Borstar processes

As mentioned in section 7.1, technologies have been developed in recent years wherein combinations of processes are used to produce polyethylene. A case in point is the Borstar process developed by Borealis and started up in 1995. Borstar is capable of producing the entire range of polyethylenes from LLDPE to HOPE (14). 

The Borstar process employs a small loop prepolymerization reactor (see section 3.6 for a discussion of the advantages of prepolymerization). Ziegler-Natta catalysts and triethylaluminum cocatalyst are commonly used but the process is capable of using single site catalysts (15). 

The Borstar process involves the use of two cascaded reactors. In the first stage, ethylene is polymerized in supercritical propane by the addition of a transition metal catalyst in a loop reactor, which leads to low-molecular-weight polyethylene. The reaction mixture is then transferred into a gas-phase reactor in which high-molecular-weight polymers are formed. The direct result of this two-stage process is an intimate mixing of the two polymer fractions, which differ in their molar masses. 

The catalytic nature of the Borstar process, whereby polymerization proceeds at a transition metal center. A profound knowledge of metal-organic chemistry is also required to achieve a targeted design of exactly the catalyst geometry required to create the desired molar masses. 

Many different loop reactor configurations are used in industrial processes. The loop can be either in a vertical (Phillips and Spheripol processes [72, 73]) or in a horizontal position (USl process). The pipe can also be bent into multiple legs to increase the reaction volume. Several loops can be arranged in series to produce bimodal polymer, as in the case of Spheripol and Borstar processes [74]. Alternatively, the series of loop reactors can be operated as one single unit to increase average residence time and throughput. 

Borstar is an industrial olefin polymerization plant/technology, which combines different polymerization processes and reactor units, utilizing an advanced catalytic system. In the present work, a detailed model for the dynamic and steady-state simulation of this industrial plant has been developed. A comprehensive kinetic model for the ethylene-1-butene copolymerization over a two-site catalyst was employed to predict the MWD and CCD in the Borstar process. The Sanchez-Lacombe equation of state (S-L EoS) was employed for the thermodynamic properties of the polymerization system and the phase equilibrium calculations in the process units. 

Examples of these types of processes are the Spheripol process and the Borstar process... 

With the Borstar process technology it is possible to produce a portfolio for use in economic manufacture of a full range of polypropylene applications from low melt flow to high flow applications, as well as high impact copolymers. 

The viability of the Lurgi MTF process was first demonstrated at a unit operated jointly with Statoil at Statoil s methanol plant in Norway [49] from 2001 to 2004. The skid-mounted MTP unit comprised of three reactors used 360kg/day methanol feed per reactor. In 2003, to confirm the quality of the propylene obtained in the MTP demonsfration unit, samples were sent to Boreahs s hmovation center in Rpmiingen, Norway, where it was polymerized with Boreahs s Borstar process to a polypropylene that met all specifications, and converted into thermoformed cups. The results from the demonsfration and further tests proved that the MTP catalyst Ufe exceeds 1 year of operation. The results also showed that the zeoUte-based catalyst could be easily regenerated more than a dozen times. 

Borstar A catalytic process for polymerizing ethylene. Use of two reactors, a loop reactor and a gas-phase reactor, allows better control of molecular weight distribution. The loop reactor operates under super-critical conditions to avoid bubble formation. Either Ziegler-Natta or metallocene catalysts can be used. The first commercial unit was installed in Porvoo, Finland, in 1995. 

Borstar PE process, for Ziegler-Natta industrial production,... 

Borstar A catalytic process for polymerizing ethylene or propylene, subdivided into Borstar PE and Borstar PP. Use of two reactors — a loop reactor and a gas-phase reactor — allows better control of molecular weight distribution. The loop reactor operates under supercritical conditions to avoid bubble formation. Either Ziegler-Natta or metallocene catalysts can be used. The latest version, Borstar PE 2G, uses a single, multizone gas-phase reactor to make polymers that have bimodal molecular weight distributions. Developed by Borealis A/S. The first commercial unit, for polyethylene, was installed in Porvoo, Finland, in 1995. The first polypropylene plant was operated by Borealis in Schwechat, Austria, in 2000. In 2005, Borstar s total capacity for PE and PP was 1.3 million tons. 

Application The Borstar polyethylene (PE) process is used when producing bimodal and unimodal linear low density (LLDPE), medium density (MDPE) and high density (HDPE) polyethylene using loop and gas-phase low pressure reactors in series. All products can be produced in one cycle. 

Description Polyethylene with densities of 918-970 kg/m3 and melt flowrate of 0.1-100 can be produced with the Borstar PE process. Currently, Ziegler Natta catalysts are used, but there is a potential to use single-site catalysts latter. 

Application The Borstar polypropylene (PP) process is a versatile technology. Through the choice of reactor combinations, homopolymers, random copolymers, heterophasic copolymers, and very high-rubber content heterophasic copolymers can be produced. 

Description Polypropylene with a melt flowrate ranging from 0.1 to 1,200 can be produced with the Borstar PP process. Currently, Ziegler Natta catalysts are used, but there is a potential to use single-site catalysts latter. When producing homopolymers and random copolymers, the process consists of a loop reactor and a gas-phase reactor in series. One or two gas-phase reactors are combined with this arrangement when heterophasic copolymers are produced. Propylene, catalyst, cocatalyst, donor, hydrogen, and comonomer... 

The development of the Borstar PE process, by Borealis, is a relatively recent development in multi-reactor processes. The foundation of this process is the utilization of supercritical propane as diluent in the slurry loop reactor.438 Operating the slurry loop in a supercritical condition provides several advantages over the tradition diluent (isobutane). The solubility of PE drops markedly at the supercritical point of propane, allowing the process to operate... 

Cascaded processes are suitable for bimodal Spherilene PE from LyondellBasell (Covezzi 1995 Galli 1995) and Borstar PE from Borealis and Borouge (Avela et al. 1998)... 

The Borstar PP process developed by Borealis can operate at temperatures above the critical temperature of the reaction medium. This process uses a loop reactor and gas-phase reactor in series for the production of homopolymer. Additional gas-phase reactors are required for the production of impact copolymers. The first commercial scale plant using this process started in 2000. Basell has announced the development of the Spherizone process using a recirculating gas-phase reactor (Covezzi paper). The reactor contains two zones that can be operated under different conditions, enabling the production of multiphase specialty copolymers in a single reactor. This reactor was first used in a commercial scale plant in 2002. 

Dynamic Simulation of the Borstar Multistage Olefin Polymerization Process... 

This study deals with the development of a dynamic model for an industrial olefin polymerization plant (Borstar ). The model captures the dynamic behaviour of the different process units, and accounts for molecular polymer properties and thermodynamic properties of polymer mixtures using an advanced equation of state. The model validity is tested against industrial data. 

In this work a mesoscale/macroscale level approach of the Borstar plant is attempted focusing on the study of average polymer properties, dynamic behaviour and control of process units. To describe the kinetic of ethylene-1-butene copolymerization in the plant a unified kinetic scheme for the three reactor units based on a two-site Ziegler catalyst is employed (Table 1). The symbol denotes the concentration of live copolymer chains of total length n ending in an i monomer unit, formed at the k catalyst active site. Pp and denote the concentrations of the activated vacant catalyst sites of... 

In this study a comprehensive mathematical model for the dynamic simulation of the Borstar olefin polymerization plant has been presented. The agreement of model predictions to steady-state plant data was satisfactory and simulation of several operating points of the plant is feasible. Verification of dynamic profiles predicted by the model with real dynamic data renders this model a potential tool for the optimisation of the process operation. 

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