Reactors screw

A schematic of a continuous bulk SAN polymerization process is shown in Figure 4 (90). The monomers are continuously fed into a screw reactor where copolymerization is carried out at 150°C to 73% conversion in 55 min. Heat of polymerization is removed through cooling of both the screw and the barrel walls. The polymeric melt is removed and fed to the devolatilizer to remove unreacted monomers under reduced pressure (4 kPa or 30 mm Hg) and high temperature (220°C). The final product is claimed to contain less than 0.7% volatiles. Two devolatilizers in series are found to yield a better quaUty product as well as better operational control (91,92). 

Index Entries Screw reactor computational fluid dynamics modeling backflow hydrolysis. 

In the hardwood hydrolysis experiment with the screw reactor, NREL researchers found that overmixing and an uneven flow pattern existed in the reactor. These factors have a negative effect on biomass hydrolysis. To enhance the screw conveyor reactor s performance, it was necessary to redesign the reactor to achieve adequate mixing and an even flow pattern. In the present work, CFD was utilized to analyze the flow behavior in the screw conveyor reactor, and a new screw design was proposed based on CFD analysis. 

Figure 3 shows the flow pattern in the bottom part of the screw reactor along the vertical panel of baffles. Flow in the bottom zone is mostly rotational, with strong backflow observed in this area. Figure 4 shows the flow pattern in the horizontal panel along the baffle. Apparently, the flow along this panel can be divided into two zones, each of which moved along the reactor wall, met, and then moved downward. 

Fig. 3. Flow pattern in bottom part of screw reactor (A) two-dimensional view (B) three-dimensional view.

Fig. 4. Flow pattern of screw reactor along horizontal panel of baffle.

Figure 10 shows the path lines in the bottom screw zone for the original screw reactor and the redesigned reactor. The path lines clearly show... 

Fig. 9. Positive axial velocity contour (backflow) of redesigned screw reactor.

Highly viscous polymeric reactions (e.g., the hydrolytic polyamide reaction) are often carried out in a gear-pump reactor (Tadmore and Klein, 1970). This type of reactor is often difficult to operate because the clearance of the gear teeth is increased by wear caused by flow and the reaction process. For smaller viscosity of the melt, a screw reactor or a twin-screw extruder is often used. Sterbecek et al. (1987) used a twin-screw extruder (i.e., Wemer-Pfleiderer extruder ZSK 83) for studying fast ion-catalyzed polymerization (6-caprolactam) in a melt. They indicated that power input and quality of product in such a reactor depends on the slot width between reactor wall and impeller in a twin screw extruder. They provided an optimum design of a twin-screw reactor for a fast ion-catalyzed polymerization in a melt. 

The twin-screw reactor is useful for polymeric operations because it provides... 

Design parameters for novel reactors such as rotating-cylinder reactors, thin-film reactors, propeller loop reactors, screw reactors, and multidisk reac-... 

An alternative process based on two sequential catalytic cracking stages aimed at obtaining gasoline and diesel from waste plastics or heavy oil/waste plastics mixtures is shown in Figure 3.16 [99]. The catalyst employed in the first step is made up of powder alumina, waterglass and HZSM-5 zeolite and is mixed up directly with the waste plastics in a screw reactor preferably at 600-700°C. The second catalytic step consists in a fixed... 

The main products derived from the thermal degradation of LDPF in the screw reactor at the set operating conditions were gasoline and middle distillates. Serrano et al. [11] showed that the flow in the screw kiln is sufficient to avoid overcracking of heavy fractions into smaller hydrocarbons such as gas which commonly occurs in batch processes. 

The majority of the scientific literatnre devoted to pyrolysis of plastics is focused on the development of equipment or processes having recycling as their ultimate goal. Many of these have been introdnced in previous chapters and include studies using fluidized beds [61-77], cycled-sphere reactors [78, 79], fixed-bed reactors [80, 81], rotary kilns [82], screw reactors [83] and rotating cone reactors [84]. In all these studies the chemical analysis of the pyrolysis prodncts has been an important goal in order to asses the behavionr of the pyrolysis of plastics. 

Conversion of UO2 to UF4 proceeds with anhydrous hydrogen fluoride (dry process) in fluidized bed, screw-reactor or moving bed reactor... 

Uranium(IV) oxide is the starting material for uranium(lV) fluoride production in which uranium(lV) oxide is generally reacted with anhydrous hydrogen fluoride. This difficult to carry out exothermic reaction proceeds either in a fluidized bed, in moving bed reactors, or in screw-reactors. To achieve as complete as possible reaction in fluidized bed reactors, two fluidized bed reactors are connected in series. Screw-reaetors are also preferably connected in series. In moving bed reactors the reduction zone and the hydrofluorination are arranged above one another in a plant. The uranium(IV) oxide produced by the reduction of uranium(VI) oxide with hydrogen is very reactive and is eompletely reaeted with HF at temperatures between 500 and 650°C to uranium(lV) fluoride. 

Fig. 14. Conversion profiles in a screw reactor at different distances from the output of the reaaor (figures near curves denote the distance from the output)...

Based on the promising results a pilot plant covering the complete process chain is about to be constructed in cooperation with Lurgi on the KIT site. The 2-MW (500-kg biomass input capacity) fast pyrolysis plant based on a transported bed (twin screw) reactor was commissioned in 2008. A 5-MW high-pressure entrained flow gasifier equipped with a cooling screen and... 

There are different tubular and column plug flow reactors as well as screw reactors [1]. Plug flow reactors are used for various gas-phase reactions occuring within industrial-scale production, particularly for the reactions of nitrogen oxide oxidation, ethylene chloration, and high-pressure ethylene polymerisation. They are also used for some liquid-phase and gas-liquid reactions, e.g., styrene polymer production in a column, plastic and rubber production, synthesis of ammonia and methanol, and sulfation of olefins [2]. 

The cationic copolymerization of trioxane with ethylene oxide, 1,3-dioxolane, and suchlike is initiated either with strong protonic acids or Lewis acids, for example BF3. Molecular weight is controlled by the catalyst concentration and monomer purity, and also by chain transfer agents such as methylal [248], which may lead to more stable end groups. Most processes are run below the melting temperature of the polymer (164-167°C) in precipitating agents or in bulk, and are carried out in kneaders or double-screw reactors [249, 250], but there are also some descriptions of melt processes [251]. 

The gas-phase technique is an economical method of hydrolysis which seems to be adaptable to the industrial practice. The temperature of hydrolysis must, however, not exceed 180°C. On an industrial scale the hydrolysis may be performed in a screw reactor in order to improve temperature control. 

N EHaye, S., Rigal, L., Larocque, R, Vidal, P.F., 1996. Extraction of hemiceUuloses from poplar, Populus tremuloides, using an extruder-type twin-screw reactor a feasibility study. Bioresource Technology 57 (1), 61-67. 

In continuous industrial free-radical polymerization processes, many different types of reactors are used [1]. They are continuous-flow stirred tank reactors, tower reactors, horizontal linear flow reactors, tubular reactors, and screw reactors. In some processes, different types of reactors are used together in a reactor train. In stirred tank reactors, no spatial concentration and temperature gradients exist, whereas in linear flow or tubular reactors, concentration and temperature vary in the direction of flow of the reacting fluid. Specially designed reactors such as screw reactors or extruder reactors are also used to produce specialty vinyl polymers. In this chapter, some important characteristics of continuous reactors used in industrial free-radical polymerization processes are discussed. 

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