Tube Micro Reactors

Reactor 3 [R 3] Porous-polymer Rod in Tube Micro Reactor... 

Reactor type Porous-polymer rod in tube micro reactor Polymer load 10%... 

Figure 4.2 Schematic of the porous-polymer rod in a tube micro reactor [3].

This class of hybrid components comprises chip micro-reactor devices, as described in Section 4.1.3, connected to conventional tubing. This may be H PLC tubing which sometimes has as small internals as micro channels themselves. The main function of the tubing is to provide longer residence times. Sometimes, flow through the tube produces characteristic flow patterns such as in slug-flow tube reactors. Chip-tube micro reactors are typical examples of multi-scale architecture (assembly of components of hybrid origin). 

D microfabricated micro mixers (see Section 4.1.5) may be connected to tubes for reasons of residence time prolongation, similar to chip-tube micro reactors (see Section 4.1.4). The tube may also have the function of creating distinct hydro-dynamic features (see Section 4.1.4). 

The reactor built for this purpose is usually a 1/4-in. ( 6 mm) tube that holds a few cubic centimeters of catalyst. A micro reactor is shown on Figure 2.2,2 that is typical in research work.. 

Other types of non-micro-channel, non-micro-flow micro reactors were used for catalyst development and testing [51, 52]. A computer-based micro-reactor system was described for investigating heterogeneously catalyzed gas-phase reactions [52]. The micro reactor is a Pyrex glass tube of 8 mm inner diameter and can be operated up to 500 °C and 1 bar. The reactor inner volume is 5-10 ml, the loop cycle is 0.9 ml, and the pump volume adds a further 9 ml. The reactor was used for isomerization of neopentane and n-pentane and the hydrogenolysis of isobutane, n-butane, propane, ethane, and methane at Pt with a catalyst. 

One of the most interesting theorems of Worz et al. is that they see a serious potential for micro reactors to permit small-scale production of some different sort [110-112]. Micro channels serve as an ultra-precise measuring tool, whereas production is done in channels about 10 to 100 times larger, i.e. miUimeter-sized channels. The limit of tube diameter of industrial production reactors is reported to be 2 cm hence any new reactor of smaller characteristic dimensions bears some potential for improvement. Worz et al. conclude with the remark that the above strategy could be the most important result of their studies [110-112]. 

Selectivity may also come from reducing the contribution of a side reaction, e.g. the reaction of a labile moiety on a molecule which itself undergoes a reaction. Here, control over the temperature, i.e. the avoidance of hot spots, is the key to increasing selectivity. In this respect, the oxidative dehydrogenation of an undisclosed methanol derivative to the corresponding aldehyde was investigated in the framework of the development of a large-scale chemical production process. A selectivity of 96% at 55% conversion was found for the micro reactor (390 °C), which exceeds the performance of laboratory pan-like (40% 50% 550 °C) and short shell-and-tube (85% 50% 450 °C) reactors [73,110,112,153,154]. 

A complete reactor module was built, consisting of the actual micro reactor and an encasement that serves for temperature setting [28], The latter consists of two parts, a furnace for setting the high temperature in the reactor inlet collection zone and in the reaction zone and a cooler for the outlet collection zone. The micro reactor has a housing with standard tube connections. An electric furnace serves for heating, Temperatures can be measured in the furnace, at the furnace/micro reactor border and in the outlet collection zone. For thermal insulation, a 2 mm ceramic... 

GP 4] [R 5] For an undisclosed methanol derivative, no hot spot (close to 0 K rise) was found for the construction-material silver micro reactor (operational temperature 390 °C) hot spots of 160 and 60 K were found for laboratory pan-like (40% 50% 550 °C) and short sheU-and-tube reactors, respectively, using elemental silver [1,49-51, 108]. 

All conventional reactors, tested before using the micro reactor (simply since micro reactors were hardly available at that time), only fulfilled the demands of one measure, at the expense of the other measures. For instance, a single-tube reactor can be operated nearly isothermally, but the performance of the oxidative dehydrogenation suffers from a too long residence time. A short shell-and-tube reactor provides much shorter residence times at improved heat transfer, which however is still not as good as in the micro reactor. 

This class is the simplest of all micro reactors and certainly the most convenient one to purchase, but not necessarily one with compromises or reduced fimction. HPLC or other tubing of small internal dimensions is used for performing reactions. There are many proofs in the literature for process intensification by this simple concept. As a micro mixer is missing, mixing either has to be carried out externally by conventional mini-equipment or may not be needed at all. The latter holds for reactions with one reactant only or with a pre-mixed reactant solution, which does not react before entering the tube. 

Reactor 1 [R 1] Electrothermal Tubing-based Micro Reactor... 

Reactor type Electrothermal tubing-based micro reactor Tubing length 1.5 m... 

Figure 4.1 Flow scheme of a plant comprising an electrothermal tubing-based micro reactor configured for ethylene polymerization [1],...

Reactor type Liquid/liquid micro chip disUibutor-tube reactor Capillary tube length (reactor) 500-1800 mm... 

A chip-type micro reactor array comprises parallel mixer units composed of inverse mixing tees, each followed by a micro channel that it is surrounded by heat exchange micro channels (so called channel-by-channel approach similar to the tube-in-tube concept). Such an integrated device was developed as a stack of microstructured plates made of a special glass, termed Foturan (Figure 4.26). The integrated device was attached to PTFE tubes of various lengths. 

P 9] DL-l-Phenylethylamine and 4-amino-l-benzylpiperidine were dissolved in 0.1 M NaOH aqueous solution [23]. 3-Nitrobenzoyl chloride and 3,5-dinitrobenzoyl chloride were used as ethyl acetate solutions. The concentration of all reactants was set to 0.01 M. Syringe pumps served for liquid feed. The flow rate was 50 plmin and room-temperature processing was applied. No further temperature control was exerted as the reaction is only mildly exothermic. After having passed the micro reactor, the phases were settled in test-tubes and the organic phase was withdrawn for analysis. 

OS 10] [R 10] [P 9] The specific interfadal area was varied for a phase-transfer reaction for four amide formations from two amines and two acid chlorides [23[. This was done by filling the solutions in normal test-tubes of varying diameter (1-5 X cm ) and using a micro reactor which had the largest specific interface (45 X cm ). The yields of all foiu reactions are highly and similarly dependent on... 

Figure 4.43 Benchmarking of untreated and pre-treated Y-piece micro reactors to a commercial micro test-tube for the hydrolysis of p-nitrophenyl-/ -D-galactopyranoside. Y-piece micro reactor ( ) commercial micro test-tube ( ) pre-treated Y-piece microreactor (A) [26],...

GL 19] [R 9] [P 20] The temperature range of a micro-reactor test imit is similar to that of a mini batch reactor, whereas the range for pressure operation is different (temperature micro reactor, 20-80 °C mini batch, 20-100 °C pressure micro reactor, 1-11 bar mini batch, 1-100 bar) [70], This is caused by the choice of glass as tube material for the micro reactor and may be overcome in the future by choosing stainless steel. 

Toluene disproportionation was carried out in a high-pressure continuous flow micro reactor. Granular catalyst (32-64 mesh, 2.5 cm ) was loaded into a stainless steel tube reactor. Toluene was fed at a rate of 10 cm h (liquid) in the flow of H2S(0.2vol.%)/H2 mixture gas (200 cm min b at 623K and 6MPa. The effluent was analyzed by gas chromatography (Shimadzu, GC-9A) by a flame ionization detector (FID). 

The theoretical foundation for this kind of analysis was, as mentioned, originally laid by Taylor and Aris with their dispersion theory in circular tubes. Recent contributions in this area have transferred their approach to micro-reaction technology. Gobby et al. [94] studied, in 1999, a reaction in a catalytic wall micro-reactor, applying the eigenvalue method for a vertically averaged one-dimensional solution under isothermal and non-isothermal conditions. Dispersion in etched microchannels has been examined [95], and a comparison of electro-osmotic flow to pressure-driven flow in micro-channels given by Locascio et al. in 2001 [96]. 

In Section 8.3.3, the safety performance of the tubular reactor was compared to the stirred tank reactor. This comparison can now be extended to a micro reactor. For this, we take a 10 m3 stirred tank vessel, a tubular reactor with 10 mm tube diameter length 1 m, and a micro reactor with 0.1 mm tube diameter and length 1 cm. We compare the following criteria that are important for the reactor safety ... 

Figure 3.29 (a) Oxygen concentration profile at the inlet and outlet of the compartments of the high-throughput micro reactor. The inlets of the sampling tubes have to penetrate into the compartments to minimize flow cross-over, (b) Area averaged oxygen concentration at one capillary outlet. Total flow velocity 50 (1), 75 (2) and 100 cm3 min-1 (3) [55] (by courtesy of ACS). 

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