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Oxidation of butenes in maleic anhydride with vanadium-phosphorus catalysts prepared by coprecipitation with colloidal SiO2
OXIDATION OF BUTENES IN MALEIC ANHYDRIDE WITH VANADIUM-PHOSPHORUS CATALYSTS PREPARED BY COPRECIPITATION WITH COLLOIDAL Si02* L. S. AKIMOVA, ]3. t~. SEREBRYAKOVand I. K. KOLOHIN All-Union Technological Research Institute for the Preparation and Treatment of Low Molecular Weight Olefins, Baku
(Received 5 May 1970)
"CoPR~CIPITATION" with a binder such as the sol of metasilicic acid or silica-sol [1] has recently been used successfully for the synthesis of some complex oxide catalysts. A detailed study has been previously made of the synthesis, structural characteristics and catalytic activity of bismuth-molybdenum catalysts prepared from silica-sol [2]. These catalysts have a high absolute activity and can be used in oxidizing ammonolysis of propylene [1] and oxidizing dehydrogenation of n-butenes [2]. The technology of preparing catalyst carriers has been simplified considerably because of the use of silica-sol as binder. It is interesting to extend this method of synthesizing complex catalysts to other catalytic systems, particularly in "fluidized ~' bed. This is necessitated by the fact that silica-sol makes it possible to use a very modern method of atomizing drying. In this study this method was used to prepare vanadium-phosphate catalysts which are most effective in preparing maleic anhydride by oxidation of n-butenes [3]. To prepare the catalysts ammonium metavanadate, phosphoric acid and silica-sol having the following properties were used: SiO2 30 % wt.; ~qa20 0.6% wt.; stability with a pit of 9.5 was over 3 years; the dimensions of colloidal Si02 particles were 10-20 A; the specific surface of the dry residue was 150-200 m2/g. The catalysts were synthesized as follows: 85% H3P04 (vanadium : phosphorus atomic ratio being 1 : 1) was added to an aqueous solution of ammonium metavanadate at 70 ° and, while stirring, the requisite amount of silica-sol was added. The solution was evaporated while stirring, dried at 120 ° and calcined at 400-420 ° for 6 hr. The mass obtained was crushed, and a 80-100/~ fraction separated and pelletized. By this method a series of catalyst samples was prepared containing: 1, 5, 10, 20, 40, 60, 80% wt. SiO~. The dependence of the specific surface and average pore radius of catalysts on SiO2 content is shown in Fig. 1. Specific surface was determined chromato* Neftekhimiya 1], No. 4, 545-547, 1971. 143
144
L.S. AxrMOVAet
al.
graphically from the heat desorption of nitrogen and pore volume b y the Innes method [4]. The catalytic activity of the samples obtained by oxidation of n-butenes to maleie anhydride was determined b y a dynamic method using a circulatory apparatus with a reactor 25 mm in diameter in a stationary catalyst layer. mole % 100 L=_ :
1
80 80= 7O
s,m
60 5O
O.4
5O 40 30
!
Oq
1000 8O0 6O0
f
¢0 30 20
O.Z 1o
01 t
lO 20 30 O0 50 60 70 80
°/o S i Oz FIG. 1
10 0
t
510 ZO 40 Si02
60 wf.,%
FIG. 2
FIG. 1. Dependence of the specific surface and average pore radius of catalysts on Si O content: 1 --specific surface, m2/g; 2--pore volume (Vpore),ml/g; 3 --average pore radius, A FIG. 2. Effect of SiO, content oi1 the catalytic activity of samples. Temperatu re 4550 contact time 0.9 scc; 1--conversion, ~; 2-4--product yield (mole ~); maleic anhydride (2), COs (3), light acids (4). n-Butenes (80% vol. but-2-ene and 20% vol. but-l-ene), the raw material, were prepared b y dehydration of sec-butanol over 7-AlcOa. Air was the oxidizing agent. The process was carried out below the minimum explosive range of the butene-air mixture, the concentration of n-butenes of the gas mixture being 1% vol. An investigation of the activity of a series of samples of variable SiO~ content shows that with an increase in Si02 content from 0 to 60% wt., the selectivity of n-butene oxidation to maleic anhydride increases. With 100% conversion of n-butenes the yield of maleic anhydride increases from 52 to 72 mole %. A marked increase in the selectivity of the catalyst was observed with very small additions of SiO2 (1% wt.) which m a y possibly be due to the effect of modifying promotion (Fig. 2). From these results the optimum SiO2 content in the catalyst was found to be between 50 and 60% wt. A vanadiumphosphorus catalyst containing 60% wt. SiO2 was therefore chosen for subsequent investigation.
Oxidation of butenes in maleie anhydride
145
Using this catalyst a study was made of the effect of temperature and contact time on n-butene conversion and yields of maleie anhydride and carbon dioxide. With a contact time of 0.25 sec maximum process selectivity
mole%
1
IOO
,o
Bo 8o 70 6o
5o
mole % 80 o
oo
60
ao
00 ~
o
?
OOo!
"
2o IO 0
o
.I
I
000
o#0
I
075 °C
I
I
l
I
I
I
I
1
1
I'"
I^
I.
0"0 0"8 f'2 1"6 2.0 Z-O z',sec FI~. 4
Fro. 3
FIG. 3. Effect of process temperature on the activity of V20s.P~Os.60~/~ wt. SiO~ catalyst with a contact time of 0.25 see. Notations are the same as in Fig. 2. FIG. 4. Effect of contact time on the activity of a V205 .P~05.60~ wt. Si02 catalyst at a temperature of 410°. 1-3--Product yield (mole ~): maleic anhydride (1), CO~ (2), light acids (3). was at 440 °. A reduction in temperature increased the yield of light acids while an increase in temperature intensified C02 formation (Fig. 3). Kinetic curves plotted at 440 ° (Fig. 4) point to parallel-sequential reactions by the system maleic anhydride-n-butenes-~
A
~COz light acids
As shown by this information, ~ vanadium-phosphorus catalyst prepared by coprecipitation with colloidal silica enables us to carry out n-butene oxidation to maleic anhydride with a yield of 75 mol.% of the n-butenes passed through, which is equivalant to a consumption coefficient of 660 kg n-butenes per ton maleic anhydride. I t should be noted t h a t for a catalyst previously described [5] this value is 1040 kg n-butenes per ton maleic anhydride.
146
L.S. A~MOVA et al. SUMMARY
A s t u d y w a s m a d e of t h e o x i d a t i o n o£ n - b u t e n e s in maleic a n h y d r i d e w i t h V - P c a t a l y s t s p r e p a r e d b y c o p r e c i p i t a t i o n w i t h colloidal silica. W i t h an o p t i m u m SiO~ c o n t e n t in t h e c a t a l y s t of 6 0 % wt. t h e yield of maleic a n h y d r i d e w a s 75 m o l e ~ . REFERENCES 1. U.S.A. Pat. 2904580, 1959; Chem. Abstrs. 55, 9213, 1960. U.S.A. Pat. 2920098, 1960; Chem. Abstrs. 55, 16387, 1960 2. L. S. P,KII~IOVA, K. M. MEKHTIEV, B. Ro SEREBRYAKOV, I. K. KOLCHIN and M. A. DALIN, Zh. fiz. khimii 42, 2527, 1969 3. Yu. D. KERNOS, Kand. dis., Mosk. in-t tonkoi khim. tekhnol., Moscow, 1962 4. Oil and Gas J. 12, 162, 1956 5. Yu. D. KERNOS and B. L. MOLDAVSKII, Neftekhimiya 2, 4, 1962
(Received 5 May 1970)
"CoPR~CIPITATION" with a binder such as the sol of metasilicic acid or silica-sol [1] has recently been used successfully for the synthesis of some complex oxide catalysts. A detailed study has been previously made of the synthesis, structural characteristics and catalytic activity of bismuth-molybdenum catalysts prepared from silica-sol [2]. These catalysts have a high absolute activity and can be used in oxidizing ammonolysis of propylene [1] and oxidizing dehydrogenation of n-butenes [2]. The technology of preparing catalyst carriers has been simplified considerably because of the use of silica-sol as binder. It is interesting to extend this method of synthesizing complex catalysts to other catalytic systems, particularly in "fluidized ~' bed. This is necessitated by the fact that silica-sol makes it possible to use a very modern method of atomizing drying. In this study this method was used to prepare vanadium-phosphate catalysts which are most effective in preparing maleic anhydride by oxidation of n-butenes [3]. To prepare the catalysts ammonium metavanadate, phosphoric acid and silica-sol having the following properties were used: SiO2 30 % wt.; ~qa20 0.6% wt.; stability with a pit of 9.5 was over 3 years; the dimensions of colloidal Si02 particles were 10-20 A; the specific surface of the dry residue was 150-200 m2/g. The catalysts were synthesized as follows: 85% H3P04 (vanadium : phosphorus atomic ratio being 1 : 1) was added to an aqueous solution of ammonium metavanadate at 70 ° and, while stirring, the requisite amount of silica-sol was added. The solution was evaporated while stirring, dried at 120 ° and calcined at 400-420 ° for 6 hr. The mass obtained was crushed, and a 80-100/~ fraction separated and pelletized. By this method a series of catalyst samples was prepared containing: 1, 5, 10, 20, 40, 60, 80% wt. SiO~. The dependence of the specific surface and average pore radius of catalysts on SiO2 content is shown in Fig. 1. Specific surface was determined chromato* Neftekhimiya 1], No. 4, 545-547, 1971. 143
144
L.S. AxrMOVAet
al.
graphically from the heat desorption of nitrogen and pore volume b y the Innes method [4]. The catalytic activity of the samples obtained by oxidation of n-butenes to maleie anhydride was determined b y a dynamic method using a circulatory apparatus with a reactor 25 mm in diameter in a stationary catalyst layer. mole % 100 L=_ :
1
80 80= 7O
s,m
60 5O
O.4
5O 40 30
!
Oq
1000 8O0 6O0
f
¢0 30 20
O.Z 1o
01 t
lO 20 30 O0 50 60 70 80
°/o S i Oz FIG. 1
10 0
t
510 ZO 40 Si02
60 wf.,%
FIG. 2
FIG. 1. Dependence of the specific surface and average pore radius of catalysts on Si O content: 1 --specific surface, m2/g; 2--pore volume (Vpore),ml/g; 3 --average pore radius, A FIG. 2. Effect of SiO, content oi1 the catalytic activity of samples. Temperatu re 4550 contact time 0.9 scc; 1--conversion, ~; 2-4--product yield (mole ~); maleic anhydride (2), COs (3), light acids (4). n-Butenes (80% vol. but-2-ene and 20% vol. but-l-ene), the raw material, were prepared b y dehydration of sec-butanol over 7-AlcOa. Air was the oxidizing agent. The process was carried out below the minimum explosive range of the butene-air mixture, the concentration of n-butenes of the gas mixture being 1% vol. An investigation of the activity of a series of samples of variable SiO~ content shows that with an increase in Si02 content from 0 to 60% wt., the selectivity of n-butene oxidation to maleic anhydride increases. With 100% conversion of n-butenes the yield of maleic anhydride increases from 52 to 72 mole %. A marked increase in the selectivity of the catalyst was observed with very small additions of SiO2 (1% wt.) which m a y possibly be due to the effect of modifying promotion (Fig. 2). From these results the optimum SiO2 content in the catalyst was found to be between 50 and 60% wt. A vanadiumphosphorus catalyst containing 60% wt. SiO2 was therefore chosen for subsequent investigation.
Oxidation of butenes in maleie anhydride
145
Using this catalyst a study was made of the effect of temperature and contact time on n-butene conversion and yields of maleie anhydride and carbon dioxide. With a contact time of 0.25 sec maximum process selectivity
mole%
1
IOO
,o
Bo 8o 70 6o
5o
mole % 80 o
oo
60
ao
00 ~
o
?
OOo!
"
2o IO 0
o
.I
I
000
o#0
I
075 °C
I
I
l
I
I
I
I
1
1
I'"
I^
I.
0"0 0"8 f'2 1"6 2.0 Z-O z',sec FI~. 4
Fro. 3
FIG. 3. Effect of process temperature on the activity of V20s.P~Os.60~/~ wt. SiO~ catalyst with a contact time of 0.25 see. Notations are the same as in Fig. 2. FIG. 4. Effect of contact time on the activity of a V205 .P~05.60~ wt. Si02 catalyst at a temperature of 410°. 1-3--Product yield (mole ~): maleic anhydride (1), CO~ (2), light acids (3). was at 440 °. A reduction in temperature increased the yield of light acids while an increase in temperature intensified C02 formation (Fig. 3). Kinetic curves plotted at 440 ° (Fig. 4) point to parallel-sequential reactions by the system maleic anhydride-n-butenes-~
A
~COz light acids
As shown by this information, ~ vanadium-phosphorus catalyst prepared by coprecipitation with colloidal silica enables us to carry out n-butene oxidation to maleic anhydride with a yield of 75 mol.% of the n-butenes passed through, which is equivalant to a consumption coefficient of 660 kg n-butenes per ton maleic anhydride. I t should be noted t h a t for a catalyst previously described [5] this value is 1040 kg n-butenes per ton maleic anhydride.
146
L.S. A~MOVA et al. SUMMARY
A s t u d y w a s m a d e of t h e o x i d a t i o n o£ n - b u t e n e s in maleic a n h y d r i d e w i t h V - P c a t a l y s t s p r e p a r e d b y c o p r e c i p i t a t i o n w i t h colloidal silica. W i t h an o p t i m u m SiO~ c o n t e n t in t h e c a t a l y s t of 6 0 % wt. t h e yield of maleic a n h y d r i d e w a s 75 m o l e ~ . REFERENCES 1. U.S.A. Pat. 2904580, 1959; Chem. Abstrs. 55, 9213, 1960. U.S.A. Pat. 2920098, 1960; Chem. Abstrs. 55, 16387, 1960 2. L. S. P,KII~IOVA, K. M. MEKHTIEV, B. Ro SEREBRYAKOV, I. K. KOLCHIN and M. A. DALIN, Zh. fiz. khimii 42, 2527, 1969 3. Yu. D. KERNOS, Kand. dis., Mosk. in-t tonkoi khim. tekhnol., Moscow, 1962 4. Oil and Gas J. 12, 162, 1956 5. Yu. D. KERNOS and B. L. MOLDAVSKII, Neftekhimiya 2, 4, 1962