Phenol purification (deacification) with Amberlyst polymeric catalysts

Phenol Purification :
Deacidification

In the production of phenol and acetone by the cumene hydroperoxide (CHP) process, sulfuric acid is typically used to catalyze the peroxide cleavage reaction. To prevent the formation of color bodies and other undesirable by-products, and to minimize corrosion, it is then necessary to remove these traces of sulfuric acid prior to downstream distillation and purification. Although the acid could potentially be neutralized by addition of caustic, this results in the formation of inorganic salts such as Na2SO4 which can form scale in distillation column reboilers. An alternative technology that has been used successfully for many years is to remove the sulfuric acid by contacting the cleavage product mixture or the crude phenol with a weak base resin. The acid removal takes place via the following chemical reaction:

R'-NR₂ + H₂SO₄ R'-NR₂H+HSO₄^-

The resin can be regenerated and reused after exhaustion by passing caustic through the bed which returns the resin to the free base form via the following chemical reaction:

R'-NR₂H+HSO₄^- + 2 NaOH R'-NR₂ + 2 Na₂SO4 + 2 H₂O

The most common process configuration is a 3-bed merry-go-round system in which two beds are in adsorption (acid removal) service while the third bed is regenerating. Such a system, with the bed sequencing, is shown in the following figure.

Column Position
Step	Loading	Polishing	Regenerating
1	A	B	C
2	B	C	A
3	C	A	B

Because water and the CHP cleavage product stream have limited mutual solubility, it is usually necessary to use sweetening on and sweetening off steps between the process service cycle and regeneration steps. These sweetening steps can best be accomplished with acetone which is available in the process and which is fully miscible with either stream. For example, following exhaustion of the resin, the cleavage product mixture can be displaced by passing 2-3 bed volumes of acetone through the column, followed by water displacement and caustic regeneration. Similarly, following the regeneration final rinse, the water can be displaced with 2-3 bed volumes of acetone prior to introduction of the cleavage product feed.

Process conditions

Typical process conditions are shown in the following table.

Process composition	Cleavage product or phenol with HCl or H2SO4 at 10-20 ppm
Influent temperature	80 °C
Flow rate	3 BV/h
Operating capacity	0.8 g/L_{R minimum}
Regenerant type	4% Sodium hydroxide
Regeneration mode	Co-flow
Conversion step	4% NaOH at 4 BV/h for 30-45 min (80-120 g NaOH/L_R)
Regeneration flow rate	4 BV/h for 30 minutes (minimum 80 g NaOH /L_R)
Effluent quality	Maximum 0.05 ppm HCl or H2SO4 in phenol