Reaction Kinetics and Reactor Modelling For Crude Glycerol Autothermal Reforming to Hydrogen Rich Gas

Abstract

Biomass as a source of hydrogen production has gained great cognizance amongst researchers. The growing trend of energy is geared towards renewable energy sources for which crude glycerol serves as a viable source for hydrogen production. The most widely studied feedstock for hydrogen production is methane (CH4). In this work, crude glycerol which is a bi product in biodiesel production is considered because it produces higher number of moles of hydrogen than methane and also, adds up to the effective use of crude glycerol as a source of hydrogen. The kinetics for this system was studied over S/C ratio of 2.6 and O2/C 0.125 using 5% Ni/CeZrCa. Both power law and mechanistic kinetic models were studied. The overall power law model for crude glycerol autothermal reforming process was investigated with a pre-exponential factor of 4.3×1010 mol/gcat.min and activation energy of 8.78×104 J/mol. The reaction orders with respect to crude glycerol, water and oxygen are 1.04, 0.54 and 1.78 respectively. The absolute average deviation of 5.84 % which showed a good correlation between the predicted and experimental rate. Afterwards, both power and mechanistic models were developed for steam reforming, total oxidation and CO2 Methanation. For steam reforming, Eley Rideal approach best described the rate with for the surface reaction step being the rate determining step (AAD<10 %). The kinetics of Total oxidation reaction was best described by the power law model with an AAD of less than 1 %. The mechanistic model that describes the TOR process was the molecular adsorption of crude glycerol with an AAD of 14.6 % via Langmuir Hinshelwood Hougen- Watson approach. CO2 methanation yielded an AAD of 5.8 % for the adsorption of carbon iii dioxide (CO2) by the Eley Rideal mechanism. There was no kinetic data on CO thus, the water gas shift reaction was not considered in this study. Numerical modelling was performed based on the derived kinetics using both finite difference and finite element techniques. Both one (1) and two (2) dimensional reactor models were developed based on pseudo homogenous and heterogeneous models. The average absolute deviations obtained for one (1) dimensional model were 10% and 12.73% for pseudo homogenous and heterogeneous model respectively. For the 2–dimensional models, an AAD of 12.08 % for pseudo homogeneous and 13.1 % for heterogeneous was obtained where a 1-dimensional pseudo homogenous model was found to accurately model the fixed bed reactor. The results obtained were validated and it showed good correlation with experimental values. Thus, the obtained kinetic and numerical modelsaccurately depict the system under study.