Zeolitization process

Waters of intermediate hardness frequently contain fair amounts of other constituents and there is often a tendency for the scale to be loosely attached, permitting corrosion to occur irregularly underneath. In most waters the bicarbonate content is less than the hardness, but a few natural waters are known where the reverse is the case. These waters have been partially softened by the zeolite process which occurs underground, and then contain sodium bicarbonate which, together with the high concentration of chloride and other minerals, may accelerate attack. 

Sodium Cation Exchanger (Zeolite) Process. This is the most widely used water-softening process in industrial, commercial, institutional and household applications. Hard water is softened by flowing it, usually downward, through a bed (2 feet to over 8 feet in thickness) of a granular... 

Water, after passing through the zeolite process, contains as much bicarbonate, Sulfate and chloride as the raw water, only die calcium and magnesium having been exchanged for the sodium ions. There is no... 

Hoi-Lime Zeolite Softening. In this process hydrated lime is employed to react with the bicarbonate alkalinity of the raw water. The precipitate is calcium carbonate and is filtered from the solution. To reduce silica, the natural magnesium of the raw supply can be precipitated as magnesium hydroxide, which acts as a natural absorbent fur silica. These reactions are carried out in a vat or tank that is located just head of the zeolite softener tank. The effluent from this tank is filtered and then introduced into the zeolite softener. There is always some residual hardness leakage from the hot-process softener to be removed in the final zeolite process. The hot lime process operates at about 220T (I04°C). At this temperature the potential for the exchange of sodium for hardness ions is greater than at ambient temperature, and the result is a lower hardness effluent than is achieved at ambient temperatures. This system is shown schematically in Fig. 2. 

Demineralization, like the zeolite process, involves ion exchange. The metal ions are replaced with hydrogen ions by means of the process and equipment described for the hydrogcn-zcolitc system (see Hot Lime Zeolite—Split Stream Softening, previously described). In addition, the salt anions (bicarbonate, carbonate, sulfate and chloride) are replaced by... 

Zeolite processes. There is a simple and remarkably effective method of removing hardness from water. This scheme utilizes a reversible metathetical reaction between calcium and magnesium salts and substances called zeolites. 

In this section, we detail our results on the nucleation and growth of zeolite crystals with Si/Al ratios between 1 and 2. Various perturbations, including the effects of reaction time, D20, CH30H and C2Hs0H on the zeolite process are examined. A narrow range of starting compositions and reaction conditions are chosen, so that the effects of the perturbations can be evaluated with a minimum set of variables. These results are discussed in the context of present theories of zeolite growth in the next section. 

At alcohol levels of 50 volume percent or higher, hydroxysodalite crystals are formed at rapid rates (-200 minutes). The role of alcohol on the zeolitization process was examined with ethanol at temperatures of 90-95 C. 

In order to understand the influence of alcohol on the zeolitization process, it is useful to summarize the structural aspects of alcohol-water mixtures. Considerable work has been done in this area. It is well-recognized that at low alcohol concentrations the viscosity, reciprocal self-diffusion coefficient, the dielectric relaxation time and NMR relaxation times of the water molecules are all greater than that of pure water.(21-241 These observations indicate that addition of alcohol to water at low levels leads to an increased structure of water.(25) This concept is also supported by X-ray diffraction studies(26) and is commonly referred to as hydrophobic hydration.(27) On a molecular level, this effect... 

Another UOP zeolitic process that produces petrochemical feedstocks is the MaxEne process (27). The MaxEne process, another member of the Sorbex family of processes, separates C5 to Cn full-range naphtha into an extract stream containing more than 90 wt-% normal paraffins and a raffinate stream containing over 99 wt-% non-normals, namely isoparaffins plus naphthenic and aromatic hydrocarbons. The high normal-paraffin content of the extract makes it a preferred feedstock for a naphtha steam cracker, and the absence of normal paraffins in the raffinate makes it a preferred feedstock for catalytic reforming. 

Zeolites are used in separation processes for extracting p-xylene and m-xylene at high purity and recovery. There are zeolitic processes for converting C3-C7 paraffins into aromatics. In addition, zeolitic processes can co-produce aromatics and chemical-grade light olefins, or co-produce superior feedstocks for catalytic reformers and naphtha crackers. 

Titanium(III) exchanged 3A zeolite can also split water according to Eyring and coworkers (18). Illumination with visible light causes the evolution of h rogen as evidenced by mass spectrometry. As with the silver system described above, the titanium 3A zeolite process is not catalytic and loses reversibility. A detailed report concerning the electron paramagnetic resonance spectra of the titanium(III) 3A zeolite system has also been recently reported (19). 

In order to improve the olefin yield, zeolites which are more acidic than zeolite-Y are added to the matrix. These are mainly based on the smaller pored zeolite ZSM-5. This zeolite processes smaller molecules produced by the main cracking process and continues the cracking to smaller olefins and aromatics. 

Table 3 shows an example of the comparative performances of these three processes. All of them can produce a 99+% N2 enriched product gas. The two zeolite processes also produce a 85-90% O2 enriched product gas. The O2 product purity of the carbon sieve process is, however, low. This shows that different adsorbents can be married with different process schemes to obtain similar product purities but different process performances (recovery, productivity, product pressure, etc.). 

Comparison of the block diagrams of the Rhodia process and the previous classical process in figures 14.1 and 14.2, respectively, reveals the simplifications resulting from the zeolite process. 

If we compare process blocks diagrams (Figure 14.3) and amount of effluent of the classical Lewis acid process and the zeolite process for acetoveratrole, we have almost the same figures as with acetoanisole - so the competitive advantage for economics and for sustainable development is obvious. This is also a breakthrough for such technology. 

This zeolite process is a good example of how a new process can at the same time be cost efficient and environmentally friendly. This technology has now been adapted to the industrial synthesis of acetoveratrole using the same type of process. 

H. Suzuki, Composite membrane having a surface layer of an ultra-thin film of cage shaped zeolite, processes for production thereof, US Patent 4 699 892 (1987) assigned to Suzuki. 

TJor a long time, the Institute of Applied Chemistry of Naples Univer-sity has been systematically investigating the zeolitization process of glasses, either volcanic (7) or synthetic, with composition near (8, 9) or different (4) from that of the natural ones. 

The second zeolite process, which was developed by CR L, is based on the concept of catalytic distillation (48—51), which is a combination of... 

Adsorptive properties that help the adsorption step of the process inhibit the desorption step. The real processes are further complicated by non-isothermal operation, non-isobaric process steps, adsorption kinetics, gas channeling and maldistribution, etc. It is often necessary to experimentally evaluate the performance of the zeolite-process combination in a pilot scale unit before the optimum process design and adsorbent selection can be made. 

A comprehensive discussion of diffusion in zeolites and its simulation is presented in Keil et al. [2000] and Smit and Krishna [2003] have illustrated the potential of molecular simulations in zeolitic process design. 

The size and shape of crystals of minerals can be ascertained by interpreting the SEM micrographs of the raw materials (viz., fly ash) and the end products obtained from the zeolitization process [8]. The SEM micrographs of fly ash reveal flie presence of spherical particles of size 50-80 pm along with broken hollow spheres. 

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