Efficient Temperature Control

In the case of a stirred tank reactor with a jacket, the heat transfer area or 

---

Only a few microwave reactors equipped with efficient temperature control systems for safe microwave synthesis at laboratory scale are currently available on the market. These systems lead to reproducible operating conditions. 

Let us first restrict to the simpler and more frequently encountered case that the feed mixture consists of vapors of a single component B in the carrier gas A. The optimum device, both at ambient and elevated pressure, will then be a saturator which contains component B in the solid or liquid state (Fig. 2). On its way through the saturator, the carrier gas A is loaded with vapors of B. Since its vapor pressure depends exponentially on the temperature, the saturator must be thoroughly thermostated. An externally thermostated water or oil bath circulating through a jacket around the saturator is often the best solution. If temperatures above ca. 200 °C are required, a saturator surrounded by a stirred bath of molten salt with an efficient temperature control can be used alternatively. 

At the present time, all industrial plants operate in the vapor phase, although certain developments have been conducted to achieve the oxychlorinatkm of ethylene in the liquid phase, particularly by Kellogg. In this case, transformation takes place around 170 to 185 C at between 15 and 2.10 Pa absolute, in the presence of a catalyst system based on promoted cuprous and cupric chlorides, with more efficient temperature control by vaporization of part of the reaction medium and better performance, but with acid... 

The effects of fy, Fv, and FL on the temperature T are indirect and rather slow, while that of Ws is direct and faster. Therefore, from the 24 loop configurations of Table 23.1, only numbers 1, 3, 7, 9,14, and 18 look promising for efficient temperature control. 

Fluid-fluid systems are widely used for chemical transformations. Examples are halogenations, hydrogenations, and hydroformylations for gas-liquid reactions and nitrations, polymerizations, and cyclization for liquid-liquid systems. In addition, two-phase slug flow reactors can be used to get narrow residence time distribution at low liquid Reynolds numbers as demonstrated in chapter 3. Most of the reactions mentioned above are highly exothermic and heat evacuation is an important issue for efficient temperature control. 

It is known that microchannel reactors, due to their small dimension and well defined structure have many advantages compared to conventional fixed bed reactors. The main ones are an efficient temperature control and well defined flow patterns. As the channel diameters are in the order of micrometers, microreactors operate under laminar flow conditions resulting in a parabolic velocity profile. But, due to the short radial diffiision times the radial concentration profile is flat, resulting in a narrow residence time distribution of the reactant. The latter characteristic is of crucial importance in the actual sbufy. Only reactors with an uniform residence time can be used to get meaningful kinetics information under periodic operation at short cycle periods [9]. 

Although the applications to A-acyliminium ions, alkoxycarbeniumions, and benzylic cations were successful, it seems to be difficult to apply the method to less stabilized cations. The applicability of the cation pool method inebitably depends upon the stability of the cation that is accumulated. The cation flow method [20, 21] which involves generation of carbocations in a microflow electrochemical system should be much more favorable because of short residence times and efficient temperature control. 

In a highly integrated system like the one in Fig. 21.5 it is important to have a stable and efficient temperature control, both in stationary and dynamic operation. The most difficult temperature to control is that of the reformer. This is because the heating power for the reformer is not... 

Empty columns are characterized by the absence of materials or devices for the continuous dispersion of the phases, which does not mean that internal heat exchangers are excluded. In fact, the insertion of heat exchangers in such reactors easily permits a continuous and efficient temperature control. 

---