TPS _ K0 Polymerisation Reaction details

K0 Polymerisation Reaction

1. Resins Polymerisation Reaction 11/11/2024

2. Polymerisation Polymerisation takes place in 1 of 4 80 m 3 reactors. The catalyst for the reaction is TiCl 3 which is activated via the isoprenyl aluminium. The first contact that the solid TiCl 3 has with the alkyl is when it is introduced into the hot mother liquor stream as the reactor is being charged with the 37 m 3 of mother liquor. Note the reactor has already been emptied from the previous batch and flushed with 12 m 3 of mother liquor (used to empty most of the outer-cooler). Isoprenyl aluminium is not a pure compound it is a mixture of C 5 and C 4 alkyls in a ratio of ~ 4:1 Al (C 5 H 11 ) 2.4 (C 4 H 9 ) 0.6 The TiCl 3 solid has an open structure more like a cauliflower than a billiard ball this is activated by the IPRA as below

3. Polymerisation reaction

4. Polymerisation description The example shown (taken from a text book) shows triethyl rather than isoprenyl aluminium as the activator The titanium ion has unfilled 3d –orbitals which may be co-ordinated to the π electrons from the double bond of the vinyl (ethylene) monomer In this way the polymer chain grows as the monomer molecules are inserted one after the other, into a polarised titanium-carbon bond. The polymer grows out of the active centre, rather as a hair grows from the root On addition of the comonomer to the reactor the growing polymer chain is able to react with the comonomer in addition to reacting with more ethylene molecules, this results in short chain branches being formed . Using butene as a comonomer the branch (R in the above equation) is CH 2 CH 3 – while for pentene it is CH 2 CH 2 CH 3 This has important consequences as it modifies the properties of the solid polymer, the branched chains (particularly in very long molecules) gives the material toughness

5. Control of reactor conditions

6. Initial reaction It is important that the gas rate at the start of the polymerisation is low (2 - 2.5 tph) and that the temperature when is gas is introduced is also low 74 C ; this results in a builds up in pressure (as the ethylene is slow to react) The ideal pressure build up has been determined to be 200 -350 kPa, these conditions cause the catalyst surface to break open and react with the alkyl to form new and numerous surfaces on which the polymerisation can occur The low gas rate is maintained for 800 kg of ethylene addition Comonomer, (Butene for the Natural products and Pentene for PE 100), is then introduced after ~50 - 200 kg of ethylene has been added. The amount and rate of comonomer addition varies for the type of product being produced The ethylene gas rate is increased (typically to 4.5 tph) after the addition of 800 kg of ethylene. The reactor temperature increases to 80 C (the reaction is exothermic) and is maintained at this temperature for the remainder of stage 1 (Prepoly) by jacket and outer-cooler cooling using plant water. The amount of comonomer used varies between 30 kg (for GE4760) and 310 kg (for GF7740F) depending on the grade being produced; as does the overall amount of ethylene used in stage 1(~ 5 tonne for GF7660 and ~ 9 tonne for HDF193)

7. Prepoly reaction conditions From the pressure curves it can be seen that as the temperature rises (it very quickly reaches 80 C ) the pressure in the reactor decreases – indicating very rapid reaction. Ethylene and comonomer gas is forced into solution ( Raoults & Henry’s law) to replace the gas bubbles in the solvent that have been consumed The reaction is at the solid catalyst surfaces suspended in the solvent and requires the monomer and comonomer molecules to get to these surfaces If for some reason the pressure continues to rise in prepoly ; usually as a result of some impurity in the gas (O 2 , H 2 O, CO 2 , CO, CH≡CH ) then this shows that reaction is not occurring and if the pressure in the reactor reaches > 500 kPa the batch is dumped (to the hot solvent vessels) It is important not to send any dead batches to the DSV as this will cause Gels in the product being produced

8. Effect of comonomer Increasing the butene amount from 100 kg to 270 kg is shown to promote more rapid reaction in the first stage (pressure drops from the peak pressure more rapidly and to a lower amount). This also has an effect on the reaction in the second phase less reaction (higher pressure) Decreasing the butene from 100 kg to 27 kg has the opposite effect - slower reaction in stage 1 (less drop in pressure) and higher reaction in stage 2 (lower pressure)

9. Reaction control

10. Different polymerisation conditions Resins uses the batch process to polymerise two different types of polyethylene chains In prepoly (or stage 1) very large polymer chains are produced – For each of the grades the length and amount of chains of this type are determined by the amount of nitrogen sparging that occurs when charging a reactor (nitrogen removes hydrogen from the previous batch), while the relative amount of prepoly will determine what force is required to process the polymer. At the end of stage 1 a sample is taken (2 -3 times per week) for a viscosity number ( Vz ) this is used to determine the molecular weight that has been made in this stage The amount of comonomer used determines the number of short chain branches that are formed, the higher the comonomer the lower the density of the final product Polymerisation in stage 1 is at 80 C , this is to minimise the amount of comonomer that reacts with itself and forms waxes In stage 2 (homopoly) the large hydrogen atmosphere produces short chains here we polymerise at a higher temperature 85C as very little comonomer is present

11. Molecular weight – Prepoly and homopoly

12. Description of the molecular weight distribution From the previous picture, the red line is an indication of what molecular weight is produced in the first stage. If we have more nitrogen sparging (remove more hydrogen) then the red curve moves to the right, while the amount of stage 1 determines the height of this curve The blue curve is a representation of the average molecular weight produced in the second or homopoly phase of the batch. The larger the amount of hydrogen introduced before the start of stage 2 the more the blue curve moves to the left The green curve is a typical GPC (gel permeation chromatography) measurement of HDF193. Most other Resins grades do not show as pronounced bimodal type distribution The MH catalyst makes a broad molecular weight product; other catalyst systems make narrower products

13. Resins grades Grade Mi5 MFR Density Application Stage 1 H2 atm HD079 23 0.956 IM cartridges 8.6 t 200 kPa start HD039 13 0.954 IM bins 8.6 t 160 kPa start GE4760 2.5 19 0.598 Water bottles 5.3 t 4 kPa (S) /490 (H) GF7660 1.6 23 0.954 HIC bottles 5.0 t 490 kPa homo GF7740F2 1.6 13 0.944 Tape 6.4 t 13 kPa (S) /80 (H) GM7655 0.5 26 0.949 HIC large Bot. 6.0 t 490 kPa homo HDF193 0.3 30 0.947 pipe 8.8 t 580 kPa homo GM4755F 0.2 33 0.949 Film 7.1 t 410 kPa homo