HEX reactor

Agitated cell reactor or Agitated tube reactor (ACR or ATR) 

Stator-rotor spinning disc reactor (Stator-rotor SDR) 

---

Among the various technologies, HEX reactors play an important part in PI since many chemical reactions are temperature dependent The principle of the H EX reactor consists in combining a reactor with a H EX in only one unit. The following are the benefits of using HEX reactors with PI ... 

The four main parameters that are important to transpose a reaction from batch reactor to continuous HEX reactor are thermal behavior, hydrodynamics, reactor dynamics, and residence time. 

A comparison of the heat transfer performance of different reactors presented in Table 12.1 shows the main advantages of HEX reactors [10]. 

The volume of HEX reactor is generally small therefore product holdup is small. 

The main limitation of HEX reactors is the short residence time, typically from a few seconds to a few minutes. Indeed, the apparatuses are smaller than the traditional ones and fast flow velocities are necessary in order to maintain good level of heat-transfer coefficients. However, as described in the previous paragraph, the highlighted transfer properties of HEX reactors allow us to operate in a few minutes, whereas it takes many hours in batch or semibatch mode. 

The literature proposes a relatively large number of HEX reactors that have been designed and built of different materials such as glass, stainless steel, polyether ether ketone (PEEK), and silicon carbide (SiC). A presentation can be found in Amdoimaz et al. [13]. 

The ShimTec reactor from Chart Industries [18, 19] is an example of a HEX reactor with diffusion-bonded plates (Figure 12.2). The reactor is composed of three plates one process plate sandwiched between two utility plates. All the units are made of 316 stainless steel, unless stated otherwise. Swagelok fittings are used for all the connections. 

The geometrical data and characteristic sizes of the HEX reactor studied in our lab are described in Table 12.2. 

This new prototype of the HEX reactor made of ceramic (SiC) has been developed in under a collaboration between BOOSTEC and our laboratory [22]. BOOSTEC is a French innovative small and medium enterprise (SME), specializing in a high-performance all-SiC components and systems. The sintered SiC provides a unique combination of key advantages for the production of high-performance components or systems ... 

Influence ofthe Compacity Factor and of the Material of HEX Reactors... 

One of the major interests of the HEX reactor is to offer a large ratio surface to reaction volume. Therefore, even if most of the time the laminar flow regime is not suitable to enhance transport phenomena with a moderate overall coefficient, the heat performances are expected to be high, since the compacity factor is always large. This fact is clearly exhibited in Table 12.4, where the results relative to the various HEX reactors studied in our laboratory have been plotted. 

Table 12.4 Comparison of different HEX reactors according to the heat transfer performances.

This section presents the different methods used to characterize the performances of the HEX reactors related to... 

A number of reactions presenting different characteristics have been carried out in HEX reactors [28]. In the following, some of those that exhibit different intensification opportunities are discussed ... 

Feasibility of HEX Reactors 279 Table 12.8 Operating conditions of oxidation reaction experiments. 

Comparison between the heat exchanged per unit of volume during oxidation experiment in the Shimtec reactor and the maximal heat exchanged in a classical batch reactor (with a double jacket) highlights the effectiveness of the former. Indeed, in oxidation reaction experiments, a mean value of the heat exchanged per unit of volume in the HEX reactor is estimated with utility stream temperature of 47 °C ... 

The feasibility of operating highly exothermic reactions in a HEX reactor has been demonstrated, some considerations can also be given concerning the inherently safer characteristics of an intensified continuous HEX reactor. This type of evaluation has been conducted on the OPR, using the esterification of propionic anhydride by 2-butanol as test reaction [36, 37]. 

In the field of PI, the transposition of the chemical reaction operation from batch to continuous mode represents a critical point. In this chapter, some examples of HEX reactors, allowing this transposition, have been presented. 

New chemical synthesis routes leading to a better productivity and increased selectivity could be defined with regard to the new opportunities offered by HEX reactors. For example, they can lead to solvent-free operation or operations with at least dramatically reduced amount of solvent, to increase the reaction temperature or to engage in more efficient catalysis. 

Examples of chemical reactions have been presented and carried out in different types of HEX reactors. Applications such as oxidation, nitration, hydrosilylation, are still in progress in the industrial companies... 

From the process safety point of view, the evaluation of the intrinsic safe character of HEX compared to batch or semibatch reactors has been investigated [33, 37]. Two points clearly show the interest in the HEX reactors ... 

A number of H EX reactors are presented in the literature, some of which have been designed for a specific chemistry. It is necessary to remember the necessary flexibihty and polyvalence which are required in fine chemicals or pharmaceutical industries. Nevertheless, owing to the low holdup and the rapidity of putting HEX reactors in operation, one can imagine types of H EX reactors devoted to a portfoho of reactions linked to the exothermicity, product characteristics (such as corrosion) or to the nature of the phases (hquid-hquid, gas-liquid, solid, etc.). 

Anxionnaz, Z., Cabassud, M., Gourdon, C., and Tochon, P. (2008) Heat ex-changer/reactors (HEX Reactors) concepts, technologies State-of-the-art. Chem. Eng. Process., 47, 2029-2050. 

Figure 20.22. Use of HEX reactors for reducing by-product formation1321 (courtesy BHR Solutions)...

For highly exothermic reactions the so-called HEX reactors present a very promising option. The basic common feature of all HEX reactors is much more favorable heat transfer conditions in comparison with conventional reactors (heat transfer coefficients typically 3500-7500 W/m2K, heat transfer areas up to 2200 m2/m3). A HEX reactor developed by BHR Group Ltd. (Figure 14) was able to decrease the by-product formation in one of ICI Acrylics processes by 75% (41) and to decrease the processing time in a Hickson Welch fine chemical process from 18 hours to 15 minutes, saving 98.6% of batch time (42). 

High-intensity inline devices are often used to mix fluids in the process industries. Such devices include simple pipes, baffled pipes, tees, motionless mixers, dynamic mixers, centrifugal pumps, ejectors, and rotor/stator mixers. In addition to their traditional application in physical processes such as mixing and dispersion, such devices can provide very effective environments for mass transfer and chemical reaction to take place. Furthermore, combining effective inline mixing with heat transfer is the basis of combined heat exchanger reactors (HEX reactors). 

---