Experimental Analysis of Catalytic Gasification of Waste Polymers

1. Title:  Experimental Analysis of Catalytic Gasification of Waste Polymers

    

 (2) [Undergraduate] Student Researchers:

• Samuel O. Sanya

• Aliandra Barbutti

• Eric M. Lange

• Jade Moten

• UC Obiako

(3) Faculty Mentor:

• Dr. Jorge Gatica

   

 (4) Abstract

Catalytic gasification, or “gasification”, is one effective method which can be applied to promote low-temperature conversion of solid waste to energy.  This research focuses on advancing the knowledge of a catalytic gasification process as a potential in-situ resource utilization and waste management alternative.  This research has significance in a variety of engineering applications, but it is of particular relevance towards reducing landfill waste or as an in-situ resource generation system for space exploration beyond LEO. 

Furthermore, this process evolves through a reaction mechanism consisting of two liquid-phase oxidation reactions of long-chain polymers, complemented by two gas-phase reactions.  Using a laboratory grade reactor, gasification of polyethylene with a ruthenium catalyst was performed to produce a gas mixture consisting of hydrogen, methane, carbon monoxide, carbon dioxide, and water.

The gas mixture was analyzed by Gas Chromatography (GC) and post-processed using statistical analysis. Calibration of the GC using chromatographic standards enabled the formulation of an equation to calculate the composition of the gaseous products for different reaction times. Fundamental reactor design equations along with stoichiometry calculations were then used for determinations of percent polymer gasified as well as reaction selectivity of the gasification process.

            Additional characterization of the solid residuals was performed using Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM).  Quantification of the DSC spectra was used to correlate the thermal characterization of the residues with the unconverted polyethylene (or non-gasified) after the reaction was quenched. Lastly, the SEM provided information on the microstructure of the residues, their atomic composition, and preliminary assessment of the possibility of catalyst recovery.

            Additional research focused on the main fuel producing gasification reaction, the Sabatier (also referred to as “methanation”) reaction.  Determinations for the Sabatier reaction kinetics were made analyzing previously collected experimental data.  The kinetic parameters determined were the catalyst coefficient (“n”), the activation energy (“E_a”) , and the specific rate constant (“k_o”).  

The research is an outgrowth to previous kinetic determinations available for the reaction. Indeed, the data used to perform the kinetic analysis was originally collected by Lunde and Kester in the 1970s (Ind. Eng. Chem., Process Des. Develop., Vol. 13, No. 1, pp. 27-32, 1974).  While these authors also performed a kinetic analysis; their study was based on a simplified analysis and yielded only approximate kinetic parameters.  The kinetic analysis presented here is based on fundamental reactor design equations and was accomplished using numerical techniques not readily available at the time of Lunde and Kester’s analysis.  The experimental data was split into two sets of data: one set used for parameter estimation, and second set to be used for validation purposes. Comparison with the original approach followed by Lunde and Kester is also provided.

The following values were determined for the kinetic parameters of the Sabatier reaction: a catalyst coefficient of 0.26 ± 0.03, an activation energy of 65 ± 4 kJ/mol, and a specific rate constant of 8.9 ± 1.3 (mol/hr/kg/atm⁵).

A model with these kinetic parameters was formulated. Validation analysis yielded an R² value of 0.9969 for the results found here as opposed to an R²of 0.9661 found for the parameters reported by Lunde and Kester.