Deactivation and Testing of Hydrocarbon-Processing Catalysts

Chapter 22

Improved Methods for Testing and Assessing Deactivation from Vanadium Interaction with Fluid Catalytic Cracking Catalyst Downloaded by UNIV OF TENNESSEE KNOXVILLE on August 13, 2015 | http://pubs.acs.org Publication Date: June 6, 1996 | doi: 10.1021/bk-1996-0634.ch022

Bruce Lerner and Michel Deeba Engelhard Corporation, 101 Wood Avenue, Iselin, NJ 08830-0770

Test methods for studying the effect of vanadium on FCC catalyst have been developed. Vanadium tolerance is important as it relates to catalyst deactivation. A simple, effective, and inexpensive test has been developed which takes the best features from other test methodologies and combines them; the test is termed the Engelhard Transfer Method (ETM). Resultsfromthe test have provided data which may be used to infer the mechanism of vanadium transport in these systems. It appears that vanadium moves via a solid state interparticle transfer and not by liquid or gas phase movement. The test design also allows for the incorporation of other feed contaminants such as sulfur or nitrogen oxide gases. The importance of including sulfur in vanadium trap evaluation is shown by demonstrating its effect on trap materials.

In recent years the refining industry has addressed the importance of upgrading the "bottom of each barrel" to optimize refinery economics based on the changing product slate and price structure of crude. An increased number of oil refineries are now processing at least a portion of resid or heavy crude as a feed stock (1). Processing resid can negatively affect yields of valuable products relative to a light feed. To counter this, catalyst design must address the following aspects: upgrading bottoms, minimize coke and gas formation, maximize catalyst stability, and minimize deleterious selectivity due to contaminant metals such as nickel and vanadium. Particular attention must be paid to the mediation of contaminant metals. Nickel and vanadium are contained wdthin the crude oil as their respective porphyrins and napthenates (2). As these large molecules are cracked, the metals are deposited on the catalyst. Nickel which possesses a high intrinsic dehydrogenation and hydrogenolysis activity drastically increases the production of coke and dry gas (particularly H2) at the expense of gasoline. Vanadium on the other hand interacts with the zeolitic component of a cracking catalyst and leads to destruction of its crystallinity. This results in reduced activity as well as an increase in non-selective amorphous silica-alumina type cracking. Supported vanadium also has an intrinsic

0097-6156/96/0634-0296$15.00/0 © 1996 American Chemical Society

In Deactivation and Testing of Hydrocarbon-Processing Catalysts; O'Connor, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

Downloaded by UNIV OF TENNESSEE KNOXVILLE on August 13, 2015 | http://pubs.acs.org Publication Date: June 6, 1996 | doi: 10.1021/bk-1996-0634.ch022

22. LERNER & DEEBA

Vanadium Interaction with FCC Catalyst

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dehyrogenation activity which increases hydrogen and coke make, albeit it is significantly less than the contribution due to nickel. A long compilation of open and patent literature attests to the effort and quantity of research which has been directed towards resolving metals tolerance. Advances in this area have been nicely reviewed by several authors (3,4,5). So far nickel has been most successfully controlled by addition of an antimony additive in a process developed by Phillips Petroleum in the late 1970's (6). This technology remains a practiced method for nickel control particularly in low to moderate levels, however in recent years the concern over the toxicity of antimony to the environment has reemphasised the need for effective yet benign nickel passivators. Vanadium passivation has been a more difficult challenge to overcome. In reviewing the literature it is quickly realized that a host of materials have been studied for vanadium passivation and some have been commercialized. However, not all materials perform equally. In fact, actual unit performance may vary significantly from that predicted by testing methods commonly used in many laboratories. The ultimate performance of an FCC catalyst in the presence of vanadium is related to the chemistry and thermodynamics of the catalysts' trapping system and the affinity for vanadium over competitive species. The testing of candidate materials is important in order to judge their relative performance. Different test methods approach the reality of actual unit conditions to varying degrees. The desire to mimic the actual unit is often offset by considerations of complexity, time, and cost. One aspect of the present paper will be to discuss a simplified, yet elegant test procedure called the Engelhard Transfer Method (ETM) (7) which can easily and realistically assess the interaction of vanadium with FCC catalyst. The test is a rapid, efficient, and cost-effective way of testing for vanadium tolerance. In designing a working catalyst or catalyst component a fundamental understanding of the chemistry or mechanism at hand is extremely useful. It has become accepted that aluminum, alkali, or rare earth vanadate formation is the end result of vanadium-zeolite interaction. Whether this is due to eliminating charge neutrality of the sieve resulting in structural collapse or creation of a low melting eutectic composition (8) is still a matter of opinion although probably neither is exclusive. The means by which vanadium makes its way to a site of potential interaction is also debated. In general two camps exist: one which contends vanadium pentoxide is formed and is transported as a liquid, upon melting, through the catalyst (9); the other proposes that vanadic acid is formed which is volatile and travels via gas phase transport (10). Data presented hereinfromthe development of ETM suggest a third mechanism which may offer a more accurate model of vanadium migration. Many of the materials used to trap vanadium by chemical reaction also share a similar chemistry with the oxides of sulfur a prevalent contaminant in FCC feed stocks. Sites which trap vanadium are thereby competed for by sulfur species. Results obtained by incorporating a feed contaminant, such as sulfur, in a competition with vanadium demonstrate the importance of including sulfur in vanadium tolerance testing and will be discussed. The ETM test offers the ability to study what happens under just such a competition.



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DEACTIVATION AND TESTING OF HYDROCARBON-PROCESSING CATALYSTS

Experimental. Two catalysts were used in this study. The first is a standard Engelhard commercial fluid cracking catalyst whose typical properties are given in Table 1. In vanadium trapping studies this catalyst was combined with a commercial Engelhard vanadium trap based on MgO in a 70:30 ratio cat:trap. Others catalyst samples are laboratory prototypes for this study, and were prepared by combining 25% USY in a Si02-Ai203-Kaolin matrix. 5 wt% of Barium or Strontium Titanate, vanadium passivators, were included in two samples. A control sample which has 75% of its composition as the matrix formulation and no trap component was also prepared. Properties of the control and the titanate containing catalysts were essentially identical and are also given in Table 1. Table 1. Physical and Chemical Properties of Catalysts Property Lab Catalyst Commercial Catalyst 64.7 Si0 (wt%) 65.6 26.5 A1 0 (wt%) 29.6 0.16 Na 0 (wt%) 0.28 1.18 ReO (wt%) 1.02 170 Total Surface Area* (m /g) 224 118 Zeolite Surface Area* 154 (m2/g) 0.145 Pore Volume (cc/g) 0.274 1 - Steamed 1500F/4h/100% stm 2

2

3

2

2

Metals impregnation was done according to the Mitchell Method (11). In this method the catalyst sample is impregnated with vanadium napthenate (ALFA) diluted with cyclohexane. After air drying for several hours the sample is calcined at 600 F for 1 hour and then at 1100 F for 1 hour. The samples are subsequently steamed for 4 hours at 1450 F in an atmosphere of 90% steam and 10% air. The Engelhard Transfer Method makes use of the same steaming apparatus as is conventionally used to steam deactivate FCC catalyst. Simply, a bed of material is supported on afritin a quartz tube and the tube placed vertically inside a three zone tube furnace. Steam, air, and nitrogen (if desired) flow upwards through the bed and fluidize it. In the method inert particles of calcined clay are impregnated with 10,000 15,000 ppm V by the Mitchell method and are abbreviated as V/in. These particles are highly calcined kaolin clay microspheres with a very low surface area (xn) (KJ/mole) Reductive H^S elim.2 MO Oxidative SO4 form . Mg -193 -92 Ca -77 -208 Ba +33 -317 Nd -593 -317 D

1

3

1- 780 C, MO + SO3 = MSO4

2- 500 C, MSO4 + 8H =MO + H S +3 H 0 3- value @ 650 C 2

2

2

Conclusions. It is necessary to test a catalyst's stability and performance under high vanadium conditions for materials which will be processing metals laden feedstocks. The Engelhard Transfer Method offers the benefits of both the Mitchell Method and


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Vanadium Interaction with FCC Catalyst

LERNER & DEEBA

5% SrTi03

A

O

Control

5%SrTi03noS

Deactivation and Testing of Hydrocarbon-Processing Catalysts

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