Decalin Dehydrogenation for In-Situ Hydrogen Production to Increase Catalytic Cracking Rate of n-Dodecane

Date of Award

2018

Degree Name

M.S. in Chemical Engineering

Department

Department of Chemical Engineering

Advisor/Chair

Advisor: Matthew DeWitt

Abstract

Catalytic cracking of paraffinic hydrocarbons is a widely utilized industrial process, but catalyst deactivation over time requires regeneration or replacement of the catalyst bed. A gaseous hydrogen co-feed can be used to promote hydrocracking and decrease deactivation of the catalyst due to coke formation or active site poisoning. One potential alternative approach to extend the lifetime of a cracking catalyst is to generate molecular hydrogen in-situ via catalytic dehydrogenation of a cycloparaffin. In this effort, studies were performed using model compounds to investigate the impact of catalyst configuration and operating conditions on overall performance. For the purpose of this testing, decalin was selected as a model cycloparaffin, with n-dodecane used as a model n-paraffin compound. A blended cycloparaffin/n-paraffin feed was studied in a dual catalyst flow reactor system, containing both a dehydrogenation and cracking catalyst. Testing was performed with either the dehydrogenation catalyst upstream or with the two catalysts physical mixed. Products and reactant conversion rates from these studies were compared to those from a baseline n-paraffin cracking study, with no cycloparaffin or dehydrogenation catalyst present.Several commercially available Zeolite catalysts were initially screened for n-dodecane cracking activity to identify an appropriate cracking catalyst for further study. A Zeolite Y catalyst provided adequate n-dodecane reactivity for observation of reactor configuration impact. Prior to the dual-bed and mixed-bed studies, a synthesized Pt/Al2O3 dehydrogenation catalyst was studied independently with neat decalin feed as well as a blended decalin/n-dodecane feed, for the purpose of determining appropriate reactor conditions to be used in subsequent testing. Using the selected Zeolite Y catalyst, extended duration testing was performed at 400°C and 500 psig to characterize the activity and deactivation rate for n-dodecane cracking, to provide a baseline for subsequent comparison. Similar testing was performed with the Zeolite Y catalyst to investigate the impact of blending decalin or naphthalene with the normal paraffin.A dual-bed reactor configuration utilized the Pt/Al2O3 dehydrogenation catalyst in-line and upstream of the Zeolite Y catalyst, with a 1:1 volumetric blend of decalin/n-dodecane at 400°C and 500 psig. The dehydrogenation bed successfully promoted decalin dehydrogenation for generating in-situ molecular hydrogen. However, minimal initial n-dodecane conversion was observed, which was speculated to be due to strong adsorption of naphthalene dehydrogenation product onto the Zeolite Y catalyst, reducing the number of available active sites. After 240 minutes, n-dodecane conversion in the dual-bed reactor system was higher than the baseline, while decalin conversion was very high for the entire duration. In a mixed bed configuration, the two catalyst beds were physically mixed with identical testing conditions. This configuration was intended to reduce the absolute naphthalene concentration on the Zeolite Y catalyst and eliminate the inhibition which occurred in the dual bed configuration. The mixed bed configuration promoted higher initial conversion and lower deactivation rate compared to all other feed/reactor configurations. Overall, it was determined that catalytic dehydrogenation of a cycloparaffin can be successfully employed to increase conversion of a normal paraffin in a catalytic cracking reactor, although future work could further optimize catalyst selection/loading, reactor configuration, and reaction conditions.

Keywords

Chemical Engineering, catalytic paraffin cracking, catalytic cycloparaffin dehydrogenation, fixed-bed flowing reactor, catalyst deactivation, decalin

Rights Statement

Copyright © 2018, author

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