Dirk Willard, contract staff engineer
Hemlock Semiconductor, Hemlock, Mich.
At our batch specialty chemicals plant the production manager wants us to use waste isohexane as a cleaning solvent. He proposes pumping the isohexane, which is available from a nearby process, into our columns prior to cleaning for startup. The commissioning engineer opposes using it on the grounds that a safer cleaning solvent, such as spent methanol or acetone, could be available. He suggests using methanol because it's cleaner. We're cleaning two knockout pots and two distillation columns that have been used for several months in the production of fish oil (eicosapentaenoic acid and docosahexaenoic acid). The material safety data sheet for fish oil shows the following: closed-cup flash point, 149°C; auto-ignition point, unknown; and conditions to avoid, "oxygen." The columns each contain one eight-ft. bed of structured packing. Normally, the columns operate at a maximum of 100-torr with electric thermosiphon reboilers. The condensers use chilled glycol. (See Figure 1 for proposed cleaning process.) What do you think of the commissioning engineer's objection? Is there a better approach for cleaning the process?
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