Distributions of Aromatics, Nitrogen, and Sulfur inCracked Liquid Products from Microactivity Tests

Siauw Ng,*,† Yevgenia Briker,† Yuxia Zhu,† Thomas Gentzis,† Zbigniew Ring,†Craig Fairbridge,† Fuchen Ding,‡ and Sok Yui§

National Centre for Upgrading Technology, 1 Oil Patch Drive, Suite A202, Devon, Alberta,Canada T9G 1A8, Beijing Institute of Petrochemical Technology, Daxing, Beijing, China, and

Syncrude Research Centre, 9421-17Avenue, Edmonton, Alberta, Canada T6N 1H4

Received January 10, 2000. Revised Manuscript Received March 6, 2000

The fluid catalytic cracking (FCC) unit produces gaso-line and diesel fuel from heavy gas oil. In FCC research,the most commonly used batch reactor system is themicroactivity test (MAT) unit described in an ASTM testmethod.1 The MAT test is simple and cost-effective. Itrequires only small quantities of catalyst (4-9 g) and gasoil (usually <2.5 mL) for evaluation. This is an advantageof using the MAT unit over the riser pilot plant, but isalso a drawback as the former produces very smallamounts of liquid product (usually <2 mL) for furtheranalyses. Despite the development of advanced analyticaltools that provide GC octane2,3 and molecular structure4

of hydrocarbons in the gasoline fraction, little informationexists on the characterization of light cycle oil (LCO) andheavy cycle oil (HCO) fractions derived from a MAT unit.This communication describes several techniques bywhich the hydrocarbon composition in each fraction, andthe distribution of nitrogen and sulfur by boiling pointcan be determined in cracked liquid products from theMAT unit and be compared with a pilot plant study.5

Two feeds, provided by Syncrude Canada Ltd., wereused in this study: (a) a solvent deasphalted oil (DAO,as-received) derived from Canadian oil-sands bitumen,and (b) a hydrotreated deasphalted oil (HTDAO) from (a),with the 343 °C- fraction removed by distillation. Bothfeeds contained about 37 wt % 524 °C+ fraction. Table 1gives a summary of feed properties. After hydrotreatingfollowed by distillation, HTDAO showed improved qualityover DAO in general. However, contents of nitrogen,microcarbon residue, and aromatics of HTDAO stillremained relatively high.

Catalytic cracking was performed using either a fixed-bed reactor (at 530 °C for DAO) or a fluid-bed reactor (at510 °C for HTDAO) in a MAT unit (Zeton Automat IV).Both reactors were loaded with 5 g of Engelhard Dimen-sion 60 equilibrium catalyst. Catalyst-to-oil ratio wasvaried to obtain different conversions (the portion of the

feed converted to 216 °C- products including gas andcoke). Catalyst contact time was kept constant at 30 s.Details of the experiments were reported elsewhere.6 Aspecially designed liquid receiver with extra large volume(300 mL) was used to collect over 99 wt % of liquidproducts that were free of contamination by solvents (e.g.,CS2). Liquid products (0.3-1.1 mL depending on thecatalyst-to-oil ratio), without prior separation, were char-acterized for simulated distillation (ASTM 2887) anddistributions of aromatics, nitrogen, and sulfur by boilingpoint by a gas chromatograph (GC) with a mass-selectivedetector (GC-MSD; Robinson method was used for cal-culation), and a GC with Antek nitrogen chemilumines-cence detector (GC-NCD) and Sievers sulfur chemilumi-nescence detector (GC-SCD). Nitrogen and sulfur standardsolutions, and a mixture of normal paraffins were usedto establish N and S calibration factors and the retentiontime-boiling point relationship for GC-NCD and GC-SCD.Statistics showed that for two solutions, each containing21.16 µg N/mL and 31.45 µg S/mL, the standard devia-tions were 0.240 µg N/mL and 0.777 µg S/mL correspond-ing to 1.13 and 2.47% relative standard deviation (RSD)for nitrogen and sulfur, respectively. Using simulateddistillation, the hydrocarbon types from GC-MSD weredetermined for gasoline (IBP-220 °C), LCO (220-343°C), and HCO (343 °C-FBP).

Table 2 shows the interpolated analytical data ofcracked liquid products at five conversions. Aromaticcontents of gasoline fractions from the two feeds increasedat higher conversion. This was due to the enriching effect(gradual depletion of saturates while aromatics are notcrackable in FCC) and the formation of aromatics result-ing from hydrogen transfer in secondary reactions.7 Upon

* Author to whom correspondence should be addressed at NationalCentre for Upgrading Technology. Phone: 780-987-8709. Fax: 780-987-5349. E-mail: sng@nrcan.gc.ca.

† National Centre for Upgrading Technology.‡ Beijing Institute of Petrochemical Technology.§ Syncrude Research Centre.(1) ASTM D 5154-91. Determining the Activity and Selectivity of Fluid

Catalytic Cracking (FCC) Catalysts by Microactivity Test.(2) Anderson, P. C.; Sharkey, J. M.; Walsh, R. P. J. Inst. Petr. 1972,

58, 83-94.(3) Yatsu, C. A.; Keyworth, D. A. Oil Gas J. 1990, Mar. 26, 64-73.(4) Buchanan, J. S.; Nicholas, M. E. J. Chrom. Sci. 1994, 32, 199-

203.(5) Yui, S.; Matsumoto, N.; Sasaki, Y. Oil Gas J. 1998, Jan. 19, 43-

51. (6) Ng, S. H. Energy Fuels 1995, 9, 216-224.

Table 1. Summary of Feedstock Propertiesa

feed DAO HTDAO

density @ 15.6 °C, g/mL 0.9776 0.9430343 °C- by simulated distillation, wt % 10.8 1.5524 °C+ by simulated distillation, wt % 38.1 36.9total nitrogen, wppm 3050 2450sulfur, wt % 3.54 0.70microcarbon residue, wt % 5.37 2.00aromatics by GC-MS, wt % 61.8 57.5conversion precursors,b wt % 62.9 72.0LCO precursors,c wt % 18.6 14.9

a From ref 5. b Conversion precursors (wt %) ) saturates +monoaromatics + polars. c LCO precursors ) diaromatics + 2 &3-ring aromatic sulfur.

945Energy & Fuels 2000, 14, 945-946

10.1021/ef000005h CCC: $19.00 © 2000 American Chemical SocietyPublished on Web 06/27/2000

cracking, DAO produced more aromatics in gasoline thanHTDAO. This observation was in line with feed qualitydata. For the same feed the heavier fraction generallycontained more aromatics with LCO containing the most.This was because the LCO precursors (mostly diaromat-ics) in the feed were relatively stable whereas the heavieraromatic compounds in the feed formed more coke athigher conversion. The small variation in aromatics ofHCO with increased conversion for HTDAO was mainlythe net result between coke formation and aromaticsenrichment.

Nitrogen concentration decreased with conversion inall fractions of both feeds with the exception of HCOwhich showed an increase in nitrogen concentration withhigher conversion (nitrogen concentration in HCO fromDAO exhibited a minimum). This result suggested that,unlike in the other fractions where nitrogen was removedto form ammonia, any nitrogen that remained in HCOat high conversion was associated with aromatic ringsand was enriched as conversion increased. Some remov-able nitrogen species might exist in DAO which was nothydrotreated. This could explain the decrease in nitrogenin HCO with conversion for DAO.

Sulfur concentration in the liquid product from HTDAOwas much lower than that from DAO as a result of sulfurremoval in the feed by hydrotreatment. Again, the

increase in sulfur in products from HTDAO and DAOwith conversion was indicative of the association of sulfurwith aromatic rings, which were enriched at higherconversion. For DAO feed, the observed initial decreasein sulfur concentration with conversion suggested thatthe sulfur species being removed were present as mer-captans and sulfides, which were less refractory and wereeasily removed at lower conversion.

Table 3 compares the analyses of liquid products fromthe MAT unit with those of a pilot plant study5 at twoconversion levels. Despite the differences in reactorsystems, operating principles, and analytical methodsused, results from the two systems at the same conversionlevel were quite comparable, at least they were in thesame order. For aromatics and sulfur, the agreement wasreasonably good, and only for nitrogen in LCO were thevalues from MAT lower. The comparison indicates thatthe MAT unit in combination with the use of appropriateanalytical techniques may provide useful information toreflect the qualities of pilot plant liquid products.

Supporting Information Available: A figure showing thevariation of liquid product yields with conversion and a tablecontaining additional liquid product analyses including densitiesand detailed hydrocarbon compositions of gasoline fractions bya PIONA analyzer, and analyses of the total liquid products(TLPs). This material is available free of charge via the Internetat http://pubs.acs.org.

EF000005H

(7) Scherzer, J. Octane-Enhancing Zeolite FCC Catalysts: Scientificand Technical Aspects, Chemical Industries, Volume 42; Marcel Dek-ker: New York, 1990; pp 94-95.

Table 2. Analyses of Liquid Products

conversion, wt %

analysis analyzer product feed 53.0 57.0 60.0 63.0 67.0

aromatics, wt % GC-MSD

gasoline DAO 58.2 59.7 61.3 63.4HTDAO 50.1 53.7 56.5 59.2 62.9

LCO DAO 84.9 85.7 87.0 89.6HTDAO 78.6 80.0 81.2 82.7 85.0

HCO DAO 83.1 84.4 85.7 87.4HTDAO 73.1 73.4 73.6 73.8 74.1

sulfur, wppm GC-SCD

gasoline DAO 5396 4074 4000 5841HTDAO 667 610 600 618 687

LCO DAO 30350 25340 25660 34380HTDAO 6733 6599 6762 7153 8028

HCO DAO 38580 31120 31840 45490HTDAO 9125 9404 9948 10780 12330

nitrogen, wppm GC-NCD

gasoline DAO 69 63 56 48HTDAO 25 31 35 40 45

LCO DAO 513 471 433 388HTDAO 487 436 397 359 308

HCO DAO 3572 3370 3363 3658HTDAO 3127 3292 3415 3539 3703

Table 3. Comparison of Analyses of Liquid Products

conversion, wt %

55.0 65.0

analysis product feed MAT pilot plant5 MAT pilot plant5

aromatics, wt % LCO DAO 84.7 88.1HTDAO 79.3 78.9a 83.8 89.2a

sulfur, wppm

gasoline DAO 6971 6600b 4643HTDAO 632 570b 646 410b

LCO DAO 36650 31000c 28838HTDAO 6615 6300c 7540 7600c

HCO DAO 48080 40600c 36850HTDAO 9201 9600c 11491 11400c

nitrogen, wppmLCO DAO 543 900d 410

HTDAO 461 1000d 333 1060d

HCO DAO 3815 2980d 3467HTDAO 3210 2990d 3621 3530d

a By supercritical fluid chromatography (SFC). b By Mitsubishi Kagaku tracer sulfur analyzer TS-02. c By LECO SC-432DR. d ByMitsubishi Kagaku total nitrogen analyzer TN-05.

946 Energy & Fuels, Vol. 14, No. 4, 2000 Communications