Discussion

          In the design of a new acrylic acid facility, many decisions had to be made concerning process
improvements. One such decision was concerning the installation of a packed bed reactor. Upon
completion of a case study of the packed bed reactor performance in the acrylic acid process, the
finding were very disappointing. The largest problem in using a packed reactor is that the feed must
be outside the explosive limits or under the minimum oxygen concentration to avoid runaway reactions.
This results in larger separation costs for a reactor with a conversion below that of the 90% propylene
conversion obtainable in the fluidized bed. Also, the packed bed reactor is very sensitive to inlet
temperature and pressure, making it that much more less attractive. The fluidized bed should be operated
at 290 ⁰C where a propylene conversion of 90% is obtained. Raising the reactor temperature will result
in lower conversions.

          The alterations to the process heat integration are shown in Figures 7 and 8. These waste heat
boilers will generate in excess of $2 million annually for the new plant. Heat exchanger E-302, along with
a process water injection system and V-301, will effectively replace the quench tower from the current
process. The process water used will either by piped from a supplier or fed from a 3.2 million gallon tank
on site. This tank will hold one month's supply of process water. This water is at ambient temperature
(25⁰C) and is introduced into the reactor effluent by a system of four injection jets shown in Figure 9.
Each jet will inject 2 gallons per minute into the process stream for quenching.

Figure 9: Apparatus for quenching stream exiting reactor, R-301

         In examing the acid distillation column, it was found that the necessary product purities could be
obtained at a lower pressure that 7.0 kPa. By running the column at 6.5 kPa the condenser and reboiler
duties are reduced by decreasing the reflux rate. These subtle changes result in a savings of $338,000 in
the column cost and another $64,904 per year in utility costs in the column.

    These proposed changes represent a $54 million increase in the Net Present Value of the acrylic acid
process.

Letter of Transmittal
Executive Summary
Introduciton
Results
Discussion
Conclusions
Recommendations
References