Effects of catalyst activity, catalyst particle shape (sphere, cylinder with different diameters), size (i.e., diffusion length), catalyst distribution (uniform vs. eggshell type distribution for a spherical particle), and process conditions (temperature, pressure, methanol to water ratio, and conversion level) on the catalyst effectiveness factor and methanol selectivity inside the catalyst pellet toward favorable hydrocarbons has been investigated. We utilize kinetic parameters for methanol conversion rate, Olefin (selectively ethylene and propylene), and aromatics (favorably benzene and ISO-butane) formation rate determined from experiments with a highly active synthesized ZSM-5 catalyst. Catalyst has been shaped by the pre-modified binder and other additives to enhance the conversion rate. It is found that the use of small spherical particles (0.2−0.5 mm) or eggshell distribution for larger spherical particles with catalyst layer thickness less than approximately 0.13 mm is needed to avoid the negative impact of diffusional limitations on olefin selectivity under typical operating conditions. İt has been demonstrated, diffusional limitations in an industrial scale reactor play a crucial role in olefin selectivity and catalyst performance. For industrial-scale reactors with binder-shaped catalyst, diffusional limitations can be avoided by using a cylindrically formed catalyst by the diameter of 2mm with the addition of an optimum amount of binder at base case conditions (550 ºC, 1.2 bar, and Methanol/water molar ratio of 2). İt was shown that activity of cylinder-shaped ZSM-5 catalyst by the diameter of 2mm is 3 times higher than 4mm cylinder and 1.5 times higher than spherically shaped by the diameter of 1mm. One of the benefits of The present work is to address the issue of the shape optimization of the catalyst pellet to enhance its effectiveness. This will lead to improved efficiency of the heterogeneous reactor configuration, and will ultimately help the overall economics of the process. The experimental case study here has been approved by analyzing the shaped catalyst by BET, SEM, and XRD. The selectivity issue has been analyzed by Gas chromatography toward the conversion of methanol to light olefins.
Anahtar Kelimeler: Zeolite, Methanol conversion, Ligth olefins, effectiveness factor, thiele module
|
