Micro Reactors for Gas-phase Reactions

The design of multichannel micro reactors for gas-phase reactions is typically based on a stack of micro structured platelets. For strongly endothermic or exothermic reactions, it lends itself to alternate between layers of reaction channels and heat-... 

Micro Reactors for Gas-phase Reactions 265 covar plata of waiter hou fr>g... 

Kolb G, Hessel V (2004) Micro-Structured Reactors for Gas Phase Reactions. Chem Eng J 98 1-38... 

Kolb G and Hessel V. Micro-stmctured reactors for gas phase reactions. Chem Eng J 2004 98(1-2) 1-38. 

Kolb, G. and Hessel, V. (2004) Micro-structured reactors for gas phase reactions. Chemical Engineering Journal, 98, 1-38. 

G. Kolb, V. Hessel, V. Cominos, et ol. Selective oxidations in micro-structured catalytic reactors—For gas-phase reactions and specifically for fuel processing for fuel cells. Catal. Today 2007, 120, 2-20. 

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. 

Felcht reports on Degussa s activities in cooperation with partners from academia and industry to develop innovative industrial-scale micro-structured reactors for making large-tonnage products by liquid- and gas-phase reactions [137]. The aim is to make the potential of micro reactors more widely available for a larger variety of processes, naturally with focus on Degussa s fine and specialty chemical productions. Also, the aim is to circumvent traditional problems of scale-up. 

Innovation - advocates and opponents origin from microtechnology list of microfabrication techniques selectivity and efficiency as main driver for industrial implementation special properties and general advantages of micro reactors process-development issues BASF investigations on liquid/liquid and gas-phase reactions micro reactors as ideal measuring tools production in micro reactors as exception, the rule will be transfer to mm-sized channels [111],... 

BASF activities have shown that one can make money by investigating gas-phase reactions for process development. If Degussa and Krupp-Uhde have built a very large micro reactor with outer dimensions of more than 1 m, obviously there must be an economic reason for that. 

Performing this reaction primarily served as a model to show the feasibility of micro flow processing for soHd/Hqnid reactions [19]. In a similar way as for catalyzed gas-phase reactions, micro-reactor processing was expected to show benefits in terms of mass and heat transfer. Particularly this relates to transfer enhancement when using porous media. 

Both catalytic reactions were investigated in the gas phase under atmospheric pressure using a glass fixed bed micro-reactor Prior to the reaction given amount of the catalyst (fraction 0.5-0.71 mm) was in situ activated at 500 °C for 2 h (N2 stream 40 ml min"1) In the case of toluene disproportionation the reaction temperature was 500 °C, WHSV 2-20 h"1, concentration of toluene in a stream was 18.5 mol%. Toluene alkylation was studied at the reaction temperature 250 °C. WHSV related to toluene was 10 h"1, concentration of toluene was 18.5 mol% and toluene to isopropyl alcohol molar ratio was 9.6. 

Sample integrations similar to pharmaceutical approaches were already examined in 1997 [39]. Here, a chip-like microsystem was integrated into a laboratory automaton that was equipped with a miniaturized micro-titer plate. Microstructures were introduced later [40] for catalytic gas-phase reactions. The authors also demonstrated [41] the rapid screening of reaction conditions on a chip-like reactor for two immiscible liquids on a silicon wafer (Fig. 4.8). Process conditions, like residence time and temperature profile, were adjustable. A third reactant could be added to enable a two-step reaction as well as a heat transfer fluid which was used as a mean to quench the products. 

A major problem in using microstructured reactors for heterogeneously catalyzed gas-phase reactions is how to introduce the catalytic active phase. The possibilities are to (i) introduce the solid catalyst in the form of a micro-sized packed bed, (ii) use a catalytic wall reactor or (iii) to use novel designs. Kiwi-Minsker and Renken [160] have discussed in detail these alternatives. 

Gas-phase operation often uses premixed gases, which have to be heated to the reaction temperature. Owing to the faster reactions for gas-phase processes, typically being on the second scale, micro heat exchangers are proper reactor solutions [9]. 

P. L. Mills, J.S. McCracken and T. M. Delaney, Novel Micro-Scale Reactor for Liquid Phase and Gas-Liquid Catalyzed Reactions with On-Line GC Analytical System Sampling, Paper 288d presented at the 1999 AIChE Annual Meeting, Dallas, November 1-5,1999. 

Guettel R, Turek T. Assessment of micro-structured fixed-bed reactors for highly exothermic gas-phase reactions. Chemical Engineering Science 2010 65 1644-1654. 

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