Optimal startup operation of simulated moving bed chromatographic processes

Abstract: SMB represents one of the widely established periodic adsorption processes and its periodic and nonlinear dynamics presents a significant challenge to the formulation and solution of the optimal startup issue. A multistage startup concept allowing to adjust operating conditions stage-wise is proposed. The startup problem is then formulated aiming at driving the system towards the reference cyclic steady state (CSS) in an optimum manner. A tailored decomposition algorithm is developed to tackle the resulting optimization problem and guarantee numerical tractability. The feasibility of the solution approach is demonstrated on a binary separation with nonlinear competitive isotherms. It is found that the new startup policy dramatically reduces transient time and desorbent consumption. The startup performance in terms of product concentration and purity is also evaluated quantitatively

A new solar fuels reactor concept based on a liquid metal heat transfer fluid: Reactor design and efficiency estimation

Abstract A new reactor concept for two-step partial redox cycles is presented and evaluated by transient simulation that considers heat and mass transfer along with reaction kinetics. The major difference between the reactor described herein and previous designs is that the conversion from solar to chemical energy is divided into two steps: sunlight-to-thermal energy conversion accomplished with a liquid metal based receiver, and the thermal-to-chemical conversion accomplished with a separately optimized array of reaction chambers. To connect these two conversion steps, liquid metal is used as a high temperature heat transfer fluid that feeds the solar energy captured in the receiver to the reactor. The liquid metal also facilitates efficient heat recuperation ($80%) between the reaction chambers. The overall thermal-to-chemical efficiency from the thermal energy in the liquid metal to the chemical energy in the hydrogen fuel is estimated to be 19.8% when ceria is employed as the reactive oxygen storage material. This estimated efficiency is an order of magnitude higher than previous designs and the reactor concept discussed herein identifies important insights that apply to solar-fuel conversion in general

Model-based techno–economic analysis of an integrated synthetic natural gas production system with direct air capture and water electrolysis

In this study, a techno-economic analysis is performed for an integrated system of carbon capture and utilization (CCU). The proposed system utilizes CO2 captured by a direct air capture (DAC) process using a metal–organic framework adsorbent. The captured CO2 is converted into a methane product, or synthetic natural gas (SNG), using hydrogen produced by water electrolysis. Rigorous mathematical models are used for the mass and energy balances in the major components of the proposed integrated system, allowing us to estimate the capital and operating costs and energy consumption. A sensitivity analysis is also performed to identify model parameters that significantly affect the SNG cost. Our analysis indicates that the thermal and electrical energies required to produce SNG are 0.409 MJ/Nm3-SNG and 19.6 kWh/Nm3-SNG, respectively, and the cost of SNG is within the range of 1.43–2.60 $/Nm3-SNG

Reaction Kinetics of Concentrated-Acid Hydrolysis for Cellulose and Hemicellulose and Effect of Crystallinity

Batch experiments for the hydrolysis of xylan and pure cellulose (Avicel) hydrolysis and the decomposition of xylose and glucose were performed at varying sulfuric acid concentrations in the range of 10 to 50 wt.% and varying temperatures in the range of 80 to 100 °C. Increasing the temperature and acid concentration hastened the hydrolysis and the sugar decomposition rates. The hydrolysis rate of Avicel was much slower than that of xylan because of its crystallinity. The kinetic parameters for the concentrated acid hydrolysis reaction were estimated for both glucose and xylose reaction paths. The effect of initial cellulose crystallinity on the acid hydrolysis rate was also investigated, such that the cellulose was treated with various concentrations of phosphoric acid. A dramatic reduction in the cellulose crystalline index was observed when the phosphoric acid concentration was in a narrow range around 80 wt.%. It was found that the hydrolysis rate significantly increased with the decrease in initial cellulose crystalline index

Interactive multi-objective optimization of Simulated Moving Bed processes using IND-NIMBUS and IPOPT

In this paper, efficient optimization techniques are used to solve multi-objective optimization problems arising from Simulated Moving Bed (8MB) processes. SMBs are widely used in many industrial separations of chemical products and they are very challenging from the optimization point of view. With the help of interactive multi-objective optimization, several conflicting objectives can be considered simultaneously without making unnecessary simplifications, as it has been done in previous studies. The optimization techniques used are the interactive NIMBUS™ method and the IPOPT optimizer. To demonstrate the usefulness of these techniques, the results of solving an 8MB optimization problem with four objectives are reported

Modeling of Nucleation, Growth, Dissolution, and Disappearance of Paracetamol in Ethanol Solution for Unseeded Batch Cooling Crystallization with Temperature-Cycling Strategy

A population balance model (PBM) is developed for unseeded batch crystallization, with temperature-cycling strategies to control the crystal size distribution. The model is able to predict the evolution of crystal size distributions of crystallizing paracetamol from ethanol solutions considering the characteristics of primary nucleation, secondary nucleation, growth, dissolution, and disappearance of crystals. Process analytical technology (PAT) tools were employed to collect solute concentration data and crystal size distribution data. This model employs a boundary condition to describe the disappearance of crystals in temperature-cycling strategies where the temperature is increased and decreased repeatedly. As a result, the obtained model can describe the evolution of crystal size distribution when repetition of cooling and heating is carried out. Moreover, this model can be applied to investigate phenomena that are challenging to explain with experimental data alone, thereby we can gain insight and optimize the operation of the process