FCC Catalyst Evaluation

1.0 Introduction

 Catalyst management is a very important aspect of the FCC process.

Selection and management of the catalyst, as well as how the unit is

operated, are largely responsible for achieving the desired products.

Proper choice of a catalyst will go along way toward achieving a

successful cat cracker operation.

Catalyst change-out is a relatively simple process and allows a

refiner to select the catalyst that maximizes the profit margin.

Although catalyst change-out is physically simple, it requires a lot of

homework.

As many catalyst formulations are available, catalyst evaluation

should be an ongoing process; however, it is not an easy task to

evaluate the performance of an FCC catalyst in a commercial unit

because of continual changes in feedstocks and operating conditions

in addition to inaccuracies in measurements. Because of these

limitations, refiners sometimes switch catalysts without identifying

the objectives and limitations of their cat crackers. To ensure that a

proper catalyst is selected, each refiner should establish a

methodology that allows identification of ‘real’ objectives and

constraints and ensures that the choice of the catalyst is based on

well-thought-out technical and business merits.

In today’s market, there are over 120 different formulations of FCC

catalysts. Refiners should evaluate catalysts mianly to maximize

profit opportunity and to minimize risk. The right catalyst for one

refiner may not necessarily be right for another.

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2.0 Catalyst Selection Methodology

One of the most important parameters that specify the

competitiveness of a refinery FCC unit is the proper selection of

catalyst, since the catalyst type determines both quantity and quality

of the catalytic cracking products. Laboratory of Environmental Fuels

and Hydrocarbons evaluates FCC catalysts, through MAT tests,

specifying each catalyst activity and selectivity.

 For the above purpose a Short Contact Time Microactivity Test

unit (SCT-MAT) was constructed in CPERI, at the beginning of 1999, in

order to replace the conventional MAT unit, as an attempt to follow

the worldwide inclination of short residence times during the FCC

reaction. The unit's excellent performance along with the compatible

results derived by comparing it with the FCC pilot plant soon lead to

the construction of an identical unit (January, 2001).

Catalysts are evaluated following a standard FCC evaluation

protocol. Initially the catalysts are deactivated; either by metal

deposition or by steaming sieved and finally tested in one of CPERI's

MAT units. At least eight different tests are carried out for a specific

catalyst and for each test detailed experimental and normalised mass

balances are quoted. The individual product yields are plotted vs.

conversion and catalysts evaluation is completed by comparing their

product yields at a constant conversion level (65%wt).

The microactivity test (MAT) unit was originally designed to

determine the activity and selectivity of either equilibrium or

laboratory deactivated fluid catalytic cracking (FCC) catalysts.

Currently, the MAT unit is accepted as a tool to perform general

laboratory scale FCC research and testing because of its simple

operation and cost effectiveness. The unit only requires small

quantities of catalyst and gas oil for each MAT test, compared with

barrels of materials needed for a pilot-scale riser run.

2

A comprehensive catalyst selection methodology will have the

following elements:

1. Optimize unit operation with current catalyst and vendor. a. Conduct test run. b. Incorporate the test run results into an FCC kinetic model. c. Identify opportunities for operational improvements. d. Identify unit’s constraints. e. Optimize incumbent catalyst with vendor.

2. Issue technical inquiry to catalyst vendors. a. Provide Test run results. b. Provide E-cat sample. c. Provide Processing objectives. d. Provide Unit Limitations.

3. Obtain vendor responses. a. Obtain catalyst recommendation. b. Obtain alternate recommendation. c. Obtain comparative yield projections.

4. Obtain current product price projections. a. For present and future four quarters.

5. Perform economic evaluations for vendor yields. a. Select catalyst for MAT evaluations.

6. Conduct MAT of selected list. a. Perform physical and chemical analyses. b. Determine steam deactivation conditions. c. Deactivate incumbent fresh catalysts to match incumbent E-cat d. Use same deactivation steps for each candidate catalyst.

7. Perform economic analysis of alternatives. a. Estimate commercial yield from MAT evaluations.

8. Request commercial proposals. a. Consult at least two vendors. b. Obtain references. c. Check references.

9. Test the selected catalyst in a pilot plant. a. Calibrate the pilot plant steaming conditions using incumbent E-cat.

b. Deactivate the incumbent and other candidate catalysts.c. Collect at least two or three data points on each by

varying catalyst-to-oil ratio.

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10. Evaluate pilot plant results.a. Translate the pilot data.b. Use the kinetic model to heat-balance the data.c. Identify limitations and constraints.

11. Make the catalyst selection.a. Perform economic evaluation.b. Consider intangibles-research, quality control, price,

steady supply, manufacturing location.c. Make the recommendations.

12. Post selection.a. Monitoring transitions-% changeover.b. Post transition test run.c. Confirm computer model.

13. Issue the final report.a. Analyze benefits.b. Evaluate selection methodology.

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3.0 Reactors Used for FCC Studies

Catalytic cracking catalyst development requires the adequate

evaluation of catalyst performance. Different kinds of laboratory

reactors are available to evaluate catalyst performance. These

reactors include fixed bed, fluidized bed, stirred batch, differential,

recycle, and pulse reactors (Weekman, 1974: Sunderland, 1976).

The testing of catalyst at the laboratory scale can serve many

purposes. One possibility is the need of improving catalyst

formulation or altogether to develop a new catalyst (Mooreheed et

al., 1993). However, a common task for a bench scale unit is to

compare the relative performance of two or more catalysts

(Mooreheed et al., 1993).

Regarding the specific approach used for FCC catalysts, very

frequently catalyst evaluations are done on the basis of a

microactivity test (MAT). MAT studies are hindered by mismatching of

industrial operating conditions. Thus, MAT studies with long catalyst

time-on-stream, low hydrocarbon partial pressures, and cumulative

coke content do not represent industrial operation.

It is our view that to represent, in a laboratory scale unit, the

reaction environment of a commercial riser, the operation of this unit

has to be carefully controlled. The present dissertation considers in

this respect, a novel CREC Riser Simulator invented by de Lasa

(1992) at the University of Western Ontario.

3.1-Microactivity Test (MAT)

The Micro Activity Test (MAT) has been a main tool for basic

FCC research, and this includes catalyst selection and feedstock

evaluation (O’Connor and Hartkamp, 1988; Campagna et al., 1986).

This test was developed due to its simplicity, reproducibility, and

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quickness of evaluation in comparison to tests in a continuous pilot

plant.

The MAT technique is an ASTM procedure (ASTM D-3907-88)

which was developed on the basis of using a fixed bed of 4 grams of

catalyst, operated with a continuous oil vapour feed for 75 seconds at

a temperature range of 480-550oC and using an average catalyst/oil

ratio of about 3. The standard MAT has had limited success predicting

commercial unit performance and has provided limiting information

about product selectivity (Mauleon and Courcelle, 1985; O’Connor

and Hartkamp, 1988; Mooreheed et al, 1993). There are important

warnings in the technical literature about the value of the data

obtained in the MAT for catalyst selection. Some authors claim,

without fundamentally based arguments, that the MAT could provide

some kind of relative comparison on catalyst activity and coke make

selectivity (Humphries and Wilcox, 1990).

Although the MAT unit can provide some data for catalyst

screening, several important differences exist between MAT and the

commercial FCC unit (Mooreheed et al, 1993) as follows;

a-) The MAT reactor is based on a cylindrical (ASTM design) catalyst

fixed bed with a flow of feedstock flowing through a bed of catalyst. A

commercial riser uses instead an upflow of oil and catalyst circulating

together (Mooreheed et al, 1993).

b-) The MAT uses a cumulative catalyst time on stream of 75 second

while a commercial riser uses a short contact time of 3-5 second.

c-) The MAT employs a reactant partial pressure much lower than the

one of the commercial riser: 0.05 atm for MAT and 1.5 atm for the

commercial riser.

d-) Coke profiles develop in the 150 mm long catalyst bed of the MAT

and the catalyst deactivates at different rates. On the other hand, in

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the riser all catalyst particles experience the same feed exposure

having at the riser outlet uniform coke concentration.

e-) The operation of the MAT provides average results over a 75

second period. These results are by nature different than those taken

after 3-5 seconds contact time in the riser. For instance, this

difference explains the low olefinicity of the MAT products

(Mooreheed et al, 1993).

f-) The MAT cannot provide information about catalyst attrition since

it is a fixed bed unit.

As a result of the above described inadequacies, some

modifications have been suggested to the MAT to provide a more

reliable method for catalyst testing (O’Connor and Hartkamp, 1988;

McElhiney, 1988, Mott, 1987; Tasi et al., 1989). However, and despite

the proposed modifications the MAT still allows coke profiles and

temperature differences. Consequently, the kinetic modeling of

catalytic cracking reactions using the standard MAT test is rather

unreliable, and a number of strong approximations are needed

(Froissier and Bernard, 1989).

Corma et al., (1994) highlighted the limitations and the

inadequacies of MAT unit to compare different FCC catalysts made

from different materials. These authors pointed out that when two

different FCC catalysts, one made from ultrastable Y-zeolite and the

other was made of SAPO-37, which had a faujasite structure with

different framework composition, were used in the MAT, the tests

performed were not reliable. It was recommended, by these authors,

to use different tools with short contact times and based on mini-

fluidized beds.

3.2- Pilot plant unit.

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A successful scale up procedure is essential for further

advancement of any chemical technology. Usually, if the tested

catalyst passes the bench scale reactor test (like the MAT), the

following level of demonstration is the pilot plant unit. In this respect,

it is extremely important to bridge the differences between the lab-

scale and commercial FCC units. According to Carter and McElhiney

(1989), circulating riser pilot plants can provide the best small-scale

simulation of commercial FCC yields.

Several pilot plants are available for the FCC process, with the

favored ones being those with a riser reactor and continuous catalyst

regeneration (Yang and Weatherbee, 1989). Davison Circulating Riser

(DCR) unit is one of the most effective FCC pilot plants. It includes an

adiabatic riser reactor where the reactor temperature is maintained

by controlling the circulating rate of the hot regenerated catalyst.

This process is identical to the commercial unit. This unit can work in

the isothermal mode for certain kinetic studies. It is reported that this

unit can be used to process heavy oils and it can be also used for

catalyst studies. The DCR unit is 12 feet in height and it has a

catalyst and vapor residence time of about 6 and 3 sec respectively

(Yang and Weatherbee, 1989).

While, these pilot plant units provide, in principle, good

simulation for commercial FCC units, they are expensive, difficult and

costly to operate, and they are not suited to test large number of

catalyst samples. Furthermore, there is an intrinsic difficulty to

operate these pilot plants isothermally, showing some limitations in

catalyst/oil ratios and contact times (Corella et al., 1986).

3.3- CREC Riser Simulator

As stated, one of the most important challenges for FCC

catalyst development has been the one of simulating catalyst

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performance under commercial conditions and in this respect, a

laboratory scale unit is needed (Book and Zhao, 1997).

The Riser Simulator is a novel unit invented by de Lasa (1987)

to overcome the technical difficulties of MAT units. This unit can be

used for several purposes: a) to test industrial catalysts at

commercial conditions (Kraemer, 1990), b) to carry out kinetic and

modeling studies for certain reactions, c) to develop adsorption

studies (Pruski, 1996). d) to use the data of this unit for assessing the

enthalpy of cracking reactions.

The different characteristics and advantages of the CREC Riser

Simulator can be summarized as follows:

a-) Temperature, reaction time, cat/oil can be varied in a wide range,

b-) Different feedstocks (VGO, gas oil, and model compounds) can be

tested,

c-) Different chemical reactions such as alkylation, hydrogen transfer,

transalkylation, and coke formation can be investigated,

d-) Catalyst regeneration is simple and can be conducted at typical

regeneration conditions,

e-) For testing a catalyst, only a small catalyst sample (0.8 g) can be

used throughout many runs at different temperatures, contact times,

and cat/oil ratios,

f-) For testing a feedstock, only a small amount of feed (0.16 g) is

needed,

g-) The Riser Simulator can be operated in a broad range of total

pressures,

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h-) The Riser Simulator can be used in the fluidized bed mode with

active mixing of catalyst particles. In this respect, perfect mixing with

the absence of coke profiles and gas channeling can be obtained with

all catalyst particles being exposed to the same reaction

environment.

In conclusion, and in order to obtain reliable cracking results,

the appropriate tools have to be used in conducting reaction runs. For

example, it is well known that to measure catalyst activity and

selectivity of FCC catalysts a number of conditions have to be met: a)

a short contact time, b) fluidized bed conditions, c) appropriate

temperatures, d) adequate hydrocarbon partial pressure, e)

representative cat/oil ratio. The CREC Riser Simulator, experimental

tool employed in the present study, allows to study FCC catalyst

performance under relavant conditions used in commercial units and

this secure the value.

1. STEAMING

The evaluation of fresh catalysts normally includes a

deactivation step that precedes the actual activity test. This

deactivation typically involves the steaming of a catalyst sample at

temperatures ranging from 550 to 930 oC for 2 to 24 hr. The primary

objective is to deactivate a fresh catalyst such that its performance in

the activity test is representative of what is observed when testing a

commercially deactivated sample of the same catalyst. In this way,

prediction of commercial performance for new catalysts can be

made. In addition, the steaming was used in this study to vary the

unit cell size.

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Y-Zeolite

Matrix

SiO ·Al O 2 3 2

520-710 µm

Figure 3.1. Particles of FCC catalyst.

11

Laboratory steaming of fresh FCC catalysts is generally done in the

presence of 100 percent steam in fluidizing nitrogen while

temperature is increased to the desired target. Steam, obtained by

vaporization of injected water, was introduced and the nitrogen flow

was stopped. After a specified period of time (6 hr), the water

injection was stopped, the nitrogen was introduced again and the

temperature was set back to an ambient level. Then the catalyst was

unloaded and screened to remove fines, if necessary. The steaming

temperature was varied in order to change the unit cell size and

hence, a large range of unit cell sizes was obtained.

For all runs, the catalyst was steamed at constant temperature for

6 hr. For example, a part of fresh catalyst B was steamed at 810 oC

for 6 hr, while other parts of fresh catalyst B were steamed for 6 hr at

760 and 710 oC, respectively.

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4.0 CATALYST EVALUATION

The catalytic experiments were carried out in a microactivity test

(MAT) unit which is basically a fixed bed reactor, which has been

designed according to ASTM D-3907 method. The following section

describes the experimental setup, and the experimental procedures.

4.1 Experimental Apparatus

A schematic diagram of the MAT unit used in this study is shown in

Fig. 4.1. The main parts of the unit are:

• Syringe (used for feed addition)

• Syringe heater

• Syringe pump

• Furnace

• Glass reactor

• Liquid product collection system

• Gas product collection system

• Analytical balance and weights

• Chromatographic equipment

• Carbon analyzer

The syringe was 2.5 ml and used for VGO addition. The syringe

should be equipped with a multiport, high-pressure valve to allow

nitrogen and VGO entry to the reactor through a common feed line.

The syringe heater was used to heat the syringe to 40±5 oC

using a heat lamp. The syringe pump has to be able to deliver

uniform flow of 1±0.03 g of VGO in 30 sec.

13

Figure 4.1: Schematic for the MAT unit.

14

A three-zone furnace was used – middle zone of 150 mm length and

top and bottom zones of 75 mm length each. The temperature

controllers of the three zones were calibrated to achieve a constant

temperature 520±1 oC over the whole length of the catalyst bed

(actual bed temperature).

A glass reactor of 15.6 mm internal diameter was used.

Dimensions and details of the reactor are given in Figure 4.2. Quartz

wool is usually put beneath and above the catalyst bed. The liquid

product was collected in a glass receiver (Fig. 4.3).

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Figure 4.2 MAT reactor

16

Figure 4.3: Liquid receiver.

17

The balance was used to weigh the catalyst sample, liquid receiver

before and after the reaction, and the syringe before and after the

reaction. Analytical weights were of precision grade or calibrated

against a set of certified standard weights. An accurate balance was

very significant for mass balance.

Liquid product was analyzed by GC to determine the boiling range

distribution by simulated distillation. The gasoline boiling range was

from 0 to 221 oC, light cycle oil (LCO) from 221 to 343 oC, and heavy

cycle oil (HCO) from 343 to 650 oC. The GC was equipped with flame

ionization detector (FID). The column for simulated distillation is 1/8

x 20 inches stainless steel, 10% UC-W982 on 80/100 mesh

Chromosorb PAW. This column was attached to the FID with a 0.030

inch jet.

Gaseous product was analyzed by another GC to determine its

composition as hydrogen, and C1 to C5 hydrocarbon. A thermal

conductivity detector (TCD) was used. The analytical columns were:

Reference column: 20 inch, 2% OV-101 on 100/120 mesh, Chromosorb W-HP.

Analytical columns: 1A. 5 ft, 35% DC-200 on 80/100 mesh, Chromosorb P-AW

1B. 24 ft, 20% bis(2-methoxyethyl) adibate on 80/100 mesh, Chromosorb P-AW

2. 6 ft. Porapak Q, 80/100 mesh

3. 10 ft, molecular sieve 13X, 45/60 mesh

All columns were 1/8-inch OD stainless steel.

The carbon analyzer used was CS244 (LeCo Corp.). Oxygen was

supplied to the unit directly.

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Demands on the MAT lab involve more than the simple rating of

catalyst activities. At the very least, there is sufficient interest in

characterizing the coke and hydrogen producing properties of a

catalyst to require collection and analysis of the gas and to determine

the carbon on the discharged catalyst. Calculation of a weight

balance is another reason for obtaining samples for gas and coke

analyses. Most MAT laboratories are capable of obtaining mass

balance of around 95% in studies using VGO feedstocks. A major

interest for the MAT is in obtaining product selectivity data because it

is recognized that this inexpensive laboratory test can provide good

replication of plant yields if suitable chromatographic technology is

used with both the liquid and gaseous products .

MAT operating conditions are shown in Table 4.1. The commercial

vacuum gas oil (VGO) was obtained from Neghishi Refinery and its

properties are shown in Table 4.2.

Before testing the prepared catalysts the MAT unit was examined

by running a commercial catalyst. The same catalyst, conditions and

almost the same catalyst amount was tested twice to investigate the

reproducibility of the unit. The MAT data for both runs is shown in

Table 4.3. Hence, it can be said that the unit was ready to examine

the prepared catalysts.

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Table 4.1: Mat operating conditions

Temperature 520 oC

Feed rate 1 g/30 sec

Amount of catalyst 0.5–3.0 g

Feed type VGO

Table 4.2: MAT feed oil properties

Specific gravity (15/4 _C) 0.8821

Sulfur (wt %) 0.18

Conradson carbon (wt %) 0.09

Refractive index (15 _C) 1.4719

Bromine number 3.2

Ni (ppm) <1

V (ppm) <1

Distillation data (vol. %) ASTMD-1160 Temp. (_ o C)

10 376 oC50 437 oC90 518 oC

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Table 4.3: The yield reproducibility of MAT unit

Test 1 2

cat/oil ratio 2.78 2.82

Conv. (wt%) 68.3 67.5Component Yield (wt%)

H2 0.70 0.60

C1 0.26 0.28

C2 0.20 0.21

C2 0.36 0.39

C3 0.54 0.55

C3 4.86 4.82

iC4 4.00 3.87

nC4 0.60 0.59

t2C4 2.08 1.97

1C4 1.58 1.52

iC4 1.98 1.91

c2C4 1.58 1.50

Total C4 7.23 6.91

C5 + Gasoline 48.41 47.97

LCO 19.12 18.37

HCO 12.61 14.17

Coke 1.66 1.74

Total 99.93 99.93

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4.2 Procedure

In the MAT test, 3 g of catalyst was packed in the glass reactor

(Fig 4.2). The reactor was installed in a vertical tube furnace and

purged with nitrogen until it attained the required temperature (520

oC). Vacuum gas oil (VGO) was pumped using the syringe pump at a

controlled rate to deliver 1 g over 30 sec. The feed passed through a

pre-heater before it contacted the catalyst bed.

In the MAT setup, as shown in Fig. 4.1, the reactor outlet was

connected to the liquid product receiver immersed in an ice bath. The

outlet of the receiver was connected to a gas holder from which

water was displaced. Following the injection of the VGO, the MAT

reactor was swept with an inert gas (usually nitrogen) for a period of

time sufficient to sweep all vapors from the reactor and to transfer all

non-condensed material into the gas holder. This stage was called

stripping and it usually lasted around 25 min. At this point the

products of the reaction were collected in three locations: the coke

and a small amount of liquid residue are in the reactor; most of the

liquid are in the receiver; and the gaseous products are in the gas

holder. After the stripping stage, the liquid receiver was removed

from the ice bath and warmed to 25 oC in order to remove the liquid

product easily from the receiver. Nitrogen should flow to the gas

collector to remove the volatile materials that would otherwise be

lost during handling. Following the gas sweep, the liquid receiver was

disconnected, sealed and weighed. The volume of gas product and

flush nitrogen was equal to the volume of liquid displaced from the

gas holder. Then the furnace was switched off and the reactor

removed and cooled by air. Catalyst was removed from the cooled

reactor after the run. The quartz wool which was placed above the

22

catalyst bed was removed so that the spend catalyst could be

analyzed for carbon individually. Liquid holdup in the bottom of the

reactor was typically measured by using filter paper and weighing it

after wiping. Collecting this liquid was important for accurate mass

balance.

4.3 Product Analysis

A. Coke

Coke deposition on spent catalysts was determined by a common

combustion method. In this method, a carbon analyzer Cs 244 (LeCo

Corp.) was used. Oxygen was supplied to the unit directly. A small

amount of spent catalyst (0.25 g) was used for the desired analysis.

The sample was burned completely, which converted all carbon to

carbon dioxide. Carbon dioxide was removed by Kolt adsorption, so

that by re-measuring the volume of gaseous products, carbon

dioxide, and thus carbon, could be determined.

B. Liquid Product Yields

Simulated distillation by ASTM method D-2887 was used to

determine the boiling range distribution of the liquid receiver

contents. This method was used to give three different boiling ranges

as follows:

36–221 oC gasoline wt%

221–343 oC light cycle oil (LCO) wt%

343–650 oC heavy cycle oil (HCO) wt%

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C. Gaseous Products

A sample of gaseous product was analyzed by a GC to determine

its composition such as, nitrogen, hydrogen, and C1–C5

hydrocarbons. The amount of C5 found in the gas must be added to

the (gasoline range) in the liquid.

4.4 CHARACTERIZATION OF CATALYSTS

The catalyst properties, such as zeolite content, the unit cell size

of the zeolite, and the surface area determine the activity and

selectivity of the catalyst. Instrumental methods were used to

characterize the FCC catalyst particle both fresh and steamed.

Instrumental methods were used to characterize the changes that

occur in the catalyst during the FCC process. These changes were

related to desirable or undesirable changes in the selectivity and

activity of the catalyst.

In most advanced technology catalysts, the zeolite is designed to

hydrothermally dealuminate in a controlled and stable way to the

intended unit cell size and surface area. Catalyst characterization is

essential in order to define key features and to understand

variabilities in catalyst performance. For FCC catalysts, the important

characteristics are surface area, acidity, and unit cell size.

4.5 Catalyst Evaluation

The catalytic reaction experiments are carried out, in the

present study, using a novel Riser Simulator unit. The Riser Simulator

is basically a mini fluidized bed reactor operating in the batch mode

with intense gas recirculation. The following section describes the

24

experimental setup, and the experimental procedure adopted during

this study.

4.5.1 Experimental Apparatus

Experimental catalytic cracking runs were carried out in a Riser

Simulator reactor in operation at CREC-UWO laboratory. The reactor

was connected to a vacuum box through a four-port valve. The

cracked products were removed from the Riser Simulator at the end

of the pre set reaction period. A time/actuator assembly linked to the

feed injection system controlled the four-port valve. The vacuum

system was connected to a manually operated six-port sampling

valve. This sampling valve was connected on-line to the gas

chromatograph. Furthermore, the Riser Simulator reactor and the

vacuum box were equipped with pressure transducers to monitor the

pressure during and after the reaction periods. Both the reactor and

the vacuum system were supplied by separated heating systems and

both were well insulated.

The feed injecting system includes a gas tight syringe

connected to switches to control the timer/actuator assembly on the

four port valve and the data acquisition system. The data acquisition

system allowed monitoring the change of pressure with time from

both the reactor and the vacuum box. A schematic diagram of the

experimental setup is given in Fig. 4.4. All main parts of the set-up

will be discussed in detail in the following section

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4.5.1.1 Riser Simulator

The novel Riser Simulator is the center of the experimental

setup for catalytic cracking testing. This reactor was designed and

manufactured at CREC-UWO. The Riser Simulator was made out from

lnconel, which is a high temperature nickel alloy. The reactor consists

of four main components: the reactor shells, the catalyst basket, the

impeller, and the impeller drive-housing unit.

The reactor is composed of two shells, the top and bottom

sections. While the top shell is fixed on the steel reactor support

frame, the lower shell is removable. The lower shell is attached to the

upper shell section by means of a series of eight bolts and nuts. The

upper shell also includes the impeller, which is operated by an

electric belt-driven motor. A manual motor controller adjusts the

speed of the impeller. The top shell also contains three ports, two of

which are connected to the four ports valve. The third port is hooked

up to the reactor pressure transducer.

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RISER RISER SIMULATORSIMULATOR

TTPP11

INJECTION INJECTION PORTPORT

22

33

11

77

44 88

55

66

VACUUM BOXVACUUM BOX

MFCMFC

GC GC -- MSMS

PP22

VV11

VV55

VV22

VV44

VV33

4 PORT 4 PORT VALVEVALVE

6 PORT 6 PORT VALVEVALVE

VENTVENT VACUUMVACUUM HeHe NN22 (L)(L)

HH22Air Air

ArAr

RISER RISER SIMULATORSIMULATOR

TTPP11

INJECTION INJECTION PORTPORT

22

33

11

77

44 88

55

66

VACUUM BOXVACUUM BOX

MFCMFC

GC GC -- MSMS

PP22

VV11

VV55

VV22

VV44

VV33

4 PORT 4 PORT VALVEVALVE

6 PORT 6 PORT VALVEVALVE

VENTVENT VACUUMVACUUM HeHe NN22 (L)(L)

HH22Air Air

ArAr

Fig 4.4: Schematic diagram for the experimental setup.

27

The lower reactor shell includes both the injection port and the

catalyst basket. The catalyst basket is designed to fit inside the

annular space of the bottom shell. The catalyst basket contains top

and bottom porous inconel disks, and this prevents the catalyst from

being entrained out of the basket into the other sections of the

reactor. Furthermore, this design allows free gas motion through the

basket. The porous disks are kept in place in the catalyst basket by

two snap rings. The two shells are tightly secured using a flexitallic

gasket pressure seal manufactured out of an inconel graphite

composite material.

Each of the shells has its own sets of heaters. The bottom

section contains four cartridge heaters each heaters having a

resistance of around 29 . Because of the high temperature involved

in the system, the top section of the Riser Simulator, including the

impeller shaft and packing gland assembly, needs heat dissipation.

With this end a cooling system is implemented utilizing cold tap

water as the coolant.

Figure 4.5 shows a cross-sectional view of the Riser Simulator. A

comprehensive description of the construction and operation of this

novel unit are given by Kraemer (1987) and Pruski (1996).

4.5.1.2 Injector system

The injector system consists of a gas tight glass syringe, which

is fitted with a parallel threaded support rod and a threaded disc

placed between two nuts limiting the motion of the syringe plunger.

The disc is fixed at the support rod, allowing the syringe to intake, for

every injection, a fixed amount of feedstock from the reservoir

chamber.

The injector system contained two electrically actuated micro-

switches fixed at opposite ends of the sliding support rod. While one

28

of the switches controls the data acquisition system, the other

controls the timer/actuator assembly of the four-port valve.

Fig 4.5: A schematic diagram for the Riser Simulator.

29

In the sample position of the three-way valve, the syringe is

attached to the feedstock (gas oil and/or model compound) container.

The syringe fills the required feedstock amount when the plunger is

pulled all the way back. Meanwhile, the plunger presses against one

of the switches, preventing data acquisition pressure signals.

The feed syringe is connected to its needle. Thus, when the

plunger is pushed all the way forward, the feed sample is delivered to

the reactor. At this point, the micro-switch is released, hence

initiating the data acquisition program. Moreover, when the plunger is

fully pushed forward, presses against another switch connected to

the timer/actuator assembly of the 4-port valve. Consequently, the

timer starts to count down the pre-set reaction time, upon which the

timer would activate the actuator. The 4-port valve is then opened by

the actuator, equalizing the pressure between the reactor and the

vacuum box, thereby terminating the reaction.

4.5.1.3 4-Port and 6-port valves

The reactor is connected to the air/argon supply through a 1/8

inch 4-port valve. The other end of this valve is used to connect the

reactor with the vacuum box. In both positions, there are always two

paths available through the valve for the reaction products to move

along. In the open position, the reaction products are transfered

through the valve, into the reactor through an inlet port. Then, they

move out of the reactor through an outlet port, back into the valve

and finally they reach the vacuum box. In the closed position,

however, the reactor is completely isolated from the rest of the

system and connected to itself through two of the four ports of the

valve.

The sample injection valve (1/8” 6-port chromatographic valve)

is installed between the vacuum box and the GC. For both positions,

there are always two independent loops for the gases to pass

30

through. While one path connects the vacuum box to the

vent/vacuum pump, the other joints the helium carrier gas with the

GC detector. The position of the valve determines the path which

includes the sample loop.

4.5.1.4 Vacuum System

The vacuum system consists of a 485 cm3 stainless steel

cylinder fixed between the 4-port and the 6-port valves. These

components together with two on-off valves, two three- way valves,

and two position selector valves are placed inside a heated box. The

V1 valve (Fig 4.3) is connected between the air/argon gas supply

bottles and the first “on-off” valve. This valve connects the gas bottle

to the reactor and to the gas system. In addition, V1 connects to the

4-port valve through V2 (Fig 4.4). Finally, V2 allows the separation of

the entire system from the gas supply.

The stainless steel cylinder works as a sink for the reaction

products. It has a large volume. In addition, an important pressure

difference, with respect to the reactor, facilitates a quick and easy

removal of reaction products as well as unreacted hydrocarbons. This

rapid evacuation is needed to prevent further progress of cracking

reactions after the pre-set time.

The second isolation valve V3 is essential to control product

sampling (Fig 4.3). This valve is set in closed position during post

reaction evacuation period keeping the reaction products within a

volume of set dimensions.

The second three-way valve (V4) is connected between V3 and

the vacuum pump/vent line. This valve allows to incorporate or

remove the vacuum pump in the path of the exhaust gases going to

the fume hood. The main function of vacuum pump is to reduce the

pressure within the vacuum box to around 0.5 psia (almost vacuum)

prior to the reaction test. Between the second isolation valve (V3)

31

and the vent line/vacuum pump, there is a glass bottle. This glass

bottle provides a lower pressure than the one in the vacuum box and

an extra driving force for filling the sample loop of the 6-port valve.

4.5.1.5 Heating and Insulation

Heating tapes and insulation cover all of the connecting lines

between the vacuum box and the two chromatographic valves. There

are six heating tapes, each of them is connected to a Variac- type

power supply. This system helps to keep the lines at high

temperature, preventing hydrocarbon condensation in the lines and

valves. Furthermore, the reactor is insulated to maintain close to

isothermal operating conditions. Maximum temperature deviation

during experiments is only of a few degrees centigrade.

4.5.1.6 Control Devices

4.5.1.6.1 Temperature control

There are two independently powered controlled heater

systems. One controller keeps the reaction temperature constant at

around 525°C by means of four heating rods. These heaters are

inserted in the bottom shell of the Riser Simulator. However, the top

section of the Riser Simulator is directly heated using two smaller

insertion rod heaters directly powered by Variacs.

4.5.1.6.2 Pressure Transducers

32

The reactor and the vacuum box are provided by two identical

Omega pressure transducers, series PX-303. Figure 4.3 shows P1 and

P2 which represent the location of the reactor and the vacuum box

transducers respectively. Each transducer is powered by its own

power supply. Furthermore, these transducers have a calibrated span

of 0-50 psia with 0.25% accuracy, 1 ms response time and a 0.5-5.5

Volt output signal range. The transducers are also equipped with

protective pressure snubbers to take care of any sudden pressure

spikes or fluctuations.

4.5.1.6.3 Thermocouples

Several thermocouples are mounted around the Riser Simulator

reactor to accurately monitor the temperature. Two thermocouples

are connected to the reactor and the valve block. Other

thermocouples are fixed at the following places:

a)- Impeller shaft cooling jacket (20°C-40°C)

b)- Upper reactor shell section (425°C-475°C)

c)- Lines from the reactor to the 4-port valve (275°C-300°C)

d)- 4-port valve body (225°C-250°C)

e)- Vacuum box (350°C-390°C)

f)- Lines between 6-port valve and vacuum box (225°C-250°C)

g)- 6-port valve sampling loop (250°C-275°C)

h)- Line from 6-port valve to GC (275°C-300°C)

i)- Gas oil reservoir (50°C-75°C)

33

Note that the values in brackets indicate typical temperature

ranges using in the various Riser Simulator ranges.

34

4.6- Analytical Equipment

4.6.1 Gas Chromatograph System

The GC system, used in the present study, consists of a HP5890

gas chromatograph, a HP3392A integrator, gas supply bottles and

connecting lines, valves and associated wiring.

The GC contains a 25 m long capillary column, an FID-type

detector and a temperature controlled oven. While helium is used as

the sample carrier gas, air and hydrogen are used as the gases for

the FID detector. Furthermore, liquid nitrogen is used to facilitate the

initial cryogenic operation of the GC temperature program. The liquid

nitrogen cools the GC oven to –30°C. The flow of liquid nitrogen is

administered by a solenoid valve actuated from the GCs’ internal

oven temperature controller.

The HP3392A integrator allows strip chart recording as well

integration of the GC detector signal. The integrator is connected to

the GC via the HP-IL instrument network cabling system.

A Mettler balance is used to accurately weigh the catalyst

sample. A Hamilton gas tight syringe was calibrated for the different

feedstock used in the present study. Analytical weights are of

precision grade or calibrated against a set of certified standard

weights. Availability of this balance is of major importance for good

mass balance calculations.

4.5.2-Coke analyzer

Coke deposited on spent catalysts is determined, in the present

study, by a common combustion method. In this method, a carbon

analyzer Cs-244 (Leco Corp.) is used. Oxygen is supplied to the unit

directly. A small amount of the spent catalyst (0.25 g) is used for the

analysis. The coke laid out on the sample during reaction

experiments is burned completely converting the carbonaceous

35

deposit into carbon dioxide. The moles of carbon dioxide formed are

measured, and thus the coke formed is determined.

4.6- Procedure

Both CAT-LC and CAT-SC were used in the present study. The

reaction conditions adopted during the present study are close to

those used in an industrial FCC unit. Both catalysts were tested at

four different contacts times (3, 5, 7,and 10sec). In the case of

cumene, four different reaction temperature levels were used: 400,

450, 500, and 550oC. However, in the case of 1,3,5 TIPB six different

temperatures were considered 350, 400, 450, 500, 525 and 550oC. In

addition, for all experiments, one catalyst to oil ratio of C/O=5 was

employed (feed weight =0.16g and catalyst weight=0.81g). More

than three repeat runs were conducted at each experimental

condition.

Regarding the experimental procedure in the Riser Simulator,

every experimental run uses 0.81g of catalyst in the Riser Simulator

basket. The system is sealed and tested for any pressure leaks by

applying special liquids around the reactor and vacuum box and

monitoring any pressure changes in the system. The reactor is then

heated to the reaction temperature. The vacuum box is heated to

around 250oC and is evacuated at around 0.5 psi to prevent any

condensation of hydrocarbons inside the box. The heating of the

Riser Simulator is conducted under continuous flow of inert gases

(argon) and the process usually takes around 3 hours until reaching

thermal equilibrium. At this point the GC is started and its

temperature lowered to –30°C. This temperature is kept for 3 minute,

then increased at a rate of 15°C/min up to 240°C. The GC is left at

240°C for 1 minute, and then the temperature is increased at a rate

of 40°C/min up to 300°C. Then, the temperature is left at 300°C for

20 minutes to ensure that all the hydrocarbons present in the reacted

gases are eluted from the capillary column.

36

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39