The Sabatier process is promising for carbon dioxide utilization and energy storage. However, the serious problem that limits more comprehensive industrial applications is catalyst deactivation due to the temperature runaway phenomenon. The inert particle dilution approach, including the mixing dilution method and layered dilution method is applied to solve this problem. Based on the lattice kinetic scheme-lattice Boltzmann method (LKS-LBM), the effects of three parameters in bed dilution structure reconstructed by the discrete element method (DEM) on temperature distribution and carbon conversion rate were discussed, so as to investigate the relationship between packing structure and temperature distribution. Furthermore, numerical results indicated that an optimal bed dilution structure, which not only can control the peak temperature below the critical temperature to avoid coking and sintering of catalyst, but also can improve the carbon conversion rate by almost 18% compared with the structure without dilution under the same circumstance.
A new method for integrated ionic liquid (IL) and absorption process design is proposed where a rigorous rate-based process model is used to incorporate absorption thermodynamics and kinetics. Different types of models including group contribution models and thermodynamic models are employed to predict the process-relevant physical, kinetic, and thermodynamic (gas solubility) properties of ILs. Combining the property models with process models, the integrated IL and process design problem is formulated as an MINLP optimization problem. Unfortunately, due to the model complexity, the problem is prone to convergence failure. To lower the computational difficulty, tractable surrogate models are used to replace the complex thermodynamic models while maintaining the prediction accuracy. This provides an opportunity to find the global optimum for the integrated design problem. A pre-combustion carbon capture case study is provided to demonstrate the applicability of the method. The obtained global optimum saves 14.8% cost compared to the Selexol process.
This paper investigates the effect of inlet shape, entrance length and turbulence promoters on mass transfer by using 3D printed electrolyzers. Our results show that the inlet design can promote turbulence and lead to an earlier transition to turbulent flow. The Reynolds number at which the transition occurs can be predicted by the ratio of the cross-sectional area of the inlet to the cross-sectional area of the electrolyzer channel. A longer entrance length results in more laminar behavior and a later transition to turbulent flow. With an entrance length of 550mm, the inlet design did no longer affect the mass transfer performance significantly. The addition of gyroid type turbulence promoters resulted in a factor 2 to 4 increase in mass transfer depending on inlet design, entrance length and the type of promoter. From one configuration to another, there was a minimal variation in pressure drop (<16 mbar).
Molecular simulation has emerged as an important sub-field of chemical engineering, due in no small part to the leadership of Keith Gubbins. A characteristic of the chemical engineering molecular simulation community is the commitment to freely share simulation codes and other key software components required to perform a molecular simulation under open-source licenses and distribution on public repositories such as GitHub. Here we provide an overview of open-source molecular modeling software in Chemical Engineering, with focus on the Molecular Simulation Design Framework (MoSDeF). MoSDeF is an open-source Python software stack that enables facile use of multiple open-source molecular simulation engines, while at the same time ensuring maximum reproducibility.
Cylindrical lamps are usually equipped in the tubular UV reactor to offer UV radiation. This paper describes the axisymmetric characteristics of UV radiation from the cylindrical UV lamp. Axisymmetric lamp emission models are developed in a two-dimensional axisymmetric space for the line source, the superficial source and the volumetric source. The present axisymmetric lamp emission models are easy to understand and of simple mathematical expressions. The experimental data in literature is used to validate the present axisymmetric lamp emission models. Good agreements have been obtained between the experimental data and the computations. A comparison show that the present models obtain the identical results as previous models.
Weisz-Prater number (NW-P) is often applied to assess the internal diffusion effect in heterogeneous catalytic reactions. However, the traditional calculation method with excessive empirical reference values affects the accuracy remarkably. A series of Pt/HPMo/SBA-15 catalysts with the pore size as a single variable were prepared to calculate the NW-P with a developed model combining the diffusion-reaction kinetic method. Utilizing dimensionless variables, internal effectiveness factor (η) and Thiele modulus (Φ_n), and the apparent activities over catalysts with different diffusion capacity, NW-P is obtained with improved accuracy. For the diffusion effect on the hydrotreatment of n-C16, according to the more precise NW-P, the pore size should be not less than 10 nm to avoid the step-limitation of internal diffusion in the premise of adequate acid sites. Using the novel method, a conclusion is drawn that the formation of m-i-C16 is more susceptible to internal diffusion than the consumption of n-C16.
A micro membrane adsorber with deep-permeation nano structure (DPNS) has been successfully fabricated by flowing synthesis. The nanoparticles are in situ assembled in membrane pores and immobilized in each membrane pores along the direction of membrane thickness. The nanoparticles with a lower size and thinner size distribution can be achieved owing to the confined space effect of the membrane pores. As a concept-of-proof, the nano ZIF-8 and ZIF-67 are fabricated in porous membrane pores for Methyl orange (MO) and Rhodamine B (RhB) adsorption. The adsorption rate is increased significantly owing to the enhanced contact and mass transfer in the confined space. The adsorption capacity for the RhB is also increased, since the size of the nanoparticles assembled in membrane pores is smaller with more active sites exposed. This micro membrane adsorber with DPNS has good reusability, and can provide a promising prospect for industrial application.
In this study, effect of swirling addition on the liquid mixing behavior of multi-orifice-impinging transverse jet mixer has been investigated by planar laser induced fluorescence as well as large eddy simulation (LES). In the case of swirling addition into the jet flow, there exists an optimized swirling jet angle or optimized jet-to-cross velocity ratio for the fixed mixer configuration. A larger swirling jet angle will make the flow dominated by the swirling, resulting in a slower mixing process. Interaction of swirling crossflow with no-swirling injected streams, or with swirling injected streams in the opposite direction is beneficial for the mixing. LES predictions show that many small vortices are produced homogenously due to intensified impingement in the case of opposite swirling directions, leading to a relative fast mixing process in several milliseconds. Whereas the mixing is restrained when the swirling directions of two flows are the same.
The study proposed an isotopes-tagging method for investigation of reactions under the atmosphere of product gas. To illustrate this method, the calcination kinetics of calcium carbonate Ca13CO3 in CO2 atmospheres were investigated by monitoring 13CO2 produced using a micro fluidized bed reaction analyzer (MFBRA). The results demonstrated that the presence of CO2 in the reaction atmosphere increases the apparent activation energy. The increase in the apparent activation energy is, however, significantly overestimated by the TGA because of the excessive suppression by stagnated product gas inside the sample crucible. Comparatively, the results from the MFBRA are due primarily to the thermal equilibrium limitation, because the gas diffusion in the MFBRA is essentially eliminated. It is thus concluded that the MFBRA is quite capable of acquiring the real kinetics of reactions in such inhibitory atmospheres. atmosphere.
This study proposes a multiperiod mixed integer linear programming model for the management of a single municipal solid waste (MSW) treatment plant with sustainability as the objective. Discrete and continuous variables define the capacity selections for diverse MSW technologies, and the operation of the MSW network, respectively. The economic target is considered to maximize the net present value. The environmental impact is the minimization of a normalized environmental objective function (NEOF). The social target is the maximization of jobs. An interesting feature about the research work is the requirement of biodrying technologies for MSW moisture content control. Due to the conflicted nature among the sustainability components, a multi-objective optimization (MO) is carried out to find the Pareto optimal solutions. The MO results show that the Pareto optimal solutions vary around profit range of US$ 4.9-8.5 billion, NEOF impact range of 3.2-3.6 units, and social benefit range of 2700-4828 jobs.
As an attractive alternative technology for the separation of long chain olefin and paraffin, a novel silver-based deep eutectic solvent (Ag-DES) was prepared and utilized for 1-octene/n-octane separation. Comprehensive reactive extraction separation experiments were performed to highlight the Ag-DES concentration and operating temperature discriminations using compounds with different ratio of 1-octene/n-octane. The novel Ag-DES showed optimal separation performance regarding 1-octene/n-octane and possessed the highest levels separation selectivity in the range 3.75-16.74 with excellent circulation stability in our best knowledge. Furthermore, FT-Raman measurements and quantum chemistry calculation were conducted to elucidate the interaction mechanism of Ag-DES in the separation of 1-octene and n-octane, which revealed that both chemical complexation and strong physical attraction existed in the complex of Ag-DES with 1-octene rather than n-octane. This study lends important insight for the development of Ag-DES reactive extraction separation process for the energy-efficient long chain α-olefin purification from F-T synthesis products.
Editorial – The third “Futures” issueThis month’s volume of AIChE Journal is the third “Futures” issue. I think now we’ve established a tradition. This is my favorite issue each year.Each year we invite a group of early career researchers to contribute their pioneering works. I have sought the input of the AIChE Journal editorial team and consulting editorial board to identify contributors. The criterion is that the prospective author be seven or less years removed from her or his initial appointment as an academic, industrial, or national lab researcher.During the publication year we have a session at the Annual AIChE meeting where several of the authors have the opportunity to present their research. (This being the year of COVID-19, these presentations will unfortunately be virtual.)The “Futures” issue parallels the annual “Founders” issue; while the “Founders” issue celebrates the scholarly legacies of the greats from our profession, the “Futures” issue recognizes the research of emerging scholars.I hope that you enjoy this third installment of the “Futures” series.On behalf of the AIChE Journal editorial team, we look forward to your input and suggestions. As always, thanks for your support of
The existing methods of flexibility index are mainly based on mixed-integer linear or nonlinear programming methods, making it difficult to readily deal with complex mathematical models. In this article, a novel solution strategy is proposed for finding a reliable upper bound of the flexibility index where the process model is implemented in a black box that can be directly executed by a commercial simulator, and also avoiding the need for calculating derivatives. Then, the flexibility index problem is formulated as a sequence of univariate derivative-free optimization (DFO) models. An external DFO solver based on trust-region methods can be called to solve this model. Finally, after calculating the critical point of the model parameters, the vertex enumeration method and two gradient approximation methods are proposed to evaluate the impact of process parameters and to evaluate the flexibility index. A reaction model is studied to show the efficiency of the proposed algorithm.
The low effectiveness factor of catalyst pellet caused by high internal diffusion limitation is a common issue in fixed-bed reactor. Nevertheless, hierarchical structured catalyst provides a promising solution for the contradiction between reaction activity and diffusion efficiency in large catalyst pellets. Herein, we studied the effect of pore structure parameters of the meso-macroporous catalyst on Fischer-Tropsch synthesis performances through experiment and pellet scale reaction-diffusion simulation. The pellet simulation firstly elucidated the reason for the significant improvement on activity and product selectivity for the meso-macroporous catalyst observed in our experiment. Further optimization via pellet simulation indicated the critical influences of wax filling degree and that the perfect matching between reaction and mass transfer rates by increasing macropore size and adjusting porosity within pellet enables the C5+ space-time yield to the maximum. This work could provide a theoretical guideline for the engineering design of the hierarchical structured catalyst pellet.
The complexity of lipid feedstocks and the lack of data on physical properties hinder the simulation of oleochemical processing units. In this work, an iterative lumping approach is proposed to define an adequate number of key components such that diversification between lipid feedstocks becomes possible, while keeping the determination of physical properties as required for process modelling manageable. As a case study, the iterative lumping approach is used for simulation and optimization of a fatty acid distillation plant. For predicting vapour-liquid equilibria of fatty acids, the best results were acquired using the property method UNIQ-HOC. Using the iterative lumping approach, 11 key components were selected to represent the feedstock. The process model properly predicts the product composition, yield, purity and heat duty. The most important process parameters are found to be side-reflux-ratio, reboiler-outlet-temperature and heat-duty of the pitch-distiller. For optimization, an increase of the side-reflux-ratio and reboiler-outlet-temperature, is recommended.
To assess the techno-economic screening of HTL oil for various feedstock, it is crucial to have information on molecular composition of the feed and products. There are limitations of existing analytical methods to identify and quantify all the molecules present in the bio-fuel. Therefore, there is a need to find alternate ways to quantify the molecular composition of feed and expected products. The modelling work on bio-oil is developed based on a mathematical approach using simple analytical results like CHNO along with structural analysis of oil like FTIR, NMR analysis for HTL derived oil from microalgae. This mathematical framework is further extended to predict the molecular composition of HTL-oil obtained from feedstocks like mixed plastic waste, sludge etc. A multi-dimensional molecular matrix is developed based on the distributions of side chains, aromatic rings, and olefinic carbon on top of core molecules. Optimum parameters are found using appropriate optimization algorithms.
In this work, methods based upon nonequilibrium thermodynamics are elucidated to predict stationary states of chemical reactions in nonequilibrium plasma, and limits for energy conversion efficiency. Two example reactions are used: CO2 splitting and NH3 synthesis, with emphasis on CO2 splitting. Expectations from the theoretical framework are compared to experimental results for both reactions, and reasonable agreement is obtained. The conclusion is that the probability of observing either reactants or products increases with the amount of energy dissipated by that side of the reaction as heat through collisions with hot electrons. The side of the reaction that dissipates more energy as heat has a higher probability of occurrence. Furthermore, endergonic chemical reactions in nonequilibrium plasma, such as CO2 splitting at low temperature, require an intrinsic energy dissipation to satisfy the 2nd law of thermodynamics – a sufficient and necessary waste. This intrinsic dissipation limits the maximum theoretical energy conversion efficiency