Ageing step

A typical material balance as well as chemical compositions are given in Table 5. The raw materials are metered into the makeup tanks in the proper ratios. Crysta11i2ation takes place in a separate crysta11i2er. An intermediate aging step at ambient temperature may be requited for the synthesis of certain high purity 2eobtes. 

The mechanism for sulfonation of hydrogenated fatty esters is accepted as a two-stage process. A rapid sequence of reactions leads to the formation of intermediates having approximately 2 1 stoichiometry of sulfur trioxide to ester. In the subsequent slower and higher temperature aging step, the SO is released for further reactions and the starting material conversion proceeds to completion (133). 

The next stage is neutralization of the alkenesulfonic acids with NaOH yielding water-soluble sodium alkenesulfonates, and hydrolysis of the sultones leading to sodium 3-hydroxyalkanesulfonates and sodium 4-hydroxyalkanesulfon-ates. The proportion of the latter two compounds in the mixture will depend on the conditions employed in the aging step. A hydrolysis temperature of 150-160°C and a hydrolysis time of 40-45 min ensures virtually complete hydrolysis of sultones 1,3-sultones will be present in ppb quantities and 1,4-sultones in ppm quantities. 

The effect of chain length on the pseudo rate constant is shown in Fig. 18. Clearly, the optimum chain length for AOS is 16 carbon atoms. However, at this optimum the rate of oil solubilization for AOS is still below that observed for the reference compound DOBS 103, a sodium alkylbenzenesulfonate with 10-13 carbon atoms in the alkyl chain. Increasing the chain length of IOS subjected to an aging step before hydrolysis with NaOH (IOSa in Fig. 18) leads to a continuously increasing rate of oil solubilization. The highest rate was... 

Neutralization of organic acid within 1 min after sulfonation reactor. A separate aging step is not needed under commercial reactor conditions Short residence time falling film reactor required to avoid thermal breakdown of R0S03H... 

A Method Involving Separate Nucleation and Aging Steps. 97... 

A new method involving separate nucleation and aging steps was reported by Zhao et al. [20]. The key features of this method are a very rapid mixing and nucleation process in a colloid mill followed by a separate aging process. The design of the colloid mill is schematically illustrated in Fig. 2. 

Fig. 3 TEM micrographs of Mg/Al - CO3 LDHs with different Mg /Al ratios prepared using the new method using rapid mixing and nucleation in a colloid mill followed by a separate aging step (a-c) and conventional coprecipitation at constant pH (d-f). The new method affords smaller crystallites with a much narrower range of length. Reprinted with permission from [20]. Copyright ACS Journal Archives...

This method has also been successfully applied in the synthesis of Cu(II)-containing LDHs, although well crystallized materials are difficult to prepare as a consequence of the Jahn-Teller distortion found in the coordination shell of Cu(II) [70,71]. Incorporation of Ni(II) in the layers was found to improve the crystallinity and structural stability of such LDHs. For the synthesis of Cu/Ni/Al - CO3 and Cu/Ni/Mg/Al - CO3 LDHs [70] by the method with separate nucleation and aging steps, LDHs with both smaller particle size and narrower distribution of particle size were obtained compared with those prepared using a conventional coprecipitation method, similar to the case for Mg/Al-C03 LDHs [20]. Well crystallized Cu/Ni/Cr-COs LDHs [71] were obtained when the Cu/Ni/Cr atom ratio ranged from 1 2 1 to 1 3 1 in the reaction mixture with hydrothermal aging conditions at 180 °C for 4 h. 

The dispersion of the precipitate changes with the degree of supersaturation and its evolution during precipitation. Low supersaturation leads to poorly dispersed solids. Highly dispersed solids are thermodynamically unstable and tend to lose dispersion (Ostwald ripening). This takes place during the process of precipitation itself. If the effect is desired, a special maturation (or ageing) step is carried out at the end of the precipitation. 

Figure 5.3.9 (A) Simplified geometric model [46, 89] for the preparation of industrial Cu/ZnO catalysts comprising subsequent meso- and nanostructuring of the material from [56], In a first micro structure directing step (mesostructuring), the Cu,Zn coprecipitate crystallizes in the form of thin needles of the zincian malachite precursor, (Cu,Zn)2(0H)C03. In a second step, the individual needles are decomposed and demix into CuO and ZnO. The effectiveness of this nanostructuring step depends critically on a high Zn content in the precursor, which in zincian malachite is limited to Cu Zn ca. 70 30 due to solid-state chemical constraints [75]. Finally, interdispersed CuO/ZnO is reduced to yield active Cu/ZnO. (B) Chemical memory Dependence of catalytic activity in methanol synthesis on the conditions of the coprecipitation and aging steps, from [85].

Achieving 100% crystallization in CET occurred by adding submicrometer seed crystal that did not sediment even in the static state (Figure 5) [11]. Without seeding, sufficient crystallization was not obtained even after a 15-h aging step in the crystallization process [17],... 

After the fermentation and aging steps the beer is cloudy, despite the fact that after aging the beer is separated from most of the sedimented yeast and tank bottoms. This cloudiness results from the remaining yeast cells—yeast concentrations of approximately 200,000 ceUs/mL are common for beer after separation from the tank bottoms—and from the haze-forming components of beer. 

These results point out that ageing step offers a simple way to strongly modify the texture of silica hydrogels. A further precipitation of alumina in the aged silica gel stops the... 

The complete mechanism of OPIDN has not been elucidated. However, there is good evidence that the disease is initiated by a concerted two-step reaction involving inhibition and aging of a critical amount of a protein called neuropathy target esterase (neurotoxic esterase, NTE) in target neural tissues. The net result of the aging step is the rapid formation of a... 

Supersaturation and mixing environments must be designed to minimize or eliminate unexpected nucleation beyond that required for seed. A seed age step must be added if needed. 

The nitrogen physical adsorption results show that SG-500 catalyst has a higher BET surface area SGI-500 and 1-500 samples (Table 1). When the catalysts are calcined at 700 or 800°C,or when they are aged under the reaction mixture at 500°C for 72 h, no significant BET surface area loss is observed for samples SGI and I. However, a considerable decrease of the surface area is observed for SG-500. In addition, it is important to note that the SG samples still show the highest BET surface areas for the different calcination temperatures and after the ageing step. 

Furthermore, it is also important to note that a pronounced metal sintering occurs over the I and SGI catalysts compared to SG. Indeed, compared to the samples calcined at 500°C, the 1-800 and the SGI-800 catalysts kept, respectively, only 20 % and 14 % of the initial metallic dispersion values, whereas 71 % of the Initial metallic dispersion is kept for the SG-800 catalyst (Table 1). This result suggests a relatively higher resistance to sintering for the SG catalyst, which is also observed during the ageing step under reaction mixture. 

---