Characterization and Catalyst Development - American Chemical

Chapter 12

Evaluation of Fluid Cracking Catalysts A Comparative Study of Testing Philosophies E. L . Moorehead, M . J. Margolis, and J . B. McLean

Downloaded by UNIV OF PITTSBURGH on February 12, 2015 | http://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0411.ch012

Engelhard Corporation, Edison, N J 08818

Fluid catalytic cracking (FCC) i s one of the major refining processes within today's petroleum industry. For the majority of refineries this process represents the primary conversion unit for producing gasoline directly from gas oil. While discussions about FCC tend to group all units into one, average type, there are i n fact many differences among FCC units. These differences include configuration, operation, and feedstock. For each refiner there i s usually some limiting parameter i n the unit that controls the overall operation. This may be catalyst circulation, attrition, coke selectivity (either too much or too l i t t l e ) , or gas selectivity (compressor - either wet (LPG) or dry gas limits). Depending upon the needs of the refiner he may be limited by any one of these at various times as he moves from a maximum octane operation to a maximum gasoline operation or switches from a light gas o i l to a heavier gas o i l feed. The selection of the proper catalyst provides f l e x i b i l i t y to address these requirements i n a manner otherwise unavailable. In order to provide the refiner with as much f l e x i b i l i t y as possible, catalyst vendors have developed a variety of FCC catalysts to meet specific demands. While all catalysts incorporate zeolites as the core, the type and amount vary widely. At present there are probably 100 catalyst variations that are available depending upon the specific application. Differences i n catalysts can be significant; for example, zero versus 3 weight % REO, or 15 versus 40 % zeolite or surface areas ranging from 100 to 400 M /G . Alternatively, differences can be very subtle. While this provides the refiner with a variety of choices, it also presents a problem i n how to best evaluate various catalysts. In an effort to understand how the petroleum industry addresses the problem of fresh FCC catalyst evaluation, a survey of testing philosophies from 15 companies was conducted. The objective was to identify the merits of various steaming procedures as well as catalyst testing. The results of the survey show that each laboratory has a unique testing program, with wide differences being practiced i n both steam deactivation and Micro Activity (MAT) 2

0097-6156/89/0411-0120$06.00/0 © 1989 American Chemical Society

In Characterization and Catalyst Development; Bradley, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


12.

MOOREHEAD ET AL.

Evaluation of Fluid Cracking Catalysts

121

testing. Steaming severities range from 1350°F for 17 hours to 1600°F for 4 hours. Seme prefer slow heating of the catalyst while others practice "shock" treatment. Some treat a l l catalysts the same independent of application, while others steam deactivate to a constant conversion or other measurable physical property. For catalyst testing the same wide range of approaches exist. While an ASTM MAT test does exist, no laboratory was found to practice i t in total. MAT temperatures vary from 900 to 1000°F, with catalyst/oil ratios of 3 to 6 and WHSV's of 10 to 40. Some laboratories test a l l catalysts at constant conversion by either adjusting steaming severity or maintaining steaming severity while varying C/0 i n the MAT unit. To understand the benefits of various testing procedures a comparative study of testing approaches was conducted using three different Engelhard FCC catalysts. The catalysts selected represent a range from a f u l l octane catalyst containing USY to a gasoline catalyst containing REY. The objective was to identify a preferred testing procedure that gave catalyst properties and product selectivity results that agree with cxammercial performance. The conclusions from this comparative study as well as a discussion of the approaches of testing used i n the industry w i l l be discussed i n this paper. Experimental Three Engelhard FCC catalysts, identified as catalysts A, B, and C representing typical gasoline, partial octane and octane catalysts were prepared for comparing various test methods. Chemical and physical properties are presented i n Table 1. The laboratory steamings were performed at the conditions listed i n the appropriate tables using a shock steaming method. This method calls for the near instantaneous steaming of 100 grams of a catalyst by introducing the catalyst to a pre-heated steam environment. Catalyst addition i s conducted i n less than or equal to 15 minutes such that the temperature drop within the steaming reactor does not exceed 30°F. Catalysts are unloaded hot, giving near instantaneous cooling. Evaluations of steamed catalysts were performed with a MAT unit using a standard mid-continent gas o i l . The MAT conditions varied and are identified i n the tables. Selectivities were determined from gas chrexnatographic analysis of liquid and gaseous products by Hewlett-Packard, simulated d i s t i l l a t i o n hardware and Carle., Refinery Gas Analyzer Systems, respectively. Carbon on catalyst analyses were performed by IEC0. Surface area measurements were conducted using ASTM method D4365-85 for both fresh and steamed samples. A l l other physical and chemical analysis were performed by standard techniques. Results and Discussion Laboratory evaluation of the catalytic performance of fresh FCC catalysts involves steaming and activity testing. The latter i s most often performed using a microactivity test (MAT). While there are other parameters that are important i n comparing total performance of catalysts like attrition and fluidization, this paper



122

CHARACTERIZATION AND CATALYST DEVELOPMENT

focuses only on steaming and MAT testing. A recent paper by Rawlence et. a l . (1) provides a general overview for a l l the parameters involved i n the laboratory evaluation of FOC catalysts. While ASTM procedures for both steaming and MAT testing have been established (ASTM D-4463 and D-3907, respectively), a general survey of the petroleum industry indicates that neither of these methods are specifically practiced. Instead, each laboratory has developed individualized steaming and MAT testing procedures that best suit their needs. While many laboratories perform complete ctemical and physical analyses on fresh FOC catalysts, the vast majority do not perform such analyses on the steamed catalysts. The latter actually represent the catalysts evaluated while the former are i n essence a "precursor". While i t may be argued that fresh properties can be used as an indicator of steamed properties, a thorough evaluation of catalysts should include an examination of the steamed chemical and physical properties. Steaming Steam deactivation of fresh FCC catalysts i s required to reduce the activity to a level appropriate for MAT testing. The choice of steaming conditions determines the physical and chemical characteristics of the catalyst. Therefore, under constant M A T conditions, steaming conditions are responsible for the observed activity and selectivity. Laboratory steaming of fresh FCC catalysts i s generally done i n the presence of 100 percent steam i n a fluidized bed configuration. Catalysts are usually loaded at ambient temperature and i n the presence of fluidizing nitrogen, the temperature i s increased to the desired target. Steam, obtained by vaporization of injected water, i s then introduced and the nitrogen flow i s stopped. After a specified period of time, the water injection i s stopped and the nitrogen i s introduced again and the temperature i s set back to an ambient or low level. Having reached the desired temperature the catalyst i s unloaded and may be screened to remove fines. Alternatively, the catalyst can be introduced into a hot steam environment as opposed to the more gentle temperature ramp identified. The rapid addition of the catalyst to a hot reactor i s referred to as a shock steaming. A summary of steaming procedures that are generally employed i s presented i n Table 2. From this l i s t i t can be observed that a wide range of steaming severities are used. In general, the minimum temperature i s 1300°F, with a maximum of 1600°F. While steaming i s used to a r t i f i c i a l l y deactivate a fresh sample, such that i t represents a typical "equilibrium" sample, the approaches used to achieve this are varied. A number of laboratories use a fixed time and vary temperature to achieve a range of deactivated samples that when evaluated i n a MAT unit w i l l have a range of conversions so that they can make an assessment of catalyst stability and selectivity. An alternative approach for steaming uses a fixed temperature but the time i s varied to generate a hydrothermal stability curve. Temperatures i n the range of 1400-1500°F are generally used with times ranging from 5-60 hours. Preferred times however, tend to be 4-24 hours. The times employed can be tied to either a target


12.

123


MOOREHEAD ET AL.


Table 1 FRESH CATALYST PROPERTIES ENGELHARD DYNAMICS CATALYSTS Catalyst

A KEY

B REY/USY

C USY

Wt% REO Zeolite Index UCS, ft Surface Area: n^/g Zeolite Matrix Total

2.7 6 24.76

1.5 17 24.74

0.0 32 24.64

108 33 141

158 63 221

237 106 343

Table 2 SUMMARY OF STEAMING CBNDITIONS FKECAK^ATION ASTM ENGELHARD

STEAMING TEMPERATURE °F

STEAMING TIME. HRS.

None None 1100/1 hr 1100/1 hr

1292-1562 1300-1600* 1350-1454 1350-1550* 1360-1430 metals

5 4 17 4

1100/4 None 1200/3 None 1112/4 1112/3 1300/1 1000/1 None 1000/1 None

1375 1382-1490 1400 § 15 psig 1400 & 1500* 1400 & 1500 1418 1425* 1430-1525 1475* 1475 1500

4.75 17 5 & 10 5 5 15 4 5-80/20% s/a 5 6 &6 4

hrs hrs hrs hrs hr hr hr

*Shock Addition Method


124


conversion or some physical property. The deactivated samples are then evaluated i n a MAT unit under a standard set of conditions. A third approach involves one steaming severity i n conjunction with varying MAT conditions (usually cat/oil) to achieve equivalent conversions (2). While this method provides for equivalent steaming of a l l catalysts i t provides very l i t t l e information on the relative stability of the catalysts to be evaluated. A fourth approach involves a variation from variable temperature/constant time by blending different ratio s of deactivated samples to represent the irihomogeneity of aanmercially deactivated samples (3). This method i s not used to any extent at this time. For a l l of these alternatives the goal i s to produce a sample that has chemical and physical properties that are indicative of ccxnmercially deactivated catalyst (1). For example, i f the goal of steaming i s to target only the unit c e l l size, then i t might be concluded that one steaming severity i s needed. As suggested by McElhiney (2), this would be 1500°F for 5 hours. What this approach overlooks i s that i t does not account for expected changes i n MAT activity, zeolite content or total surface area. Figure 1 shows that an equilibrated Unit Cell Size (UCS) for a zero rare earth catalyst (catalyst C) can be obtained at relatively mild steaming conditions; but as presented i n Figure 2, the MAT activity and surface areas w i l l continue to change with steaming. As the differences between catalysts become greater, the need to be aware of these other parameters becomes more important. This i s particularly true when comparisons between gasoline and octane catalysts are to made. While this comparison may not be performed by a particular laboratory i t appears that the currently employed steaming procedures were developed for gasoline catalysts and their application to octane catalysts has to be investigated. By way of example, Figure 3 shows the effect of steaming severity on zeolitic surface area (ZSA) for catalyst A and C. Also identified are typical values for equilibrium catalysts. What i s seen i s that the conditions needed to deactivate A to typical equilibrium ZSA are different than for C. I f C i s deactivated using the preferred conditions for A, then activity and surface areas are not i n line with commercial experience. I f the reverse i s true, then A i s deactivated too severely. The need to have more than one steaming procedure for extremely different catalysts has been proposed by Magee et. a l . (8) i s consistent with ccxnmercial observations i n that a zero rare earth catalyst w i l l generally have a lower equilibrium MAT activity than a gasoline catalyst. The difficulty, of course, i s that i t i s not practical to have a unique steaming procedure for every catalyst. However, i t i s practical to target steaming severity such that the steamed properties for groups of catalysts are representative of what w i l l be observed cxxnmercially. An obvious question becomes does i t matter which steaming philosophy i s practiced? As w i l l be discussed later the ranking of catalysts can be effected by the manner i n which they are steamed. As such, i t i s important that whatever approach i s selected, the time or temperature be severe enough to reach a reasonable degree of deactivation as measured by UCS, surface area and MAT activity.


1



MOOREHEAD ET AL.

125


UCS (Angstroms)

4

12

8

STEAMING TIME (Hrs.: A (REY)

• 1450 F

C (USY)

9 1450 F

A (REY)

9 1500 F

C (USY)

9 1500 F

Figure 1. Unit C e l l Size E q u i l i b r a t i o n i s Dependent on Steaming Conditions.

Figure 2. Catalyst.

MAT Conversion and ZSA Continue t o Decline f o r USY



126


Figure 3. STEAMED CATALYST PROPERTIES Z e o l i t e Surface Area Reduction t o EQ Level i s C a t a l y s t Dependent.


12. MOOREHEADETAL.


121


MAT TESTING The micanoactivity test (MAT) was developed as a means of measuring the relative activities or conversion of FOC catalysts. As illustrated i n Figure 4, the MAT unit i t s e l f uses small amount of catalyst (less than 10 grams), and small amounts of o i l (less than 5 grams) i n a heated, fixed bed configuration. The rate of o i l injection or delivery time i s controlled by the use of a syringe pump. The catalyst/oil (C/0) ratio i s defined by the weic^it of catalyst/weight of o i l . The weight hourly space velocity (WHSV) i s defined as 3600/(C/0) * 0 i l injection time (seconds). For the ASTM MAT test procedure the conditions are 900^F, 3 C/0, 75 second injection time and 16 WHSV. Product o i l or syncrude i s collected i n a chilled receiver with light gas collected i n a glass receiver usually by the displacement of water. The syncrude and gas are analyzed chromatographically and the percent carbon on the spent catalyst i s determined instrumentally. Conversion (weight percent) i s defined as 100 minus (weight percent light cycle o i l plus heavy cycle oil) on a weight % of feed basis. A kinetic term called activity i s expressed as a simple second order rate expression defined as conversion/ (100conversion). Like the case for steaming, there are a variety of procedures used for MAT evaluations, none of which follow the current ASTM protocol i n a l l respects. A summary of procedures used within the industry i s presented i n Table 3. One unique observation for MOT testing i s that testing philosophies i n Europe tend to be different than the US. In Europe, MAT testing i s characterized by short injection times, less that 25 seconds, giving rise to higher space velocities, usually greater than 30 Hr-1. Like steaming, where we identified various approaches there are an equal number for MAT testing; constant temperature and cat/oil, constant temperature and vary cat/oil. The latter i s usually performed by varying the o i l weight as opposed to catalyst weight, and may involve either constant or variable space velocity depending upon what injection time i s used. I f the C/0 ratio i s varied but the the injection time i s fixed, then the space velocity i s changed. Alternatively, the injection time can be varied to maintain a constant space velocity. The former approach i s probably the most common. Using a severity relationship described by Wollaston, et. a l . (4) that relates severity to cat/oil and WHSV, the greatest change i n reactor severity i s obtained with this methodology. Comparison of Steamincr/MAT Procedures The objective of MAT testing i n many labs i s to compare both activity and selectivity differences between catalysts. Given that a variety of testing approaches are i n practice, what effects do these methods have on ranking of catalysts? To answer this question the three catalysts summarized i n Table 1 were evaluated using seven different steaming/MAT approaches. Table 4 summarizes the seven methods evaluated. The definitions for cut points i n this study are C5-421°F (gasoline), 421-602°F (LOO) and 602°F-plus (bottoms). Dry gas includes H2, H2S and C1-C2 hydrocarbons. LPG are the C3-C4



#

0 C COOLANT

Figure 4.

.CALIBRATION GAS INLET

PRESSURE I EQUILIB. TUBE

I GAS COLLECTION 1 RESERVOIR

Englehard's MAT Process Flow Scheme.

NITROGEN

ON LINE CHROMATOGRAPHIC GAS ANALYSIS

WATER RESERVOIR


00

12. MOOREHEADETAL.

129


Table 3 SUMMARY OF MAT PROCEDURES


MAT Temperature °F ASTM ENGELHARD

Cat/Oil Ratio

850 900 900 900 910 915 925 950 950 950 950 950 - 1022 975 985 986

Delivery Time. Sec. WHSV Hr-1

2 3.0 Vary 2.79 5 3.0 1.875 5-9 2.5 - 5.5 4.0 4.5 4.5 1.5 - 4.5 3.3 6.0

300 75 75 94 48 N/A 75 35 45 - 75 18 40 40 B>C) and that IPG and dry gas are inversely related (A

Characterization and Catalyst Development - American Chemical

Recommend Documents