Patent Description:
Methionine hydroxy analogs, such as <NUM>-hydroxy-<NUM>-(methylthio)butanoate (HMTBA), are in the liquid form and are organic acids with strong acidity. Liquid hydroxymethionine can be prepared by cyanohydrin hydrolysis, in which methylthiopropanal is reacted with hydrocyanic acid to prepare <NUM>-hydroxy-<NUM>-(methylthio)butyronitrile (HMTBN). Under the action of sulfuric acid, <NUM>-hydroxy-<NUM>-(methylthio)butyronitrile is hydrated into <NUM>-hydroxy-<NUM>-(methylthio)butanamide, and then, under the action of sulfuric acid, <NUM>-hydroxy-<NUM>-(methylthio)butanamide is hydrolyzed into a hydrolysis product containing liquid hydroxymethionine, ammonium sulfate, and ammonium bisulfate. It is necessary to remove ammonium sulfate and ammonium bisulfate from the hydrolysis product to obtain high-purity liquid hydroxymethionine.

In order to facilitate transportation, especially at low temperature in winter, and subsequent processing, it is desirable to reduce the viscosity of liquid hydroxymethionine.

<CIT> and <CIT> disclose mixtures comprising a methionine hydroxy analog and an oligomer thereof.

The inventors have found that by removing salts, particularly ammonium sulfate and ammonium bisulfate, from a methionine hydroxy analog to a certain extent, the equilibrium between a monomer and an oligomer of the methionine hydroxy analog can be adjusted, and changes in the amount and the ratio unexpectedly affect the viscosity of the product.

In one aspect, the present disclosure provides a mixture, containing:.

In another aspect, the present disclosure provides a method for processing a mixture containing a methionine hydroxy analog and an oligomer thereof, including the following steps:.

The above and other features and advantages of the present disclosure will become apparent from the following detailed description of the embodiments and the appended claims.

The present disclosure will be further described with reference to the drawings:.

Unless otherwise specified, the following definitions are provided to illustrate and define the meaning and scope of various terms used in the present disclosure.

Herein, the term "mixture" refers to a combination of two or more different substances.

The term "AS" refers to ammonium sulfate with a molecular formula of (NH<NUM>)<NUM>SO<NUM>.

The term "BAS" refers to ammonium bisulfate with a molecular formula of NH<NUM>HSO<NUM>.

The term "HMTBA" refers to <NUM>-hydroxy-<NUM>-(methylthio)butanoate, also known as methionine hydroxy analog or liquid methionine.

The term "ATS" refers to an ammonium salt of <NUM>-hydroxy-<NUM>-(methylthio)butanoate (HMTBA).

The term "TOS" refers to total organic sulfur. It is a measure of the content of sulfur-containing organic compounds in a sample.

The term "HPLC" refers to high performance liquid chromatography.

The term "DMW" refers to demineralized water.

The term "MMP" refers to methylthiopropanal.

Unless otherwise specified, amounts and percentages are based on weight.

The present disclosure provides a mixture containing a methionine hydroxy analog and an oligomer thereof, and a preparation method thereof. By reducing the content of ammonium sulfate and ammonium bisulfate in the mixture to be less than <NUM> wt%, the content of water in the mixture is increased, and the total amount of a monomer, a dimer, and a trimer of the methionine hydroxy analog is increased to make the viscosity of the mixture at <NUM> lower than <NUM> mPa·s.

As a cyanohydrin hydrolysis product, the mixture containing a methionine hydroxy analog as a main component may contain salts such as ammonium sulfate (AS), ammonium bisulfate (BAS), an ammonium salt of <NUM>-hydroxy-<NUM>-(methylthio)butanoate (ATS), and methionine (MTN). The inventors have found that the salts are not only undesired impurities, but also factors affecting the viscosity of the mixture. AS and BAS can be removed from the mixture by the ion exchange resin processing, the ion exchange resin processing is combined to a preparation process to circulate an effluent, so that no waste water will be discharged from the whole process. Furthermore, the removed salts can be recycled, so no solid waste will be produced. Therefore, the process can effectively utilize resources and is environmentally-friendly.

In some embodiments, a mixture is obtained by cyanohydrin hydrolysis, in which the total amount of salts is <NUM>-<NUM> wt%, and AS and BAS are main components. For example, the total amount is <NUM>-<NUM> wt%, and the total amount of ATS and MTN is less than <NUM> wt%, particularly less than <NUM> wt%.

AS and BAS are removed to a certain extent by processing the mixture with ion exchange resins.

In some embodiments, the mixture is processed to obtain a mixture below, which includes:.

In some embodiments, the ratio of monomer: dimer: trimer by weight is <NUM>-<NUM>: <NUM>-<NUM>: <NUM>-<NUM>.

In view of the quality of the product, the monomer is appropriate. The relatively low content of salts and the relatively high content of water in the mixture break the equilibrium between the monomer and the oligomer and make the content of the monomer increase. The dimer and the trimer are less appropriate, and the viscosity of them is higher than the viscosity of the monomer, so the relatively high content of monomer helps reduce the viscosity of the mixture.

Particularly, the mixture contains <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt% or <NUM> wt% of water, and/or less than <NUM> wt% of ammonium sulfate and ammonium bisulfate. In some embodiments, the mixture contains less than <NUM> wt% of ammonium sulfate, and less than <NUM> wt% of ammonium bisulfate.

Because the content of salts is reduced, and the content of water is increased, the viscosity of the mixture can be reduced to be lower than <NUM> mPa·s at <NUM>. Particularly, the viscosity at <NUM> is lower than <NUM> mPa·s. In some embodiments, the viscosity at <NUM> is lower than <NUM> mPa·s.

The mixture of the present disclosure can be used as a feed additive. For example, the mixture is used in a nutritional composition for animals or humans, and the nutritional composition can be dried as a solid for subsequent use. For example, the mixture can be spray-dried, and the low content of salts and the appropriate viscosity can solve some problems in the spray drying process, such as precipitation and difficult processing.

As shown in <FIG>, the present disclosure provides a method for processing a mixture containing a methionine hydroxy analog and an oligomer thereof, including the following steps:.

In some embodiments, steps S1 and S2 respectively include removing NH<NUM>+ with a cation exchange resin, and removing SO<NUM><NUM>- an anion exchange resin. For example, step S1 includes:.

In some embodiments, before step S1, the mixture containing a methionine hydroxy analog and an oligomer thereof contains less than <NUM> wt% of water, particularly less than <NUM> wt% of water; and more than <NUM> wt% of ammonium sulfate and ammonium bisulfate, particularly more than <NUM> wt% of ammonium sulfate and ammonium bisulfate, and more particularly <NUM>-<NUM> wt% of ammonium sulfate and ammonium bisulfate. In some embodiments, before step S1, the viscosity of the mixture containing a methionine hydroxy analog and an oligomer thereof at <NUM> is higher than <NUM> mPa·s.

The cation exchange resin may be a strong-acid cation exchange resin, for example, a strong-acid cation exchange resin having sulfonic groups as exchange groups, or a weak-acid cation exchange resin, for example, a weak-acid cation exchange resin having carboxy groups as exchange groups. Particularly, the cation exchange resin is a strong-acid cation exchange resin. In some embodiments, a skeleton structure of the cation exchange resin is a styrene-divinylbenzene copolymer, ion exchange groups are sulfonic groups, sizes of <NUM>% or above of particles are in a range of <NUM>-<NUM>, an exchange capacity is equal to or higher than <NUM> mmol/mL, a specific surface area is equal to or greater than <NUM><NUM>/g, and the content of water is <NUM>-<NUM>%. The anion exchange resin may be a weak-base anion exchange resin, for example, a weak-base anion exchange resin having primary, secondary, and tertiary amines as exchange groups, or a strong-base anion exchange resin, for example, a strong-base anion exchange resin having quaternary ammonium groups as exchange groups. Particularly, the anion exchange resin is a weak-base anion exchange resin, for example, a skeleton structure of the anion exchange resin is a methacrylate polymer, ion exchange groups are tertiary amines, sizes of <NUM>% or above of particles are in a range of <NUM>-<NUM>, an exchange capacity is equal to or higher than <NUM> mmol/mL, a specific surface area is equal to or greater than <NUM><NUM>/g, and the content of water is <NUM>-<NUM>%. Before the first use, the resins are activated, for example, the cation resin is activated with <NUM> wt% sulfuric acid, and the anion resins is activated with <NUM> wt% ammonia water, so that the resins are saturated with H+ or OH-.

At the ion exchange step, a feed liquid passes through the resins to remove salts (ammonium ions or sulfate ions) from the feed liquid. Parameters, such as the feed temperature, a feed rate (in BV/h), and the volume (in BV) of a feed liquid processed with <NUM> BV of resin, can affect an ion exchange result.

With regarding to the viscosity of a mixture to be processed, the feed temperature is higher than <NUM>. However, if the temperature is too high, the service life of the resin will be shortened. In some embodiments, steps S1 and S2 are performed at the temperature of <NUM>-<NUM>, and particularly performed at <NUM>.

A rate of a feed liquid entering a resin column may affect a desalting efficiency. In some embodiments, steps S1 and S2 are performed at a rate of <NUM>-<NUM> BV/h, particularly performed at a rate of <NUM>-<NUM> BV/h.

A capacity (C, in mL/g) of a resin refers to an amount of NH<NUM>+ or SO<NUM><NUM>- that can be exchanged per unit volume of the resin. It is determined by measuring NH<NUM>+% and SO<NUM><NUM>-% at the inlet and outlet, and measuring the weight of the feed liquid passing through the resin in saturated BV. For example, a capacity of the cation exchange resin is calculated by the following formula.

A capacity of the anion exchange resin is calculated by the following formula.

The capacity of the resin, and the number of ions to be removed with the resin are used to determine BV of the resin required for the processing. BV of the used cation exchange resin and anion exchange resin may be different.

In some embodiment, for the cation exchange resin, the resin becomes saturated when processing <NUM> BV, such as <NUM> BV, of feed liquid, and the anion exchange resin becomes saturated when processing <NUM> BV, such as <NUM> or <NUM> BV, of feed liquid, which is the maximum volume of a mixture processed with <NUM> BV of resin. Otherwise, the content of salts at the outlet of the ion exchange resin is unsatisfactory. Therefore, at each of steps S1 and S2, <NUM> BV of ion exchange resin is used to process at most <NUM> BV, particularly at most <NUM> BV, of mixture containing a methionine hydroxy analog and an oligomer thereof.

In some embodiments, after step S2, the concentration of NH<NUM>+ in the mixture containing a methionine hydroxy analog and an oligomer thereof is <NUM>-<NUM>%, such as <NUM>-<NUM>%, for example, about <NUM>%, the concentration of SO4<NUM>- is <NUM>-<NUM>%, such as <NUM>-<NUM>%, for example, about <NUM>%, and/or the pH at <NUM> is <NUM>-<NUM>, such as <NUM>-<NUM>, for example, about <NUM>, about <NUM>, about <NUM> or about <NUM>.

At steps S1 and S2, after becoming saturated, the ion exchange resins are washed with water, such as DMW, to remove the remaining TOS on the resins. At step S3, the ion exchange resin of each of steps S1 and S2 is washed with water, such as DMW, to obtain an aqueous eluent, and the aqueous eluent is used to dilute a mixture containing a methionine hydroxy analog and an oligomer thereof before step S1. An effluent obtained by the washing of step S3 is recycled into the process, so that no waste water will be produced.

In some embodiments, the water used at step S3 is not heated before flowing into the resin column because there is no special requirement for the temperature of this step.

The volume of water used for washing is a factor affecting the overall efficiency of the method. If the volume of water used at the washing step is insufficient, a certain amount of TOS will remain on the resin, and this amount of TOS will enter a regeneration solution at step S4 to cause contamination and product loss. In some embodiments, at step S3, at least <NUM> BV, for example, at least <NUM> BV, of water is used to wash the ion exchange resin of each of steps S1 and S2.

In some embodiments, step S3 is performed at a rate of <NUM>-<NUM> BV/h, particularly performed at a rate of <NUM>-<NUM> BV/h.

After the washing of step S3, the ion exchange resins are regenerated and used for the next processing cycle, in which a generation solution passes through the resin to remove NH<NUM>+ and SO<NUM><NUM>-, and the resin is saturated again with H+ and OH-. Regeneration of step S4 includes:.

In some embodiments, the desorption solution and/or the cleaning solution are recirculated in the preparation process of HMTBA.

<FIG> is a schematic diagram of a preparation process of HMTBA in which a desorption solution and/or a cleaning solution obtained by the resin processing are recirculated. A preparation system of HMTBA by cyanohydrin hydrolysis may include at least a cyanohydrin preparation unit, an HMTBA preparation unit, and an AS preparation unit. In the cyanohydrin (HMTBN) preparation unit, MMP and hydrogen cyanide (HCN, prepared from ammonia and natural gas) are used to prepare cyanohydrin. A certain amount of sulfuric acid and water are further introduced into the unit. The desorption solution and/or the cleaning solution can be added into the unit to replace a certain amount of water. In the HMTBA preparation unit, HMTBN is used to prepare HMTBA under the action of H<NUM>SO<NUM>, and an effluent can be processed by the method of the present disclosure to obtain a mixture containing HMTBA and low content of salts. In the AS preparation unit, all effluents containing AS (at different AS% concentrations) from other units are processed, water is evaporated, and crystallization is performed to obtain solid pure AS serving as a by-product. A desorption solution and/or a cleaning solution containing AS can be delivered to the unit.

In some embodiments, the desorption solution and/or the cleaning solution can be used as a feed liquid in the AS preparation unit or used as feed water in the cyanohydrin hydrolysis unit.

In some embodiments, the concentration of the sulfuric acid solution is <NUM>-<NUM> wt%, particularly <NUM>-<NUM> wt%, and the concentration of the ammonia solution is <NUM>-<NUM> wt%, particularly <NUM>-<NUM> wt%. The sulfuric acid solution can be prepared from <NUM> wt% sulfuric acid, and the ammonia solution can be prepared from <NUM> wt% ammonia water or ammonia gas.

If the volume of the regeneration reagent used in the regeneration step is insufficient, an efficiency of the next ion exchange processing cycle will not be <NUM>%. The degree of regeneration can be assessed by the following parameters, such as the pH or the content of NH<NUM>+ and/or SO<NUM><NUM>- at the regeneration outlet, and the volume of a solution (in BV) that passes through the resin to achieve the desired specification at the regeneration outlet.

In some embodiments, at step S41, the pH of an effluent from the cation exchange resin is lower than <NUM>, and/or the concentration of NH<NUM>+ is less than <NUM>%. The pH of an effluent from the anion exchange resin is greater than <NUM>, and/or the concentration of SO<NUM><NUM>- is less than <NUM>%.

In some embodiments, step S4 is performed at the temperature of <NUM> to <NUM>, and/or step S4 is performed at a rate of <NUM> BV/h to <NUM> BV/h, particularly performed at a rate of <NUM> BV/h to <NUM> BV/h.

In some embodiments, at step S41, at least <NUM> BV, particularly <NUM>-<NUM> BV, of above sulfuric acid solution is used, and/or at least <NUM> BV, particularly <NUM>-<NUM> BV, of above ammonia solution is used. In some embodiments, <NUM> BV of <NUM> wt% H<NUM>SO<NUM> solution is used, and <NUM>-<NUM> BV of <NUM> wt% ammonia solution is used.

In some embodiments, <NUM> wt% of H<NUM>SO<NUM> solution passes through the cation exchange resin until the pH of an effluent is smaller than <NUM> to regenerate and activate the resin, and <NUM> wt% of NH<NUM>·H<NUM>O solution passes through the anion exchange resin until the pH of an effluent is greater than <NUM> to regenerate and activate the resin.

After the regeneration of step S41, the ammonia water or sulfuric acid solution remaining in the columns needs to be washed out to ensure effective ion exchange and avoid a small amount of acid/base in TOS. At step S42, water, such as DMW, passes through the resin columns to remove a regeneration reagent and make the pH of an effluent from the cation exchange resin be <NUM>-<NUM>, and/or the pH of an effluent from the cation exchange resin be <NUM>-<NUM>, and a cleaning solution is collected and recycled into the process, for example, used as feed water in the cyanohydrin hydrolysis unit. In some embodiments, at step S42, each resin is washed with at least <NUM> BV, particularly at least <NUM> BV, of water. For example, the cation exchange resin is washed with at least <NUM> BV, particularly at least <NUM> BV, of water, and the anion exchange resin is washed with at least <NUM> BV, particularly at least <NUM> BV, of water.

At step S43, the cation exchange resin and the anion exchange resin are washed with the mixture containing a methionine hydroxy analog and an oligomer thereof. Particularly, at step S43, the cation exchange resin and the anion exchange resin are washed with the mixture containing a methionine hydroxy analog and an oligomer thereof that is processed with resins, that is, the mixture is processed at steps S1 and S2, so that the columns are filled with a mixture containing HMTBA and low content of salts instead of water prior to the start of adsorption in a new processing cycle. It avoids dilution/contamination of the processed product with water.

In some embodiments, steps S1 to S4 are performed at the same time on at least two groups of ion exchange resins, and each group of ion exchange resins includes at least one cation exchange resin and at least one anion exchange resin. Particularly, the at least two groups of ion exchange resins do not undergo the same step at the same time. Much particularly, at least one group of ion exchange resins undergoes steps S <NUM> and S2, and at least one group of ion exchange resins undergoes step S4, so that the ion exchange processing (steps S <NUM> and S2) can be performed on at least one group of ion exchange resins at any time. Therefore, the processing can be performed in a continuous manner for consistent results.

AS and BAS in a mixture can be reduced to be less than <NUM> wt% by the method of the present disclosure. For <NUM> of removed AS, <NUM> of AS is produced. However, the removed salts and newly produced salts can be recirculated in the preparation process, can reach the solid AS preparation unit, and then can be processed into a solid AS by-product. Therefore, the method will not produce solid waste.

The following examples and comparative examples are provided to help understanding of the present disclosure, but should not be construed to limit the scope of the present disclosure. Unless otherwise specified, all parts, percentages, concentrations, etc. are based on weight. The following measuring methods and procedures are used for the evaluation of the following examples and comparative examples.

Characterization methods will be described below. Unless otherwise specified, all measurement were performed at room temperature.

Unless otherwise specified, all reagents were analytically pure, water was distilled water or equivalently pure.

The pH of a solution was directly measured by using a calibrated pH meter (InLab® <NUM> Combined Electrode, made by Mettler, or an equivalent) while the solution was vigorously stirred. The pH meter was calibrated before any measurement, and automatically corrected for temperature.

Buffer solutions with the pH of <NUM> and <NUM>: product code <NUM> and <NUM>, were made by Panreac, or equivalents.

Total organic sulfur (TOS) was measured based on oxidization of thioether groups with a bromine oxidizer (generated in situ from a mixture of bromide/bromate ester and an acid medium) to sulfoxide. An equivalent point was determined by potentiometry.

<NUM> of potassium bromide (product code <NUM>, made by PANREAC, or an equivalent) was dissolved in distilled water, <NUM> of <NUM>% hydrochloric acid (product code <NUM>, made by PANREAC, or an equivalent) was added, and the volume of the system was made up to <NUM> with distilled water.

Bromine: <NUM> N, product code <NUM>, made by PANREAC, or an equivalent.

METTLER DL <NUM>, DL <NUM> or DL <NUM> titrator, or an equivalent, equipped with double-pin platinum electrodes (product code DM <NUM>), combined with a polarization module DK <NUM> (used for METTLER DL <NUM> and DL <NUM>).

About <NUM>-<NUM> of acid phase to be analyzed was weighted out by using an analytical balance, and transferred into a titration beaker. About <NUM> of titration medium was added to titrate.

The content of AS and BAS was calculated based on measurement of sulfate ions and ammonium.

Ammonium was measured by potentiometric titration using a standard solution of sodium hydroxide (NaOH).

The content of ammonium was determined by titration using a basic compound of known normality. The titration was performed in a non-aqueous medium to highlight the potential step due to the presence of bisulfate ions.

Sodium hydroxide: 1N, product code <NUM>, made by PANREAC, or product code SO0441, made by SCHARLAU, or an equivalent. Isopropyl alcohol QP (technical pure).

Titrator METTLER DL <NUM> or DL <NUM>, or an equivalent.

Combined with a pH electrode used for a non-aqueous medium (DG <NUM> or an equivalent).

About <NUM> of sample was weighed out, and <NUM> of isopropyl alcohol was added. The system was titrated to an equivalence point of ammonium ions.

Sulfate ions were measured by potentiometric titration using a standard solution of lead perchlorate (Pb(ClO<NUM>)<NUM>).

The content of sulfate ions was determined by titration using a standard solution of lead perchlorate.

Pb(ClO<NUM>)<NUM> solution: <NUM> ORION <NUM>.

Potentiometer (Titrando <NUM> Metrohm or an equivalent).

Saturated calomel electrode (ex: Tacussel n° XR <NUM><NUM><NUM>) or Ag/AgCl (filled with tetraethylammonium perchlorate saturated with ethanol).

About <NUM> of sample was weighed out, and dissolved in <NUM> of acetone/water mixture (v/v=<NUM>/<NUM>). The system was titrated to an equivalence point of sulfate ions.

The content of water was determined by normal Karl Fischer titration using a KARL-FISCHER reagent in an anhydrous solution of iodine and sulfurous acid anhydride. An equivalent point was determined by precise discoloration.

The determination was performed by titration using a KARL-FISCHER reagent in an anhydrous solution of iodine and sulfurous acid anhydride. In the presence of water, iodine oxidizes sulfurous acid anhydride, which was then reduced to iodide. At the equivalent point, the excess reagent caused the color to change from yellow to dark red. In order to better detect the end point, polarized platinum electrodes were used.

Methanol used for measurement of content of water (low content of water), product code <NUM>, made by PANREAC, or a HYDRANAL solvent for volumetric Karl Fischer, product code <NUM>, made by RIEDEL DE HAËN.

KARL-FISCHER reagent solution (<NUM><NUM> = <NUM> of water), product code RE <NUM>, made by SCHARLAU, or a HYDRANAL titrant <NUM>, made by RIEDEL DE HAËN, product code <NUM>, or product code <NUM>, made by PANREAC.

Titrator METTLER DL <NUM> or DL <NUM>/DL <NUM>, equipped with double-pin platinum electrodes (DM <NUM> or an equivalent) and a polarization module DK <NUM> (only in DL <NUM>).

An analytical medium is neutralized in a titration beaker. Once the analytical medium is in the neutral condition, about <NUM> of sample is added to the titration beaker. The titrator starts and titrates the system to the equivalence point; and the titrator stops automatically and gives a result based on water%.

Monomers, dimers, and trimers of HMTBA were determined by HPLC (Agilent, HPLC <NUM>, chromatographic column: Nucleosil <NUM>-<NUM> C18 (<NUM> × <NUM>), UV detector, eluent: acetonitrile/water, <NUM>/min, <NUM>, <NUM> bar).

The viscosity was determined by a standard method using a CANNON-FENSKE capillary viscometer for transparent liquids, suitable for the viscosity range to be measured (<NUM> series), standards ASTM D <NUM> and ISO <NUM>. The viscometer comes with a calibration certificate.

Resins used in the examples were provided by SUNRESIN, which are listed in details in Table <NUM> and Table <NUM>.

The device is composed of two jacket type glass columns (one is used for a cation exchange resin, and the other is used for an anion exchange resin), a cation exchange resin washing system, an anion exchange resin washing system, and a demineralized water washing system. The jacket could be filled with water at the temperature required by the test. The columns were filled with a required amount (i.e. <NUM> bed volume (BV)) of resin. A mixture to be processed, a sulfuric acid solution, an ammonia solution or demineralized water passed through the columns via a peristaltic pump to be subjected to regeneration, ion exchange or washing. A feed rate of the column can be precisely controlled by the peristaltic pump.

Parameters for ion exchange were fixed to <NUM> BV/h (<NUM> BV = <NUM>) and <NUM>. Tests on two capacities were performed, and the pH, TOS, NH<NUM>+, and SO<NUM><NUM>- at the outlet of the resin were monitored. <NUM>,<NUM> of mixture containing a methionine hydroxy analog was fed into each volume in the system, and an initial effluent (<NUM>-<NUM> BV) was discarded. Then, all effluents containing TOS were collected (after <NUM> BV, and <NUM> BV of cleaning water). A capacity of the resin was calculated by the following formula. Results are shown in Tables <NUM> and <NUM>. <MAT> <MAT>.

<NUM>,<NUM> of mixture containing a methionine hydroxy analog was continuously fed into a system (for the cation exchange resin, <NUM> BV = <NUM>, and for the anion exchange resin, <NUM> BV = <NUM>), the mixture first passed through the cation exchange resin and then passed through the anion exchange resin at a flow rate of <NUM> BV/h and <NUM>. Each BV of the sample was analyzed. Results are shown in Table <NUM> below.

A procedure of Example <NUM> was the same as that of Example <NUM>, and the difference was that a feed liquid contained <NUM>% of NH<NUM>+ and <NUM>% of SO<NUM><NUM>-, and an effluent was collected when BV was equal to <NUM>.

TOS, water, NH<NUM>+, SO<NUM><NUM>-, and the pH at the outlet were monitored and summarized in Table <NUM>.

A sample was processed by the method of Example <NUM>, and then mixed with a mixture that was not processed with ion exchange resins to obtain a mixture containing AS and BAS at a different concentration. The sample was characterized to determine an effect of the content of salts on the equilibrium between a monomer and an oligomer. Example <NUM> was a processed sample, and Example <NUM> was a sample formed by mixing the processed sample with an unprocessed solution, in which the final content of AS+BAS was <NUM>%.

Comparative Example <NUM> was the same as Examples <NUM> and <NUM>, and the difference was that a mixture that was not processed with ion exchange resins was used.

It can be seen from the results, when the content of ASBAS is reduced, the content of water is increased. The sum of M+D+T is obviously affected by the content of salts, that is, as the content of salts is reduced, the content of M+D+T is increased. Under the condition of low content of salts, the sum of M+D+T can be close to <NUM>%.

The samples of Examples <NUM> (Example <NUM>) and <NUM> (Example <NUM>) were characterized to determine an effect of the content of salts on the viscosity.

Comparative Example <NUM> was the same as Examples <NUM> and <NUM>, and the difference was that a mixture that was not processed with ion exchange resins was used and contained about <NUM>% of AS+BAS.

After the ion exchange processing, the columns were respectively washed with <NUM> BV of demineralized water at a rate of <NUM> BV/h. The cation exchange resin was regenerated with <NUM> BV of <NUM>% sulfuric acid at a rate of <NUM> BV/h, and the anion exchange resin was regenerated with <NUM>-<NUM> BV of <NUM>% NH<NUM>·H<NUM>O at a rate of <NUM> BV/h. <NUM>-<NUM> BV of demineralized water was introduced into the columns at a rate of <NUM> BV/h, and the mixture purified with the resins was introduced into the columns. Then, the columns could be used for the next processing cycle.

Claim 1:
A mixture, comprising:
<NUM>-<NUM> wt% of a methionine hydroxy analog and an oligomer thereof, in which more than <NUM> wt% being monomer, dimer and trimer, and the ratio of monomer: dimer: trimer by weight being <NUM>-<NUM>: <NUM>-<NUM>: <NUM>-<NUM>;
<NUM>-<NUM> wt% of water; and
less than <NUM> wt% of ammonium sulfate and ammonium bisulfate;
wherein a viscosity of the mixture at <NUM> is lower than <NUM> mPa·s.