• Energy Research

Fossil fuel depletion, global warming, climate change, and steep hikes in the price of fuel are driving scientists to investigate commercial and environmentally friendly energy carriers like hydrogen. Steam methane reforming (SMR), a current commercial route for H2 production, has been considered the best remedy to fulfill the re- quirements. Despite the remarkable quantity of H2 produced by the SMR, this technology still faces major challenges such as catalyst deactivation due to the sintering of metal nanoparticles, coking, and generation of a large quantity of CO2. Firstly, the effects of catalyst types, kinetic models, and operating conditions on high-yield H2 production, the evolution path from gray to blue, via the conventional SMR are comprehensively reviewed. Secondly, exploiting intensified techniques such as membrane technology, sorption, fluidization, and chemical looping for SMR to blue H2 are discussed in detail. Further, a novel and sustainable path for the SMR process, hybridizing the use of novel materials and emerging technologies to produce turquoise H2, is proposed. Finally, the critical points for steam reforming process technology that can help leverage environmental, social, and governance (ESG) profiling have been discussed.

Global warming, climate change, fossil fuel depletion and steep hikes in the price of environmentally friendly hydrocarbons motivate researchers to investigate CO2 hydrogenation for hydrocarbons production. However, due to the reaction complexities and varieties of produced species, the process mechanism and subsequently estimation of the kinetic parameters have been controversial yet. Therefore, estimating the kinetic parameters using Artificial Bee Colony (ABC) and Differential Evolution (DE) optimization algorithms based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism is proposed as a possible remedy to fulfil the requirements. To this end, a one-dimensional heterogeneous model comprising detailed reaction rates of reverse water gas shift (RWGS), Fisher-Tropsch (FT) reactions and direct hydrogenation (DH) of CO2 is developed. It is observed that ABC exhibiting 6.3% error in predicting total hydrocarbons selectivity is superior to DE algorithm with 32.9% error. Therefore, the model employed the estimated kinetic parameters obtained via ABC algorithm, is exploited for products distribution analysis. Results reveal that maximum 73.21% hydrocarbons (C1–C4) selectivity can be achieved at 573 K and 1 MPa with 0.85% error compared to the experimental value of 72.59%. Accordingly, the proposed model can be exploited as a powerful tool for evaluating and predicting the performance of CO2 hydrogenation to hydrocarbons process.

Auto-thermal reforming (ATR), a combination of exothermic partial oxidation and endothermic steam reforming of methane, is an important process to produce syngas for petrochemical industries. In a commercial ATR unit, tubular fixed bed reactors are typically used. Pressure drop across the tube, high manufacturing costs, and low production capacity are some disadvantages of these reactors. The main propose of this study is to offer an optimized radial flow, spherical packed bed reactor as a promising alternative for overcoming the drawbacks of conventional tubular reactors. In the current research, a one dimensional pseudo-homogeneous model based on mass, energy, and momentum balances is applied to simulate the performance of packed-bed reactors for the production of syngas in both tubular and spherical reactors. In the optimization section, the proposed work explores optimal values of various decision variables that simultaneously maximize outlet molar flow rate of H2, CO and minimize molar flow rate of CO2 from novel spherical reactor. The multi-objective model is transformed to a single objective optimization problem by weighted sum method and the single optimum point is found by using genetic algorithm. The optimization results show that the pressure drop in the spherical reactor is negligible in comparison to that of the conventional tubular reactor. Therefore, it is inferred that the spherical reactor can operate with much higher feed flow rate, more catalyst loading, and smaller catalyst particles.

Abstract Climate change and global warming, as well as growing global demand for hydrocarbons in industrial sectors, make great incentives to investigate the utilization of CO2 for hydrocarbons production. Therefore, finding an in-depth understanding of the CO2 hydrogenation reactors along with simulating reactor responses to different operating conditions are of paramount importance. However, the reaction mechanisms for CO2 hydrogenation and their corresponding kinetic parameters have been disputable yet. In this regard, considering the previously proposed Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism, which considered CO2 hydrogenation as a combination of reverse water gas shift (RWGS) and Fischer-Tropsch (FT) reactions, and using a one-dimensional pseudo-homogeneous non-isothermal model, kinetic parameters of the rate expressions are estimated via fitting experimental and modelling data through a novel swarm intelligence optimization technique called dragonfly algorithm (DA). The predicted reactants conversion using DA algorithm are closer to the experimental data (with about 4% error) comparing to those obtained by the artificial bee colony (ABC) algorithm, and are in significant agreement with available literature data. The proposed model is used to assess the effect of reactor configuration on the performance and temperature fluctuations. Results show that axial flow spherical reactor (AFSR) and radial flow spherical reactor (RFSR) exhibiting the same surface area with that of the cylindrical reactor (CR), i.e., AFSR-2 and RFSR-2-i are the most efficient exhibiting hydrocarbons selectivity of 40.330% and 40.286% at CO2 conversion of 53.763% and 53.891%. In addition, it is revealed that the location of the jacket has an essential role in controlling the reactor temperature.

Abstract Global warming, fossil fuel depletion and energy security are driving scientists to investigate the mechanism of hydrocarbons production from CO 2 hydrogenation. The need for more comprehensive understanding on mechanism of CO 2 hydrogenation to hydrocarbons remains controversial because of the complex reaction mechanism and a large number of involved species. The micro mechanism of CO 2 hydrogenation to hydrocarbons has been considered as a possible remedy to fulfill the requirements. This review comprehensively discusses two processes: reverse water gas shift (RWGS) and CO 2 hydrogenation to hydrocarbons. The review includes reaction mechanisms and catalyst effects on yields and rates. In addition, the review outlines each of the Fischer-Tropsch (FT) micro mechanisms. The review infers some mechanisms from existing work and proposes a new mechanism that improves several predictions. These mechanisms form the design basis for optimal reactor design.

Abstract Direct CO2 hydrogenation to hydrocarbons is a promising method of reducing CO2 emissions along with producing value-added products. However, reactor design and performance have remained a challenging issue because of low olefin efficiency and high water production as a by-product. Accordingly, a one-dimensional non-isothermal mathematical model is proposed to predict the membrane reactor performance and statistical analysis is used to assess the effects of important variables such as temperatures of reactor (Tr:A), shell (Ts:B) and tube (Tt:C) as well as sweep ratio (θ:D) and pressure ratio (φ:E) and their interactions on the products yields. In addition, the optimized operating conditions are also obtained to achieve maximum olefin yields. Results reveal that interacting effects comprising AB (TrTs), AC (TrTt), AE (Trφ), BC (TsTt), CE (Ttφ), CD (Ttθ) and DE (θφ) play important roles on the product yields. It is concluded that higher temperatures at low sweep and pressure ratios can maximize the yields of olefins, while simultaneously the yields of paraffins are minimized. In this regard, optimized values for Tr, Ts, Tt, θ and φ are determined as 325 °C, 306.96 °C, 325 °C, 1 and 1, respectively.

The development of an efficient reactor for hydrocarbons (C2–C4) production through hydrogenation of CO2, requires a deep understanding of the operating conditions effects. Subsequently, a model is proposed to analyze the reaction rates and investigate the sensitivity of hydrocarbons yield and products distribution to the variations of temperature, pressure and space velocity (SV). Besides, Thiele modulus and effectiveness factor are calculated for all of the reactions considered in the model. Results reveal that simultaneous occurrence of both endothermic reverse water gas shift (RWGS) and exothermic Fischer-Tropsch (FT) reactions, may be the main reason of temperature and rate fluctuations at the fixed-bed reactor inlet. In addition, increasing temperature and pressure, and decreasing SV can shift the process to produce more light olefins. Finally, sensitivity analysis demonstrates that reactor behavior is independent of the changes in pressure and SV at high temperature, which is an indication of high temperature dependency of this process. These findings can be effectively employed to achieve a better insight about appropriate operating conditions of hydrocarbons production via hydrogenation of CO2.