Heat Added to the Reactor

Rate of heat transfer from exchanger to reactor 

Solving Equation (12-16) for the exit temperature of the heat exchanger fluid yields 

For large values of the heat exchanger fluid flow rate, the exponent will be small and can be expanded in a Taylor scries (c = 1 - c + - ) where second-order terms are neglected in order to give 

Valid only for large heat transfer fluid flow rates  

Steady-State Nonisolhermal Reactor Design—Flow Reactors with Heat Exchange Chapter 12 

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When the heat flow varies along the length of the reactor as in a tubular reactor, Equation 6-25 can be integrated along the length of the reactor to obtain the total heat added to the reactor ... 

Equation 5.2.12 is the integral form of the energy balance equation for batch reactors, relating the reactor temperature, T t), to the extents of the independent reactions, the heat added to the reactor, Q(t), and the mechanical work done... 

Rate heat added to the reactor, energy/time... 

In the previous section, we derived Equation (8-28), which relates conversion to temperature and the heat added to the reactor, Q. Let s stop a minute and consider a system with the special set of conditions of no work. K l = 0, adiabatic operation = 0, and then rearrange (8-27) into the form... 

In the most common production method, the semibatch process, about 10% of the preemulsified monomer is added to the deionised water in the reactor. A shot of initiator is added to the reactor to create the seed. Some manufacturers use master batches of seed to avoid variation in this step. Having set the number of particles in the pot, the remaining monomer and, in some cases, additional initiator are added over time. Typical feed times ate 1—4 h. Lengthening the feeds tempers heat generation and provides for uniform comonomer sequence distributions (67). Sometimes skewed monomer feeds are used to offset differences in monomer reactivity ratios. In some cases a second monomer charge is made to produce core—shell latices. At the end of the process pH adjustments are often made. The product is then pumped to a prefilter tank, filtered, and pumped to a post-filter tank where additional processing can occur. When the feed rate of monomer during semibatch production is very low, the reactor is said to be monomer starved. Under these... 

In a typical example (33) a fresh feed of 8% polybutadiene rubber in styrene is added with antioxidant, mineral oil, and recycled monomer to the first reactor at 145 lbs./hr. The reactor is a 100-gallon kettle at approximately 50% tillage with the anchor rotating at 65 rpm. The contents are held at 124°C and about 18% conversion. Cooling is effected via the sensible heat of the feed stream and heat transfer to the reactor jacket. In this reactor the rubber phase particles are formed, their average size determined and much of their morphology established. Particle size is controlled to a large measure by the anchor rpm. 

At the beginning of the batch cycle, both the reactor liquid and the jacket water are at 203°F. At this point in lime, catalyst is added to the reactor and a reaction occurs which generates heat at a constant rate of 15,300 Btu/min. At this same moment in time, makeup cooling water at 68°F is fed into the jacket at a constant 832 lb ,/min flow rale. 

The composition of the gas produced is determined by the thermodynamic equilibrium of these reactions at the exit temperature, which is given by the adiabatic heat balance based on the composition and flow of the feed, steam and oxygen added to the reactor. 

The hydrocarbon feedstock is reacted with a mixture of oxygen or air and steam in a sub-stoichiometric flame. In the fixed catalyst bed the synthesis gas is further equilibrated. The composition of the product gas will be determined by the thermodynamic equilibrium at the exit pressure and temperature, which is determined through the adiabatic heat balance based on the composition and flows of the feed, steam and oxygen added to the reactor. The synthesis gas produced is completely soot-free [28]. 

Let Q be the total heat added to a reactor per mole of entering reactant A, and let this heat also include the losses to the surroundings. Then Eq. 20, the energy balance about the system, is modified to... 

Each term in the preceding equations has units of energy/time. Note the signs on each term indicating that heat is removed or added to the reactor. We preserve the minus sign on A Hji because we are more interested in exothermic reactions for which A Hr < 0. The student can recognize each term on the right side from the steady-state enthalpy balance we derived in the previous section from the thermodynamics of a steady-state flow system. 

The view-cell reactor is made of titanium and has two sapphire windows, a gas inlet valve and an outlet valve, as shown in Figure 3. The view cell is interfaced with a pressure transducer, a thermocouple, and a pressure relief valve. The pressure and temperature are computer-monitored during the reaction. 0.6 ml of 50 wt% H2O2/H2O (10.41 mmoles), 0.20ml of pyridine (2.47 mmoles), or some other base, was dissolved in 5 ml of acetonitrile or methanol, and was added to the reactor. 2.2 ml of supercritical CO2 was charged after lOOmg of propylene (2.38 mmoles) had been added to the reactor. The reactor was heated with a band heater at 40 - 70°C for 3, 6, 12, and 24 hr reaction periods. Following a batch conversion experiment, the amounts of products formed were determined by GC and GC/MS. 

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