Floating catalyst

The heavier portion of the fresh and laboratory steamed catalyst (Float B) exhibits a decreased micropore volume with respect to the lighter portion (Float A), suggesting that the density fractionation within each catalyst reflects the presence of a finite range of zeolite crystallinities. Particularly for the fresh catalyst, this inhomogeneity is small (Table VIII). 

Initial Blend wt% V Initial wt. % V corrected on catalyst Float (cat.) wt% V Sink (trap) wt% V Pickup Factor % V Trap/% V Cat. 

The results obtained in the catalysed reactions can be explained by considering the position of the catalyst in the reaction mixture. In spite of the stirring, the catalyst powder is mainly present in the bottom layer of the reactor containing the peroxide phase. The low solubility of 1-octene in this aqueous layer, together with the preferential uptake of polar compounds in the Ti-MCM-41 pores, causes an olefin deficiency near the active sites. This situation changes when the catalyst is incorporated in PDMS. First of all, the density of this composite membrane makes the catalyst float at the interphase between both phases. 

Prepare a saturated solution of sodium sulphide, preferably from the fused technical sodium polysulphide, and saturate it with sulphur the sulphur content should approximate to that of sodium tetrasulphide. To 50 ml. of the saturated sodium tetrasulphide solution contained in a 500 ml. round-bottomed flask provided with a reflux condenser, add 12 -5 ml. of ethylene dichloride, followed by 1 g. of magnesium oxide to act as catalyst. Heat the mixture until the ethylene dichloride commences to reflux and remove the flame. An exothermic reaction sets in and small particles of Thiokol are formed at the interface between the tetrasulphide solution and the ethylene chloride these float to the surface, agglomerate, and then sink to the bottom of the flask. Decant the hquid, and wash the sohd several times with water. Remove the Thiokol with forceps or tongs and test its rubber-like properties (stretching, etc.). 

The premise that discontinuous short fibers such as floating catalyst VGCF can provide structural reinforcements can be supported by theoretical models developed for the structural properties of paper Cox [36]. This work was recently extended by Baxter to include general fiber architecture [37]. This work predicts that modulus of a composite, E can be determined from the fiber and matrix moduli, Ef and E, respectively, and the fiber volume fraction, Vf, by a variation of the rule of mixtures,... 

Composites fabricated with the smaller floating catalyst fiber are most likely to be used for applications where near-isotropic orientation is favored. Such isotropic properties would be acceptable in carbon/carbon composites for pistons, brake pads, and heat sink applications, and the low cost of fiber synthesis could permit these price-sensitive apphcations to be developed economically. A random orientation of fibers will give a balance of thermal properties in all axes, which can be important in brake and electronic heat sink applications. 

Fig. 3. Vapor-grown carbon fibers obtained by substrate method w ith diameter ca. 10 /xrn (a) and those by floating catalyst method (b) (inserted, low magnification).

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