Patent Application: US-201414249955-A

Abstract:
the provided is a preparation method of a platinum / tin / alumina catalyst which comprises platinum as an active component having high activity to direct dehydrogenation of n - butane , tin capable of preventing platinum particles from being sintered and maintaining a size of the platinum particles to be small , thereby improving dispersibility and increasing an amount at an active site during the dehydrogenation and also capable of suppressing carbon deposition , thereby increasing stability of the catalyst , and as an support for supporting them , an alumina support which is known as being suitable for direct dehydrogenation of n - butane and is capable of maintaining high dispersibility of the platinum with high thermal and mechanical stability , and a method for producing high value - added c4 olefins through direct dehydrogenation of inexpensive n - butane by using the catalyst prepared by the preparation method .

Description:
in order to achieve the above object , the present invention provides a preparation method of a platinum / tin / alumina catalyst for direct dehydrogenation of n - butane comprising the following steps : ( a ) preparing a tin precursor solution by dissolving a tin precursor and an acid in a first solvent ; ( b ) impregnating the tin precursor solution on a basic alumina support ; ( c ) obtaining tin / alumina in which tin is impregnated on the alumina support by heat drying and heat treating a product obtained from the step ( b ); ( d ) preparing a platinum precursor solution by dissolving a platinum precursor in a second solvent ; ( e ) impregnating the platinum precursor solution on the tin / alumina prepared in the step ( c ); and ( f ) obtaining the platinum / tin / alumina catalyst for direct dehydrogenation of n - butane by heat drying and heat treating a product obtained from the step ( e ). the tin precursor used in the step ( a ) may be any precursor as long as it is a precursor typically used . in general , it is desirable to use at least one selected from a group consisting of tin chloride , tin nitride , tin bromide , tin oxide and tin acetate . in particular , it is desirable to use the tin chloride ( tin ( ii ) chloride ). an amount of the tin precursor used in the step ( a ) is not particularly limited , but in order to prepare the platinum / tin / alumina catalyst capable of maintaining high activity for a long time as the object of the present invention , a tin content is 0 . 5 to 10 wt %, and desirably 1 wt %, based on the total weight of a final platinum / tin / alumina catalyst . if tin is added in an amount of more than 10 wt %, platinum active sites in the prepared catalyst are decreased , thereby resulting in a decrease in catalytic activity , which is not desirable . meanwhile , if tin is added in an amount of less than 0 . 5 wt %, the tin does not perform its ability for preventing the platinum from being sintered and maintaining a small particle size of the platinum , thereby resulting in improvement of dispersibility and suppressing carbon deposition , which is not desirable . the acid used in the step ( a ) exists at room temperature in the form of a liquid ( solution ) and may be , but not limited to , at least one selected from a group consisting of hydrochloric acid , nitric acid , sulfuric acid , hydrofluoric acid and phosphoric acid . the first solvent and the second solvent respectively used in the step ( a ) and the step ( d ) may be selected from , but not limited to , water and alcohol , and desirably may be water . preferably , the alumina used in the step ( b ) may be basic alumina . typically , alumina can be classified into acidic alumina , neutral alumina , and basic alumina . herein , the criteria for classification to acidic alumina , neutral alumina and basic alumina may be a ph in a state where alumina is dispersed in water , and the basic alumina has a ph of 9 . 0 to 10 . 0 , the neutral alumina has a ph of 6 . 5 to 7 . 5 , and the acidic alumina has a ph of 6 . 0 or less . among the acidic alumina , alumina having a ph of 4 . 0 to 6 . 0 may be classified as weakly acidic alumina . the present invention first discloses that since the basic alumina is used , a catalyst having high activity and high c4 olefin selectivity can be prepared . the purpose of the heat drying in the step ( c ) is to remove remaining moisture after impregnating the tin . therefore , a drying temperature and a drying time can be determined according to typical drying conditions for removing moisture . for example , a drying temperature may be determined in a range of 50 to 200 ° c ., and preferably 70 to 120 ° c ., and a drying time may be determined in a range of 3 to 24 hours , and preferably 6 to 12 hours . further , the purpose of the heat treatment in the step ( c ) is to synthesize tin / alumina , and the heat treatment is carried out at 350 to 1000 ° c ., and preferably at 500 to 800 ° c . for 1 to 12 hours , and preferably for 3 to 6 hours . if the heat treatment is carried out at a temperature lower than 350 ° c . or for a time shorter than 1 hour , tin / alumina is not sufficiently synthesized , which is not desirable . if the heat treatment is carried out at a temperature higher than 1000 ° c . or for a time longer than 12 hours , a phase of tin / alumina can be modified , which is not desirable . the platinum precursor used in the step ( d ) may be any precursor as long as it is a precursor typically used . in general , it is desirable to use at least one selected from a group consisting of chloroplatinic acid , platinum oxide , platinum chloride and platinum bromide . in particular , it is desirable to use the chloroplatinic acid . further , an amount of the platinum precursor used in the step ( d ) is not particularly limited , but in order to prepare the platinum / tin / alumina catalyst capable of maintaining high activity for a long time as the object of the present invention , a platinum content is 0 . 5 to 10 wt %, and preferably 1 wt %, based on the total weight of the final platinum / tin / alumina catalyst . if platinum is added in an amount of more than 10 wt %, it becomes difficult to obtain a catalyst having high dispersibility of the platinum and expensive platinum may be overused , which is not desirable . meanwhile , if platinum is added in an amount of less than 0 . 5 wt %, active sites of the platinum as an active metal for the direct dehydrogenation of n - butane are not sufficiently formed and it becomes difficult to produce c4 olefins with high selectivity and high yield , which is not desirable . the purpose of the heat drying in the step ( f ) is to remove remaining moisture after impregnating the platinum . therefore , a drying temperature and a drying time can be determined according to typical drying conditions for removing moisture . for example , a drying temperature may be determined in a range of 50 to 200 ° c ., and preferably 70 to 120 ° c ., and a drying time may be determined in a range of 3 to 24 hours , and preferably 6 to 12 hours . further , the heat treatment in the step ( f ) can be carried out at a temperature of 400 to 800 ° c . for 1 to 12 hours , and preferably at a temperature of 500 to 700 ° c . for 3 to 6 hours , whereby the platinum / tin / alumina catalyst can be obtained . the purpose of the heat treating the dried solid sample is not only to obtain platinum / tin / alumina catalyst but also to suppress modification of the catalyst when the prepared catalyst is used in the direct dehydrogenation of n - butane considering a reaction temperature of the reaction . if the heat treatment is carried out at a temperature lower than 400 ° c . or for a time shorter than 1 hour , the platinum / tin / alumina catalyst is not sufficiently formed , which is not desirable . if the heat treatment is carried out at a temperature higher than 800 ° c . or for a time longer than 12 hours , a crystalline phase of the platinum / tin / alumina catalyst can be modified to a phase unsuitable to be used as a catalyst , which is not desirable . further , exemplary embodiment of the present invention provides a method for producing c4 olefins through direct dehydrogenation of n - butane on a platinum / tin / alumina catalyst prepared by the above - described method . a reactant of the direct dehydrogenation of n - butane is a mixed gas containing n - butane and nitrogen , and a volume ratio of the n - butane to the nitrogen is 1 : 0 . 2 to 10 , and preferably 1 : 0 . 5 to 5 , and more preferably 1 : 1 . if a volume ratio of the n - butane to the nitrogen is out of the above - described range , deactivation may rapidly occur due to coking during the direct dehydrogenation of n - butane , or activity or selectivity of the catalyst may be decreased , resulting in a decrease in production of c4 olefins , and there may be a problem with safety of the process , which is not desirable . when the reactant in the form of a mixed gas is supplied to a reactor , an injection amount of the reactant can be regulated by using a mass flow controller . the injection amount of the reactant may be set such that a weight hourly space velocity ( whsv ) can be 10 to 6000 cc · hr − 1 · gcat − 1 , and preferably 100 to 3000 cc · hr − 1 · gcat − 1 , and more preferably 300 to 1000 cc · hr − 1 · gcat − 1 with respect to the n - butane . if a weight hourly space velocity is less than 10 cc · hr − 1 · gcat − 1 , production of c4 olefins is too small , which is not desirable . if a weight hourly space velocity is more than 6000 cc · hr − 1 · gcat − 1 , coking and deposition rapidly occurs due to by - products of the reaction , which is not desirable . a reaction temperature for carrying out the direct dehydrogenation of n - butane may be desirably 300 to 800 ° c . and more preferably 500 to 600 ° c ., and it is most desirable to maintain a reaction temperature at 550 ° c . if the reaction temperature is lower than 300 ° c ., a reaction of the n - butane is not sufficiently activated , which is not desirable . if the reaction temperature is higher than 800 ° c ., a decomposition reaction of the n - butane mainly occurs , which is not desirable . according to the present invention , a platinum / tin / alumina catalyst can be easily prepared through a simple preparation method , and a high reproducibility in preparing the catalyst can be attained . further , by using the platinum / tin / alumina catalyst according to the present invention , it is possible to produce c4 olefins , which has been gradually increased in demand and value all over the world , from n - butane which is less useful . thus , it is possible to add a high value to c4 fractions . furthermore , since a single production process capable of producing c4 olefins by using the platinum / tin / alumina catalyst according to the present invention is obtained , an increasing demand for c4 olefins can be met without newly installing naphtha cracking center facilities , whereby financial benefits can be gained . fig1 is a graph showing a difference in yield among platinum / tin / alumina catalysts during direct dehydrogenation of n - butane carried out on each of the platinum / tin / alumina catalysts according to example 1 and comparative example 1 for 270 minutes ; fig2 is a graph showing a difference in selectivity among platinum / tin / alumina catalysts during direct dehydrogenation of n - butane carried out on each of the platinum / tin / alumina catalysts according to example 1 and comparative example 1 for 270 minutes ; and fig3 is a graph showing a distribution chart of products with respect to reactants of direct dehydrogenation of n - butane using respective platinum / tin / alumina catalysts after the direct dehydrogenation of n - butane carried out on each of the platinum / tin / alumina catalysts according to example 1 and comparative example 1 for 270 minutes . hereinafter , the present invention will be explained in more detail with reference to exemplary embodiments . however , these exemplary embodiments are provided just for illustration , but do not limit the present invention . preparation of platinum / tin / alumina ( pt / sn / al 2 o 3 ( b )) catalyst by impregnating tin and platinum in serial order on basic alumina ( aluminum oxide ) by using basic alumina ( aluminum oxide ; manufactured by acros ) to prepare tin / alumina impregnating tin to be in an amount of 1 wt %, 0 . 038 g of tin ( ii ) chloride dihydrate as a tin precursor was put into a beaker to be dissolved in a small amount of hydrochloric acid ( 0 . 37 ml ) and distilled water ( 15 ml ). when the tin precursor was completely dissolved in the solution prepared as such , 2 . 0 g of the basic alumina was added thereto and heated at 70 ° c . with stirring until the distilled water was completely evaporated . as a result , a solid material remained . then , the solid material was additionally dried in an oven at 80 ° c . for 12 hours , and a resultant sample was heat treated in an electric furnace in an air atmosphere at 600 ° c . for 4 hours . as a result , tin / alumina impregnating tin in an amount of 1 wt % on alumina was obtained . 0 . 053 g of chloroplatinic acid hexahydrate as a platinum precursor was put into a beaker to be dissolved in distilled water ( 10 ml ) such that a platinum content could be 1 wt % in 2 . 0 g of the tin / alumina sample obtained as such . when the platinum precursor was completely dissolved in the solution , 2 . 0 g of the prepared tin / alumina was added to the precursor solution and then stirred at 70 ° c . until the distilled water was completely evaporated . then , a remaining solid material was additionally dried in an oven at 80 ° c . for 12 hours , and a resultant sample was heat treated in an electric furnace in an air atmosphere at 550 ° c . for 4 hours . as a result , a platinum / tin / alumina catalyst was prepared , and the prepared catalyst was named pt / sn / al 2 o 3 ( b ). preparation of platinum / tin / alumina ( pt / sn / al 2 o 3 ( n )) catalyst by impregnating tin and platinum in serial order on neutral alumina ( aluminum oxide , activated ) by using neutral alumina ( aluminum oxide , activated ; manufactured by sigma - aldrich ) to prepare tin / alumina impregnating tin to be in an amount of 1 wt %, 0 . 038 g of tin ( ii ) chloride dihydrate as a tin precursor was put into a beaker to be dissolved in a small amount of hydrochloric acid ( 0 . 37 ml ) and distilled water ( 15 ml ). when the tin precursor was completely dissolved in the solution prepared as such , 2 . 0 g of the neutral alumina was added thereto and heated at 70 ° c . with stirring until the distilled water was completely evaporated . as a result , a solid material remained . then , the solid material was additionally dried in an oven at 80 ° c . for 12 hours , and a resultant sample was heat treated in an electric furnace in an air atmosphere at 600 ° c . for 4 hours . as a result , tin / alumina impregnating tin in an amount of 1 wt % on alumina was obtained . 0 . 053 g of chloroplatinic acid hexahydrate as a platinum precursor was put into a beaker to be dissolved in distilled water ( 10 ml ) such that a platinum content could be 1 wt % in 2 . 0 g of the tin / alumina sample obtained as above . when the platinum precursor was completely dissolved in the solution , 2 . 0 g of the prepared tin / alumina was added to the precursor solution and then stirred at 70 ° c . until the distilled water was completely evaporated . then , a remaining solid material was additionally dried in an oven at 80 ° c . for 12 hours , and a resultant sample was heat treated in an electric furnace in an air atmosphere at 550 ° c . for 4 hours . as a result , a platinum / tin / alumina catalyst was prepared , and the prepared catalyst was named pt / sn / al 2 o 3 ( n ). preparation of platinum / tin / alumina ( pt / sn / al 2 o 3 ( a )) catalyst by impregnating tin and platinum in serial order on acidic alumina ( aluminum oxide , activated ) by using acidic alumina ( aluminum oxide , activated ; manufactured by sigma - aldrich ) to prepare tin / alumina impregnating tin to be in an amount of 1 wt %, 0 . 038 g of tin ( ii ) chloride dihydrate as a tin precursor was put into a beaker to be dissolved in a small amount of hydrochloric acid ( 0 . 37 ml ) and distilled water ( 15 ml ). when the tin precursor was completely dissolved in the solution prepared as such , 2 . 0 g of the acidic alumina was added thereto and heated at 70 ° c . with stirring until the distilled water was completely evaporated . as a result , a solid material remained . then , the solid material was additionally dried in an oven at 80 ° c . for 12 hours , and a resultant sample was heat treated in an electric furnace in an air atmosphere at 600 ° c . for 4 hours . as a result , tin / alumina impregnating tin in an amount of 1 wt % on alumina was obtained . 0 . 053 g of chloroplatinic acid hexahydrate as a platinum precursor was put into a beaker to be dissolved in distilled water ( 10 ml ) such that a platinum content could be 1 wt % in 2 . 0 g of the tin / alumina sample obtained as above . when the platinum precursor was completely dissolved in the solution , 2 . 0 g of the prepared tin / alumina was added to the precursor solution and then stirred at 70 ° c . until the distilled water was completely evaporated . then , a remaining solid material was additionally dried in an oven at 80 ° c . for 12 hours , and a resultant sample was heat treated in an electric furnace in an air atmosphere at 550 ° c . for 4 hours . as a result , a platinum / tin / alumina catalyst was prepared , and the prepared catalyst was named pt / sn / al 2 o 3 ( a ). preparation of platinum / tin / alumina ( pt / sn / al 2 o 3 ( wa )) catalyst by impregnating tin and platinum in serial order on weakly acidic alumina ( activated alumina ) by using weakly acidic alumina ( activated alumina ; manufactured by sigma - aldrich ) to prepare tin / alumina impregnating tin to be in an amount of 1 wt %, 0 . 038 g of tin ( ii ) chloride dihydrate as a tin precursor was put into a beaker to be dissolved in a small amount of hydrochloric acid ( 0 . 37 ml ) and distilled water ( 15 ml ). when the tin precursor was completely dissolved in the solution prepared as such , 2 . 0 g of the weakly acidic alumina was added thereto and heated at 70 ° c . with stirring until the distilled water was completely evaporated . as a result , a solid material remained . then , the solid material was additionally dried in an oven at 80 ° c . for 12 hours , and a resultant sample was heat treated in an electric furnace in an air atmosphere at 600 ° c . for 4 hours . as a result , tin / alumina impregnating tin in an amount of 1 wt % on alumina was obtained . 0 . 053 g of chloroplatinic acid hexahydrate as a platinum precursor was put into a beaker to be dissolved in distilled water ( 10 ml ) such that a platinum content could be 1 wt % in 2 . 0 g of the tin / alumina sample obtained as above . when the platinum precursor was completely dissolved in the solution , 2 . 0 g of the prepared tin / alumina was added to the precursor solution and then stirred at 70 ° c . until the distilled water was completely evaporated . then , a remaining solid material was additionally dried in an oven at 80 ° c . for 12 hours , and a resultant sample was heat treated in an electric furnace in an air atmosphere at 550 ° c . for 4 hours . as a result , a platinum / tin / alumina catalyst was prepared , and the prepared catalyst was named pt / sn / al 2 o 3 ( wa ). with the platinum / tin / alumina catalyst prepared by the method of preparation example 1 , a direct dehydrogenation of n - butane was carried out . detailed experimental conditions of the reaction were as follows . a reactant used in the direct dehydrogenation of n - butane of example 1 was a c4 mixture containing n - butane in an amount of 99 . 65 wt %, and a composition thereof was as shown in table 1 below . a linear quartz reactor was installed in an electric furnace for the catalytic reaction , and the quartz reactor was filled with the catalyst . in order to activate the catalyst prior to the reaction , a reducing process was carried out . in the reducing process , a temperature of a fixed bed reactor was increased from room temperature to 570 ° c . and maintained at 570 ° c . for 3 hours , and a mixed gas for reduction was injected such that a ratio of hydrogen to nitrogen became 1 : 1 , and an amount of the catalyst was set such that an injection rate became 600 cc · hr − 1 · gcat − 1 with respect to the hydrogen . then , a temperature of the reactor was decreased to 550 ° c ., and the c4 mixture containing n - butane and the nitrogen were allowed to pass through a catalyst layer at 550 ° c . direct dehydrogenation of n - butane was carried out as such . in this case , a gas for reaction was injected such that a ratio of the n - butane to the nitrogen became 1 : 1 , and an injection rate was set to be 600 cc · hr − 1 · gcat − 1 with respect to the set amount of the catalyst and the n - butane . a product contained by - products ( methane , ethane , ethylene , propane and propylene ) caused by cracking , by - products such as i - butane caused by isomerization , and unreacted n - butane in addition to c4 olefins ( 1 - butene , 2 - butene , i - butene , and 1 , 3 - butadiene ) as main products of the present reaction . thus , a gas chromatography was used to separate and analyze the product . a conversion rate of n - butane , and c4 olefin selectivity and yield in the direct dehydrogenation of n - butane carried out on the platinum / tin / alumina catalyst prepared in preparation example 1 were calculated by equations 1 , 2 , and 3 as follows . the direct dehydrogenation of n - butane was carried out on the platinum / tin / alumina catalyst prepared in preparation example 1 for 270 minutes . development of reaction activity with time for 270 minutes was as shown in table 2 . development of change in c4 olefin yield was as shown in fig1 and development of change in c4 olefin selectivity was as shown in fig2 . further , a reaction result at the time of 270 minutes during the reaction was as shown in table 3 and fig3 . referring to table 2 , table 3 , and fig1 to 3 , in the case of the direct dehydrogenation of n - butane carried out by using the catalyst pt / sn / al 2 o 3 ( b ), deactivation tended to gradually occur as time passed ( the conversion rate and yield decreased ), whereas the selectivity tended to increase . it is deemed that the deactivation occurred due to coking and deposition as reported in several prior documents . the selectivity of c4 olefins ( 1 - butene , 2 - butene , i - butene , and 1 , 3 - butadiene ) was as high as 90 % or more , and main by - products were cracked materials ( methane , ethane , ethylene , propane , and propylene ). reaction activity in direct dehydrogenation of n - butane using platinum / tin / alumina catalysts ( pt / sn / al 2 o 3 ( n ), pt / sn / al 2 o 3 ( a ), and pt / sn / al 2 o 3 ( wa )) respectively prepared by methods of comparative preparation examples 1 to 3 for comparison with the result of reaction activity in the direct dehydrogenation of n - butane using the platinum / tin / alumina catalyst ( pt / sn / al 2 o 3 ( b )) prepared by using the basic alumina ( aluminum oxide ) in preparation example 1 , direct dehydrogenation of n - butane was carried out in the same manner as example 1 except that the platinum / tin / alumina catalysts ( pt / sn / al 2 o 3 ( n ), pt / sn / al 2 o 3 ( a ), and pt / sn / al 2 o 3 ( wa )) respectively prepared by using the neutral alumina ( aluminum oxide , activated ), the acidic alumina ( aluminum oxide , activated ), and the weakly acidic alumina ( activated alumina ) by the methods of comparative preparation examples 1 to 3 were used . a reaction result of comparative example 1 was as shown in tables 4 to 7 and fig1 to 3 . development of reaction activity with time for 270 minutes in direct dehydrogenation of n - butane using the catalyst pt / sn / al 2 o 3 ( n ), the catalyst pt / sn / al 2 o 3 ( a ), and the catalyst pt / sn / al 2 o 3 ( wa ) was as shown in table 4 , table 5 , and table 6 , respectively . development of change in c4 olefin yield was as shown in fig1 and development of change in c4 olefin selectivity was as shown in fig2 . further , a reaction result at the time of 270 minutes during the reaction was as shown in table 7 and fig3 . referring to tables 4 to 7 , and fig1 to 3 , in the activity experiments of the catalysts respectively prepared in comparative preparation examples 1 to 3 , all of the catalysts tended to be deactivated as time passed ( the conversion rate and yield decreased ), whereas the selectivity tended to increase . by comparison with the result of example 1 , the catalyst pt / sn / al 2 o 3 ( b ) prepared in preparation example 1 by impregnating tin and platinum in serial order on basic alumina ( aluminum oxide ) had higher activity and selectivity than the catalysts ( pt / sn / al 2 o 3 ( n ), pt / sn / al 2 o 3 ( a ), and pt / sn / al 2 o 3 ( wa )) respectively prepared by the methods of comparative preparation examples 1 to 3 , and particularly had high c4 olefin selectivity . further , the results of example 1 show that a deactivation degree of the catalyst was decreased as time passed . accordingly , it was confirmed that the catalyst pt / sn / al 2 o 3 ( b ) prepared by impregnating tin and platinum in serial order on basic alumina ( aluminum oxide ) according to the present invention was most suitable as a catalyst for direct dehydrogenation of n - butane . patent document 1 : u . s . pat . no . 6 , 433 , 241 b2 ( a . wu , c . a . drake ) aug . 13 , 2002 patent document 2 : u . s . pat . no . 6 , 187 , 984 b1 ( a . wu , c 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