V Zhyznevskiy - Metacrylonitrile obtaining by isobutylene, tert-and isobutyl alcohols oxidative amonolysis - страница 1

Страницы:
1  2  3 

CHEMISTRY & CHEMICAL TECHNOLOGY

Vol. 3, No. 1, 2009 Chemistry Vyacheslav Zhyznevskiy and Volodymyr Gumenetskiy

METACRYLONITRILE OBTAINING BY ISOBUTYLENE, TERT-AND ISOBUTYL ALCOHOLS OXIDATIVE AMONOLYSIS

Lviv Polytechnic National University 12 Bandera str., 79013 Lviv, Ukraine

Received: December 12, 2008

© Zhyznevskiy V., Gumenetskiy V. 2009

Abstract. Metacrylonitrile obtained by oxidative amonolysis over different oxidative catalysts has been investigated. Instead of isobutylene an alternative raw material has been investigated for the metacrylonitrile synthesis.

Key words: catalysis, metacrylonitrile, catalyst, promoter.

1. Introduction

It is well-known [1] that methacrylic acid (MAA), its esters (methyl methacrylate (MMA) first of all) and metacrylonitrile (MAN) are valuable monomers of chemical industry and are widely used in various branches of industry. MAN is used for the production of antifreeze rubbers, polymeric resins and additives for oils and lubricants. Amide or MAA and its esters may be obtained by MAN hydrolysis. The isobutylene oxidative amonolysis over corresponding catalysts [1] is the most rational and economic method for MAN obtaining. For instance, Bi-Mo-Ox system with different promoters is used for the propylene and isobutylene oxidative amonolysis [1]. Such multicomponent systems as mixture of Co, Ni, Fe, As, W and Te oxides are also suggested. The search of advanced methods for the known systems and obtaining of new ones are continued in order to enhance MAN yield. In particular, the present authors with collaborators suggested Fe-Te-Mo-Ox system with different promoters for the olefins oxidation, oxidative dehydration and oxidative amonolysis [2]. The process is carried out over Bi-Mo-Ox catalysts at 643-703 K and higher temperatures. The reaction time is prior to 6 s depending upon the catalyst activity. Such time provides the olefin conversion till 80 % with the selectivity by MAN about 80-85 % [1]. -HCN, CH3N and СО+СО2 are the by-products, where two former products are commercial ones. This article deals with the investigations of catalysts which are more effective than Bi-Mo-Ox systems.

2. Experimental

The procedures of catalysts preparing and experimental methods of products analysis are presented

in [3].

At first Mo12-Sb1,0-Ox catalytic system which was effective for isobutylene oxidation to metacrolein (MA) was investigated. It is known from literature that Mo-Sb-Ox catalysts with different additives have relatively high selectivity at the oxidation of isobutylene to MA [2] and tellur oxides increase their activity and selectivity [4]. Therefore, first of all we investigated Mo-Sb-Ox catalyst with tellur. It has been established that Mo12Sbj 0Те1 0 is the most optimal catalyst by the selectivity of MAN obtaining. At isobutylene oxidative amonolysis over such catalysts a great amount of MA apart from MAN formation is formed. Sometimes MA yield exceeds MAN yield. Since MA is an intermediate product of MAN formation, these catalysts have small effeciency at the reaction of MA amonolysis. For instance, at 733 K under experimental conditions (flow reactor with the impulse feed of the reaction mixture of the following composition (mol %): ;'С4Н8 - 2; О2 - 5; NH3 - 3 in helium; contact time is 2.4 s) the isobutylene conversion is 43 %, the selectivity by MA

is 49.5 % and 44.6 % - by MAN; CO+CO2 is the rest.

Thus, in spite of the fact that these catalysts are sufficiently effective at the isobutylene oxidation into MA, they cannot be catalysts for the isobutylene oxidative amonolysis. The change of process conditions does not result in the MAN high yield.

3. Results and Discussion

Our investigations were aimed at the Fe-Te-Mo-Ox catalytic system which has also high efficiency at the isobutylene oxidation into MA. First of all we investigated the effect of active components pH precipitation upon the catalytic properties of the system. Solution pH was changed from the neutral value (pH = 7) to alkali value

(pH = 12) and acid value (pH = 1). It has been established that under above-mentioned conditions at 613 K and contact time 2.4 s at pH = 7 the isobutylene conversion was 93.6 %, the selectivity by MA was 37.4 % and 58.0 % - by MAN. At pH = 12 the isobutylene conversion was 97.1 %, the selectivity - 45.7 % by MA and 49.7 % - by MAN. At pH = 1 the isobutylene conversion was 77.3 %, selectivity by MA - 40.3 % and 56.7 % - by MAN. Thus, MAN yields were: 93.6-0.58 = 54.3 % (at pH = 7), 97.1-0.497 = 48.2 % (at pH = 12) and 77.3-0.567 = =43.8 % (at pH = 1).

One can see from above-mentioned results that the catalyst precipitated at pH = 7 is the best by MAN yield. Investigated catalysts were prepared at pH = 7 with the ratio Fe:Te:Mo = 1:0.85:1 and optimum ratio between the promoter and Mo, which was established due to the effect of promoter concentration on catalytic properties.

3.1. The Effect of Alkaline-Earth Promoters on Fe-Te-Mo-Ox Catalytic Properties

The effect of potassium promoter on Fe-Te-Mo-Ox catalytic properties was investigated at the isobutylene oxidative amonolysis into MAN.

KNO3, which is decomposed to K2O while roasting, was used for the catalyst preparation. We choose this element because in [5] authors show that KNO3 is the best for the Fe-Te-Mo-Ox catalyst promoter by MA yield. We prepared a series of catalysts with various concentrations of the promoter (K/Mo atomic ratio was 0.01-0.5). The obtained results are presented in Fig. 1.

Х, %

 

Si, %

100 ? 80 -

 

 

 

- 100

- 80

60 і

f

 

 

? 60

40 -

 

 

 

1 40

20 -

 

 

 

- 20

0 I

 

і і

1

- 0

0      0,1     0,2     0,3     0,4 0,5

KNO3/Mo

Fig. l. The effect of KNO3/Mo ratio on the catalytic properties of the Fe-Te-Mo-Ox catalyst at the contact time of 2.4 s and temperatures 643 K (1, 2, 3) and 613 K (4, 5, 6). Isobutylene conversion - Х.     (1, 4); selectivity by MA -SMf (2, 5) and selectivity by MAN - Sman (3, 6). The reaction mixture composition (mol %): іС4Н8 - 2; О2 - 5; NH3 -3. Flow rate (Vf ) is 0.56 cm3/s, impulse volume (Vimp ) is 6.2 cm3, the flow reactor with impulse feed.

One can see from Fig. 1 that the best catalyst by MAN yield is the catalyst with K/Mo ratio equaling to 0.1 (MAN yield is 84.3 %). Almost the same yield is obtained over the catalyst with the ratio of 0.05. It has been established that increase of the K/Mo ratio over 0.1 decreases the olefins conversion and the selectivity by MAN but increases the selectivity by MA. When K/Mo ratio equals to 0.5 at temperature of 643 K olefin conversion and the selectivity by MAN decrease to 42.8 and 37.5 respectively.

The effect of temperature and contact time on the isobutylene conversion and the selectivity by products of oxidative amonolysis over optimal catalyst (KNO3/Mo = = 0.1) is represented in Table 1. Process conditions are shown in Fig. 1.

Table 1

Dependence of isobutylene conversion and selectivity by products upon temperature and contact time over optimal by MAN yield catalyst (KNO3/Mo = 0.1)

Тр, К

ХіС4Н8, %

SMA, %

SMAH, %

SC0+C02, %

643

99.2 (87.7)

6.8 (26.3)

85.0 (71.9)

7.1 (1.7)

613

97.2 (69.7)

11.7 (24.6)

84.7 (75.1)

3.6 (0.3)

583

94.6 (32.5)

16.1 (33.7)

82.2 (66.3)

1.7 (—)

Note: contact time is 2.4 s for values without brackets and 0.6 s for values in brackets.

Table 2

Effect of temperature and contact time on catalytic properties of Fe-Te-Mo-Ox catalyst promoted with barium nitrate (Ba/Mo = 0.l) at the isobutylene oxidative amonolysis

Тр, К

ХіС4Н8, %

SMA, %         SMAN, %

SC0+C02, %

583

1 97.0 (47.3) 1 11.7 (28.3) | 86.9 (71.7) |

1.4 (—)

613

97.8 (81.5)

8.0 (22.0)   86.4 (77.3)

5.6 (0.7)

643

99.0 (94.7)

6.1 (16.6)   86.0 (80.4)

8.9 (3.0)

Note: contact time is 2.4 s for values without brackets and 0.6 s for values in brackets. Conditions are shown in Fig. 1.

The increase of temperature from 583 to 643 K and contact time from 0.6 to 2.4 s increases the selectivity by MAN. Under optimal conditions (T = 643 K and тк = 2.4 s) over the better catalyst the general selectivity by MAN+MA (the latter may be returned to the reactor inlet) is 84.3 + 6.8 = 91.1 %. This sum equals to 88.0 % over the catalyst with KNO3/Mo = 0.05, so the first catalyst is a better one.

The effect of barium promoter with the ratio Ba/Mo = 0.1 [5] was investigated at the reaction of isobutylene oxidative amonolysis (Table 2).

Results from Table 2 show that at x, = 0.6 s increase

к

of temperature increases the selectivity by MAN and decreases the selectivity by MA. At xk = 2.4 s both selectivities by MAN and MA decrease. The increase of

contact time also increases the selectivity by MAN. The maximum MAN yield (85.1 %) was obtained at 643 K and Tk = 2.4 s. Just such conditions may be considered as

optimum ones for the isobutylene oxidative amonolysis    643 K and т = 2.4 s.

for the majority of investigated catalysts due to the higher activation energy of MA compared with MAN. Maximum yield of MAN equals to 60.2 % was obtained over K3 at

over FeTe085MoOx promoted by Ba(NO3)2. Under these conditions MA (the selectivity by MA is 6.1 %) is also presented in the reaction products, as well as MAN and total oxidation products. MA may be returned into the process. The increase of the selectivity by MAN and decrease of the selectivity by MA may be explained by the fact that MA is an intermediate product of nitrile formation. The low yield of total oxidation products may be explained by the presece of NH3 in the reaction mixture, which blocks strong acid centers of the system surface, where destructive and total oxidation of organic substrates takes place. Alkaline-earth promoter of the catalyst plays the same role.

The effect of magnesium promoter. E. Dvonchova [5] shows that at the isobutylene oxidation Fe-Te-Mo-Ox catalyst promoted with Mg(NO3)2, which decomposes to MgO at heating, is the best catalyst among catalysts of such a type promoted with alkali-earth metals regarding to MA yield. We investigated the effect of Mg2+ nitrate on the catalytic properties of this catalyst at the isobutylene oxidative amonolysis. Our results are represented in Table 3.

The increase of Mg/Mo ratio from 0.01 to 0.2 considerably increases the catalyst activity. At 583 K olefin conversion increases from 16.9 to 70.3 %. The maximum selectivity by MAN (82.4 %) is obtained at this temperature over K1 with a promoter minimum amount. However, since olefin conversion is very low (16.9 %),

MAN yield is only 13.9 %.

The increase of temperature decreases the selectivity by MAN and increases the selectivity by MA

In our work [6] we have shown that stable salts of alkaline-earth promoters have the higher efficiency by the yield of partial oxidation products compared with their nitrates which are decomposed into oxides at high temperatures. Therefore, it was advisable to study the effect of MgSO4 on the catalytic properties of Fe-Te-Mo-Ox catalyst and compare obtained results with the data from Table 3, where Mg(NO3)2 was a promoter.

The effect of MgSO4 concentration on the catalytic properties of Fe-Te-Mo-Ox at the isobutylene oxidative amonolysis at different temperatures (613-673 K) and contact times (1.2-3.6 s) is represented in Table 4. The same effect but over the optimal by MAN yield catalyst (MgSO4/Mo = 0.2) is represented in Fig. 2.

One can see from Fig. 2a that under experimental conditions MAN maximum yield (80.5 %) is achieved at 583 K and contact time 3.6 s over K8 catalyst with MgSO4/Mo = 0.2. It is considerably higher than over the catalyst promoted with Mg(NO3)2 over which the yield is only 26.9 % at 583 K and Tk = 2.4 s. At higher temperature (643 K) and Tk = 2.4 s the MAN yield is 44.4 % and maximum yield obtained over K3 is 60.2 % , that is less by 20.3 % in comparison with the catalyst promoted with

MgSO4.

Thus, anion of the promoter salt also affects the catalytic properties.

The effect of temperature and contact time over the optimal catalyst promoted with MgSO4 is also represented also in Fig. 2a. At contact time of 3.6 s MAN yield decreases from 80.5 % at 583 K to 45 % at 673 K.

Table 3

Effect of magnesium nitrate amount on catalytic properties of Fe-Te-Mo-Ox catalyst at the isobutylene

oxidative amonolysis to the metacrylonitrile (impulse flow reactor, V = 0.56 cm3/s; Vm

6.2 cm3,

%k = 2.4 s, reaction mixture composition (mol %): «С4Н8 - 2; О2 - 5; NH3 - 3 in the helium)

Mg/Mo ratio

Т, К

Х, %

Selectivity by:, %

MAN yield, %

 

 

 

МА

MAN

 

0.01 (К0

583

16.9

17.6

82.4

13.9

 

613

41.8

34.9

64.3

26.9

 

643

68.3

49.0

49.0

33.5

0.02 (К2)

583

31.3

30.8

69.1

22.3

 

613

57.7

47.4

50.7

29.2

 

643

84.2

49.8

47.3

39.8

0.05 (К3)

583

80.0

49.2

48.5

38.8

 

613

97.1

55.1

40.6

39.4

 

643

98.4

32.9

61.2

60.2

0.14)

583

64.8

39.0

59.1

38.3

 

613

72.2

40.7

55.2

40.0

 

643

98.9

38.1

54.9

54.3

0.25)

583

70.3

61.5

38.2

26.9

 

613

93.6

61.6

37.3

34.9

 

643

99.1

49.2

44.9

44.4

Effect of MgSO4 on catalytic properties of the oxide catalyst (Fe:Te:Mo = 1:0.85:1) at

oxidative amonolysis (conditions are shown in Fig. 1)

Table 4 the isobutylene

Mg/Mo ratio

 

Т, К

Х, %

Selectivity by:, %

MAN yield, %

 

 

 

 

MA

MAN

 

 

 

703

80.5

72.2

6.9

5.5

 

1.2

673

71.7

78.6

24.0

17.2

 

 

643

62.8

61.2

35.0

22.0

 

 

703

92.3

57.6

18.6

17.1

0.05О

2.4

673

80.8

48.8

36.2

29.2

 

 

643

74.5

43.1

48.3

36.0

 

 

703

97.0

64.4

11.9

11.5

 

3.6

673

95.9

65.0

14.0

13.4

 

 

643

88.1

66.9

19.3

17.0

 

 

673

86.0

59.9

16.4

14.1

 

1.2

643

74.6

46.3

40.0

29.8

 

 

613

48.4

29.1

58.9

28.5

 

 

673

90.1

52.7

24.2

21.8

0.1 (К)

2.4

643

88.6

42.3

43.4

38.4

 

 

613

67.3

21.5

68.2

45.9

 

 

673

92.8

44.3

35.4

32.5

 

3.6

643

90.9

35.2

50.4

45.8

 

 

613

85.2

18.1

71.4

60.8

 

 

643

100.0

76.5

76.5

0.5 (К,)

1.2

613

82.9

6.9

67.5

55.9

 

 

583

67.8

5.9

86.4

58.5

Note: Results obtained over K8(Mg/Mo) are represented in Fig. 2

Х, В % 100

80

60

40

20

0

S, %

100

80 60 40 20

іТ, К

0

Т, К

583

613

643

673

583

613

643

673

b

Fig. 2. Effect of temperature and contact time on the isobutylene conversion (X) and metacrylonitrile yield (B) (a) as well as on the selectivity by MA and MAN (b) over optimal Fe-Te-Mo-Ox catalyst promoted with MgSO4 (Mg/Mo = 0.2): (a) isobutylene conversion (1-3), MAN yield (4-6); (b) selectivity by MAN (1-3) and by MA (4-6) at tk = 1.2; 2.4 and

Страницы:
1  2  3 


Похожие статьи

V Zhyznevskiy - Metacrylonitrile obtaining by isobutylene, tert-and isobutyl alcohols oxidative amonolysis