Reactor Selection for Upgrading Hemicelluloses: Conventional and Miniaturised Reactors for Hydrogenations

This work presents an advanced reactor selection strategy that combines elements of a knowledge-based expert system to reduce the number of feasible reactor configurations with elaborated and automatised process simulations to identify reactor performance parameters. Special focus was given to identify optimal catalyst loadings and favourable conditions for each configuration to enable a fair comparison. The workflow was exemplarily illustrated for the Ru/C-catalysed hydrogenation of arabinose and galactose to the corresponding sugar alcohols. The simulations were performed by using pseudo-2D reactor models implemented in Aspen Custom Modeler® and automatised by using the MS-Excel interface and VBA. The minichannel packings, namely wall-coated minichannel reactor (MCWR), minichannel reactor packed with catalytic particles (MCPR), and minichannel reactor packed with a catalytic open-celled foam (MCFR), outperform the conventional and miniaturised trickle-bed reactors (TBR and MTBR) in terms of space-time yield and catalyst use. However, longer reactor lengths are required to achieve 99% conversion of the sugars in MCWR and MCPR. Considering further technical challenges such as liquid distribution, packing the reactor, as well as the robustness and manufacture of catalysts in a biorefinery environment, miniaturised trickle beds are the most favourable design for a production scenario of galactitol. However, the minichannel configurations will be more advantageous for reaction systems involving consecutive and parallel reactions and highly exothermic systems.

Selection, Sizing, and Modeling of a Trickle Bed Reactor to Produce 1,2 Propanediol from Biodiesel Glycerol Residue

Propylene glycol, also known as 1,2 propanediol, is one of the most important chemicals in the industry. It is a water-soluble liquid, considered by the U.S. Food and Drug Administration as safe to manufacture consumer products, including foodstuffs, medicines, and cosmetics. This chemical has essential properties, such as solvent, moisturizer, or antifreeze, in addition to a low level of toxicity. This paper aims to present the selection, simulation, and dimensioning of a trickle bed reactor at a laboratory scale. The sizing was validated with other authors. Two predictive models have been considered for reactor modeling, intrinsic kinetics and coupled intrinsic kinetics, along with mass transfer equations and the wetting of the catalyst particles. The model was implemented using Aspen Custom Modeler® (20 Crosby Dr. Bedford, MA 01730, EE. UU.) to study the reactor behavior in terms of conversion. The results show the profiles of different variables throughout the reactor and present higher glycerol conversion when mass transfer is added to the model.

Modeling and Multi-Criteria Optimization of a Process for H2O2 Electrosynthesis

This article introduces a novel laboratory-scale process for the electrochemical synthesis of hydrogen peroxide (H2O2). The process aims at an energy-efficient, decentralized production, and a mathematical optimization of it is presented. A dynamic, zero-dimensional mathematical model of the reactor is set up in Aspen custom modeler®. The proposed model constitutes a reasonable compromise between complexity and convergence. After thoroughly determining the reaction kinetics by adjustment to experimental data, the reactor unit is embedded in an Aspen Plus® flowsheet in order to investigate its interaction with other unit operations. The downstream contains another custom module for membrane distillation. Electricity appears as a resource in the process, and optimization shows that it reaches product purities of up to 3 wt.-%. Both the process optimization and the adjustment of the reaction kinetics are treated as multi-criteria optimization (MCO) problems.

DETAILED EVALUATION OF PERVAPORATION MODELING TO OBTAINING ANHYDROUS ETHANOL

Pervaporation requires operation at mild temperatures and provides low energy consumption, which makes this technology economically attractive. However, pervaporation is not yet a widespread process in the industry. One of the justifications is the complexity in the quantification of variables related to the membrane in the most diverse conditions. This factor results in the absence of generic models in the simulation software. This work aims at the rigorous phenomenological modeling of a pervaporation process using a polyetherimide membrane intended for the dehydration of ethanol. The model was developed on the Aspen Custom Modeler™ platform. Two approaches were implemented and compared: PERKAT and PERVAP models, being the last one the best model. The main variables of the process were evaluated. It was possible to verify the capacity of separation of the pervaporation module in breaking the barriers of the azeotrope, reaching a product with a high level of purity in ethanol, and recovery of up to 99.8%. In addition, the generic PERVAP model was exported to Aspen Plus™ and a cascade pervaporation unit was simulated. The specific energy consumption was calculated and compared to that of traditional separation processes. A 70% reduction was obtained compared to the most economical distillation configuration.

Methyl-Tert-Butyl-Ether Synthesis Reactor Modelling and Optimization Using an Aspen Custom Modeler

A pseudo-homogeneous model of methyl-tert-butyl-ether (MTBE) synthesis in a multi-tubular packed-bed reactor has been developed using an Aspen Custom Modeler (ACM) for selecting optimum operating strategies, for the maximization and enhancement of MTBE production, and isobutylene consumption, respectively. The model accounts for mass, energy and momentum balances; and the effectiveness factor is evaluated in a onedimensional pseudo-homogeneous model. The kinetic investigation contains kinetic rate expressions as given by the effectiveness factor for accounting the resistance of pellets in terms of mass and heat transfer. An activity coefficient can be used in order to systematically obtain a new steady-state solution. The model used literature-based correlations for the estimation of heat transfer coefficients. The value of the coefficient for gascoolant heat transfer can be adjusted by using a tuning coefficient in order to enrich the process data. Reasonable agreement was found between model predictions and data under similar conditions. The studies concerning model sensitivity compute the optimum temperature, pressure, feed flow rate, methanol/isobutylene ratio, heat removal rate, etc. of the reactor and suggest optimum operating conditions of the reactor.