Process for the distillation of a mixture of isomeric diisocyanatodiphenylmethanes
A diphenylmethane and diisocyanic acid technology, applied in the purification/separation of isocyanic acid derivatives, organic chemistry, etc., can solve the problem of high operating costs of multi-step distillation
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Embodiment 1
[0040] A single-stage distillation is carried out using a dividing wall column of the type shown in Figure 1 . 5.9 kg / h of isomer mixture (stream E-I) consisting of 0.6% wt.2,2'-MDI, 11.1% wt.2,4'-MDI and 88.3% wt.4,4'-MDI was introduced In the dividing wall column E in the area of the dividing wall. Three product streams are withdrawn from the dividing wall column: 0.15 kg / h, consisting of 23.5% wt.2,2'-MDI, 75.0% wt.2,4'-MDI and 1.5% wt.4,4'-MDI Overhead stream E-II, and 0.95 kg / h side stream consisting of 0.05% wt.2,2'-MDI, 54.90% wt.2,4'-MDI, 44.05% wt.4,4'-MDI E-IV, and 4.8 kg / h bottom stream E-III with 99% isomeric purity of 4,4'-MDI. The purity of the 4,4'-MDI can be increased by sending the bottom stream E-III to an additional distillation column without dividing walls.
[0041] The material exchange element used in the dividing wall column has a 500m 2 / m 3 Textile fiber filler of exceptional surface area. 67% wt. of liquid was introduced into the pre-fraction...
Embodiment 2
[0043] As shown in Figure 2, two-stage distillation is carried out, the traditional distillation column A is used in stage 1, and the dividing wall column F is used in stage 2. Referring to Figure 2, 6.3kg / h, composed of 2,2'-MDI (0.6%wt.), 2,4'-MDI (11.1%wt.) and 4,4'-MDI (88.3%wt.) The isomer mixture of is fed to rectification column A (stream A-I). At the top, a 1.55 kg / h mixture consisting of 2.3% wt.2,2'-MDI, 42.0% wt.2,4'-MDI and 55.7% wt.4,4'-MDI is drawn out of the rectification column A (stream A-II). The bottom product of column A (stream A-III, 4.8 kg / h) contained high purity (97% wt.) 4,4'-MDI. The pressure at the top of column A is 6 mbar. The reflux at the distillate exit point was 6.5:1. The rectification section has 8 separation stages while the stripping section has 18 separation stages.
[0044] Overhead stream A-II is fed to dividing wall column F. During the distillation process, 0.15kg / h, by 24.5%wt.2,2'-MDI, 75.3%wt.2,4'-MDI and 0.2%wt.4,4'-MDI The ...
Embodiment 3
[0047] A single-stage distillation was carried out using a dividing wall column E shown in FIG. 1 . 6.33kg / h, composed of 0.6%wt.2,2'-MDI, 10.8%wt.2,4'-MDI, 87.9%wt.4,4'-MDI and 0.7%wt. higher boiling impurities The isomer mixture of is sent to dividing wall column E (feed stream E-I). The bottom stream E-III was 0.4 kg / h and consisted of 99% wt. 4,4'-MDI and 1% wt. of impurities. Overhead stream E-II is a mixture of isomers consisting of 2.4% wt.2,2'-MDI, 41.0% wt.2,4'-MDI and 56.6% wt.4,4'-MDI. As side stream E-IV, 4,4'-MDI was withdrawn at a rate of 4.37 kg / h with a purity of 98.9% wt.
[0048] The material exchange element used in the dividing wall column E has a 500m 2 / m 3 Textile fiber filler of exceptional surface area. 67% wt. of liquid was introduced into the pre-fractionation zone and 33% wt. of liquid into the main fractionation zone. The pressure at the top of the column was 6 mbar. The reflux at the outflow point of the distillate is 6.5:1, and the reflux at...
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