High Impact Polystyrene:
Short name : HIPS
Density : 1.04 g/cc
Properties : toughness, processability, recyclability.
Applications : In electronic business, computer and printer bodies, refrigerator components, toys, novelties, disposable etc.
High Impact Polystyrene Manufacturing Process Description:
The raw materials significantly consist of styrene, zinc stearate and liquid paraffin.
Styrene is very reactive and readily undergoes homopolymerization. Strong acids and peroxides can initiate the reaction. All current styrene manufacturing starts with ethylbenzene, followed by a conversion to crude styrene, which then requires finishing to produce the pure product in the following procedure.
- Alkylation of benzene to ethylbenzene using Friedel-Craft’s process in presence of aluminium chloride and ethyl chloride or hydrochloric acid.
- Dehydrogenation of ethylbenzene (endothermic) to styrene in presence of iron oxide promoted with potassium or chromium oxides.
Zinc Stearate as an internal lubricant (about 0.15%) is added to the feed.
Liquid paraffin as a chain transition agent (about 2%) is added to the feed.
The high impact polystyrene manufacturing process facility consists of various facilities as detailed below:
1. Feed solution tank
6. Extrusion & Pelletisation
7. Product Packing
- FEED TANK: –
It consists of feed preparation tank, LP(liquid paraffin) holder transfer pump GAF filter. The known quantity of Styrene is taken into feed preparation tank from M6 tank and TRS tank (if available). Chemicals like Zinc Stearate, LP, toners, etc are added.
Zinc Stearate is added as an external lubricant, whereas Liquid paraffin is added as an internal lubricant, toners are added to give colour to the product. After adding chemicals, agitation is started to ensure proper mixing.
After proper mixing feed will be transferred to kettle though filter to remove undissolved particles and to avoid external chemical contamination entry. Minimum one hour is taken to transfer feed to the tower.
- PRE POLYMERIZATION:
It consists of kettles with agitators, tower feed pumps and jacket hot oil pumps, condensers and vacuum pumps. Feed is given to the kettles from ESRM pumps. Initiators are added to activate the styrene monomer. Kettles are maintained at nearly 120-140 oC by evaporative cooling method and temperature is given to reactors (Kettles) by circulating hot oil through jackets.
These are maintained under vacuum about 550 mmHg. To maintain this high-pressure vacuum Liquid Ring pumps are used. LRPs are connected to kettles through overhead condensers such that the styrene vapours arising from the kettles are condensed and recycled through QVF to separate water particles if any, these water particles are drained frequently.
In kettles, nearly 50% of conversion is taking place. The partially polymerized mass is transferred to towers by using gear pumps.
The polymerized material is subjected to further polymerization in tower type reactors. Tower reactors are divided into 5 zones, numbered serially from top to bottom. Towers consist of hot oil jacket, inner coils, and three overhead condensers.
Towers are nearly maintained at 210oC. This temperature is maintained by circulating hot oil through the jacket and inner coils. The vapours coming from towers are condensed in overhead condensers and the condensed liquid is collected in PMT(pure monomer tank) . To separate water from liquid QVF is used. The polymerized material is transferred to DV preheater by using gear pumps.
- PREHEATING & DE VOLATILISATION:
The polymerized material is preheated in DV preheater to flash out higher boiling materials. The preheater is maintained at about 200oc-230oc. The polymerized material from towers is transferred into DV preheater from the bottom and then sent to devolatilizer from top.
DV is maintained under vacuum to flash off the residual monomer and higher boiling fractions. Vacuum is nearly maintained at 740 mmHg. The vaporized material is condensed in DV overhead condenser, the condensed liquid is collected in DV day tank. The collected liquid in PMT & DV day tanks is redistilled in still and reused again.
The volatilized liquid is pumped through screen pack to die head. Screen pack is used to separate unwanted contamination.
- EXTRUSION & PELLETISATION:
DV bottom polymer passes through the die head to USG (Under strands granular system). The die head temperature is maintained at a range of 180- 230oC. In USG system product strands are cut into 3*3 mm size pellets under circulating water and dried in drying section and screened for oversize and undersize if any.
The external lubricant is added using vibro feeders. The screened product is conveyed to product silos by using the pneumatic conveying system.