Conference Agenda

Agriculture is a key sector of the Ukrainian economy, relying heavily on large quantities of fertilizers to maintain global competitiveness. Despite domestic production capabilities, Ukraine imports approximately €5.5 million of nitrogen fertilizers annually. Nitric acid, a critical raw material in fertilizer production, plays a significant role in this context. Enhancing local nitric acid production is essential for bolstering economic security and diversifying supply chains. Beyond agriculture, nitric acid is also a vital intermediate in various industrial processes. Commercially, nitric acid is typically produced through the stepwise catalytic oxidation of ammonia with air.

This study aims to enhance the heat and shaft-power integration of existing nitric acid production processes to optimize waste heat recovery and identify opportunities for improving process efficiency. The plant under investigation employs a dual-stage pressure nitric acid production process with a capacity of 50 tons per hour of HNO₃ (100% equivalent). The process utilizes 3.9 MPa steam and cooling water as utilities. Air and nitrous oxide compressors are powered by waste heat from tail gases, which are harnessed in dual-pressure turbines. The exothermic reaction, conducted under pressure on a catalyst bed to produce nitric oxide, is used for medium-pressure steam generation.

This work investigates the existing nitric acid plant by developing a steady-state digital twin in the Aspen HYSYS environment. A process integration methodology, incorporating a graphical analytical tool, was employed to identify energy inefficiencies in the existing system. The authors concurrently analyzed the thermal energy and expansion potential of tail gases to efficiently meet the heating, cooling, and power demands of the main process, while also increasing steam generation through waste heat recovery, all without compromising plant throughput. As a result, a retrofitted process concept was proposed, featuring an updated process flowsheet and enhanced waste heat utilization. The proposed retrofits result in a 30% reduction in steam and a 34% reduction in cooling water usage, while simultaneously increasing steam generation by 17%. These utility savings translate to a 10% increase in plant throughput, achieved with the existing primary process equipment (including columns, compressors, and turbines) and an updated heat recovery network.

In the context of Industry 4.0 and the growing emphasis on sustainable chemical production, the development of processes that maximize efficiency and minimize environmental impact is crucial. This study presents a novel, intensified process for the production of γ-valerolactone (GVL) from levulinic acid, utilizing a reactive distillation column that seamlessly integrates reaction and separation in a single unit. GVL is a versatile platform chemical with applications ranging from biofuels to green solvents and polymer precursors, making it an important product in the shift towards renewable and sustainable chemicals. This innovative approach eliminates the need for conventional multi-step operations, significantly reducing equipment footprint, energy consumption, and overall process complexity.

A multi-objective optimization framework, based on the Differential Evolution with Tabu List (DETL) algorithm, was employed to tackle the highly nonlinear and nonconvex nature of the process. Key parameters, including the number of stages, reflux ratio, feed location, and the placement of reactive stages, were optimized to strike a balance between economic feasibility, environmental sustainability, and operational efficiency. The optimization results demonstrated substantial improvements, with a 57% reduction in total annual cost (TAC), a 55% decrease in environmental impact (Eco Indicator 99, EI99), and a 63% reduction in energy demand compared to traditional production methods. Additionally, the optimized process achieved a 25% increase in GVL production, meeting the required product purity specifications. This intensified reactive distillation strategy represents a significant advancement in sustainable chemical processing, offering a more eco-friendly and cost-effective alternative to conventional GVL production technologies while aligning with global goals for greener industrial practices.

Despite the potential of electrification in transportation, diesel will remain one of the main fuels for decades to come. Total or partial replacement of diesel with biodiesel is one of the solutions to decrease the global warming potential of diesel engines. However, biodiesel has limited performance in cold weather and requires the use of biodiesel additives. In this context, it is important to choose biodiesel additives from non-edible, inexpensive, renewable sources. Ethyl levulinate, an ester derived from levulinic acid that can be produced from sugarcane, is a promising candidate biodiesel additive because it improves the cold flow properties of biodiesel and reduces soot emissions of diesel and biodiesel. In this work, a reactive distillation column was designed and optimized to promote the esterification of levulinic acid and ethanol to produce ethyl levulinate. Because of the volatility order of the components involved in this esterification process (ethanol, water, ethyl levulinate, and levulinic acid), levulinic acid was chosen as the excess reactant. A central composite design of experiments was used to assess the process design. These results were used together with response surface methodology to determine the optimized design conditions. Production cost was calculated based on ethanol price, capital cost, and operating expenses. The results showed that the optimized reactive distillation column using excess levulinic acid provides a production cost lower than that of an equivalent process comprised of a continuous stirred reactor followed by conventional distillation.

As the global energy demand continues to grow, the production of fossil fuel alternatives such as biodiesel have led to an increase in the by-product crude glycerol (Gly). The availability and low cost of crude Gly makes it an attractive feedstock to generate high-value chemicals such as triacetin (TA), a fuel additive ^[1]. However, crude Gly (30-60 wt.%) requires purification first via physio-chemical treatment to remove impurities such as ashes, water and matter organic non-glycerol (MONG) ^[2].

Our work explores the use of highly impure animal-byproduct crude Gly purifying it and using it as feedstock for esterification with acetic acid (AA) using Amberlyst 36, a commercial catalyst. The in-series reaction network generates the intermediates monoacetin (MA), diacetin (DA) and finally TA along water as a by-product. Based on experimental results and using Aspen custom modeler (ACM) V12.1, an Eley-Rideal (ER) model with a water adsorption term was developed, with a residual mean square error (RMSE) and variation explained (VE) of 0.0941 and 98.2%, respectively ^[2].

Process design and simulation in continuous mode was conducted using Aspen Plus V12.1 after exporting the ACM reactor model, which assumed a well-mixed isothermal CSTR operating at steady state. The plant generates approximately 18,000 tons yr^-1 of TA (≥99.5 wt.%) assuming 8000 hours of annual operation. The plant begins with Gly pretreatment, in which a purified Gly stream from a physio-chemical treatment plant (82 wt.%) ^[3] undergoes vacuum distillation to further increase its purity to 96 wt.%. The stream is then mixed with AA and enters the reactors operating at 110ºC and 1.0 atm. The resulting stream is further processed to recover and recycle remaining AA via azeotropic distillation using hexane as an entrainer. The TA is recovered by liquid-liquid extraction using water as a solvent. Any unconverted Gly, MA and DA are also recovered and recycled to the reactors. The process attains a Gly conversion and TA yield of 100% and 73%, respectively ^[4].

Furthermore, the factorial method ^[5] was used to calculate the capital expenditure which was found to be £41.4 million. The total annualised cost (TAC) was found to be £35.3 million yr^-1 assuming a plant-life time of 20 years and interest rate of 5%. Additionally, a CO₂ tax assuming £50 ton_(CO2)^-1 was also considered, leading to a minimum selling price at of £1.8 kg_(TA)^-1 to start making profit. Finally, a LCA was performed based on cradle-to-gate approach using Sphera (GaBi), which highlighted that the effects on climate change, fossil depletion and freshwater consumption, with values of 44.3 kg_(CO2), 13.5 kg_(oil), and -2.3 m³ per kg_(TA)^-1, respectively^[4].

[1] A. Sandid, V. Spallina, J. Esteban. Fuel Process. Technol., 253 (2024) 108008.

[2] A. Sandid, T. Attarbachi, R. Navarro-Tovar, M. Pérez-Page, V. Spallina, J. Esteban, Chem. Eng. J., 496 (2024) 153905.

[3] T. Attarbachi, M. Kingsley, V. Spallina, Ind. Eng. Chem. Res., 63 (2024) 4905-4917.

[4] A. Sandid, V. Zurba, S. Zapata-Boada, R. Cuellar-Franca, V. Spallina, J. Esteban, Sustain. Prod. Consump., (2024, Submitted).

[5] R. Sinnott, G. Towler, Chemical Engineering Design, 2020, pp. 275-369.

Syngas fermentation of steel mill offgas can provide (1) sustainable processes to replace petrochemical isopropyl alcohol (isopropanol) and acetone production and (2) reduce greenhouse gas emissions from the steel industry. Syngas fermentation using Clostridium autoethanogenum can convert the energy-rich steel mill offgas (50% CO, 10% H₂, 20% CO₂, 20% N₂) to isopropyl alcohol, acetone or a mixture. The product yield depends on the genetic modifications done to the microorganism¹. Typically in bioprocess development there is a big focus on achieving an as high as possible Titer, Rate and Yield (TRY)². However, the possibility of multi-product processes is usually not considered for bioprocesses. Therefore, this study investigated the effects of product Titer and Yield during gas fermentation on the downstream processing (DSP) and the overall economic and environmental sustainability of the industrial-scale process.

The process design, in Aspen Plus V12.0, was based on the detailed syngas fermentation modelling to IPA³ and the gas fermentation DSP design using vacuum distillation and extractive distillation for the purification of IPA and acetone mixtures⁴. Three yield scenarios estimated from the pilot results¹ were modelled stoichiometrically⁵ and studied with either (i) 90% product selectivity to IPA, (ii) acetone or a (iii) mixture of isopropyl alcohol (80%) and acetone (10%) with acetate and biomass as other main byproducts. The CO volumetric mass transfer rate during gas fermentation is a key process parameter³ and was increased to 10 g/L/h. In addition, (iv) a high CO volumetric mass transfer rate (14.9 g/L/h) has been studied for (iii) to investigate whether its sustainability effect diminishes. The complete process models have been extended with complete wastewater treatment and recycle of the process streams.

The four scenarios are compared in terms of economic and environmental sustainability. Environmental sustainability was assessed through cradle-to-gate LCA (ReCiPe 2016 (H)) including all three emission scopes for the Global Warming Potential, Stratospheric Ozone Depletion, Fine Particulate Matter Formation, Marine and Freshwater Eutrophication, Human Carcinogenic Toxicity, Land use and Water use.

The impact of syngas fermentation product yields and titers gave insight into the effects and trade-offs for industrial-scale economic and environmental sustainability. This puts the lab-focus on highest TRY into the large-scale plant-level perspective. Thus, integration of process modelling and economic and environmental trade-off assessment is required to choose the right product formulation and improve biotechnology parameters that are relevant for industrial-scale sustainability.

1. Liew, F. E. et al. Nat Biotechnol (2022).

2. Noorman, H. J. & Heijnen, J. J. Chem Eng Sci (2017).

3. Brouwer, G. J. A., Shijaz, H. & Posada, J. A. Computer Aided Chemical Engineering (2024).

4. Janković, T., Straathof, A. J. J. & Kiss, A. A. Journal of Chemical Technology and Biotechnology (2024).

5. Heijnen, J. J. & Van Dijken, J. P. Biotechnol Bioeng (1992).

Acetic acid is an important chemical, with an annual demand of 17 Mt and many applications in the synthesis of plastics, dyes, insecticides and drugs. The standard fossil route to synthesize acetic acid relies on fossil natural gas-based methanol and carbon monoxide in the so-called Cativa process, involving four reaction steps (Le Berre et al., 2014). Research efforts currently focus on identifying pathways to replace fossil carbon with renewable carbon (i.e., CO₂, chemical waste, biomass and biogas) in chemicals production. While this shift to renewable carbon often reduces CO₂ emissions, it can lead to burden shifting, by which one environmental category improves at the expense of worsening others (Medrano-García et al., 2022).

In the context of sustainable acetic acid synthesis, the existing environmental studies are scarce and mainly focus on carbon footprint, not delving into other impact categories. To tackle this research gap, here we compare the environmental performance of alternative single-step acetic acid synthesis routes with the fossil, green and biogas-based conventional process. Moreover, for the first time, we analyze the absolute sustainability level of these synthesis pathways based on the Sustainable Development Goals (SDGs), which is computed considering the transgression levels attained relative to the Earth's carrying capacity defined by the Planetary Boundaries (PBs). Recently, the PBs concept was linked to the SDGs (Sala et al., 2020), opening the door for SDG-based assessments of industrial systems. More precisely, we here quantify the transgression level (TL) using the impacts computed with the EF v3.1 and LANCA v2.5 for land use, and the downscaled PBs determined following some sharing principles. We employ process simulation (Aspen Plus v12) and literature data to model three acetic acid synthesis pathways: the business-as-usual (BAU) methanol carbonylation, the novel gas-to-acid (GTA) methane carboxylation and semi-artificial photosynthesis (SAP) using captured CO₂ with cysteine and water as potential electron donors.

Our results show that all evaluated acetic acid synthesis pathways outperform the fossil BAU in terms of climate change impact. However, burden-shifting is still found in human toxicity, eutrophication and minerals and metals resource use. The absolute sustainability analysis reveals that most instances of this collateral damage occur within the safe operating space (SOS), that is, within the allocated fraction of the PBs to acetic acid production. Despite the overall improvements, all the evaluated scenarios transgress at least one of the impact categories associated with the assessed SDGs. All in all, we show how it is possible to improve the sustainability level of the BAU, and demonstrate that absolute sustainability assessments provide very valuable insights in the evaluation of alternative synthesis pathways.

References

Le Berre, C., Serp, P., Kalck, P., Torrence, G.P., 2014. Acetic Acid, in: Ullmann’s Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, pp. 1–34.

Medrano-García, J.D., Charalambous, M.A., Guillén-Gosálbez, G., 2022. Economic and Environmental Barriers of CO2-Based Fischer-Tropsch Electro-Diesel. ACS Sustain. Chem. Eng. 10, 11751–11759.

Sala, S., Crenna, E., Secchi, M., Sanyé-Mengual, E., 2020. Environmental sustainability of European production and consumption assessed against planetary boundaries. J. Environ. Manage. 269.