【発明の詳細な説明】[Detailed description of the invention]
本発明はα−ヒドロキシイソ酪酸を脱水反応さ
せてメタクリル酸を製造する方法に関する。
α−ヒドロキシイソ酪酸を製造する方法は、例
えば特公昭43−9528により知られている。しかる
にこの反応においてはα−ヒドロキシイソ酪酸の
転化率が不完全であり、またその分解等により多
量の副生成物が生成してメタクリル酸収率を低下
させる。たとえば上記脱水反応を液相下行い生成
するメタクリル酸を水と共に留出させた場合、そ
の残渣中には多量の未反応のα−ヒドロキシイソ
酪酸及び副反応生成物が存在する。
本発明者等はこの未反応のα−ヒドロキシイソ
酪酸を回収する目的でこの反応残渣を加水、加熱
したのち脱水反応系に戻した処、反応残渣中の副
反応生成物がメタクリル酸に転化するのでメタク
リル酸の選択率が向上し、メタクリル酸製造装置
全体の総合収率が著しく高くなることを見出し、
本発明に到達した。
既ち本発明は、α−ヒドロキシイソ酪酸を脱水
反応させてメタクリル酸を製造する方法におい
て、脱水反応生成物から水及びメタクリル酸を除
き、残りを加水、加燃処理したのち脱水反応系に
戻すことを特徴とするメタクリル酸の製造方法で
ある。
本発明においてα−ヒドロキシイソ酪酸から脱
水反応によりメタクリル酸を製造する方法として
は公知の方法が利用できるが、触媒としてアルカ
リ金属あるいはアルカリ土類金属の酸化物、水酸
化物、ハロゲン化物、炭酸塩、アルコラート、リ
ン酸塩、有機酸塩、さらにはアミン、ホスフイ
ン、イオン交換樹脂、ゼオライト、アルミナ、シ
リカ、第4級アンモニウムハロゲン化物等が使用
し得る。脱水反応の反応温度、反応時間は使用す
る触媒の種類によつて最適条件が選択されるが、
一般に温度100〜350℃、好ましくは160〜250℃、
反応時間5〜300分、好ましくは30〜180分の範囲
が適当である。
脱水反応器の形式としては、反応生成物が接触
し、反応生成物が蒸発その他の手段によつて反応
系外に速やかに抜出されるものであればいずれも
使用可能であり、たとえば、外部に循環加熱蒸発
器を備えた槽型反応器、攪拌機付ジヤケツト反応
釜、薄膜上昇式蒸発器とサイクロンセパレーター
(気液分離)を組合せたもの等が挙げられる。反
応方式としては回分式、半連続式、連続式のいず
れでも行うことができるが、反応生成物は可及的
速やかに系外に留去されることが望ましい。
脱水生成物からの水及びメタクリル酸の分離は
蒸留塔を用いる。設置する蒸留塔の形式として
は、充填塔、多孔板塔、その他通常の蒸留操作に
使用される各種気液接触装置が使用される。
蒸留塔の操作条件は、脱水反応条件によつて決
められるべきものであるが、塔頂温度50〜150℃、
還流比0.1〜5の範囲から選ばれる。以上の条件
で蒸留することにより反応生成物を留出させた
後、更に別の蒸留塔で水およびメタクリル酸を分
離し、しかるのちにその残りを加水、加熱して反
応器に戻す。
加水、加熱方法としは、無触媒または酸性触媒
存在下50〜150℃で0.5〜5時間加熱処理すれば良
い。酸性触媒としては脱水反応系においてα−ヒ
ドロキシイソ酪酸の脱水反応を阻害しないもので
あることが必要で、たとえば蟻酸、酢酸、酪酸等
の脂肪族カルボン酸、安息香酸、フタル酸等の芳
香族カルボン酸、燐酸、硼酸等の無機酸、陽イオ
ン交換樹脂等が使用される。加水加熱処理装置と
しては攪拌機付ジヤケツト反応釜あるいは管型反
応器、スチームジヤケツトを備えたラインミキサ
ー等が使用される。
本発明では、次の実施例に示す如く、反応生成
物よりメタクリル酸および水を分離した後の残り
の溶液を加水、加熱することにより、α−ヒドロ
キシイソ酪酸からメタクリル酸への選択率および
収率が改善され、この加水、加熱処理後の液を脱
水反応器に循環することにより非常に優れたメタ
クリル酸製造装置の総合収率が得られる。
実施例 1
攪拌機付500c.c.フラスコにα−ヒドロキシイソ
酪酸300g、水酸化ナトリウム18gを仕込み、フ
ラスコ上部にマグマホンパツキング充填層
(20φX300)および還流冷却器を取付けた。加熱、
攪拌しながらあらたにα−ヒドロキシイソ酪酸
150Kg/Hrを供給した。またこの際重合防止のた
め、供給液にp−メトキシフエノール0.6g/Hr
を溶解し、更に脱水塔塔底部より空気を吹込ん
だ。
反応器温度195〜200℃とし、生成する蒸気をそ
のまま冷却したのち、マグマホンパツキング充填
層(20φX300)を充填した蒸留装置に直接連続的
に供給して蒸留を行い、塔頂からはメタクリル酸
と水の共沸物10.2g/Hr(メタクリル酸80.3wt
%、水19.7wt%)を留出させた。塔底からはメタ
クリル酸11.9wt%、α−ヒドロキシイソ酪酸
46.6wt%、副生成物41.5wt%を含む留出液が39.5
g/Hrで得られた。
次に塔底留出液を100c.c.のフラスコ中で水5
g/Hrと共に100℃で加熱攪拌した後、この塔底
留出液のみを前述と同様の方法で脱水反応させ
た。この結果、水18.2wt%、メタクリル酸53.5wt
%、α−ヒドロキシイソ酪酸9.0wt%、副生成物
19.3wt%を含む留分が44.5g/Hrで得られた。
これよりα−ヒドロキシイソ酪酸の転化率が97.3
%、メタクリル酸収率が90.5%となり、メタクリ
ル酸選択率は93.0%となる。
比較例 1
実施例1において、塔底留出液への水の添加お
よび加熱処理を行わずに脱水反応を行つた。
この結果、水6.8wt%、メタクリル酸39.5wt%、
α−ヒドロキシイソ酪酸5.8wt%、副生成物
47.9wt%を含む留分が39.5g/Hrで得られた。
これよりα−ヒドロキシイソ酪酸の転化率が98.5
%、メタクリル酸収率が84.0%となり、メタクリ
ル酸選択率は85.3%となる。
実施例 2
攪拌機付500c.c.フラスコにα−ヒドロキシイソ
酪酸300g、水酸化ナトリウム18gを仕込み、フ
ラスコ上部にマグマホンパツキング充填層
(20φX300)および還流冷却器を取付けた。加熱、
攪拌しながらあらたにα−ヒドロキシイソ酪酸
150Kg/Hrを供給した。またこの際重合防止のた
め、供給液にp−メナキシフエノール0.6g/Hr
を溶解し、更に脱水塔塔底部より空気を吹込ん
だ。
反応器温度195〜200℃、塔頂温度115℃、還流
比1.0の条件で蒸留して得られる塔頂留出物を、
更にマグマホンパツキング充填層(20φX300)を
充填した蒸留装置2基に直接連続的に供給して蒸
留を行い、第1塔塔頂からは低沸物および水とメ
タクリル酸の共沸混合物を、第2塔塔頂からはメ
タクリル酸のみを連続的に留出させた。第2塔塔
底液は100c.c.のフラスコ中で水5g/Hrと共に
100℃で加熱攪拌した後、脱水反応器に循環した。
この結果、各成分の流量は次の如くとなつた。
α−ヒドロキシイソ酪酸の転化率は80.6%、メタ
クリル酸の収率は80.0%、メタクリル酸の総合収
率(メタクリル酸生産量/α−ヒドロキシイソ酪
酸供給量)は99.2%に相当する。
The present invention relates to a method for producing methacrylic acid by dehydrating α-hydroxyisobutyric acid. A method for producing α-hydroxyisobutyric acid is known, for example, from Japanese Patent Publication No. 43-9528. However, in this reaction, the conversion rate of α-hydroxyisobutyric acid is incomplete, and a large amount of by-products are produced due to its decomposition, etc., reducing the yield of methacrylic acid. For example, when the above dehydration reaction is carried out in a liquid phase and the produced methacrylic acid is distilled out together with water, a large amount of unreacted α-hydroxyisobutyric acid and side reaction products are present in the residue. In order to recover this unreacted α-hydroxyisobutyric acid, the present inventors added water to the reaction residue, heated it, and then returned it to the dehydration reaction system, whereupon the side reaction product in the reaction residue was converted to methacrylic acid. We discovered that this improves the selectivity of methacrylic acid and significantly increases the overall yield of the entire methacrylic acid production equipment.
We have arrived at the present invention. Already, the present invention provides a method for producing methacrylic acid by dehydrating α-hydroxyisobutyric acid, in which water and methacrylic acid are removed from the dehydration reaction product, the remainder is subjected to hydration and combustion treatment, and then returned to the dehydration reaction system. This is a method for producing methacrylic acid characterized by the following. In the present invention, any known method can be used to produce methacrylic acid from α-hydroxyisobutyric acid by dehydration reaction, but the catalyst may be an alkali metal or alkaline earth metal oxide, hydroxide, halide, or carbonate. , alcoholates, phosphates, organic acid salts, as well as amines, phosphines, ion exchange resins, zeolites, alumina, silica, quaternary ammonium halides, and the like can be used. The optimum conditions for the reaction temperature and reaction time of the dehydration reaction are selected depending on the type of catalyst used.
Generally temperature 100~350℃, preferably 160~250℃,
A suitable reaction time is 5 to 300 minutes, preferably 30 to 180 minutes. Any type of dehydration reactor can be used as long as the reaction products come into contact with each other and the reaction products are quickly extracted from the reaction system by evaporation or other means. Examples include a tank reactor equipped with a circulation heating evaporator, a jacket reaction vessel with a stirrer, and a combination of a thin film ascending evaporator and a cyclone separator (gas-liquid separation). The reaction may be carried out in a batch, semi-continuous or continuous manner, but it is desirable that the reaction product be distilled out of the system as quickly as possible. A distillation column is used to separate water and methacrylic acid from the dehydrated product. The type of distillation column to be installed includes a packed column, a perforated plate column, and various other gas-liquid contact devices used in ordinary distillation operations. The operating conditions of the distillation column should be determined by the dehydration reaction conditions, including a column top temperature of 50 to 150℃,
The reflux ratio is selected from the range of 0.1 to 5. After distilling the reaction product under the above conditions, water and methacrylic acid are separated in another distillation column, and the remainder is then added with water, heated, and returned to the reactor. As for the hydration and heating method, heat treatment may be performed at 50 to 150° C. for 0.5 to 5 hours without a catalyst or in the presence of an acidic catalyst. The acidic catalyst must be one that does not inhibit the dehydration reaction of α-hydroxyisobutyric acid in the dehydration reaction system, such as aliphatic carboxylic acids such as formic acid, acetic acid, and butyric acid, and aromatic carboxylic acids such as benzoic acid and phthalic acid. Acids, inorganic acids such as phosphoric acid and boric acid, cation exchange resins, etc. are used. As the hydrothermal treatment apparatus, a jacketed reaction vessel with a stirrer, a tubular reactor, a line mixer equipped with a steam jacket, etc. are used. In the present invention, as shown in the following example, the selectivity and yield from α-hydroxyisobutyric acid to methacrylic acid is increased by adding water and heating the remaining solution after separating methacrylic acid and water from the reaction product. By circulating the liquid after addition of water and heat treatment to the dehydration reactor, a very excellent overall yield of the methacrylic acid production apparatus can be obtained. Example 1 A 500 c.c. flask equipped with a stirrer was charged with 300 g of α-hydroxyisobutyric acid and 18 g of sodium hydroxide, and a magmaphone packing packed bed (20φ×300) and a reflux condenser were attached to the top of the flask. heating,
Add α-hydroxyisobutyric acid while stirring.
150Kg/Hr was supplied. At this time, to prevent polymerization, p-methoxyphenol 0.6g/Hr was added to the feed solution.
was dissolved, and air was further blown into the bottom of the dehydration tower. The reactor temperature is set to 195-200℃, and the generated vapor is cooled as it is, then directly and continuously fed to a distillation apparatus packed with a magmaphone packing bed (20φ x 300) for distillation, and methacrylic acid is distilled from the top of the column. and water azeotrope 10.2g/Hr (methacrylic acid 80.3wt
%, water 19.7wt%). From the bottom of the tower, 11.9wt% methacrylic acid and α-hydroxyisobutyric acid
Distillate containing 46.6wt% and by-products 41.5wt% is 39.5%.
g/Hr. Next, the bottom distillate was placed in a 100 c.c. flask with 5 ml of water.
After heating and stirring at 100° C. with g/Hr, only the bottom distillate was subjected to a dehydration reaction in the same manner as described above. As a result, water 18.2wt%, methacrylic acid 53.5wt%
%, α-hydroxyisobutyric acid 9.0wt%, by-products
A fraction containing 19.3 wt% was obtained at 44.5 g/Hr.
From this, the conversion rate of α-hydroxyisobutyric acid is 97.3
%, the methacrylic acid yield is 90.5%, and the methacrylic acid selectivity is 93.0%. Comparative Example 1 In Example 1, the dehydration reaction was carried out without adding water to the bottom distillate and without performing heat treatment. As a result, water 6.8wt%, methacrylic acid 39.5wt%,
α-Hydroxyisobutyric acid 5.8wt%, by-product
A fraction containing 47.9 wt% was obtained at 39.5 g/Hr.
From this, the conversion rate of α-hydroxyisobutyric acid is 98.5
%, the methacrylic acid yield was 84.0%, and the methacrylic acid selectivity was 85.3%. Example 2 A 500 c.c. flask equipped with a stirrer was charged with 300 g of α-hydroxyisobutyric acid and 18 g of sodium hydroxide, and a magmaphone packing packed bed (20φ×300) and a reflux condenser were attached to the top of the flask. heating,
Add α-hydroxyisobutyric acid while stirring.
150Kg/Hr was supplied. At this time, to prevent polymerization, 0.6 g/Hr of p-menaxyphenol was added to the feed solution.
was dissolved, and air was further blown into the bottom of the dehydration tower. The overhead distillate obtained by distilling under the conditions of reactor temperature 195 to 200°C, tower top temperature 115°C, and reflux ratio 1.0,
Furthermore, distillation is carried out by directly and continuously feeding the distillate into two distillation units packed with magmaphone packing packed beds (20φ x 300), and from the top of the first column, low-boiling substances and an azeotropic mixture of water and methacrylic acid are Only methacrylic acid was continuously distilled from the top of the second column. The bottom liquid of the second column is placed in a 100 c.c. flask together with 5 g/Hr of water.
After heating and stirring at 100°C, the mixture was circulated to a dehydration reactor. As a result, the flow rates of each component were as follows.
The conversion rate of α-hydroxyisobutyric acid was 80.6%, the yield of methacrylic acid was 80.0%, and the total yield of methacrylic acid (methacrylic acid production amount/α-hydroxyisobutyric acid supply amount) was 99.2%.
【表】
このように蒸留塔の塔底液を加水加熱処理し、
脱水反応器に循環する場合には、メタクリル酸の
総合収率が著しく向上する。[Table] In this way, the bottom liquid of the distillation column is subjected to hydrothermal treatment,
When recycled to the dehydration reactor, the overall yield of methacrylic acid is significantly improved.