CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No. 10-2019-0149580 filed Nov. 20, 2019, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to shaped dehydrogenation catalysts and a process for converting paraffins to olefins, using the same. More particularly, the present disclosure relates to a dehydrogenation catalyst having single-atom cobalt loaded onto a silica-based molded support, a preparation method therefor, and a method for producing olefins by dehydrogenating corresponding paraffins, particularly light paraffins in the presence of the dehydrogenation catalyst.

2. Description of the Prior Art

Light olefins, such as ethylene, propylene, butylene, so on, are main chemical raw materials used as building blocks for chemical products (oxo-alcohols, acrylonitrile, propylene oxide, butanol, acrylic acid, etc.) and plastic products (polypropylene, ethylene-propylene rubber, etc.), finding a broad range of applications in the petrochemical industry. Inter alia, propylene, which is a colorless compound of low boiling point, is traded typically at a polymer grade (at least about 99.5% purity), chemical grade (about 90-96% purity), and refinery grade (about 50-70% purity).

Generally, light olefins are produced by thermal cracking of naphtha or kerosene under supply of steam (that is, steam cracking). However, with the growth of demand on light olefins, thermal cracking-type methods have difficulty in meeting the growing demand. In response to the demand, various synthesis methods (for example, catalytic cracking processes of light fractions, etc.) have been proposed. The products obtained by the steam cracking, catalytic cracking, etc. are typically a mixture of various hydrocarbons including methane, ethane, propane, and C5/C6+ paraffinic hydrocarbons as well as olefins (ethylene, propylene, etc.).

The composition of mixed hydrocarbons can be adjusted by modifying operation conditions of the processes. However, such modification cannot be a sufficient strategy when a market demand is higher for a specific product than other co-products. For example, market demands particularly for propylene in many regions are rapidly growing than for ethylene. Such low olefin yields from which conventional commercial processes suffer require catalyst reaction technologies for increasing selectivity for olefins as much as possible.

Examples of commercial dehydrogenation techniques in current use are summarized in Table 1, below.

TABLE 1CATOFINOleflexUhdeSABICManufacturerLummusUOPLrupp-UhdeSABICReactorAdiabaticAdiabaticDH + ODH-Adiabaticfixed bedmoving bedAdiabaticfixed bedand FBROperationCyclicContinuousCyclicCyclictypeFeedstockC3-C4C3-C4C3-C4C3CatalystCr-basedPt-Sn-Pt-Sn-Pt-Sn-loadedbasedbasedbasedcatalystloadedloadedloadedcatalystcatalystcatalystRxn. Temp.565-649550-620DH: 550-590560-600(° C.)ODH: about600Rxn. Press.03-0.52-35-60.1-6(bar)Cycle time15-30 min.—8 hrs15-30 min.

For the commercial processes exemplified above, a feedstock in a mixed gas form is supplied while chromium- or platinum-based (e.g., Pt—Sn) catalysts are mainly employed. Iron oxide-based catalysts and gallium/zeolite catalysts are also known to be applicable to the dehydrogenation of paraffins. In addition, although generally undergoing a regeneration process after being inactivated with the generation of coke during reactions, dehydrogenation catalysts are required to maintain catalytic activity during multiple cycles of regeneration.

In recent years, there has been a growing interest in catalyst technology for utilizing all metal elements supported on a support. Conventional metal-supported catalysts have catalytic metal particles assembled on the supports. Given a broad size distribution and irregular morphologies, the assembled metal particles cannot take full advantage of metal active sites and thus have undesirable influence on catalyst activity or selectivity. In contrast, single-atom catalysts provide the advantage that catalyst activity can be maximized by downsizing metal nanostructures to metal active sites distributed to an atomic level.

In this regard, there is a technique known to convert propane to propylene through dehydrogenation in the presence of a catalyst having a single-atom type active metal (e.g., zinc) supported onto a support such as silica (e.g., ACS Catal. 2014, 4, 4, 1091-1098). In this document, a mixed gas containing 3% of propane and the balance of argon (Ar), which is an inert gas, is used as a reactant with the aim of selectively converting paraffins to the corresponding olefins while suppressing the formation of by-products. However, a feedstock containing a low content of paraffins is improper from the viewpoint of commerce. Furthermore, the catalyst may be thermally unstable in a high temperature reaction of about 500 to 600° C. and in a dehydrogenation processes that proceed in high temperature and regeneration conditions because the catalyst is thermally treated at as low as of 300° C.

There is therefore a need for a better catalytic activity that is highly stable and shows maximum advantage of single-atom catalysts. Particularly, single-atom catalysts have been difficult to commercialize because shaped catalysts do not guarantee single atom characteristics.

SUMMARY OF THE INVENTION

An embodiment according to the present disclosure provides a single-atom cobalt (Co) loaded dehydrogenation catalyst that not only exhibits excellent catalytic stability, but also is made of a molded body suitable for commercialization, and a preparation method therefor.

An embodiment according to the present disclosure provides a dehydrogenation process which can attain higher conversion of paraffins even for a feedstock containing a high concentration of paraffins and excellent selectivity for corresponding olefins.

Provided according to a first aspect of the present disclosure is a method for preparation of a cobalt-based, shaped single-atom catalyst, the method comprising the steps of:

combining a silica binder and a silica powder for support material in an aqueous medium to prepare a molding paste;

molding the paste into a silica-based, molded support;

contacting the silica-based, molded support with an alkali metal salt in an aqueous medium to form an alkali metal-treated, silica-based, molded support, before or after which pH adjustment is made with a base, wherein at least a part of the alkali metal ions are electrostatically adsorbed on the surface of the silica-based, molded support;

contacting the alkali metal-treated, silica-based, molded support with an aqueous solution of a first cobalt precursor to form a first cobalt- and alkali metal-containing, silica-based, molded support, the aqueous solution of the first cobalt precursor being adjusted in pH by adding a base thereto, with the first cobalt precursor having an oxidation number of 3+, wherein at least a part of the cobalt ions having an oxidation number of 3+ is electrostatically adsorbed on the alkali metal-treated, silica-based, molded support; and

thermally treating the first cobalt- and alkali metal-containing silica-based, molded support,

whereby the cobalt having an oxidation number of 2+ and the alkali metal having an oxidation number of 1+, respectively, exist in an isolated form of single-atom on the silica-based, molded support while the cobalt having an oxidation number of 2+ is tetrahedrally coordinated at the three-membered siloxane ring present on the surface of the silica-based, molded support.

According an exemplary embodiment, the method may further comprise the steps of: contacting the first cobalt- and alkali metal-containing silica-based, molded support with an aqueous solution of a second cobalt precursor having an oxidation number of 3+ to form a second cobalt- and alkali metal-containing silica-based, molded support, the aqueous solution of the second cobalt precursor being adjusted in pH by addition of a base thereto; and

thermally treating the second cobalt- and alkali metal-containing silica-based, molded support.

Provided according to a second aspect of the present disclosure is a method for preparation of a cobalt-based, shaped single-atom catalyst, the method comprising the steps of:

combining a silica binder and a silica powder support material in an aqueous medium to prepare a molding paste;

molding the paste into a silica-based, molded support;

contacting the silica-based, molded support with an alkali metal salt in an aqueous medium to form an alkali metal-treated, silica-based, molded support, before or after which pH adjustment is made with a base, wherein at least a part of the alkali metal ions are electrostatically adsorbed on the surface of the silica-based, molded support;

contacting the alkali metal-treated, silica-based, molded support with an aqueous solution of a first cobalt precursor to form a first cobalt- and alkali metal-containing, silica-based, molded support, the aqueous solution of the first cobalt precursor being adjusted in pH by adding a base thereto, with the first cobalt precursor having an oxidation number of 3+, wherein at least a part of the cobalt ions having an oxidation number of 3+ is electrostatically adsorbed on the alkali metal-treated, silica-based, molded support;

contacting the first cobalt- and alkali metal-containing, silica-based, molded support with an aqueous solution of a second cobalt precursor to form a second cobalt- and alkali metal-containing, silica-based, molded support, the aqueous solution of the second cobalt precursor being adjusted in pH by adding a base thereto, with the second cobalt precursor having an oxidation number of 3+;

thermally treating the second cobalt- and alkali metal-containing silica-based, molded support,

whereby the cobalt having an oxidation number of 2+ and the alkali metal having an oxidation number of 1+, respectively, exist in an isolated form of single-atom on the silica-based, molded support while the cobalt having an oxidation number of 2+ is tetrahedrally coordinated at the three-membered siloxane ring present on the surface of the silica-based, molded support.

Provided according to a third aspect of the present disclosure is a dehydrogenation catalyst, comprising:

a silica-based, molded support having an alkali metal adsorbed thereon; and

cobalt, as an active metal, loaded to the silica-based, molded support,

wherein the dehydrogenation catalyst is a cobalt-based, molded single-atom catalyst in which the cobalt having an oxidation number of 2+ and the alkali metal having an oxidation number of 1+, respectively, exist in an isolated form of single-atom on the silica-based, molded support while the cobalt having an oxidation number of 2+ is tetrahedrally coordinated at the three-membered siloxane ring present on the surface of the silica-based, molded support.

Provided according to a fourth aspect of the present disclosure is a method for production of an olefin, the method comprising the steps of:

providing a feedstock containing a light paraffin;

subjecting the feedstock to dehydrogenation at a temperature of 500 to 700° C. under a pressure of 0.3 to 2 bar in presence of the catalyst described above; and

recovering the olefin corresponding to the light paraffin from the dehydrogenation product.

