Acrylonitrile, Acrylic Fibre, Modified Acrylic Fibre, Polyurethane | Chemical Technology - Chemical Engineering PDF Download

Acrylonitrile, Acrylic Fibre, Modified Acrylic Fibre, Polyurethane

Acrylic fibres are third largest class of synthetic fibre after polyester and nylons. Commercial acrylic fibre was developed by Dupont in US as Orlon while modified acrylic fibre was developed by Union carbide as Dynel.  In acrylic fibre monomer is acrylonitrile while in case of modified acrylic fibre acrylonitrile is co polymerised with Vinylidiene chloride vinyl chloride. The halogenated monomers impart flame resistance and are suitable for home furnishing, protective coatings, sleepwear, and hospital blankets.  Characteristics of acrylic fibre and modified acrylic fibre are mention in Table M-VIII 7.1.

Acrylic fibres are soft, light weight, durable strong, high crease recovery, color fastness to both washing & sunlight, easy care- easy laundry &low maintenance cost, high abrasion resistance, good aesthetics-high lustre, good wicking action- helps in quick transfer of moisture & sweat resulting in quick drying, no allergic and non toxic, resistance to mild & insects, oils, chemicals. It is very resistant to deterioration from sunlight exposure.

Polyurethane are another important polymer which find application in manufacture of flexible, high resilience foam seating; rigid foam insulation panels, microcellular foam seals and gaskets; durable elastomeric wheels tires; automotive suspension bushings, electrical potting compounds; high performance adhesives; surface coatings and surface sealants; synthetic fibre

Table M-VIII 7.1:  Major Synthetic Fibers and Their Characteristics 

Acetylene Route     

Ethylene Oxide Route 

Acrylonitrile (CH₂=CH-CN)

Figure M-VIII 7.1:  Various Routes for the Manufacture of Acrylonitrile 

Acrylonitrile by Ammoxidation of Propylene 

Acrylonitrile by Ammoxidation of Propylene A typical acrylonitrile plant consists of reactor section, acrylonitrile recovery section, acrylonitrile purification section and HCN purification section. Propylene, ammonia and air are fed to fluidised bed catalytic reactor where ammoxidation of propylene – a highly exothermic reaction occurs. Manufacturing process technology shown in Figure M-VIII 7.2.
Process steps involve are

• Catalyst preparation: bismuth and molybednum  
• Mixing of propylene, ammonia qnd oxygen in 1:1:6
• Reaction section: Macrylonitrile acetonitrile, hydrogen cyanide , unreacted ixture of propylene, ammonia and oxygen are fed to fludised bed reactor. Various product from reactor are qnd oxygen. Reaction is higly exothermic.
• Removal of ammonia
• Absorption of absorbable component from ammonia free gas in water to separate the non-condensable and unconverted propylene, propane, nitrogen, CO and CO₂.
• Stripping of organic components and separation of HCN
• Separation of Acrylonitrile and acetonitruile which are close boiling  boiling compounds. And are separated by extractive distillation  using water as solvent. A dil solution of acrylonitrile is separated  which is recovered and concentrated
• Purification of acetonitrile
• Final purification of acrylonitrile

 Reactions: 

Formation of acrylonitrile occurs by the following reaction:

Overall reaction:  

Side reactions: 

Figure M-VIII 7.2: Process Technology of Acrylonitrile Manufacture

Acrylic Fibre Manufacture

Acrylic fibres are third largest class of  synthetic fibre after  polyester and nylons. Commercial acrylic fibre was developed by Dupont in US as Orlon while modified acrylic fibre was developed by Union carbide as Dynel. 

Figure M-VIII 7.3: Process Flow Diagram of Manufacture of Acrylic Fiber  

Polyurethane 

The polyurethanes which were discovered by Otto Bayer and co-workers in 1937  are versatile class of thermosetting polymers and offer the elasticity of rubber combined with toughness and durability of metal. Worldwide demand for polyurethane expected to grow at CAGR of 5.8percent from 12.0 million tones tones in 2010 to 116.88 million tones in 2016, with Asia pacific region accounting for over 60percent of this figure, according to GBI research. The global market value of polyurethane will rise in the coming years, with thermal insulation becoming a key material application. According to GBI research flexible and rigid polyurethane foams made up the bulk of the total endues segment in 2010, accounting for 60percent of the full amount .

Polyurethane is polymer formed by combining two or more isocyanate functional group and two or more hydroxyl groups. The alcohol and isocyanate groups combine to form a urethane linkage. Polyurethanes made by addition of polyols and polyfunctional isocyanates. Commonly used isocyanates are toluene di-isocyanate (TDI), diphenyl methane diisocyanate (MDI), Hexamethylene di-isocyanate (HDI).

Polyols may be either polyether polyols or polyester polyols. However, polyether polyols are more commonly used. Catalyst used in polyurethane manufacture are–aliphatic and cycloaliphatic tertiary amines and organic tin compounds. Typical reaction involved by reaction of poly isocynates and poly hydroxy compounds is: 

 NOC-R-NCO + NHO-R'-OH→(R-NH-COO-R'-OCO-NH)_n 

_{Diisocynate  Diol Linear polyurethane}

Polyurethane Foam 

Poloyuretane rigid foam are characterized by good structural strength, excellent adhesion to most substance, processing flexibility and long life. Rigid polyurethane foams are most widely preferred insulation and find application in refrigerator, manufacture of thermo-ware, cold sore panel, refrigerated trucks and wagons. A rigid polyurethane foam is a cellular polymer in which the individual small cells are filled with a gaseous blowing agent which imparts the remarkably low thermal conductivity to these foams