Oxidation of visbreaker bitumens

Short Communications

Oxidation

of visbreaker

C. Giavarini

and S. Saporito

bitumens

Dipartimento di lngeneria Chimica, Roma, Italy (Received 14 February 7989)

Vniversit.5

Degli

Studi

di Roma,

Via Eudossiana

78, 00184

A series of oxidation tests was carried out on a small-scale blowing unit fed with two different visbreaker (VB) bitumens, and with two straight-run (SR) soft bitumens for reference. The purpose was to study the possibility of applying the blowing process to VB feeds, and to evaluate process kinetics and product characteristics. The results showed that industrial blowing of VB bitumens is feasible and that the rate of reaction can be expressed by a first order equation with respect to change in softening point. Production of distittate oils was quite high, especially when iron trichloride was used as a catalyst; in industrial application it is suggested that VB bitumens may be oxidized without any catalyst, the kinetics of the non-catalytic process being satisfactory. Air consumption was unsteady compared with the SR operation, and plugging of the air coil was more frequent. (Keywords: bitumen; oxidation; catalysis)

Petroleum residues and bitumens are frequently blown with air to modify their physical and rheological properties, and thus adapt them to special of bitumens, applications 1.2 Oxidation while appearing to be relatively easy, is in fact a complicated sequence of reactions and interactions. The main reactions are dehydrogenation, condensation, and polymerization of unsaturated species, and the predominant trend is the formation of more complex materials of higher molecular weight’.‘. Reaction variables and catalysts are reported in the literature6”‘. Industrial oxidation (blowing) is normaIly carried out on straight run bitumens and residues with a catalyst, usually iron trichloride. At present, there is no information about industrial application of blowing on visbreaker bitumens. Visbreaking is a

type of mild thermal cracking process, which has been revived because it offers economic advantages to many refining schemes’ ‘.I3 The visbreaking capacity in Europe was almost doubled during the years 1980-1987, up to ~1500000 BPSD; in Italy it tripled in the same period, reaching about 15% of the topping capacity. Visbreaker (VB) residues (7545% of the feed) can be used to produce bitumens by a further vacuum distillation process14s’ ‘. In previous work16, using a differential scanning calorimeter, it was demonstrated that VB bitumens are more sensitive to oxidation than straight run bitumens. This behaviour seems to indicate that VB bitumens are good starting materials for the production of blown bitumens. The purpose of the present work was to study the possibility of applying the blowing

Table 1 Properties of bitumens used as a feed for the blowing _._______ _ ~~~

process on VB products, and to evaluate process kinetics and products characteristics. EXPERIMENTAL Design and equipment

The asphalt blowing apparatus (Figure]) was designed to blow about 6-7 kg of bitumen in a batch process. The reactor was of stainless steel construction, 27 cm in diameter and 36 cm in height. It was charged about half full of bitumen, with the remaining volume available for vapour. A circular perforated coil was installed in the bottom of the reactor and used as a gas disperser; bitumen mixing was ensured by a stirrer rotating at 30rpm. An outlet line in the bottom of the reactor was used for taking samples and for draining the reactor on

process ~__

Penetration (ASTM D5) (0.1 mm)

Softening point (ASTM D36) (“C)

FRAASS (IP 80) (“C)

Viscosity at 60°C (Pa s)

~..~ Asphaltenes (IP 143) Iwt%)

C,, (n.m.r.) (wt%)

Sample

Crude

SR-1

Ural Russian

80% 20%

> 300

22

< -20

6.1

6.1

27

SR-2

Kirkuk Russian

70% 30%

,300

30

< -20

11.0

7.0

28

VB-I

Kirkuk R. Budran

60% 40%

>300

32

< -20

11.2

11.5

33

VB-2

C. Sharan Vega

85% 15%

-20

21.4

14.8

35

_-

.

172

35.8

-~ ’ Extrapolated

001~2361/89/070943~4$3.00 (’ 1989 Butterworth & Co. (Publishers)

Ltd.

FUEL,

1989,

Vol 68, July

943

Short Communications Laboratory

stove

1

I

ml PI

F

Pl

Bitumen feed

PI FI

Air f

1

I

I

Electric/ heoter

I’

m_.____z_ _ )duats 1 wwenlc

”!I

- Blown bitumen r, --___

I

---___

______I--------___

_----

Figure 1 Experimental bitumen blowing apparatus

completion of the run. A thermocouple well and a safety valve were installed on the reactor top. To heat the bitumen, and to maintain approximately isothermal operation, the reactor was equipped with an external jacket containing circulating hot oil. The oil was heated by two 1000 Watt conical heaters, and maintained at 240°C by a voltage regulator. Spent vapours and gases left by the top of the reactor, through distillate traps and condensers chilled to - 20°C by a cryogenic system. Before entering the reactor and after leaaving the condensers, the inlet and outlet gases were metered by mass flow indicators. Oxygen content in the effluent gas was measured by an 0, analyser. The inlet gas was either air or nitrogen, taken from cylinders. The air was used as the reactant; nitrogen was provided for safety reasons and to control the reaction when the temperature of the system became too high. Using valves, it was possible to switch immediately from air operation to nitrogen operation, although this emergency procedure was not necessary during the present work. Operating procedure A weighed quantity of bitumen (about 6 kg), preheated to 135°C in a laboratory stove, was charged to the reactor. When needed, the exact amount (0.3 wt%) of iron trichloride catalyst was added. The stirrer was started and the charge was heated by the circulating hot oil. After

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FUEL, 1989,

Vol 68, July

Table 2

Typical results of blowing tests on straight run bitumens Blowing time (h)

Sample: SR-1” Penetration (0.1 mm) Softening point (“C) Penetration index FRAASS (“C) Viscosity at WC (Pa s) Asphaltenes (wt%) Sample: SR-2b Penetration (0.1 mm) Softening point (“C) Penetration index FRAASS t”C) Viscosity at 60°C (Pa s) Asphaltenes (wt%)

1

2

262

114 43.0 - 1.0

58 13.0

100 15.7

274 39 + 1.21

136 46.5 +0.75

.~

3

59 55.3 +0.46 - 17.5 1497 19.1

4

21 16.5 f1.85

_ 1895 23.5

59 58 + 1.05 - 14.0 397 18.0

43 71 11.6 13.4 _. ~ ..~_ “Temperature, 234236°C; Air flow rate, 200 NI h-’ kg-‘; 0.3% FeC1,.6H,O bTemperature, 239-241 “C; Air flow rate, 125 Nl h- 1kg- ’ ; 0.3% FeC1,.6H,O

the charge had reached z 23o”C, air was introduced into the reactor at a flow rate of 125 or 2OONl h- ’ per kilogram of bitumen. As the reaction proceeded, the bitumen temperature rose because of the exothermic heat of reaction; temperature control at 235-240°C was quite easy due lo the relatively small mass of the reacting bitumen. The experimental temperatures were similar to those adopted in most industrial operations, usually 235-250°C (average 240°C). The duration of each test was ~4 h; samples were withdrawn each hour or

half hour and characterized following ASTM or IP procedures. Viscosity at 60°C was measured by a rotational rheometer (Haake). Each test was repeated two or three times, depending on the agreement among the test data. Plugging of the air perforated coil occurred twice during VB bitumen operation. Materzals

Four different bitumens were used for blowing: two were straight-run (SR) reference bitumens, and two were

Short Communications v&breaker (VB) bitumens. The flocculation ratio16 of the VB residues from which the bitumens were obtained, was 6&62. The characteristics of the bitumens are listed in Table I. Following industrial practice, all tests on SR bitumens were carried out using 0.3 wt% FeC1,.6H,O (reagent grade) as a catalyst; however, some tests on VB bitumens were carried out without any catalyst. RESULTS

AND DISCUSSION

Tables2 and 3 report typical results of blowing tests involving straight run and visbreaker bitumens, respectively. Oxidation of the reference SR bitumens was carried out in the presence of catalyst, following industrial practice8,‘, while VB bitumens were oxidized both with and without catalyst. The experimental results show that the oxidation of VB soft bitumens is possible both in the presence and absence of a catalyst; in comparison with the noncatalytic reaction, the use of iron trichloride enables the reaction time to be reduced by nearly one-half, for the same order changes in penetration, softening point, viscosity, and asphaltene content of the bitumen. Air rate influenced the product quality, but not as much as expected (see e.g. oxidation of sample VB- 1 in Table 2). As far as reaction kinetics is concerned, reference can be made to a number of works reported in the literature’ ’ -“. The simplest kind of reaction that tits batch air blowing is an irreversible first order batch reaction. Lockwood” stated that the rate of reaction up to 260°C could be expressed by a first-order equation with respect to change in softening point. The integrated form of the equation was: In R/R,=kt where R and R, represent softening points at times t and 0, respectively. The overall reaction rate constant k depends on liquid diffusion, chemical reaction and gaseous diffusion. Corbett’ related the change in softening point to the mole % oxygen in air and to the space velocity of air. Patwardhan” studied the reaction kinetics with respect to changes in composition in bitumen components, and noted that although both bitumen composition and physical properties contributed significantly to the performance of bitumen, there was little correspondence between them, and hence the two kinetic studies had to be conducted independently. He confirmed that the change in softening point with time followed perfect first-order kinetics, and that the effect of temperature on the rate constant was governed by an Arrhenius dependency. As the present experiments were carried out at about the same temperature, it was not possible to calculate the rate constant-temperature correlation.

Table 3

Typical

results of blowing

tests on visbreaker

bitumens Blowing

1 Sample: VB-1” Penetration (0.1 mm) Softening point (“C) Penetration index FRAASS (“C) Viscosity at 60°C (Pa s) Asphaltenes (wt%) Sample: VB-1 b Penetration (0.1 mm) Softening point (“C) Penetration index FRAASS (“C) Viscosity at 60°C (Pa s) Asphaltenes (wt%) Sample: VB-I’ Penetration (0.1 mm) Softening point (“C) Penetration index FRAASS (“C) Viscosity at 60°C (Pa s) Asphaltenes (wt%) Sample: VB-2” Penetration (0.1 mm) Softening point (“C) Penetration index FRAAS (“C) Viscosity at 60°C (Pa s) Asphaltenes (wt%) a Temperature, ‘Temperature, LTemperature, “Temoerature. ’ Bloiing time

234-236’C; 2355237 C; 2355237’C; 234-236 C: 3.5 h

Air Air Air Air

flow flow flow flow

time (h)

2

4

191 31.5 -1.4

109 43.5 -1.0

68 15.0

187 16.9

204 40.0 +0.07

102 45.8 -0.48

46 15.5

146 11.2

92 47.3 -0.34

42 62 + 0.99

54 53.5 --0.18 - 13.0 1120 19.9

30 57 -0.7

60 53.5 + 0.09 - 14.5 679 19.9

46 63 + 1.4

3s 16.5 +2.9 - 10.5 2.5 x IO4 23.2

16’ 100.0e + 4.06’

22.3

21.4

17.4

4039 22.0

52 48.5 - 1.5

24 61.3 -0.31

IS 76.8 +1.25

4 106.5 +2.4

120 19.6

184 22.4

860 24.1

5562 25.5

rate, rate, rate, rate.

200 125 200 125

Figure 2 shows the correlation between In R/R, and the blowing time for the tests reported in Tables2 and 3. It is evident that first-order kinetics are followed not only by SR bitumens, but also by VB products. Oxidation kinetics of noncatalysed VB bitumens are satisfactory, although lower than those of catalysed bitumens. In the presence of a catalyst, the kinetics of the VB bitumens studied are similar or higher than those of the SR soft bitumens considered. Figure 3 reports the oxygen content of the efhuent gas versus blowing time, for three typical tests. Oxygen consumption was more gradual for SR bitumens, while in the case of VB samples, after an initial strong oxygen absorption, a rapid decrease in 0, consumption was observed, especially for the catalysed bitumens. The initial absorption was probably due to the higher reactivity of the VB bitumens that contain unsaturated oletinic compounds. However, the blowing process involves both linking of oxygen to the hydrocarbon molecules and the replacement of hydrogen (to form water). VB bitumens are highly aromatic (see C,, content in Table I), and therefore cannot be

Nl Nl Nl Nl

h - ’ kg- ’ ; no catalyst hh’ kg-‘; no catalyst h-r kg-‘; 0.3% FeCl,.6H,O h-r kg-‘; 0.3% FeCl,.6H,O

dehydrogenated as much as the less aromatic SR types. This helps explain why SR bitumens are oxidized more gradually than VB bitumens. Blowing of VB bitumens produced appreciable amounts of condensate oil, which collected in traps and condensers at the top of the reactor. The percentage of such oils was I. l--2.0% of the original bitumen for SR bitumens, 2.0-3.8% for non-catalysed VB bitumens, and 465.3% in the case of VB bitumens. The condensate oil collected during oxidation of VB bitumens was highly paraffinic and practically solid at room temperature; it seems likely that it was produced not only by distillation but also by cracking reactions. This is confirmed by the paraffinic nature of the condensate (since it is known that paraffmic side-chains are easily cracked) and by the increase in quantity in the presence of FeCl, catalyst. Being acidic in nature, iron trichloride increased the rate of cracking, and thus produced more distillate oils. It follows that cracking and successive distillation of the cracked products could be partly responsible for the higher penetrations and viscosities observed during oxidation of the catalysed VB bitumens.

FUEL, 1989, Vol 68, July

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Short Communications 2

3

1.0

G

h 5

0.5

I

2 Time (h)

3

Figure 2 Kinetics of bitumen air blowing on the basis of softening point (SR bitumens, dotted line); A, SR-1 (200 Nlh-‘kg-‘, catalysed); 0, SR-2 (125 Nlh-‘kg-‘, catalysed); 0, VB-1 (200 Nlh-‘kg-‘, no catalyst); 0, VB-2 (125 Nlh-‘kg-‘, no catalyst); w, VB-1 (200 Nlh~‘kg-I, catalysed); v, VB-2 (125 Nl h~‘kg-‘, catalysed)

I

I

I

2

I

3 Time (h)

I

4

Figure 3 Oxygen content of effluent gas (125 Nlh-’ of air per kg bitumen): n , SR-1, catalysed; A, VB-1, no catalyst; v, VB-2, catalyst

9 10 II 12 13

CONCLUSIONS Visbreaker bitumens can be blown in an industrial process giving oxidized products with satisfactory properties. Production of condensate oil is quite high, especially if an acidic catalyst (such as FeCI,) is used, so it is suggested that VB bitumens may be oxidized without using any catalyst. The kinetics of the non-catalytic process are satisfactory, though slower than those observed for catalytic oxidation of SR bitumens. The rate of reaction can be expressed by a first-order equation with respect to

946

FUEL, 1989, Vol 68, July

change in softening point. Air consumption is high at the beginning but drops later, and is less regular than during the operation on SR bitumens. Plugging of the air coils could be more frequent than for SR bitumen oxidation, due to the small carbon particles contained in visbreaker feeds.

68(7/g),

14 15

16 17

1

Abraham,

19

H. in ‘Asphalt

and Allied Substances’ Part 2, Van Nostrand, New York, USA, 1961, pp. 165-178

20

65

Giavarini, C. Fuel 1984, 63(11), 1515 Giavarini, C. ‘Characterization studies on visbreaker residues and bitumens’, Fuels SC. and Techn. Int., submitted for publication Giavarini, C. Fuel 1981, 60(5), 401 Lockwood, D. C. Petr. R&er 1959, 38(3),

18

REFERENCES

Barth, E. J. in ‘Bitumen Science and technology’, Gordon and Breach, New York, USA, 1962, pp. 386-423 Goppcl, J. M. and Knotnerus, J. ‘Fundamentals of bitumen blowing’ Proc. 4th World Petr. Congr., Roma. Italy, 1955, Sec. III/G, Paper 2, pp. 399413 Senolt, H. Bitumen, Teere, Asphalre, Peche 1969, 20(12), 563 Moschopedis, S. E. and Speight, J. Furl 1975, 54, 210 Shearon, W. H. and Hoiberg, A. J. Ind. Eny. Chem. 1953,45(10), 2122 Corbett, L. W. Id. Eny. Process Des. Der. 1975, 14(2), 181 Giavarini, C. ‘Activators for Asphalt Oxidation’ Proc. Int. Symposium on ‘Progressi nella tecnologia dei Bitumi’, Milano, Italy, 29 Sept-1 Ott 1981, pp. l-8 Giavarini, C. and Tombolini, A. Riv. Combusrihili 1982, 36(3), 81 Bahl, J. S. and Sigh, H. Reo. Insr. Franc. P&role 1983, 38(3), 413 Allan, D. E. and Martinez, C. H. Chem. Eng. Prog. 1983, 1, 85 Hus, M. Oil gas J. 1981, 15(79), 109 Giavarini, C. Chimica Industria. 1986,

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Patwardhan, S. R. and Khade, S. B. Ind. Eng. Chem. Process Des. Dell. 1981,21(l), 154 Phillips, C. R. and Hsieh, I.-C. Fuel 1985, 64(7), 985 Yoshiki, K. S. and Phillips, C. R. Fuel 1985,64(11), 1591