Continuous autoclave reactor

Continuous stirred-tank reactors (CSTRs) are used for large productions of a reduced number of polymer grades. Coordination catalysts are used in the production of LLDPE by solution polymerization (Dowlex, DSM Compact process [29]), of HDPE in slurry (Mitsui CX-process [30]) and of polypropylene in stirred bed gas phase reactors (BP process [22], Novolen process [31]). LDPE and ethylene-vinyl acetate copolymers (EVA) are produced by free-radical polymerization in bulk in a continuous autoclave reactor [30]. A substantial fraction of the SBR used for tires is produced by coagulating the SBR latex produced by emulsion polymerization in a battery of about 10 CSTRs in series [32]. The CSTRs are characterized by a broad residence time distribution, which affects to product properties. For example, latexes with narrow particle size distribution cannot be produced in CSTRs. 

Low-density polyethylene (density = 0.915-0.935 g cm ) has long been manufactured by free-radical polymerization using continuous autoclave reactors. The autoclave reactor shown schematically in Fig. 3a is a typical multizone ethylene polymerization reactor. The reactor is typically a vertical cylindrical vessel with a large LID ratio. The reacting fluid is intensely mixed... 

For a single continuous autoclave reactor of volume V to which ethylene and initiator are supplied, the following simple modeling equations can be derived ... 

When the reactor consists of more than one compartment, the behavior of downstream compartments are strongly dependent on those of upstream compartments. For the two-compartment continuous autoclave reactor. Fig. 3 illustrates the temperature of the second compartment as a function of the... 

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. 

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. 

Gulf Research and Development Co. Two of the coals were processed in the Gulf continuous flow reactor, fed at the rate of about 1.5 kg coal/hr for 15-18 hrs. The third coal was processed in a conventional batch autoclave run. In all three runs, the coal was processed at about 400 °C and 3000 psi pressure of hydrogen using a proprietary catalyst. In the continuous runs, distillate from previous experiments was used as vehicle while in the autoclave experiment, partly hydrogenated phenanthrene was used. The vehicle-to-coal ratio was 2 1. In each case the reaction products were filtered on a steam-heated Buchner funnel. 

The polymerizations were carried out in a pressurized continuous polymerization reactor of 8 1 capacity (Autoclave Engineers). While most of the polymerization runs actually would not have required pressure, all runs were carried out at 2.5 x 10 Pa (Nj), which was convenient for the AN/VBr runs. The dispersion polymerization, at a water/monomer ratio of 3.5 (by weight), was catalyzed by a persulfate — bisulfite iron system... 

In the Bayer process, ground bauxite is digested with aqueous sodium hydroxide (200 to 350 g/L sodium hydroxide) at temperatures of 140 to 250°C in autoclaves or in continuous tube reactors, in which the hydrated aluminum hydroxide is dissolved as sodium aluminate. The iron-containing very finely divided so-called red mud is then separated in thickening and filter units and washed. Ca. 1 to 2 t of red mud is produced per t aluminum oxide. 

For example the conversion of cellulose was studied in autoclaves with residence times of up to 1 h at 200-400 °C and 8-18 MPa [138, 139]. It was found that sodium carbonate as a catalyst suppresses the formation of char and oil and mainly water-soluble products were formed. At 400 and with a Ni catalyst, CH4 and CO2 were found as major products in the gas phase. Batch reactor experiments [140, 141] used for the formation of a CH4-rich gas from biomass, waste model compounds and real waste waters, were also carried out at 350 °C, 20 MPa, and reaction times of 60-120 min. It was shown that aromatic and aliphatic hydrocarbons as well as oxygenates are converted to a CH4-rich fuel gas in the presence of hydrogenation catalysts. The results were confirmed in continuous-flow reactor experiments with residence times of 10 min and longer for conversions of 90 % or more. In any case, without the high reactivity of biomass in and with near-critical water, methane formation at low temperatures would not be possible. 

Autoclave Reactor An autoclave reactor is a batch or continuous reactor usually operating at moderate-to-high pressures > 1 bar and a pressurized liquid or gaseous environment. 

The typical feature of this process is the fluidised bed reactor which widens at its top to reduce the gas velocity and entrainment of particles. Continuously fed flows of catalyst, monomer and hydrogen are mixed thoroughly in the fluidised bed. A large cooler in the loop for gas recirculation draws off the reaction heat Ifom the considerable gas volume flows. In this system, the fluidised bed reactor acts like a back-mixing autoclave reactor there is no excessive separation of coarse particles. For copolymerisation, a second fluidised bed reactor is added (as shown in Figure 3.15). The reaction conditions are below 88 °C and 4 MPa. 

Batch polymerisation is realised in autoclave reactors which operate on a cycle of phases at increased levels of temperature where the time and pressure parameters are carefiilly adjusted in order to gradually convert the monomer into polymer. The design of the plant is realised in order to optimise the sequences of different autoclaves, giving better continuity to production. The low quantity of product produced per each batch operation and the higher flexibility of the process, make the batch process suitable for the production of speciality polyamides. Batch polymerisation is also suitable for producing copolymers of polyamide 66 and polyamide 6, using partially caprolactam as the raw material together with nylon salt. 

How long a space time is required for a continuous tube reactor to achieve the same conversion as was obtained in the autoclave at 20 min ... 

A semi-batch reactor is more difficult to analyze mathematically because at least one of the reactant or product species enters or leaves the system boundaries, thus specific applications should be modeled [1,5]. However, the most typical application for a semi-batch reactor is the presence of one reactant initially contained in a stirred tank reactor and a second reactant continuously added to the reactor, with no flow out of the reactor. The addition of a gas to participate in a liquid-phase reaction is one of the more common situations involving a semi-batch reactor, especially because the rate of addition of the gas can be controlled to keep its partial pressure essentially constant as well as providing quantitative information about the rate of reaction. In addition, there is frequently little or no change in the volume of the liquid phase. Well-mixed autoclave reactors coupled with gas pressure controllers, mass flow meters and computers can nicely provide continuous, real-time rate data related to heterogeneous catalysts used in such gas/liquid systems [6-8]. Again, it must be emphasized that experiments must be performed and/or calculations made to verify that no heat or mass transfer limitations exist. 

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