Reactor flow micro

This involves knowledge of chemistry, by the factors distinguishing the micro-kinetics of chemical reactions and macro-kinetics used to describe the physical transport phenomena. The complexity of the chemical system and insufficient knowledge of the details requires that reactions are lumped, and kinetics expressed with the aid of empirical rate constants. Physical effects in chemical reactors are difficult to eliminate from the chemical rate processes. Non-uniformities in the velocity, and temperature profiles, with interphase, intraparticle heat, and mass transfer tend to distort the kinetic data. These make the analyses and scale-up of a reactor more difficult. Reaction rate data obtained from laboratory studies without a proper account of the physical effects can produce erroneous rate expressions. Here, chemical reactor flow models using matliematical expressions show how physical... 

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. 

Sichere Chemie in Mikroreaktoren, Frankjurter Allgemeine Zeitung, December 1995 Plant cells as model for micro-reactor development micro-fabrication techniques DuPont s investigations DECHEMA s initiation of micro-reactor platform BASF s investigations general advantages of micro flow [238]. 

OS 31] [R 16a] [P 23] On increasing the temperature, the reaction rate for nitration of benzene increases (Figure 4.53), as usually to be expected for most organic reactions [31]. For a capillary-flow micro reactor, more than doubling of the reaction rate was determined on increasing the temperature from 60 to 90 °C. 

OS 33] ]R 16h] [P 25] For the nitration of a single-ring aromatic in a capillary-flow micro reactor, experiments were performed at two temperature levels, 60 and 120 °C [94]. Owing to the assumed increase in conversion rate with higher temperature, attempts were made to compensate for this by decreasing the capillary length at otherwise constant dimensions. For the 60 °C experiment, a very low... 

OS 31] ]R 16a] ]P 23] For benzene nitration, the results achieved in the capillary-flow micro reactor were benchmarked against results claimed in the patent literature (see Table 4.2) [97]. An analysis of conversion, by-product level, reaction time and reaction rate showed that the results achieved in micro reactors and conventional equipment are competitive, i.e. were similar. As tendencies, it seemed that the micro reactor can lead to a lower by-product level owing to its better temperature guiding and that reaction times can be further shortened. However, the corresponding results are not absolutely comparable in terms of reaction conditions and hence further data are required here. 

P 75/The protocol relies on sequential filling of selected charmels or parts of them in a chip micro reactor [17]. Thus, a short description of the micro reactor flow configuration is needed to understand details of the protocol. 

Figure 16.2 Comparison of performance of mixed flow reactors treating micro- and macrofluids for zero- and second-order reactions with 8 = 0.

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). 

Activity Measurements. To test catalytic properties of various samples partial oxidation of methanol to formaldehyde was studied in a flow micro-reactor operating under normal atmospheric pressure (10). For each run about 0.2 g of catalyst sample was used and the activities were measured at 173 C in the absence of any diffusional effects. The feed gas consisted of 72, 2 and by volume of nitrogen, oxygen and methanol vapor respectively. Reaction products were analysed with a 10% Carbowax 20 M column (2m long) maintained at 60 C oven temperature. 

M 39] [P 37] Using an azo-type competitive reaction, the selectivities were compared for the P- and V-type micro mixers having straight and oblique fluid injection, respectively [41]. In this way, laminar- and turbulent-flow mixing achieved by vertical interdigital microstructured mixers can be compared. The selectivities of the turbulent V-type mixer are better to some extent as compared with the P-type device however, neither approaches the characteristics of the ideal tubular reactor. The micro devices, however, are better than a conventional jet mixer. 

Integrated reactors One type of integrated reactor is micro structured heat exchanger/reactor concepts, which may work as cross- or counter-flow reactors. Another type couples endothermic and exothermic reactions in two separate flow paths normally operated in the co-current mode. Both reactor types are designed as prototype components of future fuel processors for mobile applications. 

Flego [1] recommends the use of micro devices for automated measurement and microanalysis of high-throughput in situ characterization of catalyst properties. Murphy et al. [5] stress the importance of the development of new reactor designs. Micro reactors at Dow were described for rapid serial screening of polyolefin catalysts. De Bellefon ete al. used a similar approach in combination with a micro mixer [6], Bergh et al. [7] presented a micro fluidic 256-fold flow reactor manufactured from a silicon wafer for the ethane partial oxidation and propane ammoxidation. 

The reaction is also influenced by the heat of reaction that develops during the conversion of the reactants, a problem in tubular screening reactors. In micro structures, the heat transport through the walls of the channels is facilitated owing to their small dimensions. The catalysts are deposited on the walls of these micro structures and will thus have the appropriate environment for exothermic reactions by enabling fast quenching of the reaction with near isothermal conditions. Hence also the heat and mass balance in the reactor will be decoupled, which permits the analytical description of the flow in the screening reactor. 

Methanol conversion to hydrocarbons has been studied In a flow micro reactor using a mixture of C-methanol and ordinary C-ethene (from ethanol) or propene (from Isopropanol) over SAPO-34, H-ZSM-5 and dealumlnated mordenlte catalysts In a temperature range extending from 300 to 450 °C. Space velocities (WHSV) ranged from 1 to 30 h. The products were analyzed with a GC-MS Instrument allowing the determination of the Isotopic composition of the reaction products. The Isotope distribution pattern appear to be consistent with a previously proposed carbon pool mechanism, but not with consecutive-type mechanisms. 

Vapor phase experiments were performed in a fixed-bed continuous down-flow micro-reactor with a diameter of 12 mm at atmospheric pressure. Prior to reaction, the catalyst sample (0.10 g, except 0.15 g for SZ) was calcined at 500 °C for 3 hours in a 30 cmVmin flow of air. The sample was then purged with 0.50 cmVmin He for 0.5 hr at the reaction temperature. Reactant feed rates were 0.33 cmVmin of 0.99 vol % NOj /He and 0.17 cmVmin of He saturated with toluene by passing through a toluene reservoir kept at 0°C. Reactions were performed at 150,170 and 200 °C and partial pressures of 2.3 torr toluene and 5-15 torr NOj. The toluene space velocity (WHSV) was 0.148 for the SZ and 0.221 for all other catalysts. Toluene was used as the internal standard for the calibration of the mono-nitrotoluene products. 

The experiments were carried out with a continuous flow micro-reactor at... 

A. Renken, L. Kiwi-Minsker, Chemical reactions in continuous flow micro-structured reactors, in N. Kockmann (Ed.), Micro Process Engineering, Advanced Micro and Nano Systems, 173-201Wiley-VCH, Weinheim, 2006, p. 173. 

Reaction Studies. The reaction system consisted of a flow micro-reactor using helium as a carrier gas bubbled through a saturator containing 2-propanol. The partial pressure of 2-propanol was adjusted by controlling the temperature of the saturator. Approximately 200-400 mg of the layered hydroxide were heated In the reactor under a flow of helium In order dehydrate and dehydroxylate the material. The partial pressure of 2-propanol was maintained at 100 torr and the helium flow was varied between 10-20 ml/min. The in-situ calcination temperature was varied between 400-500°C and the reaction temperature between 150-350°C. Analyses of the reactants and the products were performed by an on-line GC fitted with a capillary column. 

A potential solution to the issue of limited penetration depth could be to add a microwave reactor externally to a large batch reactor and cycle the reaction mixture through a loop continuously. However, this is effectively using the conventional reactor as a reservoir while processing small quantities of reaction mixture in the microwave field and, overall, it offers no advantage. Another solution is to either process smaller volumes in batch mode or else use a continuous-flow micro-wave reactor. These are the options that most investigators of microwave scale-up have used. 

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