Nano-sized reactors

A continuous cross-flow filtration process has been utilized to investigate the effectiveness in the separation of nano sized (3-5 nm) iron-based catalyst particles from simulated Fischer-Tropsch (FT) catalyst/wax slurry in a pilot-scale slurry bubble column reactor (SBCR). A prototype stainless steel cross-flow filtration module (nominal pore opening of 0.1 pm) was used. A series of cross-flow filtration experiments were initiated to study the effect of mono-olefins and aliphatic alcohol on the filtration flux and membrane performance. 1-hexadecene and 1-dodecanol were doped into activated iron catalyst slurry (with Polywax 500 and 655 as simulated FT wax) to evaluate the effect of their presence on filtration performance. The 1-hexadecene concentrations were varied from 5 to 25 wt% and 1-dodecanol concentrations were varied from 6 to 17 wt% to simulate a range of FT reactor slurries reported in literature. The addition of 1-dodecanol was found to decrease the permeation rate, while the addition of 1-hexadecene was found to have an insignificant or no effect on the permeation rate. 

Nano-sized manganese-carbonyl subspecies on MCM-41 have been prepared by impregnation of Mn2(CO)io under UV irradiation followed by an ultrasound treatment. From XANFS characterization, the formation of highly dispersed species with a formal oxidation state of -t-2.2 is proposed. These systems could be used as nanometric reactors [23]. 

The synthesis of nano-sized particles from CaCC>3 and BaCC>3 was carried out in a recurrent reactor equipped with stirrer and was close to reactor with ideal mixing. Chemical interaction between CO2 and the corresponding alkali suspension (dispersed in organic phase) takes place in the reactor. The process is endothermic so the device was equipped with cooling jacket. A diagram of the device is shown in Fig. 1. 

Ideal plug-flow conditions can also be established in so-called nano-flow reactors with catalyst particle sizes from 50 to 200 pm. These reactors were operated in 16-and 64-barrel mode at Avantium for the regression of intrinsic kinetics [4],... 

Aerosol reactors are used to synthesize nano-size particles. Owing to their size, shape, and high specihc surface area, nanoparticles can be used in a number of applications such as in pigments in co.smetics, membranes, photo-catalytic reactors, catalysts and ceramics, aitd catalytic reactors. 

Fig. 6.5 Comparison of the behavior of commercial micro-sized ceria (blue) with that of nanosized ceria (2-10 nm, empty circles) and nano-sized AI2O3-modified ceria (empty squares 3 % alumina triangles, 10 % alumina). The DMC yield in five consecutive cycles of reaction remains constant. In each cycle the same amount (50 mg) of catalyst (Ce02 or modified ceria) was placed in a reactor with 4 mL of MeOH, at 408 K for 3 h under 5.0 MPa of CO2. Adapted with permissirai from [45]. Copyright (2010) Elsevier...

Since the pioneering work of Charles J. Pedersen, Donald J. Cram and Jean-Marie Lehn, macrocyclic chemistry attracted a considerable attention from chemists all over the world [1-4]. An ability of macrocycles to be highly selective receptors (host molecules) for a number of metal and organic cations or anions, as well as for the small or even huge (e.g. fiillerenes) neutral organic substances is the reason of that interest [5-8]. The design of molecular devices such as molecular containers and reactors on one hand, and molecular switches (based on catenanes and molecular knots) on the other hand is another area of the macrocyclic chemistry application. So, the macrocyclic chemistry plays an important role in the material science, especially in the constmction of nano-sized materials on the bottom-up principles [5, 6, 9-11]. 

Control of the particle size while retaining precise control over the release rate is enabled by compartmentalization of the sol-gel solution into droplets of definite size. This can be achieved by emulsification of the sol-gel solution by mixing it with a solution composed of a surfactant and a non-polar solvent (Figure 2.13). When an active molecule is located in the aqueous droplet of a W/O emulsion, encapsulation occurs as the silicon precursors polymerize to build an oxide cage around the active species. By changing the solvent-surfactant combination, the particle size can be varied from 10 nm to 100 pm as the size of the particles is controlled by the size of the emulsion droplet, which acts as a nano-reactor for the sol-gel reaction (Figure 2.13). 

Comparison is always of interest. Table 14.3 gives a comparison between the mean sizes of nano copper powders prepared with various technologies, different reaction agents and in various reactors. It appears that the SCISR has significant superiority for the preparation of nano materials by liquid reaction- precipitation. 

The rotary speed of the propellers exhibits a turning influence on the average size of the product this is similar to the results obtained by Chen et al. [165] in their investigation on an analogous problem in a stirred tank reactor and also similar to the results on the preparation of nano copper described in the previous chapter. It results from the mutual effect between macro- and micro-mixing, as mentioned before. 

The molecular size pore system of zeolites in which the catalytic reactions occur. Therefore, zeolite catalysts can be considered as a succession of nano or molecular reactors (their channels, cages or channel intersections). The consequence is that the rate, selectivity and stability of all zeolite catalysed reactions are affected by the shape and size of their nanoreactors and of their apertures. This effect has two main origins spatial constraints on the diffusion of reactant/ product molecules or on the formation of intermediates or transition states (shape selective catalysis14,51), reactant confinement with a positive effect on the rate of the reactions, especially of the bimolecular ones.16 x ... 

It has been concluded that, in most cases, catalytic reactions over zeolites occur within their intracrystalline cages and channels. Zeolite catalysts can therefore be considered as a succession of nano or molecular reactors. The consequence is that the activity, selectivity, but also the stability of all the reactions carried out over zeolite catalysts, depend (slightly or significantly) on the shape and size of cages, channels and of their apertures, hence that shape selectivity is a general characteristic of zeolite catalyzed reactions. 

Ordered mesoporous materials, due to their periodic and size-controllable pore channels and high surface areas, have been regarded as a nano-reactor to construct novel ordered and well dispersed nanostructured composites with controlled size and size distribution.[303] A number of studies have reported on the encapsulation of guest materials, such as metal oxides,[304] semiconductors, metal sulfides,[305] carbon, metals,[306] and polymers into mesoporous silica hosts. 

The concept of nanofluids to further intensify microreactors has been discussed by Fan et al. [17]. The nano-fluids are suspensions of solid nano-partides with sizes typically of 1-100 nm in traditional liquids such as water, glycol and oils. These solid-liquid composites are very stable and show higher thermal conductivity and higher convective heat transfer performance than traditional liquids. They can thus be used to enhance the heat transfer in nanofluids in compact multifunctional reactors. A nanofluid based on Ti02 material dispersed in ethylene glycol showed an up to 35% increase in the overall heat transfer coefficient and a... 

---