Cyclohexane, Caprolactam, Nylon 6 Adipic Acid (Part - 2) | Chemical Technology - Chemical Engineering PDF Download

Nylon 6 

Nylon 6 is produced from polymerisation of caprolactam. Process steps involved in production of Nylon 6 involve the following steps

• Caprolactam melting and addition of additives
• Polymerisation: Batch/continuous and chips production
• Chips washing and drying
• Spinning of nylon
• Recovery section

Caprolactam is polymerised to Nylon 6 polymer by ring opening polymerisation at 240-270 ⁰C in presence of water, which opens the ring structure of the caprolactam to give amino caproic acid. Reacting SO₂ with ammonium nitrite & ammonium carbonate which results in production of hydroxylamine disulphonate finally hydrolysis of hydroxylamine disulphonate at 95 ^oC to yield hydroxylamine sulphate & ammonium sulphate as by-product. Process flow diagram for nylon 6 manufacturing is shown in Figure M-VIII 5.4.  

Figure M-VIII 5.4: Manufacture of Nylon 6 

Nylon 66 

Nylon 66 is produced by polymerisation of adipic acid & hexamethylene diamine. Manufacturing process flow diagram for nylon 66 is shown in Figure M-VIII 5.5. Process step involved in manufacture of Nylon 66  

• Production of nylon salt (hexamethylene diammonium adipate) by reaction of adipic acid & hexamethylene diamine
• Concentration of nylon salt
• Polymerisation of nylon salt into a jacketed vessel equipped with internal coils and heated by dowtherm
• Cooling and chips production
• Spinning of nylon 66 chips · Recovery section
• Nylon salt (hexamethylene diammonium adipate) is prepared by mixing adipic acid and hexamethylene diamine in 1:1 molar ratio.  

Figure M-VIII 5.5: Process of Nylon 66 manufacture  

• Adipic acid is the basic raw material for the manufacture of Nylon 66
• World overall demand for adipic acid is growing by 3.6% during 2000-2010.
• Adipic acid is manufactured from number of starting raw materials like phenol, cyclohexane, tetrahydrofuran, etc. Various routes for adipic acid manufacture 

Adipic Acid  

Various routes of adipic acid manufacturing is shown in Figure M-VIII 5.6 

 Adipic acid Hexamethylenediamine Hexamethylene diammonium adipate  

 (Nylon salt)

 [-HN(CH₂)₆NHOC(CH₂)₄co-] + 2x.H₂O 

 Poly (Hexamethylene Adipamide) or Nylon 

Figure M-VIII 5.6: Various Routes for Manufacture of Adipic Acid  

Process 

Cyclohexane is oxidised by air to form cyclohexanol &cyclohexanone in presence of cobalt naphthenate catalyst at temperature of 145-150 ^oC. The cyclohexanol and cyclohexanone mixture is oxidised to adipic acid in presence of nitric acid using ammonium metavanadate and copper scrap at 60-80 ^oC. The adipic acid formed is crystallised, centrifuged and finally dried with hot air.  

Hexamethylene diamine is another intermediate for the manufacture of Nylon 66.  Hexamethylene diamine is manufactured by the catalytic hydrogenation of adiponitrile. Hexamethylene diamine is manufactured by catalytic hydrogenation of adiponitrile in presence of catalyst either by high pressure process (60-65 MPa) or low pressure process (3 MPa).   Catalyst in low pressure is nickel whereas in case of high pressure process it is cobalt and copper. Process flow diagram for the manufacture of  Hexamethylene diamine  is given in Figure M-VIII 5.7 

 NC(CH₂)₄CN + 2 H₂    →HN=CH(CH₂)₄CH=NH  

Figure M-VIII 5.7: Process flow diagram for Hexamethylene diamine