Residual sodium content

The process is facilitated by low residual sodium contents of the zeolite. 

The realumination process strongly depends on parameters such as the residual sodium content of the parent material, duration of treatment, temperature, concentration of the realuminating solution and the kind of base. 

TABLE II. The effect of residual sodium content on the products... 

Several cationic forms were prepared from Na-Y. Nearly 95% of Na ions were exchanged by K and Ca ions with chloride solutions. These zeolites named K-Y and Ca-Y were progressively exchanged by NH4 ions and transformed in K-H-Y and Ca-H-Y forms. La ions were introduced in a zeolite NH4-Y, in which the residual sodium content is only 1%, by repeated exchange with LaCl solutions. The samples were heated in dry air at 380° and 550°C for 15 hours. 

Figure 14 gives the Njj lines obtained with five different samples of H-ZSM-5 zeolites [43]. For their preparation, the sodium precursors were first calcined at S00°C in air for 10 hours. Then the calcined samples were converted to ammonium form by repeated ion exchange with 1 M ammonium nitrate solutions. The protonic form was obtained by air calcination at 500°C for 10 hours and the residual sodium content measured by atomic absorption was less than 0.02%. Sample B was produced by acid leaching sample A with a 0.1 N solution of HCl at room temperature. Table 4 gives some of the bulk and surface properties of these samples. 

Zeolites, by being in a half way between amorphous silica-alumina and fluorinated alumina, were early recognized as potential components of bifunctional isomerization catalysts. The earliest report of zeolites being used in this application deal on Pt containing X and Y structures (3). They found that the activity increased from the Na to the Ca to the decationized forms. The residual sodium content, and therefore the final acidity of the Pt or Pd HY zeolite catalysts was critical for these type of catalysts (2,4-6). However, to make a successful commercial catalyst the following characteristic have to be accomplished by the zeolitic component ... 

Removal of sodium from the early Y-zeolites remained an urgent priority for catalyst manufacturers who were attempting to increase gasohne yield and obtain catalysts with higher thermal stabihty. Experimental woik with Y-zeohte had confirmed the benefits of a catalyst with low residual sodium content, but repeated exchange with ammonimn sdts was too expensive to be used commercially. Consequently the Y-zeolite produced commercially was not sufficiently stable. 

Either acid or base catalysis may be employed. Alkaline catalysts such as caustic soda or sodium methoxide give more rapid alcoholysis. With alkaline catalysts, increasing catalyst concentration, usually less than 1% in the case of sodium methoxide, will result in decreasing residual acetate content and this phenomenon is used as a method of controlling the degree of alcoholysis. Variations in reaction time provide only a secondary means of controlling the reaction. At 60°C the reaction may takes less than an hour but at 20°C complete hydrolysis may take up to 8 hours. 

Alkalinity and hardness (dissolved Ca24 and Mg2+, Box 12-3) are important characteristics of irrigation water. Alkalinity in excess of the Ca2+ + Mg2+ content is called residual sodium carbonate. " Water with a residual sodium carbonate content equivalent to 2.5 mmol H+/L is not suitable for irrigation. Residual sodium carbonate between 1.25 and 2.5 mmol H+/L is marginal, whereas si.25 mmol H+/L is suitable for irrigation. 

The bronzes are decomposed in a stream of oxygen and hydrogen chloride at 600° C. The residue of sodium chloride is titrated with standard silver nitrate solution, giving the sodium content of the sample. Tungsten is determined by precipitation of tungstic acid and ignition to tungsten (VI) oxide in the residue from the above treatment. Before analysis all of the samples analyzed were leached successively with concentrated ammonia and hydrochloric and hydrofluoric acids. 

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