Quartz chips

The reactor is an 8-mm i.d. quartz tube located in a tube furnace. The quartz tube is packed with 20 by 30 mesh catalyst particles. The catalyst bed is positioned in the tube using quartz wool above and below the bed, with quartz chips filling the remainder of the reactor. The furnace temperature is controlled by a thermocouple inserted into the reactor tube and positioned about 3 mm above the catalyst bed. This allows operation at constant feed temperature into the reactor. 

The average size and surface area of quartz chips were 50 to 70 mesh and 0.29 g/m respectively. The effect of the quartz chips on the reaction were already discussed in a previous work. A flow rate of 10 mL/min of argon (1%) in helium was used as an internal standard to obtain the semi-quantitative data. 

The total conversions of catechol, 3-methylcatechol, hydroquinone, 2-methyl-hydroquinone, and 2,3-dimethyldhydroquinone were compared in the presence and absence of the nanoparticle iron oxide in quartz chips beds. It is evident that the presence of nanoparticle iron oxide lowered the temperature for a given conversion by about 180°C for all starting materials. In Fig. 12.4, representative results of the comparison are shown for catechol and hydroquinone over nanoparticle iron oxide/quartz mixture and quartz only, as a function of temperature. Each data point in Fig. 12.4 represents the averaged result of more than two experiments under the same conditions and a fresh catalyst was used for each new experiment. Catechol showed lower reactivity (50% conversion) than hydroquinone (100% conversion) at 260°C in the presence of the catalyst. This could be attributed to two phenomena. When the dihydroxybenzenes approach the catalyst surface in a co-planar fashion, intermolecular hydrogen bonding will lower the adsorption of catechol onto the catalyst surface and its interaction... 

EIGURE 12.4. Conversion of catechol (C) ( , ) and hydroquinone (H) (, 0) over the nanoparticle iron oxide/quartz chips ( , ) and quartz chips (D.O) as a function of temperature with a feed rate of 18 X 10 mmol/min and an oxygen concentration of 3%. 

As we presented above, the presence of quartz in the temperature range studied had no effects on the decomposition of dihyroxybenzenes. To further investigate this point and show the different effects of iron oxide and quartz on the product distribution, we present the product distribution for two cases of nanoparticle iron-oxide mixed with quartz chips and only quartz chips. Comparison in product distribution over nanoparticle iron oxide/quartz mixture and quartz was carried out with 3% of oxygen andl8 x 10 mmol/min of feedrate for starting materials, and at reaction temperatures that resulted in a comparable conversion of dihydroxybenzenes (e.g., 80%). Figure 12.6 shows the average spectra of the products obtained from MBMS for two cases with about 80% catechol conversion that was achieved at 300°C in the presence of iron oxide... 

FIGURE 12.6. Product distribution resulting at 80% conversion of catechol over (a) iron oxide/quartz chips at 300 C and (b) only quartz chips at 480 C with 18 x 10 mmol/min and 3% of oxygen. 

FIGURE 12.10. Effect of oxygen concentration on the fractional concentration of products resulting from catechol cracking over iron oxide/quartz chips with a feed rate of 18 x 10 mmol/min at (a) 280°C and (b) 330°C for primary (P) and secondary I (S-I)products that are derived by factor... 

FIGURE 12.13. Four classes of possible products from 3-methycatechol cracking over quartz chips in the temperature range of 280 to 480 C (a) Primary, (b) secondary I, (c) secondary II, and (d) tertiary products that are derived by factor analysis. 

Thermolysis of 505 mg of l-(5-methylbicyclo[3.3.1]non-l-yl)-2-propynone (4) is effected by passing a dilute solution down a column packed with quartz chips and with N2 flow (62(UC/14 Torr). Bulb-to-bulb distillation of the crude product (85 " C/0.04 Torr) yields 446 mg of a mixture that is 91% of the desired tricyclic enone and 9% of a mixture of four other isomeric components (by GC). An analytical sample is prepared by silica gel chromatography mp 41.9-43.6°C. 

The butane isomerization process developed by the Universal Oil Products Co. is shown in Figure 4. In this process (3), the feed is maintained essentially in the liquid phase under pressure. Part of the feed is by-passed through a saturator, where it dissolves aluminum chloride. The feed later picks up hydrogen chloride and passes through the reactor, which is packed with quartz chips. Some insoluble liquid complex is formed, and this adheres to the quartz chips. The aluminum chloride in the feed is preferentially taken up by the complex, which thus maintains an active catalyst bed. The complex slowly drains through the reactor, losing activity en route. It arrives at the bottom in essentially spent condition and is discarded. Aluminum chloride carried overhead in the reactor products is returned to the reactor from the bottom of the recovery tower. The rest of the process is the same as in the vapor-phase processes. 

Catalyst life, gal. isobutane per lb. bauxite bauxite quartz chips complex in SbCls... 

As shown, the ratio was very high on zeolite catalysts, while that on mesoporous silica was as low as those on AMS and quartz chip. The high ratio on zeolites can not be explained by classical mechanism of acid-catalyzed cracking supposing higher stability of tertiary carbenium ion and its cracking by P-scission, because this supposition predicts that the reaction (2) proceeds in preference to the reaction (1). Rather, a-scission of carbocation [12] may rationalize the higher C3/C4 ratio on zeolite catalysts. 

In the cases of mesoporous silica, AMS and quartz chip, the 0.5 C3/C4 ratio being close to unity means that two reactions proceed with almost equal probability to each other. This is in accordance with the classical radical mechanism of alkane cracking supposing that the energy required to form tertiary radical is not so different from that required for secondary radical and that both radicals are cracked by P-scission mechanism shown below [13]. Thus, the results shown in Fig. 4 strongly suggest that isohexane is cracked via the radical mechanism on the mesoporous silica catalysts, or, in other words, MCM-41, both with and without aluminum impurity, and FSM-16 exhibit radical type catalytic function. 

Figure 2.15 Schematic representation for the process of immobilization of the stationary phase in the channel, (a) Microfabricated quartz chip with cross channel design (b) PDMS slab bonded reversibly to the quartz, defining the location of the stationary phase (c) quartz with stationary phase particles immobilized in the separation channel after removing the PDMS cover (d) bonding of PDMS and quartz after oxygen plasma treatment [71].

Nakanishi et al. [70] pressed two quartz chips at a load of 1.3 MPa at room temperature for 24 h to produce enclosed channels. Satoh [156] used a low temperature and low external load technique for silicon-silicon bonding using water glass. Weinert et al. [157] used oxygen and argon plasma for... 

Ujiie et al. [204] fabricated quartz chips for NCE and reported the separation of rhodamine B and sulforhodamine at 14.4 and 66.6 cm separator lengths. The buffer was 20 mM phosphate buffer at 2kV applied voltage and the separation was achieved in 70 seconds. Wakida et al. [205] reported a high throughput characterization for dissolved organic carbon in environmental waters within 2 minutes using NCE. The authors collected water samples from 10 sampling points at the Hino River that flows into Lake Biwa. Shin et al. [206] described NCE (PDMS) with fluorescence detection for analyses of atrazine. 

Various wet and dry etch methods have been employed to micromachine fused quartz chips in a similar manner as in glass etching. However, the RIE method can be more effectively employed to etch quartz than can glass. Both wet and dry etch methods for fused quartz are summarized in Table 2.6. 

Normally, one-level etching was performed, but in some applications (e.g., pre-channel filter), a two-level etching method was also performed [148]. BOE etch was chosen over HF etch for quartz because BOE produced a smoother etch (0.23 urn RSI )) than did HF (0.55 pm RSI )) [149]. The cross section of an etched channel in a quartz chip is shown in Figure 2.11 [1006]. 

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