JP3979189B2 - Process for producing aromatic carbonates - Google Patents

Description

【０００４】
式（２）の反応は極めて遅いので、通常はフェノールとジメチルカーボネートとを反応させて、メチルフェニルカーボネートとこれに対して少量のジフェニルカーボネートを含む反応液を生成させ、次いでこの反応液中のメチルフェニルカーボネートを式（３）により不均化させてジフェニルカーボネートとジメチルカーボネートを生成させる。
【０００５】
式（１）の反応は遅く、かつ反応平衡が原系側に著るしく偏っているので、反応を促進する方法が種々提案されている。例えば特開平６−２３４７０７号公報には、複数の撹拌槽を直列に接続し、最前段の撹拌槽にフェノール類を供給し、ジメチルカーボネートは各撹拌槽に供給する反応方法が記載されている。この反応方法では各撹拌槽の気相部のガスは、それぞれの撹拌槽に付設されている蒸留塔で蒸留して、副生したメタノールを塔頂から留去し、ジメチルカーボネートを含む塔底液はそれぞれの撹拌槽に循環している。撹拌槽間の反応液の移送はサイフォンにより行われる。また、別法として、ジメチルカーボネートを最後段の撹拌槽だけに供給する方法も記載されている。この反応方法では、各撹拌槽の気相部のガスはその直前の撹拌槽の液相中に供給され、最前段の撹拌槽の気相部のガスは付設されている蒸留塔で蒸留して、副生したメタノールを塔頂から留去し、ジメチルカーボネートを含む塔底液は最前段の撹拌槽に循環している。この反応方法においても撹拌槽間の反応液の移送はサイフォンにより行われる。
【０００６】
特開平８−１８８５５８号公報には、気相部が共通で液相部が複数の区画に区分されている反応器を用いて、その最前段の区画にフェノールとジメチルカーボネートとを供給する反応方法が記載されている。反応液は各区画を順次経由して最後段の区画から抜出される。気相部のガスは付設されている蒸留塔で蒸留して、副生したメタノールを塔頂から留去し、ジメチルカーボネートを含む塔底液は反応器に循環される。
【０００７】
【発明が解決しようとする課題】
しかしながら、従来提案されているこれらの反応方法は、それなりに有効な方法ではあるが、未だ満足すべきものではない。従って本発明はジアルキルカーボネートとフェノール類との更に改良された反応方法を提供しようとするものである。
【０００８】
【課題を解決するための手段】
本発明によれば、複数の反応帯域から成り、反応液が各反応帯域を順次経由して反応器から流出するようになっている反応器を用いて、フェノール類とジアルキルカーボネートとを反応させてアルキルアリールカーボネートを含む反応液を生成させる芳香族カーボネート類の製造方法において、反応原料の供給をフェノール類の少なくとも一部は最上流の反応帯域に供給し、ジアルキルカーボネートはいずれかの反応帯域に供給し、上流から下流に向って反応帯域の圧力を上昇させ、最上流の反応帯域を除き各反応帯域の気相部からガスを抜出してこれをその直前の反応帯域に供給し、かつ最上流の反応帯域の気相部からガスを抜出して蒸留塔で蒸留し、副生したアルキルアルコールを塔頂から留去し、塔底からジアルキルカーボネートを含む反応液を抜出していずれかの反応帯域に循環することにより、反応を効率よく進行させることができる。
【０００９】
【発明の実施の形態】
本発明では、反応器として複数の反応帯域から成るものを用いる。反応帯域の数は２であってもよいが、３以上であるのが好ましい。反応帯域の数を多くするほど一般的に反応遂行上は有利であるが、逆に設備費が嵩む。反応遂行上の利点と設備費とを勘案すると、反応帯域の数は１０以下、特に７以下とするのが好ましい。一般的には最も好ましい反応帯域の数は３〜５である。
【００１０】
反応器への原料の供給は、フェノール類の少なくとも一部は最上流の反応帯域に供給する。すなわち最上流の反応帯域か又はこれを含むいくつかの反応帯域に分割供給する。通常は最上流の反応帯域だけに供給するのが好ましい。分割供給する場合でも供給量の５０％以上、特に７０％以上は最上流の反応帯域に供給するのが好ましく、かつ残余も主として次の反応帯域など最上流に近い反応帯域に供給するのが好ましい。これに対しジアルキルカーボネートは必ずしも最上流の反応帯域に供給する必要はない。ジアルキルカーボネートは沸点が低いので、これを最上流の反応帯域に供給するとこの帯域の気相部から抜出したガスを蒸留して、副生したアルキルアルコールを系外に除去する蒸留塔の負荷を増大させる。従ってジアルキルカーボネートの５０％以上、特に７０％以上は、後半分の反応帯域（反応帯域の数が（２Ｎ＋１）個の場合には（Ｎ＋１）番目以降の反応帯域）に供給するのが好ましい。通常はジアルキルカーボネートの全量を後半部の反応帯域に供給する。供給はいくつかの反応帯域に分割して行うのが好ましく、また最下流の反応帯域にも供給するのが好ましい。
【００１１】
反応器内では液相と気相とは向流方向に移動する。すなわち液相は最上流の反応帯域から各反応帯域を順次経由して最下流の反応帯域に移動し、気相部のガスは最下流の反応帯域から各反応帯域を順次経由して最上流の反応帯域に移動する。最上流の反応帯域の気相部のガスは付設されている蒸留塔で蒸留して、副生したアルコールを塔頂から留出させて除去し、塔底から抜出されるジアルキルカーボネートを含む塔底液はいずれかの反応帯域に循環させる。通常は最上流の反応帯域に供給するか又はこの帯域を含むいくつかの反応帯域に分割供給する。
【００１２】
本発明では反応器内の圧力を、最上流の反応帯域の圧力が最も低く、最下流の反応帯域の圧力が最も高くなるように、上流から下流に向けて圧力が高くなるようにする。反応器内におけるアルキルアリールカーボネートの濃度は後段の反応帯域ほど高いので、若し反応条件が各反応帯域を通して同一ならば、後段の反応帯域ほど反応量が低下する。しかし後段ほど圧力を高めると、圧力が高い方が反応原料であるジアルキルカーボネートの液相への溶解が促進されるので、後段の反応帯域における反応量の低下を阻止することができる。反応帯域間の圧力差は通常は０．１〜２ｋｇ／ｃｍ²以下、特に０．３〜０．７ｋｇ／ｃｍ²であるのが好ましい。
【００１３】
本発明では、このように後段になるほど反応帯域の圧力を高くするので、反応帯域間の液相の移動はポンプにより行う。これに対し反応帯域間の気相の移動は、圧力差により行うことができる。その好ましい態様の一つでは、反応帯域の気相部からその直前の反応帯域の液相部に延びる連絡管を設け、両帯域間の圧力差により後段の気相部のガスが前段の液相中に導入されるようにする。これにより後段の気相部のガス中のジアルキルカーボネートが前段の液相中に溶解するのを促進することができる。また各反応帯域には気相中のジアルキルカーボネートの液相中への溶解を促進するため、気相と液相とを混合する混合装置を設けるのが好ましい。
【００１４】
本発明では上記したように反応帯域間を液相と気相とを向流で移動させ、かつ後段の反応帯域ほど圧力を高くする以外は、常法に従って反応を行わせればよい。すなわち反応温度は１５０〜２５０℃、特に１８０〜２００℃が好ましく、かつ後段の反応帯域ほど高温にして反応を促進するのが好ましい。また、最上流の反応帯域の気相部から抜出したガスからの副生アルコールの除去は、この反応帯域の液相中の副生アルコールの濃度が１０重量％以下、好ましくは５重量％以下、特に１重量％以下となるように行うのが好ましい。
【００１５】
本発明によれば、反応器として、内部が複数の帯域に区画されており、それぞれの帯域の圧力を独立に設定できるものであればよいので、安価な装置を用いることができる。また各反応帯域の反応条件を独立に設定できるので、運転管理が容易である。
【００１６】
【実施例】
以下に反応器を複数の反応帯域に分割し、かつ後段の反応帯域ほど圧力を高くすることの効果をモデル的に示す実験例により、本発明を更に具体的に説明するが、本発明はこれに限定されるものではない。
実験例１
反応器として内部が隔壁によりＮｏ．１〜Ｎｏ．３の３つに区画されているものを用いた。各区画の容積は約１リットルであり、Ｎｏ．１区画とＮｏ．２区画との間、及びＮｏ．２区画とＮｏ．３区画との間には、反応液の移送を行うためのポンプが設置されている。またＮｏ．３区画の気相部とＮｏ．２区画の液相部との間、及びＮｏ．２区画の気相部とＮｏ．１区画の液相部との間にはガスの移送を行うための連絡管が設置されている。
【００１７】
この反応器のＮｏ．１区画に、フェノールを１６０ｇ／Ｈｒ、触媒のジブチルスズオキサイドを３ｇ／Ｈｒ、ジメチルカーボネートを１８００ｇ／Ｈｒで連続的に供給し、各区画ともその容積の半分が液で満たされるようにして、Ｎｏ．３区画から液を抜出し、Ｎｏ．１区画から気相部のガスを抜出した。Ｎｏ．１区画を１７０℃、７ｋｇ／ｃｍ²Ａ、Ｎｏ．２区画を１７５℃、７．５ｋｇ／ｃｍ²Ａ、第３区画を１９０℃、８ｋｇ／ｃｍ²Ａとして反応を行ったところ、第３区画からの反応液の抜出量は約５６０ｇ／Ｈｒで、そのメチルフェニルカーボネートの濃度は約１０重量％であった。
【００１８】
比較実験例１
反応器として特開平８−１８８５５８号公報に記載されているような、内部が液相部のみ隔壁でＮｏ．１〜Ｎｏ．３の３つに区画されており、気相部は共通となっているものを用いた。各区画の容積は約１リットルである。この反応器のＮｏ．１区画にフェノールを１６０ｇ／Ｈｒ、ジメチルカーボネートを１８００ｇ／Ｈｒ、触媒のジブチルスズオキサイドを３ｇ／Ｈｒで連続的に供給し、各区画ともその容積の半分が液で満たされるようにしてＮｏ．３区画から液を抜出し、気相部からガスを抜出した。圧力を８ｋｇ／ｃｍ²Ａ、Ｎｏ．１区画を１８０℃、Ｎｏ２区画を１８５℃、Ｎｏ．３区画を１９０℃として反応を行ったところ、第３区画からの液の抜出量は約５５０ｇ／Ｈｒで、そのメチルフェニルカーボネートの濃度は約８．５重量％であった。
実験例１と比較実験例１とを対比すると、前者の方がメチルフェニルカーボネートの収量が約２０％ほど多い。また、Ｎｏ．１区画及びＮｏ．２区画の温度はいずれも前者の方が１０℃ほど低い。このことは反応器に供給するエネルギーが前者の方が少なくて済むことを意味している。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a method for producing an alkylaryl carbonate or diaryl carbonate by reacting a dialkyl carbonate with a phenol.
[0002]
[Prior art]
It is known to react alkyl dicarbonates with substituted phenols such as phenol and cresol (hereinafter collectively referred to as phenols) to produce alkyl aryl carbonates and diaryl carbonates. The most common is the production of methyl phenyl carbonate and diphenyl carbonate from dimethyl carbonate and phenol. This reaction is known to proceed as follows.
[0003]
[Chemical 1]

[0004]
Since the reaction of the formula (2) is extremely slow, usually, phenol and dimethyl carbonate are reacted to form a reaction solution containing methylphenyl carbonate and a small amount of diphenyl carbonate, and then the methyl in the reaction solution Phenyl carbonate is disproportionated according to formula (3) to form diphenyl carbonate and dimethyl carbonate.
[0005]
Since the reaction of formula (1) is slow and the reaction equilibrium is significantly biased toward the original system, various methods for promoting the reaction have been proposed. For example, JP-A-6-234707 describes a reaction method in which a plurality of stirring tanks are connected in series, phenols are supplied to the foremost stirring tank, and dimethyl carbonate is supplied to each stirring tank. In this reaction method, the gas in the gas phase part of each stirring tank is distilled in a distillation column attached to each stirring tank, and methanol produced as a by-product is distilled off from the top of the tower, and a liquid at the bottom containing dimethyl carbonate. Circulates in each stirred tank. The reaction liquid is transferred between the stirring tanks by a siphon. As another method, a method of supplying dimethyl carbonate only to the last stirred tank is also described. In this reaction method, the gas in the gas phase part of each agitation tank is supplied into the liquid phase of the immediately preceding agitation tank, and the gas in the gas phase part of the foremost agitation tank is distilled in an attached distillation column. The by-produced methanol is distilled off from the top of the tower, and the bottom liquid containing dimethyl carbonate is circulated in the foremost agitation tank. Also in this reaction method, the reaction solution is transferred between the stirring tanks by a siphon.
[0006]
Japanese Patent Application Laid-Open No. 8-188558 discloses a reaction method in which phenol and dimethyl carbonate are supplied to the foremost compartment using a reactor having a common gas phase portion and a liquid phase portion divided into a plurality of compartments. Is described. The reaction solution is extracted from the last compartment through each compartment in turn. The gas in the gas phase is distilled in an attached distillation tower, and methanol produced as a by-product is distilled off from the top of the tower, and the bottom liquid containing dimethyl carbonate is circulated to the reactor.
[0007]
[Problems to be solved by the invention]
However, although these conventionally proposed reaction methods are effective as such, they are not yet satisfactory. Accordingly, the present invention seeks to provide an improved process for the reaction of dialkyl carbonates with phenols.
[0008]
[Means for Solving the Problems]
According to the present invention, phenols and dialkyl carbonate are reacted with each other using a reactor that is composed of a plurality of reaction zones and in which a reaction solution flows out of the reactor via each reaction zone in turn. In the method for producing aromatic carbonates that produce a reaction liquid containing alkylaryl carbonate, at least a part of phenols is supplied to the most upstream reaction zone, and dialkyl carbonate is supplied to any of the reaction zones. Then, the pressure in the reaction zone is increased from upstream to downstream, the gas is extracted from the gas phase portion of each reaction zone except for the most upstream reaction zone, and this gas is supplied to the immediately preceding reaction zone, and the most upstream A gas is extracted from the gas phase part of the reaction zone and distilled in a distillation tower, and the by-produced alkyl alcohol is distilled off from the top of the tower, and dialkyl carbonate is contained from the bottom of the tower. By circulating in any of the reaction zone by withdrawing the reaction solution, it is possible to proceed the reaction efficiently.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a reactor comprising a plurality of reaction zones is used. The number of reaction zones may be 2, but is preferably 3 or more. Increasing the number of reaction zones is generally more advantageous for carrying out the reaction, but conversely increases the equipment cost. Considering the advantages in carrying out the reaction and the equipment cost, the number of reaction zones is preferably 10 or less, particularly 7 or less. In general, the most preferred number of reaction zones is 3-5.
[0010]
In the feed of the raw material to the reactor, at least a part of the phenols is fed to the most upstream reaction zone. That is, the supply is divided into the most upstream reaction zone or several reaction zones including this. Usually, it is preferable to supply only to the most upstream reaction zone. Even in the case of divided supply, 50% or more, particularly 70% or more of the supply amount is preferably supplied to the most upstream reaction zone, and the remainder is preferably supplied mainly to the most upstream reaction zone such as the next reaction zone. . On the other hand, the dialkyl carbonate is not necessarily supplied to the most upstream reaction zone. Dialkyl carbonate has a low boiling point, so if it is supplied to the most upstream reaction zone, the gas extracted from the gas phase of this zone is distilled to increase the load on the distillation column that removes by-produced alkyl alcohol out of the system. Let Therefore, 50% or more, particularly 70% or more of the dialkyl carbonate is preferably supplied to the reaction zone for the latter half (when the number of reaction zones is (2N + 1), the (N + 1) th and subsequent reaction zones). Usually, the entire amount of dialkyl carbonate is fed to the reaction zone in the latter half. The supply is preferably carried out by dividing it into several reaction zones, and it is also preferred to supply it to the most downstream reaction zone.
[0011]
In the reactor, the liquid phase and the gas phase move in the countercurrent direction. That is, the liquid phase moves from the most upstream reaction zone to the most downstream reaction zone via each reaction zone in sequence, and the gas in the gas phase section flows from the most downstream reaction zone to each most upstream reaction zone. Move to reaction zone. The gas in the gas phase part of the most upstream reaction zone is distilled in an attached distillation column, and the by-produced alcohol is distilled off from the top of the column to remove it. The bottom of the column contains dialkyl carbonate extracted from the bottom of the column. The liquid is circulated to either reaction zone. Usually, it is supplied to the most upstream reaction zone or divided into several reaction zones including this zone.
[0012]
In the present invention, the pressure in the reactor is increased from upstream to downstream so that the pressure in the most upstream reaction zone is the lowest and the pressure in the most downstream reaction zone is the highest. Since the concentration of the alkylaryl carbonate in the reactor is higher in the subsequent reaction zone, if the reaction conditions are the same throughout the reaction zones, the reaction amount decreases in the subsequent reaction zone. However, when the pressure is increased in the latter stage, the higher the pressure, the more the dissolution of the dialkyl carbonate, which is the reaction raw material, in the liquid phase is promoted, so that it is possible to prevent a reduction in the reaction amount in the latter reaction zone. The pressure difference between the reaction zones is usually 0.1 to ² kg / cm ² or less, preferably 0.3 to 0.7 kg / cm ² .
[0013]
In the present invention, the pressure in the reaction zone is increased in the later stage as described above, so that the liquid phase is moved between the reaction zones by a pump. On the other hand, the movement of the gas phase between the reaction zones can be performed by a pressure difference. In one of the preferred embodiments, a communication pipe extending from the gas phase part of the reaction zone to the liquid phase part of the reaction zone immediately before is provided, and the gas in the gas phase part of the rear stage is caused to flow from the liquid phase of the front stage by the pressure difference between the two zones. To be introduced inside. Thereby, it can accelerate | stimulate that the dialkyl carbonate in the gas of the gas phase part of a back | latter stage melt | dissolves in the liquid phase of a front | former stage. Moreover, in order to accelerate | stimulate melt | dissolution in the liquid phase of the dialkyl carbonate in a gaseous phase in each reaction zone, it is preferable to provide the mixing apparatus which mixes a gaseous phase and a liquid phase.
[0014]
In the present invention, as described above, the reaction may be carried out according to a conventional method, except that the liquid phase and the gas phase are moved countercurrently between the reaction zones and the pressure in the subsequent reaction zone is increased. That is, the reaction temperature is preferably 150 to 250 ° C., and particularly preferably 180 to 200 ° C., and the reaction is preferably performed at a higher temperature in the subsequent reaction zone. Further, the removal of by-product alcohol from the gas extracted from the gas phase part of the most upstream reaction zone is such that the concentration of by-product alcohol in the liquid phase of this reaction zone is 10 wt% or less, preferably 5 wt% or less, It is particularly preferable to carry out so as to be 1% by weight or less.
[0015]
According to the present invention, any reactor can be used as long as the reactor is divided into a plurality of zones and the pressure in each zone can be set independently. In addition, since the reaction conditions for each reaction zone can be set independently, operation management is easy.
[0016]
【Example】
Hereinafter, the present invention will be described in more detail with reference to an experimental example in which the reactor is divided into a plurality of reaction zones and the effect of increasing the pressure in the subsequent reaction zone is modeled. It is not limited to.
Experimental example 1
As a reactor, the inside is No. by a partition wall. 1-No. What was divided into 3 of 3 was used. The volume of each compartment is about 1 liter. 1 section and No. Between two compartments and No. 2 and No. A pump for transferring the reaction liquid is installed between the three sections. No. No. 3 gas phase part and No. Between the two-phase liquid phase part and No. 2 gas phase part and No. A connecting pipe for transferring gas is installed between the liquid phase part of one section.
[0017]
No. of this reactor. In one section, phenol was continuously fed at 160 g / Hr, catalyst dibutyltin oxide at 3 g / Hr, and dimethyl carbonate at 1800 g / Hr, so that half of the volume was filled with liquid in each section. The liquid was extracted from the three compartments. The gas in the gas phase was extracted from one compartment. No. One section is 170 ° C., 7 kg / cm ² A, No. When the reaction was carried out at 175 ° C. and 7.5 kg / cm ² A for the second compartment and 190 ° C. and 8 kg / cm ² A for the third compartment, the amount of the reaction solution extracted from the third compartment was about 560 g / Hr. The concentration of methyl phenyl carbonate was about 10% by weight.
[0018]
Comparative Experiment Example 1
As described in Japanese Patent Laid-Open No. 8-188558 as a reactor, the inside is a partition wall only with a liquid phase part, and No. 1-No. 3 was divided into three, and the common gas phase portion was used. The volume of each compartment is about 1 liter. No. of this reactor. In one compartment, phenol was supplied at 160 g / Hr, dimethyl carbonate at 1800 g / Hr, and catalyst dibutyltin oxide at 3 g / Hr, and each compartment was filled with half of its volume. The liquid was extracted from the three compartments, and the gas was extracted from the gas phase part. The pressure was 8 kg / cm ² A, No. No. 1 section is 180 ° C., No. 2 section is 185 ° C. When the reaction was performed at 3 ° C. at 190 ° C., the amount of liquid extracted from the third compartment was about 550 g / Hr, and the concentration of methylphenyl carbonate was about 8.5% by weight.
Comparing Experimental Example 1 with Comparative Experimental Example 1, the former yields about 20% more methylphenyl carbonate. No. 1 section and No. The temperature in the two compartments is about 10 ° C. lower in the former. This means that the former requires less energy to be supplied to the reactor.

Claims (5)

Reaction that includes alkylaryl carbonate by reacting phenols with dialkyl carbonate using a reactor that consists of multiple reaction zones and the reaction liquid flows out from the reactor via each reaction zone in sequence. In the method for producing aromatic carbonates for producing a liquid, at least a part of phenols is supplied to the most upstream reaction zone, and the dialkyl carbonate is supplied to one of the reaction zones, from upstream to downstream. The pressure in the reaction zone is increased, gas is extracted from the gas phase portion of each reaction zone except for the most upstream reaction zone, and this gas is supplied to the immediately preceding reaction zone, and the gas phase in the most upstream reaction zone The gas is extracted from the section and distilled in a distillation tower, the by-produced alkyl alcohol is distilled off from the top of the tower, and a liquid containing dialkyl carbonate is extracted from the bottom of the tower. Wherein the circulating in any of the reaction zones. The gas in the gas phase part of the reaction zone is supplied to the reaction zone immediately before the two reaction zones through a connecting pipe extending from the gas phase part of the reaction zone to the liquid phase part of the reaction zone immediately before. The method according to claim 1, wherein the method is performed by a pressure difference of The method according to claim 1 or 2, wherein a mixing device for mixing the liquid phase and the gas phase is installed in each reaction zone. The method according to any one of claims 1 to 3, wherein the temperature of the reaction zone is increased from upstream to downstream. The method according to any one of claims 1 to 4, wherein at least a part of the reaction raw material dialkyl carbonate is supplied to the reaction zone in the latter half.