טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAharon Madai
SubjectReduction of Greenhouse Gases in a Loop Reactor and a Loop
Reactor Absorber
DepartmentDepartment of Chemical Engineering
Supervisor Professor Emeritus Sheintuch Moshe
Full Thesis textFull thesis text - English Version


Abstract

The loop reactor (LR) network, which consists of a closed sequence of several catalytic fixed bed reactors with periodical change of the feed/outlet position, has been studied theoretically and experimentally. There are two major advantages of such a reactor configuration. The first is the option of exploiting thermal storage capacity of the catalyst, which can act as a regenerative heat exchanger - this advantage has been pointed out in the case of low-concentration volatile organic compounds (VOC). The second advantage is that of a rotating hot-spot, with a pulse shaped profile. The loop reactor concept is extended here to a system of VOC oxidation coupled with CO2 adsorption in the cold area. The new system referred to as reactor adsorber (LRA), allow oxidizing very low VOC concentrations and adsorbing the CO2 in order to get a clean effluent.

Loop reactor: This work is the first experimental demonstration of the LR for catalytic oxidation of low-concentration volatile organic compounds (VOC). The constructed experimental system, incorporating three reactors in a loop with feedback control has been successfully operated for ethylene and methane oxidation. A typical characteristic of such a system is the formation of a moving thermal front. An appropriate control of the valves switching causes the thermal front to move inside the system in a loop (periodic steady state), preventing the system from extinction. Since downstream-moving pulses develop temperatures higher than the adiabatic rise, the understanding of the dynamics of the moving thermal front in the loop reactor system is critical for optimal reactor operation. Increasing feed flow rate and VOC concentration leads to higher front velocities and higher reactor maximal temperatures. The experimental results are in a good agreement with the developed analytical approximations and with the simulation results.

Loop Reactor-adsorber: We extend the loop reactor concept to VOC oxidation and periodic CO2 adsorption and desorption on a bed packed with catalyst and zeolite adsorber. Its operation incorporates three steps: combustion-adsorption, desorption and cooling. The timing of these steps, the corresponding flow rates as well as the effect of various operating condition, are examined using a one-dimensional reactor-adsorber model, in order to achieve an optimal design. The CO2 recovery degree achieved is 60-80% with a corresponding effluent concentration during desorption step that is 15-25 times the stoichiometric. An experimental system has been constructed and is currently being tested.