Continuous stirred-tank reactor weight distribution

Reactor Conditions for Experimental Runs. Operating conditions for the continuous, stirred tank reactor runs were chosen to study the effects of mixing speed on the monomer conversion and molecular weight distribution at different values for the number average degree of polymerization of the product polymer. 

Continuous Stirred Tank Reactors. (CSTR). The first analysis of continuous reactors for polymerization was by Denbigh (14). He treated the same mechanisms in a CSTR that Gee and Melville (21) had treated in a batch reactor. The problem is simpler in a steady state CSTR since the equation for each dead and live specie is an algebraic rather than a differential equation. These are solved sequentially. The PSSA is not needed. He predicted a narrower molecular weight distribution for a continuous chain polymerization than for the same polymerization carried... 

Continuous Stirred Tank Reactors. Biesenberger (8) solved for the MWD with condensation polymerization in a CSTR, analogous to the treatment Denbigh (14) provided for the other two mechanisms. In this case, the variable residence time distribution leads to an extremely broad MWD with even the maximum weight fraction at the lowest molecular weight (monomer). The dispersion index approaches infinity as the condensation is driven to completion in a stirred tank reactor. A sequential analytical solution of the algebraic equations was obtained with a numerical evaluation of the consecutive equations. 

Reactors used in ethylene polymerizations range from simple autoclaves and steel piping to continuous stirred tank reactors (CSTR) and vertical fluidized beds. Since the 1990s, a trend has emerged wherein combinations of processes are used with transition metal catalysts. These combinations allow manufacturers to produce polyethylene with bimodal or broadened molecular weight distributions (see section 7.6). 

The Hoechst slurry process was improved over the years and has evolved into what is now called the Hostalen process. Hostalen is a slurry-cascade process that is capable of producing a wide range of molecular weight distributions of HOPE. The modern Hostalen process employs 2 continuous stirred tank reactors that can be run in series or in parallel to produce unimodal and bimodal HOPE (11). 

Continuous-flow stirred tank reactors are widely used for free-radical polymerizations. They have two main advantages the solvent or monomer can be boiled to remove the heat of polymerization, and fairly narrow molecular weight and copolymer composition distributions can be achieved. Stirred tanks or... 

Batch, semi-batch and continuous emulsion polymerizations are usually carried out in stirred tank reactors, where agitation by a stirrer is necessary. The type of stirrer chosen and its stirring speed can often affect the rate of polymerization, the number of polymer particles and their size distribution (PSD), and the molecular weight of the polymer produced. However, the effect of stirring on emulsion polymerization has never been the main research parameter in research programs [241]. This is probably due to the conflicting results obtained so far by various researchers. 

In a continuous emulsion process, two or more stirred tank reactors in series are used. Separate feed streams are continuously added into each reactor. The reactors are operated at about 68°C. The latex is transferred to a holding tank (residence time of about 4 hr) before being steam-stripped to remove unreacted monomers. In a continuous process, the residence time distribution is generally broad. A large holding tank placed downstream of the reactors provides extra time to the reaction mixture and reduces the molecular-weight distribution. 

CFSTR Continuous-flow, stirred tank reactor BR batch reactor TR tube reactor MWD molecular weight distribution. 

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