TW201004700A - Pd/c hydrogenation catalyst, preparation and use thereof - Google Patents

Abstract

A palladium/carbon hydrogenization catalyst comprises carbon granules activated a supporting material and metallic palladium as active component. A content of the metallic palladium is 0.1-5 weight%, preferably 0,2-3,5 weight%, and more preferably 0.3-0.8 weight-%, based on a total weight of the catalyst. The palladium of 45 weight% is contained within an external layer of which a depth is 0.2-20mum of the supporting material. The palladium less than 10 weight% is contained within an outermost layer of which a depth is less than 0.2mum of the supporting material. The palladium of rest weight% is contained within an inner layer of which a depth is 20-400mum of the supporting material. The invention also relates to the method of preparation and usage of palladium/carbon hydrogenization catalyst.

Description

201004700 IX. INSTRUCTIONS OF THE INVENTION: TECHNICAL FIELD OF THE INVENTION The present invention relates to a /carbon hydrogenation catalyst and a process and use thereof for the preparation of such a catalyst. [Prior Art]

The /carbon catalyst is a selective hydrogenation catalyst which can be used for the selective hydrogenation of, in particular, aromatic hydrocarbons. Specifically, the sole/carbon catalyst can be used for selective hydrogenation of an aromatic aldehyde of the formula X-aryl ring-CHO to form an anthracene ring _ch2〇h, or further hydrogenation to form xnCH3, wherein ruthenium is sulfhydryl or slow And the aromatic ring therein is a benzene ring or a naphthalene ring, wherein in the presence of hydrogen, the aromatic aldehyde is subjected to a hydrogenation reaction in an acid or an aqueous solution at 100 to 300 ° C, based on The carbon catalyst can be used for hydrofining of crude terephthalic acid and crude 2,6-naphthalene dicarboxylic acid and purification of crude p-hydroxymethylbenzoic acid, and selectively hydrogenating impurities such as aromatic aldehyde. Specifically, p-carboxybenzaldehyde (4-CBA for short) in crude terephthalic acid is hydrogenated in two steps to form 4-CBA in p-methylbenzoic acid 'crude p-hydroxymethylbenzoic acid. Hydrogenation of 2-formyl-6-naphthoic acid in methyl benzoic acid' and crude 2,6-naphthalene dicarboxylic acid to form 2-methyl-6-carotonic acid. However, since palladium is used as a single active component in the palladium/carbon catalyst, the distribution of the metal palladium on the support greatly affects the hydrogenation performance of the catalyst. In addition, since the selective hydrogenation reaction of the aromatic aldehyde is a first-order reaction, the reaction rate is fast, and it is difficult for the reactant to diffuse into the interior of the catalyst particle 201004700 during the reaction, which makes the active metal inside the particle insufficiently function. Therefore, the active metal palladium should be distributed as much as possible on the outer surface of the catalyst particles. In addition, the larger the surface area of the palladium in contact with the reactant, the better the catalytic activity. In this regard, for palladium/carbon catalysts, U.S. Patent 4,746,242 proposes to distribute the active component palladium all over the surface layer of the particles having a depth of less than 70-80 μm; U.S. Patent 6,066,589 proposes to distribute less than 5 〇wt% of palladium in the outer layer of the carrier having a depth less than that, and The amount of palladium is distributed in a carrier inner layer having a depth of 5 〇 4 〇〇 μm: and the catalyst prepared in Chinese patent CN 1457922 获得 obtains a high 4_CB Α conversion rate in a hydrotreating reaction such as crude terephthalic acid, but Up to 30% by weight of palladium is distributed in the outermost layer of the carrier having a depth of less than 〇2μηι, which directly leads to severe wear of the surface layer. Therefore, for palladium/carbon catalysts, it is desirable to further optimize the distribution of the palladium component on the support to increase catalytic activity and extend catalyst life. SUMMARY OF THE INVENTION In view of the palladium/carbon catalyst in the prior art, the present invention further reduces the distribution of the components in the outermost layer of the carrier so that the palladium component is distributed as much as possible in the outer layer and the inner layer of the carrier, while ensuring the catalytic activity. Reduce the loss of active palladium due to wear during use. Specifically, the present invention provides a palladium/carbon hydrogenation catalyst comprising activated carbon particles as a support and metal palladium as an active component, wherein the content of metal palladium is 〇l 5 wt%, preferably ruthenium based on the total weight of the catalyst. .2-3.5 Wt%, more preferably 0.3-0.8 wt%, wherein at least 45 wt% is distributed in the outer layer of the depth of 〇.2-2〇μιη, and less than l〇wt% of palladium is distributed in the depth less than The outermost layer of the carrier, and the balance is distributed in the inner layer of the carrier having a depth of melon 201004700 400 μηι. For the palladium/carbon catalyst of the present invention, wherein the activated carbon particles may be natural or shaped particles, preferably natural or shaped coconut shell carbon particles having a specific surface area of from 6 to 1 - 800 m 2 /g, preferably 8 (M5) 〇〇m2/g, a pore volume of 0.30 to 0.85 ml/g, and a particle size of 90% by weight or more of which is 4·8 mesh. For the palladium/carbon catalyst of the present invention, preferably, 45_6〇% of palladium The outer layer of the carrier is distributed at a depth of 〇2-20 μm; and preferably, the balance is distributed to the inner layer of the carrier having a depth of 20 to 180 μm. The present invention also provides a method of preparing the palladium/carbon catalyst, the method comprising The following steps are as follows: (a) selecting suitable activated carbon particles as carrier particles; (b) pre-impregnating the activated carbon particles with a competitive adsorbate at a temperature of 0-50 ° C, preferably room temperature for 5 to 60 minutes. , preferably 10-30 minutes, then filtered, and dried to obtain pre-impregnated activated carbon particles, wherein the competitive adsorbate is a concentration of from 0.01 to 0.5 N, preferably from 0.05 to 0.2 N, having a carbon number of 1 to 6 An aqueous solution of a carbon organic acid; (c) using a precursor containing palladium and The weakly acidic solution of the surfactant is loaded with palladium on the pre-impregnated activated carbon particles by dipping or spraying to obtain a supported catalyst, wherein the loading of the palladium is 〇 based on the total weight of the catalyst. .l-5wt%, preferably 0_2-3.5wto/〇, more preferably 0.3-0.8wt%, and wherein the pH of the solution is 3-6; (d) aging the loaded catalyst in air 1 - 24 hours, obtain the catalyst after aging; and (e) at 0-200 ° C, preferably 50-120 ° C, the aged 201004700 is preferably 1-4 hours, to obtain a live catalyst treated with a reducing agent. 5_1〇 hours, the catalyst after the treatment; and optionally the following steps: (10) pre-treating the activated carbon particles before the step (b), and coating the dust and loose parts of the surface of the (4) (4) with inorganic acid washing, Washing with deionized water to neutrality, and drying. For the preparation of the palladium/carbon catalyst of the present invention: In step (4), the selected activated carbon particles are natural or shaped particles.

Preferably, it is a natural or shaped coconut shell carbon particle having a specific surface area of mmVg, preferably .15〇〇m2/g, and a pore volume (p〇re ν〇ι) of 0.30-0.85〇^' preferably 0.40_0. 60 ml/g, and wherein the particle size of 9 〇wt% or more is 4-8 mesh; in the step (b), wherein the concentration of the inorganic acid used for washing is 〇·1 0.5N, and The inorganic acid is selected from the group consisting of hydrochloric acid, nitric acid, acid filling, and mixtures thereof, the purpose of which is to adjust the functional groups on the surface of the activated carbon particles, and the drying is at a temperature of 100-20 (TC, preferably 1 HM5 (rc) In step (b), wherein the low carbon organic acid is selected from the group consisting of citric acid, maleic acid, oxalic acid, lactic acid, and mixtures thereof, preferably citric acid, and wherein the drying temperature is 1 〇〇 2 〇 ( TC, preferably 11〇-150. (:; In the step (C), wherein the palladium precursor is selected from the group consisting of gasified palladium, palladium oxide, acetic acid, palladium nitrate, palladium acid and a basic salt thereof, The palladium ammonia complex and their mixture 'preferably a palladium acid, wherein the surfactant has a concentration of from 0.2 to 5% by weight, preferably from 0.5 to 5% by weight, of the surface Agent for adjusting 8201004700

Or (4) and/or dispersing properties, which may be an anionic surfactant, preferably a lunar polyoxyethylene ether sulfate alkali metal salt or an aliphatic polyoxyethylene acid acid, a specific example of ten The second courtyard based polyoxyethylene shouts sulfuric acid vinegar steel salt, twelve-burning polyoxyethylene hydrazine sulfate s de-salted salt, twelve-burning polyoxyethylene (tetra) acid s-sodium salt and twelve-sinter polyoxyethylene An acid (tetra) salt, wherein the pH of the solution is adjusted by adding a metal carbonate, a hydrogencarbonate or a hydroxide, such as sodium carbonate, carbon _, sodium hydrogencarbonate, potassium hydrogencarbonate or hydrogen. Sodium oxide, potassium hydroxide, and the like, and wherein the pre-impregnated activated carbon particles are immersed for 5 minutes, preferably 1-3 minutes at a temperature of 〇-5 ° C, preferably room temperature. Loading the palladium on the surface, or at a temperature of 0-70 C, preferably room temperature, spraying the solution onto the pre-impregnated particles at a spraying rate of 5-2 〇mi/min to load; and In step (e), the reducing agent is selected from the group consisting of formic acid, sodium formate, formazan, hydrazine hydrate, glucose, hydrogen Gas and mixtures thereof, preferably sodium formate. For the method for preparing the carbon/catalyst of the present invention, since the competitive adsorbate is used to pre-impregnate the supported carbon particles, the adsorbing sites on the carrier are partially occupied, and thus only 1 〇wt% or less of palladium is distributed on the outermost layer of the carrier having a depth of less than 0.2 μm, so that the loss of activity due to abrasion can be reduced. Therefore, the carbon/carbon catalyst of the present invention has the advantages of good stability and long life. As described above, the present invention also provides the use of the carbon/catalyst for the purification of crude terephthalic acid and crude 2,6-naphthalene dicarboxylic acid and the purification of crude p-hydroxymethylbenzoic acid. Wherein the acid solution or the aqueous solution of the crude stream is contacted with hydrogen at a temperature of 100-300 ° C in the presence of the catalyst / carbon 201004700 catalyst, thereby converting the aromatic aldehyde impurities contained therein, thereby achieving hydrorefining Or purification purposes. [Embodiment] Hereinafter, the present invention will be described in further detail by way of non-limiting examples. Catalyst Preparation Example 1 50 g of flaky coconut shell carbon particles having a particle size of 4-8 mesh, a specific surface area of l〇78 m 2 /g, and a pore volume of 〇.47 ml/g were weighed; _ Dust and surface loose parts on the surface of the granules, then pickled with 0.5N nitric acid in washing dad, wash at 8 〇, and wash for 1 hour, then wash with deionized water to neutral Finally, it was dried at l2〇〇c for 2 hours; the coconut shell was pre-impregnated with a 0.1 N aqueous solution of citric acid at room temperature for 15 minutes, then transitioned, and dried under uot for 2 hours; weighed 1.25 a palladium-containing 2% by weight aqueous solution of palladium acid, 15 g of deionized water was added thereto to prepare an impregnation solution, and 45 g of potassium dodecyl polyoxyethylene ether phosphate was added thereto, and then an appropriate amount was added. The pH of the sodium carbonate adjusting solution is 5.5, and finally 5 grams of deionized water is added to make the amount of the solution just immerse the coconut shell carbon particles. The solution is used to impregnate the pre-impregnated shell carbon particles. About 15 minutes, the palladium/carbon catalyst is obtained; the obtained catalyst/carbon catalyst is obtained It was aged in the air for 24 hours, and then reduced with an aqueous solution of sodium citrate at 80 °C for 4 hours. The strip was washed with deionized water to neutrality and dried, and finally Catalyst A was obtained. 10 201004700 • Example 2 Example 1 was repeated except that the competitive adsorbate was lactic acid and 2.00 g was weighed to contain 20 wt% of a gas aqueous acid solution to obtain a catalyst B. Example 3

Example 1 was repeated except that the coconut shell carbon particles were pickled without nitric acid, the coconut shell carbon particles were pre-impregnated with a 0.2 N aqueous citric acid solution for 20 minutes, and 2.50 g of palladium-containing 20 wt% palladium was weighed. An aqueous acid solution was obtained to obtain a catalyst C. Example 4 Example 1 was repeated except that 6.25 g of a palladium-containing 20 wt% aqueous palladium acid solution was weighed to obtain a catalyst D. Example 5 Example 1 was repeated except that 0.5 g of a palladium-containing 20 wt% aqueous solution of palladium nitrate was weighed to obtain a catalyst E. Example 6 Example 1 was repeated except that the coconut shell carbon particles were pre-impregnated with a concentration of 0.4 N aqueous lactic acid solution for 5 minutes, and 3.50 g of an aqueous solution containing 20% by weight of a make-up acid was weighed to obtain a catalyst F. Example 7 201004700 Example 1 was repeated except that the coconut shell carbon particles were pre-impregnated with a 0.04 N aqueous solution of lactic acid for 30 minutes, and 8.75 g of a palladium-containing 20 wt% aqueous palladium acid solution was weighed to obtain a catalyst G. Example 8 Example 1 was repeated except that the competitive adsorbent was an aqueous solution of a mixture of citric acid and lactic acid, 11.25 g of a palladium-containing 20 wt% aqueous solution of palladium acid was weighed, and palladium was supported on the coconut shell carbon particles by spraying. At a spraying rate of 10 ml/min, a catalyst crucible was obtained. Comparative Example 1 Example 1 was repeated except that the coconut shell carbon particles did not undergo a pre-impregnation step, and the catalyst I was obtained. Comparative Example 2 The Example was repeated except that the potassium salt of dodecyl polyoxyethylene ether phosphate was not added to the aqueous palladium acid solution to obtain Catalyst J. Comparative Example 3 The example 丨' was repeated except that the coconut shell carbon particles did not undergo the pre-impregnation step' and the dodecyl polyoxyethylene ether phosphate potassium salt was not added to the gas aqueous acid solution to obtain the catalyst K. In the present specification, 12 201004700 prepared for each of the above examples and comparative examples is determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis of the weight percentage of the supported carbon catalyst in which the carbon catalyst is loaded; The distribution of the measurements is as follows: the amount of palladium distributed in the depth of $2〇μιη and the amount distributed in the depth of $18〇μηη are measured by the electron probe energy spectrum (ΕΜΡΑ); the distribution of the atomic number is distributed in the depth of $〇.2μιη Photoelectron spectroscopy (XPS) measured.

Further, the catalyst/carbon catalyst prepared in each of the above Examples and Comparative Examples was subjected to a hydrotreating reaction of crude terephthalic acid, and the sample was analyzed by high pressure liquid chromatography. For each catalyst, a batch reaction was carried out in an autoclave, and the initial activity of the catalyst, that is, the 4-CBA conversion rate reached, was tested. The test conditions were as follows: the catalyst amount was 2.0 g; the terephthalic acid amount was 3 g. ; 4_ CBA amount is 1. gram; reaction pressure is s. OMPa (gauge pressure); and the reaction temperature is 280 ° C. For each catalyst, a continuous reaction was carried out in a continuous apparatus to test the operational activity of the catalyst and the corresponding palladium loss. The test conditions were as follows: The catalyst amount was 200.0 g; the slurry flow rate was 3 kg/h; the terephthalic acid content was 5 wt%; 4-CBA content is 35.35 wt%; reaction pressure is 8 〇 MPa (gauge pressure); reaction temperature is 280. (:; and the duration of the reaction is i 〇〇〇 hours, wherein the reaction duration for Catalyst A is 6000 hours. During the test, the conversion of 4-CB A is calculated as follows: 100% conversion = initial 4 - CBA content - after reaction 4 _ CBA bone-containing initial 4-CB A content The palladium loading, palladium distribution and initial activity evaluation results of the respective catalysts prepared in the above examples and comparative examples are given in Table 1 below. Table 1 13 201004700

❿ The results of Pd loading, Pd loss amount, and operational activity evaluation of each of the catalysts prepared in the above Examples and Comparative Examples after 1000 hours of reaction in a continuous apparatus are shown in Table 2 below.

Table 2 Catalyst Pd loading wt% (after 1000 hours of reaction) Pd loss amount 'wt% 4-CBA conversion rate, % conversion rate reduction amount, % A 0.48 0.02 97.9 1 1 B 0.76 0.04 98.0 12 C 0.96 0.04 98.3 1 1 D 2.43 0.06 98.5 1 . 1 —^: E 0.18 0.02 84.5 F 1.36 0.04 98.1 G 3.44 0.05 98.2 Η 4.40 0.08 98.3 "" I 0.40 0.10 95.5 — J 0.49 0.01 93.2 — K 0.42 0.07 97.2 ' Given in Table 3 below The catalyst prepared in the above Example 1 was obtained, j

A 14 201004700, Pd loading after 6,000 hours of reaction in a continuous unit, P (i loss amount and operational activity evaluation results. Table 3 Catalyst Pd loading wt% (after 6000 hours of reaction) Pd loss, wt% 4- CBA conversion, % conversion reduction, % A 0.43 0.07 97.6 1.4 From the data in Tables 1 and 2, each of the catalytic oximes prepared according to the present invention significantly reduced the outermost layer (^0.2 μηι) The amount of distribution, that is, the amount is controlled to be less than 10% by weight, so that these catalysts have only a very low palladium loss after 1 hour of continuous operation; in addition, palladium is mainly distributed in the outer layer (〇22〇μηη) to ensure these The initial activity of the catalyst, i.e., high 4-CBA conversion, can be achieved in a batch reaction, and the activity remains well after 1000 hours of continuous operation, i.e., the activity is only slightly reduced. It can be seen that the loading of Pd on catalyst a is still 0 43 wt% after 6000 hours of continuous operation, the loss is only 〇〇7%, and the conversion of 4_ ❹ CBA is still 97.6%, that is, the conversion rate is only reduced by 14%. ,this invention The catalyst reduces the palladium loss during operation by further optimizing the palladium distribution, thereby improving the stability of the catalyst and prolonging the life of the catalyst while maintaining the activity of the catalyst. However, the above is only a preferred embodiment of the present invention. It is to be understood that the scope of the invention is not limited thereto, that is, the equivalent equivalents and modifications of the scope of the invention and the description of the invention are still within the scope of the invention. Brief description] 15 201004700 No [Main component symbol description]

Claims (1)

201004700, X. Patent application scope: 1. A palladium/carbon hydrogenation catalyst comprising activated carbon particles as a carrier and metal palladium as an active component, wherein the metal palladium content is 0.1-5 wt based on the total weight of the catalyst. %, wherein at least 45 wt% of palladium is distributed on the outer layer of the carrier having a depth of 〇·2-20 μηι, less than 10% by weight of the carrier is distributed to the outermost layer of the carrier having a depth of less than 0.2 μm, and the balance is distributed at a depth of 20-400 μm. The inner layer of the carrier. 2. The catalyst according to claim 1, wherein the activated carbon particles are natural or shaped particles, preferably natural or shaped coconut shell carbon particles. 3. The catalyst according to claim 1 or 2, wherein the activated carbon particles have a specific surface area of 600 to 1800 m 2 /g, preferably 8 Å to 1500 m 2 /g, and a pore volume of 〇.3 〇 〇 85 ml /g, and particles having 9% by weight or more of the particles have a particle size of 4-8 mesh. 4. The catalyst according to claim 2 or 2, wherein the metal palladium is contained in an amount of 〇 2 - 3 5 wt%, preferably 0.3 - 0.8 wt%, based on the total mass of the rhodium catalyst. 5. The catalyst according to claim 2, wherein 45_6 〇Wt% of palladium is distributed on the outer layer of the carrier having a depth of 0.2-20 μm. 6. The catalyst according to claim 2 or 2, wherein the balance palladium is distributed in the inner layer of the carrier having a depth of 2〇_18〇μηι. 7. A method of preparing a catalyst according to any one of claims -6, which comprises the steps of: (a) selecting suitable activated carbon particles as the ruthenium particles; 17 201004700 (b) at 0- The activated carbon particles are pre-impregnated with a competitive adsorbent at a temperature of 50 ° C, preferably room temperature for 5 to 60 minutes, preferably 10 to 3 minutes, and then filtered and dried to obtain pre-impregnated activated carbon particles, wherein The competitive adsorbate is a low carbon organic acid aqueous solution having a concentration of 0.01-0.5 N, preferably 0·05_〇2N, having a carbon number of 1 -6; (c) using a weakly acidic solution containing a precursor and a surfactant, The loaded catalyst is obtained by impregnation or spraying on the pre-impregnated activated carbon particles, wherein the supported amount is 〇1 - 5 wt%, based on the total weight of the catalyst, preferably 0.2-3.5 wt%, more preferably 0.3-0.8 wt%, and wherein the pH of the solution is 3-6; (d) aging the supported catalyst in air for 1-4 hours to obtain an aged catalyst; (e) after the aging at 0-200 ° C, preferably 50-12 (TC temperature) The catalyst is treated with a reducing agent for 0_5_10 hours, preferably 1-4 hours, to obtain a catalyst after activation. 8. The method according to claim 7, wherein the method further comprises the following steps: (V) in step (b) Previously, the pretreatment of the activated carbon particles 'removed the dust and loose parts of the surface of the particles, washed with mineral acid, washed with deionized water until neutral, and dried. 9. According to the scope of claim 7 Or the method according to the item 8, wherein, in the step (a), the activated carbon particles selected are natural or shaped particles, preferably natural or shaped coconut shell carbon particles, and have a specific surface area of (9) 丨8〇〇 M2/g, preferably 800-1500 m2/g, a pore volume of 0.30-0.85 ml/g, preferably 〇.4〇_0.60 ml/g ' and a particle size of 9 〇wt% or more of which is 4-8 mesh. 201004700 , 9 The method according to any one of the preceding claims, wherein in the step (b), wherein the low carbon organic acid is selected from the group consisting of citric acid, maleic acid, stalk flat, lactic acid And a mixture thereof, preferably citric acid, and wherein the drying temperature is 10 The method according to any one of the preceding claims, wherein in the step (C), the palladium precursor is selected a mixture of palladium chloride, palladium oxide, palladium acetate, palladium nitrate, palladium acid and its basic salt, palladium ammonia complex and φ β, preferably qi acid. 12. According to the scope of the patent application 7- The method of any of the items 11, wherein in the step (c), the concentration of the surfactant is 〇2_5 Å, preferably 0.5-1.5 wt. /. The surfactant is an anionic surfactant selected from the group consisting of an aliphatic polyoxyethylene ether sulfate alkali metal salt and an aliphatic polyoxyethylene sulphate alkali metal salt, and a carbonate or carbonate thereof by adding an alkali metal. Hydrogen salt or hydroxide to adjust the pH of the solution according to the method of claim 12, wherein the anionic ginseng surfactant is selected from the group consisting of sodium dodecyl polyoxyethylene ether sulfate , 12 = polyoxyethylene ether sulfate potassium salt, dodecyl polyoxyethylene ether phosphate sodium salt and dodecyl polyoxyethylene ether phosphate salt removal. 14. The method according to any one of the clauses of the patent scope of claim 7-13, wherein in step (c), wherein 〇_50. 〇, preferably at room temperature, by impregnation for 0.5-6 minutes, preferably (four) W minutes, supporting palladium on the pre-impregnated activated carbon particles, or wherein 〇_7〇<t, preferably At a temperature of the shirt, the solution was sprayed onto the pre-impregnated particles at a spray rate of 5-2 〇ml/min to support the palladium. The method according to any one of claims 714, wherein in the step (e), the reducing agent is selected from the group consisting of formic acid, sodium formate, formazan, hydrazine hydrate, glucose, hydrogen, and the like. A mixture, preferably sodium formate. The method according to any one of the preceding claims, wherein in the step (b), wherein the concentration of the inorganic acid for washing is from 0.1 to 0.5 N, and the inorganic acid is selected from the group consisting of Hydrochloric acid, nitric acid, phosphoric acid, and mixtures thereof, and the drying is carried out at a temperature of 1 〇〇 2 Torr (rc, preferably 11 〇 15 Torr.) 17. The catalyst as described in claim 16 Or the use of a catalyst prepared by the method of any one of claims 7-16, which is used for hydrotreating and crude pairing of crude terephthalic acid and crude 2,6-cai dicarboxylic acid. Purification of methylol benzoic acid, wherein an acid solution or an aqueous solution of the crude stream is contacted with hydrogen at a temperature of 1〇〇3〇〇<>c in the presence of the catalyst, thereby converting the same Aromatic aldehyde impurities 20 201004700 VII. Designated representative map: (1) The representative representative of the case is: None (2) The symbol of the symbol of the representative figure is simple: None 8. If there is a chemical formula in this case, please disclose the chemical formula that best shows the characteristics of the invention: