The Addition of ZSM-5 to a Fluid Catalytic Cracking

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The Addition of ZSM-5 to a Fluid Catalytic Cracking Catalyst for Increasing Olefins in Fluid Catalytic Cracking Light Gas a

A. Farshi & H. R. Abri

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Development Engineering Department, Research Institute of Petroleum Industry, Tehran, Iran Version of record first published: 02 May 2012

To cite this article: A. Farshi & H. R. Abri (2012): The Addition of ZSM-5 to a Fluid Catalytic Cracking Catalyst for Increasing Olefins in Fluid Catalytic Cracking Light Gas, Petroleum Science and Technology, 30:12, 1285-1295 To link to this article: http://dx.doi.org/10.1080/10916466.2010.497789

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Petroleum Science and Technology, 30:1285–1295, 2012 Copyright © Taylor & Francis Group, LLC ISSN: 1091-6466 print/1532-2459 online DOI: 10.1080/10916466.2010.497789

The Addition of ZSM-5 to a Fluid Catalytic Cracking Catalyst for Increasing Olefins in Fluid Catalytic Cracking Light Gas A. FARSHI1 AND H. R. ABRI1

Downloaded by [Amir Farshi] at 05:03 06 September 2012

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Development Engineering Department, Research Institute of Petroleum Industry, Tehran, Iran Abstract The second largest source of propylene supplied for petrochemical application is from fluid catalytic cracking (FCC) units. The primary function of the FCC unit has typically been to produce gasoline. However, refiners have been taking advantage of opportunity to produce and recover more propylene from their FCC unit by increasing reaction severity via riser temperature, adding shape selective catalyst, and installing a propylene recovery unit (PRU). At a conventional FCC process propylene exists in the off gas of FCC and it is about 6 wt% of off gas by changing the FCC process parameter quantity of propylene in off gas can be more than 20 wt% by using ZSM-5 additives and increasing temperature The effects of operating parameters, such as reaction temperature, and ZSM-5 as FCC catalyst additive, on the distribution of the product and the yield of propylene were investigated on a bench-scale fluidized bed reactor. It is the aim of this work to perform an overall analysis of the yields and selectivity of hydrocarbons obtained in the vacuum gasoil conversion over FCC and ZSM-5 catalysts. The effectiveness of ZSM-5 additive in the FCC process was investigated by doing experimental work in a bench-scale setup. The experiment data of off gas analysis showed that vacuum gas oil cracking at high reaction temperatures of 450–550ıC increases the yield of propylene. Similar behavior is observed with the addition of 10–25 wt% ZSM-5 additive. The combination of the two effects (high temperature and ZSM-5 addition) makes the FCC unit an excellent source of light olefins for downstream petrochemical units. Higher FCC reactor temperatures (600–650ıC) would not have positive effects for increasing propylene yield. Keywords additive, FCC, propylene, yield, ZSM-5

1. Introduction Fluid catalytic cracking (FCC) units typically produce around 3–5 wt% propylene, depending on the feed properties, operating conditions, and the nature of the catalysts (Hollander et al., 2002). ZSM-5–based additives, although introduced more than 20 years ago as a way to increase the octane value of FCC gasoline, are now primarily being used to increase light olefins yields from the FCC unit. In fact, the use of these additives is by far the most effective way to increase light olefin yields, as typically only a few weight percent of additive in the inventory can significantly improve light olefin yields (Aitani Address correspondence to A. Farshi, Refinary Technology Development Division, Research Institute of Petroleum Industry, West Blvd of Azadi Sport Complex, Tehran 14665-137, Iran. Email: [email protected]

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Figure 1. Main reactors of FCC. (color figure available online)

et al., 2000). A bench-scale fluidized bed reactor setup with zone-type electrical furnace has been designed and built to study the role of ZSM-5 zeolite additive on propylene production in FCC process.

2. FCC Process Description The process of catalytic cracking of hydrocarbons (FCC) plays a key role in the modern refineries. The most common process is FCC, in which the oil is cracked in the presence of a finely divided catalyst, which is maintained in an aerated or fluidized state by the oil vapors. The fluid cracker consists of a catalyst section and a fractionating section that operate together as an integrated processing unit (Figure 1). The catalyst section contains the reactor and regenerator, which, with the standpipe and riser, form the catalyst circulation unit. The fluid catalyst is continuously circulated between the reactor and the regenerator using air, oil vapors, and steam as the conveying media. A typical FCC process involves mixing a preheated hydrocarbon charge with hot, regenerated catalyst as it enters the riser leading to the reactor. The charge is combined with a recycle stream within the riser, vaporized, and raised to reactor temperature (900–1,000ıF) by the hot catalyst. As the mixture travels up the riser, the charge is cracked at 10–30 psi. In the more modern FCC units, all cracking takes place in the riser. The reactor no longer functions as a reactor; it merely serves as a holding vessel for the cyclones. This cracking continues until the oil vapors are separated from the catalyst in the reactor cyclones. The resultant product stream (cracked product) is then charged to a fractionating column where it is separated into fractions, and some of the heavy oil is recycled to the riser. Spent catalyst is regenerated to get rid of coke that collects on the catalyst during the process. Spent catalyst flows through the catalyst stripper to the regenerator, where most of the coke deposits burn off at the bottom where preheated air and spent catalyst are mixed. Fresh catalyst is added and worn-out catalyst removed to optimize the cracking process.

3. ZSM Additive Development 3.1.

Introduction

Almost two decades passed between the initial discovery of ZSM-5 in 1965 and its initial commercial trial in a cracking unit in 1983. That initial commercial trial in the Neste Oil refinery, Naantali, Finland, was the product of many years of painstaking testing

ZSM-5 and Fluid Catalytic Cracking

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and analysis of ZSM-5 activity, selectivity, and stability in both laboratory- and pilotscale catalytic cracking units. ZSM-5 FCC additive development within ExxonMobil is the subject of a separate review (Degnan et al., 2000). Interestingly, the motivation for developing a ZSM-5 additive changed over the course of its development. In the early 1980s, lead was eliminated from gasoline, which prompted a search for a means to increase octane from nontraditional sources.


3.2.

Early Cracking Catalyst Evaluation

Researcher (Argauer and Landolt, 1972) first synthesized ZSM-5 in 1965. Because it was only synthesized in very small quantities (