A Study of the Dehydrochlorination of 1,2-Dichloropropane over Silica−Alumina Catalysts

Abstract

The conversions of 1,2-dichloropropane (12dcp), 1,3-dichloropropane (13dcp), and allyl chloride (3-chloropropene, 3cpd) over a silica-alumina bed have been investigated. Both 12dcp and 13dcp undergo dehydrochlorination above 500 K, mainly resulting in the two 1-chloropropene (1cpd) geometric isomers, which, above 650 K, further eliminate HCl to give propyne and burn in the presence of oxygen. Small amounts of 3cpd were also observed. 12dcp was found to react more rapidly than 13dcp. The conversion of 3cpd gives essentially CO x above 700 K and small amounts of benzene in the range 600-700 K. The reaction order is zero. The activation energy for the conversion of 12dcp was found to be 14.4 kcal/mol (60.6 kJ/mol). IR data show that a reversible adsorption step is followed by a nucleophilic substitution by an active surface oxide species, giving rise to an alkoxide species. The slow step is likely the E1 elimination of the alkoxide. The conversion of the primary 3-chloro-1-propyl carbenium ion to a 1-chloro-2-propyl carbenium ion plays a relevant role. The catalyst deactivates progressively at 523 K, its activity being nearly halved after 4 h, but it attains a plateau after 7 h. At higher temperatures, the stable total conversion of 12dcp was obtained after 10 h.

Surface Characterization of Mesoporous CoOx/SBA-15 Catalyst upon 1,2-Dichloropropane Oxidation

“…Weak bands are still detected at 3090 cm −1 (ν = CH) and in the low frequency region, typical of different isomers of chloropropene arising from dehydrochlorination process. These findings are consistent with results that were reported in an early study on the catalytic 1,2DCP conversion on silica alumina, tested in a flow reactor in the range 130–530 °C [24]. …”

A comparative study of surface acidity in the amorphous, high surface area solids, aluminium fluoride, magnesium fluoride and magnesium fluoride containing iron(III) or aluminium(III) fluorides

“…Catalytic dehydrochlorination of the chloropropanes has been investigated over various oxide catalysts [6,7]. Lewis acidic oxides effectively promote dehydrochlorination, with WO 3 and silicaalumina catalysts having the greatest dehydrochlorination activities and the lowest threshold temperature of reaction (<400 K) [6,7]. However, the most acidic catalyst of those used, zeolite ZSM-5, had one of the lowest activities for dehydrochlorination.…”

Catalytic Dehalogenation

“…This occurs readily over silica-alumina catalysts at temperatures above 500 K in excess oxygen [20]. Above 750 K, complete oxidation to CO and CO 2 begins to dominate.…”