(723d) Biopolethylene with Metallocene Catalysts: Process, Modeling & Simulation

Bioplastics or bio-based plastics are named on two key criteria viz. source of raw material and functionality of the polymer. The source of raw material for a bioplastic can be either renewable or petrochemical base. The polymers manufactured by any raw material can be either biodegradable or non-biodegradable. Bioplastics comprise, in a sizable part, or even entirely, of renewable resources. Consequently, while bioplastics are the biobased plastics, whereas, biodegradable, but petroleum-based plastics, are not considered as bioplastics. Plant based, smaller molecules, such as sugars, disaccharides, and fatty acids, are utilized as the basic raw materials in the manufacture of bioplastics.

Renewable and biodegradable polymers like polylactic acid (PLA), Polyhydroxyalkanoates (PHAs) & starch blends have been in fundamental and applied research focus in recent years to explore the substitutes for fossil fuel-based polymers & plastics backed by the reasons including sustainability, lessening in greenhouse gas emissions that adversely impact to climate change. But these polymers are not often found suitable for high temperature applications and fail to offer certain essential mechanical properties such as toughness & impact resistance. Also, these biodegradable polymers possess higher permeability than other plastics therefore, moisture and oxygen pass through it rather easily.

The chemical industry depends on ethylene as a building block. Ethylene is usually produced by the petrochemical industry from hydrocarbons as raw material (ethane, propane, or naphtha) using a catalytic or thermal cracking process. When bio-sources are concerned, starch, sugar, or lipid-rich biomass is the most efficient alternate for bio-based materials production due to its abundance and easy fermentability. Lignocellulosic biomass is another carbohydrate rich source, which contains significant amounts of cellulose, hemicelluloses, and lignin to produce a wide range of bio-based products from each of its components.

Polyethylene is an aliphatic polyolefin made through polymerization of ethylene monomer. Poltethylenes represent more than 30% of the global plastics market. Ziegler-Natta (Z-N) catalysts are employed in the industrial production of various polyolefins since 1956, which is the combination of a transition-metal salt whose metal is from groups IV to VII of the Periodic Table, and a metal alkyl whose metal is from groups I to III of the Periodic Table.

Recently developed single-site catalysts, named generically as metallocene catalysts, allow exceptional control of polymer molecular design, which yields products having improved properties. Metallocene catalyst system is the combination of bis(cyclopentadienyl)metal complexes of Group 4 (IVB), or cyclopentadienyl-substituted derivatives, and a cocatalyst, usually methylalumoxane (MAO). Metallocene catalyst system allocates the production of tailor-made polymers with properties that can be precisely designed due to their single types of sites. Metallocene based constrained geometry single site catalysts have acknowledged tremendous consideration for the stereospecific polymerization of an array of monomers.

The objective of this research is to demonstrate the viability of bio-based polymers that are not biodegradable (bio-polyethylene, bio-polypropylene) and have characteristics similar to those manufactured from traditional petrochemical sources. A mathematical model is developed to study the kinetic behavior of ethylene polymerization using novel metallocene catalysts. A detailed simulation methodology using evolutionary approach of optimization is discussed to estimate the critical parameters viz. ethylene concentration, catalyst concentration, reaction temperature, and cocatalyst to catalyst ratio. Proposed model is comprehensive in estimating the kinetic parameters as well as in characterizing the product properties such as average molecular weights, polydispersity index, short chain branching and long chain branching. In this work, the viability of less established and unconventional bio-ethylene polymerization using novel catalytic systems with an emphasis upon mathematical modelling and simulation strategies is investigated.