Petroleum Radiation Processing

211

3

Methods for

Petroleum Processing

Based on Radiation-

Thermal Cracking

3.1 RADIATION METHODS FOR HIGH-VISCOUS

OIL AND BITUMEN PROCESSING

Very shortly after the discovery of radiation-thermal cracking (RTC) of hydrocar-

bons, Topchiev et al. (1959) discussed the prospects of its commercial applications.

Most of the successful technological approaches to oil radiation processing (RP)

developed later were based on this phenomenon.

Comberg (1988) developed a method for the extraction of liquid hydrocarbon

products from fossil resources such as oil shales, tar sands, heavy oil, and coals.

The method comprised the mixing of a donor solvent and the exposure of the

mixture to gamma irradiation. The donor solvent supplied hydrogen for combi-

nation with molecules whose bonds were broken by the irradiation process. The

synergetic effect of hydrogen donors and ionizing irradiation was demonstrated in

the following examples.

Two 50 g samples of granulated oil shale were each mixed with 50 cm

3

n-heptane

designed to serve as a hydrogen donor solvent. One sample was subjected to 1 MGy

Co-60 irradiation. No protective cover was used; the sample was exposed to air.

Irradiation was carried out for 6 days at the temperature of 40°C and at atmospheric

pressure. The solvent was then drained into open beakers of known weight and

evaporated at 80°C. The yields were measured by reweighing the beakers.

The solvent-only run (without irradiation) yielded 0.1 g of a dull, thin, hard

plastic-like material coated rmly and nonuniformly distributed over the bottom and

the walls of the container. The shale irradiated in solvent yielded 0.75 g of a brown

liquid of moderate viscosity, which owed slowly, like honey, at room temperature.

The same shale samples were then each mixed with fresh 50 cm

3

supplies of solvent,

and the process including irradiation repeated.

The control sample produced no additional measurable yield while the irradi-

ated sample produced an additional 0.3 g of a lighter less viscous liquid. The total

yield from the irradiated sample was 1.05 g, 10 times the solvent-only (control)

production. The elemental analysis had demonstrated increase in the H/C ratio and

212 Petroleum Radiation Processing

considerable decrease in the nitrogen and sulfur contents as a result of shale RP

(Table 3.1). Together with the higher yield of relatively light fraction, the irradiated

samples were characterised by higher clarity and low ash content.

The next series of irradiation experiments was conducted with the medium

volatile bituminous coal (atomic H/C = 0.57). Four samples consisting of 9 g each of

coal were mixed with 9 mL of the donor solvent, tetrahydrofuran. One sample was

exposed to 1 MGy of Co-60 radiation at ambient temperature and pressure, a second

was exposed to 2 MGy, and the last two retained as control.

After irradiation, the donor solvent was removed by evaporation at about 125°C.

The remaining solid was then processed with pyridine; the control samples received

the same treatment without irradiation. The extracted material was freed of pyri-

dine at 130°C and then analyzed for carbon, hydrogen, and nitrogen. The results are

represented in Table 3.2.

The primary effect of the radiation was the increased yield of pyridine-soluble

hydrocarbons. A higher H/C ratio and reduced nitrogen content demonstrated

increased hydrogen transfer from the donor solvent. It was proposed to use the

method developed for kerogen extraction and shale oil upgrading.

The advantage of the method is an opportunity of feedstock processing at ambi-

ent temperature and pressure. However, low-rate radiolysis reactions involved in the

process result in very high irradiation doses, low yields of the target product, and

TABLE 3.1

Elemental Contents of Shale and Products

of Its Processing

Control Sample (Material Scrapped

from the Wall of the Beaker)

First

Irradiation

Second

Irradiation

H/C 1.72 1.99 1.99

N, % 0.31 0.08 0.033

S, % 6.1 1.78 0.39

Source: Comberg, H.J., Extraction and liquefaction of fossil fuels using

gamma irradiation and solvents, US Patent 4,772,379, 1988.

TABLE 3.2

Effect of Radiation Processing on Coal

Elemental Contents

Dose, MGy C H N H/C Yield, g

1 78.01 7.01 1.55 1.08 0.22

Control 84.88 6.92 2.88 0.98 0.07

2 76.6 7.45 1.25 1.17 0.45

Control 81.1 5.98 2.53 0.88 0.08