A framework for the environmental, health and safety hazard assessment for amine-based post combustion CO2 capture

Given the environmental concerns driving process developments and considering the size and scale of potential application of post combustion capture (PCC), it is important to fully understand process hazards. In this work we present an environmental, health and safety (EHS) hazard assessment framework for screening and comparing amine based PCC options. A multi-criteria assessment compares the performance of 7 m Monoethanolamine (MEA), 4 m Diethanolamine (DEA), 10 m Diglycolamine (DGA), 8 m Piperazine (PZ) and a blend of 7 m Methyldiethanolamine (MDEA) with 2 m PZ under a set of different process conditions. The EHS assessment takes into account varying circulating volumes, process conditions and potential for solvent degradation. The EHS assessment is also compared with operating costs and life cycle assessment (LCA) metrics. The EHS assessment is carried out on two levels. The first is less data intensive and provides a unified score that can be used to compare and screen process alternatives, while the second level studies the contribution of individual degradation products to different EHS hazard categories in detail. Results of the parametric study show that lean loading is an influential factor in determining first level EHS scores, process costs and environmental impacts and a trade-off is observed between EHS and LCA scores for some of the solvents. In the second level EHS assessment, the parent amine heavily influences most mass dependent hazard categories such as the fire/explosion, acute toxicity and air mediated effects category. Heat stable salts affect the solid waste category. Most degradation products are considered corrosive or irritant and therefore feature strongly in that category in addition to the parent amine. The second level EHS assessment is complemented with workplace exposure analysis to ensure the compliance with workplace threshold limits. Nitrosamines stand out for acute and chronic toxicity effects and are therefore used as an example to demonstrate the workplace exposure. Workplace amines and nitrosamine concentrations are estimated to assess long and potential short term worker exposure as a result of gas leakages and spills respectively. Indoor ventilation rates are inadequate to keep workplace amine and nitrosamine concentrations below the recommended guidelines. To reduce short term exposure effects, a steady state liquid nitrosamine concentration lower than 13.7 mM is required. The results of the parametric study show that changing process conditions can lower nitrosamine concentrations, but can also shift the contribution of the parent amine and degradation products of the other hazard categories and affect LCA metrics. The sensitivity of the EHS and LCA results to model assumptions and conditions are tested by varying inlet NOx, expected aerosols and solvent degradation levels. Low NOx levels in the flue gas are required for PZ and MDEA-PZ systems to meet the nitrosamine concentration thresholds for environmental and health concerns. This study also highlights the need to consider hazard effects during early process design phases, identifies degradation related data gaps and critical process parameters towards more environmentally benign PCC design

Multi-criteria screening of chemicals considering thermodynamic and life cycle assessment metrics via data envelopment analysis:Application to CO₂ capture

With the growing trend of incorporating sustainability principles in the chemical industry, there is a clear need to develop decision-making tools to quantify and optimise the sustainability level of chemical products and processes. In this study, we propose a systematic approach based on Data Envelopment Analysis (DEA) for the multi-criteria screening of molecules according to techno-economic and environmental aspects. The main advantage of our method is that it does not require any articulation of preferences via subjective weighting of the assessment criteria. Furthermore, our approach identifies the most efficient chemicals (according to some sustainability criteria) and for the ones found to be inefficient it establishes in turn improvement targets that can be used to guide research efforts in green chemistry. Our method was applied to the screening of 125 amine-based solvents for CO2 capture considering 10 different performance indicators, which are relevant to technical, health, safety and environmental aspects, including CO2 solubility, molar volume, surface tension, heat capacity, viscosity, vapour pressure, mobility, fire & explosion, acute toxicity and Eco-indicator 99. Our approach eliminates 36% of the solvents (as they are found to be inefficient), identifies the main sources of inefficiency (e.g., properties displaying poor values that should be improved) and ranks the best chemicals according to an objective criterion that does not rely on weights. Overall, our proposed DEA-based framework offers insightful guidance to make chemicals more sustainable

Computer-aided molecular design and selection of CO2 capture solvents based on thermodynamics, reactivity and sustainability

The identification of improved carbon dioxide (CO2) capture solvents remains a challenge due to the vast number of potentially-suitable molecules. We propose an optimization-based computer-aided molecular design (CAMD) method to identify and select, from hundreds of thousands of possibilities, a few solvents of optimum performance for CO2 chemisorption processes, as measured by a comprehensive set of criteria. The first stage of the approach involves a fast screening stage where solvent structures are evaluated based on the simultaneous consideration of important pure component properties reflecting thermodynamic, kinetic, and sustainability behaviour. The impact of model uncertainty is considered through a systematic method that employs multiple models for the prediction of performance indices. In the second stage, high-performance solvents are further selected and evaluated using a more detailed thermodynamic model, i.e. the group-contribution statistical associating fluid theory for square well potentials (SAFT-γ SW), to predict accurately the highly non-ideal chemical and phase equilibrium of the solvent–water–CO2 mixtures. The proposed CAMD method is applied to the design of novel molecular structures and to the screening of a data set of commercially available amines. New molecular structures and commercially-available compounds that have received little attention as CO2 capture solvents are successfully identified and assessed using the proposed approach. We recommend that these solvents should be given priority in experimental studies to identify new compounds

An approach for simultaneous computer-aided molecular design with holistic sustainability assessment: Application to phase-change CO2 capture solvents

We propose an approach for the simultaneous consideration of a holistic sustainability assessment framework in computer-aided molecular design (CAMD). The framework supports the assessment of life cycle (LCA) and safety, hazard and environmental (EHS) impacts from cradle-to-gate of chemicals designed through CAMD. It enables the calculation of a total of 11 sustainability-related indicators, aggregating several impact categories. A lack of models and data gaps in property prediction are addressed through a data mining approach which deploys on-line similarity assessment against existing molecules. The LCA and EHS assessment are conducted simultaneously with CAMD or after CAMD to assess the designed solvents. A case study is presented on the design of phase-change solvents for chemisorption-based post-combustion CO2 capture. The proposed approach identifies verifiably useful phase-change solvents that exhibit favourable performance trade-offs compared to a reference CO2 capture solvent. The on-line use in CAMD of sustainability criteria favours the design of hydroxyl-containing solvents

Molecular engineering of sustainable phase-change solvents: From digital design to scaling-up for CO2 capture

Phase-change solvents promise reduced energetic and environmental footprints for separation systems, including absorption-based CO2 abatement technologies. The search for efficient phase-change solvents is limited by challenges in vapour-liquid–liquid equilibrium (VLLE) prediction and in sustainability assessment. We overcome these with a digital approach to screen billions of structures and design the novel phase-change solvent S1N (N1-cyclohexylpropane-1,3-diamine) and mixture S1N/DMCA (N,N-dimethylcyclohexylamine). Screening criteria include thermodynamic and process-related properties, reactivity and sustainability of solvent production and use. VLLE phase envelopes are predicted using the SAFT-γ Mie (Statistical Associating Fluid Theory) equation of state thanks to its transferability to any structure and the implicit modelling of ionic species. Experimental validation confirms the suitability of S1N/DMCA for scaling-up, with a cyclic capacity of 1.19 mol CO2/ kg-solvent, a regeneration energy of 2.3 GJ/ton-CO2, and vapour losses and viscosity lower by 10% and 70% than those of other solvents. S1N is also safer for plant operation and working personnel