Synthesis of Strong Acid Cation Exchange Resin (II)
2. Composition of crosslinking agent
The common crosslinking agent of cation exchange resin is divinylbenzene. The isomer of the crosslinking agent divinylbenzene has a great influence on the structure of the copolymer, so it can significantly affect the rate of sulfonation reaction.
The effect of the amount of divinylbenzene on the sulfonation rate of the copolymer is very clear, but the effect of the composition of its isomers on the properties of the copolymer has not been clearly explained. The swelling ratios of styrene (ST) and 8% c-DVB 2:1/m -: p-DVB, m-DVB and p-DVB copolymer were 1.84, 1.82, 1.77 and 1.58. However, the sulfonation rate of these copolymers is not only related to the swelling ratio, but also not completely consistent with the order of the swelling ratio. The sulfonation reaction rate of ST-c-DVB and ST-2: 1/m -: p-DVB with larger swelling is much faster than ST-P-DVB, which is consistent with the above swelling sequence. However, the sulfonation rate of ST-m-DVB copolymer is very special. When the ST-p-DVB copolymer is sulfonated at 80 ℃ for four hours and the exchange capacity reaches 4.01meq/g, the sulfonation reaction of ST-m-DVB copolymer has hardly been carried out, but the exchange capacity of cation exchange resin can also reach 4.88 after 50 hours.
Further studies showed that the ratio of m-DVB to p-DVB had a great influence on the sulfonation rate of the copolymer. When pure m-DVB or p-DVB is used as crosslinking agent, the sulfonation rate of the copolymer is not large. Only when the ratio of m-DVB to p-DVB is in the range of 4:1~3:2, the sulfonation rate is large, and the maximum value of 3.90meq ·/(g · h) is reached when the ratio is 7:3.
3. Sulfonation temperature
The sulfonation rate of crosslinked polystyrene increased with the increase of temperature. Because dichloroethane (bp 83 ℃) is generally used as the swelling agent during sulfonation, sulfonation at 80 ℃ is more appropriate. In the later stage of the sulfonation reaction, the sulfonic group on the copolymer chain makes it hydrophilic, which can gradually increase the temperature, and steam and recover dichloroethane under reduced pressure. The sulfonation ends when the exchange capacity of cation resin reaches the highest value.
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