Metal Complexes in Fossil Fuels - American Chemical Society

Chapter

16

Degradation of Metalloporphyrins in Heavy Oils Before and During Processing Effects of Heat, A i r , H y d r o g e n , a n d H y d r o g e n Sulfide o n P e t r o p o r p h y r i n Species Lillian A. Rankel

Downloaded by IOWA STATE UNIV on October 18, 2014 | http://pubs.acs.org Publication Date: July 6, 1987 | doi: 10.1021/bk-1987-0344.ch016

Central Research Laboratory, Mobil Research and Development Corporation, P.O. Box 1025, Princeton, NJ 08540

Thermal and gaseous conditions during recovery, storage, d i s t i l l a t i o n , desalting and visbreaking can cause compositional changes i n heavy o i l s . This p r i o r history can effect downstream processing of the modified heavy oil. Therefore, model compound porphyrins and metalloporphyrins have been exposed to "preprocess conditions" of heat, a i r , hydrogen or hydrogen s u l f i d e . Types of changes undergone by these model compounds were determined. This was followed by treating Arabian Heavy crude and Arabian Heavy resid under similar conditions and extracting their petroporphyrins. The petroporphyrins have limited thermal s t a b i l i t y . Heating i n atmospheres containing air, hydrogen, or hydrogen s u l f i d e gases further accelerates petroporphyrin decomposition. Mechanisms for these decomposition processes are discussed. Downstream processing of compositionally modified o i l s i s considered. During recovery, storage, desalting, d i s t i l l a t i o n , and visbreaking, heavy o i l s are exposed to various thermal and gaseous conditions. These "preprocess" conditions consisting of heat, a i r , hydrogen and hydrogen s u l f i d e can cause changes i n heavy o i l components. For instance, metalloporphyrins and petroporphyrins undergo degradation to polypyrroles (e.g., b i l i n , t r i p y r r i n , and dipyrromethane derivatives) i n the presence of hydrogen s u l f i d e Q_) . This has been observed i n my laboratory with model metalloporphyrins under such mild conditions as 464°F and one atmosphere of hydrogen s u l f i d e . Using an Arabian Heavy vacuum r e s i d , i t was further shown that thermal treatment (850°F, 500 psig hydrogen + 20% hydrogen sulfide) reduced the petroporphyrin content of the asphaltene f r a c t i o n by more than 50%. A study of the r e a c t i v i t y of metalloporphyrins and petroporphyrins has now been extended to thermal exposure with a i r , hydrogen and heat. Atmospheric pressure a i r oxidation of model compound metalloporphyrins and porphyrins were studied. Also, the a i r oxidation of Arabian Heavy crude and v i s i b l e spectroscopy of the

0097-6156/87/0344-0257$06.00/0 © 1987 American Chemical Society

In Metal Complexes in Fossil Fuels; Filby, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

258

METAL COMPLEXES IN FOSSIL FUELS

methanesulfonic acid extracted petroporphyrins were examined. Some work with thermal treatment i n the presence of helium or hydrogen was done as well.


Experimental The model compounds used for t h i s study were H2(TPP) (where TPP = tetraphenylporphyrin), VO(TPP), Ni(TPP) and Ni(OEP) (where OEP = octaethylporphyrin). The a i r oxidations were carried out i n r e f l u x ing 1-methylnaphthalene (464°F) using 10 cc/min of a i r flow with 50 cc of a saturated model compound solution. Samples were withdrawn p e r i o d i c a l l y and v i s i b l e spectra measured. Arabian Heavy crude was a i r oxidized i n a tubular reactor packed with either Vycor or 10% V2O5 on alumina. Temperatures ranged from 392 to 464°F at 200 to 500 psig a i r . Arabian Heavy crude was also thermally treated at 750°F i n helium at 500 psig. Petroporphyrins from the Arabian Heavy crude were extracted with methanesulfonic acid (1-3) and v i s i b l e spectra measured. In t h i s way, the micrograms of petroporphyrin per gram of o i l were determined. Arabian Heavy 1075°F ' vacuum resid was thermally treated at 500 psig of hydrogen. Some of the thermally treated residua were pentane deasphalted (15 to 1 pentane-to-oil) and are referred to as C5- solu bles and C5-insolubles. Again, petroporphyrins were extracted with methanesulfonic acid. Calculations for micrograms petroporphyrin per gram of o i l were based on ε = 17 x 10 and an average M.W. of ~455 for the petroporphyrin. The yg porphyrin/g o i l were then calculated from the absorption of the cationic petroporphyrin at 545 nm. Chemical analyses of the crude and resid are shown i n Table I. +

3

Table I.

Analysis of Feeds

Arabian Heavy Crude % % % % %

c Η Ν 0 S

Ni, ppm V , ppm % C5-insolubles B.P.

Arabian Heavy Resid

83.3 11.8 0.16 75% of the Ni(TPP) was destroyed i n 2 hours. Another run had 0.1 g V2O5 i n VO(TPP) solution and a s l i g h t increase i n the oxidation rate occurred compared to uncatalyzed o x i dation. Using Figure 3, model compound s t a b i l i t y to i n i t i a l oxidation follows the order: Λ

/ O O N

Ni(TPP) > VO(TPP) > H (TPP) > Ni(OEP) 2

Previous work showed the same r e a c t i v i t y order for the tetraphenylporphyrin compounds when exposed to hydrogen s u l f i d e (JL). However, Ni(OEP) was as stable to attack by hydrogen s u l f i d e as Ni(TPP). The lack of oxidative s t a b i l i t y of Ni(OEP) may be due to the ease of o x i dation of the ethyl groups. Arabian Heavy Crude A i r Oxidation. The degree of a i r oxidation undergone by Arabian Heavy crude o i l depends upon pressure, tempera ture, l i q u i d hourly space v e l o c i t y (LHSV), and oxidation catalyst (Table I I ) . For instance, a i r oxidation at 500 p s i g , 392°F and 2 LHSV (Run 1) increases the oxygen content of the processed o i l to 1.55% oxygen (Table I I ) , while lower pressure (Run 3 at 200 psig) and higher temperature (464°F) give 1.28% oxygen i n the o i l . At the same temperature of 464°F, 2 LHSV (Run 2) incorporates 1.77% oxygen while 4 LHSV (Run 4) has 1.34% oxygen. V2O5 catalyst also improved oxida tion (see Runs 2 and 3). A i r versus He gas during thermal treatment gives marked differences i n oxygen content (compare Runs 3 and 5 ) .


260

METAL COMPLEXES IN FOSSIL FUELS

2.0

Ni(TPP) Feed

1.50 1.0 0.50 0.0 -0.50 -1.0 -1.50

b = 0.03 cm

-2.0 3(

350

Τ

1.0

550

400 450 500 Wavelength (nm)

0.80

1

1

600

1

Ni(TPP) 24 Hours


0.60 0.40 0.20 0.0 -0.20 -0.40 -0.60 -0.80 -1.0 I 300

_J

350

b = 0.005 cm ι t 1 1— 550 600 400 450 500 Wavelength (nm)

F i g u r e 1. A i r o x i d a t i o n o f N i ( T P P ) a t 464°F 1-methylnaphthalene.

•ur

»

300

350

ι

ι

400 450 500 Wavelength (nm)

•

>

550

F i g u r e 2. A i r o x i d a t i o n o f Ni(OEP) 1-methylnaphthalene.

i n refluxing

d 600

a t 464°F i n r e f l u x i n g


16.

RANKEL

Degradation of Metalloporphyrins in Heavy Oils

261

Table I I . A i r Oxidation or Thermal Treatment of Arabian Heavy Crude Run i n 5/8 i n tubular reactor (15 c c / v o l ) ; Reactor Packing: (1) V2O5= V2O5/alumina 10% V2O5 (12/20 mesh), (2) Vycor 12/20 mesh sized; Flow: 100 cc/min


Run Number Reaction temp., °F LHSV (hrs.-l) Reactor packing Gas used Pressure, psig Tig P/g o i l % Oxygen i n o i l

Feed

1

400 >0.1

392 2 Vycor Air 500 28.4 1.55

2 464 2 V 0 Air 200 21.3 1.77 2

5

3

4

5

464 2 Vycor Air 200

464 4

752 2 Vycor He 500 44.4 0.84

1.28

vo 2

5

Air 200 30.5 1.34

As the degree of crude oxidation increases, more petroporphyrins are degraded. A half hour exposure of Arabian Heavy crude o i l to a i r at 392°F, 500 psig a i r reduces the petroporphyrin content from 400 yg porphyrin/gram of o i l to 28.4 yg porphyrin/g o i l (Run 1). C a t a l y t i c oxidation reduces the petroporphyrin content even more (Run 2). Vanadyl porphyrins are known to promote asphalt oxidation, part i c u l a r l y as measured by increases i n ketone content (4). Oxygenation can also cause polymerization reactions and molecular weight increases. As more higher metals crudes and resids become refinery feeds, oxidation during handling could present more d i f f i c u l t i e s for refiners. Thermal Treatment of Arabian Heavy Crude and Resid. A 752°F thermal treatment of Arabian Heavy crude f o r a half hour reduces the petroporphyrin content by 90% (Table I I , Run 5). Additional heating at t h i s temperature would degrade more petroporphyrins. During a vacuum d i s t i l l a t i o n to produce r e s i d , the heavy f r a c t i o n of o i l i s exposed to temperatures around 800°F for about 15 minutes. This thermal exposure can degrade as much as 90% of the petroporphyrins. Arabian Heavy resid (Table III) contains 36.4 yg porphyrin/g o i l while i t s parent Arabian Heavy crude has 400 yg/g o i l (Table I I ) . Thus, the thermal h i s t o r y of crudes and resids can markedly change the amount of petroporphyrins present. In addition, thermal treatment can remove Ni and V and cause s i z e reduction i n the metal containing compounds (5) . Effects of Hydrogen and Hydrogen + Hydrogen Sulfide on Resid. Comparisons between thermal treatment with hydrogen and hydrogen + hydrogen s u l f i d e showed that hydrogen s u l f i d e accelerates petroporphyrin degradation (Table I I I ) . This enhanced degradation by hydrogen s u l f i d e i s more pronounced at low space v e l o c i t i e s and 750°F (Table I I I , LHSV=0.3). At 750°F thermal reactions are slower than at 850°F and the effects of hydrogen s u l f i d e can be seen. Hydrogen s u l f i d e at atmospheric pressure also causes decomposition of model compound porphyrins and metalloporphyrins under mild conditions (464°F, r e f l u x i n g 1-methylnaphthalene) (1).


262

METAL COMPLEXES IN FOSSIL FUELS Table I I I . Micrograms Petroporphyrin Per Gram Of O i l Assumed M.W.


Arabian Heavy 1075°F+ Resid C5~soluble C5~insoluble

yg Porphyrin/ g oil

455 432 520

36.4 13.8 73.0

LHSV

Processed O i l :

5.5

H2, 850°F C5-soluble C5-insoluble

455

29.0 00.0 35.6

5.5

H

455 520

27.0 00.0 35.6

1.0

H,

455

21.0

1.0

H

455

20.0

455

35.1

455

24.7

2

2

2

0.3

H,

0.3

H

2

2

+ H S (20%), 850°F C5~soluble C5-insoluble 2

850°F + H S, 2

850°F

750°F + H S, 2

750°F

Demetallation of metalloporphyrins occurs through sequential hydrogénation of the peripheral double bonds followed by f i n a l fragmentation of the ring and metal removal (1,6-8). Hydrogen s u l f i d e can also add to double bonds and therefore aid i n ring saturation (9) (Figure 4). Acid cracking of the ring and metal s u l f i d e formation can occur as well (1). Processing O i l s Exposed to A i r , H2S, H or Heat. Metal containing petroporphyrins degraded to polypyrroles by a i r , hydrogen s u l f i d e , hydrogen, or thermal exposure would probably be easier to hydrodemetallate with a catalyst (1,6-8). Depending upon the percentage of metal coordinated by the petroporphyrins, this could be s i g n i f i c a n t for hydrodemetallation processing. Estimates for petroporphyrin coordinated metal range from 10 to 60% (10). O i l molecules that have undergone a i r oxidation, hydrogen and/or hydrogen s u l f i d e addition, or thermal cracking may be easier to crack but oxygen or sulfur added to the resids by the above treatments w i l l cause processing problems. 2

Summary The model compound porphyrins Ni(TPP), VO(TPP), Ni(OEP), and H (TPP) are many times more stable to a i r oxidation, hydrogen s u l f i d e , hydrogen or heat than petroporphyrins. A i r oxidation at 464°F converts the model compounds into polypyrrolics within 24 hours while >90% of Arabian Heavy crude petroporphyrins degrade i n one half hour with a i r oxidation or are >95% degraded on V 05. At 464°F, model compound porphyrins are stable for many hours while Arabian Heavy r e s i d 2

2



16.

RANKEL

Degradation of Metalloporphyrins in Heavy Oib

Figure 3.

A i r oxidation of model compound porphyrins.

HX

HX a d d i t i o n loads to t h e r m a l c l e a v a g e of s a t u r a t e d b o n d s with polypyrrohc formation

Metal Removal

Figure 4.

Routes f o r porphyrin ring degradation by H2 or H2S.


263

264

METAL COMPLEXES

IN F O S S I L F U E L S

petroporphyrins are s i g n i f i c a n t l y decomposed i n one-half hour. When Arabian Heavy r e s i d i s exposed to a mixture of H and H S, acceler ated decomposition of the petroporphyrins i n the resid takes place. Thus petroporphyrins i n resids can be markedly decomposed by thermal treatment and exposure to reactive gases. A i r , hydrogen s u l f i d e , hydrogen or heat degraded petroporphyrins would probably be easier to c a t a l y t i c a l l y demetallate because the aromatic porphyrin ring has been disrupted. However, oxygen or s u l fur introduced into the o i l during processing might cause molecular weight increases and other problems i n r e f i n i n g these treated resids. 2

2


Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Rankel, L. A. Preprints, Div. P e t r o l . Chem., ACS 1981, 26, 689. Baker, E. W.; Yen T. F.; et al J . Amer. Chem. Soc. 1967, 89, 3631. Erdman, J . G. U.S. Patent 3 190 829, 1965. Branthaver, J . F.; Nazir, M.; et al L i q . Fuels Tech. 1984, 2, 67. Reynolds, J . G.; Biggs, W. R. Preprints, Div. P e t r o l . Chem., ACS 1985, 30, 679. Ware, R. Α.; Wei, J . J . Catalysis 1985, 93, 100. Ware, R. Α.; Wei, J . J . Catalysis 1985, 93, 122. Ware, R. Α.; Wei, J . J . Catalysis 1985, 93, 135. Khimmi, U. Russ. Chem. Rev. 1963, 32, 399. F i l b y , R. H. "The Role of Trace Metals i n Petroleum"; Yen, T. F., Ed.; Ann Arbor Science, Ann Arbor, MI, 1975; Chap. 2.

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October 16, 1986


Metal Complexes in Fossil Fuels - American Chemical Society

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