Background
The preparation of acetic acid by the reaction of carbon monoxide with methanol in the presence of a catalyst is an oxo process developed in the 40-50 s of the 20 th century. Paulik et al, Monsanto corporation, early 70 s, invented a homogeneous rhodium catalyst for oxo synthesis (US 3769329) opened up a new way for oxo synthesis. Through continuous improvement and perfection, the oxo synthesis technology using rhodium as a catalyst has become the most important production process route in the acetic acid industry and the production yield is the largest.
In the current industrial production, a square plane negative ion structure complex of rhodium is mostly adopted as a catalytic active species. Although the catalyst has good catalytic activity, the catalyst has the defect of easy conversion into trivalent rhodium and inactivation. Especially in the case of a catalyst separation cycle with a lower carbon monoxide partial pressure. In addition, in order to increase the solubility of the catalyst in the production process of acetic acid, the reaction system needs to keep higher water content and hydriodic acid, so that the water gas reaction is carried out while the catalytic rate is improved
Accelerating, consuming the raw material carbon monoxide and improving the requirement on the material of the equipment.
Around the improvement and perfection of the catalyst and the reaction system for synthesizing the acetic acid by the carbonyl group, a plurality of laboratories have carried out effective researches and made obvious progress. For example, the use of high polymers as ligands for catalysts (CN 100750, US 5281359, US 6458996) has made good progress in the study of catalysts with non-rhodium systems (GB20000419) and the addition of different kinds of promoting catalysts (US 5922911) in the reaction system, while maintaining high carbonylation activity and improving certain properties such as optimizing the ratio of the media in the reaction system, especially improving the thermal stability of the catalyst.
Disclosure of Invention
The invention aims to provide a positive and negative ion type metal catalyst for synthesizing acetic acid by methanol hydroxyl.
It is another object of the present invention to provide a process for preparing the above catalyst.
In order to achieve the purpose, the positive ion type bimetallic catalyst provided by the invention has a positive ion cis-dicarbonyl structure formed by a multidentate organic or high molecular compound containing 2 or more nitrogen and oxygen functional groups or functional units and Rh (I); the anion ligand is a complex formed by organic acid containing nitrogen and oxygen donor atoms and non-rhodium metal salt, and the structural formula is as follows:
wherein M is Ru, Sn, Cr, Pb or Zr; n is 2, 3, 4.
The positive ion ligand and the negative ion ligand are aminobenzoic acid, such as anthranilic acid, m-aminobenzoic acid or p-aminobenzoic acid.
Rh (I) in the invention is [ Rh (CO]2Cl]2、[Rh(CO)2Br]2Or [ Rh (CO)]2I]2。
The non-rhodium metal salt of the invention is RuCl3、SnCl2、PbCl2、CrCl3Or ZrCl4。
The invention provides a method for preparing the catalyst, which mainly comprises the following preparation steps:
① 1 molar parts of anion ligand and 1 molar part of inorganic base (such as NaOH and KOH) are dissolved in 50-200 molar parts of water, and the mixture is stirred and reacted for 0.5-2 hours at 40-70 ℃ to obtain organic salt ligand, wherein the reaction and product structure are as follows:
② 1mol parts of organic salt ligand obtained in the step ① and 1mol part of non-rhodium metal salt are dissolved in 50-200 mol parts of methanol aqueous solution, the molar ratio of methanol to water in the methanol aqueous solution is 2: 1, and the solution is stirred and reacted for 0.5-2 hours at the temperature of 40-70 ℃ to obtain an organic metal salt non-rhodium metal complex solution, wherein the reaction and the product structure are as follows:
③ 2 molar parts of cationic ligand with 1 molar part of Rh2(CO)4X2Dissolving the mixture in 50-200 molar parts of methanol solvent, wherein the molar ratio of a ligand N atom to an Rh atom is 1: 1, refluxing for 0.5-2 hours under stirring to obtain a monodentate coordinated ligand and rhodium complex solution, wherein the reaction and complex structure of the monodentate coordinated ligand and rhodium complex solution are as follows:
X=Cl、Br、I
④ mixing the solution of rhodium complex with monodentate coordination prepared in step ③ and the solution of organic salt non-rhodium metal complex prepared in step ② under stirring, wherein the molar ratio of non-rhodium metal M to Rh atom is 1: 1, continuously refluxing for 0.5-5 hours under stirring, cooling, precipitating with excessive ether to obtain the final product, namely, a positive and negative ion type bimetallic catalyst, the reaction and catalyst structure of which are as follows:
from the above description, it can be seen that the present invention achieves the purpose of improving the catalytic activity and stability of the catalyst by changing the molecular structure of the catalyst, and can rapidly and highly selectively catalyze the carbonylation of methanol to acetic acid under relatively mild conditions. The characteristic is determined by the special structural mode of the catalyst, namely, the positive ion part taking rhodium as an active species contains two complexes of N → Rh and O → RhA key. Generally, the coordination structure containing O → Rh coordination bond is more beneficial to the addition of methyl iodide serving as a cocatalyst in the reaction process, so that acetyl iodide (CH) serving as an intermediate species for carbonyl synthesis3COI) is easy to generate, and the catalysis is acceleratedAnd (6) carrying out the process. In addition, the anionic moiety coordination unit functions as a general promoter. The rhodium active unit and the rhodium active unit are in the same molecular structure, and the synergistic effect of the rhodium active unit and the rhodium active unit improves the catalytic promotion effect of the rhodium active unit.
The catalyst provided by the invention has the following advantages in the catalytic methanol carbonylation reaction:
① there was no detectable water gas reaction in the system.
② the reaction starts at a low initial temperature and starts when the reaction temperature reaches 120 ℃.
③ are catalytically highly active, and it can be seen in the accompanying examples that methanol is rapidly converted to acetic acid in its entirety in a short reaction time.
Detailed Description
The present invention has been described in detail in the foregoing for enabling those skilled in the art to practice the invention. The following examples are intended only to further illustrate the technical solutions of the present invention, and therefore, the specific conditions given in the examples are not intended to limit the present invention.
Example 1
Preparing a catalyst anion part non-rhodium metal complex:
weighing 0.02mol of aminobenzoic acid and NaOH which are dissolved in 2mol of water, heating to 70 ℃ for reaction for 1h, cooling, precipitating with excessive acetone, and drying to obtain sodium aminobenzoate, wherein the reaction and the structural formula are as follows:
0.01mol of sodium aminobenzoate is weighed and dissolved in a mixed solution of 1mol of methanol and 0.5mol of water, and 0.01mol of RuCl is added3Heating and refluxing for reaction for 1h under stirring, cooling, precipitating with acetone, and drying to obtain the sodium-ruthenium aminobenzoate complex, wherein the reaction and complex structure is as follows:
chromium, tin, lead and zirconium complexes of sodium aminobenzoate may also be obtained as described above, but for simplicity in this example, this is not intended to be exhaustive.
Preparing a positive and negative ion type bimetallic catalyst:
0.02mol of aminobenzoic acid and 0.01mol of [ Rh (CO)]are weighed out2Cl]2Dissolving in 3mol of methanol, stirring and reacting for 1h at 70 ℃, then adding methanol-water mixed liquor (the molar ratio of methanol to water is 2: 1) containing 0.02mol of ruthenium complex taking sodium aminobenzoate as ligand, and continuously stirring and reacting for 1h at 70 ℃ to obtain monodentate coordinated anthranilic acid and rhodium complex solution, wherein the reaction and complex structure is as follows:
the solution is cooled, precipitated with ether and filtered. Washing with 0 deg.C methanol-water (2: 1mol) mixed solution for 2 times, drying at room temperature to constant weight to obtain brown rhodium aminobenzoate-ruthenium aminobenzoate positive and negative ion type bimetallic catalyst, which has the following reaction and complex structure:
the method can also be used for preparing the positive and negative ion type bimetallic catalyst taking rhodium aminobenzoate as a positive ion and chromium, tin, lead and zirconium aminobenzoate as a negative ion. Also, for simplicity, this embodiment is not necessarily listed.
Example 2
0.32g of rhodium-ruthenium bimetallic catalyst which is prepared in example 1 and takes anthranilic acid as ligand, 1.24mol of methanol, 0.87mol of acetic acid and 0.24mol of methyl iodide are added into a 250ml zirconium pressure kettle, CO is introduced, the temperature is raised to 150 ℃, the reaction pressure is kept at 4.0MPa, the stirring speed is 500 r/min, and the reaction time is 30 min. The methanol conversion rate is 100 percent, the methyl acetate content is 0.02mol, the acetic acid increment is 1.20mol, and the acetic acid space-time yield is 20.7mol of AcOH/L.h.
Example 3
0.32g of rhodium-chromium bimetallic catalyst which is prepared by the method of example 1 and takes anthranilic acid as ligand, 1.24mol of methanol, 0.87mol of acetic acid and 0.24mol of methyl iodide are added into a pressure kettle, the temperature is raised to 180 ℃ after CO is introduced, the reaction pressure is kept at 4.0MPa, the stirring speed is 500 r/min, the reaction time is 20min, the methanol conversion rate is 100 percent, the methyl acetate content is 0.04mol, the acetic acid increment is 1.1mol, and the acetic acid space-time yield is 31.34mol of AcOH/L.h.
Example 4
0.33g of rhodium-zirconium bimetallic catalyst having anthranilic acid as a ligand prepared by the method of example 1, 1.24mol of methanol, 0.87mol of acetic acid and 0.24mol of methyl iodide were charged in a pressure vessel. After CO is introduced, the temperature is raised to 160 ℃, the reaction pressure is kept at 4.0MPa, the stirring speed is 500 r/min, the reaction time is 25min, the methanol conversion rate is 100 percent,the methyl acetate content is 0, the acetic acid increment is 1.20mol, and the acetic acid space-time yield is 25.1mol of AcOH/L.h.
Example 5
0.35g of rhodium-tin bimetallic catalyst which is prepared by the method of example 1 and takes anthranilic acid as ligand, 1.24mol of methanol, 0.87mol of acetic acid and 0.24mol of methyl iodide are added into a pressure kettle, the temperature is raised to 175 ℃, the reaction pressure is kept at 4.0MPa, the stirring speed is 500 r/min, the reaction is carried out for 25min, the conversion rate of the methanol is 100%, the content of methyl acetate is 0.03mol, the increment of the acetic acid is 1.16mol, and the space-time yield of the acetic acid is 24.9mol of AcOH/L.h.
Example 6
0.35g of the rhodium-zirconium bimetallic catalyst which is prepared by the method of example 1 and uses m-aminobenzoic acid as ligand, 1.24mol of methanol, 0.87mol of acetic acid and 0.24mol of methyl iodide are added into an autoclave. After CO is introduced, the temperature is raised to 180 ℃, the reaction pressure is kept at 4.0MPa, the stirring speed is 500 r/min, the reaction time is 20min, the methanol conversion rate is 100 percent, 0.03mol of methyl acetate is obtained, 1.17mol of acetic acid is obtained, and the time-space yield of the acetic acid is 31.1mol of AcOH/L.h.
Example 7
0.32g of rhodium-ruthenium bimetallic catalyst prepared by the method of example 1 and using anthranilic acid as a ligand, 2.48mol of methanol and 0.34mol of methyl iodide were charged into the autoclave. After CO is introduced, the temperature is raised to 180 ℃, the reaction pressure is kept at 4.0MPa, the stirring speed is 500 r/min, the reaction time is 40min, the methanol conversion rate is 100 percent, 0.8mol of methyl acetate is obtained, 1.52mol of acetic acid is obtained, and the time-space yield of the acetic acid is 20.4mol of AcOH/L.h.