![]() Long, narrow (waxy) molecules in the middle distillate boiling range enter the pores of this synthetic zeolite and are cracked to smaller molecules, mostly in the C3-C7 boiling range. 2 shows how ZSM-5 works in the MDDW process. Waxy molecules, which are predominantly normal paraffins and singly branched isoparaffins, can enter pores having such dimensions and be cracked into lower molecular weight hydrocarbons.įig. The dimensions of the straight and sinusoidal channels vary from 5.1 to 5.6 A. An artists rendition of the intersecting pore channels of ZSM-5 is shown in Fig. Much has been published about ZSM-5, including its structure, shape selectivity, and activity. The MDDW process, which was commercialized in 1978, will be used in this article as an example of a shape-selective application.1 2 Each of these processes utilizes a catalyst which contains the shape-selective zeolite, ZSM-5. ![]() has brought a number of important shape-selective applications to full commercialization.Ī descriptive list of the most common applications is shown in Table 1. The Mobil Distillate Dewaxing (MDDW) process, a shape-selective process utilizing ZSM-5 as a catalyst, has been used commercially in 21 refineries of various types: topping/reforming, visbreaking, and reforming/catalytic cracking refineries. Shape-selective catalytic technology to control cold-flow properties of middle distillates has been demonstrated during a 10-year period.
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