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Bala Subramaniam

Bala Subramaniam

Dan F. Servey Distinguished Professor

4156 Learned Hall 1530 W 15th St
Lawrence, KS 66045
Phone: (785) 864-2903
Fax: (785) 864-4967
E-mail: bsubramaniam@ku.edu

Education

  • BS, Chemical Engineering, University of Madras, India
  • PhD, Chemical Engineering, University of Notre Dame

Research Interests

 

Catalytic Reaction Engineering for Sustainable Fuels and Chemicals Production; Exploiting Supercritical and Gas-Expanded Liquids in Crystallization and Benign Chemicals Processing.

Exploiting Supercritical Fluids in Heterogeneous Catalysis

The main principles guiding the sustainable development and growth of industrial chemical processes are process intensification at mild conditions, minimization of waste and adverse environmental footprints, and enhancing inherent safety. During the last two decades, we have exploited near-critical media to develop novel catalytic processes that admit these attributes. Central to the innovations is the recognition that with relatively moderate changes in pressure, it is possible to "tune in" unique fluid properties (liquid-like density and gas-like transport) with near-critical media that are optimally suited for heterogeneous catalysis in ways such as these: (a) facile desorption and transport of heavy molecules (including coke precursors) in mesoporous catalysts, alleviating pore-diffusion limitations and improving catalyst effectiveness; (b) enhancing product selectivity; and (c) exploiting the enhanced heat capacity of near-critical media to ameliorate the problem of parametric sensitivity in exothermic reactions. Our group is currently focusing on exploiting these properties in several classes of heterogeneous catalytic reactions such as isomerizations, hydrogenations, Fischer-Tropsch synthesis, and alkylations.

PICTURE 1

Homogeneous Catalysis with Gas-Expanded Liquids

During the past decade, our group has exploited the pressure-tunable properties of "gas-expanded liquids" (GXLs) in a variety of liquid phase catalytic systems. To generate GXLs, we have exploited gases (such as CO2 and light olefins) whose critical temperatures (Tc) are in the vicinity of the reaction temperature (T) generally, T= 0.7-1.3Tc (K). Upon compression to moderate pressures (tens of bars), such gases dissolve appreciably in most conventional solvents and volumetrically expand them. The increased free volume of the resulting GXL phase (relative to the conventional liquid phase) accommodates permanent gases such as O2, CO and H2 in dramatically high concentrations. Remarkably, syngas composition can be tuned from being H2 lean (H2/CO < 1) in conventional solvents to H2 rich (H2/CO > 1) in CO2-expanded liquids, which dramatically shifts the product selectivity to the desired linear aldehyde product during olefin hydroformylation.

In collboration with academic and industrial chemists, we have demonstrated several GXL-based catalytic reaction engineering concepts including (a) highly selective hydroformylation of higher olefins at mild conditions (~40 bars, 60° C); (b) inherently safe, liquid phase ethylene epoxidation process that totally eliminates CO2 formation as a byproduct; (c) a spray reactor concept for the single step formation of high purity terephthalic acid with reduced solvent burning. Quantitative sustainability analyses of GXL-based process concepts point toward broader applications of GXLs beyond these, extending also to biomass-derived substrates.

PICTURE 2

Nanoparticle crystallization and coating with dense phase carbon dioxide

Replacement of traditional solvents with dense carbon dioxide (because of its pressure-tunable physical/transport properties and environmentally-benign nature) is receiving increased attention in crystallization processes. Specifically, we have employed CO2 as an antisolvent to precipitate polar compounds from solution, including nanoparticles of pharmaceutical compounds (insulin, paclitaxel and biological compounds) and transition metal complexes with unique function. We have also developed a fluidized-bed coating process similar to the Wurster coater using dense CO2 as the fluidizing medium as well as a drying agent. We have uniformly coated tablets, stents and other biomedical devices for controlled-release function.

Our group has also exploited GXLs to synthesize nanomaterials of transition metal complexes with unique function. For example, Co(salen) based nanoparticles provide stoichiometric O2 storage capacity and room temperature NO disproportionation activity. This discovery has led to the possibility of bottom-up design of metal nanoparticles with targeted functional property.