Process Description

The process of dehydrogenation of isopropyl alcohol to acetone starts by pumping an azeotropic mixture of isopropyl alcohol and water into a surge vessel (B9) that mixes the fresh feed with a recycled stream. The mixed stream is then pumped through heat exchanger E-401 (B7) that raises its temperature. This heat exchanger uses high-pressure steam (hps) to raise the temperature up to 234° C. This heated stream is then heated to around 350° C until it dehydrogenates, leaving a mixture of acetone, hydrogen, water, and isopropyl alcohol. The heating of the reactors (B3 and B5) is accomplished using a molten salt recycling stream, which is not modeled in our process. The molten salt stream is continuously heated using a furnace. The extremely high temperature product stream is cooled by the two heat exchangers E-402 (B10) and E-403 (B6;) the first of which drops the temperature of the stream to 45° C using a large amount of cooling water (cw,) and the second one drops the temperature of the stream to 20° C using refrigerated water. The reason that the cooling is divided into two stages is because the cooling water cannot bring the temperature of the stream below 30° C, but using refrigerated water to bring the stream down from 350° C is prohibitively expensive.

The cooled stream is then passed through a phase separator (Flash,) through which most of the hydrogen leaves from the top and the denser liquids drop out of the bottom. The hydrogen dominant stream is then scrubbed with water (STPR) to recover additional acetone. The bottom stream is a combination of acetone and water, with a smaller percentage of isopropyl alcohol. The first column (C-1) through which the stream passes separates the acetone from the mixture; the second column (C-2) recycles the isopropyl alcohol back to the surge vessel mentioned earlier for reuse. The wastewater stream from the second column is cooled from 109° C to 45° C using cw (B11.) This is done so that the wastewater is treatable in liquid form.

The heat exchangers that are used in the first column use cooling water and low pressure steam, which are relatively low cost utilities. This is also true for the second column. These heat exchangers must run at very constant rates, making them hard to optimize using cross-streams and other shortcut methods because of their heavy constraints. For the purposes of this project, however, we are allowing the minute changes in heat exchanger duty to be within the acceptable range. The heat exchanger that heats the initial feed stream as well as the two coolers between the reactor and the phase separator can also be manipulated because there are few demands on exact temperatures. The raising or lowering of a few degrees in the reactor or the phase separator does not vary the output as much as temperature fluctuations vary the reflux and output of the separation columns.