Petroleum Radiation Processing

319

5

High Dose-Rate

Radiation Processing of

Petroleum Feedstock in a

Wide Temperature Range

Practically, all experiments described in earlier chapters, as well as the methods for

oil radiation processing based on these experiments, were conducted at the time-

averaged dose rate of ionizing irradiation, which usually did not exceed a value of

5 kGy/s. Such dose rates are much smaller than the highest dose rates (100 kGy/s

and higher) provided by modern electron accelerators serially produced by industry

for various technological applications. An important role of the dose rate of ionizing

radiation in radiation cracking of petroleum was shown in Chapter 1.

A few works were published on the effect of dose rate on radiolysis of light hydro-

carbons (Nevitt and Wilson 1961, Barker 1968, Burns and Reed 1968, Gabsatarova

and Kabakchi 1969, Massaut et al. 1991). Experiments on cyclohexane irradiation

at heightened dose rates using cyclohexene for hydrogen scavenging or deuterium

labeling gave no evidence for dose rate effects occurring in radiation spurs (Nevitt

and Wilson 1961). It corresponds to the conclusion of the work (Burns et al. 1966)

that a major part of radicals in liquid hydrocarbons recombines out of spurs. A

very pronounced dose rate effect in gamma radiolysis of C

6

–C

17

hydrocarbons was

observed in the work (Massaut et al. 1991). However, behavior of the chain reactions

of hydrocarbon cracking at the high dose rates was unstudied till recently.

One of the rst attempts of oil processing with pulse electron irradiation with

a very high dose rate in a single pulse was undertaken in the works (Gaisin et al.

2003, Remnev et al. 2005). A high-current pulse electron accelerator used in these

studies had the following characteristics: electron energy, 350–550 keV; beam cur-

rent, 6.5 kA; pulse length, 60 ns; energy in a pulse, 200 J.

Irradiation of crude oil and n-pentane was carried out in an open container in

a plasma–chemical reactor where volatile components were partially dissolved in

the feedstock processed. The absorbed dose was varied by changes in the number

of pulses applied to the same target. Oil samples were irradiated by ve shots with

a time interval of 5 s between two shots. As a result, a dose of 25 kGy was taken. To

take a dose of 100 kGy, a sample was irradiated with 20 shots, 5 shots in a series with

a 5 min break between two series.

The feedstock was originally kept at room temperature. The beam action was

accompanied by explosive gas evolution, oil heating by 5°C–10°C per pulse, and

increase in the weight of irradiated feedstock by 2.5% during ve successive pulses.

320 Petroleum Radiation Processing

Figure 5.1 shows that radiation processing in this mode leads to increase in the con-

centration of heavy fractions.

Similar effects were observed in the experiments on n-heptane irradiation in

similar conditions. Table 5.1 shows that the concentration of heavy hydrocarbons

in the liquid product of oil radiation processing was higher than that in the original

n-heptane. The maximal total yield of unsaturated compounds at the absorbed dose

of 45 kGy was 7.7 mass%.

The results obtained in the works (Gaisin et al. 2003, Remnev et al. 2005) can be

considered from the positions of the radiation cracking theory set out in Chapter 1.

Considerable gas evolution during irradiation of crude oil and n-heptane, the high

values of radiation-chemical yields of products, and the high yields of unsaturated prod-

ucts testify to radiation-initiated cracking reactions. In these experimental conditions,

the cracking rate can be estimated using Equation 1.61, which can be written in the form

WkRC

p

≈ *

(5.1)

where C* is the concentration of radical states responsible for the reaction chain

propagation k

p

≈ 10

12

s

−1

.

In the state of dynamic equilibrium, concentration of radicals recombining in the

rst-order reactions is determined by Equation 1.38

R

GP

k

t

=

2

and the lifetimes of such radicals can be found from

GP

R

R

=

τ

(5.2)

60

40

20

0

50 100 150

Original oil

Irradiated oil

200

T, °C

Evaporated fraction, %

25

03

00

FIGURE 5.1 Changes in oil fractional contents after pulse electron irradiation. (Plotted

using the data from Remnev, G.E. et al., A study of the processes of hydrocar-

bon feedstock decomposition under a pulse electron beam, Proceedings of the

2nd International Conference on Non-Traditional Methods for Oil Exploration,

Preparation and Rening, Almaty, Kazakhstan, 11pp, 2005.)