JPS6327456A - Production of acetin - Google Patents

Abstract

PURPOSE:To enable the acetylation of glycerol for producing the titled compound useful as a solvent, plasticizer, etc., in the absence of catalyst without necessitating particular azeotropic agent for the removal of water, by using a specific amount of acetic acid as the acetylation agent and distilling out the produced water together with excess acetic acid. CONSTITUTION:The objective compound of formula (n is 2 or 3) is produced by acetylating glycerol with 0.6Xn<2>-0.8Xn<2>mol of acetic acid (based on 1mol of glycerol) as an acetylation agent and distilling out the produced water from the system together with excess acetic acid. The acetic acid used in the above reaction is preferably glacial acetic acid having a water-content of <=1%. Preferably, the whole acetic acid is added to the reaction system at the beginning of the reaction, however, it may be dividedly added to the system according to the progress of the reaction. The reaction temperature is 120-180 deg.C, preferably 150-160 deg.C. The produced water is distilled out together with acetic acid from the top of a distillation column attached to a reactor.

Description

[Detailed description of the invention] (Industrial application field) ゛Acetate ester of glycerin, or acetin, has three types of solvents: monoacetate, diacetate, and triacetate! It is a very useful substance industrially as a plasticizer, perfume fixative, wetting agent, etc.

(Prior Art) These acetins are industrially produced by acetylating glycerin. For example, German Patent No. 134.867 describes a method of reacting glycerin and acetic acid with a sulfuric acid catalyst to obtain a mixture of acetins. Generally, the esterification reaction between an organic acid and an alcohol is shown by the following formula.

R-COOH+R'-OH→R-COOR' For example, in addition to mineral acids such as sulfuric acid and phosphoric acid, Lewis acids such as aromatic sulfonic acids (p-toluenesulfonic acid and benzenesulfonic acid) or boron trifluoride-diethyl ether complex, and cation exchange resins (commercially available core Diamond PK216) , Amberlite IP-120B, etc.) are arbitrarily selected and used.

(Problem to be solved by the invention) This reaction is considered to be an equilibrium reaction between esterification reaction and hydrolysis reaction, and in order to improve the reaction rate of esterification, there is also a method to remove the water produced from the system at the same time. It is usually done. However, the use of acid catalysts may cause quality problems depending on the ester produced, and there is also the problem of corrosion of the reaction equipment due to the acid.Furthermore, the acid is contained in the waste liquid discharged from the manufacturing process, which can be neutralized or recovered. This requires additional steps, which may cause quality and safety issues as well as a loss of economic efficiency. However, without the use of an acid catalyst, the esterification reaction rate is extremely slow, and so far it has been considered unbeatable as an industrial production method.

In order to solve these problems, the present inventor has made extensive studies and has finally discovered a method that does not require the addition of an acid catalyst when producing acetin using acetic acid as an acetylating agent in the acetylation reaction of glycerin. The present invention has now been completed.

(Structure of the Invention) That is, the present invention provides acetylation in a method of acetylating glycerin to produce acetin represented by the general formula (1) % formula % (1) (wherein n represents an integer of 2. and 3). Acetic acid as agent, 0.6Xn to glycerin
This is a method for producing acetin, which is characterized in that 2 moles of 0°8Xn are used from 0°8Xn, and acetylation is carried out without a catalyst by distilling the produced water out of the system together with an excess of acetic acid. In other words, without using a special water entrainer (azeotropic agent) to distill the generated water out of the system, we actively increase the amount of rising vapor of acetic acid, which is an acetylating agent, to remove the generated water. This method completes the acetylation by entraining and distilling off the vapor, and therefore an excess amount of acetic acid is required compared to the theoretical amount of glycerin used. -Can be recovered through a water separation and purification process. The esterification reaction between glycerin and acetic acid is shown in formula (2).

CH2-0H CHOH+3C83COOH→ CH2-OH Glycerin Acetic Acid CH2-00CCH3 CH-000CH(2) (In the case of triacetin, the theoretical amount of acetic acid to be used is 2 times the mole of glycerin when producing diacetin, and is 3 times the mole amount).Reaction conditions for embodiments of the present invention will be described below in more detail. The raw material glycerin and acetic acid may be those currently commercially available, regardless of the manufacturing method. For acetic acid, the molar ratio of acetic acid to glycerin, which is wood vinegar rti (water content is 1% or less), is 2.4 to 3.2 times by mole when the target acetin is diacetin, and 5.4 to 5.4 times when the target acetin is triacetin. It is 7.2 times the mole. In each case, if the amount of acetic acid is smaller, the desired acetylation is not achieved, and it becomes necessary to add acetic acid, which is complicated. If a large amount of acetic acid is used for correspondence, diacetin will be acetylated to triacetin, and in the case of triacetin, the amount of recovered vinegar M will be extremely large, leading to loss of economic efficiency. If triacetin with high purity is desired, the objective can be easily achieved by treating an acetin mixture containing triacetin as the main component, for example, with the acetic anhydride method described in the above-mentioned German Patent No. 134.867.

Furthermore, although it is convenient for the reaction operation to add the entire excess amount of acetic acid to the reaction system at the beginning of the reaction, it may also be added in portions as the reaction progresses.

The reaction temperature can range from 120 to 180°C, but is preferably from 150 to 160°C; if the temperature is lower than that, the produced H2O cannot be distilled off quickly and the esterification reaction itself becomes slow. Although the reaction rate is high at temperatures exceeding 160'C, there may be problems with the quality of the product obtained.

Although the reaction pressure can be carried out in a wide range of pressures from reduced pressure to increased pressure, it is preferable to carry out the reaction at normal pressure considering the use of a normal reaction apparatus. The reaction time is set depending on how long it takes to complete esterification, but there is also a balance with the charging molar ratio. For example, when producing an acetin mixture containing diacetin as the main component, if the charging molar ratio is about 3, the reaction time is about 10 hours, and the resulting acetin mixture has a composition of 28% monoacetin and 5% diacetin.
7% triacetin 15%. If the time is shorter than this, the ratio of monoacetin will be high and the ratio of triacetin will be low. On the other hand, if the reaction is carried out for more than 10 hours, the proportion of triacetin gradually increases, but the proportion of diacetin does not increase so much, and the amount of triacetin produced eventually exceeds that of triacetin. Water produced during the reaction is distilled out from the top of a distillation column attached to the reactor together with acetic acid. This distillate is separated into acetic acid and water by a separate acetic acid recovery device, the acetic acid is fed into the angular reaction system, and the water is treated as wastewater.

If the acetic acid-water separation and purification process cannot be used, a water entrainer (e.g., benzene, etc.) is used to distill the water from the top of the column, and the separated lower layer water is drained and the upper layer entrainer is attached to the reactor. Of course, it is also possible to cycle the reflux liquid to the top of the distillation column. Even in this case, the gist of the present invention does not change. Excess acetic acid and low-boiling impurities are distilled off from the reaction crude liquid thus obtained using a continuous or batch distillation column, and then rectification is performed to obtain the product acetin.

As an apparatus used for this rectification, a thin film evaporator such as an FFE may be used in addition to a conventional continuous or batch distillation column. In any case, the product acetin can be easily obtained as a distillate through commonly used distillation or evaporation.

Examples will be given below to explain the present invention in more detail.

Example-1 Method for producing diacetin (compositional analysis was by GC analysis method) Glycerin 10309 and vinegar 1111813g were charged into 51 flasks equipped with a 40φ1ON perforated plate column, and reacted for 10 hours at a can temperature of 180'C. (About 2.7 moles of glycerin) As the reaction progresses, a water-acetic acid mixture is distilled from the top of the column. After 10 hours, the distillate had a concentration of 4999. Its composition is 138.4% vinegar and 63.4% water. The composition of the can liquid at this time was 127.38% vinegar, 22.10% monoacetin, 31.53% diacetin, and 6.12% triacetin. After cooling the bottom liquid to below 50'C, excess acetic acid is distilled off under reduced pressure (7 Q Torr). Vinegar distillate (Top temperature ~ 60'C) 45 (1,
Acetic acid purity 89.5% Water 10.5% Next, add the can liquid again to 80%
After cooling to below °C, acetin is purified under reduced pressure (15 Torr).

Reflux ratio (R, R) = 3 Product fraction (op temperature 147-150″C) 15009
The compositional analysis results were as follows.

Monoacetin 22.1% Diacetin 52.8% Triacetin 25.1% Example-2 Triacetin production method Using the same reaction apparatus as Example-1, glycerin 552%
g and 2,160 g of acetic acid (6 times the mole of glycerin) were charged to start the reaction. The analysis of the bottom liquid 50 hours after the start of the reaction was as follows.

Vinegar 920.85% Diacetin 9.00% Triacetin 70.93% (acetin ratio: monoacetin 0% diacetin 10.38% triacetin 89°62%) After cooling this reaction crude liquid to below 50'C, Example-1 Excess acetic acid was recovered in the same manner, and then acetin was purified.

The obtained acetin has a (Tol) temperature of 145-147°C
981 (composition: diacetin: 8.29%, triacetin: 91.71%).

Example-3 The reaction vessel temperature was kept at 150' for 50 hours in the same manner as in Example-2.
Cooled to C. 1 for diacetin present in the can liquid.
．． A non-vinegar amount of 2 moles was determined by calculation and added dropwise. Thereafter, the reaction was carried out at 150° C. for 3 hours, and all of the diacetin in the solution was converted to triacetin. Next, an example-
Excess acetic acid and acetic acid were collected in the same manner as in 1, and then triacetin was purified.

Claims (1)

[Claims] i) Glycerin is acetylated to form the general formula (1)▲mathematical formula,
There are chemical formulas, tables, etc. ▼ (1) (In the formula, n indicates an integer of 2 or 3) In the method for producing acetin, acetic acid is used as an acetylating agent, and glycerin is mixed with 0, 6 x n2. A method for producing acetin characterized by using 0.8×n2 moles and performing acetylation without a catalyst by distilling the produced water out of the system together with an excess of acetic acid.