Transesterification (or esterification) is a widely used chemical reaction in the chemical industry. Presently used homogeneous (liquid) catalysis is plagued with downstream product separation difficulties which has led the quest for heterogeneous (solid) catalysts. However, using heterogeneous catalysis is still a challenge due to mass transfer limitations in liquid/liquid/solid (L/L/S) interface corresponding to immiscible triglyceride/alcohol/catalyst phases, respectively. This proposal intends to use a novel phenomenon, heterogeneous emulsion catalysis, to remove the mass transfer bottleneck of L/L/S heterogeneous catalytic reactions.
Intellectual Merit: Our approach is to address mass transfer limitations exhibited by immiscible L/L systems while ameliorating downstream catalysts separation issues by developing a heterogeneous catalyst that acts as an emulsifier (amphiphile) which essentially will be positioned at the interface between the two immiscible liquids. According to our concept, the amphiphilic catalyst first brings the two hydrophilic and hydrophobic liquid molecules together and due to the emulsification properties of the catalyst, stabilizes the emulsion. In the mean time, the catalyst will lend its active sites for the reaction (in this case transesterification) to occur. When the catalyst is separated after reaction, the emulsion loses its stability and will coalesce to, now the products, fatty acid methyl esters and glycerol which are hydrophilic and hydrophobic liquids, respectively. This process that has eluded our attention may open up a new line of catalysts and catalytic processes that may be propagated to many applications including biorenewable energy production.
We have proven that this concept is feasible via a series of preliminary studies that have already resulted in a couple of peer reviewed publications. During these studies, we observed that titanium isopropoxide in its monomeric, dimeric, trimeric and tetrameric forms helped formation of stable nanoemulsions when subjected to ultrasonication. Further reaction of these systems resulted in fatty acid ethyl esters with some exhibiting above 133% yield increase as compared to conventionally mixed systems.
This concept of heterogeneous amphiphilic-catalytic hybrid inorganic polymers is novel and there is a knowledge gap in just about every aspect of such a catalytic system. The beauty of this concept is the ability to control the size of the heterogeneous catalyst particles by controlling the amount of water in the solution which immensely helps testing our central hypothesis, i.e., partially polymerized metal alkoxides acts as heterogeneous amphiphilic catalysts in transesterification reactions. The rationale behind this hypothesis is that the large surface area of the nanoemulsions will provide for high reaction rates. The fundamental scientific question we plan investigate is how an amphiphilic heterogeneous catalyst will function in such a nanoemulsion environment. The objectives of this application are to:
1. Evaluate the effect of particle size (metal isopropoxide oligomerization), component concentration and ultrasonic parameters on formation and stability of nanoemulsions and
2. Determine the effect of oligomerization of metal isopropoxides on fatty acid methyl esters yield.
Broader Impacts: This innovative and creative work will generate enormous economical and environmental benefits in addition to advancing our present understanding of science related to emulsion catalysis. A major educational objective is to integrate research into education via an innovative technique named "Application Centered Training" (ACT) which engages students early in their undergraduate career with real world engineering problems. This program is expected to introduce the nexus between science, math and engineering and address several issues engineering education faces today. Research Experience for Under Achieving Students (REUAS) is a concept the PI would like to experiment where minority and under represented students who are academically at risk (<2.5 GPA and < 26 standard ACT scores) will be provided with research opportunities early in their undergraduate program. The progress of these students will be tracked during the course of their undergraduate career to evaluate whether exposing them into practical research helps them resuscitate their excitement towards engineering education and the degree program.
Reactions that involve two liquid-phase reactants that are immiscible with each other are challenging to conduct due to limitations associated with mass transport. Conducting such reactions becomes even more precarious when a solid catalyst is needed to drive the reaction forward. This study was conducted with the intention of developing: 1) a catalyst that has emulsification properties to help in making the immiscible reactants dissolve in each other alleviating mass transport issues associated with such systems and 2) a process where the catalyst will phase-transform (from liquid-phase to solid-phase) while the reaction is ongoing so that the spent catalyst could be separated from the medium once the reaction is complete. To elucidate this concept, the transesterification reaction was selected. Metal-alkoxides that possess acidic and basic properties (to catalyze the reaction), amphiphilic properties (to stabilize the alcohol/oil emulsion) and that can undergo condensation polymerization when heated (to separate as a solid subsequent to the completion of the reaction) were used to test the concept. Studies included elucidating the effect of metal sites and alkoxide sites and their concentration effects on transesterification reaction, effect of various metal alkoxide groups on the phase stability of the reactant system, and kinetic effects of the reaction system. The studies revealed that several transition-metal alkoxides, especially, titanium and yttrium based, responded positively to this reaction system. These alkoxides were able to be added to the reaction medium in liquid phase and were able to stabilize the alcohol/oil system. The alkoxides were selective to the transesterification reaction giving a range of ester yields (depending on the catalyst used). It was also observed that transition-metal alkoxides were able to be recovered in the form of their polymerized counterparts as a result of condensation polymerization subsequent to completion of the transesterification reaction. This project resulted in five peer-reviewed publications (of which four has already been published/accepted and one under review). Results of this work have been presented in several international conferences. This work also resulted in one doctoral dissertation, one undergraduate thesis and also provided research experience to four undergraduate students (including those who belong to minority ethnic groups or are under-represented in Engineering).
