Continuous stirred tank reactor feed temperature

Enzyme—1.0 FP activity Substrate—SF-HM (76% < 53/x)—v0% pH— 4.05-5.2 Saccharification temperature—50°C. Dilution rate in continuous phase—0.025"J hr. Reactor conditions 4.0 liter glass stirred tank reactor Feed temperature—1°-2°C. 

The ideal continuous stirred tank reactor is the easiest type of continuous flow reactor to analyze in design calculations because the temperature and composition of the reactor contents are homogeneous throughout the reactor volume. Consequently, material and energy balances can be written over the entire reactor and the outlet composition and temperature can be taken as representative of the reactor contents. In general the temperatures of the feed and effluent streams will not be equal, and it will be necessary to use both material and energy balances and the temperature-dependent form of the reaction rate expression to determine the conditions at which the reactor operates. 

In the hazard evaluation of the process, it was found that exotherms occurred with MNB-H2SO4 mixtures at temperatures above 150°C. The initiation temperature and extent of the exotherm depend on the acid concentration. During normal operation, the temperatures in die continuous stirred tank reactors and in the continuously operated separator are between 135 and 148°C. However, operating simulation showed that for certain feed rates well out of the normal operating range, the temperature could reach 180°C and a runaway is thus possible. 

In an ideal continuous stirred tank reactor, composition and temperature are uniform throughout just as in the ideal batch reactor. But this reactor also has a continuous feed of reactants and a continuous withdrawal of products and unconverted reactants, and the effluent composition and temperature are the same as those in the tank (Fig. 7-fb). A CSTR can be operated under transient conditions (due to variation in feed composition, temperature, cooling rate, etc., with time), or it can be operated under steady-state conditions. In this section we limit the discussion to isothermal conditions. This eliminates the need to consider energy balance equations, and due to the uniform composition the component material balances are simple ordinary differential equations with time as the independent variable ... 

Numerical simulations and analyses were performed for both the continuous stirred-tank reactor (CSTR) and the plug-flow reactor (PER). A comparison between the microkinetic model predictions for an isothermal PFR and the experimental results [13], is presented in Fig. 2 for the following conditions commercial low temperature shift Cu catalyst loading of 0.14 g/cm total feed flow rate of 236 cm (STP) min residence time r = 1.8 s feed composition of H20(10%), CO(10%), C02(0%), H2(0%) and N2(balance). As can be seen, the model can satisfactorily reproduce the main features of the WGSR on Cu LTS catalyst without any further fine-tuning, e.g., coverage dependence of the activation energy, etc, which is remarkable and provides proof of the adequacy of the... 

The continuous-stirred-tank reactor (CSTR) is shown in Figure 1.3. Reactants and products flow into and out of the reactor continuously, and the contents of the reactor are assumed to be well mixed. The well-mixed assumption can be realized more easily for liquids than gases, so CSTRs are often used for liquid-phase reactions. The fluid composition and temperature undergo a step change when passing from the feed stream into the interior of the reactor the composition and temperature of the effluent stream are identical to those of the reactor. 

Polymerizations. Polymerizations were performed in solution with a 0.5-L continuous stirred tank reactor this apparatus provided polymers of constant composition. After steady-state operation was obtained (approximately three residence times, see Figure 1), 10-mL samples were periodically taken from the effluent, added to 200 xL of a hydroquinone solution, and stored at 10 °C. These samples were subsequently analyzed by HPLC to estimate the mean and variance of the residual monomer concentration and copolymer composition. The polymerization temperatures were 45 and 60 °C for the dimethylamines and 50 °C for DADMAC. The initial monomer concentration was 0.5 mol L" and the monomer feed ratio was varied between 0.3 and 0.7. Azocyanovaleric acid (ACV, Wako Chemical Co.) and potassium persulfate (KPS, BDH Chemicals) were used to initiate the reaction. The solution was agitated at 300 1 rpm for the duration of the polymerization. 

The ideal continuous stirred tank reactor is a reactor with well-stirred and back-mixed contents. As a result, instant blending of the feed with the reactor contents is assumed to occur. The composition of the contents of the reactor is uniform throughout the reactor. Consequently, the exit stream from the reactor has the same composition and temperature as the reactor contents. 

In commercial practice, polymerization is effected in a continuous-stirred-tank reactor (CSTR), a system in which all components are fed continuously and mixed, and the product is continuously discharged. For start-up, the reactor is charged with a certain amount of pH-adjusted water or the reactor is filled with overflow from another reactor already operating at steady state. The reactor feeds are metered in at a constant rate for the entire course of the production run, which normally continues until equipment cleaning or maintenance is needed. A steady state is established by taking an overflow stream at the same mass flow rate as the combined feed streams. The reaction vessel is normally an aluminum alloy this minimizes scale buildup as the wall provides a sacrificial surface. The reactor is jacketed steam may be introduced to heat the contents for start-up, but once the polymerization is initiated, water is circulated in the jacket to remove the heat of polymerization and maintain a constant temperature, usually 50-60°C. 

Figure 7.4 shows the response of the temperature T in a continuous stirred-tank reactor to a step change in feed flow rate w from 120 to 125 kg/min. Find an approximate first-order model for the process and these operating conditions. 

In the polymerization process shown in Fig. Ic [3], a fresh feed of 8% polybutadiene rubber in styrene is added with antioxidant and recycled monomer to the first reactor operating at 124 C and about 18% conversion at about 40% fillage. The agitator is a horizontal shaft on which a set of paddles is mounted. Because the temperature in each compartment can be varied, it is claimed that the linear flow behavior provided by the reactor staging results in more favorable rubber-phase morphology than would be the case if the second reactor were operated as a single continuous stirred tank reactor. 

A continuous flow stirred tank reactor (CFSTR) differs from the batch reactor in that the feed mixture continuously enters and the outlet mixture is continuously withdrawn. There is intense mixing in the reactor to destroy any concentration and temperature differences. Heat transfer must be extremely efficient to keep the temperature of the reaction mixture equal to the temperature of the heat transfer medium. The CFSTR can either be used alone or as part of a series of battery CFSTRs as shown in Figure 4-5. If several vessels are used in series, the net effect is partial backmixing. 

In the second model (Figure 5.1b), the mixed-flow or continuous well-mixed or continuous-stirred-tank (CSTR) model, feed and product takeoff are both continuous, and the reactor contents are assumed to be perfectly mixed. This leads to uniform composition and temperature throughout the reactor. Because of the perfect mixing, a fluid element can leave the instant it enters the reactor or stay for an extended period. The residence time of individual fluid elements in the reactor varies. 

Because of the dilution that results from the mixing of entering fluid elements with the reactor contents, the average reaction rate in a stirred tank reactor will usually be less than it would be in a tubular reactor of equal volume and temperature supplied with an identical feed stream. Consequently, in order to achieve the same production capacity and conversion level, a continuous flow stirred tank reactor or even a battery of several stirred tank reactors must be much larger than a tubular reactor. In many cases, however, the greater volume requirement is a relatively unimportant economic factor, particularly when one operates at ambient pres-... 

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