Dangers of Component Trapping in Distillation: : An Industrial Methanol Distillation Case Study

The formation of organic acids due to secondary reactions is an issue in industrial methanol synthesis. As such, to avoid the formation of acidic regions in the units downstream of the methanol synthesis loop, caustic dosing is a common practice in the industry. Despite these precautions, some organic acids can be left in crude methanol discharge from the methanol synthesis loop. The objective of this study was to identify if the mode of operations in the methanol distillation units that purifies the crude methanol into high purity product can potentially lead to an accumulation of trace organic acids within the main refining column, which can lead to the formation of an acidic region within the column. To carry out this work, the main refining column of an industrial methanol producer was first simulated on the industrial process simulation platform VMGSim, and then validated against available data. This simulation was then used to study the accumulation of organic acids ranging from formic acid to valeric acid, where they were added to the feed stream at a concentration of 1 ppm. The study found that propionic and butyric acid, in particular, can accumulate significantly in the middle of the column reaching a concentration of 40 to 80 ppm creating an acidic environment (PH 3.63), which can cause corrosive damage.