阅读说明：本技术 一种d,l-2-羟基-4-甲硫基丁酸盐的制备方法 (Preparation method of D, L-2-hydroxy-4-methylthio butyrate ) 是由 周荣超 廖常福 吴传隆 彭启明 周振宇 于 2020-12-30 设计创作，主要内容包括：本发明涉及有机化合物合成技术领域,尤其涉及一种D,L-2-羟基-4-甲硫基丁酸盐的制备方法,包括以下步骤：将高浓度D,L-2-羟基-4-甲硫基丁酸用水稀释至30～50wt％浓度,得到稀释液在超声波氛围下于70～100℃保温搅拌2～5h,和/或将稀释液转入高压釜,于1.0～2.0MPa、150～180℃温度下搅拌30～90min,得到水解液控温在60～80℃,加入金属化合物,搅拌反应30～60min,得到反应液直接或浓缩后进行喷雾干燥,得到D,L-2-羟基-4-甲硫基丁酸盐。本发明的制备方法采用在超声波氛围加热水解和\或高压釜加压水解来达到液体蛋氨酸二聚体及多聚体向单体的转化,得到的单体与金属化合物反应制备得到产品,具有工艺简单高效、原料利用率高、产品质量高收率高、无副产盐及废水排放清洁可持续等优点。(The invention relates to the technical field of organic compound synthesis, in particular to a preparation method of D, L-2-hydroxy-4-methylthio butyrate, which comprises the following steps: diluting high-concentration D, L-2-hydroxy-4-methylthio butyric acid with water to a concentration of 30-50 wt%, carrying out heat preservation stirring at 70-100 ℃ for 2-5 h under an ultrasonic atmosphere to obtain a diluent, and/or transferring the diluent to an autoclave, stirring at a temperature of 150-180 ℃ for 30-90 min under a pressure of 1.0-2.0 MPa to obtain a hydrolysate, controlling the temperature of the hydrolysate to be 60-80 ℃, adding a metal compound, carrying out stirring reaction for 30-60 min, and carrying out spray drying directly or after concentration to obtain the D, L-2-hydroxy-4-methylthio butyrate. The preparation method of the invention adopts the heating hydrolysis and/or the high-pressure kettle pressurization hydrolysis in the ultrasonic atmosphere to achieve the conversion of the liquid methionine dimer and the polymer to the monomer, and the obtained monomer reacts with the metal compound to prepare the product, and the preparation method has the advantages of simple and efficient process, high utilization rate of raw materials, high product quality and yield, no byproduct salt, clean and sustainable waste water discharge and the like.)

1. A preparation method of D, L-2-hydroxy-4-methylthio butyrate is characterized by comprising the following steps of:

diluting high-concentration D, L-2-hydroxy-4-methylthiobutyric acid to a concentration of 30-50 wt% by using water to obtain a diluent;

stirring the diluent at the temperature of 70-100 ℃ for 2-5 h under the ultrasonic atmosphere, and/or transferring the diluent into an autoclave, and stirring for 30-90 min at the temperature of 150-180 ℃ under the pressure of 1.0-2.0 MPa to obtain a hydrolysate;

controlling the temperature of the hydrolysate to be 60-80 ℃, adding a metal compound, and stirring for reaction for 30-60 min to obtain a reaction solution;

and (3) directly or after concentrating the reaction solution, carrying out spray drying to obtain the D, L-2-hydroxy-4-methylthio butyrate.

2. The preparation method of D, L-2-hydroxy-4-methylthiobutyrate according to claim 1, wherein the D, L-2-hydroxy-4-methylthiobutyrate is one of calcium D, L-2-hydroxy-4-methylthiobutyrate and zinc D, L-2-hydroxy-4-methylthiobutyrate chelate.

3. The method for preparing D, L-2-hydroxy-4-methylthiobutyrate according to claim 2, wherein the metal compound is one of calcium carbonate, calcium oxide, calcium hydroxide, zinc oxide, zinc hydroxide, basic zinc carbonate and zinc carbonate.

4. The preparation method of D, L-2-hydroxy-4-methylthiobutyric acid salt according to claim 1, wherein the high concentration of D, L-2-hydroxy-4-methylthiobutyric acid is 88 wt% of commercial-grade hydroxymethionine or a concentrated solution of hydroxymethionine with a concentration of 88 to 100 wt%.

5. The method for preparing D, L-2-hydroxy-4-methylthiobutyric acid salt according to claim 1, wherein the total content of dimer and polymer in the hydrolysate is less than 1.3% of the content of D, L-2-hydroxy-4-methylthiobutyric acid.

6. The method for preparing D, L-2-hydroxy-4-methylthiobutyric acid salt according to claim 1, wherein the metal compound is added in such an amount that the molar ratio of the metal ion to D, L-2-hydroxy-4-methylthiobutyric acid is 1: 2.

7. The process for the preparation of D, L-2-hydroxy-4-methylthiobutyric acid salt according to any one of claims 3 to 6, characterized in that it comprises the following steps:

diluting high-concentration D, L-2-hydroxy-4-methylthiobutyric acid to a concentration of 40-50 wt% by using water to obtain a diluent;

stirring the diluent under the ultrasonic atmosphere with the frequency of 25-40 KHz at the temperature of 85-100 ℃ for 2-5 hours to obtain a hydrolysate;

controlling the temperature of the hydrolysate to be 60-80 ℃, adding a metal compound, and stirring for reaction for 30-60 min to obtain a reaction solution;

and (3) directly or after concentrating the reaction solution, carrying out spray drying to obtain the D, L-2-hydroxy-4-methylthio butyrate.

8. The process for the preparation of D, L-2-hydroxy-4-methylthiobutyric acid salt according to any one of claims 3 to 6, characterized in that it comprises the following steps:

diluting high-concentration D, L-2-hydroxy-4-methylthiobutyric acid to a concentration of 20-40 wt% by using water to obtain a diluent;

transferring the diluent into an autoclave, and stirring for 30-90 min at the temperature of 160-180 ℃ under the pressure of 1.0-2.0 MPa to obtain a hydrolysate;

controlling the temperature of the hydrolysate to be 60-80 ℃, adding a metal compound, and stirring for reaction for 30-60 min to obtain a reaction solution;

and (3) directly or after concentrating the reaction solution, carrying out spray drying to obtain the D, L-2-hydroxy-4-methylthio butyrate.

9. The process for the preparation of D, L-2-hydroxy-4-methylthiobutyric acid salt according to any one of claims 3 to 6, characterized in that it comprises the following steps:

diluting high-concentration D, L-2-hydroxy-4-methylthiobutyric acid to a concentration of 30-50 wt% by using water to obtain a diluent;

stirring the diluent under the ultrasonic atmosphere of 30-40 KHz at the temperature of 70-100 ℃ for 2-5 h, transferring the diluent into an autoclave, and stirring at the temperature of 1.0-2.0 MPa and 150-180 ℃ for 30-90 min to obtain a hydrolysate;

controlling the temperature of the hydrolysate to be 60-80 ℃, adding a metal compound, and stirring for reaction for 30-60 min to obtain a reaction solution;

and (3) directly or after concentrating the reaction solution, carrying out spray drying to obtain the D, L-2-hydroxy-4-methylthio butyrate.

Technical Field

The invention relates to the technical field of organic compound synthesis, and particularly relates to a preparation method of D, L-2-hydroxy-4-methylthio butyrate.

Background

Hydroxy methionine is also known as methionine hydroxy analogue (abbreviated as MHA) and has the chemical name of 2-hydroxy-4-methylthiobutyric acid, and the mass content of D, L-2-hydroxy-4-methylthiobutyric acid in commercial hydroxy methionine is generally 88%, which is a dynamic equilibrium mixture of monomers and oligomers (mainly dimeric and trimeric linear acid esters). D, L-2-hydroxy-4-methylthiobutyric acid is a nutrient used for supplementing the essential amino acid methionine for animals, is an equivalent substitute of the common methionine supplement D, L-methionine (solid methionine), has the advantages of low toxicity, low rumen degradation rate, promotion of rumen microorganism synthesis, saving of protein in daily ration, reduction of nitrogen excretion in animals, less environmental pollution and the like compared with methionine, and is the most economic and effective methionine source for ruminants.

D, L-2-hydroxy-4-methylthiobutyric acid has the advantages, and has the problems of strong corrosive and irritant odor, inconvenient storage, transportation and use and the like, a special expensive liquid feeding system (Chinese patent with publication number CN 1493560A: a compound for supplementing methionine and calcium and a preparation method thereof) is required, the storage time is slightly long (4 months), and the oligomer with low nutritional value in the liquid can be increased by times (more than 50 mol%).

In order to solve the above problems and comprehensively consider the side effects of mutual antagonism of metal elements, destruction of vitamins by metal ion redox reaction, serious environmental pollution, etc. caused by adding inorganic trace elements into animal feed and premix, researchers in related fields have developed solid compound feed additives such as hydroxy methionine salt and complex, which not only contain methionine source necessary for animal growth, but also can provide calcium or other trace elements (such as magnesium, manganese, iron, cobalt, nickel, copper, zinc, etc.) necessary for animal growth. A large number of scientific experiments and production practices prove conclusively that the hydroxy methionine salt as the feed additive has the advantages of high bioavailability, stable chemical structure, easy absorption, enhancement of the immunity of livestock and poultry, reduction of anti-nutritional factors, enhancement of the formation performance of livestock and poultry and the like.

At present, the state of D, L-2-hydroxy-4-methylthio butyric acid calcium is different from the state of participating in reaction raw materials, and the preparation can be carried out by directly taking D, L-2-hydroxy-4-methylthio butyric acid as a raw material and taking D, L-2-hydroxy-4-methylthio butyric acid derivatives (such as salts, amides, esters and the like) as a raw material. For example:

chinese patent CN103641757 discloses that D, L-2-hydroxy-4-methylthiobutyronitrile is hydrolyzed into D, L-2-hydroxy-4-methylthio butyrate under the catalysis of alkali, and then the D, L-2-hydroxy-4-methylthio butyrate and soluble calcium salt react to prepare D, L-2-hydroxy-4-methylthio butyrate calcium; chinese patent CN102079719 discloses that D, L-2-hydroxy-4-methylthio butyric acid reacts with ammonia to be dehydrated into D, L-2-hydroxy-4-methylthio butyramide, and the D, L-2-hydroxy-4-methylthio butyric acid calcium is synthesized by the reaction of the D, L-2-hydroxy-4-methylthio butyramide with calcium salt after the amide is hydrolyzed into salt; chinese patent CN102399176 discloses that D, L-2-hydroxy-4-methylthiobutyronitrile is hydrolyzed under concentrated hydrochloric acid, neutralized by 30% NaOH to crystallize D, L-2-hydroxy-4-methylthiobutanamide, and the amide reacts with excessive calcium hydroxide to prepare calcium D, L-2-hydroxy-4-methylthiobutyrate; chinese patent CN101348451 discloses that D, L-2-hydroxy-4-methylthio butyric acid reacts with alcohol to form ester under the catalysis of sulfuric acid or benzenesulfonic acid, and the obtained ester is hydrolyzed with calcium oxide to prepare calcium D, L-2-hydroxy-4-methylthio butyrate. No matter what kind of D, L-2-hydroxy-4-methylthio butyric acid derivatives (such as salts, amides, esters and the like) are used as direct reaction raw materials, the uniform and non-polymerized monomer D, L-2-hydroxy-4-methylthio butyric acid is mainly obtained to improve the utilization rate of the raw materials and the quality of products, but the defects of repeated routes, complex process, byproduct inorganic salt wastewater, easy entrainment of inorganic salt or catalysts in the products and the like are all inevitable.

In addition, Chinese patent CN1493560 discloses that commercial liquid methionine directly reacts with calcium oxide or calcium hydroxide to prepare D, L-2-hydroxy-4-methylthio butyric acid calcium; chinese patent CN107879959 discloses the preparation of calcium D, L-2-hydroxy-4-methylthiobutyrate by reacting commercial grade liquid methionine with a calcium source (calcium oxide, calcium hydroxide or calcium carbonate) pre-stirred and dispersed in water, alcohol or sodium stearate; chinese patent CN104356035 discloses that liquid methionine reacts with one or more calcium sources under the catalysis of introduced ammonium bisulfate to prepare D, L-2-hydroxy-4-methylthio calcium butyrate; chinese patent CN102675171 discloses the preparation of D, L-2-hydroxy-4-methylthio butyric acid calcium by continuously introducing liquid methionine into a mixed drying agent added with a calcium source. The concentrated or commercial-grade liquid methionine directly reacts with calcium source (calcium oxide, calcium hydroxide, calcium carbonate, etc.) in the above publication, although it is directly simple, has no by-product salt waste water, and improves the reaction process of raw materials and the product state by using enhanced physics or using dispersing agent and catalyst for the reaction process. It is still inevitable that concentrated or commercial grade liquid methionine contains about 18% dimer and about 4% polymer, and these polymers directly react with calcium salt, which results in waste of liquid methionine (e.g. dimer reacts with calcium to actually consume 4 molecules of monomeric liquid methionine), and is also prone to entrapping caused by excessive calcium salt due to different actual raw materials and theoretical measurement, and even if means for improving the appearance of the final product is used, high-quality calcium D, L-2-hydroxy-4-methylthiobutyrate cannot be obtained, but a calcium salt mixture of monomer, dimer and polymer.

Chinese patent CN1235878 discloses that liquid methionine and zinc oxide aqueous solution react at a molar ratio of 1:1 at 80-90 ℃ and pH 6-8 to prepare alkaline liquid zinc methionine. The method is simple and direct, has no byproduct salt, is relatively clean and efficient, and still does not solve the problem that polymers in the liquid methionine influence the reaction and final quality of the product.

In summary, the existing preparation technology of D, L-2-hydroxy-4-methylthio butyrate has the following disadvantages: firstly, a large amount of salt and waste water are produced as byproducts; secondly, the process is complex, the route is repeated, and the cost is high; thirdly, the liquid methionine raw material contains dimer and polymer, which causes low product quality.

Disclosure of Invention

In view of the above, the present invention provides a method for preparing D, L-2-hydroxy-4-methylthiobutyrate, which comprises heating and hydrolyzing in an ultrasonic atmosphere and/or performing pressurized hydrolysis in an autoclave to convert a liquid methionine dimer and a polymer into a monomer, reacting the obtained monomer with a calcium source or a zinc source containing no interfering anions to prepare a product, and has the advantages of simple and efficient process, high raw material utilization rate, high product quality and yield, no byproduct salt, clean and sustainable wastewater discharge, and the like.

The invention solves the technical problems by the following technical means:

a method for preparing D, L-2-hydroxy-4-methylthiobutyrate, comprising the steps of:

diluting high-concentration D, L-2-hydroxy-4-methylthiobutyric acid to a concentration of 30-50 wt% by using water to obtain a diluent;

stirring the diluent at the temperature of 70-100 ℃ for 2-5 h under the ultrasonic atmosphere, and/or transferring the diluent into an autoclave, and stirring for 30-90 min at the temperature of 150-180 ℃ under the pressure of 1.0-2.0 MPa to obtain a hydrolysate;

controlling the temperature of the hydrolysate to be 60-80 ℃, adding a metal compound, and stirring for reaction for 30-60 min to obtain a reaction solution;

and (3) directly or after concentrating the reaction solution, carrying out spray drying to obtain the D, L-2-hydroxy-4-methylthio butyrate.

Preferably, the D, L-2-hydroxy-4-methylthio butyrate is one of calcium D, L-2-hydroxy-4-methylthio butyrate and zinc D, L-2-hydroxy-4-methylthio butyrate chelate.

Preferably, the metal compound is one of calcium carbonate, calcium oxide, calcium hydroxide, zinc oxide, zinc hydroxide, basic zinc carbonate and zinc carbonate.

Preferably, the high-concentration D, L-2-hydroxy-4-methylthiobutyric acid is 88 wt% of commercial-grade hydroxymethionine or a concentrated solution of hydroxymethionine with a concentration of 88-100 wt%.

Preferably, the total content of the dimer and the polymer in the hydrolysate is less than 1.3 percent of the content of the D, L-2-hydroxy-4-methylthiobutyric acid.

Preferably, the metal compound is added in an amount such that the molar ratio of the metal ion to the D, L-2-hydroxy-4-methylthiobutyric acid is 1: 2.

Preferably, the preparation method comprises the following steps:

diluting high-concentration D, L-2-hydroxy-4-methylthiobutyric acid to a concentration of 40-50 wt% by using water to obtain a diluent;

stirring the diluent under the ultrasonic atmosphere with the frequency of 25-40 KHz at the temperature of 85-100 ℃ for 2-5 hours to obtain a hydrolysate;

controlling the temperature of the hydrolysate to be 60-80 ℃, adding a metal compound, and stirring for reaction for 30-60 min to obtain a reaction solution;

and (3) directly or after concentrating the reaction solution, carrying out spray drying to obtain the D, L-2-hydroxy-4-methylthio butyrate.

Preferably, the preparation method comprises the following steps:

diluting high-concentration D, L-2-hydroxy-4-methylthiobutyric acid to a concentration of 20-40 wt% by using water to obtain a diluent;

transferring the diluent into an autoclave, and stirring for 30-90 min at the temperature of 160-180 ℃ under the pressure of 1.0-2.0 MPa to obtain a hydrolysate;

controlling the temperature of the hydrolysate to be 60-80 ℃, adding a metal compound, and stirring for reaction for 30-60 min to obtain a reaction solution;

and (3) directly or after concentrating the reaction solution, carrying out spray drying to obtain the D, L-2-hydroxy-4-methylthio butyrate.

Preferably, the preparation method comprises the following steps:

diluting high-concentration D, L-2-hydroxy-4-methylthiobutyric acid to a concentration of 30-50 wt% by using water to obtain a diluent;

stirring the diluent under the ultrasonic atmosphere of 30-40 KHz at the temperature of 70-100 ℃ for 2-5 h, transferring the diluent into an autoclave, and stirring at the temperature of 1.0-2.0 MPa and 150-180 ℃ for 30-90 min to obtain a hydrolysate;

controlling the temperature of the hydrolysate to be 60-80 ℃, adding a metal compound, and stirring for reaction for 30-60 min to obtain a reaction solution;

and (3) directly or after concentrating the reaction solution, carrying out spray drying to obtain the D, L-2-hydroxy-4-methylthio butyrate.

According to the preparation method of the D, L-2-hydroxy-4-methylthio butyrate, commercial-grade liquid methionine or liquid methionine concentrated solution is directly used for preparing the D, L-2-hydroxy-4-methylthio butyrate with low content of polymers, so that the advantages of easily available raw materials and low cost are achieved, and high-quality calcium salt and chelated zinc synthesized from white monomolecular liquid methionine can be prepared; the preparation method of the invention adopts the heating hydrolysis and/or the high-pressure kettle pressurization hydrolysis in the ultrasonic atmosphere to achieve the conversion of the liquid methionine dimer and the polymer to the monomer, and the obtained monomer reacts with the calcium source or the zinc source without interfering anions to prepare the product, and the method has the advantages of simple and efficient process, high utilization rate of raw materials, high product quality and yield, no byproduct salt, clean and sustainable waste water discharge and the like.

Drawings

FIG. 1 is a structural formula of the oligomer main component in hydroxymethionine.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The preparation method of the D, L-2-hydroxy-4-methylthio butyrate comprises the steps of firstly diluting 88 wt% of commercial-grade hydroxy methionine or a hydroxy methionine concentrated solution (concentrated liquid methionine obtained by hydrolysis and separation of cyanohydrin) with water to 30-50 wt% of concentration so as to facilitate hydrolysis of a dimer and a polymer to obtain a diluted solution, heating the diluted solution to 70-100 ℃, and stirring the mixture for 2 to 5 hours under the condition of heat preservation under the ultrasonic atmosphere of 25 to 40KHz, and/or adding the diluent into an autoclave, stirring the mixture for 30 to 90 minutes under the pressure of 1.0 to 2.0MPa and the temperature of 150 to 180 ℃, so as to hydrolyze the liquid methionine dimer and polymer into monomer D, L-2-hydroxy-4-methylthiobutyric acid, wherein the hydrolysis under ultrasonic wave and the pressurized hydrolysis can be operated independently or in combination; after the dimer and polymer in the liquid methionine are hydrolyzed (the content of the dimer and polymer in the total liquid methionine in an analysis result is lower than 2 percent as the requirement), the monomer liquid methionine water solution is controlled to be 60-80 ℃, 0.5 mole equivalent of metal compound (mainly oxide, hydroxide, carbonate or basic carbonate) of interference-free anions is added in batches, the mixture is stirred and subjected to heat preservation reaction for 30-60 min, the obtained reaction liquid is concentrated or directly subjected to spray drying, and the high-quality finished product of the D, L-2-hydroxy-4-methylthio calcium butyrate or the chelated zinc is obtained by packaging.

The D, L-2-hydroxy-4-methylthio butyrate mainly comprises calcium D, L-2-hydroxy-4-methylthio butyrate and zinc D, L-2-hydroxy-4-methylthio butyrate, and the metal compound used is one of calcium carbonate, calcium oxide, calcium hydroxide, zinc oxide, zinc hydroxide, basic zinc carbonate and zinc carbonate.

FIG. 1 is a structural formula of the oligomer main component in hydroxymethionine.

The preparation method of the D, L-2-hydroxy-4-methylthio butyrate comprises the following steps of hydrolyzing D, L-2-hydroxy-4-methylthio butyrate before synthesizing the D, L-2-hydroxy-4-methylthio butyrate, wherein the hydrolysis experiment operation is as follows:

diluting commercial-grade liquid methionine with concentration of 88 w% by adding desalted water to different concentrations, performing ultrasonic action and/or high-temperature pressurized hydrolysis under different conditions, monitoring the effect of converting dimer and polymer in the hydrolyzed liquid methionine into monomer, and detecting the content of dimer, polymer and monomer in the liquid methionine by high performance liquid chromatography. Examples 1 to 13 hydrolysis experiments of liquid methionine were performed according to the above method and the data in table 1, and the specific process conditions and experimental results of each example are shown in table 1:

TABLE 1

The data in table 1 show that ultrasonic pretreatment of liquid methionine with a certain concentration has a certain effect on the hydrolytic conversion of dimer and trimer in the liquid methionine into monomer, wherein the ultrasonic treatment effect is better than that of high-temperature hydrolysis, but the ultrasonic treatment time is longer; ultrasonic wave and high temperature hydrolysis combine the effect that the polymer conversion efficiency has effectively been promoted. In addition, according to the comparison between the preparation concentration of the liquid methionine and the conversion efficiency of the polymer, the lower dilution concentration of the liquid methionine is more favorable for the hydrolytic conversion of the polymer, but if the dilution concentration of the liquid methionine is too low, a large amount of wastewater can be generated, and the precipitation of the liquid methionine salt is not favorable.

On the basis of examples 1 to 13, the invention provides a preparation method of D, L-2-hydroxy-4-methylthiobutyrate, which comprises the following specific steps:

example 14

This example prepared calcium D, L-2-hydroxy-4-methylthiobutyrate by the following method:

weighing 200g of commercial grade 88 wt% liquid methionine, detecting that the liquid methionine contains 66 w% monomer, 18 w% dimer and 4 w% trimer, transferring the liquid methionine into a beaker, adding desalted water to dilute the liquid methionine to a concentration of 40 wt%, stirring in 85 deg.C water bath equipped with 30KHz ultrasonic vibrator for 2 hr to obtain treatment solution, transferring into 500mL autoclave, stirring for 45min at a rotating speed of 75r/min under the conditions of pressure of 1.0MPa and temperature of 170 ℃, detecting and calculating the dimer and polymer contained in the obtained hydrolysate to be 1.3 percent of the content of total liquid methionine by high performance liquid chromatography, controlling the temperature of the hydrolysate to be 60 ℃, adding suspended emulsion amounting to 43.4g of calcium hydroxide into the hydrolysate in 3 batches in equal amount, preserving the temperature for reaction for 60min, and performing spray drying on the obtained reaction feed liquid to obtain a uniform white powdery D, L-2-hydroxy-4-methylthio calcium butyrate solid product. The product was analyzed for liquid methionine content (dry basis): 87.83%, calcium content: 11.81%, liquid calcium methionine: 99.64%, loss on drying: 0.16 percent.

Example 15

This example prepares zinc D, L-2-hydroxy-4-methylthiobutyrate by the following method:

detecting that the commercial grade 88 wt% liquid methionine contains 66% monomer, 18% dimer and 4% trimer, transferring the liquid methionine into a beaker, adding desalted water to dilute the liquid methionine to the concentration of 35 wt%, stirring the mixture for 5 hours in 85 ℃ water bath provided with a 30KHz ultrasonic vibrator, calculating the content of the dimer and the polymer in the total liquid methionine to be 1.42% by adopting high performance liquid chromatography detection for the obtained hydrolysate, controlling the temperature of the hydrolysate to be 75 ℃, adding 41.86g of zinc oxide powder in 3 batches in equal amount, carrying out heat preservation reaction for 30min, and carrying out spray drying on the reaction feed liquid while the hydrolysate is hot to obtain a uniform white powdery D, L-2-hydroxy-4-methylthiobutyric acid chelated zinc solid product. The product was analyzed for liquid methionine content (dry basis): 81.74%, zinc content: 17.6%, liquid zinc methionine: 99.34 percent.

Example 16

This example prepared calcium D, L-2-hydroxy-4-methylthiobutyrate by the following method:

measuring the content of 96.7 wt% of 200g of concentrated liquid methionine, wherein the content of the concentrated liquid methionine contains 72.6% of monomer, 20% of dimer and 4.1% of polymer, adding desalted water to dilute the solution to 20 wt%, transferring the diluted solution into a 500mL high-pressure kettle, stirring the diluted solution at the rotating speed of 100r/min at the temperature of 180 ℃ under the pressure of 1.0MPa for 90min to obtain hydrolysate, calculating the content of the dimer and the polymer in the total liquid methionine to be 1.75% by adopting high performance liquid chromatography detection, controlling the temperature of the hydrolysate to be 80 ℃, adding 64.8g of calcium carbonate powder in 3 batches in an equivalent manner, carrying out heat preservation reaction for 45min, and carrying out spray drying on the reaction feed liquid to obtain a uniform white powdery D, L-2-hydroxy-4-methylthio calcium. The product was analyzed for liquid methionine content (dry basis): 87.43%, calcium content: 11.7%, liquid calcium methionine: 99.13 percent.

Comparative example 1

In this example, calcium D, L-2-hydroxy-4-methylthiobutyrate was prepared from untreated oligomer liquid methionine according to the same method as follows:

detecting the liquid methionine with the content of 66% of monomers, 18% of dimers and 4% of trimers in 200g of commercial grade 88 wt% of liquid methionine, transferring the liquid methionine into a beaker, adding desalted water to dilute the liquid methionine to 40 wt%, controlling the temperature to be 80 ℃, adding the suspended emulsion equivalent to 43.4g of calcium hydroxide in 3 batches, keeping the temperature for reaction for 60min, and carrying out spray drying on the reaction liquid while the reaction liquid is hot to obtain a micro-brown fine powdery D, L-2-hydroxy-4-methylthio calcium butyrate solid product with uneven fine particles. The product was analyzed for liquid methionine content (dry basis): 84.93%, calcium content: 11.11%, liquid calcium methionine: 96.04%, loss on drying: 0.85 percent.

Comparative example 2

In this example, calcium D, L-2-hydroxy-4-methylthiobutyrate was prepared from untreated oligomer liquid methionine according to the same method as follows:

detecting that the liquid methionine contains 66% of monomer, 18% of dimer and 4% of trimer in 200g of commercial grade 88 wt% of liquid methionine, transferring the liquid methionine into a beaker, adding desalted water to dilute the liquid methionine to 40 wt%, controlling the temperature to be 80 ℃, adding zinc oxide powder which is equivalent to 48.2g in 3 batches in an equivalent manner, preserving the temperature for reaction for 60min, and carrying out spray drying on the reaction liquid while the reaction liquid is hot to obtain a micro-brown fine powdery D, L-2-hydroxy-4-methylthiobutyric acid chelated zinc solid product with a small amount of fine particles. The product was analyzed for liquid methionine content (dry basis): 80.12%, zinc content: 16.71%, liquid methionine chelated zinc: 96.04%, loss on drying: 0.96 percent.

From the above examples and comparative examples, it can be seen that less polymer is beneficial to obtain a D, L-2-hydroxy-4-methylthiobutyrate calcium or D, L-2-hydroxy-4-methylthiobutyrate zinc chelate product with a nearly white appearance and more uniform particles, and the direct reaction of commercial-grade liquid methionine with calcium salt (or zinc salt) can obtain a liquid methionine calcium (or liquid methionine chelated zinc) product with particles, and further sieving and crushing are needed.

Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims. The techniques, shapes, and configurations not described in detail in the present invention are all known techniques.