Bisphenol A (BPA) is prepared by the reaction of one mole of acetone and two moles of phenol to give primarily the para, para´-condensation product, para, para´-isopropylidene-diphenol: 
Strong mineral acids such as hydrochloric or sulfuric can be used as catalysts. Hydrochloric acid is much preferred due to its lower boiling point and relative ease of removal from the reaction mixture. Instead of strong mineral acids, strongly acidic cation exchange resins such as the styrene/divinyl benzene type can be used with or without activity enhancing modifiers. Resin catalysts eliminate catalyst recycle and greatly mitigate equipment corrosion and wastewater treatment problems. To compensate for any activity deficit, reaction temperatures with resin catalysts can be increased to 70-80°C, compared to 50°C with concentrated aqueous or gaseous dry HCl catalyst. Compounds that contain mercapto (SH) groups or moieties that hydrolyze to mercapto groups are used in catalytic amounts of 1 percent or less of the feed to improve both the formation rate and yield of BPA. Methyl mercaptan is commonly used for this purpose. Other examples of mercaptan promoters are 3-mercaptopropionic acid and 2,2-dimethylthiazoline. The effect of the promoter is attributed to the formation of a more stable carbonium ion, which can exist in higher concentration and thus alkylate the phenol ring faster. Newer ion exchange catalysts are modified to introduce mercapto groups that accomplish the same result while keeping the promoter bound to the resin. Advantages of the ion exchange catalyzed BPA process are:
- Much lower investment and maintenance costs due to the use of less costly materials of construction
- Minimal waste water production, leading to a drastic reduction in the size of the treating system
- Simpler purification system in that catalyst recovery and recycle are not required
A detailed comparison of process and product parameters for the various processes is discussed in this report. The main factor to note is that resin catalysts have now been improved to the point of essentially the activity and selectivity of the HCI catalyst. Resin catalyzed processes are now also comparable to the HCI catalyzed process in equipment count, and they retain an advantage in less costly construction materials. Production economics for BPA using resin catalysts and mineral acids are presented. Supply/ demand outlook for BPA on a regional basis is also given.
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