Polyethylene autoclave

Plastic cover slips pieces of appropriate size cut from polyethylene autoclavable waste disposal bags. 

Polypropylene is translucent and autoclavable and has no known solvent at room temperature. It is slightly more susceptible to strong oxidizing agents than polyethylene. 

LDPE, also known as high pressure polyethylene, is produced at pressures ranging from 82—276 MPa (800—2725 atm). Operating at 132—332°C, it may be produced by either a tubular or a stirred autoclave reactor. Reaction is sustained by continuously injecting free-radical initiators, such as peroxides, oxygen, or a combination of both, to the reactor feed. 

An independent development of a high pressure polymerization technology has led to the use of molten polymer as a medium for catalytic ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization at a high pressure (see Olefin polymers, low density polyethylene) have been converted to accommodate catalytic polymerization, both stirred-tank and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C (57,83,84). CdF Chimie uses a three-zone high pressure autoclave at zone temperatures of 215, 250, and 260°C (85). Residence times in all these reactors are short, typically less than one minute. 

Mention has already been made in this chapter of metallocene-catalysed polyethylene (see also Chapter 2). Such metallocene catalysts are transition metal compounds, usually zirconium or titanium. Incorporated into a cyclopentadiene-based structure. During the late 1990s several systems were developed where the new catalysts could be employed in existing polymerisation processes for producing LLDPE-type polymers. These include high pressure autoclave and... 

F. Polyethylene polymer autoclav e type reactors usually contain 8 to 120 impellers of the same or different circulation designs on a single shaft to ensure rapid total homogeneous mixing in the reactor, w hich contains a gas at about 30,000 psi and, hence, the fluid is neither a gas or a liquid because the densities are about the same. 

Low density polyethylene is made at high pressures in one of two types of continuous reactor. Autoclave reactors are large stirred pressure vessels, which rely on chilled incoming monomer to remove the heat of polymerization. Tubular reactors consist of long tubes with diameters of approximately 2.5 cm and lengths of up to 600 m. Tubular reactors have a very high surface-to-volume ratio, which permits external cooling to remove the heat of polymerization. 

BioRad produces Bio-Spin disposable polypropylene chromatography columns (Catalog No. 732-6008) that can be packed with up to 1.2 ml gel filtration media. Their micro Bio-Spin columns hold 0.8 ml media. Both are autoclavable columns that have snap-off column tips, polyethylene media bed supports, and fit standard centrifuge tubes. 

Adamantane 2 (0.03 mol) and SF4 (0.2 mol) were reacted in a stainless steel autoclave in a conventional manner. The obtained solid mixture of fluoroadamanlanes was purified by sublimation then separated by preparative GC (10 mm x 5 m column, 25% polyethylene glycol adipate on Spherochroine. 0.2 0.5 mm). 

A number of processes have been developed to obtain products of different physical properties. The nature of the product is affected by the addition of diluents or other additives before carrying out the polymerization. Autoclaves or stirred-tank reactors, and tubular reactors, or their combinations have been developed for the industrial production of high-pressure polyethylene.206,440 Pressures up to 3500 atm and temperatures near 300°C are typically applied. 

Un-vulcanized CSM/PVC material (chloro sulphonated polyethylene/polyvinyl chloride blend) for autoclave or hot-air vulcanization applied with the two-layer adhesive system. 

The first section of this chapter describes the most important high pressure process run under homogeneous conditions to manufacture Low Density PolyEthylene (LDPE). The radical polymerization of ethylene to LDPE is carried out in tubular reactors or in stirred autoclaves. Tubular reactors exhibit higher capacities than stirred autoclaves. The latter are preferred to produce ethylene copolymers having a higher comonomer content. 

The advantages known from the production of low-density polyethylene (LDPE) become obvious also when metallocene catalysts are used under high-pressure conditions. The compressed monomer can dissolve the polymer which is formed during polymerization, which means that no additional solvent is required for the polymer. The high-pressure polymerization proceeds with a high rate, which requires a short residence time and small reactor volume. Established technology, with stirred autoclaves as well as tubular reactors, can be applied. 

Polyethylene glycol (PEG) solution Weigh 50 g ofPEG (1500 molecular weight) into a capped 200-mL bottle, add 1 mL water, and then autoclave for 30 min at 120°C. Cool to about 70°C, add 50 mL of DMEM, mix, and after cooling to ambient temperature, adjust the pH to about 7.2 with 1M NaOH (the mixture should be colored orange). Store as 1-mL aliquots at-20°C. 

Into a 5-liter autoclave, continuously stirred at a speed of 450 rpm, water, a dispersing agent, and polyethylene (powder or pellets) are introduced in the proportions set forth in Table II. After introduction of the initiator, the vinyl chloride is injected in such a quantity that, at the polymerization temperature, the vinyl chlorides partial pressure is lower than the vapor pressure of pure vinyl chloride at the same temperature. The vinyl chloride quantities compatible with this condition are easily determined by the absorption isotherms. When the pressure has dropped to at least half of its maximum value, the nontransformed vinyl chloride is removed. After filtering, washing, and drying, the product is collected. 

High pressure low density polyethylene resins are produced in two types of reactors. One is a continuous-flow mechanically stirred autoclave (origi-... 

Fig. 5 Autoclave and tubular high pressure polyethylene reactors...

Polyethylene glycol 3350 was obtained by polymerization of ethylene oxide in an autoclave at 80-100°C using as a catalyst dipotassium alcogolate of polyethylene glycol 400. 

Polyethylene Nalgene 8010 Economical, good general chemical resistance, contains no plasticizers. Not autoclavable, very stiff, translucent, flammable. 

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