Reactor multitubular

The reaction is exothermic, and multitubular reactors are employed with indirect cooling of the reactor via a heat transfer medium. A number of heat transfer media have been proposed to carry out the reactor cooling, such as hot oil circuits, water, sulfur, mercury, etc. However, the favored heat transfer medium is usually a molten heat transfer salt which is a eutectic mixture of sodium-potassium nitrate-nitrite. 

With a multitubular reactor, conversions of 74—82% per pass can be obtained while generating steam to be used elsewhere in the process (99). 

Summary of Characteristics of Falling Film Continuous SOj Sulfonation Processes. Both concentric and multitubular reactor systems suppHed by competing manufacturers have surprisingly similar operating characteristics organic feedstock loading of ca 0.4 kg/(h-mm) (circumference) for LAB, and ca 0.3 kg/(h-mm) for alcohol ethoxylates an SO concentration of 3.3—5.0 vol % SO for LAB sulfonation, and 2—3% SO ... 

Separability. One of the greatest advantages of a solid catalyst is that it can be separated easily from the products of reaction. To do this successfully requires careful control of the process conditions so that exposure of the catalyst to nonreactant liquids capable of affecting or dissolving either the catalytic material or the support is prevented or rninimi2ed. Solid catalysts typically are used in axial or radial flow beds and multitubular reactors. Many successful commercial processes maintain the reactants and products in the gas phase while in contact with the catalyst to avoid catalyst degradation problems. 

Catalysts intended for different appHcations may require their own unique types of reactor and operating conditions, but the key to designing a successful system is to use the same feedstock composition that is expected in the ultimate commercial installation and to impose so far as is possible the same operating conditions as will be used commercially (35). This usually means a reactor design involving a tubular or smaH-bed reactor of one type or another that can simulate either commercial multitubular reactors or commercial-size catalyst beds, including radial flow reactors. 

Ethylene oxide is produced in large, multitubular reactors cooled by pressurized boiling Hquids, eg, kerosene and water. Up to 100 metric tons of catalyst may be used in a plant. Typical feed stream contains about 30% ethylene, 7—9% oxygen, 5—7% carbon dioxide the balance is diluent plus 2—5 ppmw of a halogenated moderator. Typical reactor temperatures are in the range 230—300°C. Most producers use newer versions of the Shell cesium-promoted silver on alumina catalyst developed in the mid-1970s. 

Oxychlorination of Ethylene to Dichloroethane. Ethylene (qv) is converted to dichloroethane in very high yield in fixed-bed, multitubular reactors and fluid-bed reactors by reaction with oxygen and hydrogen chloride over potassium-promoted copper(II) chloride supported on high surface area, porous alumina (84) ... 

Vinyl chloride is made from ethylene and chlorine with Cu and K chlorides. The Stauffer process employs 3 multitubular reactors in series with 25 mm (0.082 ft) ID tubes (Naworski and Velez, in Leach, ed.. Applied Industrial Catalysis, vol. 1, Academic Press, 1983, p. 251). 

In the process (Figure 7-3), compressed oxygen, ethylene, and recycled gas are fed to a multitubular reactor. The temperature of oxidation... 

Figure 9-4. The Octol Oligomerization process for producing Os s and Ci2 s and Cis s olefins from n-butenes (1) multitubular reactor, (2) debutanizer column, (3) fractionation tower.

So far, consideration has been limited to chemistry physical constraints such as heat transfer may also dictate the way in which reactions are performed. Oxidation reactions are highly exothermic and effectively there are only two types of reactor in which selective oxidation can be achieved on a practical scale multitubular fixed bed reactors with fused salt cooling on the outside of the tubes and fluid bed reactors. Each has its own characteristics and constraints. Multitubular reactors have an effective upper size limit and if a plant is required which is too large to allow the use of a single reactor, two reactors must be used in parallel. 

Subject to resolution of these concerns, scaling in parallel has no obvious limit. Multitubular reactors with 10,000 tubes have been built, e.g., for phthalic anhydride oxidation. 

What is needed at this point is a correlation or other means for estimating r] at every point in the reactor. This may be done empirically for example, by running a single tube of what ultimately will be a multitubular reactor. However, some progress has been made in determining r] from first principles. We outline the salient results achieved to date. 

Tube-to-tube interactions. The problems of velocity profile elongation and thermal runaway can be eliminated by using a multitubular reactor with many small-diameter tubes in parallel. Unfortunately, this introduces another form of instability. Tubes may plug with pol5nner that cannot be displaced using the low-viscosity inlet fluid. Imagine a 1000-tube reactor with 999 plugged tubes ... 

Metal monoliths show good thermal characteristics. A typical support with herringbone channels made from Fecralloy performed satisfactory in automotive applications [27]. Modeling showed that overall heat transfer was about 2 times higher than for conventional pellets [28,29]. Hence, there is potential for structured catalysts for gas-phase catalytic processes in multitubular reactors. 

Another pilot plant, developed by at Kyoto University, was used for the Grignard exchange reaction at the same productivity as the batch reactor (10 m3) by adding only four microflow systems of the present scale (Wakami and Yoshida 2006). A multitubular reactor is the core element of the microprocessing plant (see Fig. 17). Stable yields of approximately 95% could be demonstrated for a 24-h run. 

Fig. 17. Multitubular reactor used for the Grignard exchange reaction pilot microprocess plant. (Courtesy of ACS)...

The gas-phase process, successfully commercialized independently by Bayer and USI,417 involves passing a mixture of ethylene, acetic acid and oxygen over a supported palladium catalyst contained in a multitubular reactor at 150 °C and about 5-10 atm pressure. The overall yield in vinyl acetate is about 92%, and the major by-product is C02. The catalyst consists of a palladium salt (e.g. Na2PdCl4) deposited on silica (or alumina) in the presence of a cocatalyst (e.g. HAuC14), reduced and impregnated with potassium acetate before use.384,418 The lifetime of the catalyst is about 2... 

Figure 3 Schematic of temperature profiles and hot spot formation in a multitubular reactor.

Figure 4 Various measures for the harmonization of reaction, heat transport, and pressure drop in chemical reactors benchmarked against a multitubular reactor.

The excellent heat transfer characteristics of microreactors result not only from their considerably enhanced specific heat exchange surface areas of 30,000 m2/m3—a value roughly 300 times higher than that in a conventional multitubular reactor—but also from the rapid lateral heat transfer across the channels. 

In addition to the harmonization of the underlying physical and chemical processes, the catalytic-plate heat exchanger offers a cost-effective alternative to both conventional multitubular reactors and catalytic microreactors for industrial... 

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