Ziegler slurry polymerization

Keywords High density polyethylene Process control Process design Process modelling Product portfolio Super-active catalysts Ziegler slurry polymerization... 

The Unipol process employs a fluidized bed reactor (see Section 3.1.2) for the preparation of polyethylene and polypropylene. A gas-liquid fluid solid reactor, where both liquid and gas fluidize the solids, is used for Ziegler-Natta catalyzed ethylene polymerization. Hoechst, Mitsui, Montedison, Solvay et Cie, and a number of other producers use a Ziegler-type catalyst for the manufacture of LLDPE by slurry polymerization in hexane solvent (Fig. 6.11). The system consists of a series of continuous stirred tank reactors to achieve the desired residence time. 1-Butene is used a comonomer, and hydrogen is used for controlling molecular weight. The polymer beads are separated from the liquid by centrifugation followed by steam stripping. 

PREPARATIVE TECHNIQUES Ziegler-Natta polymerization with titanium halide/ aluminum cdkyl catalyst and, optionally, ether, ester, or silane activator. Catalyst may be deposited on a magnesium chloride support. Slurry and gas phase processes are used. Catcdyst systems based on metallocenes are under development. Typical comonomers are ethylene and 1-butene. 

The Slurry Polymerization Process with Super-Active Ziegler-Type Catalyst Systems From the 2 L Glass Autoclave to the 200 m Stirred Tank Reactor... 

The Slurry Polymerization Process with Super-Active Ziegler-Type Catalyst... 

Today, the slurry polymerization process is being run all over the world with great success. The current installed capacity for the described process is around 6 million tons per year, which represents approximately one sixth of the worldwide PE-HD production. Other processes for PE-HD production are the Phillips process, operated with chromium-based catalysts, and other slurry processes also operated with Ziegler-type catalyst systems [60]. 

FIGURE 5.2. Countercurrent-flow reactor for slurry polymerization of ethylene with Ziegler catalysts (as illustrated in Koppeis Co. Inc., British Patent 826,563). 

EPM and EPDM can be produced by solution polymerization, while suspension and slurry polymerization are viable options. EPDM can be gas-phase 1,-4 hexadiene polymerized using Ziegler-Natta catalysts. Union Carbide produces ethylene propylene rubber (EPR) using modified Unipol low-pressure gas-phase technology. 

By treatment of these materials with titanium tetrachloride valuable supported catalysts for the propene Ziegler-Natta type polymerization were obtained. These catalysts were tested by slurry polymerization using triethylaluminium as cocatalyst and showed an interesting activity compared with that exhibited by a commercial catalysts. The polymer products were also characterized by measuring the molecular weight distribution by gel permeation chromatography technique. 

The synthetic isoparaffins are suitable solvents for alkyd and acrylic paint formulations. These virtually odorless solvents and their low surface tensions offer improved flow and wetting properties to the paints. The excellent wetting characteristics of these solvents are desirable in formulations such as furniture polishes, car polishes, and waterless hand cleaners. The low surface tension of these solvents reduces the amount of surfactants needed in emulsified products and affords improved wetting of pigments in ink and coating formulations. The isoparaffins are used as an inert process solvent in the manufacture of polyolefins and certain rubbers. In the slurry polymerization process the isoparaffins afford solvency for the Ziegler-type catalyst and the ethylene monomer, but no solvency for the polyolefin polymer product. 

In polyolefin manufacture the Isopar solvents act as an inert solvent for the slurry polymerization of ethylene in the presence of a Ziegler catalyst. The absence of any polar or olefin impurities in the solvent avoids any poisoning of the polymerization catalyst. The polymer is insoluble in the solvent which facilitates the rapid recovery and drying of the polymer. FDA regulation 21 CFR 178.3650 allows the use of Isopar G, H, K, and L in the manufacture of polyolefin articles for food contact. 

Starting in 1959, Solvay was one of the first companies to manufacture HDPE using the Ziegler catalyst and a slurry polymerization process and had a research laboratory active in the development of improved Ziegler catalyst systems. 

Poly (acetylenes) The most common chemical synthesis of poly (acetylene), as first effected by Shirakawa, involves use of a procedure common in the polymer world, viz. stereospecific Ziegler-Natta polymerization. In a typical procedure, a toluene slurry of AlEtj and Ti(OBu)4 (4 1) is used to coat a reaction vessel (e.g. a Schlenk tube). Acetylene gas is then admitted at pressures ranging from 2 cm to 76 cm Hg. A well-formed poly(acetylene) film starts growing in a few seconds, with polymerization generally carried out to an hour. The polymer films are washed in solvent of polymerization, and dried, when they can be peeled off to yield free standing films, with thicknesses up to 0.5 cm. 

Polymerization in a hydrocarbon slurry (usually a light-saturated hydrocarbon) was the first commercial polymerization process to utilize Phillips and Ziegler catalysts. These processes enjoy high popularity because of theit versatihty. 

Polypropylene. One of the most important appHcations of propylene is as a monomer for the production of polypropylene. Propylene is polymerized by Ziegler-Natta coordination catalysts (92,93). Polymerization is carried out either in the Hquid phase where the polymer forms a slurry of particles, or in the gas phase where the polymer forms dry soHd particles. Propylene polymerization is an exothermic reaction (94). 

We have a choice of four major polymerization techniques by which to manufacture polypropylene using Ziegler-Natta catalysts slurry, liquid propylene, solution, and gas phase. Regardless of which technique is employed, all polymerization plants must accomplish the same basic goals they must... 

Slurry phase (or suspension) process. The uniquedooldng equipment in Figure 23—5 is a loop reactor. This process also takes place in a solvent (in this case, normal hexane, isobutane, or isopentane) so that the mixture can be pumped continuously in a loop while the polymerization is taking place. Feeds (the solvent, comonomer if any, ethylene and Ziegler-Natta catalyst) are pumped into the loop and circulated. Polymerization rakes place continuously at temperatures below the melting point of the polyethylene allowing solid polymer particles to form enough to form slurry. The reaction takes place at 185—212°F and 75—150 psi. A slurry of HOPE in hexane is drawn off continuously or intermittently. 

HDPE is produced mainly by a suspension (slurry) process in various types of reactors and with various polymerization procedures. In these processes, a supported Ziegler-Natta catalyst system or a Phillips catalyst in a solvent is used. Because the temperature (80-100°C) is lower than the melting point of the polyethylene (140°C), the polymer produced is separated as a solid. This process is highly versatile and can be used to produce many kinds of polyethylenes. 

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