2.7. Purification of cadaverine and the synthesis of bio-based 1,5-pentamethylene diisocyanate

The fermentation broth contains substances such as cadaverine, bacteria, inorganic salts, soluble proteins and pigments. To purify the cadaverine, bacteria and protein in the fermentation broth are removed by membrane filtration. Saturated sodium hydroxide is added to convert the cadaverine in the fermentation broth into molecular states, and then the cadaverine and water are vaporized (separated from inorganic salts, soluble proteins and pigments). The vaporized gas is condensed to obtain the aqueous pentamethylenediamine solution and refined Distillate to remove the water, and finally obtain the product.

PDI was synthesized by the approach of carbamate decomposition as described by Sun et al. with some modifications [19]. Nitrogen was introduced into the reaction to maintain the pressure at 1.4 Mpa, and the reaction temperature was 210 °C. First, urea and cadaverine generate pentanediamine diurea, and then 1-butanol is added for alcoholysis to produce 1,5-pentanedicarbamate (PDU) [20]. Zirconium tetrachloride can be used as a catalyst. Finally, 1,5-pentamethylene diisocyanate (PDI) is obtained from PDU pyrolysis. In the reaction, the heat carrier is dioctyl sebacate and zinc picolinate is used as a catalyst. The reaction temperature is 280 °C and the vacuum degree is 0.08 Mpa.