Oxidative demetallization of petroleum asphaltenes and residua

Oxidative demetallization of petroleum asphaltenes and residua

Oxidative demetallization asphaltenes and residua of petroleum Kenneth A. Gould Corporate Research Science Laboratories, Exxon Research and Engineer...

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Oxidative demetallization asphaltenes and residua

of petroleum

Kenneth A. Gould Corporate Research Science Laboratories, Exxon Research and Engineering Company, P.O. Box 45, Linden, New Jersey 07036, USA (Received 24 January 1980)

Cold Lake asphaltenes, Arabian Heavy asphaltenes, and Cold Lake vacuum residuum were treated with a variety of oxidizing agents. Of these, reagents such as air/lOO’C and NaOH/air were found to have no appreciable demetallization activity while oxidants such as sodium hypochlorite and peroxyacetic acid exhibited high demetallization activity coupled with the ability to remove or destroy petroporphyrins. The sodium hypochlorite, however, was found to suffer from the disadvantage of causing chlorine incorporation into the feed. This oxidative demetallization appears to be a rather unselective reaction with both metals and porphyrin removal being proportional to the amount of oxidant used. Various peroxy acids were found to be effective.

Heavy petroleum crude oils such as those found in the Athabasca or Cold Lake deposits of Canada or the tar belt region of Venezuela contain high levels of organically bound vanadium and nickel, much of which is concentrated in the asphaltene fraction. The chief problem posed by these trace metals is catalyst poisoning during upgrading of these oils. For example, hydrodesulphurization catalysts such as cobalt-molybdate on alumina will eventually experience severe deactivation as a result of high metals loading and coke laydown. Another important problem associated with high vanadium and nickel content is corrosion in boilers used to burn these fuels directly. Two possible approaches to solving these problems are (1) to develop new methods of catalyst regeneration capable of dealing with catalysts deactivated by heavy oils and (2) to remove the metal contaminants prior to upgrading. We have investigated oxidation as a means of demetallization prior to conversion. BACKGROUND Much research has been devoted to the problem of removing metallic contaminants from high-boiling petroleum fractions. For example, a number of mineral acids are known to have demetallization activity. In particular, work done at Exxon has shown that liquid hydrofluoric acid is an effective demetallization reagent’,’ which removes vanadium and nickel as an insoluble precipitate. Other reagents which have been employed for vanadium removal are Cl,, SO,Cl,, N,O,, t-butyl hydroperoxide, and benzoyl peroxide3. The use of the chlorine-containing reagents, however, results in chlorine incorporation and therefore degrades rather than improves the quality of the oil. The remaining reagents listed were found to be less effective for vanadium removal than were the chlorinecontaining compounds which typically reduced the vanadium content by about 50 wt ‘A. These reagents were effective only for removal of porphyrinic vanadium and

0016-2361/80/l 00733-04S2.00 @ 1980 IPC Business Press

were less metals.3

capable

of removing

the

non-porphyrinic

EXPERIMENTAL All metals analyses were performed either by atomic absorption or by inductively coupled plasma emission spectroscopy. Soret band measurements were performed on a Beckman C5 u.v.-visible spectrophotometer in dilute tetrahydrofuran solutions. Asphaltenes were obtained by straight-chain-heptane precipitation from either Cold Lake or Arabian Heavy vacuum residua using typical de-asphaltening procedures (i.e. one part of resid is refluxed for one hour with 10 parts of heptane. The mixture is then filtered and the insoluble asphaltenes washed several times with heptane and pentane.) Oxidation

qf Cold Luke asphaltenes

with air

8.0 g of Cold Lake asphaltenes and 400 ml of toluene were introduced into a 500 ml, 3-neck, roundbottom flask fitted with magnetic stirrer, condenser, thermometer, and gas dispersion tube. The solution was heated at 100°C for 4 h while air was slowly introduced below the surface. Additional toluene was added as necessary. The solvent was then removed by rotary evaporation and the residue dried in uacuo at 80°C to yield 8.23 g of product. Oxidation qf Cold Lake asphaltenes with sodium hydroxideluir 200 ml of aqueous 50% sodium hydroxide was added to a solution of 7.0 g Cold Lake asphaltenes in 250 ml toluene. The resulting mixture was stirred rapidly for 6 h in the presence of air and then allowed to stand overnight. After addition of 500 ml distilled water and removal of the aqueous phase, the organic layer was washed with distilled water (2 x 500 ml) and aqueous 10% hydrochloric acid (100 ml). The solution was dried over sodium sulphate, filtered, concentrated by rotary evaporation, and dried in uacuo at 80°C to yield 6.9 g of product.

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Oxidative Tab/e I

demetallization

Comparative

demetallization

of petroleum

effectiveness

asphaltenes

of various oxidants

and residua:

for

of asphaltenes and oils Demetallizetion

Feed

Oxidant

V

Cold Lake Asphaltenes Cold Lake Asphaltenes Cold Lake Asphaltenes Cold Lake Asphaltenes Arabian Heavy Asphaltenes Cold Lake Vacuum Residuum

Air/l 00°C NaOHlair NaOCla Peracetic acid Peracetic acid Peracetic acid

0 4 78 73 72 80

a High levels of chlorine

Oxidation of hypochlorite

Cold

incorporation

occurred

Lake

asphaltenes

(wt %I Ni

with

0 3 37 49 59 74

sodium

A solution of 80 g of commercial 5.25% sodium hypochlorite (Chlorox) was placed in a 250 ml roundbottom flask fitted with thermometer, condenser, and magnetic stirrer. The solution was then agitated rapidly while 6.0 g of < 100 US mesh Cold Lake asphaltenes was added. The mixture was heated at 60-70°C for 4 h, neutralized with dilute hydrochloric acid, and filtered. The solid was washed with distilled water (500 ml) and dried in uacuo at 80°C to yield 6.7 g of product. Oxidation acid

of asphaltenes

and residuum with peroxyacetic

Asphaltenes (8.0 g) or residuum and chloroform (100 ml) were added to a roundbottom flask equipped with thermometer, condenser, addition funnel, and magnetic stirrer, and 30.0 g of 407; peroxyacetic acid in acetic acid solution (FMC) was added dropwise at a rate sufficient to keep the reaction mixture below 45°C. After stirring overnight excess peroxyacid was destroyed by addition of passivated Raney nickel until gas evolution ceased. The mixture was then washed with distilled water (3 x 300 ml) and 5’:;1 sodium bicarbonate (100 ml portions until organic layer was neutral), dried over sodium sulphate, filtered, concentrated and rotary evaporation, and dried in vacua at 80°C to give 8.0 g of product. In all cases, a small aliquot of solution was taken for nickel determination before addition of Raney nickel. Oxidation acetic acid

of Cold Lake asphaltenes with trijluoroperoxy-

A solution containing 2.0 g of Cold Lake asphaltenes and 2.7 g of trifluoroacetic acid in 100 ml of chloroform was treated with 8.8 g of 30”/0 hydrogen peroxide, following the same procedure outlined previously. Trifluoroperoxyacetic acid was generated in situ by the reaction of the trifluoroacetic acid and hydrogen peroxide. RESULTS

AND DISCUSSION

A variety of reagents was initially examined to obtain information on the type of oxidant necessary to achieve reasonable levels of demetallization. These reagents were air at 100°C (air/lOO”C), sodium hydroxide/air (NaOH/air), sodium hypochlorite (NaOCl), and various peroxy acids, mainly peroxyacetic acid (CH,CO,H). The oxidants were used to demetallize Cold Lake residuum asphaltenes (950 ppm V, 370 ppm Ni), Arabian Heavy residuum asphaltenes (570 ppm V, 170 ppm Ni), and whole

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K. A. Gould

Cold Lake residuum (335 ppm V, 133 ppm Ni). The effectiveness of the reagents are compared in Table 1. It can be seen that air/lWC and NaOH/air had virtually no effect on the vanadium and nickel levels while peroxyacetic acid and sodium hypochlorite were quite effective at demetallization of asphaltenes and residuum. The sodium hypochlorite, however, suffers from the distinct disadvantage of causing chlorine incorporation into the feed; both reagents caused oxygen incorporation to occur in amounts as high as 8-10 wt% depending on reaction conditions. Examination of the infrared spectra of oxidized materials implies that this oxygen was incorporated primarily as hydroxyl and carbonyl (possibly acid) functional groups. The mass balance data shown in the Experimental section indicate that a maximum of about 8-10 wt% of the asphaltenes may have been oxidized to carbon dioxide and water, although the 9&92 wt% recovery may also have been influenced by simple mechanical losses. Since peroxy acids were the only reagents in Table 1 capable of demetallization without chlorine incorporation, the remainder of this investigation was directed at this class of compounds. Table 2 shows the effect of limiting the amount of peroxyacetic acid on the per cent demetallization. It can be seen that increasing the amount of peroxyacid from 0.38 g/g of asphaltene to 3.0 g/g of asphaltene results in increasing demetallization for both vanadium and nickel. (The high value of 48 wt% nickel removal at 0.75 g/g possibly may be due to analytical inaccuracies since this high a level of nickel removal was more characteristic of the higher peroxyacid level of 1.5 g/g asphaltenes in Tables 2 and 4). This result was obtained despite the fact that, theoretically, more than sufficient oxidant was present on a mol per mol basis to remove all of the metals, even at the 0.38 g/g of asphaltenes level. This suggests that the peroxyacid is acting in a non-selective manner and is therefore being partly consumed in side-reactions such as carbon skeleton oxidation. A blank run in which acetic acid was substituted for peroxyacetic acid showed no significant amount of demetallization. The influence of the amount of oxidant on the porphyrin content was also examined. Porphyrins are important in petroleum because a substantial percentage of the metals is complexed as metalloporphyrins. One might therefore expect that reagents capable of demetallization could also influence the amount of petroporphyrins remaining after demetallization. The relative porphyrin content of the demetallized asphaltenes in Table 2 was therefore examined by measuring the strength ofthe Soret band absorption occurring in the vicinity of the 400-410 nm range. The Soret band is a very intense absorption of pure porphyrins and is very useful as a diagnostic tool for the presence of porphyrins. It should be pointed out, however, that the measurement of the broad, diffuse Soret

Tab/e 2 Effect of peroxyacetic Cold Lake Asphaltenes Peracetic Acid, g/g Asphaltene

0.38 0.75 1.5 3.0

acid level on demetallization

of

Demetallization

(wt %)

V

Ni

23 41 75 80

14 48 49 66

Oxidative Tab/e 3 Soret band intensity Lake Asphaltenes

versus peracetic

acid level for Cold

Soret Oxidant,

g/g Asphaltene

Band Absorptivitya

(K)

None 0.38 0.75 1.5 3.0 a Absorptivity

demetallization

1.64 1 .Ol 0.49 0 0 = absorbance/unit

pathlength/unit

of petroleum

asphaltenes

and residua: K. A. Gould

for the meta-chloroperoxybenzoic acid were 48 wt4: vanadium and 44 wt% nickel while those for the trifluoroperoxyacetic acid were 44 wt% vanadium and 29 wto/, nickel. These results indicate that demetallization activity is a general property of peroxy acids as well as those other oxidants described by Sugihara et (11.~. CONCLUSIONS

concentration

bands characteristic of petroporphyrins at low levels is subject to some inaccuracies. The results of these measurements are given in Table 3, and they show that porphyrin content decreases with increasing oxidant level in a manner similar to that observed for the metals. It is obvious from this data, however, that the porphyrin content decreases much more rapidly with respect to oxidant level than do the vanadium and nickel contents. This trend is shown even more clearly in Figure 1 where per cent demetallization and Soret band absorptivity are plotted as a function of oxidant level. One possible interpretation is that the peroxyacetic acid acts rapidly to destroy metalloporphyrins and liberate their associated metals while the metals held by non-porphyrin ligands are somewhat more slowly attacked and removed. Figure 1 shows that porphyrins have been completely eliminated at the 1.5 g/g asphaltenes oxidant level while there are still substantial amounts of both vanadium and nickel present. This explanation is consistent with the findings of Sugihara, Branthaver, and Wilcox3 who reported that their reagents were incapable of removing nonporphyrinic metals. A more detailed investigation of the efficacy of peracetic acid for removal of non-porphyrinic metals was undertaken. Cold Lake asphaltenes were divided into low porphyrin content and high porphyrin content fractions by separation on a solid acid. That one fraction was depleted of porphyrins compared to the other fraction is evident from their Soret band absorptivities of 0.56 and 1.54, respectively. The metals contents for the two fractions were however, approximately equal being 818 ppm V and 335 ppm Ni for the high porphyrin fraction and 798 ppm V and 370 ppm Ni for the low porphyrin fraction. The data in Table 4, taken at an oxidant level of 1.5 g/g of asphaltenes show that peroxyacetic acid is capable of removing both porphyrinic and non-porphyrinic metals from the Cold Lake asphaltenes. This particular data does not, of course, address the questions of relative rates which may, as suggested above, be quite different for the two types of metal. Finally, two experiments were conducted to learn whether the demetallization activity of peroxyacetic acid was also a property of other peroxy acids. In these experiments, demetallization was performed with metachloroperoxybenzoic acid

Two alternative paths for demetallization can be hypothesized. (1) The metal atom is attacked directly by the oxidant causing an increase in the oxidation state (e.g. V +4+V+5); such an oxidation would change the required geometry of ligands about the metal, possibly leading to destabilization of the metalloporphyrin complex; and (2) attack by the oxidant directly on the porphyrin thereby destroying the ligand which binds the metal. We feel that these experimental results tend to favour the second mechanism since decreases in both metals and porphyrins were observed with increasing oxidant level. This conclusioh is consistent with the results of Deno et al4 who found that trifluoroperoxyacetic acid attacks and cleaves aromatic rings in model compounds and coals.

Tab/e 4 Comparison of peroxyacetic and low porphyrin content fractions

High porphyrin content Low prophyrin content

acid demetallization

for high

Demetallization

Soret Band Absorptivity

fwt %I

(K)

V

Ni

Feed

Products

54

50

1.54

0

62

52

0.56

0

2’o

loo-90

t l

lo-

‘-‘&WO,H and trifluoroperoxyacetic acid (CF,CO,H), the latter being generated in situ from the reaction of trifluoracetic acid and hydrogen peroxide. The demetallization levels

Grams Vanadium Figure 1 versus oxidant level

peracetic (0).

acid

gram

asphaltene

nickel (0) and porphyrin

FUEL,

1980,

(a) contents

Vol 59, October

735

Oxidative

demetallization

of petroleum

asphaltenes

and residua: K. A. Gould

REFERENCES I Kimberlin, C. N., Jr., Ellert, H. G., Adams, C. E. and Hammer, G. P.

ACKNOWLEDGMENTS

2

The author would like to express appreciation to R. Rif and R. B. Long for their assistance with the experimental work and the preparation of this manuscript and to P. Gaines, R. Botto, and J. Elliott for the metals and Soret band analyses.

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US Pat. 3 203 892, April 19, 1963 Adams, C. E., Hammer, G. P. and Kimbcrlin, C. N., Jr. US Par. 3 245 909, February 28, 1962 Sugihara, J. M., Branthaver, J. F. and Wilcox, K. W. Am. Chem. Sot. Diu. Petr. Chem. Prepr., 1973, 18, 645-647 (a) Deno, N. C., Greigger, B. A. and Stroud, S. G. Furl 1978,57,455. (b) Deno, N. C., Greigger, B. A., Messer, L. A., Meyer, M. D. and Stroud, S. G. Ter. Lat. 1977, 20, 1703

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