Use of Distillation Simulation in Toll Manufacturing

When a distillation campaign at a toll manufacturer ran into some unexpected problems, simulation tools helped provide direction to meet the production target under a strict deadline.

Due to scheduling issues or lack of appropriate equipment, chemical companies often use the services of small toll manufacturers to generate products for customer trials or to meet unexpected product demand.

Toll distillation services were required by a client to upgrade the quality of one of its raw materials containing two closely boiling isomers. Since the reaction is carried out in a batch reactor, the mass of the batch could then be increased, the initial concentration of the reactant would be higher, and the batch reaction cycle time reduced to meet an unexpected demand for the final product. The client requires that the raw material not be identified. Henceforth, its principal components are designated as ISOM-1 and ISOM-2.

The reactant in the process is ISOM-1, which is purchased as a crude raw material nominally containing 78% ISOM-1 and 22% ISOM-2. The cost of the crude raw material was about $0.79/lb. The highest quality ISOM-1 commercially available was 95% ISOM-1 at a cost of about $2.57/lb. Purchasing high-quality ISOM-1 was not economically justifiable.

Consequently, a study was undertaken to technically and economically evaluate ways that the crude 78% ISOM-1 might be upgraded, using an outside toll distiller, to at least 96–98% ISOM-1 with minimal ISOM-1 loss in the bottoms stream.

This article describes the use of distillation simulation and process analysis techniques to guide the selection process for a distillation toller, develop the operating parameters for the distillation campaign, and provide day-to-day direction for the campaign to overcome unexpected timeline challenges caused by a delay in start-up, lower than anticipated column efficiency, a power outage, a pump seal failure, and underperformance of a rented cooling water chiller...