Background My PhD Project concerns with converting short chain organic oxygenates to fuel range hydrocarbon. This project is part of a campus wide effort to develop sustainable energy at Mississippi State University. Under this program a collaborative research group has been established called Sustainable Energy Research Center (SERC), www.serc.msstate.edu, comprising of researchers in the departments of Chemical Engineering, Forest Products, Chemistry, Agricultural and Biological Engineering to name a few. As part of this endeavor, our group under my advisor, Prof. Mark White has been developing non-Fisher Tropsch technology for biomass derived syngas to be converted to gasoline. One approach to this challenge is to first convert syngas to alcohols and then convert alcohols to gasoline. This approach while effective yields oxygenate by-products. My Project has been to study the use of titania as a catalyst to convert these by products to fuel range hydrocarbon to increase the viability of the biomass-to-gasoline technology.
Accomplishments The main oxygenate by-products formed during conversion of syngas to alcohols are acetic acid, acetaldehyde, methyl acetate and acetone. Hence initially, I performed batch reactor studies using both acid catalysts like H+/ZSM-5 and silica alumina, and base catalysts like titania and magnesium oxide. It was concluded that base catalysts yield almost no coke when reacted with these oxygenates. Then I studied interactions between these oxygenates by reacting pairs of these compounds on titania in a batch reactor. The results were documented and showed no prohibitive interactions. Then I made mechanistic studies of each of the compounds using quantum mechanics. Molecular modeling software called Spartan from Wavefunction Inc was utilized for this purpose. Hartree – Fock method was used to predict thermodynamic energies.
Acetic acid has been shown in literature as one of the most coke-causing compounds in both syngas derived products as well as in bio-mass pyrolysis products when tried to convert to hydrocarbon. Hence titania as a catalyst has all the more significance as it can convert acetic acid to acetone and subsequently acetone to mesitylene. I decided to study the acetone condensation to mesitylene much more closely as it forms an important link in converting acetic acid to hydrocarbon. Also, Acetone itself can be converted to liquid hydrocarbon. I studied this reaction in high pressure conditions similar to those employed in syngas conversion to alcohols. This was done keeping in mind the possibility of using a single bed to convert syngas to gasoline including all by-products. I had excellent success in this endeavor and reported high yield and selectivity of mesitylene from acetone. The data was presented in national meetings and I am presently writing a paper on the results. As alcohols can be easily converted to gasoline range hydrocarbon on zeolite catalyst, I wanted to show that alcohols were essentially inert on titania. This would ensure that only by-products are converted to hydrocarbon on titania and alcohols are retained as such. In course of making this study, when ethanol was reacted on titania, I found that tiny amounts of 1-butanol was found. I immediately saw an opportunity to upgrade alcohols in carbon number. This is of significance because higher alcohols (>C2) have higher energy content than lower ones. This would make them better fuel additives than ethanol. Also, previous research in our lab showed that higher alcohols can give better yields of gasoline when reacted on zeolites than methanol or ethanol. Hence I decided to pursue making 1-butanol from ethanol as well. Pacific Northwest National Laboratories (PNNL) has been working on direct conversion of syngas to higher alcohols but was successful only to make ethanol and not substantial yields of any higher ones. Hence our group collaborated with PNNL and I travelled to Richland, WA to work as an intern at PNNL for 10 weeks to show that titania can be used to convert ethanol to 1-butanol. I was successful in doing so. Also, my interaction with scientists at PNNL was a rich experience for me. After returning to Mississippi State University, I continued to work on converting ethanol to 1-butanol not only on titania but also on catalysts with similar known surface chemistry. I found that Zirconium dioxide (Zirconia) could convert ethanol to 1-butanol with much better yields than titania. Also, while titania made 1-butanol as the highest alcohol from ethanol, zirconia could convert ethanol to not only 1-butanol but also various pentanols, hexanols and even octanol. The data will be soon documented in a publication.
For the past few weeks I have been finishing up my research by studying the surface chemistry of titania. This includes Surface area analysis, Fourier Transform Infra red Spectroscopy, Transmission Electron Microscopy, Scanning Electron Microscopy, X-ray diffraction Microscopy and Thermogravimetric Analysis techniques. Also, I have been studying the surface active sites of titania using acetone condensation to mesitylene as a probe reaction. This is being performed by selectively poisoning the catalyst and running the reaction to study the loss in rate of reaction.
From the work that I performed for the last 31 months, I gave 4 presentations, received 1 provisional patent and was selected for 1 award.