Effect of the Operating Conditions in the Transformation of DME to olefins over a HZSM-5 Zeolite Catalyst

Abstract

The effect of the operating conditions (cofeeding methanol and water, temperature, space time, and feed concentration) on the reaction indices of the transformation of dimethyl ether (DME) to light olefins has been studied, using a HZSM-5 zeolite catalyst (SiO 2 /Al 2 O 3 molar ratio of 280) agglomerated with boehmite and alumina. The experiments have been carried out in an isothermal fixed bed reactor under the following conditions: 300− 400 °C, space time, 0.2−6 g cat h mol C −1 ; feed, pure DME, and diluted in He (25−90% of DME); time on stream, 18 h. The studied reaction indices are DME conversion, yields, and selectivities of the individual olefins and byproduct fractions (C 2 C 4 paraffins, C 5 + aliphatic, and BTX aromatics) and the catalyst stability. The reaction scheme is similar to that of the methanol transformation, although the reaction advance and deactivation by coke are higher in the transformation of DME, due to mainly the lower water concentration in the reaction medium. The suitable conditions to reach an olefin yield above 45% in the transformation of pure DME are (i) 375 °C and space time of 3−4 g cat h mol C −1 , and (ii) 400 °C and 1−2 g cat h mol C −1. The catalyst deactivation by coke is favored by increasing the DME concentration in the feed and is attenuated by the formation of water in the reaction medium (as a consequence of the increased temperature and/or space time).

Benzene co-reaction with methanol and dimethyl ether over zeolite and zeotype catalysts: Evidence of parallel reaction paths to toluene and diphenylmethane

“…For H-ZSM-5, it has been reported that DME is converted to hydrocarbon more quickly than methanol, but there has not yet been a thorough deactivation study comparing both oxygenates [47,105]. Remarkably, the group of Bilbao has shown that addition of methanol and water to a DME feed over H-ZSM-5 interestingly leads to lower initial activity of the catalyst, thereby supporting faster MTH kinetics for DME compared to methanol [177,178].…”

“…Furthermore, adding water to methanol or DME feeds has been shown to have a positive effect in catalyst stability over different zeolitic catalysts [177][178][179][180][181][182], very likely due to the strong competition of water with methanol, DME and hydrocarbons for the acid sites, and therefore helping to avoid the retention of coke molecules [183].…”

Nature and Location of Carbonaceous Species in a Composite HZSM-5 Zeolite Catalyst during the Conversion of Dimethyl Ether into Light Olefins

“…The bed consists of a mixture of catalyst and inert particles (silicon carbide). The reactions were carried out feeding pure DME (18 mL·min −1 ) at temperature of 325-375 • C, pressure of 1.5 atm, space times of 4 g·h·mol C −1 , during 18 h. A reaction co-feeding water has been carried out using a molar ratio H 2 O/DME 3.55 [56]. Prior to the reaction, the transformation of DME (very sensitive to the presence of water) requires an in situ conditioning treatment of the catalyst (at 550 • C with air for 2 h) in order to eliminate the water adsorbed in the acid sites of the catalyst.…”

Capability of the Direct Dimethyl Ether Synthesis Process for the Conversion of Carbon Dioxide

“…Besides, DME is a potential raw material for the production of diesel fuels (such as dimethoxymethane and polyoxymethylene dimethyl ethers, via oligomerization) [4], and chemicals (methyl acetate, formaldehyde, ethanol, among others) [5], replacing methanol. Moreover, it can replace methanol for light olefin production [6,7] and it is a H 2 vector through steam reforming [8][9][10].…”