abandoned due to the significantly limited mutual solubility.

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Comparison of Extractive and Heteroazeotropic Distillation of High-Boiling Aqueous Mixtures

The existence of two ternary azeotropes in the pressure range of 26.66–80.00 kPa has been experimentally confirmed in the benzene + perfluorobenzene + water system. The compositions and the boiling points of azeotropes benzene + water, perfluorobenzene + water, benzene + perfluorobenzene, benzene + perfluorobenzene + water (unstable node), as well as the boiling point of internal saddle azeotrope at pressures of 26.66, 53.33, and 80.00 kPa were determined. The experimental data are in good agreement with the results of other authors. The evolution of the VLE diagrams of the system under pressure changes was studied. It was shown that when the pressure increases, the azeotrope benzene + perfluorobenzene first disappears (through an internal tangential azeotrope), which confirms the predictions of other authors, and then two ternary ones (also through an internal tangential azeotrope). The compositions of azeotropes in the bifurcation state were determined in the computational experiment. 

Double Ternary Azeotropy in the Benzene + Perfluorobenzene + Water System at 26.66, 53.33, and 80.00 kPa

The phase equilibrium in an acetonitrile + water + cyclohexene + chloroform system was studied at 101.3 kPa. A prediction regarding the internal structure of the composition tetrahedron (presence/absence of one/two internal singular points) was made using thermodynamic modeling in AspenPlus V.10.0. The existence of two internal quaternary azeotropes (of node type with a minimum boiling point and of saddle type) was confirmed as a result of a full-scale experiment. Thermodynamic-topological analysis of the structure of phase equilibrium diagrams was carried out to confirm the correctness of the diagram construction.

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A. K. Frolkova

Papers

Bioethanol dehydration: State of the art

Densities and excess Volumes of Binary and Ternary Mixtures of N, N-Dimethyl sulfoxide, N,N-Dimethylacetamide, and N-Methyl-2-pyrrolidone at T = (293.15, 313.15)K and Atmospheric Pressure

Comparison of Extractive and Heteroazeotropic Distillation of High-Boiling Aqueous Mixtures

Double Ternary Azeotropy in the Benzene + Perfluorobenzene + Water System at 26.66, 53.33, and 80.00 kPa

Experimental Evidence for Double Quaternary Azeotropy’s Existence

A. K. Frolkova

Papers

Bioethanol dehydration: State of the art

Densities and excess Volumes of Binary and Ternary Mixtures of N, N-Dimethyl sulfoxide, N,N-Dimethylacetamide, and N-Methyl-2-pyrrolidone at T = (293.15, 313.15)K and Atmospheric Pressure

Comparison of Extractive and Heteroazeotropic Distillation of High-Boiling Aqueous Mixtures

Double Ternary Azeotropy in the Benzene + Perfluorobenzene + Water System at 26.66, 53.33, and 80.00 kPa

Experimental Evidence for Double Quaternary Azeotropy’s Existence

Densities and excess Volumes of Binary and Ternary Mixtures of N, N-Dimethyl sulfoxide, N,N-Dimethylacetamide, and N-Methyl-2-pyrrolidone at T = (293.15, 313.15)K and Atmospheric Pressure