Autoclave stirring

It is noteworthy that the best results could be obtained only with very pure ionic liquids and by use of an optimized reactor set-up. The contents of halide ions and water in the ionic liquid were found to be crucial parameters, since both impurities poisoned the cationic catalyst. Furthermore, the catalytic results proved to be highly dependent on all modifications influencing mass transfer of ethylene into the ionic catalyst layer. A 150 ml autoclave stirred from the top with a special stirrer... 

The catalysts were obtained from their respective commercial sources and for some of these tests they were subjected to RPT by heating them to 400°C for 2 hours under a flow of hydrogen. The enantioselective ketone hydrogenations were carried out in a 50 ml stainless steel autoclave stirred with a magnetic stirring bar with 10 to 30 mg of catalyst, 10 to 30 mg of MeOHCd, 5 ml substrate and 20 ml AcOH at 60 bar and 25°C for 30 minutes. The crotonic acid hydrogenations were carried out in an ethanolic solution at atmospheric pressure and room temperature stirred at 2000 rpm with a hollow shaft bubbling stirrer. 

Another approach to studies of hydrothermal and solvothermal reactions is to use energy dispersive diffraction. A normal size laboratory autoclave is used with a thinning of a small part to allow X-rays to penetrate the wall. Collimated slits are used to obtain diffraction from only a small volume element inside the autoclave. Stirring is necessary to prevent sedimentation of the materials. 

PEG/NaCl 100g Polyethylene Glycol 8000 (cat BP233, Fisher Scientific, Pittsburgh, PA), 116.9 g NaCl, and 475 mL H20. Dissolve PEG by autoclaving the solution (with an autoclavable stir bar in the bottle). Cool the PEG/NaCl solution on a stir plate with constant stirring to prevent phase separation. Reautoclave if phase separation occurs. 

Polyethylene is the simplest addition polymer, and we will briefly describe its polymerization process. Polyethylene, as discussed previously. Is made by opening the double bond in the ethylene molecule, and chemically bonding the monomers together in a reactor. That reactor can involve an autoclave (stirred tank) process or a tubular process. It can be done at low pressure (about 300 psi) or at pressures as high as 50,000 psi. Temperatures are controlled at some elevated level such as 125 to 250°C, but the temperature needed is very specific to the type of polymer structure desired. 

As discussed above, it was clear that ethylene/1-butene copolymers possessed significantly improved mechanical properties compared to ethylene homopolymer products, so that a commercial particle-form reactor design was needed that could provide polyethylene copolymers over a range of Flow Index values with sustained operability over extended periods of time without reactor shut down. Adding 1 -butene to the polymerization process made the autoclave stirred tank reactor even more difficult to operate, as reactor wall fouling problems persisted and in some cases polymer particle morphology was reduced due to some polymer components becoming soluble in the n-pentane. 

Most commercial processes involve copolymerization of ethylene with the acid comonomer followed by partial neutralization, using appropriate metal compounds. The copolymerization step is best carried out in a weU-stirred autoclave with continuous feeds of all ingredients and the free-radical initiator, under substantially constant environment conditions (22—24). Owing to the relatively high reactivity of the acid comonomer, it is desirable to provide rapid end-over-end mixing, and the comonomer content of the feed is much lower than that of the copolymer product. Temperatures of 150—280°C and pressures well in excess of 100 MPa (1000 atm) are maintained. Modifications on the basic process described above have been described (25,26). When specific properties such as increased stiffness are required, nonrandom copolymers may be preferred. An additional comonomer, however, may be introduced to decrease crystallinity (10,27). 

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. 

LDPE is produced in either a stirred autoclave or a tubular reactor total domestic production, divided between the two systems at 45% for tubular and 55% for autoclave, is estimated to be 3.4 million metric tons per year (5). Neither process has gained a clear advantage over the other, although all new or added capacity production in the 1990s has been through the autoclave. 

Initiators. The degree of polymerization is controlled by the addition rate of initiator(s). Initiators (qv) are chosen primarily on the basis of half-life, the time required for one-half of the initiator to decay at a specified temperature. In general, initiators of longer half-Hves are chosen as the desired reaction temperature increases they must be well dispersed in the reactor prior to the time any substantial reaction takes place. When choosing an initiator, several factors must be considered. For the autoclave reactor, these factors include the time permitted for completion of reaction in each zone, how well the reactor is stirred, the desired reaction temperature, initiator solubiUty in the carrier, and the cost of initiator in terms of active oxygen content. For the tubular reactors, an additional factor to take into account is the position of the peak temperature along the length of the tube (9). 

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. 

A hst of polyol producers is shown in Table 6. Each producer has a varied line of PPO and EOPO copolymers for polyurethane use. Polyols are usually produced in a semibatch mode in stainless steel autoclaves using basic catalysis. Autoclaves in use range from one gallon (3.785 L) size in research faciUties to 20,000 gallon (75.7 m ) commercial vessels. In semibatch operation, starter and catalyst are charged to the reactor and the water formed is removed under vacuum. Sometimes an intermediate is made and stored because a 30—100 dilution of starter with PO would require an extraordinary reactor to provide adequate stirring. PO and/or EO are added continuously until the desired OH No. is reached the reaction is stopped and the catalyst is removed. A uniform addition rate and temperature profile is required to keep unsaturation the same from batch to batch. The KOH catalyst can be removed by absorbent treatment (140), extraction into water (141), neutralization and/or crystallization of the salt (142—147), and ion exchange (148—150). 

Because of the low boiling point of ethylene oxide, reactions are generally conducted in stirred autoclaves at elevated pressures. Economic Aspects. A breakdown of saUent 1987 world supply and demand figures for HEC is given in Table 5. 

The reaction may be conducted in stirred autoclaves in the presence of hydrocarbon diluents (82,83). Like the methylceUuloses, advantage is taken of the low critical solution temperature of HPC and it is purified through multiple washings with hot water. Consequendy, very low levels of residual salts and by-products are present in the final products. 

Liquefaction. Liquefaction of coal to oil was first accompHshed in 1914. Hydrogen was placed with a paste of coal, heavy oil, and a small amount of iron oxide catalyst at 450° and 20 MPa (200 atm) in stirred autoclaves. This process was developed by the I. G. Earbenindustrie AG to give commercial quaUty gasoline as the principal product. Twelve hydrogenation plants were operated during World War II to make Hquid fuels (see CoAL... 

General procedure. LaNIs ingot (3 g) in an autoclave was evacuated at 0.1 mm, heated to 200°C under Hz at 30 atm for 10 min. After cooling to 20°C, Itie operation was repeated five times. The autoclave was cooled in dry ice-acetone, Hg was released and Ng was Introduced. The organic compound (1 mmol) m THFJ4eOH (2 1) (5 mL) was added at -78°C with stirring. Tt mixture was stirred under Ng at 0°C and then at 20°C. The catalyst was filtered, the filtrate concentrated and the residue purified by preparative TLC on silica gel. 

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