Coal is playing a major role as a reductant and as an energy source in the present world steel production due to its low cost and widespread distribution around the world. At the same time, being the largest contributor to global CO2 emissions, coal faces significant environmental challenges in terms of air pollution and global warming. Hydrogen is a promising alternative for coal in lowering the steel industry's CO2 footprint, but the availability of green hydrogen is currently limited by its high production cost. This research study focuses on developing a pressure swing adsorption (PSA) technology that will allow for continued use of coal for a smooth transition towards green hydrogen-based steel production, by better utilisation of its by-product coke oven gas to produce high purity hydrogen. A generic, fast and robust simulation tool for simulating a variety of PSA processes considering both equilibrium and kinetic effects using a detailed non-isothermal and non-isobaric model is developed in the study. The adsorption equilibrium data required for the model are calculated from experimental results using the non-linear regression data fitting method. A series of rigorous parametric studies and breakthrough tests are performed using the developed mathematical model for better understanding of the effects of different factors on the PSA process performance. With the better understanding obtained from the above-mentioned parametric studies, the model is optimised by performing several simulation tests to achieve a high process performance in terms of purity and recovery of the H2 product, productivity of the adsorbents and energy consumption for compression of gases. The optimised 14-step multi-bed PSA cycle developed in this study allows for an improved energy efficiency of coal usage by better utilisation of its by-product coke oven gas by converting it into valuable high purity (>99.999%) hydrogen product with a recovery of over 75%.

A molecular modeling study was carried out on linear polyethyleneimine (LPEI) to determine the CO2 capturing process taking into account structural changes of the material at various amounts of H2O. Until now, CO2 capture by LPEI was described as a combination of carbamic and carbonic acid formation. It was found that humidification below the melting point of LPEI leads to the formation of an LPEI/0.5H2O type of phase. Such a type of phase leads to CO2 capture exclusively via carbonic acid formation, stabilized by secondary amines via ammonium bicarbonate and H-bridged amine carbonic acid complexes. Both the strong physisorption CO2 complex and the low activation barrier for carbonic acid formation contribute to the overall process. Only in the absence of H2O, carbamic acid formation is possible. Thus, under CO2 capturing process conditions, carbonic acid formation seems to be the only option as H2O will be present in flue gas.

Since 2012, Lewatit R VP OC 1065 was reported as a promising material for direct air capture of CO₂. However, deactivation at a high pressure of CO₂ at 120 °C was reported with detrimental effects on its application. In this study, using density functional theory calculations, a quantitative description of the deactivation mechanism in the presence of CO₂ is presented. Deactivation by CO₂ follows a three-step mechanism. The first step in deactivation of the resin is self-catalyzed formation of a carbamic acid from an amine group and CO₂. The second step is decomposition of a carbamic acid to an isocyanate as the rate-determining step with an activation barrier of 144.4 kJ/mol. The third step is the H₂O-catalyzed addition of a benzyl amino group to the isocyanate, yielding an urea species, responsible for deactivation. However, the process can be made reversible by optimizing H₂O and CO₂ concentration and temperature. The identified deactivation mechanism quantitatively explains the differences between experimental CO₂ sorption data and the earlier reported dual site Langmuir model. ©

Lewatit R VP OC 1065 is a promising material for direct air capture of CO₂. However, it was found that serious oxidative degradation already started from 80 °C. In this DFT study, oxidative degradation is described as a series of well-known reactions in air-oxidation chemistry. Oxidation of the resin starts with the formation of an α-benzyl amino hydroperoxide. Thermal decomposition of the α-benzyl amino hydroperoxide is the second step and leads eventually to the corresponding amide (R(C=O)NH₂) and the half-aminal (RCH(OH)(NH₂). The half-aminal further solvolyzes predominantly to an aldehyde (RCHO). Both the amide and the aldehyde are responsible for the experimentally observed loss of CO₂ capacity as these groups are not able to capture CO₂. The rate-determining step in oxidative degradation is usually the decomposition of the hydroperoxide, but in this case the formation of the α-benzyl amino hydroperoxide cannot be excluded. The apparent contradiction between the results of Hallenbeck et al. and Yu et al. with respect to the oxygen content before and after exposure of the resin to air at high temperature is explained by the difference in H₂O content before and after and oxygen incorporation by amide and aldehyde formation after exposure to air. The loss of nitrogen content on exposure to air at high temperature is explained by the formation of aldehydes.

A common problem that faces the oil and gas industry is the formation of iron sulfide scale in various stages of production. Recently an effective chemical formulation was proposed to remove all types of iron sulfide scales (including pyrite), consisting of a chelating agent diethylenetriaminepentaacetic acid (DTPA) at high pH using potassium carbonate (K₂CO₃). The aim of this molecular modeling study is to develop insight into the thermodynamics and kinetics of the chemical reactions during scale removal. A cluster approach was chosen to mimic the overall system. Standard density functional theory (B3LYP/6-31G∗) was used for all calculations. Low spin K₄Fe(II)₄(S₂H)₁₂ and K₃Fe(II)(S₂H)₅ clusters were derived from the crystal structure of pyrite and used as mimics for surface scale FeS₂. In addition, K₅DTPA was used as a starting material too. High spin K₃Fe(II)DTPA, and K₂S₂ were considered as products. A series of K_mFe(II)(S₂H)_n complexes (m = n-2, n = 5-0) with various carboxylate and glycinate ligands was used to establish the most plausible reaction pathway. Some ligand exchange reactions were investigated on even simpler Fe(II) complexes in various spin states. It was found that the dissolution of iron sulfide scale with DTPA under basic conditions is thermodynamically favored and not limited by ligand exchange kinetics as the activation barriers for these reactions are very low. Singlet-quintet spin crossover and aqueous solvation of the products almost equally contribute to the overall reaction energy. Furthermore, seven-coordination to Fe(II) was observed in both high spin K₃Fe(II)DTPA and K₂Fe(II)(EDTA)(H₂O) albeit in a slightly different manner.

Iron sulphide scale, which exists in different forms, is common in sour oil and gas production wells. Iron sulphide hard scales are difficult to remove with acids, requiring mechanical intervention or the replacement of the production tubing. An environmentally friendly formulation with a high pH is proposed for the removal of both soft and hard iron sulphide scale from oil and gas wells. The formulation consists of DTPA (di-ethylene tri-amine penta acetic acid) in addition to K₂CO₃ as a catalyst. High pressure high temperature solubility experiments were performed under both static and dynamic conditions in the temperature range of 70–150 °C and a constant pressure of 3447.38 kPa. Several combinations of the catalyst and DTPA chelating agent were used to optimize the catalyst/DTPA ratio to achieve maximum scale solubility. Field scale samples were collected and analyzed using XRD. The scale removal efficiency of the proposed formulation outperforms that of the current formulations used in the oil industry, with the added advantage of not releasing H₂S. The optimum DTPA concentration is 20 wt% and the optimum catalyst concentration is 9 wt%, which provides a solubility of 90 % of the field scale. In addition, the ecotox profile of the proposed formulation is better than that of the currently used formulations because toxic corrosion inhibitors are not used. The maximum reported corrosion rate for the new formulation is 0.036 kg/m², which is well below the acceptable limit (< 0.227 kg/m²).

Carbon dioxide (CO₂) can electrochemically be converted to a range of products including formic acid (HCOOH) and acetic acid (CH₃COOH). The yield of the products in an electrolysis cell depends on the solubility of CO₂ in the (aqueous) mixture. In absence of experimental data, Monte Carlo simulations in the Gibbs ensemble are used to compute the VLE of the binary systems, CO₂-H₂O, CO₂-HCOOH and CO₂-CH₃COOH, and the ternary systems, CO₂-HCOOH-H₂O and CO₂-CH₃COOH-H₂O. In addition, the PC-SAFT equation of state (EoS) is used to model the VLE of these strongly associating mixtures. Both methods correctly predicts the liquid-phase compositions, but the gas-phase compositions are less accurately described. The challenges to model these systems are related to the simultaneous formation of dimers, rings, and chains, which requires accurate force fields and advanced biasing schemes in MC simulations, and association theories that can account for this effect.

Natural gas, synthesis gas, and flue gas typically contain a large number of impurities (e.g., acidic gases), which should be removed to avoid environmental and technological problems, and to meet customer specifications. One approach is to use physical solvents to remove the acidic gases. If no experimental data are available, the solubility data required for designing the sweetening process can be obtained from molecular simulations. Here, Monte Carlo (MC) simulations are used to compute the solubility of the gas molecules, i.e., carbonyl sulfide, carbon disulfide, sulfur dioxide, hydrogen sulfide, methyl mercaptan, carbon dioxide, and methane in the commercial solvents tetraethylene-glycol-dimethyl-ether (Selexol), n-methyl-2-pyrrolidone, propylene carbonate, methanol (Rectisol), and the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf₂N]). Henry coefficients of the gases in the investigated solvents are obtained from the computed solubilities. The ratio of Henry coefficients is used to compute ideal selectivities of the solvents. The solubilites and selectivities computed from MC simulations are compared with available experimental data. Some guidelines are provided to remove acidic gases using the investigated solvents. Rectisol is the best solvent for acid gas removal, but it should be used at low temperatures. Selexol and the ionic liquid have similar selectivity of sulfur compounds with respect to methane and may be used at elevated pressures and temperatures since both have low vapor pressures. The solubility of carbon disulfide, sulfur dioxide, and methyl mercaptan in these solvents is the highest. Hence, these components can be removed easily prior to hydrogen sulfide, carbonyl sulfide, and carbon dioxide in a pre-absorber.