PRIORITY CLAIM & CROSS REFERENCE

The application claims priority to Chinese Application No. 201811643291.0, filed on Dec. 29, 2018, entitled “Method For Aromatization Of Light Alkanes”, which is herein specifically and entirely incorporated by reference.

FIELD OF THE INVENTION

The present disclosure relates to the technical field of producing aromatic hydrocarbons from light alkanes, and particularly to a method for aromatization of light alkanes.

BACKGROUND OF THE INVENTION

During the dehydroaromatization process of ethane, the ethane can be selectively converted into high-value Benzene-Toluene-Xylene (BTX) products directly in the presence of a catalyst. Because of the low reactivity of ethane, the reaction temperature shall be set at least 600° C. generally, which causes severe coking of the catalyst. Therefore, the catalyst used in the dehydroaromatization reaction must be regenerable from an economical perspective.

FIG. 1illustrates the main process of dehydroaromatization of ethane in the presence of a supported metal catalyst: 1) the ethane is activated at the metal site of the catalyst and converted to ethylene; 2) the ethylene is activated at the acid site of the catalyst and converted into C6+ hydrocarbons; 3) the C6+ hydrocarbons are dehydrocyclized at the metal site to form aromatic compounds. As can be seen, the proximity between the metal and the acid site is vital for improving selectivity of aromatic hydrocarbons. Otherwise, the ethylene is prone to be excessively oligomerized and converted into heavier hydrocarbons prior to the cyclization, it will not only reduce selectivity of aromatic hydrocarbons, but also cause the formation of more coke, which results in quick deactivation of the catalyst.

The typical noble metal catalyst, supported on zeolite, is used for catalyzing the dehydroaromatization of ethane. This catalyst usually contains 0.02-0.2% of the supported metal. For the sake of facilitating the industrial application, it is necessary to combine the zeolite powder with a binder being capable of providing mechanical strength to form the catalyst particles, thereby reducing the pressure drop of catalyst bed.

Example 1 of U.S. Pat. No. 8,946,107B2 discloses a binder-free dehydroaromatization catalyst. Specifically, the active components such as platinum (Pt) are deposited on ZSM-5 powder, and the powder is then loaded into a plastic bag and pressed using an isostatic press, subsequently crushing and sieving the powder to obtain catalyst particles. However, the catalyst has poor mechanical strength and cannot be used industrially.

U.S. Pat. No. 9,144,790B2 discloses a catalyst that uses gallium (Ga) as a second metal of the catalyst to suppress undesirable catalytic activity of Pt to improve selectivity and a method for preparing the same. The method comprises mixing ZSM-5 zeolite powder with alumina and extruding the mixture to obtain an extrudate; subsequently depositing the active components such as Pt in pores of the extrudate. A binder is used for bonding individual zeolite crystal particles to keep the catalyst particle size within the optimum range for fluidized bed operations or to prevent the excessive pressure drop of the catalyst particle during operations of fixing or moving the fluidized bed.

SUMMARY OF THE INVENTION

The inventors of the present invention have discovered that when a binder and a zeolite are present simultaneously in the catalyst used in the dehydroaromatization reaction of the light alkanes, the active components such as Pt, will be deposited on the binder in addition to the zeolite; if a portion of Pt is deposited on the binder, it will result in the reduced activity of the catalyst and low selectivity of the aromatic hydrocarbons; moreover, the Pt on the binder can be easily sintered at high temperature (for example, during the process of reaction or catalyst regeneration), thus the regenerated catalyst cannot be restored to its original activity. The present invention is proposed in order to solve the aforementioned problems.

The present disclosure provides a method for aromatization of light alkanes, comprising: subjecting the light alkanes to dehydroaromatization reaction in the presence of aromatization catalysts including carriers and metal active components supported on the carriers, the metal active components include platinum (Pt), the carriers include zeolites and binders, and at least 80 wt. % of the metal active components are distributed on the zeolites.

Compared with the existing dehydroaromatization reaction, the catalyst applied by the method of the present disclosure has higher catalytic activity in dehydroaromatization and can improve selectivity of the reaction product BTX, and the regenerated catalyst shares comparative performance with the original catalyst, that is, the catalyst has the characteristics of high regenerability. In addition, the method of the present disclosure can on one hand minimize the amount of Pt on the binder by adjusting the Pt distribution and minimizing the Pt supporting on the catalyst, and on the other hand, the second active component (such as Ga) can be omitted. Even if only a small amount of Pt is present, the catalytic activity of the catalyst and the selectivity of the product BTX can be ensured, thereby the cost of the catalyst is reduced.

