Manufacturing of Platinum- and Color-Free Organosilicon Products Using Heterogeneous Platinum Catalysts

Organosilicons are used as additives in a wide variety of products and generally provide or enhance specific attributes.  Organosilicon products can serve as surface-tension lowering agents, stabilizers for polyurethane foams, additives for coating applications, antifoams, emulsifiers, sealants, etc.  One of the key reactions for making organofunctional silicon-containing products (organosilanes and organosiloxanes) is the hydrosilylation reaction between the Si-H functionality and the unsaturated substrate.  Currently, Speier’s chloroplatinic acid and Karstedt’s platinum-siloxane complex are commonly used homogeneous hydrosilylation catalysts for organosilicon manufacturing.  As a result, platinum remains either in the organosilicon product or silane heavy waste.  This causes significant precious metal waste, high color in organosilicon products due to Pt presence, and black particle formation in end products due to Pt precipitation.

In this work, we demonstrate the application of heterogeneous precious metal catalysts (e.g., Pt/Alumina and Pt/Silica) for organosilicon manufacturing.  The hydrosilylation reactions using heterogeneous Pt catalysts can be carried out in a batch reactor or a fixed-bed reactor (FBR).  In a batch process, after hydrosilylation, precious metal catalysts can be easily separated from organosilicon products by simple filtration or decantation.  Thus, Pt- and color-free organosilicon products can be obtained.  When using an FBR, pre-mixed reactants are passed through the precious metal catalyst-packed hydrosilylation reactor to make Pt- and color-free organosilicon products and no separation step is required since catalysts are retained in the FBR.  A very high Space-Time-Yield of over 10 g product/(hour · g catalyst) has been obtained for manufacturing of certain organosilicon product in a fixed-bed process.  Thus, the process of using heterogeneous catalysts in a continuous FBR shows very significant advantages: (1) production is continuous, thus manufacturing related costs can be potentially significantly reduced; (2) high product output is possible to achieve with relatively small FBR; (3) potential may be realized in a much reduced footprint of, and investment in, production units; and (4) easy recovery of precious metals, since they are retained in the FBR. 

By using the heterogeneous precious metal catalysts in hydrosilylation reactions, the resulting organosilicon products showed very low precious metal content, much reduced color, and virtually no black particle formation caused by slow precious metal precipitation.  Thus, the quality of the resulting organosilicon products is significantly improved.  After the heterogeneous precious metal catalysts are consumed (lost reactivity), they can be processed in a manner that the precious metals are recovered as elemental metal.  These benefits potentially include product quality improvements and savings.