JP3385360B2 - Method for producing isobutene - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing isobutene from n-butane in a single step by dehydrogenation / isomerization in the presence of a catalyst.

[0002]

BACKGROUND OF THE INVENTION Isobutene is an extremely important compound in the chemical industry. For example, it is a raw material for the production of methyl tertiary butyl ether (MTBE), which is an anti-knock agent for gasoline, and the production of basic chemicals such as methacrylic acid and methacrylonitrile. It is widely and widely used as a raw material or a raw material for synthesizing various polymers.

At present, isobutene is industrially produced mainly by a separation method from C4 fraction of naphtha decomposition.
Since the amount of isobutene in the C4 fraction is also limited, there is a strong demand for development of a process for synthesizing independent isobutene, which is different from the separation method.

As one of such methods, it is said that a method of dehydrogenating (thermally or oxidatively) isobutane, which accounts for about 40% of the C4 fraction, is close to practical use for the time being ( MH
oang, JF Mathews, KCPratt, Chemtech, (9), 45-48 (199
9)), From the viewpoint of effective use of fossil resources and energy saving, it is not awaited that a one-step direct synthesis method from less reactive n-butane will be required in the future.

From this point of view, research and development of a method for synthesizing isobutene from n-butane in one step have been started. Since this method is a synthetic reaction in which the isomerization of n-butane and the dehydrogenation of the isobutane formed are carried out simultaneously, the catalyst occupies an important weight, and its selectivity and yield largely depend on the catalyst used.

For this reason, catalysts mainly composed of zeolitic materials have been proposed so far (platinum / zeolite (ZSM-5) system (GD Pirngruber, K. Seshan, JALercher,
J. Catal., 186 (1), 188-200 (1999)), Zinc / ZSM-5 series (R. Byg
gningsbacka, N. Kumar, L.-E. Lindfor, Catal. Lett., 55
(3,4), 173-176 (1998))), activity, selectivity, etc. are not yet satisfactory. Further, no catalyst based on solid superacid has been reported so far.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method capable of producing isobutene in a single step with increased selectivity and yield by using n-butane having low reactivity as a raw material.

[0008]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, in a method for producing isobutene from n-butane in the presence of a catalyst by dehydrogenation / isomerization in a single step, a catalyst in which a chromium compound is supported on a zirconia-based oxide superacid is used. A method for producing isobutene is provided.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The catalyst used in the present invention is a zirconia-based oxide superacid carrying a chromium compound. In this case, the zirconia oxide superacid itself is a conventionally known one, and zirconia oxide is used as a carrier, on which an inorganic acid or a salt thereof, or an oxide (second oxide) such as boron, molybdenum, or tungsten is added. It can be obtained by supporting. Regarding such oxide superacid, for example, Makoto Hino, Kazushi Arata, “Surface”, 34 (2),
119-129 (1996) and the like.

The oxide superacid having an acid radical supported on a zirconia-based carrier oxide can be obtained by adding an inorganic acid or a salt thereof to the zirconia-based oxide of the carrier and calcining at 400 to 800 ° C. As the inorganic acid or its salt,
Examples thereof include sulfuric acid, hydrochloric acid, phosphoric acid, carbonic acid, nitric acid, boric acid and salts thereof such as ammonium salt, sodium salt and potassium salt. In the present invention, sulfuric acid, ammonium sulfate, sodium sulfate and the like are preferably used. Further, the oxide carrying the sulfate is a zirconia-based carrier oxide,
It can also be formed by the inclusion of thionyl chloride.

As a method for incorporating an inorganic acid or an inorganic acid salt into the zirconia-based carrier oxide, a method of incorporating a solution of the inorganic acid or the inorganic acid salt into the oxide by a method such as an impregnation method or a kneading method is adopted. . The zirconia-based carrier oxide used in the present invention generally has an amorphous structure. The oxide having an amorphous structure is obtained by burning a hydroxide of zirconia while avoiding its crystallization, or by oxidizing a hydroxide precursor that causes precipitation of a hydroxide by hydrolysis of a soluble salt of zirconia or an alkoxide. Alternatively, it is hydrolyzed in the presence of a base to form a precipitate of a hydroxide, the precipitate is separated, dried, and the obtained dried product is 200 to 350 ° C., preferably 250 to 350 ° C. while avoiding its crystallization. It can be easily obtained by baking at 300 ° C.

The amount supported on the zirconia-based carrier oxide is 0.01 to 0.8 gram equivalent, preferably 0.03 to 0.5 gram equivalent, per 100 g of the carrier oxide.

When an oxide superacid is produced by supporting a second oxide on a zirconia-based carrier oxide, the second oxide contains at least one element selected from boron, molybdenum and tungsten. The oxide used is tungsten, of which tungsten is particularly preferred. As a method for supporting the second oxide on the zirconia-based carrier oxide, a method of impregnating or mixing a solution of a soluble compound of an element corresponding to the second oxide into the carrier oxide and then firing the solution can be shown.

Specific examples of the soluble compound of the element corresponding to the second oxide are ammonium molybdate [(NH ₄ ) ₆ M
o ₇ O ₂₄ ] .4H ₂ O, ammonium phosphomolybdate [(NH ₄ ) ₅ PM
o _{1 2} O ₄₀ ] .xH ₂ O, ammonium metatungstate [(NH ₄ ).
₆ (H ₂ W ₁₂ O ₄₀ )]. XH ₂ O, 12 Ammonium tungstate
[(NH ₄ ) ₁₀ W ₁₂ O ₄₂ H ₂ ] .10H ₂ O, ammonium decatungstophosphate [(NH ₄ ) ₅ PW ₁₂ O ₄₀ ] .14H ₂ O, trimethyl borate,
Examples thereof include orthoboric acid. When the amount of the second oxide supported on the zirconia-based carrier oxide and the firing temperature are shown,
In the case of molybdenum oxide (MoO, Mo ₂ O ₅ ), the supported amount is 1 to
15wt%, preferably 3-8wt%, the firing temperature is 500-900 ℃
Is. For tungsten oxide _{(W 2 O 5, WO 2} , WO 5), the amount of supported 5-50 wt%, preferably 10 to 30 wt%, the sintering temperature is 500 to 900 ° C.. In the case of boron oxide, the supported amount is 1 to 10 wt%, preferably 3 to 6 wt%, and the firing temperature is 550 to 750 ° C.

In order to support the chromium compound on the oxide superacid, the chromium compound is added to the zirconia-based oxide superacid and the mixture is fired in air. As a method for incorporating a chromium compound into the carrier oxide, a physical mixing method,
Conventionally known methods such as an impregnation method and a kneading method can be adopted.

As the chromium compound, various inorganic or organic chromium compounds can be used. For example, chromium hydroxide, chromium acetate, chromium nitrate, chromium chloride, chromium sulfate, tris.
Examples include (2,4-pentadionato) chromium and bis (benzene) chromium. These chromium compounds are usually dissolved in water or an organic solvent and then contained in the zirconia-based carrier oxide. The firing temperature of the zirconia-based carrier oxide containing a chromium compound is 400 to 900 ° C, preferably 500 to 700.
It is about ℃. The loading amount of the chromium compound is 0.2 to 50 g, preferably 5 per 100 g of the carrier oxide as chromium metal.
~ 20g.

The method for dehydrogenating and isomerizing n-butane according to the present invention is carried out by dehydrogenating and isomerizing n-butane in the presence of the above-mentioned catalyst in the absence of oxygen. The reaction temperature is 400 to 800 ° C., preferably 400 to 600 ° C., and the reaction pressure is arbitrary, but normal pressure or reduced pressure is preferable. The raw material n-butane is used alone, but nitrogen,
It can be used by diluting it with an inert gas such as argon or helium gas. The mixing ratio is arbitrary.

[0018]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Example 1 10 g of zirconyl nitrate was dissolved in 250 ml of distilled water and heated to 80 ° C. Slowly add 25 ml of ammonia to form a precipitate of zirconium hydroxide. After filtration and washing, it was dried at 100 ℃ overnight (5.72g) and then calcined at 300 ℃ for 3 hours (5.04g, B
ET surface area = 252.8 m ² / g). 2 g of the obtained zirconium hydroxide was taken, and ammonium metatungstate (((N
H ₄ ) ₆ (H ₂ W ₁₂ O ₄₀ )]. XH ₂ O) 0.539 g (20 wt% in terms of tungsten)
%) And 100 ml of distilled water, and stir at 80 ° C for 3 hours.
The distilled water was evaporated to dryness, left overnight at 100 ° C, and then calcined at 600 ° C for 3 hours to obtain 2.1 g of tungsten oxide-supported zirconia (the same amount of 71.3 m ² / g). This product was mixed with 1.616 g of chromium nitrate dissolved in 100 ml of distilled water (10 wt% in terms of chromium) and mixed at 80 ° C for 3
Stir for hours. After evaporating to dryness, it was dried at 100 ℃ for 3 hours and then 600
After calcining at ℃ for 3 hours, 2.2g of chromium / tungsten oxide-supported zirconia catalyst was finally obtained (52.7m ² / g). Put 1 g of the catalyst thus obtained in a quartz reaction tube together with 2 g of quartz sand as a diluent, replace it with a mixed gas of nitrogen and n-butane (volume ratio (n-butane / nitrogen = 1/9), and flow rate of 60 ml / min. It was introduced into the reaction tube at 500 ° C. and the reaction was carried out at the same temperature for 30 minutes, and the product was analyzed by gas chromatography. The absolute yield of isobutene based on the starting material n-butane was 3.11% .By-products were other butenes (1-butene, trans- or cis-2-butene), isobutane and C1-C3.
Hydrocarbons were detected.

The n-butane conversion, isobutene selectivity and absolute yield were calculated as follows for convenience. n-Butane conversion [C (M)] = A / (A + B) x 100 (%) A: product weight B: unreacted n-butane weight In this case, product weight A is [CH ₄ + 2xC2 + 3xC3 + 4xC4]. However, in this calculation formula, CH ₄ , C 2, C 3 and C 4 respectively represent the number of moles of methane, (ethane + ethylene), (propane + propylene) and (isobutane + butenes). The unreacted n-butane weight B was defined as the number of moles of unreacted n-butane x1. Isobutene selectivity [S (i-C4 ')] = [4 x i-C4'] / A x 10
0 (%) Absolute yield of isobutene [Y (i-C4 ')] = C (M) x S (i-C4') /
100 (%) provided that i-C4 ′ has isobutene and A has the same meaning as described above.

Comparative Example 1 A reaction was carried out in the same manner as in Example 1 except that the catalyst excluding chromium was used, but the conversion of n-butane was 3.4%, the selectivity of isobutene was 7.8%, and the absolute isobutene was absolute. yield
0.26%, and the absolute yield of isobutene was about 1/1 of that of Example 1.
Was 2.

[0022]

INDUSTRIAL APPLICABILITY According to the method of the present invention, isobutene can be synthesized from n-butane having low reactivity in a single step with enhanced selectivity and yield. Therefore, it has important industrial significance from the viewpoint of effective use of fossil resources and energy saving.

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-1-288339 (JP, A) JP-A-61-249539 (JP, A) JP-A-61-167629 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C07C 5/373 C07C 11/09 B01J 23/26-23/30 B01J 21/02 C07B 61/00 300

Claims (2)

(57) [Claims] 1. A method for producing isobutene from n-butane in a single step by dehydrogenation / isomerization in the presence of a catalyst,
A method for producing isobutene, comprising using a catalyst in which a chromium compound is supported on a zirconia-based oxide superacid as the catalyst. 2. The method for producing isobutene according to claim 1, wherein the super strong acid catalyst is one synthesized from tungsten oxide and zirconia.