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Highly selective one-step formation of methyl isobutyl ketone from acetone with a magnesia supported nickel catalyst
Applied Catalysis A: General, 101 (1993) Ll-L6 Elsevier Science Publishers B.V., Amsterdam
Ll
APCAT A2559
Highly selective one-step formation of methyl isobutyl ketone from acetone with a magnesia supported nickel catalyst Luis M. Gandfa and Mario Montes Grupo de Ingenieria Q&mica, Departamento de Quimica Aplicada, Facultad de Quimica, Universidad de1 Pais Vasco, Apdo. 1072,20080 San Sebasticin (Spain) (Received 17 May 1993)
Abstract A new catalyst for the production of methyl isobutyl ketone (MIBK ) from acetone and hydrogen in one step at atmospheric pressure has been prepared. The catalyst was obtained by impregnation of MgO with an aqueous solution of nickel nitrate, dried, calcined in air and reduced in hydrogen. This catalyst showed a high selectivity to MIBK, reaching in some experiments between 60 and 80%. A loss of activity with time on stream, probably due to coke deposition was also found. An increase in reduction temperature from 300 to 500°C gives a decrease in MIBK selectivity that is due to an increase in the yield of 2propanol. Key words: acetone, methyl isobutyl ketone, nickel/magnesia
INTRODUCTION
Methyl isobutyl ketone (MIBK), is, by far, the most important product derived from acetone. This compound is mainly used as a solvent for cellulose and resin based coating systems. MIBK is produced commercially in three steps from acetone: liquid phase aldol condensation of acetone to diacetone alcohol (DAA), acid catalyzed dehydration of DAA to mesityl oxide (MSO) and selective hydrogenation of MS0 to MIBK. Recently, a one-step process from acetone to MIBK has become commercially feasible [ 11 and several catalytic systems have been claimed for this process. They mainly consist of palladium supported, for example, on KOH-A1203, MgO-SiOz [ 11, CaO-MgOCorrespondence to: Dr. M. Mantes, Grupo de Ingenieria Quimica, Departamento de Quimica Aplicada, Facultad de Q&mica, Universidad del Pak Vasco, Apdo. 1072,20060 San Sebastihn (Spain). Fax (+ 34-43) 212236.
0926-860X/93/$06.00
0 1993 Elsevier Science Publishers B.V. All rights reserved.
L2
L.M. Gandh and hi. iUontes/Appl.
Catal. A 101(1993) Ll-L6
SrO-A1203 [ 21, Nbz05 [ 31, ZrO (OH),-carbon [ 41, Ce, Hf and/or Ta oxides or hydroxides-carbon [ 51 and cation exchange resins [ 11. Very high selectivities to MIBK ( > 90% ) are described at temperatures in the 80-160°C range and acetone overall conversions near 40%. Nevertheless high operating pressures, typically 10-100 atm are a disadvantage of the single-step process. Hence, the development of catalysts which operate efficiently at atmospheric pressure is desirable. Such materials have been described. For example a nickel TiOzS& supported catalyst has been used in the range 155-270 ’ C [ 11. A catalyst consisting of palladium supported on a silicoaluminophosphate molecular sieve (SAPO-34) has been reported to give 60% selectivity to MIBK with 20% acetone overall conversion at 200” C and 1 atm [ 61. More recently the use of palladium supported on KH-ZSM-5 zeolite has been claimed to give 68% selectivity to MIBK with 45% acetone overall conversion at 250’ C and 1 atm [ 7].2Propanol and diisobutyl ketone (DIBK) are typical byproducts of these processes. In this work, the preliminary results obtained in the gas-phase acetone hydrogenation with a magnesia supported nickel catalyst are reported. This is a very promising catalyst since high MIBK selectivities can be achieved operating at 1 atm. EXPERIMENTAL
A nickel on MgC (Merck, 5862 extra pure) catalyst was prepared by pore volume impregnation, with an aqueous solution of Ni( N03)2*6H20 (Merck p.a. ). After impregnation the solid was dried overnight at 120” C and calcined in air at 450’ C for 16 h. This catalyst will be referred to as (Mg-Ni), its nickel content is 7.1 wt.-%. The support and (Mg-Ni) sample were characterized by nitrogen adsorption at 77 K (Micromeritics ASAP 2000) and X-ray diffraction (Philips APD 1710). Nickel surface areas were measured by hydrogen chemisorption at room temperature using the pulse method (Micromeritics Pulse Chemisorb 2700). Acetone hydrogenation was carried out in a fixed bed reactor operating at 1 atm and 2OO”C, with a feed stream containing 10 or 20 mol-% acetone in hydrogen. Prior to nickel surface area and catalytic activity measurements samples were hydrogen (150 cm3/min) reduced for 12 h at 300 or 500 ’ C [catalysts (Mg-Ni ) 300 and (Mg-Ni ) 500 respectively]. RESULTS AND DISCUSSION
Table 1 includes the specific surface area, SBET,and total pore volume, VP, of the support and (Mg-Ni) sample. The nickel surface area, SNi, and the extent of reduction, f, obtained after hydrogen treatment at 300 and 500’ C are also included. As can be seen, a great increase in specific surface area and total pore volume takes place during the preparation of (Mg-Ni) sample. Very low
I43
L.M. Gandia and M. Montes/Appl. Catal. A 101(1993) Ll-L6 TABLE 1 Physicochemical
properties of the samples
Sample
IBEX
MgO
33 48 -
(Mg-Ni) (Mg-Ni)300 (Mg-Ni)5OO
bZ/&-&.)
VP (cm3/ht.
)
&Vi
b2/d
f(S)
0.14 0.29 0.3 12.5
5 52
1.00 0.80 .g .z
0.60
B &
0.40 0.20 0.00
time(min) Fig. 1. Selectivities MIBK (O),DIBK
(10 mol-% acetone in the feed) of the catalysts (Mg-Ni)300: (A),and (Mg-Ni)BOO:2-propanol (W MIBK (0).
2-propanol(0
),
nickel surfacearea and extent of reductionare attainedafter hydrogenreduction at 300°C. These parameters show a great increase when the (Mg-Ni) sampleis hydrogenreducedat 500” C. Figs. 1 and 2 show the effect of hydrogen reductiontemperatureon the catalytic activity.Experimentswere carriedout at 200°C with a feed stream containing 10 mol-% acetone in hydrogen,and a W/F*,, ratio of 0.0725 (g&h mol acetone). Selectivitieswere defined as the molarfractionof the reactedacetonewhichwas convertedinto a givenproduct. Yields were defined as the molar fraction of the acetone feed which was converted into a given product. 2-Propanol and MIBK were the most abundant products found. Howeverthe (Mg-Ni)300 catalystshoweda veryhighactivity to DIBK formation duringthe first two hours on stream with selectivitiesin the 5-20% range. Methyl isobutyl carbynol (MIBC) was also found with selectivitieslower than 5%. Fig. 1 shows selectivitiesto 2-propanol and MIBK for the ( Mg-Ni ) 300 and (Mg-Ni)500 catalysts.As can be seen, relativelystable selectivitiesto MIBK, around 45%, are obtained with the (Mg-Ni)300 catalyst.However,after reduction at 500°C a dramaticdecreasein the MIBK
IA
L.M. Gandia and M. Montes/Appl.
Catal. A lOl(l993)
Ll-L6
0.50 0.40
3 .2 >
0.30 0.20 0.10 0.00
Fig. 2. Yields (10 mol-% acetone in the feed) of the catalysts (Mg-Ni)BOO: 2-propanol (O), MIBK (O),DIBK (A),and (Mg-Ni)500:2-propanol (W),MIBK (0).
selectivity takes place. In this case, selectivities to 2-propanol higher than 80% are obtained. Fig. 2 explains this result, showing that an additional activity to 2-propanol has been developed in the (Mg-Ni)500 catalyst, and at the same time its activity towards acetone aldol condensation is lowered. Fig. 2 also shows that catalytic activity decreases with time-on-stream. The MIBK formation is more affected than that of 2-propanol, thus explaining the increase of the (Mg-Ni)500 catalyst 2-propanol selectivity with time. Coke deposition could explain the activity decay since multiple condensation between intermediate products such as MS0 or MIBK with acetone will give high molecular weight compounds that could act as a coke precursors. Figs. 3 and 4 consider the effect of the feed stream composition. As Fig. 3 shows, the MIBK selectivity clearly increases when the acetone feed content increases from 10 to 20%. In this case, MIBK selectivities between 60 and 80% can be obtained, whereas f-propanol selectivity is maintained at 20%. After an hour on stream, similar trends in activity loss are found in Fig. 4 for both compositions. From these preliminary results, catalyst activation treatments, temperature and operating conditions seem to have a great influence on MIBK selectivity. The formation of MIBK will involve active sites in the catalyst for acetone aldol condensation to MSO, and for MS0 hydrogenation to MIBK. The main byproduct of this process is formed by direct acetone hydrogenation to P-propanol. The increase of (Mg-Ni ) catalyst hydrogen reduction temperature from 3Od to 500°C causes an increase in Z-propanol formation activity and a decrease in MIBK formation activity (see Fig. 2). The increase in 2-propanol formation activity can be explained by the higher amount of metallic (Ni) sites observed from the increase of metallic surface area (see Table 1) . The decrease
L.M. Gandfa and M. Montes/Appl. Catal. A 101 (1993) Ll -L6
0.00 ti 0
50
loo
150
200
w
250
time@in) Fig. 3. Selectivities of the catalyst (Mg-Ni)BOO, 10 mol-% acetone in the feed: 2-propanol (0 ), MIBK ( 0 ), and 20 mol-% acetone in the feed: 2-propanol (A ), MIBK (A )
0.30
L
0.20
3
5 0.10
0.00
Fig. 4. Yields of the catalyst (Mg-Ni)300,10 mol-% acetone in the feed: 2-propanol ( l ), MIBK ( 0 ) , and 20 mol-% acetone in the feed: 2-propanol ( A ) , MIBK (A ) .
in MIBK activity could be explained by a loss of basic sites responsible for
acetonealdolcondensation.These sitescan be basedon surfacehydroxylgroups whose activity for the acetone aldol condensation has been reported [&J-10]. The possible influence of metal-support interaction compounds with basic charactermust also be considered since NiO easily forms solid solutions with MgO [ 111.Both typesof basic sitescouldbe presentin thesecases.So Mg ( OH)z has been clearlydetected in the uncalcined (Mg-Ni) sampleX-ray diffraction pattern,and dehydroxylationshould increasewhenthe reductiontemperature increases.On the other hand, the very low extents of reductionobtained could be due to the presenceof NiO-MgO solid solutions.Both hydroxyland metal-
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L.M. Gandia and M. Montes/Appl.
Catal. A 101(1993) Ll-L6
support interaction sites will be less abundant after hydrogen reduction at 500 'C, thus explaining the higher activity to MIBK of the ( Mg-Ni ) 300 catalyst. CONCLUSIONS
A Ni/MgG catalyst with high selectivity to methyl isobutyl ketone in the acetone hydrogenation at atmospheric pressure has been described. Improved selectivities to this product can be attained by means of an optimal balance between metal and basic sites. Such a balance can be achieved by an adequate preparation and activation treatment procedure of this catalyst. Operating reaction conditions, mainly acetone/hydrogen feed ratio and temperature will also play an important role. Investigations on these factors are currently in progress in our laboratories. ACKNOWLEDGEMENTS
The scholarship support for L.M. Gandfa by the Ministerio de Education y Ciencia (Programme FPI) and the financial support by the Basque Government (Grant GV 89 No. A9) are gratefully appreciated.
REFERENCES 1 2 3 4 5 6 7 8 9 10 11
Kirk-Gthmer Encyclopedia of Chemical Technology, Vol. 13, Wiley, New York, 1979, p. 907. Y. Too and T. Nakayama, Jpn. Pat. 62 258,335 (Nov. 10,1987), (to Sumitomo Chemical co., Ltd.). T. Maki, T. Yokoyama and Y. Sumino, Jpn. Pat. 63 68,538 (Mar. 28,1988), (to Mitsubishi Chemical Industries Co., Ltd.). T. Maki, T. Yokoyama and Y. Sumino, Jpn. Pat. 63 96,147 (Apr. 27,1988), (to Mitsubishi Chemical Industries Co., Ltd.). T. Maki, T. Yokoyama and Y. Sumino, Jpn. Pat. 63 96,146 (Apr. 27,1988), (to Mitsubishi Chemical Industries Co., Ltd.). K.D. Olson, U.S. Pat. 4 704 478 (Nov. 03,1987), (to Union Carbide Corp.). P.Y. Chen, S.J. Chu, C.C. Chen, N.S. Chang, W.C. Lin andT.K. Chuang, U.S. Pat. 5 059 724 (Oct. 22,1991), (to Industrial Technology Research Institute). G. Zhang, H. Hattori and K. Tanabs, Appl. Catal., 36 (1988) 189. S. Lippert, W. Baumann and K. Thomke, J. Mol. Cat&, 69 (1991) 199. W.T. Reichle, J. Cat&, 63 (1980) 295. F. Arena, B.A. HorreIl, D.L. Cocke, A. Parmahana and N. Giordano, J. Catal., 132 (1991) 58.
Ll
APCAT A2559
Highly selective one-step formation of methyl isobutyl ketone from acetone with a magnesia supported nickel catalyst Luis M. Gandfa and Mario Montes Grupo de Ingenieria Q&mica, Departamento de Quimica Aplicada, Facultad de Quimica, Universidad de1 Pais Vasco, Apdo. 1072,20080 San Sebasticin (Spain) (Received 17 May 1993)
Abstract A new catalyst for the production of methyl isobutyl ketone (MIBK ) from acetone and hydrogen in one step at atmospheric pressure has been prepared. The catalyst was obtained by impregnation of MgO with an aqueous solution of nickel nitrate, dried, calcined in air and reduced in hydrogen. This catalyst showed a high selectivity to MIBK, reaching in some experiments between 60 and 80%. A loss of activity with time on stream, probably due to coke deposition was also found. An increase in reduction temperature from 300 to 500°C gives a decrease in MIBK selectivity that is due to an increase in the yield of 2propanol. Key words: acetone, methyl isobutyl ketone, nickel/magnesia
INTRODUCTION
Methyl isobutyl ketone (MIBK), is, by far, the most important product derived from acetone. This compound is mainly used as a solvent for cellulose and resin based coating systems. MIBK is produced commercially in three steps from acetone: liquid phase aldol condensation of acetone to diacetone alcohol (DAA), acid catalyzed dehydration of DAA to mesityl oxide (MSO) and selective hydrogenation of MS0 to MIBK. Recently, a one-step process from acetone to MIBK has become commercially feasible [ 11 and several catalytic systems have been claimed for this process. They mainly consist of palladium supported, for example, on KOH-A1203, MgO-SiOz [ 11, CaO-MgOCorrespondence to: Dr. M. Mantes, Grupo de Ingenieria Quimica, Departamento de Quimica Aplicada, Facultad de Q&mica, Universidad del Pak Vasco, Apdo. 1072,20060 San Sebastihn (Spain). Fax (+ 34-43) 212236.
0926-860X/93/$06.00
0 1993 Elsevier Science Publishers B.V. All rights reserved.
L2
L.M. Gandh and hi. iUontes/Appl.
Catal. A 101(1993) Ll-L6
SrO-A1203 [ 21, Nbz05 [ 31, ZrO (OH),-carbon [ 41, Ce, Hf and/or Ta oxides or hydroxides-carbon [ 51 and cation exchange resins [ 11. Very high selectivities to MIBK ( > 90% ) are described at temperatures in the 80-160°C range and acetone overall conversions near 40%. Nevertheless high operating pressures, typically 10-100 atm are a disadvantage of the single-step process. Hence, the development of catalysts which operate efficiently at atmospheric pressure is desirable. Such materials have been described. For example a nickel TiOzS& supported catalyst has been used in the range 155-270 ’ C [ 11. A catalyst consisting of palladium supported on a silicoaluminophosphate molecular sieve (SAPO-34) has been reported to give 60% selectivity to MIBK with 20% acetone overall conversion at 200” C and 1 atm [ 61. More recently the use of palladium supported on KH-ZSM-5 zeolite has been claimed to give 68% selectivity to MIBK with 45% acetone overall conversion at 250’ C and 1 atm [ 7].2Propanol and diisobutyl ketone (DIBK) are typical byproducts of these processes. In this work, the preliminary results obtained in the gas-phase acetone hydrogenation with a magnesia supported nickel catalyst are reported. This is a very promising catalyst since high MIBK selectivities can be achieved operating at 1 atm. EXPERIMENTAL
A nickel on MgC (Merck, 5862 extra pure) catalyst was prepared by pore volume impregnation, with an aqueous solution of Ni( N03)2*6H20 (Merck p.a. ). After impregnation the solid was dried overnight at 120” C and calcined in air at 450’ C for 16 h. This catalyst will be referred to as (Mg-Ni), its nickel content is 7.1 wt.-%. The support and (Mg-Ni) sample were characterized by nitrogen adsorption at 77 K (Micromeritics ASAP 2000) and X-ray diffraction (Philips APD 1710). Nickel surface areas were measured by hydrogen chemisorption at room temperature using the pulse method (Micromeritics Pulse Chemisorb 2700). Acetone hydrogenation was carried out in a fixed bed reactor operating at 1 atm and 2OO”C, with a feed stream containing 10 or 20 mol-% acetone in hydrogen. Prior to nickel surface area and catalytic activity measurements samples were hydrogen (150 cm3/min) reduced for 12 h at 300 or 500 ’ C [catalysts (Mg-Ni ) 300 and (Mg-Ni ) 500 respectively]. RESULTS AND DISCUSSION
Table 1 includes the specific surface area, SBET,and total pore volume, VP, of the support and (Mg-Ni) sample. The nickel surface area, SNi, and the extent of reduction, f, obtained after hydrogen treatment at 300 and 500’ C are also included. As can be seen, a great increase in specific surface area and total pore volume takes place during the preparation of (Mg-Ni) sample. Very low
I43
L.M. Gandia and M. Montes/Appl. Catal. A 101(1993) Ll-L6 TABLE 1 Physicochemical
properties of the samples
Sample
IBEX
MgO
33 48 -
(Mg-Ni) (Mg-Ni)300 (Mg-Ni)5OO
bZ/&-&.)
VP (cm3/ht.
)
&Vi
b2/d
f(S)
0.14 0.29 0.3 12.5
5 52
1.00 0.80 .g .z
0.60
B &
0.40 0.20 0.00
time(min) Fig. 1. Selectivities MIBK (O),DIBK
(10 mol-% acetone in the feed) of the catalysts (Mg-Ni)300: (A),and (Mg-Ni)BOO:2-propanol (W MIBK (0).
2-propanol(0
),
nickel surfacearea and extent of reductionare attainedafter hydrogenreduction at 300°C. These parameters show a great increase when the (Mg-Ni) sampleis hydrogenreducedat 500” C. Figs. 1 and 2 show the effect of hydrogen reductiontemperatureon the catalytic activity.Experimentswere carriedout at 200°C with a feed stream containing 10 mol-% acetone in hydrogen,and a W/F*,, ratio of 0.0725 (g&h mol acetone). Selectivitieswere defined as the molarfractionof the reactedacetonewhichwas convertedinto a givenproduct. Yields were defined as the molar fraction of the acetone feed which was converted into a given product. 2-Propanol and MIBK were the most abundant products found. Howeverthe (Mg-Ni)300 catalystshoweda veryhighactivity to DIBK formation duringthe first two hours on stream with selectivitiesin the 5-20% range. Methyl isobutyl carbynol (MIBC) was also found with selectivitieslower than 5%. Fig. 1 shows selectivitiesto 2-propanol and MIBK for the ( Mg-Ni ) 300 and (Mg-Ni)500 catalysts.As can be seen, relativelystable selectivitiesto MIBK, around 45%, are obtained with the (Mg-Ni)300 catalyst.However,after reduction at 500°C a dramaticdecreasein the MIBK
IA
L.M. Gandia and M. Montes/Appl.
Catal. A lOl(l993)
Ll-L6
0.50 0.40
3 .2 >
0.30 0.20 0.10 0.00
Fig. 2. Yields (10 mol-% acetone in the feed) of the catalysts (Mg-Ni)BOO: 2-propanol (O), MIBK (O),DIBK (A),and (Mg-Ni)500:2-propanol (W),MIBK (0).
selectivity takes place. In this case, selectivities to 2-propanol higher than 80% are obtained. Fig. 2 explains this result, showing that an additional activity to 2-propanol has been developed in the (Mg-Ni)500 catalyst, and at the same time its activity towards acetone aldol condensation is lowered. Fig. 2 also shows that catalytic activity decreases with time-on-stream. The MIBK formation is more affected than that of 2-propanol, thus explaining the increase of the (Mg-Ni)500 catalyst 2-propanol selectivity with time. Coke deposition could explain the activity decay since multiple condensation between intermediate products such as MS0 or MIBK with acetone will give high molecular weight compounds that could act as a coke precursors. Figs. 3 and 4 consider the effect of the feed stream composition. As Fig. 3 shows, the MIBK selectivity clearly increases when the acetone feed content increases from 10 to 20%. In this case, MIBK selectivities between 60 and 80% can be obtained, whereas f-propanol selectivity is maintained at 20%. After an hour on stream, similar trends in activity loss are found in Fig. 4 for both compositions. From these preliminary results, catalyst activation treatments, temperature and operating conditions seem to have a great influence on MIBK selectivity. The formation of MIBK will involve active sites in the catalyst for acetone aldol condensation to MSO, and for MS0 hydrogenation to MIBK. The main byproduct of this process is formed by direct acetone hydrogenation to P-propanol. The increase of (Mg-Ni ) catalyst hydrogen reduction temperature from 3Od to 500°C causes an increase in Z-propanol formation activity and a decrease in MIBK formation activity (see Fig. 2). The increase in 2-propanol formation activity can be explained by the higher amount of metallic (Ni) sites observed from the increase of metallic surface area (see Table 1) . The decrease
L.M. Gandfa and M. Montes/Appl. Catal. A 101 (1993) Ll -L6
0.00 ti 0
50
loo
150
200
w
250
time@in) Fig. 3. Selectivities of the catalyst (Mg-Ni)BOO, 10 mol-% acetone in the feed: 2-propanol (0 ), MIBK ( 0 ), and 20 mol-% acetone in the feed: 2-propanol (A ), MIBK (A )
0.30
L
0.20
3
5 0.10
0.00
Fig. 4. Yields of the catalyst (Mg-Ni)300,10 mol-% acetone in the feed: 2-propanol ( l ), MIBK ( 0 ) , and 20 mol-% acetone in the feed: 2-propanol ( A ) , MIBK (A ) .
in MIBK activity could be explained by a loss of basic sites responsible for
acetonealdolcondensation.These sitescan be basedon surfacehydroxylgroups whose activity for the acetone aldol condensation has been reported [&J-10]. The possible influence of metal-support interaction compounds with basic charactermust also be considered since NiO easily forms solid solutions with MgO [ 111.Both typesof basic sitescouldbe presentin thesecases.So Mg ( OH)z has been clearlydetected in the uncalcined (Mg-Ni) sampleX-ray diffraction pattern,and dehydroxylationshould increasewhenthe reductiontemperature increases.On the other hand, the very low extents of reductionobtained could be due to the presenceof NiO-MgO solid solutions.Both hydroxyland metal-
L6
L.M. Gandia and M. Montes/Appl.
Catal. A 101(1993) Ll-L6
support interaction sites will be less abundant after hydrogen reduction at 500 'C, thus explaining the higher activity to MIBK of the ( Mg-Ni ) 300 catalyst. CONCLUSIONS
A Ni/MgG catalyst with high selectivity to methyl isobutyl ketone in the acetone hydrogenation at atmospheric pressure has been described. Improved selectivities to this product can be attained by means of an optimal balance between metal and basic sites. Such a balance can be achieved by an adequate preparation and activation treatment procedure of this catalyst. Operating reaction conditions, mainly acetone/hydrogen feed ratio and temperature will also play an important role. Investigations on these factors are currently in progress in our laboratories. ACKNOWLEDGEMENTS
The scholarship support for L.M. Gandfa by the Ministerio de Education y Ciencia (Programme FPI) and the financial support by the Basque Government (Grant GV 89 No. A9) are gratefully appreciated.
REFERENCES 1 2 3 4 5 6 7 8 9 10 11
Kirk-Gthmer Encyclopedia of Chemical Technology, Vol. 13, Wiley, New York, 1979, p. 907. Y. Too and T. Nakayama, Jpn. Pat. 62 258,335 (Nov. 10,1987), (to Sumitomo Chemical co., Ltd.). T. Maki, T. Yokoyama and Y. Sumino, Jpn. Pat. 63 68,538 (Mar. 28,1988), (to Mitsubishi Chemical Industries Co., Ltd.). T. Maki, T. Yokoyama and Y. Sumino, Jpn. Pat. 63 96,147 (Apr. 27,1988), (to Mitsubishi Chemical Industries Co., Ltd.). T. Maki, T. Yokoyama and Y. Sumino, Jpn. Pat. 63 96,146 (Apr. 27,1988), (to Mitsubishi Chemical Industries Co., Ltd.). K.D. Olson, U.S. Pat. 4 704 478 (Nov. 03,1987), (to Union Carbide Corp.). P.Y. Chen, S.J. Chu, C.C. Chen, N.S. Chang, W.C. Lin andT.K. Chuang, U.S. Pat. 5 059 724 (Oct. 22,1991), (to Industrial Technology Research Institute). G. Zhang, H. Hattori and K. Tanabs, Appl. Catal., 36 (1988) 189. S. Lippert, W. Baumann and K. Thomke, J. Mol. Cat&, 69 (1991) 199. W.T. Reichle, J. Cat&, 63 (1980) 295. F. Arena, B.A. HorreIl, D.L. Cocke, A. Parmahana and N. Giordano, J. Catal., 132 (1991) 58.