Kinetics of the dehydration of 2-propanol on modified activated charcoal containing acid sites

Abstract

A study was carried out on the kinetics of the dehydration of 2-propanol on activated bone charcoal (ABC) with supported acid sites. The rate-limiting step is the loss of water from the alcohol molecule adsorbed on the acid site. The sites containing the minimum amount of water are the most active. The reaction on these sites presumably proceeds through a concerted mechanism, which is possible at sufficiently high temperatures (above 120°C).The common use of activated charcoals (AC) as supports and adsorbents is a function of their highly developed surface and porous structure, the hydrophobic nature of the carbon matrix, and their capacity to undergo chemical modification [1]. In contrast to typical acid-base catalysts such as metal oxides and cation exchangers [2-6], a functional coating not only containing chemically-attached highly acid sites but also possessing considerable thermal and hydrolytic stability in a broad pH range may be produced on the AC surface. The insignificant use of acid AC presently in catalysis is a function of the paucity of approaches and methods for the preparation of materials derived from AC with a given structure of the surface layer. This is especially true for the preparation of systems with chemically-attached surface groups. As shown in our previous work [7], samples of activated bone charcoal (ABC) with supported acid sites are extremely active catalysts for the dehydration of 2-propanol in comparison with oxide systems [2-4]: the reaction onset temperature (T o ) and temperature for 100% conversion of 2-propanol to propylene (T 100% ) are 100-110°C and 150-170°C, respectively (Table 1). Samples of ABC oxidized with H 2 O 2 or HNO 3 as well as samples containing polymethylstyrene (PMS) on the surface were used as the matrices for the deposition of acid sites. The surface acid sites were obtained by treating the ABC with sulfuric acid, phosphotungstic acid, sulfur vapor with subsequent oxidation by hydrogen peroxide, and also sulfonation of the samples with supported PMS by oleum [3]. The systems obtained were designated ABC/H 2 SO 4 , ABC-HNO 3 /H 2 SO 4 , ABC/H 7 [P(W 2 O 7 ) 6 ], ABC-HNO 3 /H 7 [P(W 2 O 7 ) 6 ], ABC/S-H 2 O 2 , and ABC-PMS/SO 3 . These samples contained a large amount of acid groups (up to 1 mmol/g) and possessed high thermal stability; decomposition of the acid groups occurred at 200-450°C [8, 9].In the present work, we studied the kinetics of the dehydration of 2-propanol in the gas phase on modified ABC samples. The kinetic study was carried out at 110-250°C in a flow system using a gradientless reactor [10]. The catalyst sample was 0.25 g and the gas mixture flow rate was 45 cm 3 /min. The reaction mixture components were analyzed by IR spectroscopy.The study of the adsorbed forms of the reagent and product was carried out by thermal-programmed desorption with mass spectrometric detection of the products (TPDMS). The ABC samples were placed in a quartz cell attached to an MKh 7304A mass spectrometer (resolution 40000), which was evacuated to 10 -4 Pa a...

Electromagnetic Microwave Absorption Performances of PVC/AC Composites

“…Activated carbon made from apricot pits, the technology required for the production of which was developed at the Institute of Sorption and Problems of Endoecology of the National Academy of Sciences of Ukraine, with particle sizes of 0. Using TGA, TPDIR and TPDMS methods, it was established that there are oxygencontaining groups in a small amount on the surface of the original carbon, the desorption of which occurs at different temperature ranges depending on their thermal stability in the form of CO and CO2 [12]. For the initial AC, a small loss of mass is observed at all temperature intervals, which indicates the presence of a small number of surface oxygencontaining groups (Figure 2).…”

Efficient carbon-based acid catalysts for the propan-2-ol dehydration

“…As the propan-2-ol catalytic dehydration over ACs functionalized with strong acidic groups gave propene mainly and diisopropyl ether traces [13,14], the propan-2-ol conversion to propene (α) and the reaction rate (r) were calculated by means of Eqs. (1) and (2), respectively…”

Chemical grafting of sulfo groups onto carbon fibers

“…introduction, one can vary the surface chemistry of carbon materials [5][6][7]. In fact, this method is promising for the preparation of advanced heterogeneous catalysts with grafted sulfo groups, which are thermostable and hydrolytically stable sites of high acidity [8][9][10].…”