טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentShoham Patrascu Michael
SubjectScaled Down Hydrogen Production in Palladium-Based Membrane
Reactors: Process Design and Experimental
Investigations
DepartmentDepartment of Chemical Engineering
Supervisor Professor Emeritus Moshe Sheintuch
Full Thesis textFull thesis text - English Version


Abstract

This research is focused on understanding and developing scaled-down H2 production schemes in Pd membrane reactors.

Measurements of methane steam reforming (MSR) and ethanol steam reforming (ESR) in a Pd membrane reactor, equipped with a 40cm long, 14mm in diameter Pd on Alumina membrane, showed that high conversion and hydrogen recovery can be achieved with sweep flow and high pressures (over 90% conversion and over 80% H2 recovery) at 525°C for 0.25 NL/min CH4 feed flow rate. Increasing pressure above 10 bars did not lead to higher fluxes due to stronger permeance inhibition. A mathematical model predicts the reactor's performance well in terms of axial temperature profile, exit compositions and permeate flow, when membrane permeance is calibrated with experimental results. The apparent permeance is significantly lower (by ~80%) than values measured in pure H2 conditions.

An on-board autothermal membrane reactor producing pure hydrogen at atmospheric pressure was analyzed mathematically. The suggested design incorporates two reactors exchanging heat; an endothermic membrane reformer, and an exothermic oxidation-reactor fed by the reforming effluents. The analysis reveals that high thermal efficiency requires temperatures higher than 550°C, and that feeding the oxidation reactor with added fuel does not improve efficiency. The effect of catalytic kinetics is small. A detailed one-dimensional model is used to study the system in terms of thermal efficiency and production rate. These are favored by higher feed flow rates, resulting in higher temperatures. Axially distributing the oxidation feed mitigates hot spots and improves efficiency and production rate. Such a non-adiabatic autothermal system can operate at efficiencies of up to ~66% and expected power density of 25 kW/m2(Pd) at maximum MSR temperature of 700°C.

Experimental investigations on MSR in the above proposed system are presented, and the work is extended to include ethanol and glycerol as reactants. The axial distribution of oxidation feed is demonstrated for temperature control. The obtained performance of the 1.3L system is 0.15 kW (LHV) equivalent H2 flow rate at efficiency of ~25%. The same process leads to comparable performance when different fuel sources are used. The mathematical model, considering membrane permeance inhibition, is validated and used for optimization. This design serves as proof of concept for on-board pure H2 generators, with flexible fuel source type, feeding an adjacent fuel cell, and holds a great promise to reduce the need for special H2 transport and storage technologies for portable or scattered applications.