(129e) Catalytic Cracking of Light Hydrocarbons over Zeolite-Based Composites for on-Purpose Propylene

Title: Catalytic cracking of light hydrocarbons over zeolite-based composites for on-purpose propylene production

Authors: Shinya Hodoshima*, Azusa Motomiya*, Ryuichi Kanai*, Shuhei Wakamatsu*, Tomoyuki Mikuriya** and Fuyuki Yagi*

Address: *Research and Development Center, Chiyoda Corporation, 3-13 Moriya-cho, Kanagawa-ku, Yokohama 221-0022, Japan

**Process Development Section, Chiyoda Corporation, Minato Mirai Grand Central Tower, 4-6-2, Minatomirai, Nishi-ku, Yokohama 220-8765, Japan

Abstract

Propylene, a basic chemical in petrochemical industry, has become significant because of its increasing demand. Conventional thermal cracking of naphtha feedstock can no longer meet the increasing demand due to its low propylene productivity. Additionally, thermal cracking processes are unfavorable in terms of energy consumption. It is thus necessary to establish any alternative method for producing propylene efficiently from widely available feedstocks such as naphtha from these viewpoints. Though catalytic cracking of light hydrocarbons (e.g., light naphtha, LPG) over zeolites in fixed-bed operation have been actively investigated as a promising choice for on-purpose propylene production, this method hasn’t been commercialized because stable catalysts, being applicable to fixed-bed reactor, are still undeveloped. In the research by our group, unique composite catalysts, consisting of MFI-type zeolites and silicon oxide, have been developed to demonstrate efficient propylene production from naphtha at moderate temperatures in fixed-bed operation. Excellent properties of the present catalysts are summarized below.

1. MFI-type zeolites containing Fe, Ga and Al species at optimized ratios, giving both high propylene selectivity to propylene and low selectivity to aromatics due to their unique acidity, were synthesized as main component. The Fe-Ga-Al-MFI zeolites combined with silicon-oxide binder were employed as composite catalysts for cracking. These catalysts exhibited the following excellent performance in cracking of C₅-C₈ hydrocarbons in fixed-bed operation: (A) High overall propylene yields at 565-635^oC (25-35 wt%); (B) Longer lifetime than 1,000 h.
2. Energy consumption in cracking reactor using the Fe-Ga-Al-MFI/SiO₂ catalyst at 565-635^oC was reduced by 50-60% compared to thermal-cracking reactor, because no thermal energy for heating diluent such as steam was needed as well as its moderate temperature. As a consequence, total amount of naphtha feedstock was estimated to be saved by 10-15%, being superior to conventional thermal cracking in terms of total energy consumption.

It was suggested on these experimental basis that catalytic cracking of hydrocarbons over the present composites in fixed-bed mode is feasible as an efficient method for on-purpose propylene production. And now we are conducting various process studies such as reactor design, total process system and so forth toward investigations with pilot plant scale.

References

[1] S. Hodoshima, A. Motomiya, S. Wakamatsu, R. Kanai, F. Yagi, Res. Chem. Intermed., 41(12), 9615-9626 (2015).

[2] S. Hodoshima, A. Motomiya, S. Wakamatsu, R. Kanai, F. Yagi, Micropor. Mesopor. Mater., 233, 125-132 (2016).