Industrial and Laboratory Nitrations

25 Effect of Gamma Radiation on Vapor Phase Nitration of Propane 1

2

ROBERTO LEE, TAE CHUNG, and LYLE F. ALBRIGHT

Downloaded by NATL UNIV OF SINGAPORE on November 8, 2017 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0022.ch025

Purdue University, West Lafayette, Ind. 47907 1 2

Present address: Monsanto Company, St. Louis, Mo. Present address: Upjohn Co., North Haven, Conn.

Gamma radiation has been found to affect the kinetics and the course of several chemical reactions (1-6). Beneficial effects are frequently obtained for free-radical reactions. The present investigation was made to determine the effects of radiation on vapor-phase n i t r a t i o n . The following mechanism is generally considered to be predominant when propane i s nitrated (7-9): HN0 + HO-

+

3

C

3 8 H

+

H 0 #

*

C H - + H0N0 3

7

2

·Ν0 C

-

2

3 7* H

+

H

C H N0 3

7

2°

2

+

HO-

During the nitration reaction, oxidation steps also occur and C-C bonds are broken. Products obtained include nitromethane (NM), nitroethane (NE), 1-nitropropane (1-NP), 2-nitropropane (2-NP), aldehydes, other oxygenated products, o l e f i n s , carbon dioxide, carbon monoxide, and water (10-13). The approximate ranges of the operating variables reported (7-14) for the process include temperatures from 370 to 450°C, pressures from atmospheric up to about 200 p s i , and contact times from 0.5 to 4.0 sec. The mole ratios of propane to n i t r i c acid have ranged from 1:1 in a s a l t bath reactor (14) to 20:1 in commercial nitrators (7). Several additives (oxygen, chlorine, bromine, and ozone) which apparently promote free radical formation have been found to improve conversion and a l t e r product distribution (11-13). Experimental Details The stainless-steel flow reactor used was similar to the one employed by Liebenthal et a l . (3) for the partial oxidation of propane. I t was heated e l e c t r i c a l l y , as were the i n l e t and outlet lines to the reactor to prevent condensation. The 344

Albright and Hanson; Industrial and Laboratory Nitrations ACS Symposium Series; American Chemical Society: Washington, DC, 1976.


25.

LEEE TAL.

Effect

of Gamma

Radiation

345

Cobalt-60 source used provided a gamma radiation intensity of about 195,000 roentgens per hour. The reactor could be inserted inside the Co-60 source for irradiated runs. Alternatively, gaseous or l i q u i d propane was sometimes irradiated in a stainless-steel c e l l prior to the n i t r a t i o n step. The exposure time was generally about 3 seconds for the gaseous propane and 40 to 50 hours for the l i q u i d . The flow sheet for the equipment and the product recovery procedure resembled those employed by Albright et a l . (9). In runs involving oxygen and chlorine, the reagent was introduced to the gaseous mixture of propane and n i t r i c acid just before the reactants entered the reactor. The entering mixture was maintained in a l l runs at about 120-150°C. The feed materials used were as follows: propane 99 + % purity, oxygen 99 + % purity, and n i t r i c acid 70 weight %. Results Eleven sets of nitration experiments, consisting of 58 runs, were made. The operating conditions and pertinent results are summarized in Table I. Propane did not nitrate at temperatures below 370°C with or without gamma radiation. Above 460°C excessive decomposition occurred. The n i t r i c acid conversions and nitroparaffin product distributions in general correlate well with the average reactor temperature which was determined using four thermocouples positioned at various heights in the reactor thermowell. This average reactor temperature was also u t i l i z e d to calculate the contact time. Without additives, both unirradiated and irradiated runs had optimum n i t r i c acid conversions of 27-28% at 425-430°C. These series of runs were made using propane-to-nitric acid ratios of 6:1 and 10:1. Irradiation of propane gas prior to i t s introduction to the reactor did not s i g n i f i c a n t l y increase conversion. When l i q u i d propane was irradiated for 40-50 hours and the resulting propane was nitrated, n i t r i c acid conversions increased to 31%. In terms of product d i s t r i b u t i o n , the relative amounts of NM and NE were quite low as indicated by the r e l a t i v e l y high molecular weight of the nitroparaffin products, as shown in Table I. The amounts of 1-NP increased and 2-NP decreased with temperature increases; each of these compounds occurred in r e l a t i v e l y large quantities. Gamma radiation did not change nitroparaffin product distribution appreciably, but somewhat more scattering of data occurred. The average molecular weight of nitroparaffins in a l l cases tended to decrease s l i g h t l y as the temperature increased. Nitration reactions "catalyzed" with oxygen at an oxygen-ton i t r i c acid ratio of 1.05, produced the following results:



7.

6.

5.

4.

3.

2.

1.

Unirradiated Reactor Unirradiated Reactor Irradiated Reactor Irradiated Reactor Irradiated Propane Gas Irradiated Liquid Propane Irradiated Liquid Propane

Nitration without Addi t i ves 1.1 1.2 1.1 1.2 1.9 1.5 1.2

4

9

6

6

3

7

3

Contact Time, Sec

4.1

8.5

15.9

6.2

10.9

6.4

10.1

Av. Mole Ratio of Propane to N i t r i c Acid

412-433

400-449

423-436

413-441

408-449

398-451

409-439

Temp. Range, °C

Summary of Nitration Runs

28.3-30.9

11.5-30.8

27.4-28.3

14.0-31.1

13.7-27.4

4.4-27.2

15.9-26.9

3

HN0 Conversion Range, %

79.6-83.1

83.5-87.8

82.2-86.6

81.6-83.0

82.9-83.2

78.6-84.6

82.5-83.3

Average Molecular Weight of * Nitroparaffins

The molecular weights of nitropropanes, nitroethane, and nitromethane are 89, 75, and 61 respectively

I.

Νο· of Runs

Table I



III.

II.

Unirradiated Reactor Irradiated Reactor

2.

1.

Unirradiated Reactor Irradiated Reactor

Nitration with Chlorine

2.

1.

Nitration with Oxygen

0.24 0.22

14.2 13.0

1.2

4

1.07

1.2

8

3

11.1

1.1

5

1.05

Av. Mole Av. Mole Ratio of Ratio of Additive Propane to N i t r i c Acid Of N i t r i c Acid

10.9

Contact Time, Sec.

417- 450

416- 452

387-459

377-440

Temp. Range, °C

Summary of Nitration Runs (cont.)

1.1

No. of Runs

Table I

18.0-22.1

19.8-22.7

21.6-39.4

26.9-36.6

HNO, Conversion Range, %


84.3-85.8

84.8-85.5

77.0-78.2

76.5-82.5

Average Molecular Weight of Nitroparaffins

ι

3

a

> F

S3

w

to

348

INDUSTRIAL AND LABORATORY NITRATIONS


1.

The optimum conversion for the unirradiated series of runs was 36.6% at about 400°C. The corresponding optimum conversion for the irradiated runs was about 39.4% at 420°C. 2. Gamma radiation had little or no effect on product composition. Chlorine was used as an additive in a series of runs with residence times of about 1.2 seconds and a ratio of propane-tonitric acid of 13.5. The mole ratio of chlorine to nitric acid was 0.2. Chlorine tended to lower nitric acid conversions, suppress C-C bond breakage, and promote 2-NP formation. The maximum conversion was about 23% for both irradiated and unirradiated runs. Gamma radiation had little effect on either nitric acid conversions or product composition. Discussion of Results and Conclusions The reason why irradiation caused relatively small but nevertheless significant increases of nitric acid conversions in some cases but had little or no effect in others is not known. The small amounts of hydrogen, methane, ethane detected after liquid propane was irradiated are not thought to be beneficial in improving nitric acid conversions. Of interest, irradiation increases the rates of oxidation of both hydrogen and paraffins (4,5); these results combined with the results of the present investigation suggest that radiation activates in some manner oxygen. It was surprising that irradiation did not increase nitric acid conversions when chlorine was used as an additive; chlorination reactions are often significantly affected by radiation (2,3). Clearly more information is s t i l l needed to explain the results of the present investigation. Abstract Propane was nitrated with nitric acid in a tubular flow reactor which could be subjected to 195,000 roentgens per hour of gamma radiation from a Cobalt-60 source. The reaction was investigated at operating conditions of commercial interest. Irradiation of the reacting mixture had little effect on the nitric acid conversion, except when oxygen was added to the reactants or when liquid propane was irradiated prior to reaction. Under these conditions, a 10 to 15% relative increase was noted. The product distribution was unaffected by radiation.


25. LEE ET AL.

Effect of Gamma Radiation

349

Literature Cited 1. 2.


3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Crean, L . E . , Mins, L . S . , and Martin, J.J., Chem. Eng. Prog., 56, 73 (Oct., 1960). Harmer, O.E., Anderson, L . C . , and Martin, J.J., Chem. Eng. Prog. Symposium Series 50, No. 11, 253 (1954). Liebenthal, J.L., Albright, L . F . , and Sesonske, Α., Proceedings of Second United Nations International Conference on Peaceful Use of Atomic Energy, 29, 107 (1959). Martin, J.J., Chem. Eng. Prog. 54, No. 2, 66 (1958). Nield, L.A. and Albright, L . F . , Journal Chem. Eng. Data 10, 275 (1965). Royals, E . E . , "Advanced Organic Chemistry", Prentice-Hall, New Jersey (1958). Albright, L . F . , Chemical Engineering 73, 12, 149 (1966). Albright, L . F . , Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Edition, Vol. 13, pp. 784-796 (1967). Albright, L . F . , Locke, S.A., MacFarlane, D.R., and Glahn, G.L. Ind. Eng. Chem., 52, 221 (1960). Bachman, G.B., Addison, L.M., Hewett, J.V., Kohn, L . , and Millikan, Α., J. Org. Chem., 17, 906-13 (1952). Bachman, G.B., Atwood, M.T., and Pollack, M., J. Org. Chem., 19, 312-323 (1954). Bachman, G.B., Hewett, J.W., and Millikan, A . G . , J. Org. Chem. 17, 942-54 (1952). Bachman, G.B. and Standish, N.W., J. Org. Chem., 26, 570 (1961). Coldiron, D.C., Albright, L . F . , and Alexander, L . G . , Ind. Eng. Chem., 50, 991 (1958).


Industrial and Laboratory Nitrations

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