阅读说明：本技术 一种色度稳定的2-甲基-4-乙酰氧基-2-丁烯醛的制备方法 (Preparation method of 2-methyl-4-acetoxyl-2-butenal with stable chromaticity ) 是由 程晓波 吕英东 张涛 林龙 张旭 翟文超 罗朝辉 于 2021-06-29 设计创作，主要内容包括：本发明公开了一种色度稳定的2-甲基-4-乙酰氧基-2-丁烯醛的制备方法,包括以下步骤：(1)2-亚甲基-4-乙酰氧基丁醛和助剂、溶剂在催化剂的作用下,发生气-固-液三相临氢异构反应生成2-甲基-4-乙酰氧基-2-丁烯醛；(2)反应达到指定的转化率后,终止反应,降温并过滤出固相催化剂；(3)精馏分离体系中的溶剂、加氢副产物、未反应的原料,得到产品2-甲基-4-乙酰氧基-2-丁烯醛；其中步骤(1)所述的助剂为一种或多种具有氨基和羰基两种官能团的有机化合物,基于所使用的原料2-亚甲基-4-乙酰氧基丁醛,助剂用量为10-100ppm。本发明提供的2-甲基-4-乙酰氧基-2-丁烯醛色度低,长期存储过程中稳定性好,色度增长慢,能够更好地满足下游需求。(The invention discloses a preparation method of 2-methyl-4-acetoxyl-2-butenal with stable chromaticity, which comprises the following steps: (1) 2-methylene-4-acetoxy butyraldehyde, an auxiliary agent and a solvent are subjected to a gas-solid-liquid three-phase hydroisomerization reaction under the action of a catalyst to generate 2-methyl-4-acetoxy-2-butenal; (2) after the reaction reaches the specified conversion rate, terminating the reaction, cooling and filtering out the solid-phase catalyst; (3) rectifying the solvent, the hydrogenation by-product and the unreacted raw material in the separation system to obtain a product 2-methyl-4-acetoxyl-2-butenal; wherein the assistant in the step (1) is one or more organic compounds with both amino and carbonyl functional groups, and the assistant is used in an amount of 10-100ppm based on the raw material 2-methylene-4-acetoxy butyraldehyde. The 2-methyl-4-acetoxyl-2-butenal provided by the invention is low in chroma, good in stability in a long-term storage process and slow in chroma growth, and can better meet the downstream requirements.)

1. A preparation method of 2-methyl-4-acetoxyl-2-butenal with stable chromaticity is characterized by comprising the following steps:

(1) in a system of 2-methylene-4-acetoxy butyraldehyde, an auxiliary agent, a solvent and a catalyst, gas-solid-liquid three-phase hydroisomerization reaction is carried out to generate 2-methyl-4-acetoxy-2-butenal;

(2) after the reaction reaches the specified conversion rate, terminating the reaction and filtering out the catalyst;

(3) purifying the reaction liquid to obtain a product 2-methyl-4-acetoxyl-2-butenal;

wherein, the assistant in the step (1) is selected from organic compounds with amino and carbonyl functional groups, and the assistant is preferably used in an amount of 10-100ppm based on the raw material 2-methylene-4-acetoxy butyraldehyde.

2. The method of claim 1, wherein the auxiliary agent comprises one or more of N, N-diethylformamide, N-methylacetanilide, N-dimethylformamide, N-dimethylacetamide, N-diethylacetamide;

preferably, the adjuvant is used in an amount of 20 to 60ppm based on the starting material 2-methylene-4-acetoxybutyraldehyde.

3. The method according to claim 1 or 2, wherein the catalyst in step (1) is Al₂O₃A supported noble metal catalyst, wherein the noble metal is selected from one or more of Pd, Pt and Rh; preferably, the noble metal content is from 1 to 10% based on the mass of the catalyst.

4. The process according to any one of claims 1 to 3, wherein the mass of the noble metal in the catalyst in the step (1) is 0.05 to 0.2% of the mass of the starting material, 2-methylene-4-acetoxybutyraldehyde.

5. The process according to any one of claims 1 to 4, wherein the solvent in step (1) is one or more of toluene, xylene and ethylbenzene.

6. The method according to any one of claims 1 to 5, wherein the mass ratio of the solvent to the 2-methylene-4-acetoxybutyraldehyde in the step (1) is 1 to 5: 1.

7. the process according to any one of claims 1 to 6, wherein the reaction temperature in step (1) is 30 to 110 ℃ and the reaction time is 2 to 10 hours.

8. The method according to any one of claims 1 to 7, wherein the hydrogen concentration of the hydrogen and nitrogen mixed gas introduced into the reaction kettle in the hydroisomerization reaction in the step (1) is selected from 0.5% to 10%;

preferably, the space velocity for introducing the hydrogen and nitrogen mixture is 100-.

9. The process of any one of claims 1 to 8, wherein step (2) controls the conversion of the feedstock to 55 to 90%.

10. The method of any one of claims 1 to 9, wherein the 2-methyl-4-acetoxy-2-butenal obtained in step (3) has a product color of < 30Hazen and an average increase in color of < 10Hzaen when stored at 40 ℃ for 12 months.

Technical Field

The invention relates to a preparation method of 2-methyl-4-acetoxyl-2-butenal with stable chromaticity, belonging to the field of chemical intermediate preparation.

Background

2-methyl-4-acetoxyl-2-butenal (pentanal) is an important intermediate for synthesizing vitamin A. Due to the importance of the pentanal in the vitamin A synthesis industry, the synthesis process of the pentanal is a long-term research hotspot.

The preparation of 2-methyl-4-acetoxy-2-butenal is now known and the advantages or disadvantages of the various routes are discussed in detail in the literature.

Patent US5453547 discloses a synthetic route for the preparation of pentanal starting from dimethoxyacetone, the reaction formula is as follows: reacting dimethoxyacetone with acetylene and hydrogen to generate a compound 2, reacting the compound 2 with acetic anhydride to generate a compound 3, isomerizing the compound 3 under the action of a Cu catalyst to obtain a compound 4, and hydrolyzing the compound 4 to finally obtain the pentanal. The disadvantages of the route are that the process route is long, the yield is low, and the total yield of the route is 35-45%.

Patent US5424478 discloses a synthetic route for the preparation of pentanal starting from isoprene. Isoprene and sodium hypochlorite are added to obtain two types of configuration addition products, acylation is carried out under the action of acetic acid to obtain a compound 8, and then dimethyl sulfoxide (DMSO) is used as an oxidant to prepare the pentanal. The method can generate a large amount of waste water and cause serious pollution. The synthetic route is as follows:

patent US4124619 discloses a synthetic route to the preparation of pentanal starting from butenediol. The method comprises the steps of taking a compound 10 as a raw material, acylating with acetic anhydride to obtain a compound 11, performing addition reaction with synthesis gas under the catalytic action of Rh catalyst to obtain a compound 12, further performing decarboxylation to obtain an isomer 13 of pentanal, and performing hydroisomerization on the isomer 13 in a hydrogen atmosphere to obtain 2-methyl-4-acetoxyl-2-butenal. The method does not generate waste water, is relatively environment-friendly and reasonable, but needs to use expensive noble metal catalysts. The synthetic route is as follows:

patent CN101092355A discloses a synthetic route for preparing pentanal using isoprene as starting material. According to the method, isoprene is taken as a raw material, and is directly added with tert-butyl hypochlorite to obtain a compound 16, and hexamethylenetetramine is taken as an oxidant to obtain pentanal. The step route is short, but the preparation process of tert-butyl hypochlorite is complex, the requirement on storage conditions is high, and a large number of byproducts are generated. The preparation process is shown as the following formula:

patent CN101723827A provides a route for preparing five-carbon aldehyde using 2-halogenated ethanol as starting material. The method uses 2-halogenated ethanol as a starting material, obtains a compound 19 after acylation in acetic anhydride, reacts with phosphite ester to obtain a compound 20, and is subjected to condensation reaction with dimethoxyacetone to obtain a compound 21, and further hydrolysis is carried out in acid to obtain the pentanal. The method has less pollution to the environment, but the reaction steps are longer. The synthetic process route is shown as the following formula:

patent US4873362 describes a process for the preparation of penta-aldehydes from ethylene oxide. According to the method, ethylene oxide is used as a raw material, after the ethylene oxide and acetic acid are subjected to ring-opening addition, a compound 24 is prepared, an oxidation reaction is carried out on the compound and oxygen under the catalysis of Ag to prepare an intermediate 25, and the intermediate 25 and propionaldehyde are subjected to reaction and condensation to obtain the pentanal. The intermediate 25 of this process is extremely unstable and the selectivity of the condensation reaction with propionaldehyde is difficult to control. The process route is shown as the following formula:

patent CN103467287A discloses a synthetic route for preparing five-carbon aldehyde using ethylene oxide and acrolein as starting materials. According to the method, acrolein and ethylene oxide are used as initial raw materials, and react under the action of an organic phosphine reagent to generate a compound 28, the compound is further acetylated to obtain an intermediate 29, and hydroisomerization is carried out under the action of a Pd catalyst to obtain the pentanal. This process also presents unstable intermediate 29 and consumes large amounts of expensive organophosphinic reagents in the route. The synthesis process comprises the following steps:

one of the main disadvantages of the 2-methyl-4-acetoxyl-2-butenal prepared by the prior art is that the product chromaticity is higher and the product growth is faster, the downstream of the 2-methyl-4-acetoxyl-2-butenal is mainly applied to the synthesis of vitamin A, and the color of the vitamin A synthesized by taking the high-chromaticity 2-methyl-4-acetoxyl-2-butenal as a raw material is yellow, so that the shelf life and the service performance of a vitamin A commodity are seriously influenced.

Disclosure of Invention

The invention aims to provide a preparation method of 2-methyl-4-acetoxyl-2-butenal with stable chromaticity. The chroma of the prepared 2-methyl-4-acetoxyl-2-butenal is less than 30Hazen, and the chroma increase is less than or equal to 10Hzaen after the 2-methyl-4-acetoxyl-2-butenal is stored for 12 months at 40 ℃. The chromaticity can be measured by referring to a general color number measuring method and taking Hazen as a measuring unit.

After systematic study on the reasons for the increase in the chromaticity of 2-methyl-4-acetoxy-2-butenal during long-term storage, the inventors found that the acidic substance in 2-methyl-4-acetoxy-2-butenal was responsible for the sharp increase in the chromaticity of 2-methyl-4-acetoxy-2-butenal during long-term storage. The chroma of the 2-methyl-4-acetoxy 2-butenal product can be increased mainly because: the hydrogen ions can catalyze the 2-methyl-4-acetoxyl 2-butenal to carry out cyclization reaction to generate a 2-methyl-4-acetoxyl 2-butenal dimer or polymer with a larger conjugated structure. The acidic substances in the system are generated from a plurality of sources, including: (1) 2-methylene-4-acetoxy butyraldehyde can generate hydrogenolysis reaction in the reaction process to generate acetic acid; (2) the 2-methyl-4-acetoxyl-2-butenal can be oxidized to generate an acidic substance in the storage process; (3) the 2-methyl-4-acetoxy 2-butenal is slowly decomposed to generate an acidic substance during storage, and the decomposition under acidic conditions is accelerated. The present invention has been accomplished based on this finding.

In order to achieve the above purpose, the invention adopts the following technical scheme:

the preparation method of the 2-methyl-4-acetoxyl-2-butenal with stable chromaticity comprises the following steps:

(1) 2-methylene-4-acetoxy butyraldehyde, an auxiliary agent and a solvent are subjected to a gas-solid-liquid three-phase hydroisomerization reaction under the action of a catalyst to generate 2-methyl-4-acetoxy-2-butenal;

(2) after the reaction reaches the specified conversion rate, terminating the reaction, cooling and filtering out the solid-phase catalyst;

(3) rectifying the solvent, the hydrogenation by-product and the unreacted raw material 2-methylene-4-acetoxy butyraldehyde in the separation system to obtain a product 2-methyl-4-acetoxy-2-butenal;

wherein the auxiliary agent in the step (1) is one or more organic compounds with both amino and carbonyl functional groups, and the dosage is 10-100ppm based on the mass of the 2-methylene-4-acetoxy butyraldehyde.

The catalyst in the step (1) of the invention is Al₂O₃A supported noble metal catalyst, the noble metal is selected from one or more of Pd, Pt and Rh, preferably Pd; the noble metal content is from 1 to 10%, preferably from 4 to 5%, based on the catalyst; the mass of the noble metal in the catalyst is 0.05-0.2 percent of that of the raw material 2-methylene-4-acetoxy butyraldehyde, preferably 0.1-0.15 percent％。

In the step (1) of the present invention, the solvent is one or more of toluene, xylene and ethylbenzene, preferably toluene; the mass ratio of the solvent to the 2-methylene-4-acetoxybutyraldehyde is 1-5: 1, preferably 2-3: 1.

In the step (1) of the invention, the isomerization reaction temperature is 30-110 ℃, preferably 60-85 ℃, and the reaction time is 2-10h, preferably 4.5-5 h.

In the hydroisomerization reaction process in the step (1), a bubbling kettle device is adopted for experiment, and the volume concentration of hydrogen in the hydrogen-nitrogen mixed gas introduced into the reaction kettle is selected from 0.5-10%, preferably 1-5%; the space velocity of the hydrogen and nitrogen mixed gas is 100-.

The auxiliary agent in step (1) of the present invention is an organic compound having both amino and carbonyl functional groups, including but not limited to one or more of N, N-diethylformamide, N-methylacetanilide, N-dimethylformamide, N-diethylacetamide, N-dimethylacetamide, preferably N, N-diethylformamide; the amount of the auxiliary used is 10 to 100ppm, preferably 20 to 60ppm, based on the starting material 2-methylene-4-acetoxybutyraldehyde used.

The 2-methyl-4-acetoxyl-2-butenal obtained in the step (3) of the invention contains a trace amount of auxiliary agent, but does not influence the downstream. The auxiliary agent used in the invention has the following functions: (1) in the reaction process, the catalytic effect of the catalyst can be improved, the hydrogenolysis side reaction is inhibited, and the generation of acetic acid is reduced; (2) during the storage process, the decomposition of the 2-methylene-4-acetoxy-butyraldehyde can be inhibited, and the acid value is prevented from increasing; (3) during the storage process, the oxidation rate of the 2-methyl-4-acetoxyl-2-butenal can be weakened, and the acid value can be prevented from increasing.

In order to ensure the accurate addition of the auxiliary agent, the auxiliary agent and the 2-methylene-4-acetoxy butyraldehyde are usually premixed and then added into the reaction system for reaction.

In the step (2), the reaction is monitored in real time by using gas chromatography in the reaction process, and the conversion rate of the raw materials is controlled to be 55-90%.

In the step (2), the temperature is reduced to be below 40 ℃.

The step (3) of the invention adopts an intermittent rectification scheme to refine the 2-methyl-4-acetoxyl-2-butenal, which belongs to the existing conventional separation technology in the field and does not need to be detailed. The recycled unreacted raw materials can be directly mixed with the raw materials to participate in the reaction.

The chroma of the obtained 2-methyl-4-acetoxyl-2-butenal is less than 30Hazen, and the average chroma increase is less than or equal to 10Hzaen after the 2-methyl-4-acetoxyl-2-butenal is stored for 12 months at 40 ℃.

The invention has the following outstanding effects:

in the prior art, the chroma of 2-methyl-4-acetoxyl-2-butenal is higher and the chroma is increased in the storage process, the auxiliary agent is added in the reaction process, so that a five-carbon aldehyde product also has a trace amount of auxiliary agent, the auxiliary agent is used for controlling the acid value in the product, the chroma of the product can be greatly reduced, the product is stable to store, the chroma of the obtained 2-methyl-4-acetoxyl-2-butenal is less than 30Hazen, the average chroma increase is less than or equal to 10Hzaen after the product is stored for 12 months at the temperature of 40 ℃, and the quality of the VA product is favorably improved.

Detailed Description

The technical solutions of the present invention are further described below, but not limited thereto, and modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the scope of the technical solutions of the present invention.

Gas chromatography conditions:

the chromatographic type is as follows: agilent WAX 1701.42249

Carrier gas: high purity nitrogen gas

Sample introduction mode: automatic sample injector

Nitrogen flow rate: 64.5ml/min

Vaporization chamber temperature: 280 deg.C

Split-flow sample introduction, split-flow ratio: 1: 40

Sample introduction amount: 0.2. mu.l

Column flow rate 1.5ml/min

Column temperature: first-order temperature programming, wherein the initial temperature is 100 ℃, the temperature is kept for 2 minutes, then the temperature is raised to 230 ℃ at the speed of 15 ℃/min, and the temperature is kept for 15 minutes; the total running time is 25.67min

The detector temperature is 300 DEG C

And (4) selecting an external standard method for quantification.

Some of the examples indicate the reagent specifications and sources

Test apparatus in the examples

Instrument for measuring the position of a moving object	Manufacturer of the product	Model number
			Colorimeter	HACH Lange	LICO 400
Bubbling kettle	Boluming medicine	5L

Example 1

Weighing 0.4g N, N-diethylformamide and 99.6g of 2-methylene-4-acetoxybutyraldehyde, mixing to prepare a solution, wherein the concentration of the auxiliary agent is 0.4%; weighing 4g of a solution with 0.4% of additive concentration and 396g of 2-methylene-4-acetoxybutyraldehyde to obtain a hydroisomerization reaction raw material (with the additive concentration of 40 ppm);

1200g of xylene, 10g of 5% Pt/Al are weighed₂O₃Catalyst additionAdding into a 5L bubbling kettle, heating to 90 deg.C, adding the prepared hydroisomerization reaction raw material 2-methylene-4-acetoxybutyraldehyde containing 40ppm of auxiliary agent into the reaction kettle, and introducing 2L/min mixed gas (2% H)₂/98％N₂) Starting the reaction; after reacting for 4 hours, cooling to 30 ℃ to stop the reaction, and sampling to obtain the raw material conversion rate of 78.7% and the selectivity of 91% for 2-methyl-4-acetoxyl-2-butenal; filtering the catalyst, and separating the auxiliary agent, the hydrogenation byproduct and the unreacted raw material 2-methylene-4-acetoxyl butyraldehyde in a batch distillation tower separation system to obtain a product 2-methyl-4-acetoxyl-2-butenal; the product color was measured to be 25Hazen and after 12 months of storage at 40 ℃ the increase in color was measured to be 6 Hazen.

Example 2

Weighing 0.1g N, N-dimethylformamide and 99.9g of 2-methylene-4-acetoxybutyraldehyde, mixing to prepare a solution, wherein the concentration of the auxiliary agent is 0.1%; weighing 4g of a solution with 0.1% of additive concentration and 396g of 2-methylene-4-acetoxybutyraldehyde to obtain a hydroisomerization reaction raw material (with the additive concentration of 10 ppm);

800g of toluene, 8.89g of 4.5% Pt/Al were weighed₂O₃Adding a catalyst into a 5L bubbling kettle, heating to 65 ℃, adding the prepared hydroisomerization reaction raw material 2-methylene-4-acetoxybutyraldehyde containing 10ppm of the auxiliary agent into the reaction kettle, and introducing 890mL/min of mixed gas (1% of H)₂/99％N₂) Starting the reaction; after 4.5h of reaction, the temperature is reduced to 30 ℃ to stop the reaction, and the conversion rate of the raw material is 68.3 percent and the selectivity of the 2-methyl-4-acetoxyl-2-butenal is 92.9 percent by sampling; filtering the catalyst, and separating the auxiliary agent, the hydrogenation byproduct and the unreacted raw material 2-methylene-4-acetoxyl butyraldehyde in a batch distillation tower separation system to obtain a product 2-methyl-4-acetoxyl-2-butenal; the product color was measured to be 26Hazen and after 12 months of storage at 40 ℃ the increase in color was measured to be 7 Hazen.

Example 3

Weighing 1g N, N-dimethylformamide and 99g of 2-methylene-4-acetoxybutyraldehyde, mixing to prepare a solution, wherein the concentration of the auxiliary agent is 1%; weighing 4g of a solution with the aid concentration of 1% and 396g of 2-methylene-4-acetoxybutyraldehyde to obtain a hydroisomerization reaction raw material (with the aid concentration of 100 ppm);

400g of ethylbenzene and 15g of 4% Rh/Al are weighed₂O₃Adding a catalyst into a 5L bubbling kettle, heating to 70 ℃, adding the prepared hydroisomerization reaction raw material 2-methylene-4-acetoxybutyraldehyde containing 100ppm of the auxiliary agent into the reaction kettle, and introducing 4.5L/min of mixed gas (5% H)₂/95％N₂) Starting the reaction; after the reaction is carried out for 5 hours, the temperature is reduced to 30 ℃ to stop the reaction, and the conversion rate of the raw material is 82 percent and the selectivity of the 2-methyl-4-acetoxyl-2-butenal is 90.3 percent by sampling; filtering the catalyst, and separating the auxiliary agent, the hydrogenation byproduct and the unreacted raw material 2-methylene-4-acetoxyl butyraldehyde in a batch distillation tower separation system to obtain a product 2-methyl-4-acetoxyl-2-butenal; the product color was measured to be 12Hazen and after 12 months of storage at 40 ℃ the increase in color was measured to be 6 Hazen.

Example 4

Weighing 0.2g N, N-diethylacetamide and 99.8g of 2-methylene-4-acetoxybutyraldehyde, mixing to prepare a solution, wherein the concentration of the auxiliary agent is 0.2%; weighing 4g of a solution with 0.2% of additive concentration and 396g of 2-methylene-4-acetoxybutyraldehyde to obtain a hydroisomerization reaction raw material (with the additive concentration of 20 ppm);

500g of xylene, 20g of 1% Pt/Al are weighed₂O₃Adding a catalyst into a 5L bubbling kettle, heating to 80 ℃, adding the prepared hydroisomerization reaction raw material 2-methylene-4-acetoxybutyraldehyde containing 20ppm of the auxiliary agent into the reaction kettle, and introducing 4L/min of mixed gas (10% H)₂/90％N₂) Starting the reaction; after 5.5h of reaction, the temperature is reduced to 30 ℃ to stop the reaction, and the conversion rate of the raw material is 55 percent and the selectivity of the 2-methyl-4-acetoxyl-2-butenal is 89.9 percent by sampling; filtering the catalyst, and separating the auxiliary agent, the hydrogenation byproduct and the unreacted raw material 2-methylene-4-acetoxyl butyraldehyde in a batch distillation tower separation system to obtain a product 2-methyl-4-acetoxyl-2-butenal; the product color was measured to be 25Hazen and after 12 months of storage at 40 ℃ the increase in color was measured to be 6 Hazen.

Example 5

Weighing 0.6g N-methylacetanilide and 99.4g of 2-methylene-4-acetoxybutyraldehyde, mixing to prepare a solution, wherein the concentration of the auxiliary agent is 0.6%; weighing 4g of a solution with 0.6% of additive concentration and 396g of 2-methylene-4-acetoxybutyraldehyde to obtain a hydroisomerization reaction raw material (with the additive concentration of 60 ppm);

1000g of toluene, 8g of 10% Pd/Al are weighed₂O₃Adding a catalyst into a 5L bubbling kettle, heating to 85 deg.C, adding the prepared hydroisomerization reaction raw material 2-methylene-4-acetoxybutyraldehyde containing 60ppm of auxiliary agent into the reaction kettle, and introducing 2L/min of mixed gas (8% H)₂/92％N₂) Starting the reaction; after reacting for 6h, cooling to 30 ℃ to stop the reaction, and sampling to obtain the raw material conversion rate of 90% and the selectivity of 2-methyl-4-acetoxyl-2-butenal of 93.1%; filtering the catalyst, and separating the auxiliary agent, the hydrogenation byproduct and the unreacted raw material 2-methylene-4-acetoxyl butyraldehyde in a batch distillation tower separation system to obtain a product 2-methyl-4-acetoxyl-2-butenal; the product color was measured to be 12Hazen and after 12 months of storage at 40 ℃ the increase in color was measured to be 8 Hazen.

Comparative example 1

1200g of xylene, 10g of 5% Pt/Al are weighed₂O₃Adding a catalyst into a 5L bubbling kettle, heating to 90 ℃, adding 400g of auxiliary-free hydroisomerization reaction raw material 2-methylene-4-acetoxybutyraldehyde into the reaction kettle, and introducing 2L/min mixed gas (2% H)₂/98％N₂) Starting the reaction; after reacting for 4h, cooling to 30 ℃ to stop the reaction, and sampling to obtain the raw material conversion rate of 80% and the selectivity of 2-methyl-4-acetoxyl-2-butenal of 84.9%; after the catalyst is filtered, a hydrogenation byproduct and unreacted raw material 2-methylene-4-acetoxyl butyraldehyde are separated in a batch distillation tower to obtain a product 2-methyl-4-acetoxyl-2-butenal; the product color was measured to be 120Hazen and after 12 months of storage at 40 ℃ the increase in color was measured 219 Hazen.