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Properties of Raw Saudi Arabian Grey Kaolin Studied by Pyrrole Adsorption and Catalytic Conversion of 时间:2018-08-28 22:23   来源:未知   作者:admin   点击: 次 Abstract:This current article demonstrates how X-ray fluorescence spectroscopy (XRF) was employed to reveal the major constituents of a sample of natural grey Saudi kaolin. The XRF results showed that it contained 52.90 wt.% silica together with 14.84 wt.% alumina. Additionally, this paper presents a study on the effect of holding times (i.e., 6, 12, 18, and 24 h) using pyrrole adsorption and methylbutynol test reaction (MBOH) on the Saudi grey kaolin (raw material). Temperature-programmed desorption of pyrrole (pyrrole-TPD) results indicated that increases in thermal conductivity detector (TCD) signals are directly proportional to increases in the heat activation holding time. Notably, a raw Saudi grey kaolin sample heated at a holding time of twenty-four hours resulted in the most intense TCD signal. Further, the MBOH transformations produced 3-methyl-3-buten-1-yne (MBYNE), as the main product, indicating the dehydration of MBOH due to the acidic sites of Saudi grey kaolin. The basic catalysis route was operative at the beginning of the reaction as acetone was observed only during the initial thirty-five minutes of the reaction then later dispersed entirely. Its disappearance is attributed to the high silica content of the test sample.
1. Introduction
  In terms of their various industrial applications, clay materials play an important role in the production of ceramics, cement [1–3], environmental protection, and wastewater treatment [4, 5]. In order to clearly understand the uses of clay materials, researchers investigate their properties [6, 7] and endeavor to identify and explain their characteristics at their models level: micro and nano [8, 9]. A number of characterizations methods such as differential thermal analysis (DTA), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray fluorescence (XRF), and X-ray diffraction (XRD) are employed to examine the properties, morphological structures, and the chemical compositions of different clays [10–12]. Moreover, the gas phase reaction of methylbutynol (MBOH) is also studied to provide information about acidity and basicity features [13]. MBOH decomposition will lead to the formation of acetone and acetylene with respect to the basic properties of the material. Conversely, the formation of 3-methyl-3-buten-1-yne (MBYNE) and 3-methyl-2-buten-1-al (prenal) products is due to dehydration of MBOH on weak acid sites of the material and MBOH isomerization on its strong acid sites, respectively. Other products like 2-hydroxy-2-methyl-3-butanone (HMB) and 3-methyl-3-buten-2-one (MIPK) are produced over amphoteric sites of the investigated materials [14–18]. The MBOH reaction is widely used to differentiate acidic and basic sites for the materials. The predominant three possible reaction pathways are presented in Scheme 1 [15].
  Scheme 1: Different reaction pathways for catalytic conversion of methylbutynol [15].
Furthermore, another technique called pyrrole adsorption is also widely utilized for characterization of the clays. The reactive pyrrole-TPD techniques validate the basic properties of the material. The pyrrole aromatic compound is considered as an amphoteric molecule which gives an access for a hydrogen bonding through its NH group allowing it to react with the Lewis basic sites of the material sample [13, 14]. Saudi grey kaolin has been characterized using the following techniques: differential thermal analysis (DTA), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray fluorescence (XRF), and X-ray diffraction (XRD). To the best of our knowledge, none of the techniques reported in the literature makes use of the pyrrole-TPD and methylbutynol test reaction (MBOH) methods to investigate the properties of raw Saudi grey kaolin. In the present study, the pyrrole-TPD technique was used to investigate the basic properties of Saudi grey kaolin, while the MBOH conversion reaction was employed to study the catalytic performance of the clay.