Grantee Research Project Results
1999 Progress Report: Heuristic Reactor Design for Clean Synthesis and Processing - Separative Reactors
EPA Grant Number: R825370C055Subproject: this is subproject number 055 , established and managed by the Center Director under grant R825370
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: The Consortium for Plant Biotechnology Research, Inc., Environmental Research and Technology Transfer Program
Center Director: Schumacher, Dorin
Title: Heuristic Reactor Design for Clean Synthesis and Processing - Separative Reactors
Investigators: Mullins, M. E. , Kline, Andrew A. , Rogers, Tony N.
Institution: Michigan Technological University
EPA Project Officer: Aja, Hayley
Project Period:
Project Period Covered by this Report: January 1, 1998 through January 1, 1999
RFA: Exploratory Environmental Research Centers (1992) RFA Text | Recipients Lists
Research Category: Center for Clean Industrial and Treatment Technologies (CenCITT) , Targeted Research
Objective:
This project intends to develop a prototype Heuristics and Reactor Design (HARD) system to aid engineers in the conceptual design and engineering of clean chemical processes. There are two core tasks in the initial phase of the effort both aimed at separative reactor processes: the development of mathematical models for 1) the reactive distillation process and 2) catalytic membrane reactors. The resulting models can be used as a screening tool to determine the suitability of a given reaction for these processes. The completed models will be integrated into an expert system resource along with other existing models for chemical reactor design.
Progress Summary:
Currently there are no existing design models for catalytic membrane reactors; and although commercial software from several simulation companies is available for distillation related modeling, they are not specifically tailored to reactive distillation process. Therefore, it is important to construct a model based on the unique features of reactive distillation in a packed column. The reactive distillation model was completed in 1998. The work over the past year has focused on the development and analysis of models for catalytic membrane reactors; especially those based upon zeolite membrane systems.
Supported zeolite membranes can have high selectivity for the separation of gas mixtures, but typically have low permeation rates. Several methods have evolved for the preparation of continuous ZSM-5 membranes over the last ten years. Most of these are passive techniques that utilize precipitation onto the surface from dilute solutions or the surface application of gel precursors. We have investigated the use of an electrophoretic deposition method based on the in-situ hydrothermal method which was developed previously. Application of an electric potential across the support in solution allows for improved control of membrane density and thickness. The membranes have been characterized via SEM and X-ray diffraction. The rates of gas permeation through the membranes has been characterized using H2, N2, Ar, n- and iso-butane, SF6 and toluene in a continuous flow system. The membranes have been determined to be crack free and have selectivity's similar to those published in the literature. The major difference between membranes prepared with the electrophoretic method and those prepared by existing methods is an improved overall transfer rate and better control over the membrane properties. Higher transfer rates in zeolite films may facilitate the use of these membranes in separative reactor systems.
Zeolite ZSM-5 is chemically and thermally stable and has previously been used as an adsorbent in pressure swing adsorption plants. However, the practical application of zeolites in the form of inorganic membranes has been limited due to low specific permeation rates that have been obtained. The rates of permeation, and hence the total molar fluxes, directly depend upon the membrane thickness. In turn, a requirement for producing a thin-film membrane is that the zeolite crystallite size should also be very small. Several techniques have been developed in order to obtain a thin, uniform zeolite layer on porous substrate materials. One of these methods is the dilute precursor solution synthesis, or sol-gel, process. Previous work using a hydrothermal synthesis method has produced supported zeolite films 10 microns thick with 2-micron crystals via precipitation. Our investigation has focused on modifying these dilute solution hydrothermal synthesis methods by using electrophoretic deposition. By its application we hope to control and reduce the membrane thickness and individual crystallite size. In this process an applied electric potential is used to attract the zeolite particles to a porous ceramic substrate surface prior to precipitation from solution. A systematic study of the ZSM-5 films produced via electrophoretic deposition has been conducted. The physical and chemical composition of the membranes has been characterized via SEM and X-ray diffraction. The gas permeation characteristics for each membrane were characterized using H2, Ar, N2, n-butane, iso-butane, toluene, and SF6. Residual ZSM-5 powder from the synthesis was also used to characterize the film material's adsorption and diffusion parameters.
To evaluate the membranes produced, a permeation cell apparatus was designed to hold the membrane tubes. It allows for two inlet streams, a sweep stream of pure argon and the feed containing the gas species of interest. One stream is directed down the axis of the membrane and the other stream flows around the outside of the tube, i.e.-the membrane side. Under normal operations the feed enters the system on the membrane side of the tube. Omega mass flow control valves maintain a steady flow on both streams. The cell is constructed of 316 stainless steel, approximately four inches in length and 1-3/4 inches in diameter. The cell is placed within an automatically controlled tube furnace allowing for isothermal diffusion studies at various temperatures. A sampling capillary for the mass spectrometer is inserted through septa at the two outlets of the permeation cell to provide "real-time" analysis of the outlet gases.
The approach used in the membrane reactor model is based upon a Stephan-Maxwell approach for mass transport. Since the diffusion in a microporous membrane can be in the form of discrete molecules, a continuum approach similar to Fick's law is no longer appropriate. The inadequacy of the Fickian approach is particularly pronounced for multi-component flux analysis. An algorithm based on the Stephan-Maxwell model is used to predict the behavior observed in laboratory membrane permeation studies.
In order to explain the lower permeation rates a thermodynamic model of the transport process must be used. It is necessary to use a modeling system that can account for the non-Fickian thermodynamics of a zeolite system, such as the Maxwell-Stefan approach. Krishna and Wesselingh present an extensive review of this subject. This multicomponent form equates the vector of micropore molar fluxes, Ns. Here is the fluid mixture density, is the porosity of the particles, and the total saturation concentration is qsat. [Ds] is the square matrix of Fick micropore diffusivities. Finally, Q is the gradient of fractional surface occupancy across the membrane.
A catalytic membrane reactor model has been developed based upon a Stephan-Maxwell formulation for mass transfer, and incorporated into a radial reactor model. Comparisons to in-house permeation studies for zeolite membranes are being completed. This algorithm was incorporated into a simple radial reactor model to predict the performance of tube-type catalytic membrane reactors. In the near future, a comparison of model results to actual data on dehydrogenation of toluene will be made.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this subprojectSupplemental Keywords:
RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Sustainable Industry/Business, cleaner production/pollution prevention, Sustainable Environment, Chemistry, Technology for Sustainable Environment, Monitoring/Modeling, Civil/Environmental Engineering, computing technology, Civil Engineering, New/Innovative technologies, Engineering, Environmental Engineering, cleaner production, clean technologies, clean technology, reactors, modeling, computer simulation modeling, membrane reactors, Heuristics and Reactor Design (HARD) system, chemical processing, mathematical models, pollution preventionMain Center Abstract and Reports:
R825370 The Consortium for Plant Biotechnology Research, Inc., Environmental Research and Technology Transfer Program Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R825370C032 Means for Producing an Entirely New Generation of Lignin-Based Plastics
R825370C042 Environmentally Conscious Design for Construction
R825370C046 Clean Process Advisory System (CPAS) Core Activities
R825370C048 Investigation of the Partial Oxidation of Methane to Methanol in a Simulated Countercurrent Moving Bed Reactor
R825370C054 Predictive Tool for Ultrafiltration Performance
R825370C055 Heuristic Reactor Design for Clean Synthesis and Processing - Separative Reactors
R825370C056 Characterization of Selective Solid Acid Catalysts Towards the Rational Design of Catalytic Reactions
R825370C057 Environmentally Conscious Manufacturing: Prediction of Processing Waste Streams for Discrete Products
R825370C064 The Physical Properties Management System (PPMS): A P2 Engineering Aid to Support Process Design and Analysis
R825370C065 Development and Testing of Pollution Prevention Design Aids for Process Analysis and Decision Making
R825370C066 Design Tools for Chemical Process Safety: Accident Probability
R825370C067 Environmentally Conscious Manufacturing: Design for Disassembly (DFD) in De-Manufacturing of Products
R825370C068 An Economic Comparison of Wet and Dry Machining
R825370C069 In-Line Copper Recovery Technology
R825370C070 Selective Catalytic Hydrogenation of Lactic Acid
R825370C071 Biosynthesis of Polyhydroxyalkanoate Polymers from Industrial Wastewater
R825370C072 Tin Zeolites for Partial Oxidation Catalysis
R825370C073 Development of a High Performance Photocatalytic Reactor System for the Production of Methanol from Methane in the Gas Phase
R825370C074 Recovery of Waste Polymer Generated by Lost Foam Technology in the Metal Casting Industry
R825370C075 Industrial Implementation of the P2 Framework
R825370C076 Establishing Automated Linkages Between Existing P2-Related Software Design Tools
R825370C077 Integrated Applications of the Clean Process Advisory System to P2-Conscious Process Analysis and Improvement
R825370C078 Development of Environmental Indices for Green Chemical Production and Use
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
Main Center: R825370
155 publications for this center
36 journal articles for this center