PILLARED FORMS

The crystals obtained at 800°C have a square pillar form and almost all of them are hollowed in the central part of the cross section. At 1100°C the formation of specially shaped deposits is observed along with the growth of dendritic crystals of CoB (about 5 mm in length). 

In the first picture, numerous stripes seen on the slope are the fine steps. The top of the crystal soon became flat, and then became like the top of a hammer. As time passed by, the top became bigger, and then, a rectangular pillar formed. 

Here we report the synthesis and catalytic application of a new porous clay heterostructure material derived from synthetic saponite as the layered host. Saponite is a tetrahedrally charged smectite clay wherein the aluminum substitutes for silicon in the tetrahedral sheet of the 2 1 layer lattice structure. In alumina - pillared form saponite is an effective solid acid catalyst [8-10], but its catalytic utility is limited in part by a pore structure in the micropore domain. The PCH form of saponite should be much more accessible for large molecule catalysis. Accordingly, Friedel-Crafts alkylation of bulky 2, 4-di-tert-butylphenol (DBP) (molecular size (A) 9.5x6.1x4.4) with cinnamyl alcohol to produce 6,8-di-tert-butyl-2, 3-dihydro[4H] benzopyran (molecular size (A) 13.5x7.9x 4.9) was used as a probe reaction for SAP-PCH. This large substrate reaction also was selected in part because only mesoporous molecular sieves are known to provide the accessible acid sites for catalysis [11]. Conventional zeolites and pillared clays are poor catalysts for this reaction because the reagents cannot readily access the small micropores. 

More recently, polyoxocations have been used to prepare pillared forms of interlayered clays that are related to the hydroxy-interlayered analogs found in... 

The characteristics of di-L-phenylalanine sulfate monohydrate crystals were investigated. Crystals of this compound were found to adopt two morphologies, i.e. needle form and thin plate form in the industrial plant. The former were metastable crystals and the latter were stable crystals which belonged to the same crystal system( monoclinic) as the pillar form crystals observed by powdered X-ray diffraction and solubility analyses. The needle form appeared at concentrations of L-phenylalanine higher than30g/dlat pH 1.7 to 2.0. On the other hand, the thin plate form appeared when the pH was below 1.0, or excess impurities (peak-A) derived from the mother liquid were accumulated in the crystallization liquid. 

The industrial crystallization process examined is outlined in Figure l.The filtered fermentation broth was fed to the vacuum evaporator and concentrated to 28 g/dl then the pH was adjusted within the range of 1.7 to 2.0 with sulfuric acid. When this solution was cooled continuously through a two-stage crystallizer whose temperature were 40 and 25 C, the pillar form crystals of the sulfate salt of l phenylalanine formed and were easily separated by centrifugation. 

Materials Di-L-phenylalanine sulfate monohydrate in the pillar form To 28 g/dl slurry of L-phenylalanine, 1.1 equivalents by volume of sulfuric acid were added with stirring at 60 C, and then cooled to room temperature with stirring. The pillar form crystals came out, the crystals were filtered then washed with water and dried in a vacuum desiccatorwith sulfuric acid. 

Measurement of solubility of the needle form and the pillar form crystals For measurement, 30 ml of saturated sodium sulfate solution and 20 g of di-I phenylalanine sulfate monohydrate either in the needle form or pillar form were added at 10 to 60 0, into 50 ml glass tubes with a spiral stirrer. Then, the contents were set in a water bath regulated with an accuracy of 0.5 C for each experimental temperature. After stirring for about 24 hours, an aliquot was taken with a cotton-stopped pipette, and the concentration of L-phenylalaninein the filtrate was determined by HPLC (Type 638-50 Hitachi Co., Inc. Japan). 

Velocity of transition between the needle form and pillar form Measured amounts of the needle-shaped crystals were placed in 50 ml glass tubes with a spiral stirrer.To each tube was then added 40 ml of a saturated solution of the needleform at the e3q>erimentaltemperature and then the contents were stiiredfor agiven period. The treated crystals were separated and dried in a vacuum desiccator. The amount of the needle form was measured by the X-ray diffraction method. The operational temperatures were 30,40 or 60°C. Twenty or 60 % of the pillar form crystals were added to the saturated solution of the needle form as the saturating body. The velocity of the transition of the needle form into pillar form crystals was calculated according the following equation ... 

Changes in crystal shape from the pillar form to the thin plate form... 

Characteristics of the two forms of crystals The crystal appearances and other characteristics of the two types of crystals obtained from the industrial plant are summarized in Table 1. The gel-like highly viscous slurry obtained from the pipe line contained more than 30 g/dl of L-phenylalanine as needle form crystals.On the other hand, the slurry obtained from the outlet of the centrifuge consisted of thin plate form crystals as described above. These two types of crystals were different from the ordinary pillar form crystals. Figure 2 shows the powdered X-ray diffraction chart of these two forms of crystals. The chart of the thin plate form crystals had the same pattern as the pillar form crystals reported by Matsuishi(2). 

On the other hand the chart of the needle form crystals showed a different peak from the pillar form crystals. The solubility data of di-L-phenylalanine sulfate monohydrate and sodium sulfate are shown in Figure 3.These experimental results show that the needle form crystals is more soluble than the pillar form crystals. 

Thus, the needle form crystals are the meta-stable form and the pillar form crystals are the stable form in solution. 

TVansition from the needle form to the pillar form In the solution containing more than 30 g/dl of di-L-phenylalanine sulfate at 60 T, needle form crystals were often observed with cooling in the laboratory. These conditions are similar to those in the industrial plant under which formation of needle form crystals has been observed. Needle form crystals are formed at concentrations of di-L-phenylalanine sulfate in excess of 30 g/dl at pH 1.7 to 2.0. The transition time required from the needle form crystals obtained from the industrial plant to pillar form was 22 hours at 60"C even when the pillar form crystals which amounted to 50% of the solute in a saturated solution was added. When no seed was added, the needle form crystals remained unchanged for more than 80 hours at 60" C. 

Assuming that the velocity of the transition of the needle form is caused by the dissolution of the needle form crystals and crystallization of the pillar form due to the difference in the solubility of the two crystal forms,the velocity of the transition might be a function of the degree of supersaturation of the pillar form, and will be presented by the following equation(5) ... 

The k values obtained from the experiments in which pillar form crystals were added at50%( ) were as follows 2.12X10 at60°C, I.VSXIO atSO C, 1.47X10 2 at35°C. 

The elution chart for impurities of crystals and mother liquid obtained from a Protein Column 1-125 are presented in Figure 4. There was no difference other than peak A between the pillar form and the thin plate form crystals. Although the amount of peak A detected in the mother liquid of the thin plate form crystals was almost the same as that in the mother liquid of the pillar form crystals, peak A was detected only in the thin plate form crystals. The location of peak A was close to that of L-phenylalanine, so this compound must have characteristics similar to those of L-phenylalanine. Thus, peak A might be one of the factors which affect the change from pillar form to thin plate form crystals. Future studies should be performed to identify the structure of peak A substance and clarify the influence of this substance on the change in the crystal appearance. 

The needle form crystals obtained from the industrial plant showed hardly any transformation to the pillar form without seed. When more than 20% of the pillar form crystals was added as seed, the transition was observed at higher temperatures. The transition enthalpy was estimated 12.2 kJ/mol. 

Thin plate form crystals belonged to the same crystal form as pillar form crystals and was obtained by the suppressed growth in the direction of the a-axis. This crystal form usually appeared under conditions of (a) pH less than 1 and (b) inclusion of the mother liquid at more than 40% in crystal cakes. 

The chief difference between laponite and montmorillonite is the high degree of disorder and delamination of laponite, which also persists in the pillared forms. The enhanced adsorption in comparison with montmorillonite results from the increas accessible surface area and may also be related to the more hydrophobic character of the bare silicate surface [8]. 

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