Microreactors modeling

Bohm, L.L. Bilda, D. Breuers, W. Enderle, H.F. Lecht, R. The microreactor model-guideline for PE-HD process and product development. In Ziegler Catalysts. Recent Scientific Innovations and Technological Improvements, Fink, G., Millhaupt, R., Brintzinger, H.H., Eds. Springer-Verlag Berlin, 1995 387 00. 

This case study permitted us to show that even relatively complex biochemical reactions can be performed inside liposomes, even if they have to be carried out at temperatures between 55 and 95°C. On the other hand, these experiments also demonstrated the main difficulty when working with conventional liposomes the likelihood that an individnal liposome can host all ingredients is relatively small. At the concentrations of plasmid DNA and DNA polymerase applied for the presented PCR experiments in liposomes, the probability that an average-sized liposome (having a diameter of 180 nm, as evalnated by freeze-fractnre electron microscopy) may contain both enzyme and DNA template was calcnlated to be <0.5%. In addition, inside such a model averagesized liposome there were enough nucleotides present so that three to fonr newly synthesized DNA molecnles conld be prodnced. These calcnlations also confirmed why the yield of obtained prodnct was relatively modest. And they demonstrated that, for the design of a better microreactor model, it was inalienable that substrate molecules could be added externally. 

Akbari M H, Ardakani A H S and Tadbir M A (2011), A microreactor modeling, analysis and optimization for methane autothermal reforming in fuel cell applications , Chem Eng J, 166,1116-1125. 

S.R. Deshmukh, A.B. Mhadeshwar, D.G. Vlachos, Microreactor modeling for hydrogen production from ammonia decomposition on ruthenium, Ind. Eng. 

Hardt, S. (2011) Microreactors — modeling and simulation, in Ullmann s Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH, Weinheim. Published online July 15, 2011. doi 10.1002/14356007.kl6Jd)l. pub2. 

Bohm, L. L, Franke, R., Thum, G., The microreactors as a model for the description of the ethylene polymerization with heterogeneous catalysts, in Kaminsky, W., Sinn, H. (Eds.), Transition metals and organometallics as catalysts for olefln polymerization, pp. 391-403, Springer-Verlag, Berlin (1988). 

However, the detailed description of the FT product distribution together with the reactant conversion is a very important task for the industrial practice, being an essential prerequisite for the industrialization of the process. In this work, a detailed kinetic model developed for the FTS over a cobalt-based catalyst is presented that represents an evolution of the model published previously by some of us.10 Such a model has been obtained on the basis of experimental data collected in a fixed bed microreactor under conditions relevant to industrial operations (temperature, 210-235°C pressure, 8-25 bar H2/CO feed molar ratio, 1.8-2.7 gas hourly space velocity, (GHSV) 2,000-7,000 cm3 (STP)/h/gcatalyst), and it is able to predict at the same time both the CO and H2 conversions and the hydrocarbon distribution up to a carbon number of 49. The model does not presently include the formation of alcohols and C02, whose selectivity is very low in the FTS on cobalt-based catalysts. 

This intermediate scale affords a preliminary validation of the intrinsic kinetics determined on the basis of microreactor runs. For this purpose, the rate expressions must be incorporated into a transient two-phase mathematical model of monolith reactors, such as those described in Section III. In case a 2D (1D+ ID) model is adopted, predictive account is possible in principle also for internal diffusion of the reacting species within the porous washcoat or the catalytic walls of the honeycomb matrix. 

Kinetic analysis—The model of the test microreactor was based on the following equations, whose symbols are defined in the Notation. They represent the adaptation of the general Eqs. (33) and (34) in Section IV to the specific reacting system herein considered. 

The experiment in Fig. 36 has been analyzed according to the usual plug-flow model of the test microreactor. In this case, the ammonia mass balance equations were modified in order to include the oxidation reaction R5 in Table V, which was considered to proceed via adsorbed ammonia NH3. Moreover, the mass balance for gaseous nitrogen was introduced... 

The kinetic analysis of the whole set of transient data collected over the powdered SCR catalyst has been addressed using the dynamic ID isothermal heterogeneous plug-flow model of the test microreactor (Chatterjee et al., 2005 Ciardelli et al., 2004a) described in Section IV. 

Altogether, the data reported in this section indicate a very good predictive quality of the model simulations this implies in the first place that the SCR kinetics estimated over powdered catalyst were successfully validated at this bigger scale. However, the excellent agreement between monolith data and model predictions based on intrinsic kinetics also confirms the accurate model description of physical phenomena, specifically external and intraporous mass transfer, which were not significant in the microreactor runs over the powdered catalyst, but played an important role in the monolith runs, as pointed out by the direct comparison in Fig. 44. 

Diffuse reflectance FTIR spectra of the ground Mo03/Al203 catalysts were recorded on an FTIR instrument (Nicolet, Model 740, MCT detector). The microreactor in the flow system was replaced by an FTIR cell. The cell used a Harrick diffuse reflectance accessory (DRA-2CO) fitted with a controlled environmental chamber (HVC-DRP). Spectra (500 scans, 4 cm 1 resolution) were presented in Kubelka-Munk units and recorded at RT. 

The reaction system consisted of a flow stainless steel microreactor operated at 5 MPa and 523-623 K. Hydrogen and carbon monoxide were supplied to the reactor through mass flow controllers (Brooks). Products were sampled through heated lines into an on-line gas chromatograph equipped with TCD and FID detectors, with a Porapak Q + R column for Ci products and a Tenax column for hydrocarbons (C,-C13) or alcohols (Cj-Cfi), respectively. Reaction products were identified with a gas chromatograph-mass spectrometer (Hewlett-Packard Model 5971), using a 60 m DB-1 capillary column (J W Scientific). 

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