Polyethylene production process

Although each production process yields ash that is essentially chemically equivalent, the various products differ ia physical properties and ia contaminants as shown ia Table 6. Hopper cars, pneumatic tmcks, supersacks, and multiwaH kraft bags with polyethylene liners are the usual shipping containers. 

High density polyethylene (HDPE) is defined by ASTM D1248-84 as a product of ethylene polymerisation with a density of 0.940 g/cm or higher. This range includes both homopolymers of ethylene and its copolymers with small amounts of a-olefins. The first commercial processes for HDPE manufacture were developed in the early 1950s and utilised a variety of transition-metal polymerisation catalysts based on molybdenum (1), chromium (2,3), and titanium (4). Commercial production of HDPE was started in 1956 in the United States by Phillips Petroleum Company and in Europe by Hoechst (5). HDPE is one of the largest volume commodity plastics produced in the world, with a worldwide capacity in 1994 of over 14 x 10 t/yr and a 32% share of the total polyethylene production. 

The final step in the process of standardizing our columns was to try and maintain the high quality of columns from batch to batch of gel from the manufacturer. This was done by following the basic procedures outlined earlier for the initial column evaluation with two exceptions. First, we did not continue to use the valley-to-peak ratios or the peak separation parameters. We decided that the D20 values told us enough information. The second modification that we made was to address the issue of discontinuities in the gel pore sizes (18,19). To do this, we selected six different polyethylenes made via five different production processes. These samples are run every time we do an evaluation to look for breaks or discontinuities that might indicate the presence of a gel mismatch. Because the resins were made by several different processes, the presence of a discontinuity in several of these samples would be a strong indication of a problem. Table 21.5 shows the results for several column evaluations that have been performed on different batches of gel over a 10-year period. Table 21.5 shows how the columns made by Polymer Laboratories have improved continuously over this time period. Figure 21.2 shows an example of a discontinuity that was identified in one particular evaluation. These were not accepted and the manufacturer quickly fixed the problem. 

Figure 7. Polyethylene separator production process (I) Mixing and Extrusion...

The alternative is hexane, which because of the explosion hazard requires a more expensive type of extractor construction. After the extraction the product is dull gray. The continuos sheet is slit to the final width according to customer requirements, searched by fully automatic detectors for any pinholes, wound into rolls of about 1 m diameter (corresponding to a length of 900-1000 m), and packed for shipping. Such a continuous production process is excellently suited for supervision by modern quality assurance systems, such as statistical process control (SPC). Figures 7-9 give a schematic picture of the production process for microporous polyethylene separators. 

The production process is comparatively simple, even though — of course — the respective know-how is also decisive. The equipment for the production of sintered PVC separators is suitable in size and production capacity to be operated on its own by individual, medium-sized, starter battery plants, in contrast to the far larger units required for the production of polyethylene pocket material. 

A detailed description of the production process and the properties of polyethylene separators can be found in Sec. 9.2.2.1, so only the modifications, which are important for traction battery separators are covered here. 

The production process for polyethylene separators (Sec. 9.2.2.1) as well as the characteristic properties (see Sec. 9.2.2.1 and 9.2.3.1) have already been described in detail above. Deviating therefrom, the desire for low acid displacement has to be added for separators in open stationary batteries. This can be met either by decreasing the backweb thickness or by increasing the porosity the latter, however, is at the expense of separator stability. 

In the production of polyethylene, this process is repeated thousands of times. The basic repeating structure can be pictured as... 

It is traditional to begin books about polyurethanes by defining the class of polymers that has come to be known as polyurethanes. Unlike olefin-based polymers (polyethylene, polypropylene, etc.), the uniqueness of polyurethane is that it results not from a specific monomer (ethylene, propylene, etc.), but rather from a type of reaction, specifically the fonnation of a specific chemical bond. Inevitably, the discussion in traditional books then progresses to the component parts, the production processes, and ultimately the uses. This is, of course, a logical progression inasmuch as most tests about polyurethanes are written for and by current or aspiring PUR (the accepted abbreviation for conventional polyurethanes) chemists. Unlike discussions about polyolefins where the monomer, for the most part, defines the properties of the final product, a discussion of PURs must begin with the wide variety of constituent parts and their effects on the resultant polymers. 

High-density polyethylene (HDPE) bottles in multi-serve and single-serve sizes are used for juice drinks that appeal- mainly in the chill cabinet (short shelf-life distribution) section. This is probably more to do with the product process... 

The discovery of the Ni effect led to the invention of polyethylene production catalysed by TiCI4 combined with Et3Al, the so-called the Ziegler catalyst, in 1953. Soon after, the process for isotactic polypropylene was invented by Natta using a slightly modified catalyst prepared from TiCl3 and Et3Al, which is called the Natta catalyst (eq. 1.7) [7],... 

In contrast to polyethylene production, solution polymerisation at high temperature is rarely applied for isotactic polypropylene, but some special-purpose polypropylene grades are manufactured (Figure 3.57) [51]. However, the solution process, which yields isotactic polypropylene with a very low level of impurities, is characterised by high overall costs. The solution process is being used to make atactic polypropylene, to which it seems more suited [43],... 

Synthetic polymers based on polyesters and co-polyesters are some of the most expensive biopolymers. Feedstock is expensive compared with biopolymers based on renewable resources and the production process is more complex and costly. Synthetic types can cost up to three times the price of commodity polymers such as polyethylene and polypropylene. 

Energx A process for making LLDPE (linear low-density polyethylene). Developed by Eastman Chemical in the 1990s and used at its plant in Longview, TX. Licensed to Chevron Chemical in 1999 for use at its plant in Baytown, TX. By 2002, licenses had been granted in Europe, North America, and Asia. A variation, Energx-DCX, uses a supported catalyst (Sylopol DCX) made by W.R. Grace. The polyethylene products have the trade name Hifor. 

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. 

Blown film extrusion is perhaps the most widely used extrusion technique, by production volume. Billions of pounds of polyethylene are processed annually by this method to make products such as grocery sacks and trash can liners. In a blown film system (Figure 14-30), the melt is generally extruded vertically upward through an annular die. The thin tube is filled with air as it travels up to a collapsing frame that flattens it before it enters the nip rollers, which pull the film away from the die. The flattened tube then travels over a series of idle rollers to a slitter,... 

The development of these catalysts marked a great progress in polyethylene production, making it possible to develop high yield processes which are simpler and more economic than the traditional ones. They were not, however, suitable to produce isotactic polypropylene. 

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