Reactor intermediate

Eigure 2 shows that even materials which are rather resistant to oxidation ( 2/ 1 0.1) are consumed to a noticeable degree at high conversions. Also the use of plug-flow or batch reactors can offer a measurable improvement in efficiencies in comparison with back-mixed reactors. Intermediates that cooxidize about as readily as the feed hydrocarbon (eg, ketones with similar stmcture) can be produced in perhaps reasonable efficiencies but, except at very low conversions, are subject to considerable loss through oxidation. They may be suitable coproducts if they are also precursors to more oxidation-resistant desirable materials. Intermediates which oxidize relatively rapidly (/ 2 / i — 3-50 eg, alcohols and aldehydes) are difficult to produce in appreciable amounts, even in batch or plug-flow reactors. Indeed, for = 50, to isolate 90% or more of the intermediate made, the conversion must... 

For more complex equipment, the columns might contain measurements for internal distillatiou, batch-reactor intermediate conditions, or tubular-reactor between-bed conditions. Some of these... 

Japanese researchers very carefully followed the oxidation of sodium sulfide Na2S (A) to sodium thiosulfate Na2S203 (R) in a batch reactor. Intermediates were measured and the results found were sketched in Fig. E8.3. 

Epmddation. It also takes place in several series of reactors, each with four elements, in the presence of chcmical-grade propjdene, injected at the inlet to each reactor. Intermediate heat exdiangers remove the heat liberated. Readence time is about 11/4 hours. Excess propytene b recovered under pressme in a senes of two depropanizers. Purge takes i lace in a third column, separating part of the propane introduced with Che propylene feedstock. 

Continuous Reactors. A variety of continuous reactor systems are used commercially, but the most common are comprised of a number of stirred-tank reactors (CSTR) connected in series. Operation normally Involves pumping all ingredients into the first CSTR and removing the partially converted latex from the final reactor. Intermediate feed streams can also be employed. Detailed reviews... 

AHTR-IT Advanced High-Temperature Reactor-intermediate temperature... 

In the segment for regeneration of CaBr2from CaO, heat at 600°C is rejected. It is used to help drive the SC-CO2 Brayton cycle. However, because that heat supply is not sufficient, the Brayton cycle also receives heat from the flibe loop. The flibe then returns to the reactor intermediate heat exchanger (MX) at 650°C. 

Reactors taller than 30 ft (9,150 mm) should be treated much like towers (.see Chapter 10) for platform requirements except that, for reactors, intermediate platforms and ladders are required only for ac-ce,ss to temperature instruments, sample probe.s, cataly.st unloading nozzles at stacked ve.s.sels, and maximum ladder runs. Becau.se of the eamomics of platform bracket welding or client preference, however, reaaors mu,st. sometimes be. surrounded bv. steel... 

Van de Vusse [1] pointed out that selectivity with respect to I increases with an increase of the mass transfer coefficient (k ). In light of this observation, we have developed a new reactor of cyclonic type in which, due to strong centripetal forces on the gas bubbles, a very high k is realized [2]. This paper deals with the selectivities obtained in sulfonation of benzene with sulfur trioxide. Both neat benzene and benzene diluted with 1,2-dichloroethane were used. This reaction was selected as a model reaction for industrially important aromatic sulfation (e.g. detergents). We studied the reaction in three reactor types that greatly differ in mass transfer characteristics, i.e. in a stirred ceii reactor (low k ), a co-current gas-liquid tube reactor (intermediate k ) and in the cyclone reactor (high k ). 

Product removal during reaction. Sometimes the equilibrium conversion can be increased by removing the product (or one of the products) continuously from the reactor as the reaction progresses, e.g., by allowing it to vaporize from a liquid-phase reactor. Another way is to carry out the reaction in stages with intermediate separation of the products. As an example of intermediate separation, consider the production of sulfuric acid as illustrated in Fig. 2.4. Sulfur dioxide is oxidized to sulfur trioxide ... 

Another possibility to improve selectivity is to reduce the concentration of monoethanolamine in the reactor by using more than one reactor with intermediate separation of the monoethanolamine. Considering the boiling points of the components given in Table 2.3, then separation by distillation is apparently possible. Unfortunately, repeated distillation operations are likely to be very expensive. Also, there is a market to sell both di- and triethanolamine, even though their value is lower than that of monoethanolamine. Thus, in this case, repeated reaction and separation are probably not justified, and the choice is a single plug-flow reactor. 

Having made an initial specification for the reactor, attention is turned to separation of the reactor effluent. In addition, it might be necessary to carry out separation before the reactor to purify the feed. Whether before or after the reactor, the overall separation task normally must be broken down into a number of intermediate separation tasks. The first consideration is the choice of separator for the intermediate separation tasks. Later we shall consider how these separation tasks should be connected to the reactor. As with reactors, we shall concentrate on the choice of separator and not its detailed sizing. 

Separators working at unsteady conditions produce intermediates with compositions which do not allow them to be recycled. Alternatively, if the intermediate can be recycled, a nonoptimal recycle might produce (additional) unwanted byproducts in the reactor. 

Figure 13.1a shows two possible thermal profiles for exothermic plug-fiow reactors. If the rate of heat removal is low and/or the heat of reaction is high, then the temperature of the reacting stream will increase along the length of the reactor. If the rate of heat removal is high and/or the heat of reaction is low, then the temperature will fall. Under conditions between the two profiles shown in Fig. 13.1a, a maximum can occur in the temperature at an intermediate point between the reactor inlet and exit. 

The thermal profile through the reactor will in most circumstances be carefully optimized to maximize selectivity, extend catalyst life, etc. Because of this, direct heat integration with other process streams is almost never carried out. The heat transfer to or from the reactor is instead usually carried out by a heat transfer intermediate. For example, in exothermic reactions, cooling might occur by boiling water to raise steam, which, in turn, can be used to heat cold streams elsewhere in the process. 

Chain reactions do not go on forever. The fog may clear and the improved visibility ends the succession of accidents. Neutron-scavenging control rods may be inserted to shut down a nuclear reactor. The chemical reactions which terminate polymer chain reactions are also an important part of the polymerization mechanism. Killing off the reactive intermediate that keeps the chain going is the essence of these termination reactions. Some unusual polymers can be formed without this termination these are called living polymers. 

Single-reaction-step processes have been studied. However, higher selectivity is possible by optimizing catalyst composition and reaction conditions for each of these two steps (40,41). This more efficient utilization of raw material has led to two separate oxidation stages in all commercial faciUties. A two-step continuous process without isolation of the intermediate acrolein was first described by the Toyo Soda Company (42). A mixture of propylene, air, and steam is converted to acrolein in the first reactor. The effluent from the first reactor is then passed directiy to the second reactor where the acrolein is oxidized to acryUc acid. The products are absorbed in water to give about 30—60% aqueous acryUc acid in about 80—85% yield based on propylene. 

Alkyltin Intermedia.tes, For the most part, organotin stabilizers are produced commercially from the respective alkyl tin chloride intermediates. There are several processes used to manufacture these intermediates. The desired ratio of monoalkyl tin trichloride to dialkyltin dichloride is generally achieved by a redistribution reaction involving a second-step reaction with stannic chloride (tin(IV) chloride). By far, the most easily synthesized alkyltin chloride intermediates are the methyltin chlorides because methyl chloride reacts directiy with tin metal in the presence of a catalyst to form dimethyl tin dichloride cleanly in high yields (21). Coaddition of stannic chloride to the reactor leads directiy to almost any desired mixture of mono- and dimethyl tin chloride intermediates ... 

Efficiency of Intermediate Formation. The variation of the efficiency of a primary intermediate with conversion of the feed hydrocarbon can be calculated (22). Ratios of the propagation rate constants ( 2 / i) reactor type (batch or plug-flow vs back-mixed) are important parameters. 

Eig. 2. Efficiency to a primary intermediate as % of maximum (zero conversion) efficiency x axis is feed conversion. Parameters are oxidation rate-constant ratios ( 2 / i) for primary intermediate vs feed and reactor type A, plug-flow or batch B, back-mixed. 

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