Method for preparing iodine-doped TiO2 nano-catalyst and use thereof in heterogeneously catalyzing configuration transformation of trans-carotenoids

Abstract

The present invention relates to a method for preparing an iodine-doped TiO.sub.2 nano-catalyst and use of the catalyst in heterogeneously catalyzing configuration transformation of trans-carotenoids. The iodine-doped TiO.sub.2 nano-catalyst is prepared by a sol-gel process using a titanate ester as a precursor and an iodine-containing compound as a dopant in the presence of a diluent, inhibitor and complexing agent. The catalyst exhibits high activity for isomerization of the trans-carotenoids into their cis-isomers within a short catalytic time. The catalyst can be easily prepared and is highly efficient, economical, recyclable and environmentally friendly.

Claims

1. The method of using an iodine-doped TiO.sub.2 nano-catalyst in heterogeneously catalyzing configuration transformation of trans-carotenoids into their cis-isomers, the method comprising: dissolving trans-lycopenes or -carotenes in ethyl acetate; adding a predetermined amount of said iodine-doped TiO.sub.2 nano-catalyst; heating to refluxing in darkness for a fixed period of time to form a mixture; cooling the mixture to a room temperature; centrifuging the mixture to isolate the catalyst; and evaporating the solution under vacuum to remove ethyl acetate to form a reside product lycopene or -carotene with a high proportion of cis-configuration.

2. The method of using the iodine-doped nano-catalyst in heterogeneously catalyzing configuration transformation of trans-carotenoids according to claim 1, wherein, the method is used for catalytic isomerization of lycopene to form the reside product having 19.28% 5-cis-lycopene.

3. The method of using the iodine-doped TiO.sub.2 nano-catalyst in heterogeneously catalyzing configuration transformation of trans-carotenoids according to claim 1, wherein, the method is used for catalytic isomerization of -carotene to form the reside product having 21.33% 9-cis--carotene.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a HPLC spectrum in which the catalyst obtained in example 5 is used for catalytic isomerisation of all-trans-lycopene (purity: 90%) for 2 h following the catalyst activity evaluation in the summary of the invention. It can be known from FIG. 1 that the relative percentage of total cis-lycopenes is 79.41, of which the relative percentage of 5-cis-lycopene is 19.28.

(2) FIG. 2 is a HPLC spectrum in which the catalyst obtained in example 5 is used for catalytic isomerisation of all-trans--carotene (purity: 90%) for 2 h following the catalyst activity evaluation in the summary of the invention. It can be known from FIG. 2 that the relative percentage of total cis--carotenes is 53.77, of which the relative percentage of 9-cis--carotene is 21.33.

(3) FIG. 3 is a TEM image of the catalyst obtained in example 5. It can be seen from FIG. 3 that the catalyst is nano-sized particles.

(4) FIG. 4 is a histogram showing comparison of results of lycopene isomerisation with time in the presence of the catalyst (10 mg) obtained in example 5 and in the absence of the catalyst. It can be seen from FIG. 3 that for catalytic reaction for 1 h to 2 h, the relative percentage of total cis-lycopenes increases from 65.81 to 79.41, and for non-catalyzed thermal isomerisation, the relative percentage only increases from 18.64 to 29.84; for catalytic reaction up to 5 h, the relative percentage of total cis-lycopenes is 82.36, and for non-catalyzed reaction, the relative percentage only is 32.19. This indicates that the catalyst obtained in the present application is capable of greatly improving the isomerisation rate of lycopenes.

DETAILED DESCRIPTION OF THE INVENTION

(5) For a better understanding of the present invention, the present invention is further described below in connection with specific embodiments, but the scope of the present invention is not limited to thereto.

(6) All the reagents used in the examples of the present invention are purchased from Sinopharm Chemical Reagent Co., Ltd (China), and unless otherwise specified, are analytically pure, in which tetrabutyl titanate (relative density: 0.996) and tetraisopropyl titanate are chemically pure.

Example 1

(7) (1) 200 mg KI and 4 mg polyvinyl pyrrolidone were added into a 60 mL aqueous solution of 80% ethanol at normal temperature, and uniformly mixed to give a mixture A;

(8) (2) 10 mL tetrabutyl titanate (about 10 g) was added into 5 mL absolute ethanol, and then 0.5 mL acetic acid was added and uniformly mixed to give a mixture B;

(9) (3) the mixture B was slowly added dropwise into the mixture A at RT with vigorous stirring, and further stirred for 2 h after the addition is completed;

(10) (4) the reaction solution from the step (3) was placed into a wide-mouthed container to stand for aging for 1 day, to give a TiO.sub.2 gel;

(11) (5) the TiO.sub.2 gel from the step (4) was dried at 60 C. under a vacuum degree of 0.1 MPa for 12 h, and then initially ground into TiO.sub.2 powder; and

(12) (6) the TiO.sub.2 powder from the step (5) was calcined at 160 C. under a vacuum degree of 0.1 MPa for 2.0 h, and then re-ground into an iodine-doped TiO.sub.2 nano-catalyst.

(13) Evaluation of Catalytic Activity:

(14) To a 25 mL round-bottomed flask were added 20 mug lycopenes or -carotenes at a purity of 90%, 10 mg the catalyst and 20 mL ethyl acetate. The flask was attached with a condensing means and a nitrogen purging of oxygen means, placed in a water bath at 77 C. to react away from light for 2 h, and cooled in an ice-water bath. 100 L of the reaction solution was taken, made up to with ethyl acetate to 5 mL, and filtered through a 0.22 m filter membrane. Then, the relative percentage of each isomer was detected with a liquid chromatograph using an area normalization method at 472 nm for lycopenes and at 450 nm for 3-carotenes. Chromatographic column: YMC C30 column (5 m, 250 mm4.6 mm); mobile phase:A phase:methanol:acetonitrile=25:75, B phase: methyl t-butyl ether 100%; gradient conditions: 0-20 min, A phase from 100% to 50%, 20-40 min, A phase constant at 50%; sample solvent: ethyl acetate; flow rate: 1 mL/min; column temperature: 30 C.; and injection volume: 20 L. The relative percentage of total cis-lycopenes is 59.21, and the relative percentage of total cis--carotenes is 34.37.

(15) Materials and Process Conditions Employed in the Steps of Examples 2 to 6 are Shown in Table 1 Below:

(16) TABLE-US-00001 TABLE 1 process and step materials example 2 example 3 example 4 example 5 example 6 (1) iodine- KI KI KI KI NaI containing 600 mg 300 mg 350 mg 450 mg 400 mg compound complexing polyvinyl polyvinyl polyvinyl polyvinyl polyethylene agent pyrrolidone pyrrolidone pyrrolidone pyrrolidone glycol 30 mg 10 mg 10 mg 15 mg 20 mg aqueous 60 mL 95% 60 mL 90% 60 mL 95% 60 mL 90% 60 mL 80% ethanol ethanol ethanol ethanol ethanol ethanol solution (2) titanate tetrabutyl tetrabutyl tetrabutyl tetrabutyl tetraisopropyl ester titanate titanate titanate titanate titanate 10 mL 10 mL 10 mL 10 mL 10 mL diluent ethanol ethanol 10 mL 10 mL 10 mL 100 mL 20 mL ethanol ethanol ethanol inhibitor acetic acid acetic acid acetic acid acetic acid acetyl 5 mL 2 mL 2 mL 3 mL acetone 2 mL (3) mixing and 6 h 5 h 3 h 3 h 4 h then stirring (4) aging 6 days 3 days 5 days 4 days 4 days (5) vacuum 0.1 MPa\ 0.1 MPa\ 0.1 MPa\ 0.1 MPa\ 0.1 MPa\ drying 100 C.\12 h 80 C.\12 h 85 C.\12 h 80 C.\12 h 80 C.\12 h (6) Vacuum 0.1 MPa\ 0.1 MPa\ 0.1 MPa\ 0.1 MPa\ 0.1 MPa\ calcining 220 C.\4.0 h 180 C.\3 h 185 C.\2 h 195 C.\2 h 185 C.\2 h Evaluation total 43.51 68.51 76.27 79.41 78.65 of cis-lycopenes catalytic total 29.69 44.38 49.97 53.77 51.06 activity/ cis--carotenes relative percentage

(17) Comparing Comparative Example 1 and Comparative Example 2 with Example 5, Materials and Process Conditions Employed in the Steps are Shown in Table 2 Below:

(18) TABLE-US-00002 TABLE 2 process and comparative comparative step materials example 1 example 2 (1) iodine-containing KI 450 mg KI 450 mg compound complexing agent 0 mg polyvinyl pyrrolidone 15 mg aqueous ethanol 60 mL 90% 60 mL 90% solution ethanol ethanol (2) titanate ester tetrabutyl titanate tetrabutyl 10 mL titanate 10 mL diluent ethanol 10 mL 10 mL ethanol inhibitor acetic acid 3 acetic acid 3 mL mL (3) mixing and then 3 h 3 h stirring (4) aging 4 days 4 days (5) drying vacuum degree atmospheric 0.1 MPa\80 C.\ air\80 C.\12 h 12 h (6) calcining vacuum degree atmospheric 0.1 MPa\195 C.\ air\195 C.\2 h 2 h Evaluation total cis-lycopenes 42.26 37.53 of catalytic activity/relative total cis--carotenes 26.72 23.16 percentage

(19) It can be known by comparing catalysis results between comparative example 1 in table 2 and example 5 that, the complexing agent, polyvinyl pyrrolidone, facilitates improvement of the activity of the catalyst, possibly due to the fastening effect of polyvinyl pyrrolidone on active iodine in nano TiO.sub.2 meso-pore at a certain temperature; and it can be known by comparing catalysis results between comparative example 2 and example 5 that, the vacuum drying-vacuum calcining process facilitates improvement of the activity of the catalyst, possibly due to difficulty in oxidation of active iodine in nano TiO.sub.2 meso-pore into inactive iodate with high-valent iodine, so that the catalyst has a higher activity than that in the atmospheric air drying-atmospheric air calcining process.

(20) The invention is not in any way limited to the embodiments described above, and all equivalent modifications and variations of this invention fall within the scope of the present invention.