(566d) New Process Development for Precious Metal Recycling and Premier Organosilicon Product Manufacturing

Authors: 
Bai, H., Momentive Performance Materials
Bahr, S., Momentive Performance Materials Inc.



Organosilicon materials 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 is hydrosilylation – the reaction of a silanic-hydrogen functional compound and an olefin in the presence of a precious metal catalyst.

Currently, Speier’s chloroplatinic acid and Karstedt’s platinum-siloxane complex are commonly used homogeneous hydrosilylation catalysts for the preparation and commercial manufacturing of organosilicon compounds.  These platinum compounds are soluble either in the organosilicon product or the distillation heavy waste stream.  This results in significant precious metal waste, undesirable high product color, and black particle formation due to precipitation of reduced Pt. Resource limitations, increased demand and the high cost of precious metals (e.g., platinum) have led to focus on recovery of platinum from organosilicon hydrosilylation streams as an important source of cost savings in the chemical industry that also improve product quality.

In this paper, we will share two new processes developed at Momentive which have proved to be successful and cost-effective for precious metal recycling and the manufacture of premier organosilicon product.  By applying these new processes, the resulting hydrosilylation products showed very low precious metal content, reduced color and virtually no black particulate formation.  Thus, the quality of the resulting organosilicon products has been significantly improved.  In addition, the precious metals used during hydrosilylation reactions can be recovered as elemental metal.

Momentive’s new process for precious metal recovery can be described as an in-situ fixed-bed adsorption technology [a].  In this process, fixed-bed columns are designed to treat product streams directly between a continuous organosilicon production unit and product storage containers or directly between a continuous distillation unit and distillation heavy waste containers.  As a result, several significant process advantages have been recognized: (1) the precious metal removal is in-situ and continuous (no extra operational cost); (2) process streams are already at desirable high temperatures before entering the precious metal recovery unit (no additional heating requirement); (3) only minor modifications of the existing facilities are required (in-situ process); and (4) highly efficient precious metal recovery (> 90%) and desirable precious metal loading (> 2%) on scavengers have been achieved.  These results have been demonstrated both in lab and commercial operations.

Another new process is the use of heterogeneous precious metal catalysts (e.g., Pt/Alumina, Pt/Silica, etc.) to manufacture platinum- and color-free organosilicon products via hydrosilylation.  Use of heterogeneous precious metal catalysts allows hydrosilylation reactions to be carried out either in batch or fixed-bed reactor (FBR) configurations.  Compared to a batch-wise process, a continuous FBR process shows several significant advantages: (1) production is continuous (lower operational cost); (2) based on the high space-time-yield achieved in lab demonstration, high product output is possible at relatively small commercial-scale FBR; (3) potential for reduced footprint and investment; and (4) easy recovery of precious metals since they are retained in the FBR. 

At the end of both processes, precious metals can be refined and recovered as elemental metal.

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

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