Reactive distillation (RD) is a process intensification technique that offers major advantages over conventional technologies by enabling the integration of reaction and separation into a single apparatus. This integration introduces and exploits complex interaction between mass transfer, chemical reaction and hydrodynamics within an RD column; however, these complexities can hinder the adoption of RD by industry. Many approaches have been developed by the scientific community to advance understanding and to expedite the initialization of RD design at the conceptual level. This paper critically discusses recent developments in conceptual methods for synthesizing RD processes. This review paper is the first to consider the range of available approaches for assessing the technical feasibility, controllability, economic viability, and sustainability of RD units by taking into account various configurations in which RD is treated as a new unit operation, and as part of process synthesis in a different way of designing processes based on functions. The review also addresses complex configurations, such as advanced RD technologies. Special attention is paid to process modeling and simulation as well as to education. Knowledge gaps to be filled by further research are indicated.

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.

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.

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.

This original research contributes to enhancing the viability of biorefineries through recovering valuable by-products from the liquid remaining after the biomass pretreatment by hot liquid water. A novel downstream processing method is developed for the recovery of acetic acid, formic acid, furfural and 5-hydroxymethylfurfural (HMF) by enhanced distillation. The major challenge in this research is the processing of the highly diluted initial solution (>96 wt% water) and the thermodynamic limitations owing to possible formation of several azeotropes. This new process recovers 78.7% of the acetic acid (99.8 wt%), while the rest of it is recycled back to the biomass pretreatment step together with most of the separated water from the initial solution. Over 99.5% of formic acid, furfural and HMF is also recovered, at purities of 74.7, 98.0 and 100 wt%, respectively. Vapor recompression and heat integration are implemented to decrease the energy use. The results demonstrate a 77.4% decrease in total annual costs (from $3.44 to 0.78/kg_product), a 75.0% reduction in minimum average selling price (from $3.50 to 0.87/kg_product), an 81.1% reduction in energy requirements (from 77.41 to 14.66 kW_thh/kg_product) and an up to 99.7% decrease in CO₂ emissions (from 11.17 to 0.03 kg_CO2/kg_product).

Cylcohexanol is an essential bulk chemical that can be produced via cyclohexene hydration, a liquid-liquid two-phase reaction that is limited by the low reaction rate and the equilibrium conversion. Adding an appropriate solvent is the most promising method to break through these limitations. However, in previous works the solvent was almost blindly selected without a global consideration. In this work, a rational multiscale method is proposed for the effective selection of an economical and sustainable solvent for the direct hydration of cyclohexene. At the molecular scale, liquid-liquid phase equilibrium was estimated using group contribution methods to rapidly screen the potential solvent candidates from a range of organics, based on the partition coefficient. At the reactor scale, the candidates were experimentally investigated to pick out the solvents that could significantly improve the conversion, without introducing side reactions or deactivating the catalyst. At the process scale, the total annual cost (TAC), CO₂ emission, and other metrics were calculated to evaluate the eco-efficiency of all solvents. Using this multi-scale method, acetophenone was selected as an eco-efficient solvent from over 100 organics, resulting in the reduction of TAC by 8 % and CO₂ emission by 17 % in the production process. Using acetophenone also led to the increase of cyclohexanol yield from 12.3 % to 27.6 % without the occurrence of side reactions and catalyst deactivation.

This study provides novel details about the industrial use of cyclic distillation in the production of food-grade alcohol, which confirmed the theoretical predictions of increasing separation efficiency. Increasing the profitability of the production of ethanol food grade is primarily associated with an increase in product quality and reduction of energy costs per unit of production. One of the ways to solve these problems is to improve the ethanol purification technology by using cyclic distillation, which allows reduction of energy costs and higher productivity by removing impurities at a higher concentration (leading also to waste reduction). The purification of ethanol from impurities (head and intermediate type) is carried out in hydro-selection columns. Critically, the volatility of most components depends on the actual ethanol concentration on the stage. This study investigated the distribution of ethanol on the trays depending on the water feed stage to the column and showed the optimal distribution of hydro-selective water in an industrial column to allow the highest possible separation efficiency of components during cyclic distillation. A cyclic distillation column with 15 Maleta trays was superior in separation capacity and performance as compared to a traditional column with 50 bubble cap trays.

BACKGROUND: Isopropanol and acetone production by syngas fermentation is a promising alternative to conventional fossil carbon-dependent production. However, this alternative technology has not yet been scaled up to an industrial level owing to the relatively low product concentrations (about 5 wt% in total). This original research aims to develop cost-effective and energy-efficient processes for the recovery of isopropanol and acetone from highly dilute fermentation broth (>94 wt% water) for large-scale production (about 100 kt_IPA+AC y⁻¹). RESULTS: Vacuum distillation and pass-through distillation enhanced with heat pumps or multi-effect distillation were efficiently coupled with regular atmospheric distillation and extractive distillation in several innovative intensified downstream processes. Over 99.2% of isopropanol and 100% of acetone were recovered as high-purity end-products (>99.8 wt%). Advanced heat pumping (mechanical vapor recompression) and heat integration techniques were implemented to decrease total annual costs (0.109–0.137 USD kg_IPA+AC⁻¹), reduce energy requirements (1.348–2.043 kW_th h kg_IPA+AC⁻¹) and lower CO₂ emissions (0.067–0.191 kg_CO2 kg_IPA+AC⁻¹), resulting in highly competitive recovery processes. CONCLUSION: The proposed three novel isopropanol and acetone recovery processes from dilute broth significantly contribute to the expansion of sustainable industrial fermentation. Furthermore, this original research is the first one to develop novel pass-through distillation technology for the complex isopropanol–acetone–water system. All the designed processes are highly economically competitive and environmentally viable. In addition to recovering efficiently both isopropanol and acetone, the designed downstream processes offer the possibility to enhance the fermentation process by recycling all the present microorganisms and reducing fresh-water requirements.

This paper explores the basis on which reliable screening of distillation sequences for energy-efficient separation of zeotropic multicomponent mixtures can be carried out. A case study for the separation of natural gas liquids is used to demonstrate the approach. To solve this generic problem, a screening algorithm has been developed using optimization of a superstructure for sequence synthesis using shortcut models, in conjunction with a transportation algorithm for the synthesis of the heat integration arrangement. Different approaches for the inclusion of heat integration are explored and compared. The best few designs from this screening are then evaluated using rigorous simulation. It has been found that separation problems of the type explored can be screened reliably using shortcut distillation models in conjunction with the synthesis of heat exchanger network designs. Non-integrated designs using thermally coupled complex columns show much better performance than the corresponding designs using simple columns. However, once heat integration is included the difference between designs using complex columns and simple columns narrows significantly.

The hydrogenation of CO₂ to methanol is a technology that converts a greenhouse gas into a valuable chemical compound that efficiently stores energy. Several alternatives to perform this process have been proposed, but they are either not thermally self-sufficient and depend on using external fuel, or the power usage per ton of methanol is insufficiently optimized, or part of the raw materials must be purged and therefore there is a loss of methanol yield. This original study aims to develop a novel thermally self-sufficient process for e-methanol production (at practically 100% yield along with water by-product of 0.37 kg_water/kg_product) that only uses green electricity. The main innovation of the process is an effective thermally self-sufficient heat-integration scheme that only needs 0.0059 m³_water/kg_methanol combined with using a dividing wall column to recover the unreacted CO₂ and obtain high purity methanol. In addition, the pressure reduction in the reaction-separation loop is limited to the pressure drop of the circuit to minimize the overall green electricity use to only 656 kWh per ton methanol, resulting in net CO₂ emissions of −1.13 kg_CO2/kg_MeOH or 0.78 kg_CO2/kg_MeOH when the plant operates with green or grey hydrogen and electricity, respectively. Finally, the operating pressure in the reactor is optimized at 65 bar to minimize the total annualized cost.

BACKGROUND: Epichlorohydrin (ECH) production is an important industrial process, owing to its importance in windmill blade manufacture, but it suffers from several drawbacks such as high energy use, large wastewater production and low atom efficiency. This original study investigates a novel chlorohydrin-free technology with an enhanced separation system for ECH production. Rigorous process simulations were performed in Aspen Plus for the classic and novel processes, and a fair techno-economic and sustainability comparison was made between the new catalytic oxidation route and the classic chlorohydrin process. RESULTS: For the hydrogen peroxide (HP) process route, a novel separation system was developed using methanol as solvent, which enables high purity of ECH. Moreover, allyl chloride (ACH) purification was optimized using thermally coupled distillation to improve the energy efficiency of ACH production. The novel HP process provides 88% higher atom efficiency, about 10% higher yield and a smaller amount of by-products, as well as a 13% increase in production capacity and major savings of 98% in wastewater production, while also achieving lower energy use (<40 MJ kg⁻¹ ECH) and reduced carbon dioxide emission (1.13 kg kg⁻¹ ECH). CONCLUSION: The developed HP process route is feasible and economically viable. Also, it can be partly retrofitted to existing ECH plants based on the chlorohydrin route. As both processes use the same intermediate product, only the ECH part of a classic process would be replaced by the novel route, while keeping the common ACH part. This approach is the most profitable, as only 55% of capital expenditure is required for this modification, while the plant would benefit from all the improvements provided by the novel process.

There are only a handful of process control structures applied to the neat operation of both homogeneous and heterogeneous reactive distillation, for two-reactants / two-products one-reaction systems. All of these control structures employ inferential temperature control (or concentration analyzers) at some location in the column to balance the reaction stoichiometry. This original study proposes a new class of control structures applicable to heterogeneous reactive distillation. The novel idea, common to all control structures, is based on monitoring the inventory of the reactant involved in the heterogeneous azeotrope. The organic reflux (or the organic reflux / aqueous distillate ratio) is used to detect the excess or deficiency of the reactant, based on which the fresh feed rate is adjusted such that the reaction stoichiometry is balanced. This control philosophy is simple and easy to implement in different ways as illustrated by several case studies. The performance of the proposed control structures depends on the system studied. For some systems, the performance is better, as good or nearly as good as that of the literature control structures. But for other systems, the performance is poor or the structure even fails to control the process, due to the insufficient feedback from inventory measurements.

Monoethanolamine is an essential chemical used as feedstock in the production of detergents, emulsifiers, pharmaceuticals, polishes, corrosion inhibitors, and chemical intermediates. It is produced industrially by treating ethylene oxide with aqueous ammonia, but the reaction also leads to di- and tri-ethanolamine as less desired by-products. This study is the first to propose an intensified process for the production of ethanolamines combining reactive distillation (RD) and dividing-wall column (DWC) technologies. The process was optimized to maximize the MEA selectivity (over 71%), as the ratio of the products can be controlled by the stoichiometry of the reactants. Rigorous process simulations and sensitivity analysis of key process parameters have been carried out using Aspen Plus, for a plant with a production capacity of 11.5 ktpy ethanolamines. The overall process has been designed to produce ethanolamines with minimal energy utilization and reduced capital cost. Economic and sustainability analysis have been carried out showing the key benefits of the proposed process as compared to the conventional one used in industry: CapEx reduction of 7.3%, OpEx savings of 42%, and TAC improvements of 31.3%.

Among other fuel additives — such as MTBE, ETBE, or TAME — 2-methoxy-2-methyl heptane (MMH) can increase the fuel octane number and reduce the CO emission. MMH can be obtained through the exothermal etherification of 2-methyl-1-heptene and methanol. Lately, many researchers have developed more and more efficient processes considering the kinetics corresponding to an endothermal reaction. However, in this work we demonstrate that the reaction is actually quite exothermal, and this has strong impact on the designed process. Also, the vapor–liquid equilibrium data predicted by UNIQUAC model for 2-methoxy-2-methyl heptane and 2-methyl-2-heptanol mixture reveals that product purification is more difficult, and it requires more energy to recover and obtain MMH with high purity. Considering these aspects, the 54.87 ktpy process developed in this paper is more realistic and energy intensive (1.82 kW h/kg MMH), with a TAC of 5.3 M$/year. The controllability of the process is proven for ±20% changes of 2-methoxy-2-methyl-heptane production rate.

Two chemistry routes are known for 4-hydroxybutyl acrylate production: the direct esterification of acrylic acid with 1,4-butanediol, and the transesterification of methyl acrylate with 1,4-butanediol. However, very scarce information in the literature is available about industrial production, or design and operation of production processes. In this study, we propose three novel reaction–separation–recycle processes for 4-hydroxybutyl acrylate production by direct esterification based on solid catalyst. Use of solid catalysts may avoid well-known issues of the liquid catalysts like recovery and re-use of the catalyst, difficult product recovery, and corrosion. Due to the nature of the chemical system and reactions conditions, the chemistry is not 100% selective towards the acrylate, important amounts of diacrylate by-product being formed. All processes use fixed-bed tubular reactors to perform the reactions and distillation-based equipment to achieve the required separations. While all processes have a similar separation sequence, each has its key particularities: the RSR-A process accepts the loss of reactants due to formation and elimination from the process of the diacrylate, RSR-B converts the diacrylate into its reactants in the esterification reactor, while RSR-C converts the diacrylate in a dedicated hydrolysis reactor. A key element in the separation sequence is the use of pressure-swing distillation to make the difficult split of the alcohol/acrylate/diacrylate ternary mixture. All processes are capital and energy intensive. The economic analysis shows that the RSR-A process has the most favorable economics: a total annualized cost of 2 million $/y and a specific annualized cost of 100 $/t of product. A control structure for the RSR-C process is presented, the dynamic simulations showing its efficiency in rejecting various disturbances.

Ammonia plays critical role as the second most produced chemical commodity with around 80% used in producing nitrogen-based fertilizer. Considering the decline of reserves of fossil-based feedstocks it is imperative to shift towards greener alternatives. However, such green ammonia processes are far from being economically viable. This makes natural gas-based ammonia synthesis the best available technology currently, but this faces critical difficulties as natural gas supply could widely vary due to declining reserve or changing sources, posing another key challenge to improve the efficiency of affected ammonia production. This study is the first to investigate the effect of variable natural gas composition (within the range of 83–99.99% vol dry methane; towards lean gas) on an industrial ammonia production process with maintained key operating parameters value such as steam to carbon ratio (S/C), hydrogen over nitrogen ratio (H/N), etc. The sensitivity analysis shows that sustained energy efficiency of the process is possible, confirming the conventional ammonia plant's ability to withstand changes in feedstock and fuel supply. In addition, lean gas yielded a positive impact on the raw material intensity and CO₂ emissions with average reductions of 1.17% and 1.79% per each 4% methane content increase, respectively.

Acetic acid is an essential chemical used in the production of many chemical products. Using methanol as bio-building block, the acetic acid produced may be incorporated in bio-based products. This study deals with enhancing the efficiency of separations in a process using a homogeneous catalyst, which is the most applied today industrially. Several configurations for downstream processing by distillation are investigated using effective combinations of fully thermally coupled columns, namely, dividing-wall columns, alone or combined with heat pumps. The results indicate that the three-column direct sequence may be effectively replaced by a two-column sequence. Overall, the total annual cost is reduced by 34 %. The cost of compressor may be paid back in 1.5 years by the saved energy. Low energy intensity is achieved by tight integration with the reaction section.

Process Systems Engineering (PSE) is a discipline that deals with decision-making, at all levels and scales, by understanding any complex process system using a holistic view and a systems thinking framework. A closely related discipline (considered usually a part of PSE) is the Computer Aided Process Engineering (CAPE) which is a complementary field that focuses on developing methods and providing solution through systematic computer aided techniques for problems related to the design, control and operation of chemical systems. Nowadays, the ‘PSE’ term suffers from a branding issue to the point that PSE no longer gets the recognition that it deserves. In chemical engineering education the integrative systems frame for process design, control and operations is virtually absent. Its application potential in process industry lags relative to academic research progress and results. This work aims to provide an informative industrial and academic perspective on PSE (focused on the European region), arguing that the ‘systems thinking’ and ‘systems problem solving’ have to be given priority over just applications of computational problem solving methods. A multi-level view of the PSE field is provided within the academic and industrial context, and enhancements for PSE are suggested at their industrial and academic interfaces to create win-win situations.