(159c) Changing Compositions Impacts Pressure Control

A chlorosilane intermediate material is purified via distillation campaigns on a shared asset. Customer requirements for higher quality resulted in a need to process the material twice through the same towers to remove different impurities. During the second pass the tower pressure was uncontrollable and the plant has lived with this for years. Pressures would rapidly swing up and down causing dramatic shifts in column temperature profile and inventories inside the tower. This has resulted in low yield and product quality challenges. Several attempts were made to resolve the issue but with no success.

A thorough investigation revealed the composition of the feed during this second pass was not compatible with the installed pressure control scheme. The tower runs at vacuum pressure for this product and the control scheme requires the presence of a higher volatility species to hold tower pressure. The volatile components are removed on the first pass leaving very little to hold pressure steady during the second. Once this was identified, the addition of a noncondensible was included in the pressure control scheme and this instantly resolved the problem. The process has been able to achieve record yields and reduce significant costs. No capital was needed to resolve this long term issue.