Additives

Depolymerization Is a Unique Property of PIB

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Depolymerization Is a Unique Property of PIB
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Additive and finished lubricant applications are the largest consumers of polyisobutylene (PIB) due to their high-temperature depolymerization advantages. This makes them environmentally superior to mineral oils in two-stroke engines such as motorcycles, as well as in other automotive lubricant applications.

Because of this characteristic depolymerization behavior, PIB does not leave behind sludge or soot during the thermal decomposition process, in contrast to mineral oils and other thermoplastic polymers. Its superior properties might also explain why global lubricant additive companies like Lubrizol, Infineum, and Chevron Oronite have their own PIB production facilities.

Useful C4 Stream

In general, a Mixed-C4 stream refers to the hydrocarbons containing four carbons produced in petroleum refining or naphtha cracking facilities.

Mixed-C4 is a by-product of the production of ethylene, which is the scale and standard of the petrochemical industry and is another raw material axis consisting of six to seven types of compounds. Because of this, it is necessary to build a separate facility, C4 complex, to obtain each component.

Figure 1. Mixed-C4 Streams

Source: KEMAT 

In the case of naphtha cracker, after extracting butadiene from Mixed-C4, the remaining component of C4 Raffinates is called mixed-butylene, which is about 50% after butadiene (BD) extraction.

C4 Raffinate-1 consists of isobutylene (50%), n-butene (45%), butane-like (5%), etc. and is mainly used as a raw material for the manufacture of PIB, methyl tert-butyl ether (MTBE), methyl methacrylate (MMA) and Isobutylene Isoprene Rubber (IIR).

Figure 2. Components of Naphtha Crackers Mixed-C4
Source: SRI International report
Mixed-C4Raffinate-1Raffinate-2
ComponentComposition (%)ComponentComposition (%)ComponentComposition (%)
Principal ComponentButadiene35% to 50%Isobutylene45% to 50%1-Butene45%±10%
Other ComponentIsobutylene25%±10%1-Butene50%±15%2-Butene30%±10%
Other Component1-Butene18%±10%2-Butene50%±15%n-Butane25%±10%
Other Component2-Butene10%±5%n-Butane5%±10%Isobutane25%±10%
Other Componentn-Butane3%±2%Isobutane5%±10%
Other ComponentIsobutane1% or less

C4 Raffinate-2 is composed of n-butene (90%), butane (10%), and 1-butene is used as a comonomer for the production of linear low-density polyethylene (LLDPE). 2-butene was mostly used previously for gasoline through alkylation, but it has recently been used in olefine conversion unit (OCU) facilities to expand propylene production.

Isobutylene is the second most useful component of Mixed-C4 after 1,3-BD, and it is used as a raw material for PIB and MTBE products and more. When building large-scale petrochemical complexes, BD, MTBE and PIB plants are usually built simultaneously in consideration of regional and market characteristics to increase the utilization of C4 active ingredients.

Figure 3.  TGA Data of Polybut 200(Mn=2400) and Polybut 30(Mn=1300) from KEMAT 

Source: KEMAT 

Polymerized using isobutylene, one of the useful C4 components, PIB has a wide range of applications in many industries due to its various properties.

Depolymerization

A unique physical property of PIB is depolymerization.

Chemically, PIB is a tertiary carbon-type molecule, which is easily degraded due to its low bond stability and has a different pattern of degradation than other polymeric materials. PIB shows this depolymerization mechanism that is decomposed into butene monomers and enables clean and almost complete volatilization when thermal degradation proceeds.

Experimental data also shows a clean thermal degradation of PIB.

Figure 4. Carbon Residue Test of Polybut 200(Mn=2400) and Polybut 30(Mn=1300) by ASTM D189

Conclusion

PIB products are basically viscous liquid polymers, which are chemically stable and resistant to oxidation by light and heat. Almost all grades are relatively colorless, odorless, and non-toxic. The distribution of molecular weight is relatively narrow, so the quality and uniformity is good, and the sulfur content is insignificant. 

Due to these major physical and chemical properties, it is used as an important intermediate and raw material in various industrial fields. In particular, the above unique depolymerization properties of PIB play an important role in the application of automotive lubricants and can be used as an intermediate material that meets current major industrial trends as well as eco-friendly needs.  

Youngho Hwang is an advisor and senior vice president, APAC with KEMAT.