Cross-Linked Smectites. V. Synthesis and Properties of Hydroxy-Silicoaluminum Montmorillonites and Fluorhectorites

Abstract--Novel promising modified days adsorbents were synthesized by intercalating hydroxy-Al polymer associated with poly(ethyleneoxide) in the interlayer of montmorillonite. Two different PEOs of low molecular weight (600) and high molecular weight (100,000) were used. In both cases, the resulting materials are hydrolyticaUy stable and display a slightly better crystallinity than the materials prepared in the absence of PEO. Thermal analysis and infrared spectroscopy indicate changes in the PEO molecular conformation after intercalation revealing interactions between the polycations and the organic molecules. The chain length of the polymer has a strong influence on the surface area of the pillared materials obtained after calcination at 500~ The use of the high molecular weight polymer leads to products with a higher specific surface area (about 400 m2/g) whereas the lower molecular weight compound does not modify significantly the surface areas. This behavior can be explained by the different nature of the species intercalated in the interlayer. PEO(600) leads to isolated organometallic species whereas PEO(100,000) seems to lead to a network of complexed polycations linked by ethylene oxide units. In the case of the PEO(100,000), high amounts of polymer in the pillaring solution provoke a partial dissolution of the octahedral layer of the clay.

Section: Introductionmentioning

confidence: 99%

Intercalation of Al₁₃-Polyethyleneoxide Complexes into Montmorillonite Clay

Montargès¹

1995

“…Also the systematic incorporation of specific organic and inorganic complexes, generating pillared clays with a specified range of basal and lateral spacings, has stimulated interest in smectite synthesis (Lahav et al, 1978;Breen et al, 1985;Pinnavaia et al, 1985;Sterte, 1986;Sterte and Shabtai, 1987;Singh and Kodama, 1988). Pillared clays may be used simultaneously as molecular sieves and catalysts, e.g., in oil cracking reactions involving large organic molecules (Barrer, 1978;Ocelli, 1983Ocelli, , 1987Rupert et al, 1987;W.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Paragenesis of Na-Beidellite as a Function of Temperature, Water Pressure, and Sodium Activity

Kloprogge

1993

Abstract--In the chemical system NayO-AIyO3-SiO2-HyO, the stability field of Na-beidellite is presented as a function of pressure, temperature, and Na-and Si-activity. NaoT-beidellite was hydrothermally synthesized using a stoichiometric gel composition in the temperature range from 275* to 475~ and at pressures from 0.2 to 5 kbar. Below 275~ kaolinite was the only crystalline phase, and above about 500~ paragonite and quartz developed instead of beidellite. An optimum yield of 95% of the Nao.7-beidellite was obtained at 400~ and 1 kbar after 20 days. Gels with a Na-content equivalent to a layer charge lower than 0.3 per O20(OH)4 did not produce beidellite. They yielded kaolinite below 325~ and pyrophyllite above 325~ With gels ofa Na-content equivalent to a layer charge of 1.5, the Na-beidellite field shifted to a minimum between temperatures of 275 ~ and 200~ This procedure offers the potential to synthesize beidellite at low temperatures. Beidellite synthesized from NaL0-gel approach a Na~.35 composition and those from Nat. 5-and Nazo-gels a Naj.s composition.

“…Cation exchange, swelling in water, and incorporation of organic and inorganic complexes to produce pillared clays have been studied to investigate the technical utilization of natural clays (Loeppert et al, 1979;Breen et al, 1985;Goh and Huang, 1986;Plee et al, 1987;Schutz et al, 1987;Sterte and Shabtai, 1987;Olivera et al, 1988). The high costs of recovering the smectites, which usually have an unreliable quality and a large variation in impurity content, cause the industrial demand for natural smectites in these applications to be limited (Torii and Iwasaki, 1987).…”

Section: Introductionmentioning

confidence: 99%

Characterization of Synthetic Na-Beidellite

Kloprogge

1990

Ahstract--Na-beidellite, a member of the smectite group, was grown hydrothermally from a gel of composition 0.35NazO.2.35A1zO3.7.3SiO2 in NaOH solutions at a pH between 7.5 and 13.5, a pressure of 1 kbar, and a temperature of 350"C. The synthetic Na-beidellite was characterized by means of scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, electron microprobe, inductively coupled plasma-atomic emission spectroscopy, and thermogravimetric analysis. The unit-cell parameters of the orthorhombic cell are: a = 5.18, b = 8.96, and c = 12.54/~. The cation-exchange capacity was determined to be 70 meq/100 g. A maximum of 40 wt. % water was present and reversibly lost by heating to about 55"C. The loss of water caused a decrease of the basal spacing to 9.98/~. At temperatures >600"C, the Na-beidellite started to dehydroxylate, reaching its maximum in the range 600"-630"C. At 1100*C the remaining solid recrystallized to A16Si20~a (mullite) and SiO2 (cristobalite).