Chemical Impregnation of Silica

An early patent that describes the chemical impregnation of silica was filed on August 1,1979 and is summarized below in (V). 

This patent describes the preparation of silica-supported catalysts in which a dried silica was reacted with a mixture of magnesium and aluminmn alkyls (heptane solution of dibutylmagnesium/triethyl aluminum) followed by treatment with TiCl or a catalyst in which the dried silica was treated with only a magnesium alkyl (butyl, ethyl magnesium - BEM) followed by treatment with TiCl  

In Example 1, Davison Grade 952 silica was dried at 600 C for five hours in a glass column in which the silica was fluidized with 

The ethylene polymerization of this catalyst was carried out in an autoclave reactor at 221°F in isopentane as the slurry solvent in the presence of triisobutylaluminum as cocatalyst and 50 psig of hydrogen and sufficient ethylene to achieve a total reactor pressure of 550 psig. The catalyst activity was 10,540 g of PE/g of catalyst/ hr, which corresponded to an activity of 146,000 g PE/g Ti/hr. The granular polyethylene product obtained was considered suitable for a particle-form slurry process such as the Phillips slurry process. The polyethylene sample displayed a Melt Index (I value of 0.70 and a High Load Melt Index ) value (HLMI) of 3 1 with a HLMI/MI ratio of 45, which indicates tfiat the polyethylene molecular weight distribution was of an intermediate value. 

This patent teaches a chemical impregnation of silica method where a dried silica is slurried into a non-coordinating solvent such as heptane, reacted with a heptane solution of butyl, ethyl magnesium (BEM) to provide a first intermediate material that is then reacted with a silicon compound with the general formula (EtO) SiMe,  

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Table 2.4 Examples of the chemical impregnation of silica method.

In this paper, the bulk material was obtained by impregnation of the silica host with GFP solution and nanosised by sonication, preserving the features of both the biomolecule and the mesoporous structure. An exhaustive physical chemical characterisation of the nanosized materials was performed by structural (X-Ray Diffraction, Transmission Electron Microscopy), volumetric and optical (photoluminescence spectroscopy) techniques. 

Lapidus, A., Krylova, A., Kazanskii, V., Borovkov, V., and Zaitsev, A. 1991. Hydrocarbon synthesis from carbon monoxide and hydrogen on impregnated cobalt catalysts. Part I. Physico-chemical properties of 10% cobalt/alumina and 10% cobalt/ silica. Appl. Catal. 73 65-81. 

The hydrophobicity of some monoazoic dyes was determined by RP-TLC. The chemical structure of analytes are depicted in Fig. 3.1. RP-TLC plates were prepared by impregnating silica plates for 24 h in a hexane-paraffin oil (90 10, v/v) mixture. Mobile phases consisted of methanol-0.5 M HC1 mixed in various volume ratios. Methanol concentration varied between 30-60 per cent in steps of 6 and 3 per cent. The RM value characterizing molecular hydrophobicity was calculated by... 

Radiochemical purity determinations consist of separating the different chemical substances containing the radionuclide. The radiochemical purity of labeled pharmaceuticals is typically determined by paper chromatography (paper impregnated with silica gel or silicic acid). The most frequently used radioisotope is technetium-99m obtained by daily elution with saline... 

In this section, only the surface modification techniques will be discussed, and not the impregnation, sol-gel or co-precipitation techniques. Furthermore, it is not our aim to fully cover all chemical modifications on the silica surface. We merely want to present in introduction to and an insight in the fast expanding field of silica modifications, in order to create new catalysts, sensors and immobilizators. 

Organic binder in ceramic honeycomb rotor was removed by heating it for 5 hrs in 600 C before impregnation of zeolite. Heat treated rotor was soaked in zeolite (UOP HISIV 1000 and HISIV 3000) dispersed slurry with silica sol (Nissan Chemical ST-30) or alumina sol (Nissan Chemical AS-520) as a binder. The amount of binder addition was vairied to 3, 5, 7 wt%. BET surface area and SEM micrograph was analyzed with respect to type of binder and its amount. 

Chemical stability of carbon over the entire pH range has led to considerable interest in the development of carbon-based stationary phases for RPC. Porous graphitised carbon with sufficient hardness, well-defined and stable pore structure without micropores, which ensures sufficient retention and fast mass transfer can be prepared by a complex approach consisting of impregnation of the silica gel with a mixture of phenol and formaldehyde followed by formation of phenol-formaldehyde resin in the pores of the silica gel, then thermal carbonisation and dissolution of the silica gel by hydrofluoric acid or a hot potassium hydroxide. solution [48. The retention and selectivity behaviour of carbon phases significantly differs from that of chemically bonded pha.ses for RPC. Carbon adsorbents have greater affinity for aromatic and polar substances so that compounds can be separated that are too hydrophilic for adequate retention on a Cix column. Fixed adsorption sites make these materials more selective for the separation of geometric isomers [49]. 

Figure 122 shows the results of three series of two-step activations, each of which included one of these chemical dehydroxylation methods. Silica-titania (2.5 wt% Ti) was calcined at 871 °C in air, CO, or CS2. Each support was impregnated with 1 wt% Cr as dicumenechromium(O) in hexane. Then samples were subjected to a second calcination in dry air at lower temperatures ranging from 160 to 871 °C. These catalysts were tested at 107 °C for polymerization activity and the resultant polymer was recovered and analyzed. 

The physico-chemical properties of the supports and vanadium oxide catalysts are listed in Table 2. The catalysts are labeled XVj/M, where X corresponds to the % by weight of vanadium, V to vanadium, p to the preparation method (imp=impregnation, graf=grafting) and M to the support. No marked effect of the deposition of titanium oxide on the specific surface area of the silica was detected in the case of the support TSm, while, in the case of the vanadium-based catalysts, a decrease in Sbet was observed. The vanadium surface densities are calculated as number of vanadium atoms per square nanometer of catalyst (V/nm oat) to facilitate a comparison of the samples prepared on different surface area supports [6]. The vanadium contents of the samples are quite smaller than the theoretical monovanadate monolayer coverage of 2.3 VO,/nm" [6]. 

Charring reagents have been incorporated by dipping layers to avoid spraying of corrosive chemicals. For example, silica plates have been impregnated with 4% sulfuric acid in methanol [53] or ammonium bisulfate [54]. 

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