Continuous Fixed-Bed Hydrosilylation Process Using Heterogeneous Platinum Catalysts

My doctorial research under the supervision of Dr. Winston Ho at The Ohio State University largely contributed to the areas of polymeric gas-separation membranes for fuel processing and proton-exchange membranes for fuel cells [1].  Joining Momentive Performance Materials in 2008, I have been very pleased to be able to contribute to the area of precious metal recovery and recycling using the in-situ fixed-bed adsorption technology [2] or the heterogeneous precious metal catalysis technology [3].  My work in separations over the past 10 years has greatly benefited the academic research community, as well as the chemical and organosilicon industries.  As part of the separations division for AIChE, I will present the recent process development work at Momentive Performance Materials, focusing on the manufacturing of platinum- and color-free organosilicon products using heterogeneous platinum catalysts [3], particularly in a fixed-bed continuous process, and I will present the potential significant industrial benefits achievable from this innovation.

   Currently, Speier’s chloroplatinic acid and Karstedt’s platinum-vinylsiloxane complex are commonly used for preparation and commercial manufacturing of organosilicon compounds. These platinum compounds are soluble in the organosilicon streams (homogeneous platinum catalysts), which have resulted in tremendous precious metal loss and an undesirable high color of un-distilled organosilicon products.  Faced with resource limitations, rising costs and increased demand of precious metals, a significant business effort has been ongoing to recover platinum from hydrosilylation streams within the organosilicon industry. 

   In this session, Siloxane-A will be used as a model organosilicon product to demonstrate the feasibility of manufacturing this material using a heterogeneous catalysis process, particularly in a continuous fixed-bed process.  Data has shown that in a fixed-bed heterogeneous catalysis process, higher Siloxane-A product conversion was observed with (a) increased temperature of the reactor column; (b) increased excess amount of one reactant; and (c) reduced feed rate of reactant mixture (increased residence time of hydrosilylation).  These observations are consistent with reaction kinetics of hydrosilylation.  With a reactor temperature of 140 °C at 10 mol-% excess of one reactant and a space time (ratio of the empty column space to the reactant mixture flow rate) of 10 minutes, a hydrosilylation conversion of 98 percent was achieved, which can be considered a reaction completion.  This is equivalent to a high space time yield (mass of product produced during a certain period of time with a certain amount of catalyst packing) of over 10 grams of product / (hour · gram of solid catalyst). 

   In terms of the manufacturing production rate, this process would potentially allow very high Siloxane-A product commercial output with a much intensified commercial-scale fixed-bed reactor, in comparison to the traditional batch-wise reactor.  In addition, the Siloxane-A from this new process was a Pt- and color-free premier organosilicon product with much improved quality when compared to traditional Siloxane-A produced by homogeneous catalysts.  At the time of the catalyst column changeover, such packed heterogeneous platinum catalysts could be easily recovered as they were retained stationary in the fixed-bed reactor, and these used solid catalysts could be processed in a manner (e.g., incineration) in which platinum could be recovered as an elemental metal.

   In this honorary session, I would like to thank Dr. Winston Ho for his support, enthusiasm, encouragement and guidance during my doctorial research at The Ohio State University.  I would also like to thank Winston Ho for his influence and inspiration throughout the past 11 years, which has led to the success of my careers in both academia as well as the chemical and organosilicon industries.

[1]  H. Bai and W.S.W. Ho, “Recent developments in fuel-processing and proton-exchange membranes for fuel cells”, Polym. Int., 60, 26-41, 2011 (Review Article).

[2]  H. Bai, “In situ platinum recovery and color removal from organosilicon streams”, Ind. Eng. Chem. Res., 51, 16457-16466, 2012.

[3]  H. Bai, “Manufacturing of platinum- and color-free organosilicon products using heterogeneous platinum catalysts”, Ind. Eng. Chem. Res., 53, 1588-1597, 2014.