Recipient Organization
UNIVERSITY OF WASHINGTON
4333 BROOKLYN AVE NE
SEATTLE,WA 98195
Performing Department
Bioresource Science and Engineering
Non Technical Summary
Ethylene is one of the major products of the petroleum industry, and the oligomerization of ethylene is a process that is responsible for generating a large numbers of chemicals and intermediates, such as plastics, plasticizers, lubricants, and surfactants. In this project, we will study oligomerization reactions with the ethylene at supercritical conditions (temperature greater than 9.4º C and pressure greater than 50.6 bar). It is well known that supercritical conditions promote greater solubility for organic compounds, so it is hypothesized that supercritical ethylene suppresses coke formation and affects the selectivity of oligomerization reactions. We will carry out solubility studies as a basis for analysis, and will investigate the mechanisms of oligomerization of subcritical and supercritical ethylene over nickel-based heterogeneous catalysts.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
The overall goal of this proposal is to start a new research direction, focused on the use of supercritical fluids on heterogeneous catalysis. Specifically, the proposed work involves a novel, environmentally friendly route for production of Alpha olefins via oligomerization of ethylene. This route: 1) uses heterogeneous catalysts, thereby not requiring organic solvents; 2) takes advantage of the low critical point of ethylene (9.4 °C and 50.6 bar) to carry out oligomerization of ethylene at supercritical conditions, 3) uses properties of supercritical ethylene as a reaction medium to enhance reaction rates and remove coke from the catalysts. The process proposed includes temperatures around 120 -200°C to promote the reaction kinetics of oligomerization reactions, and pressures above 50.6 bar to ensure desorption of long chain oligomers from the catalyst surface, preventing catalyst deactivation. This new process is unique because it allows catalyst regeneration in-situ, building on kinetic and thermodynamic fundamental concepts to develop an application for heterogeneous catalysis in supercritical fluids.The following specific research objectives summarize the main questions we will address with the reseach work:1) To understand how the solubility of coke molecules and their precursors in ethylene varies with process conditions, and how this solubility correlates with catalyst activity and regeneration (Task 1, Task 3);2) To identify the overall reaction pathways and calculate kinetic rates for the elementary steps in the oligomerization process at supercritical conditions, highlighting the differences between the steps and their rates under sub-supercritical and supercritical conditions (Task 2, Task 3)
Project Methods
Task 1. Solubility Studies: In order to undertand the effect of supercritical ethylene on oligomerization from a molecular point of view, we need to know solubility of the coke molecules and their precursors at the exact conditions we will be doing the oligomerization reactions, so the first part of the project will investigate how the solubility of long oligomers changes as we move from subcritical to supercritical conditions. Samples of hexene, octane, decene, dodecene, and actual coke from oligomerization experiments will be placed (one at a time) in the packed bed reactor, without the catalyst. Initially, we will perform control experiments with helium as carrier gas, to verify the possibility that the coke molecules could leave the bed due to volatility. Next, we will flow ethylene at the same flow rate, temperature and pressure at which we will perform the runs in future tasks. We will use an impinger to collect the long oligomers. These experiments will provide the baseline information required for the interpretation of data in the reaction and regeneration studies.Task 2. Overall Reactions Pathways: The goal of this task is to identify the overall reaction pathways involved in oligomerization, comparing supercritical conditions to sub-supercritical. The strategy for the identification of the reaction pathways will consist in varying the contact time of the ethylene molecules with the catalyt, or in other words, we will vary the WHSV by changing the ethylene flow. This will cause products from primary reactions to desorb before further reactions, allowing their identification. flow. This will cause products from primary reactions to desorb before further reactions, allowing their identification.Task 3. Kinetic Model: Once the reaction pathways are known based on results from Task 2, we will fit the proposed model to experimental data in order to estimate the rates of individual reactions. For this purpose, we will carry out experiments with varying mass of catalyst in the bed, in such a way that we can apply the design equation for a packed bed reactor for each one of species. Once the kinetic model is constructed and rate constants for individual reaction pathways are calculated, we will assess the success of this Task by testing our model predictions against thermodynamic calculations for equilibrium composition obtained by minimizing the Gibbs free energy of the system. A comparison with experimental data obtained in the continuous system will serve as additional confirmation of the model accuracy.