The isobaric vapor–liquid equilibrium (VLE) data of the binary mixture of methylcyclohexane (1) + toluene (2) at 101.3 kPa; the pseudoternary mixture of methylcyclohexane (1) + toluene (2) + gamma-valerolactone (GVL) (3) with the entrainer-to-feed ratio (E/F) = 1 (mass basis) at 50, 80, and 100 kPa, and E/F = 2 and 3 at 100 kPa; and the pseudoternary mixture of methylcyclohexane (1) + toluene (2) + 1-methylpyrrolidin-2-one (NMP) (3) with E/F = 1 at 100 kPa were measured using a Fischer Labodest VLE602 ebulliometer. The reliability of the experimental VLE data was tested and confirmed by Van Ness and Fredenslund thermodynamic consistency tests. The experimental results indicate that the presence of GVL and NMP increases the relative volatility of methylcyclohexane to toluene; therefore, both entrainers remove a close-boiling behavior in the mixture. Non-random two-liquid (NRTL) and universal quasi chemical (UNIQUAC) thermodynamic models were applied in the experimental data correlation to obtain the optimum binary interaction parameters. For the mixture involving GVL, the experimental VLE data were accurately correlated by NRTL and UNIQUAC. However, NRTL has more accurate results compared with UNIQUAC. For the mixture containing NMP, both the UNIQUAC and NRTL models show favorable regression results.@en

The butanediols (BDOs), 2,3-, 1,4- and 1,3-butanediol, are platform chemicals that are mainly produced from fossil hydrocarbons but may be obtained through fermentation. However, low product concentration, by-product formation and high boiling temperatures of BDOs hinder downstream processing and increase overall fermentation costs. This study increases the competitiveness of industrial biotechnology by designing a large-scale process (broth processing capacity of 160 ktonne/y) for the final purification of BDOs after fermentation (recovery >99 %). It includes an initial preconcentration step in a vacuum distillation column to remove most water and light impurities. The initial removal of most of the water and the use of a heat pump system allowed significant energy reduction. At the heart of the process is an integrated dividing-wall column that can efficiently purify BDO from the remaining light and heavy impurities. Moreover, a single process design was proven effective in purifying different BDOs to > 99.4 wt%. This was cost-effective (total purification costs of 0.208 – 0.243 $/kgBDO) and energy-efficient (with primary energy requirements of 1.854 – 2.176 kWthh/kgBDO). The proposed purification sequence can be used for each BDO type, which offers flexibility in developing sustainable bioprocesses for BDO production.@en

Distillation is widely used for separating liquid mixtures, but its high heating demand poses challenges for achieving net-zero emissions. This study presents an innovative approach to electrifying distillation for load adaptability and flexible operation, aligning with dynamic electricity markets driven by renewables. The approach integrates flash vapor circulation and thermal storage into the distillation to optimize power usage and capitalizes on economic opportunities from load-flexible operation in response to fluctuating electricity pricing. A methanol/water distillation case study, using two typical electricity pricing scenarios, demonstrates that the proposed approach is more economically efficient than mechanical vapor recompression distillation, especially in lowering operational costs when the latter operates under fixed electricity pricing. However, compressor capital costs significantly impact overall costs, with sensitivity analysis examining different cost models. This approach can be applied to general distillation, allowing integration with the power sector and demand response programs, while enhancing flexibility, decarbonization, and efficiency.

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Gravitation dictates the allowable flow phases and the achievable mass transfer rates in classic distillation columns, which are tall for that exact reason. High-gravity (HiGee) devices use a high centrifugal field to increase the interfacial area through high-speed rotating packing, resulting in a large enhancement of gas–liquid mass transfer and thus smaller equipment volumes. HiGee is an effective process intensification approach to enhance both reaction and separation efficiency. Combining reaction and distillation in a HiGee equipment (R-HiGee) is a topic that attracts significant attention. This paper summarises recent developments in HiGee (reactive) distillation technologies, including process synthesis and design, modelling and analysis of rotating packed bed systems, and equipment design. It also highlights future directions for developments in order to facilitate the systematic evaluation and application of high-gravity (reactive) distillation technologies.@en

The valorisation of green hydrogen and captured CO2 to produce chemicals or energy carriers holds immense potential to reduce GHG emissions. Among them, formic acid (FA) is an essential chemical with diverse applications and a growing market demand. Furthermore, due to liquidity at ambient conditions and its chemical stability, it is a promising hydrogen carrier. However, its direct thermochemical synthesis from CO2 hydrogenation still faces significant challenges due to a high thermodynamic barrier. This study presents a novel and eco-efficient process design for a 50 kta FA production from CO2 and green H2. Initially, CO2 is converted to CO as an intermediate compound that undergoes a carbonylation reaction with methanol to form methyl formate, which is then hydrolysed into FA. The major challenges of this new proposed process lie in the purification of CO and the energy-intensive downstream separation of FA. The former is addressed by using the COPure™ technology, which combines chemical and physical absorption, while the latter requires the use of process intensification techniques to minimize the energy and capital expenses. The newly designed process achieves high molar yields of 95 % for CO2 and 96 % for H2 with a specific energy intensity of 21.8 MJ/kg of FA. Notably, the CO2 emissions can be reduced by almost half as compared to the existing FA synthesis from fossil fuels, coupled with a 64 % reduction in electricity usage and 20 % decrease in steam requirements.@en

Methanol and DME are highly efficient fuels and relevant building blocks that can be synthesized by CO₂ hydrogenation. While several alternatives for methanol production by CO₂ hydrogenation have already been developed at a commercial scale, DME production is still based on methanol dehydration. In this sense, the development of bifunctional methanol synthesis/dehydration catalysts is a clear opportunity for the simultaneous coproduction of methanol and DME in a single-step process. Although a few alternatives for DME-methanol coproduction have been proposed, either they need external fuels or refrigerants, or part of the CO₂ used as raw material is purged, resulting in a loss of methanol and DME yields. This work presents a novel thermally self-sufficient process that hydrogenates CO₂ into methanol and DME in a single reactor at 100 % yield (only water as a byproduct at 0.94 kg_water/kg_product), that only consumes air, cooling water (0.006 m³ _water/kg_products) and electricity (net CO₂ emissions of −1.20 or 0.64 kg_CO2eq/kg_products when the plant is operated with green or grey electricity, respectively). The innovative design, based on the combination of a top-divided wall column, an integrated heat network, and limited pressure drop in the reaction-separation loop, results in a thermally self-sufficient process that uses only 0.76 kWh per kg products.

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Propionic acid is a valuable platform chemical that is usually produced via fossil routes. As these are energy-intensive and eco-unfriendly processes, fermentative production of propionic acid is becoming more attractive. However, the complex downstream processing (due to low achievable product concentrations, high water content, presence of by-products and thermodynamic constraints), presents a potential barrier to scale-up this technology. This original research proposes a novel intensified large-scale (production capacity of ∼ 20 ktonne/y) process for the final recovery of propionic acid after the initial biomass and counterion removal. Vacuum distillation steps ensure the recovery of a high-purity succinic acid product (>99.9 wt%) and a water stream that may be recycled to the fermentation to reduce the fresh water requirements. The main unit that follows is a highly integrated heat pump-assisted dividing-wall column (DWC), which allows the effective separation of propionic (>99.9 wt%) and acetic acid (99.4 wt%) products. Alternatively, it can serve as a reactive DWC that performs the esterification and separation of methyl propionate (99.8 wt%), methyl acetate (91.0 wt%) as higher added value products, and water by-product. If needed, extractive distillation can be implemented additionally to recover methyl acetate at higher purity (99.9 wt%). Overall, both options are proven to be economically interesting (recovery costs of 0.399 – 0.469 $/kg considering the product price of 1.349 – 1.802 $/kg) and environmentally attractive (3.206 – 3.678 kWthh/kg).@en

PDO (1,3-propanediol) is a platform chemical that is obtained by petrochemical routes and by fermentation. The latter needs relatively complex downstream processing after fermentation, due to the modest concentration of the high-boiling product, and the presence of microorganisms and many impurities in the fermentation medium. This novel research proposes an original large-scale (production capacity of 23 – 32 ktonne/y) process for the final purification of PDO and dominant by-products, from the fermentation of glucose or glycerol. Following the initial microfiltration, diafiltration, ultrafiltration and ion exchange steps, heat pump-assisted vacuum distillation was implemented to remove most of the water from the broth. Afterwards, an advanced highly-integrated dividing-wall column was designed to allow the final purification of PDO (product purity > 99.9 wt%) from light and heavy by-products. Fermentation by-products that are present in significant amounts can also be recovered and valorized. Overall, the developed final purification processes demonstrate cost-effectiveness (0.150 – 0.274 $/kg) and energy-efficiency (1.258 – 3.175 kWthh/kg) which contributes to the competitiveness of the overall downstream processing (0.256 – 0.384 $/kg and 1.487 – 3.496 kWthh/kg).@en

Downstream processing of natural gas liquids (NGL) provides feedstock needed for plastic production, upgraded fuels and heating, but it is one of the largest high-pressure and energy intensive processes. This original study is the first to integrate novel process intensification options from a holistic viewpoint for the full process covering all sections: 1) NGL recovery, 2) NGL fractionation, and 3) isomerization. Intensified fluid separation technologies (e.g. complex columns, thermal coupling, and heat pumps) are explored and integrated into a full NGL process to improve the energy efficiency and mitigate GHG emissions, and to establish the limits of operation, utility usage, and specific product costs. All NGL processes are rigorously simulated in Aspen Plus, and evaluated based on a fair economic and sustainability analysis. The enhanced recycle split vapor process for NGL recovery results in a full heat recovery for the reboiler of the demethanizer (2.9 MW energy savings), while the enhanced gas subcooled process results in 17.9% reduction of the refrigerant duty, 20.2% reduction of the electrical duty, and 19.9% reduction of the total utility cost. For the NGL fractionation section, heat pump assisted double dividing wall process improves energy intensity for a fraction of the utility cost although requiring external incentives (e.g., carbon tax) to become commercially viable. The total utility costs as well as GHG emissions are reduced up to 30% and 49%, respectively, while the specific product cost reduces to $23.45/t or $24.38/t with carbon tax. The heat pump assisted recycled isomerization process for the last section increased AKI from 65.3 to 89.6, with 19.1% reduction of utility usage and 42.4% reduction of carbon emission.

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Valorization of carbon dioxide towards value added chemicals can drastically mitigate the increased CO2 levels in the atmosphere. In this context, formic acid is a versatile bulk chemical with promising market potential. The novel process design proposed in this work involves a sustainable thermochemical synthesis of formic acid from CO2, which is rigorously simulated using Aspen Plus V12 as a CAPE tool. The process relies on the reverse water-gas shift reaction (RWGS) to synthesize CO from green H2 and CO2. The purified CO is used for the synthesis of methyl formate, which is then hydrolyzed to produce formic acid. To address downstream processing energy intensity, a distillation column with a dividing wall (DWC) is employed. The designed process achieves high molar yields of 95% for CO2 and 96% for H2 with a specific energy intensity of 21.8 MJ/kg of formic acid. The new process achieves a substantial reduction of 51% in the CO2 emissions, 64% in electricity consumption and 20% in steam usage as compared to conventional fossil fuel-based FA production plants (reference case).@en

This chapter focuses on the design and control of reactive distillation (RD) columns, which are seen as an integral part of an intensified chemical process. While most of the published literature presents analyses of the RD columns as standalone process units, this work frames the RD columns within a process where recycle streams (to these columns) are present, as typical to industrial practice. These recycle streams originate from the incomplete conversion of reactants or their conversion to undesired by-products. Therefore, the unreacted reactants need to be recovered and recycled, while the by-products need to be recovered and reconverted into reactants followed by their recycle to the RD columns.

A case study of industrial importance is used to illustrate key aspects of design and control of such reactive distillation systems with recycles. The design is focused on developing the topology of the entire process and solving the mass and energy balance based on which key process performance indicators (e.g. reactant utilization, energy efficiency, material and energy intensity, and carbon dioxide emissions) can be analyzed. The control is focused on developing a plantwide strategy to achieve the material inventory (in other words, balancing the reactions' stoichiometry), along with achieving the desired production rate and product purity. Several key process changes (e.g. flowrate and composition changes) are implemented to test the proposed control structure of the plant. All this work makes use of both steady-state and dynamic, rigorous process simulations.@en

Even though industrial biotechnology is successfully used for the production of some chemicals, for many other chemicals it is not yet competitive with conventional petrochemical production. Usually, fermentation as well as downstream processing requires improvement. Downstream processing has to deal with low product concentrations, microorganisms, impurities and thermodynamic constraints (e.g., azeotropes), which often makes it very challenging and expensive, especially on a large scale. However, downstream processing of biochemicals has not attracted as much attention as upstream fermentation processes. In that context, this perspective paper offers a lightly referenced scholarly opinion about the downstream processing performance of different bioalcohols after fermentation. Due to the stronger toxicity effects on microbes, the achievable concentrations of monohydric aliphatic alcohols in the fermentation broth decrease with the increasing chain length. Specifically, the concentrations used here are 6.14, 5.00, 1.61 and 0.24 wt% of ethanol, isopropanol, isobutanol and hexanol, respectively. More dilute fermentation broths lead to more complex recovery processes. According to our previous work, the total purification costs increase from 0.080 USD kg−1 for ethanol, 0.109 USD kg−1 for isopropanol and 0.161 USD kg−1 for isobutanol to 0.529 USD kg−1 for hexanol. A similar trend is noticeable for the energy usage (0.960, 1.348, 2.018 and 3.069 kWthh kg−1, respectively) and the related CO2 emissions (0.164, 0.221, 0.449 and 0.555 kgCO2 kg−1, respectively). This work shows that advanced separation and purification based on process intensification principles are crucial for overall efficient production processes. The achievable product concentration in the fermentation broth – and not so much the alcohol chain length – has the biggest influence on the performance of downstream processing. Therefore, simultaneous development of both upstream and downstream processing is necessary to ensure the competitiveness and viability of industrial fermentation processes. © 2024 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).@en

Isobutanol is a highly attractive renewable alternative to conventional fossil fuels, with superior fuel properties as compared to ethanol and 1-butanol. Even though the isobutanol production by fermentation has significant potential, complex downstream processing is limiting the wide-spreading of this technology. Accordingly, this original research significantly contributes to the advancement in industrial biofuel production by developing two eco-efficient downstream processes for the industrial-scale recovery of isobutanol (production capacity 50 ktonne_IBUT/y), from a highly dilute fermentation broth (>98 wt% water). Vacuum distillation and a novel hybrid combination of gas stripping and vacuum evaporation were coupled with atmospheric azeotropic distillation to recover over 99.9 % of isobutanol as a high-purity product (100 wt%). Advanced heat pumping and heat integration techniques were further implemented to allow the complete electrification of these recovery processes. Furthermore, implementation of these techniques significantly decreased total annual costs (0.131–0.161 $/kg_IBUT), reduced energy requirements (0.488–0.807 kW_eh/kg_IBUT) and lowered CO₂ emissions (0.303–0.449 kg_CO2/kg_IBUT), resulting in highly competitive purification processes. In addition to efficiently recovering isobutanol, the designed downstream processes provide the potential to enhance the fermentation process by recycling all present microorganisms and reducing water demand. Therefore, the results of this original research substantially contribute to the advancement in industrial biotechnology and the wide-spreading of biofuel production.

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In industrial processes there are instances where heat pump assisted distillation falls short of full electrification, necessitating an auxiliary reboiler. To solve this limiting issue, this short communication proposes a new method using flash vapour circulation (FVC) to recuperate the waste heat within the heat pump cycle. This method incorporates a flash drum after the throttling valve to generate flash vapour. Rather than employing an auxiliary cooler for condensing the mixed vapour-liquid in a conventional heat pump system, the produced flash vapour is circulated back to the compressor inlet to enhance the recycled heat in the reboiler. With proper energy match, this approach has the potential to realise full electrification of distillation. The distillation of methanol/water serves as an illustrative case study, showcasing the viability of FVC which allows additional 22% energy savings, as compared to mechanical vapour recompression. Yet, this strategy may not be advantageous if the waste heat is already maximally utilised in preheating both the compressor and column inlet feed. The separation of tetrahydrofuran/water is used as case study to demonstrate the limitations of this approach.@en

Despite the huge efforts devoted to the development of the electrochemical reduction of CO2 (ECO2R) in the past decade, still many challenges are present, hindering further approaches to industrial applications. This paper gives a perspective on these challenges from a Process Systems Engineering (PSE) standpoint, while at the same time highlighting the opportunities for advancements in the field in the European context. The challenges are connected with: the coupling of these processes with renewable electricity generation; the feedstock (in particular CO2); the processes itself; and the different products that can be obtained. PSE can determine the optimal interactions among the components of such systems, allowing educated decision making in designing the best process configurations under uncertainty and constrains. The opportunities, on the other hand, stem from a stronger collaboration between the PSE and the experimental communities, from the possibility of integrating ECO2R into existing industrial productions and from process-wide optimisation studies, encompassing the whole production cycle of the chemicals to exploit possible synergies.@en

Green organic entrainers and natural deep eutectic solvents (NADESs) possessing high boiling points and decomposition temperatures, exhibit considerable potential as advanced materials for green entrainers in extractive distillation. However, there is a wide range of solvents to choose from and their properties are only rarely available for use in process design and simulation. The present study aims to assess the selection parameters and examine the performance of and select green organic entrainers and NADESs for the separation of the close boiling mixture methylcyclohexane-toluene. The evaluation carried out was based on selectivity and relative volatility values obtained by using predictive models. COSMO-RS (a unimolecular quantum chemical calculation) was employed to predict the selectivity at infinite dilution, while group contribution methods such as UNIFAC and modified UNIFAC (Dortmund) were used to predict the relative volatility. According to the calculated results, the selectivity appeared a more important selection parameter than the performance index. The relative volatility prediction using the UNIFAC and UNIFAC Dortmund methods exhibits comparable trends to the selectivity results derived from COSMO-RS. However, the use of UNIFAC and modified UNIFAC (Dortmund) in predicting the relative volatility of NADES containing mixtures is limited due to the absence of functional group parameters. This CAPE study reveals that, based on the calculated selectivity (using COSMO-RS) and relative volatility (using UNIFAC, and modified UNIFAC (Dortmund)), most of the proposed green organic entrainers and NADESs exhibit a higher or comparable selectivity and relative volatility as the benchmark entrainers. This confirms the potential of the evaluated green entrainers with higher selectivity and relative volatility to enhance the design of extractive distillation. Therefore, the cost, energy and water consumption, as well as CO2 emissions in the methylcyclohexane and toluene separation can be reduced.@en

Isopropanol-butanol-ethanol (IBE) fermentation is a superior biofuel production technology as compared to acetone-butanol-ethanol (ABE) fermentation due to the better fuel properties of the obtained products. However, low product concentrations, thermodynamic constraints and the presence of microorganisms lead to complex downstream processing that limits the competitiveness of this biofuel production method. Thus, this original research proposes a novel thermally self-sufficient and eco-efficient downstream process for industrial-scale recovery after IBE fermentation (74 ktonne/y capacity), from a highly dilute broth (>97 wt% water). Gas stripping and heat pump-assisted vacuum evaporation were implemented to separate valuable products from most of the broth. Furthermore, an advanced highly integrated heat pump-assisted azeotropic dividing-wall column was designed to recover high-purity (99 wt%) butanol biofuel and isopropanol – ethanol fuel supplement (89 wt%). The proposed purification process recovers over 99 % of biofuel products in a cost-effective (0.130 $/kg_IBE) and energy-efficient way (0.673 kW_eh/kg_IBE) while allowing full recycle of biomass and most of the separated water. Besides improving yield by continuously recovering the inhibitory products, fermentation can be further enhanced by avoiding biomass loss and reducing water requirements. Lastly, the implemented energy-saving techniques ensure complete electrification of the proposed IBE recovery process. Therefore, the original results of this research study significantly contribute to the development of sustainable biofuel production processes.

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Pass-through distillation (PTD) is a novel separation technology that can effectively overcome challenges related to using vacuum distillation in bio-based processes (defined temperature limit for evaporation that might result in very low condensation temperature). This method allows evaporation and condensation to be performed at different pressures by decoupling them using an absorption-desorption loop with an electrolyte absorption fluid. This original paper presents a process design for large-scale bioethanol recovery from fermentation broth (production capacity ~100 ktonne/y) by PTD. The flexibility of the novel PTD technology is expanded by combining it with heat pumps (PTD-HP) and multi-effect distillation (PTD-MED). Total cost and energy requirements for the recovery of high-purity bioethanol (99.8 wt%) are respectively 0.122 $/kgEtOH and 1.723 kWthh/kgEtOH for PTD-HP, and 0.131 $/kgEtOH and 1.834 kWthh/kgEtOH for PTD-MED, proving the effectiveness of the newly designed recovery processes for concurrent alcohol recovery and fermentation.@en

Distillation is widely used for separation in chemical industries, but accounts for a half of operational costs and 40% of the energy usage due to its low energy efficiency. Process intensification could effectively enhance the energy efficiency and reduce the energy requirement of the distillation processes by integrating unit operations or functions. However, there is no general methodology that enables to choose the best intensified distillation technologies among all available choices for a given separation task. This study generates a conceptual de-composed selection and decision approach by first identifying the process bottlenecks and intensification targets, and then select the most promising intensified techniques via a selection framework and decision matrix based on the identified bottlenecks and intensification targets. Two separation cases are illustrated to demonstrate the developed methodology, and the outcomes are verified with conceptual designs reported in the literature.@en

Distillation remains the leading and most frequently adopted technique for the separation and purification of condensable mixtures in numerous industries. However, the inherently poor thermal efficiency of distillation requires a large amount of thermal energy, making it the chief factor in total process energy usage and a significant emitter of carbon dioxide due to the combustion of fossil fuels. To address this issue, electrification has arisen as a popular approach to reduce carbon emissions in different processes by primarily replacing the energy source with electricity derived from renewable energy resources. This review is designed to thoroughly explore the electrification concept in decarbonizing distillation and present a detailed analysis and summary of the cutting-edge technologies used in various distillation operations. The focus is on creating electrified distillation processes and their associated utility systems, making use of a range of power-to-heat and intensification strategies, to achieve simultaneous carbon reduction and energy savings. With the increasing variety of operating environments that incorporate renewable power, this review additionally encompasses the control and operation aspects to ensure efficient management of electrified distillation processes. To further delve into the advantages of incorporating electrification into distillation, this work proposes future directions from the viewpoints of technological advancement, design optimization, operation, and real-time scheduling of electrified distillation processes. Furthermore, this review highlights the enormous potential of electrification in dramatically lowering carbon emissions and promoting sustainable practices in the distillation industry.@en