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 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

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

Distillation is widely used for fluid separation in chemical industries, but accounts for a half of the operational cost and 40–50 % of the energy usage due to its low energy efficiency. Process intensification could effectively enhance the energy efficiency as well as improve the economic performance of distillation processes by integrating unit operations or functions. However, matching suitable intensified distillation techniques systematically with given separation tasks remains a challenge. This study is the first to generate a conceptual multi-step selection and decision approach by first going through several high level questions with corresponding suggested solutions for a separation task, then identifying the process bottlenecks and intensification targets via a list of evaluation criteria. Each of the technologies goes through a pre-filled process intensification (PI) matrix, and the most promising intensified technologies are recommended, and potential solutions are compared against the task specifications. The PI matrix proposed in this work yields a short list of appropriate solutions to be designed and economically assessed, proposing a screening framework for fluid separations in order to make a rapid selection at an early stage. Several binary, ternary, and multicomponent zeotropic and azeotropic mixture separations are carried out as case studies to illustrate the application of the proposed methodology, being validated using literature data. The proposed methodology can also help reduce the search space before carrying out rigorous optimization for the synthesis and design of the distillation.@en

Ethyl acetate is a platform chemical conventionally obtained through fossil fuel routes, but more recently its production by fermentation from carbohydrates has been scaled up to a pilot scale. Yet, the complexity of downstream processing (low product concentrations in liquid broth and in off-gas, azeotrope formation, and the presence of microorganisms) may complicate industrial application. This original theoretical study is the first to develop advanced downstream processing, based on process intensification principles, for large-scale recovery (~10 kton/year) of ethyl acetate after fermentation. To minimize product losses, ethyl acetate is separated from both the liquid broth and off-gas. The final purification is performed in a highly integrated azeotropic dividing-wall column. The economic and sustainability analysis shows that using refrigeration for initial product separation from the gas phase is more cost-effective (~0.61 $/kg) and less energy-intensive (2.20–2.40 kW_thh/kg) than compression combined with high-pressure condensation using chilled water (1.09 $/kg and 9.98 kW_thh/kg).

@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.

@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

As the urgency of reducing greenhouse gas emissions increases, the chemical industry is moving towards more sustainable applications, such as substituting fossil feedstock with renewable ones. The development and implementation of novel technologies will entail momentous, system-wide changes to allow for the production of chemicals and fuels. This work aims at providing an overview of the energy requirements for the production of several chemicals by means of electrochemical reduction of CO2 (ECO2R), in order to aid the decision-making process to select the products on which further research and development efforts should focus.

The results demonstrate that the production of C1 oxygenated molecules, such as carbon monoxide and methanol, via ECO2R would have significantly lower requirements in terms of renewable energy generation when compared to fully reduced hydrocarbons (methane, ethylene) and ethanol. This would lead to a less demanding implementation of electrochemical CO2 utilisation technologies, allowing for a more streamlined deployment of ECO2R within existing supply chains.@en

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

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.

@en

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

This study investigates an innovative method to produce dimethyl ether (DME) by direct synthesis from syngas derived from biogas. The proposed process was rigorously simulated in Aspen Plus, highlighting the main sections: (i) biogas tri-reforming, (ii) dimethyl-ether synthesis, and (iii) DME purification. The tri-reforming section has a CO₂ and CH₄ conversion of 27.3% and 96.2%, respectively A novel catalyst suitable for CO₂-rich feed was chosen for the DME production to allow 60% conversion of CO₂. Product separation is achieved via several absorption and distillation columns, ensuring that the operating conditions are kept mild to avoid expensive refrigeration. An optimization analysis was performed to identify the most suitable layout of the downstream process. This was identified through the evaluation of performance indicators such as utility usage and operating expenses. A wide range of purification strategies have been evaluated, and two scenarios are proposed based on the results. Configuration A produces 5.34 ktpy DME and 1.26 ktpy methanol, while Configuration B produces exclusively 6.21 ktpy DME. The process configurations were analysed by means of key techno-economic indicators and sustainability metrics. Both processes have an energy intensity of 14.5 kWh/kg. The reforming unit has a negligible footprint as it is thermally sustained from biogas combustion, but the reboilers are the main contributors for plant CO₂ emissions. Configuration B has the best economic value with 11,634 k€ of NPV after 25 years and a payback time of 4 years.

@en

Distillation is the most used separation technology at industrial-scale, but using distillation in bio-based processes (e.g. fermentation processes to produce bioethanol) is quite challenging when mild temperatures are needed to keep the microbes alive. Vacuum distillation can be used to perform evaporation at low temperatures, but setting a low distillation pressure fixes also the condensation temperature to very low values that may require expensive refrigeration. Pass-through distillation (PTD) is an emerging hybrid separation technology that effectively combines distillation with absorption in a sorption-assisted distillation process that decouples the evaporation and condensation steps. This is achieved by inserting between the evaporation and condensation steps an absorption-desorption loop that passes through the component to be separated and allows the use of different pressures and types of heating and cooling utilities. This paper is the first to present the process design and rigorous simulation (implemented in Aspen Plus) of a new pass-through distillation process for bioethanol (∼100 ktonne/y plant capacity), proving its effectiveness in concurrent alcohol recovery and fermentation (CARAF). Combining PTD with heat pumps leads to low recovery costs of 0.122 $/kg_EtOH and energy requirements of only 1.723 kW_thh/kg_EtOH. Alternatively, combining PTD with multi-effect distillation resulted in 0.131 $/kg_EtOH recovery costs and 1.834 kW_thh/kg_EtOH energy intensity.

@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

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.

@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

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

Process Intensification (PI) is an effective way to enhance process efficiency and sustainability at affordable costs and efforts, attracting particular interest in the European area, as one of the most important chemical production areas in the world. PI primarily contributes by developing and testing new processing technologies that once integrated within a process improve the overall process performance substantially but as a result, it may alter the overall process (flowsheet) structure and its dynamic behavior. As such PI plays a key role in improving energy efficiency, optimizing resource allocation, and reducing environmental impact of industrial processes, and thereby leading to a cost-effective, eco-efficient, low-carbon and sustainable industry. However, along with opportunities, the PI new technologies have challenges related to failures in longer-term performance. In this respect, Process Systems Engineering (PSE) stance is more on integration aspects of new PI technologies into processes by making process (re)designs, doing operability studies, and performance optimizations within a supply chain setting. PSE contributes to overcoming the challenges by providing systematic approaches for the design and optimization of PI technologies. This perspective paper is a lightly referenced scholarly opinion piece about the status and directions of process intensification field from a PSE viewpoint. Primarily, it focuses on PSE perspectives towards sustainable lower energy usage process systems and provides a brief overview of the current situation in Europe. It also emphasizes the key challenges and opportunities for (new) PI technologies considering their integration in a process in terms of process synthesis and design, process flowsheet optimization, process and plantwide control, (green) electrification, sustainability improvements. Potential research directions on these aspects are given from an industrial and academic perspective of the authors.

@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

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