Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Inorganic carbon containing
Reexamination Certificate
2002-05-06
2004-06-22
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Inorganic carbon containing
C502S182000, C562S412000, C562S485000, C562S487000
Reexamination Certificate
active
06753290
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to catalyst compositions for purifying terephthalic acid, based on Group VIII metals, to methods for preparing thereof, and to a method of purifying terephthalic acid suitable for the subsequent synthesis of polyester polymers and copolymers used in the manufacture of textile fibers.
It is of importance that terephthalic acid which is used as a monomer in the manufacture of polymer fibers should have a high purity. The main controllable quality parameters of pure terephthalic acid are the content of p-carboxybenzaldehyde and colored impurities in it.
Purified terephthalic acid is derived from less pure, technical grade or “crude” terephthalic acid by hydrofining the latter (treating in the presence of hydrogen) over Group VIII metal catalysts. Crude terephthalic acid is dissolved in water at an elevated temperature, and the resulting solution is hydrogenated in a vibrated reactor or in a reactor with a stationary bed, preferably in the presence of Group VIII metal catalysts. The methods of purification, composition of the catalysts, and processes for preparing these catalysts are described in numerous patents.
DESCRIPTION OF THE RELATED ART
The activity and selectivity of catalysts for the hydrofining of terephthalic acid depend on a great number of factors, such as the content of Group VIII metal(s) in the catalyst, the type of support, the method of applying Group VIII metal(s) to the support, and also on the distribution of the metal or metals of Group VIII were applied to a support, and also on the distribution of said metal(s) over the granule of the carrier.
Known in the art is a method of hydrofining terephthalic acid [UK Patent No. 994769, 1965], wherein a palladium-on-active carbon catalyst composition displays high activity in the reaction of purifying terephthalic acid from p-carboxy-benzaldehyde impurities. As supports for palladium other compounds, such as SiO
2
, Al
2
O
3
, were also investigated. It was found that carbon carriers were the best, because they, in contrast to oxide carriers, are not subject to rapid degradation in corrosive hot aqueous solutions of terephthalic acid.
The results of investigating the influence of the nature of carbon carriers are known. It has been shown that active carbons prepared from vegetable, animal or mineral sources, preferably from coconut active carbon, are suitable for the production of palladium catalysts for the hydrofining of terephthalic acid. It is desirable that the surface area of such active carbons should be at least 600 m
2
/g, and the size of granules should correspond to 3-6 mm. In U.S. Pat. No. 4,728,630, 1988 an additional characteristic of such active carbon is introduced, namely, the pH value of its aqueous suspension. In SU Patent No. 1660282, 1997 a possibility is disclosed of using, as a suitable carrier, an active porous carbonaceous material modified with pyrocarbon. In U.S. Pat. Nos. 4,415,479, 1983; 4,421,676, 1983; and 4,791,226, 1988 it is indicated that for a more effective process of the hydrofining of terephthalic acid from p-carboxybenzaldehyde it is important to prepare catalysts with a definite size of the particles of applied palladium. The size of such particles must be not greater than 35 Å. The authors of U.S. Pat. Nos. 4,394,299, 1983 and 4,791,226, 1988 also point out a positive effect of such distribution of palladium particles in the granule of a carbon material, when they predominate on the outer surface of the granule.
In many patents it is pointed out that along with monometallic catalysts, the incorporation of Ni, Co, Cu, Fe, Mn, U, Cr, as well as Ir, Rh, Pt and Ru, into the catalyst composition may produce positive effect on the catalytic activity of palladium.
According to other group of patents [U.S. Pat. Nos. 4,629,715, 1986 and 4,892,972, 1990], the most effective action of bimetallic catalysts is attained, when the catalysts are arranged in a reactor in layers, for instance, Pd/C and Rh/C instead of one layer (Rh+Pd)/C. The authors of U.S. Pat. No. 4,892,972, 1990 even claim a method with the use of a layered catalyst bed, e.g., Ru/C+Rh/C+Pd/C.
Usually, catalysts comprising Group VIII metals, particul-arly palladium catalysts, are prepared by the adsorption of a palladium salt from solution to the carrier. In one of the processes [U.S. Pat. No. 2,857,337, 1967] such salt is treated with a water-soluble metal hydroxide or with a basic carbonate, this being followed by the reduction to metallic palladium with the help of such reducing agents as formaldehyde, glucose, glycerol, etc.
According to Keith et al. [U.S. Pat. No. 3,138,560, 1964], on addition of sodium tetrachloropalladoate or palladium chloride to many of carbon carriers, a large part of palladium immediately precipitates in the form of lustrous film of metallic palladium. Catalysts prepared by such a method usually have low activity. An opinion was voiced that palladium directly reduces to metal owing to free electrons or to the presence on the carbon surface of such functional groups as aldehydes. Palladium catalysts in the step preceding the reduction are predominantly prepared by fixing palladium in the form of an insoluble compound, so to avoid the problems of migration of palladium particles and growth of crystallites which may originate during the reduction of palladium from solution.
Though p-carboxybenzaldehyde is the most harmful impurity, which is crucial for the quality of the terephthalic acid used for the manufacture of plastics and sharply deteriorates the quality of the latter, p-toluic acid (p-TA) is also an undesirable impurity, which must be removed from the aqueous solution of terephthalic acid, obtained as a result of hydrofining. Though such removal can be achieved to a large extent owing to the greater solubility of p-toluic acid as compared to terephthalic acid, in water nevertheless substantial amounts of p-toluic acid are trapped within purified terephthalic acid crystals in the step of terephthalic acid crystallization from solution.
To avoid this disadvantage attendant to the separation of p-toluic acid, it has been proposed to decarbonylate p-carboxybenzaldehyde in aqueous solutions to benzoic acid in the presence of a palladium-on-carbon catalyst, since benzoic acid is more soluble in water than p-toluic acid [U.S. Pat. No. 3,456,001, 19691]. However, the foregoing decarbonylation of p-carboxybenzaldehyde to benzoic acid produces equimolar amounts of carbon monoxide, a well-known poison for the noble metals such as palladium [U.S. Pat. No. 4,201,872, 1980]. To minimize catalyst poisoning, in the aforementioned US Patent it is proposed to carry out the decarbonylation at relatively low process pressures so as to minimize dissolved carbon monoxide concentration in the liquid reaction medium. The process pressure also must be controlled within a closely defined pressure range. The generated carbon monoxide is purged from the reactor as a gas.
It is known [U.S. Pat. No. 4,892,972, 1990], that the use in the aforesaid purification of crude terephthalic acid of a catalyst system comprising a first layer of catalyst particles containing a metal of Group VIII of the Periodic Table of Elements supported on a carbon carrier and a second layer of palladium-on-carbon catalyst particles and the passage of the aqueous solution of crude terephthalic acid through the aforesaid first layer of rhodium-on-carbon catalyst particles and then through the second layer of palladium-on-carbon catalyst particles permits the amount of p-toluic acid produced during purification of crude terephthalic acid to be minimized. Such method of using the aforesaid catalyst system does not promote the hydrogenation of p-carboxybenzaldehyde to p-toluic acid but instead promotes the decarbonylation of p-carboxybenz-aldehyde to benzoic acid, which is more soluble than p-toluic acid in water and thus is more readily separable than p-toluic acid from terephthalic acid upon crystall
Hva Jhung Sung
Likholobov Vladimir Alexandrovich
Romanenko Anatoly Vladimirovich
Seok Park Jun
Timofeeva Maria Nikolaevna
Bell Mark L.
Hailey Patricia L.
Institut Kataliza Imeni G.K. Boreskova Sibirskogo Otdelenia Ross
Ladas & Parry
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