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Chemistry and Technology of Fuels and Oils, Vol. 42, No.3, 2006

PYROLYSIS OF VACUUM RESID BY THE PLASMA CHEMICAL METHOD

G. G. Garifzyanova and G. G. Garifzyanov UDC 665.654.2

____________________________________________________________________________________________________Kazan’ State Technological University. Plazmokhim Ltd. Scientific Organization. Translated from Khimiya

i Tekhnologiya Topliv i Masel, No. 3, pp. 15 – 17, May – June, 2006.

Vacuum resid containing heavy metals in hazard class 1 (V2O

5 with MAC = 0.002 mg/m3, etc.) is used for

production of paving asphalts, which pollutes the natural environment. The heavy metals that accumulate in the

top layer of asphalt paving together with exhaust gases come off of the roadway, are deposited in pedestrian

zones, and negatively affect human health. For this reason, it is suggested that vacuum resid be used as an

additional source of feedstock for obtaining lower olefins and scarce heavy metals.

Since the amount of light straight-run naphtha cut used in production of ethylene is decreasing, it is

becoming necessary to create new schemes for refining heavy resids – vacuum gasoil (VG) and vacuum resid – for

manufacture of petrochemical feedstock. These kinds of feedstock are the worst for production of ethylene. For

example, 300 kg of ethylene are produced from 1 ton of light naphtha and 170-180 kg are produced form 1 ton of VG.

Heavy fuel cuts predominate in pyrolysis resins, and separating the valuable components from them is a costly

process.

Many foreign firms (Hoechst, BASF, Lurgi, Japan Gasoline, Uge Industries, etc.) have developed methods

of pyrolysis utilizing the thermocontact principle of heat transfer. These processes have a different degree of

finishing off in pilot units. Crude oil and its heavy cuts are used as the feedstock. Pyrolysis of crude in a stream

of steam superheated to 2000°C, developed by Union Carbide together with the Japanese firms Kureha and Chiyoda,

is conducted at 900-1200°C and a superheated steam to feedstock ratio of 3-4 for 0.001-0.005 sec. The maximum

yields of ethylene and acetylene are respectively 29-30 and 20-22 wt. %.

Thermocatalytic cracking and UHF thermodegradation technologies are new technologies for refining

heavy crude residues [1].

0009-3092/06/4203–0172 © 2006 Springer Science+Business Media, Inc.

173

Fig. 1. Diagram of the bench unit for pyrolysis of vacuum resid: T – thermometer or

thermocouple; p – manometer; other notation in text.

Toughening the conditions by passing to the high-temperature region (1000°C and higher) and reducing

the contact time to 10-5 sec is a promising direction in the evolution of pyrolysis of petroleum residues, including

vacuum resid.

A plasma chemical process was used for refining vacuum resid in [2]. Hydrogen and methane–hydrogen

mixture (MHM) were used as the p lasma-forming gas . The thermal ef f ic iency of the p lasma je t

was 3-5 kW/m3, which corresponds to a temperature of 3227-4727°C. Industrial carbon was used as the

catalyst: up to 7 wt. % in feedstock.

A diagram of the bench unit for pyrolysis of vacuum resid is shown in Fig. 1. A plasma-chemical unit

consisting of plasmotron 1, preliminary reactor 2, reactor 5, and quenching unit 6 is the basic equipment. A plasma

jet of hydrogen or hydrogen-containing gas with the mass-average temperature values indicated above is formed

in the plasmotron. This jet is a high-temperature heat carrier and reacting medium during pyrolysis.

Feedstock III and catalyst IV enter a tank with a stirrer and jacket. Steam V is fed into the jacket. The

unit runs on vacuum gasoil fed from tank 121 by proportioning pump 11

1. Before feeding in the gasoil, the

plasma-chemical unit is blown through with nitrogen along line II and then hydrogen I is fed in. After going into

the operating mode, vacuum resid is fed to the feedstock line by pump 112 from tank 12

2.

The feedstock, in the form of a suspension with the catalyst, enters two feedstock nozzles 4 in the plasma

unit through depulser 13 and electric heater 14. For spraying it, hydrogen from tanks 9a and line I (nitrogen during

start-up of the unit) heated in electric heaters 31,2

is fed to the nozzles. To prevent solidification of the highly

viscous feedstock, a feedstock circulation line is provided in the pipeline. Ball valves are installed in the nozzles

in this line and the feedstock feed line.

Natural gas is fed into preliminary reactor 2 from tank 9b; in reacting with the plasma jet, it

generates •CH3 radicals that accelerate the pyrolysis reaction. The methane is simultaneously a hydrogen donor,

used to increase the yield of unsaturated hydrocarbons from the vacuum resid.

p T

T

I

I

II

IIIIV

V VI

II

2

3231 4

8

7

5

6

9ŕ,á10111,2

121,2 1314

p

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Decomposi t ion of hydrocarbon, res in , and asphal tene molecules takes place in the reactor,

yielding C2-C

4 unsaturated hydrocarbons, methane, hydrogen sulfide, and industrial carbon, in which all of the

metals contained in the feedstock are concentrated.

The products of pyrolysis after reactor 5 enter quenching unit 6, where propane–butane fraction is fed

from tank 10 to the radial nozzle. The flow rate of the fraction is regulated by a rotameter. During start-up,

nitrogen is fed to the nozzle of the quenching unit and its flow rate is regulated by the rotameter. Cooling

water VI is fed into the jacket of the quenching heat exchanger. After the quenching unit, the pyrolysis gases are

emitted into the atmosphere through separators 7 and 8. A sampling instrument is installed in the emission line.

Industrial carbon, where the heavy metals are concentrated, is separated from the gas in separators.

The parts and units in the plasma unit are cooled with desalinized water circulating in the cooling circuit.

The physicochemical properties of the vacuum resid used for refining (>480°C cut) are reported below:

Density at 20°C, kg/m3 991

Carbon residue (Conradson), wt. % 11.4

Ash content, wt. % 0.09

n-Heptane insolubles content, wt. % 4.75

Softening point (R & B), °C 24

Elemental composition, wt. %

C 86.35

H 10.0

S 3.1

N 0.5

O (by difference) 0.05

Metal content, wt. %

vanadium 0.046

nickel 0.014

Group chemical composition, %

hydrocarbons

paraffins and naphthenes 14.7

aromatics

light 8.7

medium 6.5

heavy 41.3

resins 24.3

asphaltenes 4.5

The results of pyrolysis of vacuum resid using low-temperature hydrogen plasma are reported in Table 1.

The effect of the temperature t and duration τ of the process on the yield of ethylene, industrial

carbon, MHM, hydrogen sulfide, C3-C

4 cut, in the experimental conditions was investigated: t = 3000-4000°C,

τ = 10-1-10-5 sec.

The maximum yield of ethylene was attained at τ = 10-5 sec and t = 3000°C; the maximum yield of acetylene

was obtained at τ = 10-3.5 sec and t = 3500°C. With an increase in the duration of the reaction, the yields of

industrial carbon and MHM increased, the yield of C3-C

4 cut decreased, and the yield of hydrogen sulfide

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at τ > 10-3 sec did not change. Acetylene was formed from ethylene during the dehydrogenation process. All

hydrocarbons except for MHM and H2S were converted into industrial carbon at t = 4000°C for 1 sec.

REFERENCES

1. B. K. Nefedov, Katal. v Promyshl., No. 1, 48-56 (2001).

2. M. F. Zhukov, I. M. Zasypkin, A. N. Timoshevskii, et al., Electric Arc Generators of Thermal Plasma [in

Russian], Vol. 17, Nauka, Novosibirsk (1999), pp. 662-663.

Experiment Indexes

1 2 3

Plasmotron efficiency, kW⋅h 10 10 10

Consumption, kg/h

vacuum resid 5 4.7 4.4

MHM 0.5 0.44 0.43

natural gas 0.4 0.4 0.4

C3-C4 cut 0.3 0.3 0.3

Power consumed for decomposing vacuum resid, kwh/kg 2 2.13 2.27

Feedstock conversion, % 100 100 100

Yield, wt. % in feedstock

acetylene 23.9 24.2 24.9

ethylene 20.16 19.8 19.6

C3-C4 cut 7.14 6.8 6.7

C5 cut 0.07 0.1 0.07

hydrogen sulfide 3.33 3.33 3.33

MHM 21.6 21.57 21.4

industrial carbon 17.1 17.5 17.3

Concentration of catalyst, wt. % 6.7 6.7 6.7

Table 1