WO2009045002A1

WO2009045002A1 - Method of preparing zinc ferrite catalysts using buffer solution and method of preparing 1,3-butadiene using said catalysts

Info

Publication number: WO2009045002A1
Application number: PCT/KR2008/005095
Authority: WO
Inventors: Young Min Chung; Tae Jin Kim; Seong Jun Lee; Yong Seung Kim; Seung Hoon Oh; In Kyu Song; Hee Soo Kim; Ji Chul Jung; Ho Won Lee
Original assignee: Sk Energy Co., Ltd.
Priority date: 2007-10-02
Filing date: 2008-08-29
Publication date: 2009-04-09
Also published as: KR20090034139A; KR100950373B1

Abstract

The present invention relates to a method of preparing a zinc ferrite catalyst using a buffer solution and a method of producing 1,3-butadiene using the zinc ferrite catalyst, and, more particularly, to a method of preparing a zinc ferrite catalyst directly using a buffer solution as a coprecipitation medium without adjusting the pH of a coprecipitation solution by additionally adding acids and bases to the coprecipitation solution, and a method of producing 1,3-butadiene using the zinc ferrite catalyst through the oxidative dehydrogenation reaction of a C4 mixture including n-butene and n-butane.

Description

[DESCRIPTION] [Invention Title]

METHOD OF PREPARING ZINC FERRITE CATALYSTS USING BUFFER SOLUTION AND METHOD OF PREPARING 1,3-BUTADIENE USING SAID CATALYSTS [Technical Field]

The present invention relates to a method of preparing a zinc ferrite catalyst using a buffer solution and a method of producing 1,3-butadiene using the zinc ferrite catalyst, and, more particularly, to a method of preparing a zinc ferrite catalyst through a precipitation process in a state in which pH of a coprecipitation solution is constantly maintained using a buffer solution as a coprecipitation medium, and a method of producing 1,3-butadiene using the zinc ferrite catalyst, in which high value-added 1,3-butadiene can be produced by the oxidative dehydrogenation of a cheap C4 mixture including impurities, such as n-butene, n-butane and the like, on the zinc ferrite catalyst. [Background Art]

Demand for 1,3-butadiene is being gradually increased in the petrochemical market.

Methods of producing 1,3-butadiene largely may include naphtha cracking, direct dehydrogenation of n-butene, and oxidative dehydrogenation of n-butene. Most commercially available 1,3-butadiene is chiefly produced through a naphtha cracking process. It is known that the supply of 1 ,3-butadiene produced through a naphtha cracking process accounts for 90% or more of the total supply thereof. Therefore, the supply and demand of 1,3-butadiene is greatly influenced by the capacity of a naphtha cracker. However, a naphtha cracking process cannot solve the unbalance of supply and demand of 1,3-butadiene due to the increased demand for 1,3-butadiene, because a new naphtha cracker must be installed to meet the increased demand for 1,3-butadiene, and also because the naphtha cracking process is not an independent process performed only to produce only butadiene, so that when the production of 1,3-butadiene is increased through the enlargement of a naphtha cracker, other basic fractions besides 1,3- butadiene are excessively produced.

As described above, since a method of producing 1,3-butadiene through a naphtha cracking process finds it difficult to cope with changes in the recent market situation, a dehydrogenation reaction in which 1,3-butadiene is obtained by detaching hydrogen from n- butene has lately attracted considerable attention as an alternative method of producing 1,3- butadiene. The dehydrogenation reaction of n-butene includes a direct dehydrogenation reaction and an oxidative dehydrogenation reaction. Since the direct dehydrogenation reaction of n-butene is an endothermic reaction, it requires high-temperature reaction conditions and thermodynamic low-pressure reaction conditions, and thus the yield of 1,3-butadiene is very low, so that it is not suitable as a commercial process [L.M. Madeira, M.F. Portela, Catal. Rev., volume 44, page 247 (2002)].

The oxidative dehydrogenation reaction of n-butene is a reaction obtaining 1,3- butadiene and water by reacting n-butene with oxygen. Since water is formed after the oxidative dehydrogenation reaction of n-butene is completed, the reaction is thermodynamically advantageous, and since the formed water serves to decrease the temperature of a reactor, the rapid change in the temperature of a catalyst layer can be prevented. Therefore, when a process of producing 1,3-butadiene at high efficiency through the oxidative dehydrogenation reaction of n-butene instead of naphtha cracking or direct dehydrogenation is developed, this process can be an efficient alternative process of independently producing 1,3-butadiene. In addition, in the case where a catalyst having activity which is not decreased even when a C4 mixture including impurities, such as n-butane and the like, is used as a reactant, a C4 raffinate- 3 mixture or a C4 mixture can be practically used as a supply source of n-butene, and thus a cheap surplus C4 fraction can be made into high value-added products. The C4 raffinate-3 mixture used in the present invention is a cheap C4 fraction obtained by sequentially separating 1,3 -butadiene, iso-butylene and 1-butene from the C4 mixture produced through naphtha cracking, and includes 2-butene (trans-2-butene or cis-2-butene), n-butane and 1-butene.

As described, in the 1,3-butadiene production process, the oxidative dehydrogenation reaction of n-butene is a reaction of producing 1,3-butadiene and water from oxygen and n- butene. Since the oxidative dehydrogenation reaction of n-butene is thermodynamically advantageous compared to the direct dehydrogenation reaction of n-butene, 1,3-butadiene can be obtained in high yield even under moderate reaction conditions. However, in the oxidative dehydrogenation reaction of n-butene, oxygen is used as a reactant, and thus it is expected that many side reactions, such as a perfect oxidation reaction and the like, occur. Therefore, it is of the utmost importance to develop a catalyst which can suppress these side reactions to the highest degree and to increase the selectivity of 1,3-butadiene. The reaction mechanism of the oxidative dehydrogenation reaction of n-butene has been never accurately known, but it is known that C-H bonds are cut from n-butene and simultaneously the oxidation-reduction reaction of the catalyst itself occurs. Therefore, composite oxide catalysts having a specific crystal structure including metal ions having various oxidation states have been used in the oxidative hydrogenation reaction [W.R. Cares, J.W. Hightower, J. Catal, volume 23, page 193 (1971)]. Up to date, Examples of catalysts known to be efficiently used to produce 1,3- butadiene through the oxidative dehydrogenation of n-butene include Ferrite-based catalysts [M.A. Gibson, J.W. Hightower, J. Catal, volume 41, page 420 (1976) / W.R. Cares, J.W. Hightower, J. Catal, volume 23, page 193 (1971) / RJ. Rennard, W.L. Kehl, J. Catal, volume 21, page 282 (1971)], tin-based catalysts [Y.M. Bakshi, R.N. Gur'yanova, A.N. Mal'yan, A.I. Gel'bshtein, Petroleum Chemistry U.S.S.R, volume 7, page 177 (1967)], bismuth molybdate- based catalysts [A.C.A.M. Bleijenberg, B.C. Lippens, G.C.A. Schuit, J. Catal, volume 4, page 581 (1965) / Ph.A. Batist, B.C. Lippens, G.C.A. Schuit, J. Catal, volume 5, page 55 (1966) / WJ. Linn, A. W. Sleight, J. Catal., volume 41, page 134 (1976) / R.K. Grasselli, Handbook of Heterogeneous Catalysis, volume 5, page 2302 (1997)], and the like.

Among the composite oxide catalysts used in the oxidative dehydrogenation reaction of n-butene, the ferrite-based catalyst has a spinel structure. Specifically, the ferrite-based catalyst is represented by AFe₂O₄ (A= Zn, Mg, Mn, Co, Cu or the like), and has a crystal structure in which oxygen (O) atoms constitute a cubic crystal, and A and Fe atoms are partially bonded between the oxygen (O) atoms [S. Bid, S.K. Pradhan, Mater. Chem. Phys., volume 82, page 27 (2003)]. This spinel-structured ferrite has an oxidation number of 2 or 3, and can be practically used as a catalyst for an oxidative dehydrogenation reaction for producing 1,3- butadiene from n-butene through the oxidation-reduction of iron ions and the interaction between oxygen ions in crystal and oxygen gases [M.A. Gibson, J.W. Hightower, J. Catal., volume 41, page 420 (1976) / RJ. Rennard, W.L. Kehl, J. Catal., volume 21, page 282 (1971)]. Generally, the catalytic activities of ferrite catalysts as oxidative dehydrogenation reaction catalysts are different from each other depending on the kinds of metals constituting two- valence cation sites in a spinel structure. It is known that, among the ferrite catalysts, zinc ferrite, magnesium ferrite and manganese ferrite exhibit good activity to the oxidative dehydrogenation reaction of n-butene, and, particularly, it is reported that zinc ferrite exhibits higher 1,3-butadiene selectivity than other ferrite catalysts [F.-Y. Qiu, L.-T. Weng, E. Sham, P. Ruiz, B. Delmon, Appl. Catal., volume 51, page 235 (1989)]. In relation to the oxidative dehydrogenation reaction of n-butene, research on the practical use of zinc ferrite-based catalysts has been reported in several patent documents and theses. Specifically, it was reported in the thesis [RJ. Rennard, W.L. Kehl, J. Catal., volume 21, page 282 (1971)] that 1,3-butadiene was obtained at a yield of 41% at a temperature of 375 ^°C by performing the oxidative dehydrogenation reaction of 2-butene using a zinc ferrite catalyst which has a pure spinel structure and is prepared through a coprecipitation method. Further, it was reported in a thesis [J.A. Toledo, P. Bosch, M.A. Valenzuela, A. Montoya, N. Nava, J. MoI. Catal. A, volume 125, page 53 (1997)] that 1,3 -butadiene was obtained at a yield of 21% at a temperature of 420 ^°C by performing the oxidative dehydrogenation reaction of 5 mol% (5 mol% of oxygen, 90 mol% of helium) of 1-butene as a reactant using a zinc ferrite catalyst.

Further, methods of preparing zinc ferrite catalysts, by which 1,3-butadiene can be obtained in high yields through the pre-treatment and post-treatment of zinc ferrite catalysts have been reported in patent documents and theses [F.-Y. Qiu, L.-T. Weng, E. Sham, P. Ruiz, B. Delmon, Appl. Catal., volume 51, page 235 (1989) / LJ. Crose, L. Bajars, M. Gabliks, U.S patent No. 3,743,683 (1973) / J.R. Baker, U.S patent No. 3,951,869 (1976)]. Further, methods of increasing the conversion ratio of n-butene and the selectivity of 1,3-butadiene in the oxidative dehydrogenation reaction of n-butene by physically mixing a zinc ferrite catalyst with metal oxides as a co-catalyst have been reported in patent documents and theses [W.-Q. Xu, Y.- G. Yin, G.-Y. Li, S. Chen, Appl. Catal. A, volume 89, page 131 (1992)]. The above reported zinc ferrite catalysts used in the oxidative dehydrogenation reaction of n-butene are single phase zinc ferrite catalysts or mixed phase zinc ferrite catalysts consisting essentially of the single phase zinc ferrite catalysts. Zinc ferrite, acting as a main component in the oxidative dehydrogenation of n-butene, is chiefly prepared by a coprecipitation method. Although methods of preparing zinc ferrite through coprecipitation are different from each other each document, a typical example of these methods is a method of adding zinc precursor and iron precursors to an excess aqueous basic reductant solution [LJ. Crose, L. Bajars, M. Gabliks, U.S patent No. 3,743,683 (1973) / J.R. Baker, U.S patent No. 3,951,869 (1976)].

In addition to the methods of improving the activity of the zinc ferrite catalyst by the methods of preparing the zinc ferrite catalyst through the pre-treatment, post-treatment and physical mixing, as attempts to increase the activity of catalyst itself, methods of increasing the activity of a catalyst through the deformation of a spinel structure by partially replacing two- valence zinc cations or three-valence iron cations with other metal cations have been reported. In particular, it is reported in the theses [J.A. Toledo, P. Bosch, M.A. Valenzuela, A. Montoya, N. Nava, J. MoI. Catal. A, volume 125, page 53 (1997) / RJ. Rennard Jr., R.A. Innes, H.E. Swift, J. Catal., volume 30, page 128 (1973)] that when a catalyst in which iron, as a three- valence cationic component, is partially replaced with chromium or aluminum is used, catalytic activity is increased.

In the oxidative dehydrogenation reaction of n-butene, when a multi-component catalyst, such as a zinc ferrite catalyst substituted with metal, a mixed phase catalyst or the like, is used, 1,3 -butadiene can be obtained in high yield compared to when a conventional zinc ferrite catalyst is used. However, since the multi-component catalyst includes various components, it is difficult to reproduce the multi-component catalyst, and thus the multi- component catalyst cannot be easily used as a catalyst for commercial use. Further, since a C4 mixture, which is a reactant used in the present invention, includes various C4 compounds in addition to n-butene, side reactions can occur in the above catalyst system including various components, and thus the activity of a catalyst and the selectivity of 1,3-butadiene may be worsened.

One of the problems occurring in the oxidative dehydrogenation process of n-butene is that, when the reactant passing through a catalyst layer includes n-butane at a predetermined amount or more, catalytic activity is decreased, and thus the yield of 1,3-butadiene is decreased [L.M. Welch, LJ. Croce, H.F. Christmann, Hydrocarbon Processing, page 131 (1978)]. Therefore, in the conventional technologies, in order to solve the above problems, pure n-butene (1-butene or 2-butene) is separated from a C4 mixture and then used as a reactant, and, even in commercial processes in which a ferrite catalyst is really used, a reactant from which n-butane is removed is used. As described above, in the catalysts and processes for producing 1,3- butadiene from n-butene through an oxidative dehydrogenation reaction, a process of separating pure n-butene from a C4 mixture is additionally required in order to use pure n-butene as a reactant, and thus the economical efficiency in the 1,3-butadiene preparation process is greatly decreased. [Disclosure] [Technical Problem]

Therefore, in order to overcome the above conventional problems, the present inventors found that a pure single-phase zinc ferrite catalyst can be prepared in a coprecipitation solution having a constant pH using a buffer solution through a coprecipitation process, and mat, when this prepared zinc ferrite catalyst is used, 1,3-butadiene can be produced in high yield using a cheap C4 mixture including n-butane and n-butene as a reactant through an oxidative dehydrogenation reaction without performing an additional n-butene separation process. Based on these findings, the present invention was completed. Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method of preparing a zinc ferrite catalyst for producing 1,3-butadiene, having a simple structure, a simple synthesis path and excellent reproducibility.

Another object of the present invention is to provide a method of producing 1,3- butadiene by directly using a C4 mixture as a reactant through an oxidative dehydrogenation reaction on the prepared zinc ferrite catalyst without performing an additional n-butene separation process. [Technical Solution]

In order to accomplish the above objects, an aspect of the present invention provides a zinc ferrite catalyst for producing 1,3-butadiene, including pure single-phase zinc ferrite prepared using a buffer solution having a pH of 6 ~ 12 as a coprecipitation medium.

In order to accomplish the above objects, another aspect of the present invention provides a method of preparing a zinc ferrite catalyst for producing 1,3-butadiene, including: a) dissolving a zinc precursor and an iron precursor in distilled water in a predetermined amount to form a precursor solution; b) preparing a buffer solution having a predetermined pH range; c) dropping the precursor solution into the buffering solution to coprecipitate zinc ferrite; d) filtering the mixed solution of the buffer solution and precursor solution to obtain a solid precipitate and then drying the solid precipitate at a temperature of 70 ~ 200 ^"C ; and e) heat- treating the dried solid precipitate at a temperature of 350 ~ 800 ^°C to obtain a zinc ferrite catalyst.

In order to accomplish the above objects, a further aspect of the present invention provides a method of producing 1,3-butadiene through the oxidative dehydrogenation reaction of a C4 mixture including n-butene and n-butane using the zinc ferrite catalyst prepared by injecting precursors into a buffer solution having a pH of 6 ~ 12 through a coprecipitation process. [ Advantageous Effects ]

According to the present invention, a zinc ferrite catalyst having a simple structure, a simple synthesis path and excellent reproducibility can be prepared through a simple process of injecting an aqueous precursor solution into a buffer solution, and thus the zinc ferrite catalyst can be easily and rapidly prepared compared to when it is prepared through a conventional coprecipitation process.

Further, when the zinc ferrite catalyst prepared according to the present invention is used, the conversion ratio of n-butene and the yield of 1,3-butadiene can be increased even when a C4 mixture including highly-concentrated n-butane is used as a reactant for an oxidative dehydrogenation reaction without performing an additional process of removing n-butane from the C4 mixture or separating n-butene from the C4 mixture, so that the expenses taken to perform the process of removing n-butane from the C4 mixture or separating n-butene from the C4 mixture can be avoided, thereby greatly improving the economical efficiency of the 1,3- butadiene preparation process.

Further, according to the present invention, since 1,3 -butadiene having high use value in the petrochemical industries can be directly produced from a C4 mixture or C4 raffinate-3 having low use value, a C4 mixture can be made into a high value-added product. Further, according to the present invention, since 1,3 -butadiene can be independently produced without installing a new naphtha cracker, the demand for 1,3-butadiene can be satisfied, so that economical profits can be obtained, thereby actively coping with changes in the market in the future.

[Description of Drawings]

FIG. 1 is a graph showing the results of X-ray diffraction (XRD) analysis of two kinds of zinc ferrite catalysts used in Example 1 of the present invention;

FIG. 2 is a graph showing the results of X-ray diffraction (XRD) analysis of three kinds of zinc ferrite catalysts used in Example 2 of the present invention;

FIG. 3 is a graph showing the results of X-ray diffraction (XRD) analysis of two kinds of zinc ferrite catalysts used in Comparative Example; and

FIG. 4 is a graph showing the change in the oxidative dehydrogenation reaction activity of C4 raffinate-3 to the pH of a buffer solution at the time of the coprecipitation of seven kinds of zinc ferrite catalysts used in Experimental Example 2 of the present invention. [Best Mode]

Hereinafter, preferred embodiments of the present invention will be described in detail.

As described above, the present invention provides a method of preparing a zinc ferrite catalyst for producing 1,3-butadiene, in which a single phase zinc ferrite catalyst for use in the oxidative dehydrogenation reaction of n-butene is prepared using a buffer solution having fixed pH through a coprecipitation process without additionally controlling the pH of a precipitation solution, and provides a method of producing 1,3-butadiene through the oxidative dehydrogenation reaction of n-butene using the zinc ferrite catalyst. According to the present invention, even when a C4 mixture including n-butane is used as a reactant, 1,3-butadiene can be produced in high yield.

The catalyst of the present invention used to produce 1,3-butadiene through the oxidative dehydrogenation reaction of n-butene is a single phase zinc ferrite catalyst. Since the properties of metal cations and oxygen in a lattice are changed depending on the crystal structure of a catalyst, the activity of the catalyst can be changed by controlling the preparation conditions of the catalyst. Therefore, the present inventors developed methods of preparing a catalyst while changing the pH of a coprecipitation solution during a process of coprecipitating zinc ferrite. In these methods, a buffer solution was used in order to more efficiently control the pH of a coprecipitation solution, thereby preparing a zinc ferrite catalyst exhibiting high activity in the oxidative dehydrogenation reaction of n-butene.

All commonly used precursors can be used as a zinc precursor and an iron precursor for preparing the zinc ferrite catalyst. Generally, chloride precursors or nitrate precursors may be used. In the present invention, zinc chloride is used as the zinc precursor, and iron chloride is used as the iron precursor. The zinc precursor and iron precursor are quantitated such that the ratio of iron/zinc is

2, mixed with each other, and then dissolved in distilled water to form a precursor solution. Further, as a medium for coprecipitating zinc ferrite, a buffer solution having a constant pH is prepared or provided. When the precursor solution is injected into the buffer solution using a syringe pump, zinc ferrite starts to be coprecipitated. In this case, the precursor solution must be injected into a large amount of the buffer solution such that the pH of the buffer solution is not changed by the injection of the precursor solution. After the precursor solution is completely injected into the buffer solution to form a mixed solution of the precursor solution and buffer solution, the mixed solution is stirred for 2 ~ 12 hours, preferably 6 - 12, such that zinc ferrite is sufficiently coprecipitated, so as to obtain a coprecipitation solution. Subsequently, the coprecipitation solution is sufficiently phase-separated such that the solid material dispersed in the coprecipitation solution is precipitated, and is then filtered using a vacuum filter to obtain a solid sample.

The solid sample is dried at a temperature of 70 ~ 200 ^°C, preferably 120 ~ 180^°C, for 12 - 16 hours, and is then heat-treated in an electric furnace at a temperature of 350 - 800 ^°C, preferably 500 - 700 ^°C , for 3 - 6 hours to prepare a pure single phase zinc ferrite catalyst.

According to the present invention, the zinc ferrite catalyst serves to convert n-butene into 1,3 -butadiene and water through an oxidative dehydrogenation reaction by detaching hydrogen from n-butene through the interaction between the iron ions and oxygen ions in a catalyst lattice and the gaseous oxygen adsorbed on the surface of the catalyst and then additionally detaching hydrogen therefrom through the oxidation-reduction reaction of the gaseous oxygen and iron ions. Therefore, the properties of the iron and oxygen ions in the catalyst lattice and the characteristics of the surface of the catalyst greatly influence the determination of the activity of the catalyst in the oxidative dehydrogenation reaction of n- butene. Accordingly, the zinc ferrite catalysts prepared using precipitation solutions having various pH values exhibit different activities from each other.

It was found through X-ray diffraction (XRD) analysis that the zinc ferrite catalysts prepared using buffer solutions having various pH values have various phase characteristics depending on the conditions under which they were made. In the case of the zinc ferrite catalyst coprecipitated in a buffer solution having a pH of 6, zinc ferrite was chiefly formed, but a -iron oxide ( α -Fe₂O₃) (III), which is known to have relatively low activity in the oxidative dehydrogenation reaction of n-butene, was also additionally formed (refer to FIG. 1). However, in the case of the zinc ferrite catalyst coprecipitated in a buffer solution having a pH of 7 ~ 12, it was found that single phase zinc ferrite was entirely formed (refer to FIGS 1 to 3). Therefore, it can be seen that the crystal phase of zinc ferrite is consistently changed depending on the pH of the buffer solution. Further, since the phase of zinc ferrite is consistently changed depending on the pH of a buffer solution, it was found that the formation of the crystal phase of zinc ferrite is not detrimentally influenced by using a buffer solution as a coprecipitation solution.

However, in a precipitation solution having a pH of 3 ~ 5, it was found that zinc ferrite was not formed, and α -iron oxide ( α -Fe₂O]) (III) was formed. Therefore, the zinc ferrite catalyst for producing 1,3 -butadiene according to the present invention was prepared using precipitation solution having a pH of 6 ~ 12. However, considering catalyst activity, it is preferred that the zinc ferrite catalyst be prepared using precipitation solution having a pH of 6 ~ 10 (refer to FIG. 4). Further, the present invention provides a method of producing 1,3-butadiene through an oxidative dehydrogenation reaction on the zinc ferrite catalyst prepared using the buffer solution by using a C4 mixture or C4 raffinate-3 as a supply source of n-butene without performing a process of removing n-butane therefrom.

According to Experimental Examples, Examples and Comparative Example of the present invention, the oxidative dehydrogenation reaction is conducted by fixing catalyst powder on a straight pyrex reactor for catalytic reaction, installing the reactor in an electric furnace to maintain the temperature of a catalyst layer constant, and then continuously passing a reactant through the catalyst layer in the reactor.

The reaction temperature for performing the oxidative dehydrogenation reaction may be 300 - 600⁰C, preferably 350 ~ 500 ^°C, and more preferably 420⁰C. The amount of the reactant passing through the catalyst layer in the reactor is set such that gas hourly space velocity is 50 ~ 500Oh^"1, preferably 100 ~ 100Oh^"1, and more preferably 300 ~ 60Oh^"1. The reactant is a mixed gas of a C4 mixture, air and steam, and the mixing ratio thereof is set such that the ratio of n-butene: air: steam is 1 : 0.5-10 : 1 —50, and preferably 1 : 3~4 : 10-30, based on n-butene. When the volume ratio of the mixed gas is more than or less than the above range, a desired yield of butadiene cannot be obtained, and problems with safety may occur due to a rapid exotheπnic reaction at the time of operation of the reactor.

In the present invention, n-butene (C4 mixture or C4 raffinate-3) and oxygen, each of which is a reactant of an oxidative dehydrogenation reaction, are supplied into a reactor, and the amount thereof is controlled using a mass flow controller. In order to remove the reaction heat of the oxidative dehydrogenation reaction and improve the selectivity of 1,3 -butadiene, steam is additionally supplied into the reactor. Specifically, steam is supplied into the reactor by injecting liquid water into the reactor using a syringe pump and simultaneously vaporizing the liquid water while maintaining the temperature of a water inlet at 150 - 300 ^°C, and preferably 180 - 250 ^°C . Further, steam is injected into the reactor, is completely mixed with other reactants (C4 mixture and air), and then passes through a catalyst layer, before it is introduced into an electric furnace.

The C4 mixture, which is a reactant used in the present invention, includes 0.5 ~ 50 wt% of n-butane, 40 ~ 99 wt% of n-butene, and 0.5 - 10 wt% of other C4 compounds. The C4 compounds include i-butane, cyclobutane, methyl cyclopropane, i-butene, and the like.

When the zinc ferrite catalyst of the present invention is used, high catalytic activity and high 1,3-butadiene yield can be obtained even when a cheap C4 mixture or C4 raffinate-3 including a large amount of n-butane which is known to inhibit the oxidative dehydrogenation reaction of n-butene is directly used as a supply source of n-butene which is a reactant. Further, the present invention is a direct catalyst synthesis technology, rather than a subsidiary technology using a conventional substitution or catalyst treatment process, and has excellent reproducibility due to a simple catalyst composition and a simple synthesis mechanism. The zinc ferrite catalyst of the present invention is advantageous in that, when it is used, 1,3-butadiene can be produced in high yield from a cheap C4 mixture or C4 raffinate-3 including impurities. [Mode for Invention]

Hereinafter, the present invention will be described in more detail with reference to the following Examples. However, the spirit and scope of the present invention is not limited thereto. Preparation Example

Precursor solution for preparing a zinc ferrite catalyst

Zinc chloride (ZnCl₂) was used as a zinc precursor, and iron chloride hexahydrate (FeCl₃ 6H₂O) was used as an iron precursor. Both the zinc precursor and the iron precursor are easily dissolved in distilled water. The respective precursors were quantitated such that the ratio of Fe/Zn is 2, mixed with each other, and then dissolved in distilled water to form a mixed solution. In this case, in order to form a sample having a uniform composition, the mixed solution was stirred using a magnetic stirrer for about 2 hours.

Preparation of buffer solution for preparing a zinc ferrite catalyst In the present invention, in order to coprecipitate zinc ferrite, a buffer solution, the pH of which can be maintained constant, was used as a coprecipitation medium. The buffer solution for preparing a zinc ferrite catalyst is directly prepared, or a commonly-used buffer solution was used as the buffer solution for preparing a zinc ferrite catalyst.

All buffer solutions can be used as the buffer solution of the present invention as long as they have constant pH values and do not form precipitates other than zinc ferrite. However, in the present invention, a buffer solution (Borax, pH = 6, 7) in which sodium tetraborate is mixed with hydrochloric acid, a commercially available buffer solution (manufactured by Samchun Chemical Co., Ltd.) and a buffer solution (pH = 1 1, 12) in which sodium hydrogen carbonate is mixed with sodium hydroxide were used.

In order to coprecipitate zinc ferrite in a buffer solution having a pH of 6 ~ 7, a buffer solution in which hydrochloric acid is mixed with an aqueous sodium tetraborate solution was prepared. Specifically, 57.2 g (0.15 mol) of sodium tetraborate decahydrate was dissolved in distilled water to form 1 L of an aqueous sodium tetraborate solution having a concentration of

0.15 M. Then, hydrochloric acid was added to the aqueous sodium tetraborate solution to form a mixed solution having a pH of 6 or 7. Subsequently, the mixed solution was stirred for about 2 hours to obtain a uniform buffer solution.

In order to coprecipitate zinc ferrite in a buffer solution having a pH of 8 ~ 10, a commercially available buffer solution, manufactured by Samchun Chemical Co., Ltd., was used.

In order to coprecipitate zinc ferrite in a buffer solution having a pH of 1 1 ~ 12, a buffer solution in which an aqueous sodium hydrogen carbonate solution is mixed with an aqueous sodium hydroxide solution was prepared. Specifically, 21.O g (0.25 mol) of sodium hydrogen carbonate was dissolved in distilled water to form 0.5L of an aqueous sodium hydrogen carbonate solution having a concentration of 0.5 M. Then, an aqueous sodium hydroxide solution was added to the aqueous sodium hydrogen carbonate solution to form a mixed solution having a pH of 1 1 or 12. Subsequently, the mixed solution was stirred for about 2 hours to obtain a uniform buffer solution.

In order to prepare a zinc ferrite catalyst, 1.42 g of zinc chloride and 5.61 g of iron chloride hexahydrate were dissolved in distilled water (250 mL), mixed with each other, and then stirred to form a precursor solution in which a zinc precursor and an iron precursor are completely dissolved in distilled water. Subsequently, the precursor solution was dropped into the above buffer solution having a pH of 6 ~ 12 to form a mixed solution, and simultaneously zinc ferrite was coprecipitated. The mixed solution was sufficiently stirred at room temperature for 12 hours using a magnetic stirrer, and was then left at room temperature for 12 hours for the purpose of phase separation. Subsequently, the mixed solution in which zinc ferrite is coprecipitated was filtered using a vacuum filter to obtain a solid sample, and then the solid sample was dried at a temperature of 175 ^°C for 16 hours. Subsequently, the dried solid sample was heat-treated in an electric furnace for 6 hours under an air atmosphere while the temperature of the electric furnace was maintained at 650 ^°C, thereby preparing zinc ferrite catalysts. The phases of the prepared zinc ferrite catalysts were observed through X-ray diffraction (XRD) analysis, and the results thereof are shown in FIGS. 1 to 3. From FIG. 1, it was found that in the case of the zinc ferrite catalyst coprecipitated in a buffer solution (Borax) having a pH of 6, zinc ferrite was chiefly formed and α -iron oxide ( α -Fe₂O₃) was also partially formed. However, from FIGS. 1 to 3, it was found that, in the case of the zinc ferrite catalyst coprecipitated in a buffer solution having a pH of 7 ~ 12, zinc ferrite was entirely formed in a single phase regardless of pH.

Experimental Example 1

Oxidative dehydroRenation reaction of C4 raffinate-3 or C4 mixture on zinc ferrite catalyst

The oxidative dehydrogenation reaction of n-butene was performed using the zinc ferrite catalyst prepared in Preparation Example under the following experimental conditions.

In the present invention, a C4 mixture was used as a reactant for the oxidative dehydrogenation reaction of n-butene, and the composition thereof is given in Table 1. The C4 mixture was introduced into a reactor together with air and steam, and a straight pyrex fixed-

l β bed reactor was used as the reactor.

The constitution ratio of the reactant was set based on the amount of n-butene in the C4 mixture. That is, the volume ratio of n-butene: air: steam was set to a ratio of 1 : 3.75: 15, and, in this case, the volume ratio of n-butene: oxygen: steam was set to a ratio of 1 : 0.75: 15. Steam, which was formed by vaporizing liquid water at a temperature of 200 ^°C, was mixed with a C4 mixture and air, and was then introduced into the reactor. The amount of the C4 mixture and the amount of air were controlled by a mass flow controller, and the amount of steam was controlled by controlling the flow rate of liquid water using a syringe pump.

The feed rate of the reactant was set such that gas hourly space velocity (GHSV) was 475 h^"1 based on n-butene in the C4 mixture, and the reaction temperature was maintained such that the temperature of the catalyst layer of the fixed-bed reactor was 420 ^°C . After the oxidative dehydrogenation reaction, since the reaction product includes carbon dioxide by perfect oxidation, side products by cracking and isomerization, and unreacted products such as n-butane etc. in addition to the main product of 1,3 -butadiene, gas chromatography was used in order to separate and analyze the reaction products. The conversion ratio of n-butene, selectivity of 1,3-butadiene and yield of 1,3-butadiene due to the oxidative dehydrogenation of n-butene on the zinc ferrite catalyst are calculated by the following Mathematical Equations 1, 2 and 3.

[Mathematical Equation 1 ] moles of reacted n-butene

Conversion ratio (%) = x 100 moles of supplied n-butene

[Mathematical Equation 2] moles of 1 ,3-butadiene formed

Selectivity (%) = x 100 moles of reacted n-butene [Mathematical Equation 3 ] moles of 1,3-butadiene formed Yield (%) = x 100 moles of supplied n-butene

[Table 1 ) Composition of C4 mixture used as reactant

Example 1 Reaction activity of catalysts prepared using buffer solution having pH of 6 and 7

The phases of the catalysts prepared using a Borax buffer solution having a pH of 6 and 7 were observed through X-ray diffraction (XRD) analysis. As a result, in the case of the zinc ferrite catalyst coprecipitated in a Borax buffer solution having a pH of 6, it was found that a mixed phase of zinc ferrite and α -iron oxide ( α -Fe₂O₃) was formed, and, in the case of the zinc ferrite catalyst coprecipitated in a buffer solution having a pH of 7, it was found that a single phase of zinc ferrite was formed (refer to FIG. 1). Meanwhile, the oxidative dehydrogenation reaction of a C4 mixture was performed using the catalysts coprecipitated in the Borax buffer solution through the same experimental method as in Experimental Example 1, and the results thereof are given in Table 2.

From the catalyst activity experiment performed using the mixed-phase catalyst prepared using a Borax buffer solution having a pH of 6, it was found that the conversion ratio of n-butene was 71.4%, the selectivity of 1,3 -butadiene was 95.2%, and the yield of 1,3- butadiene was 68.0%, and thus it can be seen that the mixed-phase catalyst of zinc ferrite and a -iron oxide ( α -Fe₂O₃) exhibits relatively excellent activity in the oxidative dehydrogenation reaction. In particular, it was found that the selectivity of 1,3-butadiene is relatively high.

The reason for this is determined that the selectivity of 1,3-butadiene in the oxidative dehydrogenation reaction is increased due to the synergetic effect between the phases in the mixed phase catalyst.

From the catalyst activity experiment performed using the catalyst prepared using a Borax buffer solution having a pH of 7, it was found that the conversion ratio of n-butene was 79.1%, the selectivity of 1,3-butadiene was 91.2%, and the yield of 1,3-butadiene was 72.1%. In the case of the catalyst prepared using a Borax buffer solution having a pH of 7, the selectivity of 1,3-butadiene is somewhat decreased, but the conversion ratio of n-butene is greatly increased, and thus the yield of 1,3-butadiene is increased, compared to the mixed- phase catalyst prepared using a Borax buffer solution having a pH of 6.

[Table 2] Reaction activity of catalyst prepared using buffer solution having a pH of 6 and 7

Example 2

Reaction activity of catalysts prepared using buffer solution having pH of 8 to 10 The phases of the catalysts prepared using a buffer solution having a pH of 8 to 10 in

Preparation Example were observed through X-ray diffraction (XRD) analysis. As a result, it was found that all of the catalysts have a single phase of zinc ferrite (refer to FIG. 2). The oxidative dehydrogenation reaction of a C4 mixture was performed using three kinds of catalysts prepared using a buffer solution having a pH of 8 to 10, and the results thereof are given in Table 3. From Table 3, it can be seen that all of the three kinds of catalysts exhibit a high n-butene conversion ratio of 78% or more, a high 1,3 -butadiene selectivity of 92% or more and a high 1,3-butadiene of 72% or more. Therefore, it is preferred that a buffer solution having a pH of 8 to 10 be used in order to prepare a high-efficiency zinc ferrite catalyst according to the present invention.

[Table 3]

Reaction activity of zinc ferrite catalyst prepared using buffer solution having pH of 8 to 10

Comparative Example

Reaction activity of catalysts prepared using buffer solution having pH of 11 and 12

The phases of the catalysts prepared using a sodium hydrogen carbonate-based buffer solution having a pH of 11 and 12 in Preparation Example were observed through X-ray diffraction (XRD) analysis. As a result, it was found that the catalysts have a single phase of zinc ferrite (refer to FIG. 3). The oxidative dehydrogenation reaction of a C4 mixture was performed using the two kinds of catalysts prepared using a sodium hydrogen carbonate-based buffer solution having a pH of 1 1 and 12, and the results thereof are given in Table 4. From Table 4, it was found that, although the catalysts include a single phase zinc ferrite, the catalysts coprecipitated under a strong basic atmosphere exhibit very low catalytic activity.

[Table 4]

Reaction activity of zinc ferrite catalyst prepared using buffer solution having pH of 1 1 and 12

Experimental Example 2

Change in reaction activity of zinc ferrite catalyst depending on pH of coprecipitation solution

As described above, from Examples 1 and 2 and Comparative Example, it could be seen that the phases and properties of the zinc ferrite catalysts are determined depending on the pH of the coprecipitation solution, and thus the reaction activity of the zinc ferrite catalysts in the oxidative dehydrogenation of n-butene is changed. In order to directly compare the difference in the reaction activities between the zinc ferrite catalysts depending on the pH of the coprecipitation solution, the results of Examples 1 and 2 and Comparative Example are shown in FIG. 4. From FIG. 4, it was found that the yield of 1,3-butadiene was curved in a volcanic shape depending on the pH of the coprecipitation solution, and thus excellent catalytic activity was exhibited in the range of 6 ~ 10 of pH. However, in the case of the zinc ferrite catalyst coprecipitated in the range of 1 1 ~ 12 of pH, zinc ferrite phase is easily formed, but the reaction activity thereof is low, and thus it can be seen that the coprecipitation under the basic conditions cannot impart positive effects to catalytic activity.

Claims

[CLAIMS] [Claim 1 ]

A method of preparing a zinc ferrite catalyst for producing 1 ,3-butadiene, comprising: a) dissolving a zinc precursor and an iron precursor in distilled water to form a precursor solution, in which an atom number ratio of zinc to iron is 1 :2; b) dropping the precursor solution into a buffering solution having a pH of 6 ~ 10 to coprecipitate zinc ferrite; c) filtering the mixed solution to obtain a solid sample; and d) drying the solid sample at a temperature of 70 ~ 200 ^°C and then heat-treating the dried solid sample at a temperature of 350 ~ 800 ^°C .

[Claim 2]

The method of preparing a zinc ferrite catalyst for producing 1,3-butadiene according to claim 1, further comprising, between the b) dropping the precursor solution and the c) filtering the mixed solution: stirring the mixed solution for 6 ~ 12 hours such that the precursor solution is sufficiently precipitated in the buffer solution. [Claim 3]

The method of preparing a zinc ferrite catalyst for producing 1,3-butadiene according to claim 1, wherein the zinc precursor is zinc chloride or zinc nitrate, and the iron precursor is iron chloride or iron nitrate. [Claim 4]

A method of producing 1,3-butadiene, comprising: a) providing a reactant mixture including a C4 mixture, air and steam; b) continuously passing the reactant mixture through a catalyst layer on which the zinc ferrite catalyst prepared using the method of any one of claims 1 to 3 to conduct an oxidative dehydrogenation reaction of the reactant mLxture; and c) obtaining 1,3-butadiene through the oxidative dehydrogenation reaction of the reactant mixture. lClaim 5] The method of producing 1,3-butadiene according to claim 4, wherein the C4 mixture comprises 0.5 ~ 50 wt% of n-butane, 40 ~ 99 wt% of n-butene, and 0.5 ~ 10 wt% of other C4 compounds. [Claim 6]

The method of producing 1,3-butadiene according to claim 4, wherein, in the a) providing a reactant mixture, the reactant mixture comprises n-butene, air and steam such that a mixing ratio of n-butene: air: steam is 1 : 3-4 : 10-30. [Claim 7]

The method of producing 1,3-butadiene according to claim 4, wherein, in the b) continuously passing the reactant mixture, the oxidative dehydrogenation reaction is performed at a temperature of 300 - 600 ^°C and at a space velocity of 50 - 5000 h^'1.