The radiation-thermal cracking of gas-oil

THE RADIATION-THERMAL CRACKING OF GAS-OIL* A. M. BRODSKII, K. P. LAVROVSKII, D. V. MAKAROV, A. N. MEZENTSEV and YU. L. FISH Institute of Petroleum Chemical Synthesis of the U.S.S.R. Academy of Sciences (Received 5 June 1962)

THE chemical changes taking place in petroleum gas-oil fractions (subsequently called gas-oil) under the action of the radiation of a nuclear reactor in the temperature range of radiation-thermal cracking (RTC) have been investigated [1, 2]. The experiments were carried out in a circulating apparatus b y the general method of Brodskii et al. [1, 3]. The resulting gaseous and liquid fractions were investigated in detail. The radiation-chemical yields of ]ight products and polymers were established and the changes in the chemical composition of the liquid products were studied. The physico-chemical characteristics of the products of radiation-thermal synthesis--"radiation-chemical polynlers"--are given. I::XPI::RIMI::NTAL AND ANALYTICAL PROCEDURE

The investigation of the decomposition of gas-oil under the combined treatment of radiation and heat was carried out under dynamic conditions in a circulating apparatus the reactor of which, with a working volume of 600 cm 3, was placed in the experimental channel of a reactor of the water-water type. The total charge of the apparatus amounted to 18-20 1. All the experiments were carried out at a temperature in the active zone of 300 °. The rate of circulation was 150-160 1./h, and the pressure in the system 3-3.5 atm. The fundamental pla,,l of the circulating apparatus has been given by Brodskii et (d. [3]. Sampling of the liqnid and gaseous products was carried ont through special sampling devices. The amotmt of gas formed otl radiolysis was measured by mea~s of a dry gas meter. The gases were a~mlysed by gas-liquid clmmmtegraphy [4]. The amount of radiation-chemic'd polymers produced was determined by vacuum distillation ~t 10-:L10 -G mm Hg b y the method used b y Brodskii et al. [3]. The deter~ination of the chemical composition of the liquid fractious before and a.fter irra.diatiou was carried out b y a standard procedure. * Neftekhimiya 2, No. 3, 332-338, 1962. 219

220

A.M. BRODSKII et al. STARTING MATERIAL

T h e s t a r t i n g m a t e r i a l was a specially t r e a t e d gas-oil f r o m sulphur-free p e t r o l e u m . T o p u r i f y it f r o m traces o f s u l p h u r it was s u b j e c t e d to h y d r o s t a b i l i z a t i o n a t a pressure of h y d r o g e n of 60 a t m a n d a space v e l o c i t y o f 0.5 h -1 o v e r a c o b a l t - a l u m i n i u m - m o l y b d e n u m c a t a l y s t . T h e presence of s u l p h u r in these e x p e r i m e n t s is undesirable in view o f t h e f o r m a t i o n f r o m it o f r a d i o a c t i v e p h o s p h o r u s t h r o u g h a (n, P ) reaction.* T h e m a i n physicochemical characteristics of this fraction are g i v e n below. EXPERIMENTAL RESULTS

In the RTC process investigated, in addition to the reactions of degradation and synthesis (the formation of gas and light fractions and the accumulation of radiation-chemical polymers) taking place in parallel, there is also a change in the chemical composition of the fractions boiling within the temperature range of the initial raw material. Physico-chemical characteristics of the initial gas-oil

(d~° 0"8485, n ~ 1.4733) Fractional composition (GOST 2177-48) Initial boiling point, °C

215

Temperature corresponding to 10~o distilled 227 . . . . . . 20% 233

.

.

.

.

.

.

.

.

.

.

.

50%

258

.

.

.

.

.

.

60% 70%

268 280

.

. .

.

.

.

.

.

.

.

30%

241

40%

250

.

.

.

.

.

.

.

.

.

80%

295

. .

. .

. .

. .

. .

. .

90% 97%

313 339

Group chemical composition of hydrocarbons, % by weight Unsaturated hydrocarbons absent Aromatic ,, 28.31 Paraffinic ,, 45.54 Naphthenic ,, 26.15 Sulphur content, % by weight (from the results 10-4 of activation analysis)

A. Gas formation. The composition of the issuing gases from the RTC of the gas oil is given in Table 1. The Table shows a decrease in the concen* After hydropurification the activation of the gas-oil with respect to radiophosphorus at a dose of 100 Mrad amounted to ~ 10-e mc/1.; without previous purification, this figure was ,~ 10-4 mc/1.

221

R a d i a t i o n - t h e r m a l c r a c k i n g o f gas-oil TABLE 1. COMPOSITION OF TtIE GAS AS A FUNCTION OF THE RADIATION DOSE

Hydrogen Methane Ethane Ethylene Acetylene Propane Propylene Isobutane n-Butane I s o b u t y l e n e Jr b u t - 1-ene But-2-ene B u t - 2 - e n e ~- d i v i n y l I s o p e n t a n e + m e t h y l b u t - 1-ene n-Pentane n - P e n t - 1-ene

Yield, G, molecules/100eV

Dose, M r a d

C o m p o n e n t s o f t h e gas, ~o b y vol. 200

400

800

Initial

Final

78.38 5.95 4.60 3.38 0.06 3.29 2.08 0.26 0.65 0.54 0.07 0.15 0.44 0.14

71.68 6.79 6"73 3-44 0.05 3.73 3.28 0.41 1.05 1-08 0.24 0.21 0.55 0.59 0.17

68.25 7.94 7.45 2.74 0.03 4.59 3.99 0.70 1.70 1.10 0-19 0.19 0.60 0-42 0.11

3.140 0-240 0.184 0.146 0.002 0.132 0.083 0.010 0.026 0.021 0.003 0.006 0.017 0.005

0-273 0.03 0.03 0.011 0.001 0.018 0.016 0.003 0-007 0.004 0.001 0.001 0.002 0.002 0.001

4-015

0.400

[

Total value of G

tration of hydrogen and an increase in the content of heavier hydrocarbon gases as the irradiation dose is increased. The same thing is shown by the radiation chemical yields given Gg~s for each component at the beginning and the end of the radiolysis process. The decrease in the hydrogen content can be explained not so much by inhibition as by the predominant decomposition in the initial stage of the paraffinic components of the starting material. Figure 1 shows that at a radiation dose of up to 100 Mrad, there is a linear relationship between the yield of gas and the dose and that at a further increase in the total dose the curve begins to approach a linfiting figure asymptotically.

20 10 -

,f7 ,=/

I 2

.~'

/,

3

I

I

/dO ZOd 300 clod 500 5dO Mpod

,;0 :og J)o ,oo s)o ffO0 Y- Mpad

FIG. 1 F[G. 2 FIG. 1. Y i e l d o f g a s e o u s p r o d u c t s as a f u n c t i o n o f t h e t o t a l dose. FIG. 2. Y i e l d Ggas as a f u n c t i o n o f t h e e n e r g y a b s o r b e d .

A. M. BRODSKII et al.

222

Figure 2 shows the total yield Ggas in molecules/100 eV of energy absorbed, calculated from the data of Fig. 1, as a function of the total dose in Mrad. As can be seen from Fig. 2, the final value of Gg~ is ~0.4. At this point, a large part of the gas consists of hydrogen. The value of Ggas after deducting the hydrogen is 0.12. B. Change in the chemical composition of the gas-oil during radiolysis. Considerable attention was devoted to a study of the chemical changes taking place directly in the liquid fractions under the action of the radiation of a nuclear reactor. TABLE

2. GROUP

CHEMICAL

AND AFTER

COMPOSITION IRRADIATION

FOR THE FRACTIONS WITH

: Yield, °/o i u n s a t u -

by wt. .

.

.

.

.

.

=

--

]~RAD

H y d r o c a r b o n s , % b y weight naph-

I rated .

OF THE GAS-OIL INITIALLY

A TOTAL DOSE OF 600

aromatie

paraffinie

thenie

60.0 42.7 50-4 I 47.7 49.1 41.8 45.3 39.6 41-4 i 34.7 39.4 I 39.9

17-2 22.0 25.8 [ 24.1 27.5 I 29.0 2 5 . 0 28.3 26.6 I 31.9 2 7 . 8 25.1

,,

Fraction, °C

Init, ial b . p . - - 2 0 0 ° 200-225 225-250 250-275 275-300 300-325

325-350 > 350 Gas-oil

6.5 11.9 22.9 22.2 13.2 12.2

7.2

10.1 -- 13.0 11.47 -4.5 17-12;-4.4 20.74 -4.3 13.79 5.1 11.22 - - i 5.3

9.84

3.9 5.73[--' -100% 1 0 0 ° o -

22.8 23.8 23-4 29.7 31.9 32.8

22.3 23.7 24.8 27.8 28-3 29.7

i 6.2 5.73

i

[

32.5 ; 48.2 39'5 I 20.8 28.0 t 24.8 i i 28.31 29.72 45.54 37"661 26.15] 26.89

Table 2 gives the group chemical comp~:)sition ~ i t h respect to the gas-oil fractions after irradiation at a total dose of 600 Mrad and, tbr CClnparis:~l~., the chemical composition of the startling material. The unsatltrat.ed pa~rlof the gas-oil after irradiation at a dose of 1000 Mrad was investigated; l h~:~ results are given in Table 3. Tile Table shows tile change in the grol~p chemical con!position as a frenetic ~ of the total (lose of c.nergy absorbed. There is a eonsiderab!e diinip.utio~ i,~ the proportions of paraffinie hydrocarbons--obviously as a results of their degradation and conversion into unsaturated aliphatie and cyelenie comi)ounds. As the dose increases, the rate of fornmtion of unsaturated eo:npouuds diminishes (see Fig. 3). The toe,~l amount of ar.:,inatie compounds depc'nds little on the dose, but aromatic hydrocarbons u itlI a double bond in side chains accumulate during the radiolysis. It is interesting that the proportion of naphthenie eompounds, both saturated and unsaturated, increases. The

223

Radiation-thermal cracking of gas-oil IN TIIE CHEMICAL COMPOSITION OF THE A FUNCTIONOF TOTALRADIATIONDOSE

TABLE 3. CHANGE

GAS-OIL AS

Dose, Mrad 600

Hydrocarbons

i

1000

i .__

Unsaturated Including: aliphatic cyclic Aromatic Including: with an unsaturated bond in a side chain Paraffinic Naphthenic Total

I

5.73 28-31

7"08 3.04 4.04 28.60

29.72 3.18 45.54 26.15

lOO%

37.66 26.89 100%

35"86 28"26 100%

bg~e,W 8.0 5.0 40 2"0

///, 100 Z00 300 400 500 5001~pad

FlO. 3. Yield of unsaturated hydrocarbons as a flmetion of the absorbed energy dose. latter p h e n o m e n o n m a y be connected with the f o r m a t i o n in the irradiation 1,roeess of complex biradieals a n d their subsequent ring-closure [l]. I n particular, biradieals m a y be formed after the n~diation splitting out of an a t o m of h y d r o g e n which t h e n takes p a r t in a displacement reaction with a h y d r o carbon radical a n d molecular hydrogen.

C. The formation of low-boiling radioly.sis products. In the radiationt h e r m a l decomposition of gas-oil, low-boiling fractions aecunmlated. Table 4 gives the a c e u n m l a t i o n of fl'aetions boiling up to 150 ° a n d from1 150 to 200 ° as a function of the radiation dose. Table 5 gives the physieo-ehemieal eh~:raeteristies a n d group composition of the low-boiling fractions boiling up to 150 and from 150 to 200 ° after irradiation. As can be seen from the Table, the yield of low-boiling f r a e t ' o n s is ~ 0.9% b y weight yer 100 Mrad.

A. •. BRODSKII et al.

224

D. Formation of radiation-chemical polymers. I n the r a d i a t i o n - t h e r m a l decomposition of gas-oil u n d e r the action of r a d i a t i o n at 300 ° , radiationchemical p o l y m e r s accumulate. Figure 4 shows the t o t a l radiation-chemical yie]d o f polymers as a function of the absorbed e n e r g y dose. The dependence of Gpolymer on the a b s o r b e d e n e r g y dose is illustrated in Fig. 5. I n our e x p e r i m e n t , this m a g n i t u d e varied from 0.45 molecules/100 eV to 0.09 molecules/100 eV. T A B L E 4. ACCUMULATION OF L I G H T FRACTIONS AS A FUNCTTO.N" OF T H E RADIATION DOSE

Dose, Mrad

0 200 500 1000

Fraction, °/o by wt. Initial i b . p . - 150 ° i 150-200° 0 1.72

2.5 3.8

i

i

3.2 4-3 5.5 8.48

The correlation in the course of change of Ga2 and Gpolymer with an increase in the t o t a l dose m u s t be noted. I n view of the p a r t i c u l a r interest which the chemical composition of the radiation-chemical polymers presents, the high-boiling residue ( > 3 5 0 °) was distilled into n a r r o w fractions; the specific gravities, refractive indices, percentages o f u n s a t u r a t e d hydrocarbons, and the molecular weights of these were d e t e r m i n e d (Table 6). Table 7 gives the physico-chemical characteristics of the residues boiling a b o v e 350 ° for the initial a n d the i r r a d i a t e d gas-oil.

% b~r w~gM

7

I

f~

8

5 4

/

3

0"2

,/

0.1

Z

10o 1,00 300 400 50Q 600/~ract

\ 100 Z00 300 400 500 680 Mp~d

FIG. 4 FIG. 5 FIG. 4. Yield of radiation-chemical polymers as a function of the absorbed energy dose. FIG. 5. Yield Gpolymer as a function of the absorbed energy dose.

R a d i a t i o n t h e r m a l c r a c k i n g o f gas-oil

225

The infra-red and ultra-violet spectra of fractions 18, 20, and 22 (see Table 6) were recorded. The latter show that even the highest-boiling fractions of those investigated contain no condensed aromatic compounds (within 1-2%)

The composition of the polymers was determined by the n - d - M method [7]. The composition was determined after hydrostabilization under mild T A B L E 5. CHARACTERISTICS AND GROUP COMPOSITION OF T H E L I G H T FRACTIONS AFTER IRRADIATION

Fraction, °C

Yield, % by

H y d r o c a r b o n s , % b y wt.

°

2O

34

Wt.

I

unsaturated i aromatic

paraffinic

naphthenic

57.9 48.1

none 24.2

l

Up to150 150-200

3.8 8.48

0.7454 0"8177

1.4179 1.4543

34.1 13.61

i ]

8.0 14.1

TABLE 6. I:)HYSICO-CHEMICAL CHARACTERISTICS OF NARROW FRACTIONS OF T H E RADIATION-CHEMICAL POLYMERS

Serial No.

Boiling range oC*

Yield, % b y weight, calculated on the polymers

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

348-350 350-356 356-363 363-368 368-375 375-381 381-387 387-392 392-398 398-402 402-409 409-415 415-422 422-427 427-433 433-440 440-447 447-453 453-459 459-467 467-471 471-475 > 475

2.0 3.9 5.2 2.2 4.1 4-0 3.6 5.5 2.1 6.0 2-4 5.2 3.0 3.8 3.8 2.4 3.5 5.1 1.5 2.6 1.8 5.1 20.0?

20

7t D

0.9110 0.9127 0.9215

0.9278 0.9315 0.9344 0.9495 0.9554 0.9739 0.9882

0.9892

0.9960

1.5088 1.5098 1.5100 1.5140 1.5158 1.5190 1.5211 1.5240 1.5258 1.5260 1.5261 1.5281 1.5301 1.5322 1.5348 1.5369 1.5392 1.5422 1.5451 1.5489 1.5499 1.5545

Molecular weight

278 284 290 296 300 308 315 324 330 335 337 344 347 349 355 357 365 371 378 407 415 424 458

Unsaturated hydrocarbons,

% 29.0 30.1 28.0 24.8 28.0 28.1 27.0 30.0 31.8 31.7 22.0 14.0 20.0 20.0 33.2 35.0 41.5 38.0 43.0 45.0 52.0 53.4

* D i s t i l l e d i n v a c u u m a t 3 m m H g , c a l c u l u t e d f r o m t h e U. O. P. m o n o g r a m . t Calculated on the initial product: ~ 1'2%.

226

A. M. BRODSKII et al. T A B L E 7.

Gas-oil

'~0

d~

Initial 0-8972 After ir- I radiation i 0.9365

CHARACTERISTICS

OF T H E R E S I D U E S B O I L I N G A B O V E 3 5 0 ~

Hydrocarbons, O70 / by wt. areunsatumatic rated 35 39

c,%

186.55 J

35

H,%

Molecular weight

Content of asphalte-

1.86

307

Absent

1.52

380

Traces

Atomic ratio H/C

13.43

88.71 11.25

nes

conditions. The proportion of carbon in aromatic structures, CA, was 21.5% and in the naphthenic part, CN, it was 38.6%; the number of aromatic rings per molecule was 0.8 and the number of naphthenic rings 1.9. From the data given it can be seen that there in so appreciable accumulation of condensed aromatic compounds and, in particular, asphaltenes in the radiation-chemical polymers. The hydrocarbons formed, except for the highest boiling ones (>475°), are close to the initial product as regards ring analysis. We may note that, according to Topchiev et al. [6], there are compounds with two naphthenic rings in one molecule in gas-oils of the type investigated. In the heaviest fractions, formed in insignificant amounts, compounds can be found with a high degree of condensation. This also follows from the composition of the fraction boiling above 475 ° with a molecular weight of 458 Eleme~tary composition, °/o by weight Carbon Hydrogen Sulphur Atomic ratio H/C

90.39 9.42 0.19 1.23

SUMMARY

I. The yields of various gases and their change during r~diolysis, showing a relative deereas~ in the formation of hydrogen during the process, have been determined. The radiation-thermal cracking of gas-oil takes ple~ee under conditions at which thermal cracking does not take place. 2. The change in the chemical composition of the liquid products has bv~en investigated. The accumulations, with olefins, of cyelenes and, partieu]arly, eyclanes, with the predominant decomposition of the paraffins has been shown. 3. The formation of high-boiling products on radiation-thermal cracking has been studied in detail. It has been shown that these products are close in ring composition "co the initial gas-oil. At the same time, their highestboiling part contains condensation products even at 300 °.

Radiation-thermal cracking of gas-oil

227

4. The distribution of p r o d u c t s (gas, gasoline, a n d h e a v y fractions) in the r a d i a t i o n - t h e r m a l cracking of gas-oil a p p r o x i m a t e s to the distribution on t h e r m a l cracking. However, to o b t a i n degrees of conversion c u s t o m a r y in industrial t h e r m a l cracking, at the t e m p e r a t u r e of R T C investigated, practically u n a t t a i n a b l e values of the total dose are necessary. *

* *

I n conclusion the a u t h o r s express their t h a n k s for assistance in c a r r y i n g out the work to N. V. Z v o n o v a n d V. B. Titov. Translated by B. J. HAZZAI~I) REFERENCES

1. A. M. BRODSKII, K. P. LAVROVSKII and V. B. TITOV, Dokl. Akad. Nauk SSSR 138, No. 5, 1961 2. A. V. TOPCHIEV and L. S. POLAK, Dokl. Akad. Nauk SSSR 130, No. 4, 789. 1960 3. A. M. BRODSKII, N. V. ZVONOV, K. P. LAVROVSKII and B. V. TITOV, Neftekhimiya 1, No. 3, 370, 1961 4. A. M. BRODSKH, K. P. LAVROVSKII, N. N. NAIMUSHIN, V. B. TITOV and Ye. D. FILATOVA, Khim. i tekh. topliva, No. 3, 30, 1954 5. A. M. BRODSKII, R. A. KALINENKO and K. P. LAVROVSKII, Khim. i tekh. topliva, No. 8, 18, 1956. 6. A. V. TOPCHIEV, S. S. NIFONTOVA, Ye. S. POKROVSKAYA and L. M. ROZENBERG, Sb. Sostav i svoistva neftei i benzino-kerosinovykh fraktsii. (In symposium: Composition and Properties of Petroleum Oils and Gasoline-kerosine Fractions.) Izd. Akad. Nauk SSSR, Moscow, p. 448, 1957 7. K. Van NES and H. Van WESTEN, Sostav maslyanykh fraktsii nefti i ikh analiz. (Composition of Oil Fractions of Petroleum and their Analysis; translation of:Aspects oftheConstitutionofMin~ral Oils. Foceign Lit~rcLture Publishing House, Moseow, 1954