JP5114712B2 - Solid acid catalyst - Google Patents

Description

  The present invention relates to a novel high-performance solid acid catalyst and a method for producing the same. The catalyst of the present invention is useful for producing chemical products with energy saving and high efficiency.

  Sulfuric acid is an essential catalyst for the production of various petrochemical products, raw materials for chemical products, general-purpose chemicals, and pharmaceuticals. However, sulfuric acid is not a catalyst that can be repeatedly recycled, and much energy and labor are required for separation of sulfuric acid and products by neutralization and waste acid treatment. For this reason, more than 15 million tons of sulfuric acid is consumed as a “non-recyclable catalyst” annually, and enormous waste of energy and waste discharge have a great impact on the environment. In addition, since sulfuric acid is highly toxic and corrosive, the labor required to ensure safety and maintain the plant cannot be ignored. Changing the acid-catalyzed reaction process, which depends on sulfuric acid, to a highly efficient process that is as environmentally friendly as possible is a major challenge for the future chemical industry. A solid acid (solid acid) that can be used repeatedly, is easy to separate and recover, and is less toxic (solid acid) is one keyword that clears this problem.

An ideal solid acid that can replace sulfuric acid is (1) has a high density of strong acid sites that function in all solvents and atmospheres including water, (2) is thermally and chemically stable, (3 ) An inexpensive material that can be synthesized from ordinary raw materials in a simple manner. Since such materials can also be used as proton conductors for polymer electrolyte fuel cells, research and development is proceeding at a rapid pace. Currently, solid acids are used in various fields, and these are ion-exchanged with inorganic oxide solid acids such as SiO ₂ -Al ₂ O ₃ , zeolite, and hydrous niobic acid (Nb ₂ O ₅ · nH ₂ O). It can be roughly divided into polymer solid acids such as resins. The inorganic oxide solid acid is thermally and chemically stable, and is an indispensable catalyst for the manufacture of various chemical products and the petrochemical industry. However, there are few materials that exhibit sufficient acid catalytic activity in water, and the acid point density is low. On the other hand, strongly acidic ion exchange resins have a high density of strong acid sites, but still have the disadvantage that their catalytic activity is much smaller than that of sulfuric acid and their heat resistance is also low.

By the way, the present inventor has found that amorphous carbon into which a sulfonic acid group has been introduced (sulfonic acid group-introduced amorphous carbon) serves as a solid acid instead of sulfuric acid, and has already filed an application (Patent Document 1, Patent Document 2). Since this material can take in a large amount of hydrophilic molecules into the bulk and can make the inside of the bulk a reaction field, acid-catalyzed reactions using hydrophilic molecules as reactants, or acids using hydrophilic molecules as solvents. A high catalytic activity is exhibited in the catalytic reaction (Non-patent Document 1). On the other hand, in some acid-catalyzed reactions with hydrophobic molecules as reactants, this material cannot incorporate hydrophobic molecules into the bulk, so only the surface sulfonic acid groups are involved in the reaction. However, due to its small surface area (usually less than 50 m ² g ⁻¹ ), some acid-catalyzed reactions with hydrophobic molecules as reactants cannot exhibit sufficient catalytic activity.

JP 2004-238311 A International Publication No. 2005/029508 Pamphlet Chemistry of Materials, (2006), 18 (13), 3039-3045.

  The present invention has been made under the technical background as described above. In an acid-catalyzed reaction using a hydrophobic molecule as a reactant, the present invention is intended to exhibit sufficient catalytic activity for amorphous carbon into which a sulfonic acid group is introduced. It aims to provide a means.

  As a result of intensive investigations to solve the above problems, the present inventor has fixed sulfonic acid group-introduced amorphous carbon to a high surface area support so that sulfonic acid can be used even in acid-catalyzed reactions using hydrophobic molecules as reactants. It has been found that the group-introduced amorphous carbon exhibits high catalytic activity.

  It is generally expected that by immobilizing an acid catalyst on a high surface area support, the activity of the catalyst will be improved (eg, the case of Nafion in Comparative Example 2 and Comparative Example 3). However, the improvement of the activity by fixing the sulfonic acid group-introduced amorphous carbon to the high surface area support was more remarkable than such expectation (Example and Comparative Example 1).

The present invention has been completed based on the above findings.
That is, the present invention provides the following (1) to (8).

(1) A solid acid catalyst comprising a high surface area support and amorphous carbon having a sulfonic acid group fixed thereto.
(2) The solid acid catalyst according to (1), wherein the high surface area support has a specific surface area of 50 m ² g ⁻¹ or more.
(3) The solid acid catalyst according to (1) or (2), wherein the material of the high surface area carrier is a mesoporous material.
(4) The solid acid catalyst according to (3), wherein the mesoporous material is mesoporous silica.
(5) Amorphous carbon introduced with a sulfonic acid group exhibits a sulfonic acid density of 0.5 mmol / g or more, and an integral intensity ratio of D band and G band in a Raman spectrum is 0.1 to 0.7. The solid acid catalyst according to any one of (1) to (4).
(6) A method for producing a solid acid catalyst, comprising a step of fixing an organic compound to a high surface area support and a step of heat-treating the organic compound fixed to the high surface area support in concentrated sulfuric acid or fuming sulfuric acid.
(7) including a step of partially carbonizing the organic compound between the step of fixing the organic compound to the high surface area support and the step of heat-treating the organic compound fixed to the high surface area support in concentrated sulfuric acid or fuming sulfuric acid. (6) The manufacturing method of the solid acid catalyst as described in (6) characterized by these.
(8) The method for producing a solid acid catalyst according to (6) or (7), wherein the step of fixing the organic compound to the high surface area support is performed under low pressure.

  When an acid catalyzed reaction is performed using a liquid acid catalyst, a large amount of energy is required for acid separation. However, since the acid catalyst of the present invention is a solid, the catalyst can be easily separated from the product. .

  In addition, the acid catalyst of the present invention can exhibit sufficient catalytic activity even in a reaction using a hydrophobic molecule as a reactant, unlike a catalyst having sulfonic acid group-introduced amorphous carbon alone.

Hereinafter, the present invention will be described in detail.
The solid acid catalyst of the present invention comprises a high surface area support and sulfonic acid group-introduced amorphous carbon fixed thereto. The solid acid catalyst of the present invention may be composed of only a high surface area carrier and sulfonic acid group-introduced amorphous carbon, but may contain other elements.

The high surface area carrier may be any material as long as it can fix the sulfonic acid group-introduced amorphous carbon. The material of the high surface area carrier is not particularly limited, and examples thereof include oxide solids such as silica, alumina, and titania, mesoporous materials made of these oxide solids, activated carbon, and the like. The specific surface area of the high surface area carrier is not particularly limited as long as the sulfonic acid group-introduced amorphous carbon is within a range where it can exhibit catalytic activity even for hydrophobic molecules, but it is preferably 50 m ² g ^-1 or more. And more preferably 100 m ² g ⁻¹ or more. High surface area carriers usually have many pores. The pore diameter of this pore is not particularly limited, but is preferably 1 to 50 nm. Further, the pores may penetrate the carrier or may not penetrate.

  The sulfonic acid group-introduced amorphous carbon is not particularly limited as long as it has acid catalytic ability. For example, the sulfonic acid group-introduced amorphous carbon described in International Publication No. Solid acids described in Japanese Patent No. 238311 can be used. In the present invention, “sulfonic acid group-introduced amorphous carbon” refers to carbon having a sulfonic acid group and having no crystal structure or having only an incomplete crystal structure.

  A preferable sulfonic acid group-introduced amorphous carbon is, for example, carbon in which both G band and D band are detected in a spectrum by Raman spectroscopy, and an integrated intensity ratio (I (D)) of D band and G band. / I (G)) can be exemplified by carbon having a value of 0.1 to 0.7. When the integral intensity ratio is less than 0.3, the number of aggregated carbon six-membered rings is small and it does not become a solid, and when it exceeds 0.7, the graphene sheet becomes large and the sulfonic acid density decreases, so that it does not function as a catalyst. The integrated intensity ratio may be 0.1 to 0.7, preferably 0.1 to 0.65, and more preferably 0.1 to 0.6. In the present specification, the D band, the G band, and their integrated intensities are defined as follows.

The D band is vibration of A1g breathing mode in a carbon six-membered ring, and its peak top appears at 1350 cm ^{−1 to} 1360 cm ⁻¹ .
G band is a vibration of E2g mode of six-membered carbon ring, the peak top appears at 1580cm ^-1 ~ ± 5cm ^-1.
The Raman spectrum consisting of the sum of both peaks was divided into two peaks with Gaussian or Gaussian-Lorentzian, and the obtained integrated intensities of the D band and G band were used as the integrated intensities.

  In addition, the sulfonic acid density of the sulfonic acid group-introduced amorphous carbon is preferably 0.5 mmol / g or more, more preferably 1.0 mmol / g or more, and further preferably 3.0 mmol / g or more. The upper limit of the sulfonic acid density is not particularly limited, but is preferably 8 mmol / g or less.

  The solid acid catalyst of the present invention can be used as a catalyst for an acid catalyzed reaction using a hydrophobic molecule as a reactant, but is not limited thereto, and can be used as a catalyst for an acid catalyzed reaction using a hydrophilic molecule or the like as a reactant. Also good. As an acid-catalyzed reaction using a hydrophobic molecule as a reactant, for example, 2,4-diphenyl-4-methyl-1-pentene and 2,4-diphenyl-4-methyl-2-pentene are produced from α-methylstyrene. Examples include reaction, alkylation in which isobutane is added to isobutene to produce isooctane, and Friedel-Crafts alkylation.

  The solid acid catalyst of the present invention can be produced by a method including a step of fixing an organic compound on a high surface area carrier and a step of heat-treating the organic compound fixed on the high surface area carrier in concentrated sulfuric acid or fuming sulfuric acid.

  As the organic compound, aromatic hydrocarbons can be used, but other organic compounds such as glucose, sugar (sucrose), natural products such as cellulose, synthetic polymers such as polyethylene and polyacrylamide. A compound may be used. The aromatic hydrocarbons may be polycyclic aromatic hydrocarbons or monocyclic aromatic hydrocarbons, and for example, benzene, naphthalene, anthracene, perylene, coronene, etc. can be used, preferably Naphthalene or the like can be used. Only one type of organic compound may be used, but two or more types may be used in combination. Further, it is not always necessary to use a purified organic compound, and for example, heavy oil containing aromatic hydrocarbons, pitch, tar, asphalt and the like may be used.

  The method for fixing the organic compound to the high surface area carrier is not particularly limited. For example, the organic compound is dissolved or dispersed in an appropriate solvent or dispersion medium, the solution is impregnated in the high surface area carrier, and then the solvent is removed. By doing so, the organic compound can be fixed to the high surface area carrier.

  Fixation of the organic compound to the high surface area support may be performed under normal pressure, but when the pores of the high surface area support do not penetrate the support, it is preferably performed under low pressure. This is because, when the pores do not penetrate the support, the organic compound may not diffuse to the deep portion of the pores under normal pressure due to air interference in the pores. The “low pressure” here is not particularly limited as long as it is within the range in which the above-described problem of diffusibility of the organic compound can be improved, but is usually about 0.9 to 0.01 atm.

  The heat treatment of the organic compound in concentrated sulfuric acid or fuming sulfuric acid can be performed, for example, in the same manner as described in International Publication No. 2005/029508. The heat treatment is required to produce amorphous carbon having a high sulfonic acid density in an inert gas stream or a dry air stream. The heat treatment temperature is not particularly limited as long as it is a temperature at which a reaction such as partial carbonization, cyclization, condensation, and sulfonation of an organic compound proceeds. Industrially, it is 50 to 350 ° C, preferably 80 to 200 ° C. is there. When the treatment temperature is less than 50 ° C, the condensation and carbonization of the organic compound is insufficient, the formation of carbon is insufficient, the sulfonic acid group may not be sufficiently introduced, and the treatment temperature is 350 ° C. If it exceeds, thermal decomposition of the sulfonic acid group may occur.

  The heat treatment time can be appropriately selected depending on the organic compound to be used, the treatment temperature and the like, but is usually 1 to 50 hours, preferably 5 to 20 hours.

  Although the quantity of the concentrated sulfuric acid or fuming sulfuric acid to be used is not specifically limited, It is 2.6-50.0 mol normally with respect to 1 mol of organic compounds, Preferably it is 6.0-36.0 mol.

  Before the organic compound is heat-treated in concentrated sulfuric acid or fuming sulfuric acid, the organic compound fixed to the high surface area carrier is preferably partially carbonized. Partial carbonization can be performed by heating an organic compound in an inert gas stream such as nitrogen or argon. The heating temperature at this time is usually 100 to 600 ° C., and the treatment time is usually 1 Minutes to 20 hours.

Hereinafter, the present invention will be described in more detail with reference to examples.
〔Example〕
Mesoporous silica SBA-15 (J. Am. Chem. Soc. 122, 10712 (2000): specific surface area 1020 m ² g ^-1 ) per 1 g, water 2 g, D-glucose 1.25 g and concentrated sulfuric acid (90% or more) 0.14 An aqueous solution in which g was dissolved was soaked, dried at 100 ° C. for 24 hours, and then partially carbonized by heating in a nitrogen stream at 550 ° C. for 3 hours. This was heated in concentrated sulfuric acid at 150 ° C. for 10 hours, and then repeatedly washed with distilled water at 80 ° C. or higher to obtain an amorphous carbon-high surface area carrier composite with sulfonic acid groups introduced. The specific surface area of this composite was 610 m ² g ⁻¹ , and 38% of its weight was confirmed to be sulfonic acid group-introduced amorphous carbon by powder X-ray diffraction and weight change due to carbon combustion. It was confirmed that 1 g of sulfonic acid group-introduced amorphous carbon in this composite had 0.95 mmol of sulfonic acid groups. The integrated intensity ratio (I (D) / I (G)) of the D band and G band in the Raman spectrum of this sulfonic acid group-introduced amorphous carbon was 0.68.

  The sulfonic acid density was measured as follows. Since almost all of the sulfur element contained in the sulfonic acid group-introduced amorphous carbon is due to the sulfonic acid group, sulfur in the sample is determined by elemental analysis by combustion (SX-Elements Micro Analyzer YS-10 (yanaco)). Then, the amount of sulfonic acid was determined. The integrated intensity ratio between the D band and G band in the Raman spectrum was determined as follows. The sample powder was placed on a sample holder of an NRS-2100 type triple monochromator Raman spectrophotometer (JASCO) and the Raman spectrum was measured. The Raman spectrum in which both the D band and the G band are observed is split into two bands, the Gaussian or Gaussian-Lorentzian, into the D band and the G band, and the resulting integrated intensities of the D band and G band are integrated. Strength.

  After adding 0.2 g of the above catalyst to 25 ml of cumene (solvent) in which 25 mmol of α-methylstyrene was dissolved, the mixture was reacted at 50 ° C. for 1 hour, and the product was quantified by gas chromatography. As a result, in addition to the unsaturated dimer (2, 4-diphenyl-4-methyl-1-pentene and 2, 4-diphenyl-4-methyl-2-pentene), which are the desired products, it is a by-product. 1,1,3-Trimethyl-3-phenylindane was also produced, but the amount produced was small. The amount of unsaturated dimer produced was 10.7 mmol, and the selectivity was confirmed to reach 99%.

(Comparative Example 1)
Carbonaceous powder was obtained by heating 20 g of D-glucose under a nitrogen gas flow at 400 ° C. for 15 hours. This powder was heated at 150 ° C. for 15 hours with stirring in 200 ml of 15 wt% fuming sulfuric acid to obtain a black powder. By repeatedly washing this with distilled water, sulfuric acid in the material was removed, and sulfonic acid group-introduced amorphous carbon was obtained.

The integrated intensity ratio (I (D) / I (G)) of D band and G band in the surface area, sulfonic acid density and Raman spectrum of this sulfonic acid group-introduced amorphous carbon is 2m ² g ^-1 and 1.5 mmol. / g and 0.59.

  After adding 0.2 g of the above catalyst to 25 ml of cumene (solvent) in which 25 mmol of α-methylstyrene was dissolved, the mixture was reacted at 50 ° C. for 1 hour, and the product was quantified by gas chromatography. As a result, it was confirmed that α-methylstyrene was hardly consumed in the reaction, and α-methylstyrene dimer was not produced at all.

(Comparative Example 2)
After adding 0.2 g of Nafion NR50 (sulfonic acid density: 0.9 mmol / g) to 25 ml of cumene (solvent) in which 25 mmol of α-methylstyrene was dissolved, the mixture was reacted at 50 ° C. for 1 hour, and the product was quantified by gas chromatography. . As a result, it was confirmed that the production amount of the unsaturated dimer as the target product was only 0.1 mmol, and the selectivity thereof was 40%.

(Comparative Example 3)
After adding 0.2 g of Nafion SAC13 (Nafion supported on high surface area silica, sulfonic acid density: 0.3 mmol / g) to 25 ml of cumene (solvent) in which 25 mmol of α-methylstyrene was dissolved, the mixture was reacted at 50 ° C. for 1 hour, The product was quantified by gas chromatography. As a result, it was confirmed that the amount of the unsaturated dimer that was the target product was only 4.4 mmol, and the selectivity was only 40%.

Claims (7)

A solid acid catalyst comprising a high surface area support having a specific surface area of 50 m ² g ^-1 or more and amorphous carbon having a sulfonic acid group fixed thereto. The solid acid catalyst according to claim 1 , wherein the material of the high surface area support is a mesoporous material. The solid acid catalyst according to claim 2 , wherein the mesoporous material is mesoporous silica. Amorphous carbon having sulfonate group introduced therein is shown a sulfonic acid density of more than 0.5 mmol / g, according to claim 1, the integrated intensity ratio of D band and G band in Raman spectrum, characterized in that it presents a 0.1 to 0.7 The solid acid catalyst as described in any one of thru | or 3 .   A method for producing a solid acid catalyst, comprising: a step of fixing an organic compound to a high surface area support; and a step of heat-treating the organic compound fixed to the high surface area support in concentrated sulfuric acid or fuming sulfuric acid. A step of partially carbonizing the organic compound between the step of fixing the organic compound to the high surface area carrier and the step of heat-treating the organic compound fixed to the high surface area carrier in concentrated sulfuric acid or fuming sulfuric acid. A method for producing a solid acid catalyst according to claim 5 . The method for producing a solid acid catalyst according to claim 5 or 6 , wherein the step of fixing the organic compound to the high surface area support is performed under a low pressure.