Autoclave reactor

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. 

Recycle and Polymer Collection. Due to the incomplete conversion of monomer to polymer, it is necessary to incorporate a system for the recovery and recycling of the unreacted monomer. Both tubular and autoclave reactors have similar recycle systems (Fig. 1). The high pressure separator partitions most of the polymers from the unreacted monomer. The separator overhead stream, composed of monomer and a trace of low molecular weight polymer, enters a series of coolers and separators where both the reaction heat and waxy polymers are removed. Subsequendy, this stream is combined with fresh as well as recycled monomers from the low pressure separator together they supply feed to the secondary compressor. 

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). 

L. Pebsworth, "Retrofit of Autoclave Reactors for the Production of HDPE to VLDPE," A.nnualMeetings AIChE, New York, Nov. 15, 1987. R. A. V. Raff and K. W. Doak, Crystalline Olefin ToljmersfioEsi Wiley Sons, Inc., New York, 1965, pp. 307,495,682. 

The SCB distribution (SCBD) has been extensively studied by fractionation based on compositional difference as well as molecular size. The analysis by cross fractionation, which involves stepwise separation of the molecules on the basis of composition and molecular size, has provided information of inter- and intramolecular SCBD in much detail. The temperature-rising elution fractionation (TREE) method, which separates polymer molecules according to their composition, has been used for HP LDPE it has been found that SCB composition is more or less uniform [24,25]. It can be observed from the appearance of only one melt endotherm peak in the analysis by differential scanning calorimetry (DSC) (Fig. 1) [26]. Wild et al. [27] reported that HP LDPE prepared by tubular reactor exhibits broader SCBD than that prepared by an autoclave reactor. The SCBD can also be varied by changing the polymerization conditions. From the cross fractionation of commercial HP LDPE samples, it has been found that low-MW species generally have more SCBs [13,24]. 

Polymerizing ethylene can occur either in a tubular or in a stirred autoclave reactor. In the stirred autoclave, the heat of the reaction is absorbed by the cold ethylene feed. Stirring keeps a uniform temperature throughout the reaction vessel and prevents agglomeration of the polymer. 

Platinum and rhodium-platinum and iridium-platinum alloys are frequently employed to line and sheath autoclaves, reactor vessels and tubes, and a wide range of equipment. Linings are generally 0-13 mm to 0- 38 mm thick, and for certain applications co-extruded platinum-lined Inconel or other metal reactor or cooling tubes are fabricated. In such cases the platinum is bonded to the base metal, but in all other instances platinum linings are of the loose type. 

The depolymerisation of PETP in supercritical methanol was caried out using a batch-type autoclave reactor. The... 

Kinetic experiments were carried out isothermaUy in autoclave reactors of sizes 300 and 600 ml. The stirring rate was typically 1800 rpm. In most cases, the reactors were operated as slurry reactors with small catalyst particles (45-90 tm), but comparative experiments were carried out with a static basket using large catalyst pellets. HPLC analysis was appHed for product analysis [22, 23]. 

Hydrogenation tests were carried out using an autoclave reactor (ICI, Wilton, UK) in the case of propanenitrile and a flow reactor operating at atmospheric pressure for ethanenitrile. 

The aim of the experiments with ethanenitrile (CH3CN) was to study hydrogenation activity more quantitatively than was possible with the autoclave reactor. Catalysts 1P30, OH5, OH20, OH30 and HT were selected for investigation. 

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. 

In this paper the effects of kinds of coal, pasting oil, catalyst and reaction temperature on coal liquefaction are illustrated, and a few kinetic models for catalytic liquefaction of five coals carried out in an autoclave reactor are proposed. 

Stimuli-responsive materials, shape-memory polymers as, 22 355-356 Stirling cycle, 8 43 Stirred autoclave, 14 89, 92t Stirred autoclave reactor, 20 216 Stirred batch RO unit, 21 644 Stirred mills, 16 615 Stirred tank bioreactors, 1 737-740 oxygen transfer driving force, 1 734 Stirred tank electrochemical reactor (STER), 9 660-662... 

FIGURE 4.10. Production of hydrogen peroxide from the reaction of H2 and O2 over Au and Au/Pd catalysts at 2°C in an autoclave reactor using aqueous methanol (CH30H,5.6 g H2O 2.9 g) as solvent with catalyst (0.05 g), the reactor was purged three times with CO2 (3 MPa) and then tilled with 5% H2/CO2 and 25% O2/CO2. 

The compressed ethylene and a peroxide initiator (catalyst) enter the autoclave reactor. An autoclave is any vessel that can be closed up and maintain pressure at elevated temperatures. In chemical applications, the ongoing reaction inside the autoclave generates heat and/or pressure. (When a doctor or dentist sterilizes his instruments in his office,. he uses an autoclave that generates superheated steam.)... 

In the suspension polymerization process, the autoclave reactor is filled with water. PVA, polyvinyl alcohol is the dispersing agent that helps stabilize the suspension. Lauroyl peroxide is the free radical catalyst that starts it all off. The reaction temperature is around 130°F, and the process takes 10—12 hours per batch, with 95% conversion. 

Recently, cross-aldol condensation of benzaldehyde with n-heptaldehyde to give jasminaldehyde (Scheme 13) has been reported a mesoporous molecular sieve Al-MCM-41 with supported MgO was the catalyst. The reactions were carried out in a stirred autoclave reactor with a molar benzaldehyde/heptanal ratio of 10 at 373-448 K (236). The results show that Al-MCM-41 is catalytically active, and its activity is significantly increased by the deposition of MgO (Table V). Increasing the amount of deposited MgO on Al-MCM-41 decreases the surface area but enhances the catalyst basicity. The basicity is well correlated with the catalytic activity, although the selectivity to jasminaldehyde is not the selectivity is essentially independent of temperature, pressure, time of the reaction, and conversion. 

Tubular reactors are most often used, although autoclave reactors are also employed. Tubular reactors consist of a number of sections, each with an inner diameter of 2-6 cm and length of 0.5-1.5 km, arranged in the shape of an elongated coil. The polymerization mixture has very high linear velocities (>10m s-1) with short reaction times (0.25-2 min). Trace amounts of oxygen (<300 ppm) are typically used as the initiator, often in combination... 

Autoclave reactors differ from tubular reactors in two respects. Autoclave reactors have much smaller length-to-diameter ratios (2-4 for single-zone and up to 15-18 for multizone reactors) and operate at a much narrower reaction temperature range. 

Table 1. Hydrogenation of aldehyde A to form the alcohol D 40°C, 30psig, 2500 rpm in autoclave reactor...

The autoclave reactors used today in the high-pressure polymerization of ethylene are single stirred-tank reactors, cascades of stirred autoclaves, and multi-chamber autoclaves. 

Autoclave reactors are operated adiabatically, which means that the heat of reaction must be removed by the fresh ethylene entering the reactor. The conversion is related, therefore, to the difference in temperature between the feed and the reactor temperature. This limits the conversion to 15 - 20%. Taking into account the fact that the percentage conversion, Ax, can be approximated by using the average specific heat, cp, the enthalpy of the polymerization,... 

Figure 5.1-8. Multi-zone autoclave reactor. E, Ethylene I, initiator P, product a, reactor b, motor c, stirrer d, connecting cable e, bearing.

The autoclave reactor process was improved when the reactors were arranged in series (Fig. 5.1-7). By feeding fresh ethylene into the line between the reactors and/or removing heat by means of coolers [14,15] the conversion could be increased above 20%. When peroxides of different activity are used the reactors can be run at different temperatures. Furthermore, the split of the feed of fresh ethylene can be varied. 

High conversion, similar to that in a tubular reactor with multiple feed, is obtained in a multi-chamber or multi-zone autoclave reactor. This is an elongated cylindrical vessel with a ratio of length to inner diameter of 10 - 12. It is subdivided by baffles and the stirrer into two to five chambers (Fig. 5.1-8, left). 

As an example, in Fig. 7.2-6 the influence of copper(II) acetate under a pressure of 195 MPa and 220°C is presented. When Cu(II) acetate was injected into an autoclave reactor... 

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