JP2004189927A - Method for recovering unreacted monomer from aqueous dispersion of vinyl chloride-based polymer - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、製造後の塩化ビニル系重合体水性分散液からの未反応塩化ビニル系単量体の回収法に関するものであり、更に詳しくは、塩化ビニル系単量体を水性媒体中で界面活性剤、重合開始剤の存在下で重合を行い得られる塩化ビニル系重合体水性分散液から未反応塩化ビニル系単量体を回収する際に、泡立ちが少なく、高効率で未反応塩化ビニル系単量体が回収できる方法に関するものである。
【０００２】
【従来の技術】
塩化ビニル系重合体水性分散液は、塩化ビニル系単量体を界面活性剤、重合開始剤の存在下、水性媒体中に分散して乳化重合、播種乳化重合、微細懸濁重合、播種微細懸濁重合等を行うことにより粒子径０．０５〜１０μｍ程度を有するラテックスとして生産されている。塩化ビニル系重合体水性分散液を製造するこれら乳化重合、播種乳化重合、微細懸濁重合、播種微細懸濁重合等の重合反応では、通常、塩化ビニル系単量体の重合転化率が７０〜９８％に到達した時点で重合反応を終了させるために、得られる塩化ビニル系重合体水性分散液中には未反応の塩化ビニル系単量体が残存している。そして、塩化ビニル系重合体水性分散液から未反応の塩化ビニル系単量体を回収した後、該水性分散液を噴霧乾燥機等により乾燥することによりペースト加工用塩化ビニル系重合体が生産されている。そのため、ペースト加工用塩化ビニル系重合体の原料となる塩化ビニル系単量体を回収し原単位を改善したり、製造・加工時の作業環境衛生上等の観点から、塩化ビニル系重合体水性分散液に残存する未反応塩化ビニル系単量体をより高効率で回収する方法が望まれている。
【０００３】
しかし、塩化ビニル系単量体を水性媒体中で界面活性剤、重合開始剤の存在下で重合して得られる塩化ビニル系重合体水性分散液からの未反応塩化ビニル系単量体の回収においては、該水性分散液は界面活性剤を含むため未反応塩化ビニル系単量体が蒸発する際に、激しい発泡を伴い、泡の飛散による製品ロスの発生や飛散した泡によるスケールリング等の機器トラブル発生等の課題を有していた。
【０００４】
これら課題を解決する方法として、塩化ビニル系重合体水性分散液からの未反応塩化ビニル系単量体の回収操作においては、通常発泡を抑制するために未反応塩化ビニル系単量体を回収する際の処理温度を低くしたり、該水性分散液から回収する際の処理速度をおそくする等の操作が行われている。しかし、これらの方法は発泡を抑制することに関してはある程度効果的であるものの、処理温度を低下した場合は未反応塩化ビニル系単量体の回収効率が低下する。また、処理速度をおそくした場合は、未反応塩化ビニル系単量体回収のための処理時間が長くなり生産効率が低下する等の課題があった。
【０００５】
そこで、これら乳化重合、播種乳化重合、微細懸濁重合、播種微細懸濁重合等で得られた塩化ビニル系重合体水性分散液からの未反応塩化ビニル系単量体の回収操作に関しては、ノズルから塩化ビニル系重合体ラテックスを蒸発缶内に貯溜された塩化ビニル系重合体ラテックスの液面全面に噴霧することで泡立ちを抑制しながら未反応塩化ビニル系単量体を回収する方法（例えば、特許文献１参照）、また、未反応塩化ビニル系単量体回収装置の後に設置した泡分離器内で泡に水蒸気を直接吹込むことで未反応塩化ビニル系単量体の回収操作により発生した泡を消泡する方法（例えば、特許文献２参照）が提案されている。
【０００６】
【特許文献１】
特開平８−３２５３２１号公報
【特許文献２】
特開平１３−８１１２７号公報
【０００７】
【発明が解決しようとする課題】
しかしながら、特開平８−３２５３２１号公報に提案の方法では、消泡という面では効果があるものの、その一方で塩化ビニル系重合体ラテックスの液面全面に噴霧する操作を行うために新たな泡立ちが発生するため、泡立ち抑制という点でその効果は満足できるものでなく、また、塩化ビニル系重合体ラテックスに残存する未反応塩化ビニル系単量体の回収効率の点でも未だ十分でない。
【０００８】
また、特開平１３−８１１２７号公報に提案の方法では、発生した泡を泡分離器内で消泡させるという点では一定の効果が見られるものの、未反応塩化ビニル系単量体の回収装置以外の泡分離器に水蒸気を供給させる等の設備が必要となる等の課題を有していた。
【０００９】
そこで、本発明は、真空蒸発塔等の未反応塩化ビニル系単量体の回収装置内で発生する泡立ちについて、塩化ビニル系重合体水性分散液の噴霧操作を特定の工程を経て行うことによって、泡立ちが抑制され、安定して高効率に未反応塩化ビニル系単量体の回収ができる製造方法を提供することにある。
【００１０】
【課題を解決するための手段】
本発明者らは、上記課題について鋭意検討した結果、塩化ビニル系重合体水性分散液から未反応塩化ビニル系単量体を回収する際に、塩化ビニル系重合体水性分散液の噴霧操作を特定の工程で行うことにより泡立ちを抑制し、安定的に高効率で未反応塩化ビニル系単量体の回収が可能となることを見出し、本発明を完成させるに至った。
【００１１】
即ち、本発明は、塩化ビニル系単量体を界面活性剤、重合開始剤の存在下、水性媒体中で重合を行い得られる塩化ビニル系重合体水性分散液から未反応塩化ビニル系単量体を真空蒸発塔により回収する際に、少なくとも下記（１）工程及び（２）工程を経ることを特徴とする塩化ビニル系重合体水性分散液からの未反応塩化ビニル系単量体の回収法に関するものである。
（１）工程：塩化ビニル系重合体水性分散液を真空蒸発塔の塔頂部に設置した空円錐型スプレーノズルにて、その噴霧液到達外周径が真空蒸発塔内周径より大きくなるように噴霧し、未反応塩化ビニル系単量体を回収する工程
（２）工程：（１）工程により得られたボトム液を真空蒸発塔の塔頂部に設置された空円錐型スプレーノズルにて真空蒸発塔内に噴霧し、且つ該塔頂部より噴霧される（１）工程により得られたボトム液の噴霧液量に対して３〜３０倍量の流量で該（２）工程により得られるボトム液を真空蒸発塔内飽和水蒸気温度以上の温度で真空蒸発塔内へ空円錐型スプレーノズルを用いて循環再噴霧し未反応塩化ビニル系単量体を回収する工程
以下に、本発明を詳細に説明する。
【００１２】
本発明の未反応塩化ビニル系単量体の回収法は、塩化ビニル系重合体水性分散液から未反応塩化ビニル系単量体を真空蒸発塔により回収する際に、少なくとも（１）工程：塩化ビニル系重合体水性分散液を真空蒸発塔の塔頂部に設置した空円錐型スプレーノズルにて、その噴霧液到達外周径が真空蒸発塔内周径より大きくなるように噴霧し、未反応塩化ビニル系単量体を回収する工程、及び、（２）工程：（１）工程により得られたボトム液を真空蒸発塔の塔頂部に設置された空円錐型スプレーノズルにて真空蒸発塔内に噴霧し、且つ該塔頂部より噴霧される（１）工程により得られたボトム液の噴霧液量に対して３〜３０倍量の流量で該（２）工程により得られるボトム液を真空蒸発塔内飽和水蒸気温度以上の温度で真空蒸発塔内へ空円錐型スプレーノズルを用いて循環再噴霧し未反応塩化ビニル系単量体を回収する工程を経る未反応塩化ビニル系単量体の回収法に関するものである。
【００１３】
本発明における塩化ビニル系重合体水性分散液とは、水性媒体中で界面活性剤、重合開始剤の存在下、塩化ビニル系単量体を重合して得られるペースト加工用の塩化ビニル系重合体水性分散液であり、その重合方法としては、例えば乳化重合法、播種乳化重合法、微細懸濁重合法、播種微細懸濁重合法等を挙げることができる。
【００１４】
ここでいう塩化ビニル系単量体とは、塩化ビニル単量体単独又は塩化ビニル単量体と塩化ビニル単量体との共重合可能なビニル単量体との混合物であり、塩化ビニル単量体と共重合し得るビニル単量体としては、例えば酢酸ビニル、プロピオン酸ビニル、ミリスチン酸ビニル、安息香酸ビニル等のビニルエステル類；アクリル酸、メタクリル酸、マレイン酸、フマル酸等の不飽和カルボン酸又はその無水物；アクリル酸メチル、アクリル酸エチル、アクリル酸ブチル等のアクリル酸エステル類；メタクリル酸メチル、メタクリル酸エチル、メタクリル酸ブチル等のメタクリル酸エステル類；マレイン酸エステル、フマル酸エステル、桂皮酸エステル等の不飽和カルボン酸エステル類；ビニルメチルエーテル、ビニルアミルエーテル、ビニルフェニルエーテル等のビニルエーテル類；エチレン、プロピレン、ブテン、ペンテン等のモノオレフィン類；塩化ビニリデン、スチレン及びその誘導体、アクリロニトリル、メタクリロニトリル等を挙げることができ、これらビニル単量体は１種以上で用いることが可能である。
【００１５】
界面活性剤としては、例えばジアルキルスルホコハク酸塩、アルキルベンゼンスルホン酸塩、アルキル硫酸塩等が挙げられ、これらは単独又は２種類以上の組合わせで用いることが可能である。
【００１６】
重合開始剤としては、例えば過硫酸カリウム、過硫酸アンモニウム、過酸化水素等の水溶性重合開始剤；ベンゾイルパーオキサイド，ｐ−クロロベンゾイルパーオキサイド等の芳香族ジアシルパーオキサイド、カプロイルパーオキサイド，ラウロイルパーオキサイド等の脂肪族ジアシルパーオキサイド、アゾビスイソブチロニトロリル，アゾビスイソバレロニトリル等のアゾ化合物、ｔ−ブチルパーオキシピバレート等の有機酸のパーオキシジエステル、ジイソプロピルパーオキシジカーボネート，ジオクチルパーオキシジカーボネート等のパーオキシジカーボネート、アセチルシクロヘキシルスルホニルパーオキサイド等の油溶性重合開始剤が挙げられる。そして、これらは単独又は２種類以上の組合わせで用いることが可能である。
【００１７】
水性媒体とは、水単独又は水を主成分とする媒体であり、例えば水、脱イオン水、蒸留水等を挙げることができる。
【００１８】
なお、本発明でいう塩化ビニル系重合体水性分散液とは、便宜上塩化ビニル系単量体の重合反応により得られた水性分散液を示し、ボトム液とは、便宜上該塩化ビニル系重合体水性分散液を真空蒸発塔により未反応塩化ビニル系単量体を回収し真空蒸発塔底部に溜まる未反応塩化ビニル系単量体をいったん回収した後の塩化ビニル系重合体水性分散液を示す。
【００１９】
本発明の未反応塩化ビニル系単量体の回収法に適応できる塩化ビニル系重合体水性分散液からの未反応塩化ビニル系単量体の回収装置の一例を図１に示し、本発明の未反応塩化ビニル系単量体の回収法を以下に具体的に説明するが、本発明はこれら例示に制限されるものではない。
【００２０】
図１中の１は（１）工程の真空蒸発塔への塩化ビニル系重合体水性分散液の入口、２は（１）工程の真空蒸発塔で回収された未反応塩化ビニル系単量体の出口、４は（１）工程の真空蒸発塔、５は（１）工程の真空蒸発塔加熱装置、６は塩化ビニル系重合体水性分散液を噴霧する空円錐型スプレーノズル、１４は（１）工程により得られたボトム液の入口、１５は（２）工程の真空蒸発塔で回収された未反応塩化ビニル系単量体の出口、１６は未反応塩化ビニル系単量体を回収した後の塩化ビニル系重合体水性分散液の出口、１７は（２）工程の真空蒸発塔、１８は（２）工程の真空蒸発塔加熱装置、１９は（１）工程で得られたボトム液を噴霧する空円錐型スプレーノズル、２０は（２）工程により得られたボトム液を噴霧する空円錐型スプレーノズル、７、１３、２１、２４、３４は熱交換器、２２は循環ライン、１２、２３，３３は循環ポンプ、3はポンプ、８、２５，２８は流量計、９、２６、２９は温度計、１０、２７は圧力計、１１、３０、３１、３２は流量調節弁を示す。
【００２１】
本発明で用いる空円錐型スプレーノズルとは、空円錐ノズルを有するものであり、空円錐ノズルとは、塩化ビニル系重合体水性分散液、ボトム液を噴霧した際の噴霧液の断面形状が基本的には中心部に液滴分布を持たない噴霧パターンを有するノズルをいい、噴霧液の投影面積の内、約２０％以上が外周部に液滴分布を有するノズルをも指すものである。また、本発明で用いる空円錐型スプレーノズルとは、上記特性を有するノズルを示すものであり、例え投影断面が四角形等の円形以外の形状を示すノズルであってもそれをも包含するものである。
【００２２】
ここで、塩化ビニル系重合体水性分散液、（１）工程により得られるボトム液、（２）工程により得られるボトム液を噴霧するスプレーノズルが空円錐型スプレーノズルでない場合は、噴霧された塩化ビニル系重合体水性分散液、ボトム液の殆どは真空蒸発塔底部に溜まっている塩化ビニル系重合体水性分散液（ボトム液）の液表面へ衝突するため、未反応塩化ビニル系単量体回収時の泡立ちが激しくなり、安定的な未反応塩化ビニル系単量体の回収が困難となる。
【００２３】
また、本発明で用いる真空蒸発塔とは、一般的に工業プロセスにおいて溶媒、単量体等を減圧下又は真空下で蒸発回収するために用いられている設備であり、特定の特殊な設備を指すものではなく、例え減圧下で使用しても便宜上真空蒸発塔と称する。
【００２４】
本発明においては、上記（１）工程及び（２）工程の少なくとも２つの工程を経ることにより、塩化ビニル系重合体水性分散液から未反応塩化ビニル系単量体を回収する際の泡立ちを抑制し、安定的に高効率で未反応塩化ビニル系単量体の回収が達成されるものであり、上記（１）工程、（２）工程のいずれかの工程が行われないような場合、未反応塩化ビニル系単量体の回収量を増加させた際には、真空蒸発塔内の泡の抑制が困難となり、真空蒸発塔内からの泡の飛散が多くなる、処理速度を低下せざるおえない、等の問題が発生し、効率的な未反応塩化ビニル系単量体の回収が困難となる。
【００２５】
そして、本発明の未反応塩化ビニル系単量体の回収法においては、上記（１）及び（２）工程を経ることにより、未反応塩化ビニル系単量体を回収する際の泡立ちを抑制し、安定的に高効率で未反応塩化ビニル系単量体の回収を行うことが可能であり、さらに高効率で安定的な未反応塩化ビニル系単量体の回収を達成する為に、上記（１）工程と上記（２）工程の中間、又は、上記（１）工程と上記（２）工程の後に付加的な未反応塩化ビニル系単量体の回収工程を行うことが可能である。その際の付加的な工程としては、本発明の目的が達成される限りにおいていかなる塩化ビニル系単量体の回収工程であってもよく、例えば上記（１）工程、（２）工程を適宜選択して付加的な工程とすることは無論、通常の真空蒸留塔等を使用した一般的な塩化ビニル系単量体の回収工程であってもよい。
【００２６】
本発明の塩化ビニル系単量体の回収法は、（１）工程として塩化ビニル系重合体水性分散液を真空蒸発塔の塔頂部に設置した空円錐型スプレーノズルにて、その噴霧液到達外周径が真空蒸発塔内周径より大きくなるように噴霧し、未反応塩化ビニル系単量体を回収する工程を行うものである。
【００２７】
（１）工程においては、塩化ビニル系重合体水性分散液中の未反応塩化ビニル系単量体の濃度が高く、泡立ちが激しいことから泡の飛散をスプレー膜により抑制するために、塩化ビニル系重合体水性分散液を真空蒸発塔内の塔頂部に設置した空円錐型スプレーノズルにより、その噴霧液到達外周径が真空蒸発塔内周径より大きくなるように噴霧、つまり噴霧液が真空蒸発塔内壁面に到達するように噴霧するものである。ここで、スプレーノズルが空円錐型スプレーノズルでない場合、噴霧液到達外周径が真空蒸発塔内周径より小さい場合、噴霧液は真空蒸発塔の塩化ビニル系重合体水性分散液に直接到達し、泡立ちが激しくなると共に真空蒸発塔内を上昇する泡のスプレー膜による抑制が悪化し未反応塩化ビニル系単量体の回収効率が低下すると共に、（２）工程の未反応塩化ビニル系単量体の回収を安定して行うことができず、結果として安定的に高効率で塩化ビニル系単量体を回収することが出来なくなる。
【００２８】
該（１）工程における空円錐型スプレーノズルの取り付け位置である塔頂部とは、塩化ビニル系重合体水性分散液の噴霧液到達外周径が真空蒸発塔内周径より大きくなる位置であればよく真空蒸発塔塔頂のみならず、その周辺部をも包含するものであり、その中でも未反応塩化ビニル系単量体の回収工程をよりコンパクトな設計とすることが可能であることから真空蒸発塔の断面の中心部に空円錐型スプレーノズルを設置することが好ましい。また空円錐型スプレーノズルの取付高さとしては、真空蒸発塔底部の塩化ビニル系重合体ラテックスの液表面から上昇する泡を空円錐型スプレー膜内部にトラップさせやすくする意味で真空蒸発塔全高の底部から１／４以上の高さに設置することが好ましい。
【００２９】
（１）工程での未反応塩化ビニル系単量体の回収効率を高め、本発明の未反応塩化ビニル系単量体の回収法をより効果的なものとするために（１）工程においては、真空蒸発塔の塔頂部から噴霧する塩化ビニル系重合体水性分散液の噴霧条件として、塩化ビニル系重合体水性分散液を真空蒸発塔内飽和水蒸気温度より５〜２５℃高い温度で噴霧する事が好ましく、さらに塩化ビニル系重合体水性分散液の安定性の点からは特に真空蒸発塔内飽和水蒸気温度より５〜２０℃高い温度で噴霧することが好ましい。また、真空蒸発塔内の圧力としては５０〜３００Ｔｏｒｒであることが好ましく、特に１３０〜３００Ｔｏｒｒであることが好ましい。
【００３０】
（１）工程における真空蒸発塔の塔径との関係では、真空蒸発塔内を上昇する泡の発生を抑える意味で、真空蒸発塔内で蒸発し上昇する水蒸気及び未反応塩化ビニル系単量体の空塔速度は０．１〜２．５ｍ／ｓｅｃの範囲で選定することが好ましく、特に０．３〜１．５ｍ／ｓｅｃが好ましい。また、空円錐型スプレーノズルのスプレー角度については任意であり、その中でも真空蒸発塔内を上昇する泡を効率良く抑制することが可能となることから１８０°未満であることが好ましく、更に１６０°以下であることが好ましい。そして、空円錐型スプレーノズルのノズル構造については任意であり、本発明の効果を得るためには、噴霧液が真空蒸発塔の内壁面に到達しうるノズルを選定することが好ましい。
【００３１】
また、（１）工程の真空蒸発塔に供給する塩化ビニル系重合体水性分散液の温度調節方法としては任意であり、その中でも加熱機の閉塞を防止する意味で塩化ビニル系重合体水性分散液に圧力０．１ＭＰａ以上の水蒸気を直接導入して調節する方法や、プレート型熱交換機を使用する事が好ましい。真空蒸発塔に供給する塩化ビニル系重合体水性分散液の流量としては、一般的に経済的な配管流速として知られている０．５〜３．０ｍ／ｓｅｃの範囲で供給することが好ましい。
【００３２】
本発明の未反応塩化ビニル系単量体の回収法は、（２）工程として（１）工程を経て得られた塩化ビニル系重合体水性分散液であるボトム液を真空蒸発塔の塔頂部に設置された空円錐型スプレーノズルにて真空蒸発塔内に噴霧し、且つ該塔頂部より噴霧される（１）工程により得られたボトム液の噴霧液量に対して３〜３０倍量の流量で該（２）工程により得られるボトム液を真空蒸発塔内飽和水蒸気温度以上の温度で真空蒸発塔内へ空円錐型スプレーノズルを用いて循環再噴霧し未反応塩化ビニル系単量体の回収をおこなうものである。
【００３３】
該（２）工程は、濡れ壁効果とフラッシングにより未反応塩化ビニル系単量体の回収効率を加速させることから真空蒸発塔内へ（２）工程により得られるボトム液を真空蒸発塔内飽和水蒸気温度以上の温度で塔頂部から噴霧される（１）工程により得られるボトム液の噴霧液量に対し３〜３０倍量の流量で循環再噴霧させるものである。
【００３４】
ここで、（２）工程により得られるボトム液の循環再噴霧を行わない場合、（２）工程により得られるボトム液の循環再噴霧液の液量が塔頂部から噴霧される（１）工程により得られるボトム液の噴霧液量に対し３倍量未満である場合、（２）工程により得られるボトム液の循環再噴霧の噴霧液温度が真空蒸発塔内飽和水蒸気温度より低い場合には、未反応塩化ビニル系単量体の回収効率が低下する。一方、（２）工程により得られるボトム液の循環再噴霧液の液量を塔頂部から噴霧される（１）工程により得られるボトム液の噴霧液量に対し３０倍より大きくした場合には未反応塩化ビニル系単量体回収設備が大がかりなものとなり、設備費用が大きくなる。また、従来方法のようにボトム液の循環再噴霧を行わずに真空蒸発塔内に滞在する塩化ビニル系重合体水性分散液を真空蒸発塔に付設した外部ジャケット等により加熱した場合には、未反応塩化ビニル系単量体の回収効率は見掛け上本発明と同程度となる可能性もあるが、未反応塩化ビニル系単量体の回収量が増加した場合には、それに伴い増加する泡の抑制が困難となり、真空蒸発塔の泡分離装置を過大なものとする必要があったり、処理速度を低下、つまり回収効率を低下する必要がある等の課題が発生する。
【００３５】
本発明の未反応塩化ビニル系単量体の回収法をより効果的なものとするための真空蒸発塔の運転条件としては、真空蒸発塔の塔頂部から噴霧する（１）工程により得られたボトム液の噴霧条件は真空蒸発塔に循環再噴霧する（２）工程により得られるボトム液中の未反応塩化ビニル系単量体の含有濃度を低下させ、回収効率を優れたものとするために真空蒸発塔内飽和水蒸気温度より０〜３０℃高い温度で噴霧することが好ましく、さらに（２）工程により得られるボトム液の循環再噴霧液の温度が真空蒸発塔内飽和水蒸気温度より０〜３０℃高い温度で噴霧することが好ましく、特にボトム液である塩化ビニル系重合体水性分散液が熱等による劣化等の影響を受けず安定性に優れることからそれぞれの噴霧液の温度が真空蒸発塔内飽和水蒸気温度より５〜２５℃高い温度であることが好ましい。また、（２）工程における真空蒸発塔内の圧力としては、５０〜３００Ｔｏｒｒであることが好ましく、特に８０〜２５０Ｔｏｒｒであることが好ましい。
【００３６】
該（２）工程における（１）工程により得られたボトム液の噴霧は、噴霧液滴がボトム液表面に直接到達することにより誘発される真空蒸発塔底部のボトム液の起泡を抑えるために、塔頂部から該ボトム液を噴霧液到達外周径が真空蒸発塔内周径より大きくなるような空円錐型スプレーノズルによる噴霧、つまり噴霧液が真空蒸発塔内壁面に到達するように噴霧を行うことが好ましい。また、（２）工程により得られたボトム液の循環再噴霧においては、噴霧液滴がボトム液表面に直接到達することにより誘発される真空蒸発塔底部のボトム液の起泡を抑えるために、真空蒸発塔底部のボトム液の液表面に噴霧される噴霧液量が全噴霧液量の４０％以下となるように噴霧することが好ましく、特に２０％以下となるように噴霧を行うことがより好ましい。
【００３７】
本発明における（２）工程での真空蒸発塔内の空円錐型スプレーノズルの取付位置としては、（１）工程により得られるボトム液噴霧用空円錐型スプレーノズルは塔頂部であり、（２）工程により得られるボトム液の循環再噴霧用空円錐型スプレーノズルは任意である。ここで塔頂部とは塔頂のみならず、塔頂付近を指すものである。その中でも効率よく真空蒸発塔内での発泡が抑制され、未反応塩化ビニル系単量体の回収効率に優れる回収法となることから共に噴霧液到達外周径が真空蒸発塔内周径より大きくなる位置とすることが好ましい。また、未反応塩化ビニル系単量体の回収工程をよりコンパクトな設計とすることが可能であることから真空蒸発塔の断面の中心部にそれぞれ空円錐型スプレーノズルを設置することが好ましい。
【００３８】
また、それぞれの空円錐型スプレーノズルの取付位置高さとしては、真空蒸発塔底部のボトム液の液表面から上昇する泡を空円錐型スプレー膜内部にトラップさせることが可能となり、未反応塩化ビニル系単量体の回収効率に優れることから塔頂部に設置する（１）工程により得られるボトム液を噴霧する空円錐型スプレーノズルは、真空蒸発塔の塔頂〜塔長さの３／４の間の位置に設置することが好ましく、（２）工程により得られるボトム液の循環再噴霧を行う空円錐型スプレーノズルは、真空蒸発塔の塔頂より塔長さの１／４〜３／４低い位置に設置することが好ましい。これら塔頂部に設置又は循環再噴霧に使用する空円錐型スプレーノズルの数には制限はなく複数個設置することも可能であり、また多段に複数個設置することも可能である。そして、これら空円錐型スプレーノズルのスプレー角度については任意であり、その中でも真空蒸発塔内を上昇する泡を効率良く抑制することが可能となることから１８０°未満であることが好ましく、更に１６０°以下であることが好ましい。そして、これら空円錐型スプレーノズルのノズル構造については任意であり、本発明の効果を得るためには、噴霧液が真空蒸発塔の内壁面に到達しうるノズルを選定することが好ましい。
【００３９】
（２）工程における真空蒸発塔の塔径との関係では、真空蒸発塔内を上昇する泡の発生を抑える意味で、真空蒸発塔で蒸発し上昇する水蒸気、及び未反応塩化ビニル系単量体の空塔速度は、０．１〜２．５ｍ／ｓｅｃの範囲で選定することが好ましく、特に０．３〜１．５ｍ／ｓｅｃが好ましい。
【００４０】
また、（２）工程における真空蒸発塔に供給する塩化ビニル系重合体水性分散液である（１）工程により得られるボトム液、循環再噴霧される（２）工程により得られるボトム液の温度調節方法としては任意であり、その中でも加熱機の閉塞を防止する意味でこれら塩化ビニル系重合体水性分散液に圧力０．１ＭＰａ以上の水蒸気を直接導入して調節する方法や、プレート型熱交換機を使用する事が好ましく、特に、未反応塩化ビニル系単量体の回収効率を高める際には塔頂部から噴霧する（１）工程により得られるボトム液の温度調整方法は、循環再噴霧を行う（２）工程により得られるボトム液に比べ液温の上昇を大きくする必要がある場合があるため、水蒸気を直接導入して調節することが好ましい。
【００４１】
（２）工程における真空蒸発塔に供給する（１）工程により得られるボトム液及び循環再噴霧される（２）工程により得られるボトム液の流量としては、一般的に経済的な配管流速として知られている０．５〜３．０ｍ／ｓｅｃの範囲で供給することが好ましい。
【００４２】
本発明の少なくとも上記（１）工程及び（２）工程を経る未反応塩化ビニル系単量体の回収法においては、（１）工程の噴霧条件、（２）工程の循環再噴霧の噴霧液量、加熱温度を所定の条件とすることにより、未反応塩化ビニル系単量体の回収量増加に伴う真空蒸発塔内の泡の上昇をスプレー膜で抑制し、未反応塩化ビニル系単量体の回収効率を高める点に特徴がある。その意味では、（１）工程の噴霧条件は真空蒸発塔底部の塩化ビニル系重合体水性分散液であるボトム液の液表面に噴霧される噴霧液量は少ない方が好ましく、（２）工程の噴霧条件は循環再噴霧される（２）工程により得られるボトム液の流量が多く、噴霧温度が高い方が好ましい。
【００４３】
本発明の回収法においては、それぞれの工程において通常真空蒸発塔に付随する機器として一般的に使用されている例えばミストセパレーター、水蒸気コンデンサー、水封式真空ポンプ等を適宜組合せて用いることも可能である。
【００４４】
本発明の方法は、塩化ビニル系重合体水性分散液から未反応塩化ビニル系単量体を回収する方法において、未反応塩化ビニル系単量体回収時の泡立ちによる回収効率の低下が改善でき、原単位の向上、環境衛生上の改善等の効果が得られる。
【００４５】
【実施例】
以下に、実施例により本発明をより詳細に説明するが、本発明はこれらによってなんら制限されるものではない。
【００４６】
以下に実施例における評価方法を詳細に説明する。
【００４７】
〜塩化ビニル重合体水性分散液中の残存塩化ビニル単量体濃度〜
得られた塩化ビニル重合体水性分散液５０ｍｇを採取し、熱分解炉（島津製作所製、商品名ＰＹＲＯＬＹＺＥＲＰＹＲ−ＩＡ）により１０５℃で１分間加熱し、ガスクロマトグラフにて塩化ビニル単量体濃度を分析定量した。分析定量した塩化ビニル単量体濃度を塩化ビニル重合体水性分散液の固形分重量あたりの残存塩化ビニル単量体量に計算し、塩化ビニル重合体水性分散液中の残存塩化ビニル単量体濃度とした。
【００４８】
〜未反応塩化ビニル単量体回収時の泡立ち〜
真空蒸発塔に設置した覗き窓から内部の泡立ちを目視で観察した。
【００４９】
合成例１（シード粒子の水性分散液の調整）
重合缶中に脱イオン水１０８００ｋｇ、塩化ビニル単量体９０００ｋｇ、重合開始剤として３，５，５−トリメチルヘキサノイルパーオキサイド９０ｋｇ、１５重量％ドデシルベンゼンスルホン酸ナトリウム水溶液１５０ｋｇを仕込んだ後、３時間ホモジナイザーを用いて均質化処理を行った後、系内の温度を４０℃にあげて重合反応を開始した。そして、重合圧力が低下した後に未反応塩化ビニル単量体を回収することによりシード粒子の水性分散液を調整した。
【００５０】
合成例２（塩化ビニル重合体水性分散液の調整）
重合缶中に脱イオン水１０５０００ｋｇ、塩化ビニル単量体１２０００ｋｇ、２０重量％ドデシルベンゼンスルホン酸ナトリウム水溶液６０ｋｇ、合成例１により得られたシード粒子の水性分散液１３２０ｋｇを仕込んだ後、重合系の温度を６４℃に昇温し重合を開始した。重合開始から重合終了までの間、２０重量％ドデシルベンゼンスルホン酸ナトリウム水溶液４８０ｋｇを連続的に添加した。
【００５１】
重合圧力が６４℃における塩化ビニル単量体の飽和蒸気圧から０．５ＭＰａ降下した時点で重合反応を停止し、２０重量％ドデシルベンゼンスルホン酸ナトリウム水溶液１２０ｋｇを添加した。未反応塩化ビニル単量体を回収し、ペースト加工用塩化ビニル重合体水性分散液を得た。得られた塩化ビニル重合体水性分散液中の残存塩化ビニル単量体濃度は１．５重量％であった。
【００５２】
実施例１
合成例２で得られた塩化ビニル重合体水性分散液を、（１）工程として、スプレー角度１２０°の噴霧ノズルを有する空円錐型スプレーノズルを塔径の中心で塔頂から０．４ｍの高さに設置した塔径０．５ｍ、塔高さ１．５ｍの覗き窓付の真空蒸発塔内に該空円錐型スプレーノズルにより連続的に２００ｌ／Ｈｒの速度で噴霧（噴霧液は真空蒸発塔内壁面に到達）供給し、未反応塩化ビニル単量体の回収を行った。
【００５３】
その際の真空蒸発塔内の圧力は１４９Ｔｏｒｒ（飽和水蒸気温度６０℃）に設定し、真空蒸発塔に供給する合成例２により得られた塩化ビニル重合体水性分散液は０．１５ＭＰａの水蒸気を直接供給して６５℃となるように調整した。
【００５４】
続いて、（２）工程として、スプレー角度１２０°の噴霧ノズルを有する空円錐型スプレーノズルを塔径の中心で塔頂から０．４ｍの高さに設置した塔径０．５ｍ、塔高さ１．５ｍの覗き窓付の真空蒸発塔内に（１）工程により得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液であるボトム液を該空円錐型スプレーノズルにより連続的に２００ｌ／Ｈｒの速度で噴霧（噴霧液は真空蒸発塔内壁面に到達）供給し、該真空蒸発塔内のボトム液を３ｍ3／Ｈｒの速度で真空蒸発塔の塔頂から０．７ｍの高さに設置した空円錐型スプレーノズル（噴霧液は真空蒸発塔内壁面に到達、外周部の液滴分布６０％）より循環再噴霧し真空蒸発塔塔底の塩化ビニル重合体水性分散液を２００ｌ／Ｈｒで抜出しながら未反応塩化ビニル単量体の回収を行った。
【００５５】
その際の真空蒸発塔内の圧力は１４９Ｔｏｒｒ（飽和水蒸気温度６０℃）に設定し、真空蒸発塔に供給する（１）工程により得られたボトム液は０．１５ＭＰａの水蒸気を直接供給して６５℃となるように調整し、循環再噴霧液を行う（２）工程により得られるボトム液はプレート型熱交換器により６５℃になるように調整した。
【００５６】
（１）工程、（２）工程を経て得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、（１）工程、（２）工程での真空蒸発塔内の泡立ち状況を表１に示す。
【００５７】
実施例２
（２）工程での（２）工程により得られたボトム液の循環再噴霧液量３ｍ3／Ｈｒの代わりに、循環再噴霧量を４ｍ3／Ｈｒとした（噴霧液は真空蒸発塔内壁面に到達、外周部液滴分布６０％）以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を行った。
【００５８】
（１）工程、（２）工程を経て得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、（１）工程、（２）工程での真空蒸発塔内の泡立ち状況を表１に示す。
【００５９】
実施例３
（２）工程での（２）工程により得られたボトム液の循環再噴霧液量３ｍ3／Ｈｒの代わりに、循環再噴霧液量を１．５ｍ3／Ｈｒとした（噴霧液は真空蒸発塔内壁面に到達、外周部液滴分布６０％）以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を行った。
【００６０】
（１）工程、（２）工程を経て得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、（１）工程、（２）工程での真空蒸発塔内の泡立ち状況を表１に示す。
【００６１】
実施例４
（１）工程での合成例２で得られた塩化ビニル重合体水性分散液の噴霧液量２００ｌ／Ｈｒの代わりに、噴霧液量を３００ｌ／Ｈｒとし、（２）工程での（１）工程により得られたボトム液の噴霧液量２００ｌ／Ｈｒの代わりに、噴霧液量を３００ｌ／Ｈｒとした（噴霧液は真空蒸発塔内壁面に到達）以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を行った。
【００６２】
（１）工程、（２）工程を経て得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、（１）工程、（２）工程での真空蒸発塔内の泡立ち状況を表１に示す。
【００６３】
実施例５
（２）工程で循環再噴霧液を行う（２）工程により得られるボトム液の液温６５℃の代わりに、循環再噴霧を行うボトム液の液温を７０℃とした以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を行った。
【００６４】
（１）工程、（２）工程を経て得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、（１）工程、（２）工程での真空蒸発塔内の泡立ち状況を表１に示す。
【００６５】
実施例６
（２）工程で循環再噴霧液を行う（２）工程により得られるボトム液の液温６５℃の代わりに、循環再噴霧を行うボトム液の液温を７５℃とした以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を行った。
【００６６】
（１）工程、（２）工程を経て得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、（１）工程、（２）工程での真空蒸発塔内の泡立ち状況を表１に示す。
【００６７】
実施例７
（１）工程で真空蒸発塔内に噴霧される合成例２により得られた塩化ビニル重合体水性分散液の液温６５℃の代わりに、塩化ビニル重合体水性分散液の液温を７０℃とし、（２）工程で真空蒸発塔の塔頂部より噴霧される（１）工程により得られたボトム液の液温６５℃の代わりに、（１）工程により得られるボトム液の液温を７０℃とした以外は、実施例５と同様の方法により未反応塩化ビニル単量体の回収を行った。
【００６８】
（１）工程、（２）工程を経て得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、（１）工程、（２）工程での真空蒸発塔内の泡立ち状況を表１に示す。
【００６９】
実施例８
（１）工程での真空蒸発塔の圧力１４９Ｔｏｒｒ（飽和水蒸気温度６０℃）の代わりに、圧力を１８８Ｔｏｒｒ（飽和水蒸気温度６５℃）に調整した以外は、実施例７と同様の方法で未反応塩化ビニル単量体の回収を行った。
【００７０】
（１）工程、（２）工程を経て得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、（１）工程、（２）工程での真空蒸発塔内の泡立ち状況を表１に示す。
【００７１】
実施例９
（２）工程での真空蒸発塔の圧力１４９Ｔｏｒｒ（飽和水蒸気温度６０℃）の代わりに、圧力を１８８Ｔｏｒｒ（飽和水蒸気温度６５℃）に調整した以外は、実施例５と同様の方法で未反応塩化ビニル単量体の回収を行った。
【００７２】
（１）工程、（２）工程を経て得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、（１）工程、（２）工程での真空蒸発塔内の泡立ち状況を表１に示す。
【００７３】
比較例１
（２）工程による未反応塩化ビニル単量体の回収を行わず、（１）工程のみで未反応塩化ビニル単量体の回収を行なった以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を行った。
【００７４】
得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、泡立ち状況を表２に示す。
【００７５】
得られた塩化ビニル重合体水性分散液中に残存する塩化ビニル単量体濃度は高いものであった。
【００７６】
比較例２
（２）工程での未反応塩化ビニル単量体の回収時に（２）工程により得られたボトム液の循環再噴霧を行わなかった以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を行った。
【００７７】
得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、泡立ち状況を表２に示す。
【００７８】
未反応塩化ビニル単量体回収時、真空蒸発塔内での泡立ちは見られなかったが、得られた塩化ビニル重合体水性分散液中に残存する塩化ビニル単量体濃度は高いものであった。
【００７９】
比較例３
（２）工程での未反応塩化ビニル単量体の回収時に（２）工程により得られたボトム液の循環再噴霧を行わず、（２）工程で用いる真空蒸発塔の外部ジャケットの温度を６５℃に調整して運転した以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を試みたが、（２）工程での運転途中より真空蒸発塔内での泡立ちが激しくなり、真空ポンプ側への泡の飛散が発生し、真空圧力が設定圧力に調整できず、運転を中止した。
【００８０】
比較例４
（２）工程で循環再噴霧を行う（２）工程により得られるボトム液の液温６５℃の代わりに、循環再噴霧を行うボトム液の液温を５５℃に調整した以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を行った。
【００８１】
得られた未反応塩化ビニル単量体回収後の塩化ビニル重合体水性分散液の残存塩化ビニル単量体濃度、泡立ち状況を表２に示す。
【００８２】
真空蒸発塔内での泡立ちはみられなかったが、得られた塩化ビニル重合体水性分散液中に残存する塩化ビニル単量体濃度は高いものであった。
【００８３】
比較例５
（１）工程で合成例２により得られた塩化ビニル重合体水性分散液を真空蒸発塔内に噴霧するスプレー角度１２０°の噴霧ノズルを有する空円錐型スプレーノズル（噴霧液は真空蒸発塔内壁面に到達）の代わりに、スプレー角度１２０°の扇型スプレーノズル（噴霧液は真空蒸発塔内壁面に未到達）を設置した以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を試みたが、それぞれの工程で共に運転当初より真空蒸発塔内の泡立ちが激しくなり、真空ポンプ側への泡の飛散が発生し、真空圧力が設定圧力に調整できず、運転を中止した。
【００８４】
比較例６
（２）工程で（１）工程により得られた塩化ビニル重合体水性分散液であるボトム液を真空蒸発塔内に噴霧する塔頂部に設置されたスプレー角度１２０°の噴霧ノズルを有する空円錐型スプレーノズル（噴霧液は真空蒸発塔内壁面に到達）及び（２）工程により得られるボトム液を循環再噴霧するスプレー角度１２０°の噴霧ノズルを有する空円錐型スプレーノズル（噴霧液は真空蒸発塔内壁面に到達）の代わりに、共に噴霧ノズルとしてスプレー角度１２０°の扇型スプレーノズル（噴霧液は真空蒸発塔内壁面に未到達）を設置した以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を試みたが、（２）工程での運転当初より真空蒸発塔内での泡立ちが激しくなり、真空ポンプ側への泡の飛散が発生し、真空圧力が設定圧力に調整できず、運転を中止した。
【００８５】
比較例７
（１）工程で合成例２により得られた塩化ビニル重合体水性分散液を真空蒸発塔内に噴霧するスプレー角度１２０°の噴霧ノズルを有する空円錐型スプレーノズル（噴霧液は真空蒸発塔内壁面に到達）の代わりに、噴霧ノズルとしてスプレー角度１２０°の充円錐型スプレーノズルを設置した以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を試みたが、運転途中より真空蒸発塔内での泡立ちが激しくなり、真空ポンプ側への泡の飛散が発生し、真空圧力が設定圧力に調整できず、運転を中止した。
【００８６】
比較例８
（２）工程で（１）工程により得られた塩化ビニル重合体水性分散液であるボトム液を真空蒸発塔内に噴霧する塔頂部に設置されたスプレー角度１２０°の噴霧ノズルを有する空円錐型スプレーノズル（噴霧液は真空蒸発塔内壁面に到達）及び（２）工程により得られるボトム液を循環再噴霧するスプレー角度１２０°の噴霧ノズルを有する空円錐型スプレーノズル（噴霧液は真空蒸発塔内壁面に到達）の代わりに、共に噴霧ノズルとしてスプレー角度１２０°の充円錐型スプレーノズルを設置した真空蒸発塔を使用した以外は、実施例１と同様の方法により未反応塩化ビニル単量体の回収を試みたが、（２）工程での運転途中より真空蒸発塔内での泡立ちが激しくなり、真空ポンプ側への泡の飛散が発生し、真空圧力が設定圧力に調整できず、運転を中止した。
【００８７】
【表１】
本発明の未反応塩化ビニル系単量体の回収法は、泡立ちが抑制され、安定して高効率に塩化ビニル系重合体水性分散液から未反応塩化ビニル系単量体の回収が可能となる等の効果に優れたものである。
【図面の簡単な説明】
【図１】；本発明の実施に使用できる未反応塩化ビニル系単量体の回収装置の一例
【符号の説明】
１ （１）工程の真空蒸発塔への塩化ビニル系重合体水性分散液の入口
２ （１）工程で回収された未反応塩化ビニル系単量体の出口
３ ポンプ
４ （１）工程の真空蒸発塔
５ （１）工程の真空蒸発塔加熱装置
６ 空円錐型スプレーノズル
７ 熱交換器
８ 流量計
９ 温度計
１０ 圧力計
１１ 流量調節弁
１２ 循環ポンプ
１３ 熱交換器
１４ （２）工程の真空蒸発塔への（１）工程により得られたボトム液の入口
１５ （２）工程で回収された未反応塩化ビニル系単量体の出口
１６ 未反応塩化ビニル系単量体が回収された塩化ビニル系重合体水性分散液の出口
１７ （２）工程の真空蒸発塔
１８ （２）工程の真空蒸発塔加熱装置
１９ 空円錐型スプレーノズル
２０ 空円錐型スプレーノズル
２１ 熱交換器
２２ 循環ライン
２３ 循環ポンプ
２４ 熱交換器
２５ 流量計
２６ 温度計
２７ 圧力計
２８ 流量計
２９ 温度計
３０ 流量調節弁
３１ 流量調節弁
３２ 流量調節弁
３３ 循環ポンプ
３４ 熱交換器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for recovering an unreacted vinyl chloride monomer from an aqueous dispersion of a vinyl chloride polymer after production. When the unreacted vinyl chloride monomer is recovered from the aqueous dispersion of the vinyl chloride polymer obtained by performing polymerization in the presence of an initiator and a polymerization initiator, foaming is reduced and the unreacted vinyl chloride monomer is efficiently recovered. The present invention relates to a method for recovering a monomer.
[0002]
[Prior art]
The aqueous dispersion of a vinyl chloride polymer is prepared by dispersing a vinyl chloride monomer in an aqueous medium in the presence of a surfactant and a polymerization initiator to perform emulsion polymerization, seeding emulsion polymerization, fine suspension polymerization, and seeding fine suspension. Latex having a particle diameter of about 0.05 to 10 μm is produced by performing turbid polymerization or the like. In polymerization reactions such as emulsion polymerization, seeding emulsion polymerization, fine suspension polymerization, and seeding fine suspension polymerization for producing a vinyl chloride polymer aqueous dispersion, the polymerization conversion of the vinyl chloride monomer is usually 70 to Unreacted vinyl chloride-based monomers remain in the obtained vinyl chloride-based polymer aqueous dispersion in order to terminate the polymerization reaction at the time of reaching 98%. Then, after recovering the unreacted vinyl chloride-based monomer from the vinyl chloride-based polymer aqueous dispersion, the aqueous dispersion is dried by a spray dryer or the like to produce a vinyl chloride-based polymer for paste processing. ing. For this reason, vinyl chloride-based monomers, which are the raw materials of the vinyl chloride-based polymer for paste processing, are collected to improve the basic unit. There is a demand for a method of recovering the unreacted vinyl chloride monomer remaining in the dispersion with higher efficiency.
[0003]
However, in the recovery of unreacted vinyl chloride monomer from an aqueous dispersion of a vinyl chloride polymer obtained by polymerizing a vinyl chloride monomer in an aqueous medium in the presence of a surfactant and a polymerization initiator. The aqueous dispersion contains a surfactant, so that unreacted vinyl chloride-based monomer evaporates, resulting in vigorous foaming, resulting in product loss due to foam scattering and scaling such as foaming. It had problems such as trouble occurrence.
[0004]
As a method of solving these problems, in the operation of recovering the unreacted vinyl chloride monomer from the aqueous dispersion of the vinyl chloride polymer, the unreacted vinyl chloride monomer is usually recovered to suppress foaming. In such a case, operations such as lowering the processing temperature or reducing the processing speed at the time of recovery from the aqueous dispersion are performed. However, although these methods are effective to some extent in suppressing foaming, when the treatment temperature is lowered, the recovery efficiency of the unreacted vinyl chloride monomer decreases. Further, when the processing speed is reduced, there is a problem that the processing time for recovering the unreacted vinyl chloride-based monomer becomes longer and the production efficiency is lowered.
[0005]
Therefore, regarding the operation of recovering the unreacted vinyl chloride-based monomer from the aqueous dispersion of the vinyl chloride-based polymer obtained by these emulsion polymerization, seeded emulsion polymerization, fine suspension polymerization, seeded fine suspension polymerization, etc. A method of recovering unreacted vinyl chloride-based monomers while suppressing foaming by spraying a vinyl chloride-based polymer latex from the entire surface of the liquid surface of the vinyl chloride-based polymer latex stored in an evaporator (for example, In addition, it was generated by the operation of recovering the unreacted vinyl chloride-based monomer by directly blowing steam into the foam in the foam separator installed after the unreacted vinyl chloride-based monomer recovery device. A method of defoaming bubbles (for example, see Patent Document 2) has been proposed.
[0006]
[Patent Document 1]
JP-A-8-325321
[Patent Document 2]
JP-A-13-81127
[0007]
[Problems to be solved by the invention]
However, although the method proposed in Japanese Patent Application Laid-Open No. 8-325321 is effective in terms of defoaming, on the other hand, new foaming occurs due to the operation of spraying the entire surface of the liquid surface of the vinyl chloride polymer latex. Because of this, the effect is not satisfactory in terms of suppressing foaming, and the collection efficiency of unreacted vinyl chloride monomers remaining in the vinyl chloride polymer latex is still insufficient.
[0008]
Further, the method proposed in Japanese Patent Application Laid-Open No. 13-81127 has a certain effect in that generated bubbles are eliminated in the foam separator, but other than a device for recovering unreacted vinyl chloride monomers. However, there is a problem that equipment for supplying steam to the foam separator is required.
[0009]
Accordingly, the present invention provides a method for spraying an aqueous dispersion of a vinyl chloride-based polymer through a specific step with respect to foaming generated in an unreacted vinyl chloride-based monomer recovery device such as a vacuum evaporation tower. An object of the present invention is to provide a production method in which foaming is suppressed and an unreacted vinyl chloride monomer can be recovered stably and efficiently.
[0010]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on the above-mentioned problems, and as a result, when recovering the unreacted vinyl chloride-based monomer from the vinyl chloride-based polymer aqueous dispersion, specified a spraying operation of the vinyl chloride-based polymer aqueous dispersion. It was found that foaming was suppressed by performing the step (1), and it was possible to stably recover the unreacted vinyl chloride monomer with high efficiency, and completed the present invention.
[0011]
That is, the present invention is a method for producing a vinyl chloride-based monomer from a vinyl chloride-based polymer aqueous dispersion obtained by polymerizing a vinyl chloride-based monomer in an aqueous medium in the presence of a surfactant and a polymerization initiator. A process for recovering an unreacted vinyl chloride-based monomer from an aqueous dispersion of a vinyl chloride-based polymer, characterized in that at least the following steps (1) and (2) are carried out when recovering by a vacuum evaporation tower: Things.
Step (1): The aqueous dispersion of the vinyl chloride polymer is sprayed with an empty cone spray nozzle installed at the top of the vacuum evaporation tower so that the outer diameter of the spray reaches the inner diameter of the vacuum evaporation tower. And recovering unreacted vinyl chloride monomer
Step (2): The bottom liquid obtained in the step (1) is sprayed into the vacuum evaporation tower by an empty conical spray nozzle installed at the top of the vacuum evaporation tower, and sprayed from the top of the tower ( The bottom liquid obtained in the step (2) is supplied into the vacuum evaporator at a temperature equal to or higher than the saturated steam temperature in the vacuum evaporator at a flow rate of 3 to 30 times the spray amount of the bottom liquid obtained in the step 1). A process of recovering unreacted vinyl chloride monomer by circulating and respraying using a hollow cone spray nozzle
Hereinafter, the present invention will be described in detail.
[0012]
The method for recovering the unreacted vinyl chloride-based monomer of the present invention comprises, at the time of recovering the unreacted vinyl chloride-based monomer from the aqueous dispersion of the vinyl chloride-based polymer using a vacuum evaporation tower, at least the step (1): The vinyl polymer aqueous dispersion is sprayed with an empty conical spray nozzle installed at the top of the vacuum evaporation tower so that the outer diameter of the spray reaches the inner diameter of the vacuum evaporation tower. Step of recovering the system monomer, and step (2): spraying the bottom liquid obtained in step (1) into the vacuum evaporation tower with an empty conical spray nozzle installed at the top of the vacuum evaporation tower The bottom liquid obtained in the step (2) is sprayed from the top of the tower at a flow rate of 3 to 30 times the amount of the sprayed liquid of the bottom liquid obtained in the step (1). Empty cone into vacuum evaporator at temperature above saturated steam temperature It relates a method for recovering the circulation re-sprayed unreacted vinyl chloride monomer through the process of recovering unreacted vinyl chloride monomer using a spray nozzle.
[0013]
The aqueous dispersion of the vinyl chloride polymer in the present invention is a vinyl chloride polymer for paste processing obtained by polymerizing a vinyl chloride monomer in the presence of a surfactant and a polymerization initiator in an aqueous medium. It is an aqueous dispersion, and examples of the polymerization method include an emulsion polymerization method, a seeded emulsion polymerization method, a fine suspension polymerization method, and a seeded fine suspension polymerization method.
[0014]
The vinyl chloride monomer referred to herein is a vinyl chloride monomer alone or a mixture of a vinyl monomer copolymerizable with a vinyl chloride monomer and a vinyl chloride monomer. Examples of the vinyl monomer that can be copolymerized with the polymer include vinyl esters such as vinyl acetate, vinyl propionate, vinyl myristate, and vinyl benzoate; and unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and fumaric acid. Acid or anhydride thereof; acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate; methacrylates such as methyl methacrylate, ethyl methacrylate, butyl methacrylate; maleic ester, fumaric ester, Unsaturated carboxylic esters such as cinnamic acid esters; vinyl methyl ether, vinyl amyl ether, vinyl Vinyl ethers such as nyl ether; monoolefins such as ethylene, propylene, butene, and pentene; vinylidene chloride, styrene and derivatives thereof, acrylonitrile, methacrylonitrile, and the like. These vinyl monomers may be used alone or in combination. It is possible.
[0015]
Examples of the surfactant include dialkyl sulfosuccinate, alkylbenzene sulfonate, alkyl sulfate and the like, and these can be used alone or in combination of two or more.
[0016]
Examples of the polymerization initiator include water-soluble polymerization initiators such as potassium persulfate, ammonium persulfate, and hydrogen peroxide; aromatic diacyl peroxides such as benzoyl peroxide and p-chlorobenzoyl peroxide, caproyl peroxide, and lauroyl peroxide. Aliphatic diacyl peroxides such as oxides, azo compounds such as azobisisobutyronitrile and azobisisovaleronitrile, peroxydiesters of organic acids such as t-butylperoxypivalate, diisopropylperoxydicarbonate, dioctyl Examples thereof include peroxydicarbonates such as peroxydicarbonate and oil-soluble polymerization initiators such as acetylcyclohexylsulfonyl peroxide. These can be used alone or in combination of two or more.
[0017]
The aqueous medium is water alone or a medium containing water as a main component, and examples thereof include water, deionized water, and distilled water.
[0018]
In addition, the vinyl chloride polymer aqueous dispersion referred to in the present invention refers to an aqueous dispersion obtained by a polymerization reaction of a vinyl chloride monomer for convenience, and the bottom liquid refers to the vinyl chloride polymer aqueous solution for convenience. This shows an aqueous dispersion of a vinyl chloride polymer after the unreacted vinyl chloride monomer is recovered from the dispersion by a vacuum evaporation tower and the unreacted vinyl chloride monomer collected at the bottom of the vacuum evaporation tower is recovered once.
[0019]
FIG. 1 shows an example of an apparatus for recovering an unreacted vinyl chloride monomer from an aqueous dispersion of a vinyl chloride polymer which is applicable to the method for recovering an unreacted vinyl chloride monomer of the present invention. The method for recovering the reactive vinyl chloride-based monomer will be specifically described below, but the present invention is not limited to these examples.
[0020]
In FIG. 1,
[0021]
The hollow cone type spray nozzle used in the present invention has a hollow cone nozzle, and the hollow cone nozzle is based on the cross-sectional shape of a vinyl chloride polymer aqueous dispersion and a spray liquid when a bottom liquid is sprayed. Specifically, it refers to a nozzle having a spray pattern having no droplet distribution at the center, and also refers to a nozzle having a droplet distribution at the outer periphery of which about 20% or more of the projected area of the spray liquid. The hollow conical spray nozzle used in the present invention refers to a nozzle having the above characteristics, and includes a nozzle having a cross-sectional shape other than a circular shape such as a quadrangle even if the projected cross section is a nozzle. is there.
[0022]
Here, when the spray nozzle for spraying the vinyl chloride polymer aqueous dispersion, the bottom liquid obtained in the step (1), and the bottom liquid obtained in the step (2) is not an empty cone type spray nozzle, the sprayed chloride is used. Most of the vinyl polymer aqueous dispersion and bottom liquid collide with the surface of the vinyl chloride polymer aqueous dispersion (bottom liquid) stored at the bottom of the vacuum evaporator, so that unreacted vinyl chloride monomer is recovered. Foaming at the time becomes intense, and it becomes difficult to recover a stable unreacted vinyl chloride monomer.
[0023]
Further, the vacuum evaporator used in the present invention is a facility that is generally used in an industrial process for evaporating and recovering a solvent, a monomer, or the like under reduced pressure or under a vacuum. It does not indicate, but is referred to as a vacuum evaporation tower for convenience even when used under reduced pressure.
[0024]
In the present invention, foaming when unreacted vinyl chloride-based monomer is recovered from the aqueous dispersion of the vinyl chloride-based polymer is suppressed through at least two of the above steps (1) and (2). However, the recovery of the unreacted vinyl chloride monomer can be stably achieved with high efficiency, and if any of the above steps (1) and (2) is not performed, When the recovered amount of the reactive vinyl chloride monomer is increased, it is difficult to suppress the bubbles in the vacuum evaporation tower, the bubbles are scattered from the vacuum evaporation tower, and the processing speed must be reduced. And it becomes difficult to efficiently recover the unreacted vinyl chloride monomer.
[0025]
In the method for recovering an unreacted vinyl chloride-based monomer of the present invention, foaming when recovering the unreacted vinyl chloride-based monomer is suppressed by passing through the above steps (1) and (2). It is possible to stably recover the unreacted vinyl chloride monomer with high efficiency, and to achieve the high efficiency and stable recovery of the unreacted vinyl chloride monomer, the above ( It is possible to perform an additional step of recovering the unreacted vinyl chloride monomer between the step 1) and the step (2) or after the step (1) and the step (2). The additional step at that time may be any vinyl chloride monomer recovery step as long as the object of the present invention is achieved. For example, the above steps (1) and (2) may be appropriately selected. Of course, the additional step may be a general vinyl chloride monomer recovery step using a normal vacuum distillation column or the like.
[0026]
In the method for recovering a vinyl chloride-based monomer according to the present invention, an aqueous cone-shaped spray nozzle provided at the top of a vacuum evaporation tower is used to carry the aqueous dispersion of a vinyl chloride-based polymer as a step (1). The step of performing spraying so that the diameter is larger than the inner diameter of the vacuum evaporation tower and recovering the unreacted vinyl chloride-based monomer is performed.
[0027]
In step (1), the concentration of unreacted vinyl chloride-based monomer in the aqueous dispersion of vinyl chloride-based polymer is high, and foaming is severe. The aqueous polymer dispersion is sprayed by an empty conical spray nozzle installed at the top of the vacuum evaporator so that the outer diameter of the spray reaches the inner diameter of the vacuum evaporator. It sprays so as to reach the inner wall surface. Here, if the spray nozzle is not an empty cone type spray nozzle, if the spray liquid outer peripheral diameter is smaller than the vacuum evaporator inner diameter, the spray liquid directly reaches the vinyl chloride polymer aqueous dispersion in the vacuum evaporator, The foaming becomes severe and the suppression of the foam rising in the vacuum evaporation tower by the spray film is deteriorated, the recovery efficiency of the unreacted vinyl chloride monomer is reduced, and the unreacted vinyl chloride monomer in the step (2) is reduced. Cannot be stably recovered, and as a result, the vinyl chloride monomer cannot be stably recovered with high efficiency.
[0028]
The tower top, which is the installation position of the empty cone type spray nozzle in the step (1), may be any position as long as the outer diameter of the aqueous dispersion of the aqueous vinyl chloride polymer dispersion reaches the spray liquid is larger than the inner diameter of the vacuum evaporation tower. It encompasses not only the top of the vacuum evaporator but also its surroundings. Among them, the vacuum evaporator can be designed to have a more compact process for recovering unreacted vinyl chloride monomer. It is preferable to install an empty conical spray nozzle at the center of the cross section. The height of the vacuum cone spray nozzle is set at the height of the vacuum evaporation tower so that bubbles rising from the surface of the vinyl chloride polymer latex at the bottom of the vacuum evaporation tower can be easily trapped inside the hollow cone spray film. It is preferable to install at a height of 1/4 or more from the bottom.
[0029]
In order to increase the recovery efficiency of the unreacted vinyl chloride monomer in the step (1) and to make the method for recovering the unreacted vinyl chloride monomer of the present invention more effective, the step (1) The condition of spraying the aqueous dispersion of the vinyl chloride polymer sprayed from the top of the vacuum evaporation tower is to spray the aqueous dispersion of the vinyl chloride polymer at a
[0030]
In relation to the diameter of the vacuum evaporator in the step (1), water vapor and unreacted vinyl chloride monomer which evaporate and elevate in the vacuum evaporator are meant to suppress the generation of bubbles rising in the vacuum evaporator. Is preferably selected in the range of 0.1 to 2.5 m / sec, particularly preferably 0.3 to 1.5 m / sec. Further, the spray angle of the empty cone type spray nozzle is arbitrary, and among them, the spray angle is preferably less than 180 °, and more preferably 160 ° because it is possible to efficiently suppress bubbles rising in the vacuum evaporation tower. The following is preferred. The nozzle structure of the hollow conical spray nozzle is arbitrary, and in order to obtain the effects of the present invention, it is preferable to select a nozzle that allows the spray liquid to reach the inner wall surface of the vacuum evaporation tower.
[0031]
The method for controlling the temperature of the aqueous vinyl chloride polymer dispersion to be supplied to the vacuum evaporation tower in the step (1) is optional. It is preferable to use a method of directly introducing steam having a pressure of 0.1 MPa or more into the vessel and adjusting the pressure, or using a plate-type heat exchanger. The flow rate of the aqueous vinyl chloride polymer dispersion to be supplied to the vacuum evaporation tower is preferably 0.5 to 3.0 m / sec, which is generally known as an economical pipe flow rate.
[0032]
In the method for recovering the unreacted vinyl chloride monomer of the present invention, the bottom liquid which is the aqueous dispersion of the vinyl chloride polymer obtained through the step (1) as the step (2) is placed on the top of the vacuum evaporation tower. Spray into the vacuum evaporation tower with the installed empty cone spray nozzle and spray from the top of the tower 3 to 30 times the amount of the spray liquid of the bottom liquid obtained in the step (1) Then, the bottom liquid obtained in the step (2) is circulated and re-sprayed into the vacuum evaporator at a temperature higher than the saturated steam temperature in the vacuum evaporator using an empty cone spray nozzle to recover the unreacted vinyl chloride monomer. Is performed.
[0033]
The step (2) accelerates the recovery efficiency of the unreacted vinyl chloride monomer by the wetting wall effect and the flushing, so that the bottom liquid obtained in the step (2) is introduced into the vacuum evaporation tower with saturated steam in the vacuum evaporation tower. The circulating re-spraying is performed at a flow rate of 3 to 30 times the sprayed liquid amount of the bottom liquid obtained in the step (1), which is sprayed from the top of the tower at a temperature not lower than the temperature.
[0034]
Here, in the case where the re-spraying of the bottom liquid obtained in the step (2) is not performed, the amount of the re-sprayed liquid of the bottom liquid obtained in the step (2) is sprayed from the top of the tower in the step (1). If the spray liquid temperature of the bottom liquid obtained in the step (2) is less than three times the spray liquid amount of the bottom liquid obtained, the spray liquid temperature of the re-spray of the bottom liquid is lower than the saturated steam temperature in the vacuum evaporation tower, The recovery efficiency of the reactive vinyl chloride monomer decreases. On the other hand, if the amount of the circulated respray liquid of the bottom liquid obtained in the step (2) is larger than 30 times the amount of the spray liquid of the bottom liquid obtained in the step (1) sprayed from the tower top, The equipment for recovering the reactive vinyl chloride monomer becomes large-scale, and the equipment cost increases. Further, when the aqueous dispersion of the vinyl chloride polymer staying in the vacuum evaporation tower without being circulated and re-sprayed with the bottom liquid as in the conventional method is heated by an external jacket or the like attached to the vacuum evaporation tower, the temperature is not increased. Although the recovery efficiency of the reacted vinyl chloride monomer may be apparently similar to that of the present invention, when the recovered amount of the unreacted vinyl chloride monomer increases, the foaming efficiency increases accordingly. It is difficult to suppress the generation of the foam, and problems such as the need to increase the size of the bubble separation device of the vacuum evaporation tower and the reduction of the processing speed, that is, the reduction of the recovery efficiency occur.
[0035]
In order to make the method for recovering the unreacted vinyl chloride monomer of the present invention more effective, the operating conditions of the vacuum evaporation tower were obtained by the step (1) of spraying from the top of the vacuum evaporation tower. The spraying condition of the bottom liquid is to reduce the concentration of the unreacted vinyl chloride-based monomer in the bottom liquid obtained in the step (2) of circulating and respraying to the vacuum evaporation tower and to improve the recovery efficiency. The spraying is preferably performed at a temperature 0 to 30 ° C. higher than the temperature of the saturated steam in the vacuum evaporation tower, and the temperature of the circulating respray liquid of the bottom liquid obtained in the step (2) is 0 to 30 than the temperature of the saturated steam in the vacuum evaporation tower. It is preferable to spray at a high temperature of ℃ ° C. In particular, since the aqueous dispersion of vinyl chloride polymer, which is the bottom liquid, is excellent in stability without being affected by deterioration due to heat or the like, the temperature of each spray liquid is set to a vacuum evaporation tower. Inner saturated steaming Is preferably 5 to 25 ° C. higher than the temperature. Further, the pressure in the vacuum evaporation tower in the step (2) is preferably from 50 to 300 Torr, and particularly preferably from 80 to 250 Torr.
[0036]
The spraying of the bottom liquid obtained in the step (1) in the step (2) is performed in order to suppress the foaming of the bottom liquid at the bottom of the vacuum evaporation tower caused by the spray droplets directly reaching the bottom liquid surface. The spraying of the bottom liquid from the top of the column is performed by an empty conical spray nozzle such that the outer diameter of the spray reaching the spray liquid is larger than the inner diameter of the vacuum evaporation tower, that is, spraying is performed so that the spray liquid reaches the inner wall of the vacuum evaporation tower. Is preferred. Further, in the circulation re-spraying of the bottom liquid obtained in the step (2), in order to suppress foaming of the bottom liquid at the bottom of the vacuum evaporation tower, which is induced by the spray droplets directly reaching the bottom liquid surface, It is preferable to perform the spraying so that the amount of the sprayed liquid sprayed on the liquid surface of the bottom liquid at the bottom of the vacuum evaporation tower is 40% or less of the total sprayed liquid amount, and more preferably the spraying is performed so as to be 20% or less. preferable.
[0037]
The installation position of the empty cone type spray nozzle in the vacuum evaporation tower in the step (2) in the present invention is such that the empty cone type spray nozzle for bottom liquid spraying obtained in the step (1) is at the top of the tower, and (2) An empty conical spray nozzle for circulating and re-spraying the bottom liquid obtained in the process is optional. Here, the tower top means not only the tower top but also the vicinity of the tower top. Among them, the foaming in the vacuum evaporation tower is suppressed efficiently, and the recovery method of the unreacted vinyl chloride monomer is excellent in the recovery efficiency, so that both the outer diameter of the spray liquid and the inner diameter of the vacuum evaporation tower are both larger. Preferably, it is a position. In addition, it is preferable to install an empty conical spray nozzle at the center of the cross section of the vacuum evaporation tower, since the recovery step of the unreacted vinyl chloride monomer can be designed to be more compact.
[0038]
In addition, the height of the mounting position of each of the empty cone spray nozzles is such that bubbles rising from the liquid surface of the bottom liquid at the bottom of the vacuum evaporation tower can be trapped inside the empty cone spray film, and unreacted vinyl chloride The hollow cone type spray nozzle for spraying the bottom liquid obtained in the step (1), which is installed at the top of the tower because of excellent recovery efficiency of the system monomer, is 3/4 of the length from the top of the vacuum evaporation tower to the tower length. The empty cone spray nozzle for circulating and re-spraying the bottom liquid obtained in the step (2) is preferably installed at a position between 1/4 to 3/4 of the tower length from the top of the vacuum evaporation tower. It is preferable to install at a low position. The number of empty conical spray nozzles installed at the top of the tower or used for circulation and re-spraying is not limited, and a plurality of spray nozzles can be installed, and a plurality of spray nozzles can be installed in multiple stages. The spray angle of these hollow cone spray nozzles is arbitrary, and among them, the spray angle is preferably less than 180 ° because it is possible to efficiently suppress bubbles rising in the vacuum evaporation tower. ° or less. The structure of these hollow conical spray nozzles is arbitrary, and in order to obtain the effects of the present invention, it is preferable to select a nozzle that allows the spray liquid to reach the inner wall surface of the vacuum evaporation tower.
[0039]
(2) In relation to the diameter of the vacuum evaporator in the step, the steam evaporating and rising in the vacuum evaporator and the unreacted vinyl chloride monomer are used to suppress the generation of bubbles rising in the vacuum evaporator. Is preferably selected in the range of 0.1 to 2.5 m / sec, particularly preferably 0.3 to 1.5 m / sec.
[0040]
Temperature control of the bottom liquid obtained in the step (1), which is the aqueous dispersion of the vinyl chloride polymer supplied to the vacuum evaporation tower in the step (2), and the bottom liquid obtained in the step (2), which is circulated and re-sprayed, The method is optional, and among them, a method of directly introducing steam at a pressure of 0.1 MPa or more into these vinyl chloride-based polymer aqueous dispersions in order to prevent clogging of the heater, or a plate-type heat exchanger. It is preferable to use it. In particular, when increasing the recovery efficiency of the unreacted vinyl chloride monomer, the method of adjusting the temperature of the bottom liquid obtained in the step (1) of spraying from the top of the tower is to perform recirculation spraying ( 2) It may be necessary to increase the temperature of the liquid as compared with the bottom liquid obtained in the step, and therefore it is preferable to directly adjust the temperature by introducing steam.
[0041]
The flow rate of the bottom liquid obtained in the step (1) and the bottom liquid obtained in the step (2), which is supplied to the vacuum evaporation tower in the step (2) and circulated and re-sprayed, is generally known as an economical pipe flow rate. It is preferable to supply in the range of 0.5 to 3.0 m / sec.
[0042]
In the method for recovering the unreacted vinyl chloride monomer through at least the above steps (1) and (2) of the present invention, the spraying conditions in the step (1) and the amount of the spray liquid for recirculation in the step (2) By setting the heating temperature to a predetermined condition, the rise of bubbles in the vacuum evaporation tower due to an increase in the amount of unreacted vinyl chloride-based monomer recovered is suppressed by a spray film, The feature is that the collection efficiency is improved. In this sense, the spraying conditions in the step (1) are preferably such that the amount of the sprayed liquid sprayed on the liquid surface of the bottom liquid as the aqueous vinyl chloride polymer dispersion at the bottom of the vacuum evaporation tower is small. The spraying conditions are preferably such that the flow rate of the bottom liquid obtained in the step (2) of circulating respraying is large and the spraying temperature is high.
[0043]
In the recovery method of the present invention, in each step, for example, a mist separator, a steam condenser, a water ring vacuum pump, etc., which are generally used as a device generally attached to the vacuum evaporation tower, can be used in appropriate combination. is there.
[0044]
The method of the present invention is a method for recovering an unreacted vinyl chloride-based monomer from an aqueous dispersion of a vinyl chloride-based polymer. Effects such as improvement in basic unit and improvement in environmental hygiene can be obtained.
[0045]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.
[0046]
Hereinafter, the evaluation method in the embodiment will be described in detail.
[0047]
~ Concentration of residual vinyl chloride monomer in vinyl chloride polymer aqueous dispersion ~
50 mg of the obtained aqueous dispersion of vinyl chloride polymer was collected, heated at 105 ° C. for 1 minute in a pyrolysis furnace (PYROLYZERPYR-IA, manufactured by Shimadzu Corporation), and analyzed for vinyl chloride monomer concentration by gas chromatography. Quantified. The analytically quantified vinyl chloride monomer concentration was calculated as the amount of residual vinyl chloride monomer per solid weight of the aqueous vinyl chloride polymer dispersion, and the residual vinyl chloride monomer concentration in the aqueous vinyl chloride polymer dispersion was calculated. And
[0048]
~ Bubbling when recovering unreacted vinyl chloride monomer ~
Bubbling inside was visually observed through a viewing window installed in the vacuum evaporation tower.
[0049]
Synthesis Example 1 (Preparation of aqueous dispersion of seed particles)
After charging 10800 kg of deionized water, 9000 kg of vinyl chloride monomer, 90 kg of 3,5,5-trimethylhexanoyl peroxide as a polymerization initiator, and 150 kg of a 15% by weight aqueous solution of sodium dodecylbenzenesulfonate in a polymerization vessel, 3 hours After performing homogenization treatment using a homogenizer, the temperature in the system was raised to 40 ° C. to start the polymerization reaction. After the polymerization pressure was lowered, an unreacted vinyl chloride monomer was recovered to prepare an aqueous dispersion of seed particles.
[0050]
Synthesis Example 2 (Preparation of aqueous dispersion of vinyl chloride polymer)
105,000 kg of deionized water, 12000 kg of vinyl chloride monomer, 60 kg of a 20% by weight aqueous solution of sodium dodecylbenzenesulfonate, and 1320 kg of an aqueous dispersion of seed particles obtained in Synthesis Example 1 were charged into a polymerization vessel. Was raised to 64 ° C. to initiate polymerization. From the start of the polymerization to the end of the polymerization, 480 kg of a 20% by weight aqueous solution of sodium dodecylbenzenesulfonate was continuously added.
[0051]
When the polymerization pressure dropped 0.5 MPa from the saturated vapor pressure of the vinyl chloride monomer at 64 ° C., the polymerization reaction was stopped, and 120 kg of a 20% by weight aqueous sodium dodecylbenzenesulfonate solution was added. Unreacted vinyl chloride monomer was recovered to obtain a vinyl chloride polymer aqueous dispersion for paste processing. The residual vinyl chloride monomer concentration in the obtained aqueous dispersion of vinyl chloride polymer was 1.5% by weight.
[0052]
Example 1
The aqueous vinyl chloride polymer dispersion obtained in Synthesis Example 2 was used as a step (1) by using an empty cone type spray nozzle having a spray nozzle with a spray angle of 120 ° at a height of 0.4 m from the top of the tower at the center of the tower diameter. Is sprayed continuously into the vacuum evaporation tower having a tower diameter of 0.5 m and a tower height of 1.5 m with a viewing window at a speed of 200 l / Hr by the empty conical spray nozzle. (Reached to the inner wall surface), and the unreacted vinyl chloride monomer was recovered.
[0053]
At that time, the pressure in the vacuum evaporation tower was set to 149 Torr (saturated steam temperature: 60 ° C.), and the aqueous vinyl chloride polymer dispersion obtained in Synthesis Example 2 supplied to the vacuum evaporation tower was directly supplied with 0.15 MPa steam. The temperature was adjusted to 65 ° C. by feeding.
[0054]
Subsequently, as a step (2), an empty cone type spray nozzle having a spray nozzle with a spray angle of 120 ° was installed at a height of 0.4 m from the top of the tower at the center of the tower diameter, and the tower diameter was 0.5 m, and the tower height was The bottom liquid, which is an aqueous dispersion of the vinyl chloride polymer after the unreacted vinyl chloride monomer recovery obtained in the step (1), is placed in a 1.5 m vacuum evaporation tower with a viewing window through the empty cone type spray nozzle. Spray is continuously supplied at a rate of 200 l / Hr (the spray liquid reaches the inner wall surface of the vacuum evaporator), and the bottom liquid in the vacuum evaporator is 3 m Three / Hr at a speed of 0.7 m from the top of the vacuum evaporator tower, a hollow conical spray nozzle (spray liquid reaches the inner wall surface of the vacuum evaporator tower, and the droplet distribution on the outer periphery is 60%). Unreacted vinyl chloride monomer was recovered while spraying and extracting the aqueous vinyl chloride polymer dispersion at the bottom of the vacuum evaporation tower at 200 l / Hr.
[0055]
At that time, the pressure in the vacuum evaporation tower was set to 149 Torr (saturated steam temperature: 60 ° C.), and the bottom liquid obtained in the step (1) of supplying to the vacuum evaporation tower was directly supplied with 0.15 MPa of steam to obtain 65%. ° C, and the bottom liquid obtained in the step (2) of performing the circulating re-spraying liquid was adjusted to 65 ° C by a plate-type heat exchanger.
[0056]
The residual vinyl chloride monomer concentration of the aqueous dispersion of the vinyl chloride polymer after the unreacted vinyl chloride monomer obtained through the steps (1) and (2) is recovered. Table 1 shows the state of foaming in the vacuum evaporation tower.
[0057]
Example 2
In the step (2), the amount of the circulated re-spray liquid of the bottom liquid obtained in the step (2) is 3 m. Three / Hr instead of 4m Three An unreacted vinyl chloride monomer was recovered in the same manner as in Example 1 except that the ratio of / Hr was used (the spray liquid reached the inner wall surface of the vacuum evaporation tower and the outer peripheral droplet distribution was 60%).
[0058]
The residual vinyl chloride monomer concentration of the aqueous dispersion of the vinyl chloride polymer after the unreacted vinyl chloride monomer obtained through the steps (1) and (2) is recovered. Table 1 shows the state of foaming in the vacuum evaporation tower.
[0059]
Example 3
In the step (2), the amount of the circulated re-spray liquid of the bottom liquid obtained in the step (2) is 3 m. Three / Hr instead of 1.5m Three An unreacted vinyl chloride monomer was recovered in the same manner as in Example 1 except that the ratio of / Hr was used (the spray liquid reached the inner wall surface of the vacuum evaporation tower and the outer peripheral droplet distribution was 60%).
[0060]
The residual vinyl chloride monomer concentration of the aqueous dispersion of the vinyl chloride polymer after the unreacted vinyl chloride monomer obtained through the steps (1) and (2) is recovered. Table 1 shows the state of foaming in the vacuum evaporation tower.
[0061]
Example 4
In place of the spray volume of 200 l / Hr of the aqueous vinyl chloride polymer dispersion obtained in Synthesis Example 2 in the process (1), the spray volume is set to 300 l / Hr, and the process (1) in the process (2) is performed. In the same manner as in Example 1 except that the spray liquid amount was 300 l / Hr instead of the spray liquid amount of 200 l / Hr of the bottom liquid obtained by (the spray liquid reaches the inner wall surface of the vacuum evaporation tower). The reaction vinyl chloride monomer was recovered.
[0062]
The residual vinyl chloride monomer concentration of the aqueous dispersion of the vinyl chloride polymer after the unreacted vinyl chloride monomer obtained through the steps (1) and (2) is recovered. Table 1 shows the state of foaming in the vacuum evaporation tower.
[0063]
Example 5
Example 1 except that the liquid temperature of the bottom liquid to be subjected to the circulating re-spray was set to 70 ° C. instead of the liquid temperature of the bottom liquid obtained at the step (2) of 65 ° C. The unreacted vinyl chloride monomer was recovered in the same manner as described above.
[0064]
The residual vinyl chloride monomer concentration of the aqueous dispersion of the vinyl chloride polymer after the unreacted vinyl chloride monomer obtained through the steps (1) and (2) is recovered. Table 1 shows the state of foaming in the vacuum evaporation tower.
[0065]
Example 6
Example 1 except that the liquid temperature of the bottom liquid to be circulated and re-sprayed was 75 ° C. instead of the liquid temperature of 65 ° C. of the bottom liquid obtained in the step (2). The unreacted vinyl chloride monomer was recovered in the same manner as described above.
[0066]
The residual vinyl chloride monomer concentration of the aqueous dispersion of the vinyl chloride polymer after the unreacted vinyl chloride monomer obtained through the steps (1) and (2) is recovered. Table 1 shows the state of foaming in the vacuum evaporation tower.
[0067]
Example 7
(1) The temperature of the aqueous vinyl chloride polymer dispersion was changed to 70 ° C. instead of the temperature of 65 ° C. of the aqueous vinyl chloride polymer dispersion obtained in Synthesis Example 2 sprayed into the vacuum evaporation tower in the step. In place of the bottom liquid temperature of 65 ° C. obtained in the step (1) sprayed from the top of the vacuum evaporation tower in the step (2), the liquid temperature of the bottom liquid obtained in the step (1) is changed to 70 ° C. An unreacted vinyl chloride monomer was recovered in the same manner as in Example 5 except that the reaction was carried out.
[0068]
The residual vinyl chloride monomer concentration of the aqueous dispersion of the vinyl chloride polymer after the unreacted vinyl chloride monomer obtained through the steps (1) and (2) is recovered. Table 1 shows the state of foaming in the vacuum evaporation tower.
[0069]
Example 8
In the same manner as in Example 7, except that the pressure of the vacuum evaporation tower was adjusted to 188 Torr (saturated steam temperature 65 ° C.) instead of the pressure of the vacuum evaporation tower 149 Torr (saturated steam temperature 60 ° C.) in the step (1). The vinyl monomer was recovered.
[0070]
The residual vinyl chloride monomer concentration of the aqueous dispersion of the vinyl chloride polymer after the unreacted vinyl chloride monomer obtained through the steps (1) and (2) is recovered. Table 1 shows the state of foaming in the vacuum evaporation tower.
[0071]
Example 9
In step (2), the pressure of the vacuum evaporation tower was adjusted to 188 Torr (saturated steam temperature: 65 ° C.) instead of the pressure of 149 Torr (saturated steam temperature: 60 ° C.). The vinyl monomer was recovered.
[0072]
The residual vinyl chloride monomer concentration of the aqueous dispersion of the vinyl chloride polymer after the unreacted vinyl chloride monomer obtained through the steps (1) and (2) is recovered. Table 1 shows the state of foaming in the vacuum evaporation tower.
[0073]
Comparative Example 1
Unreacted vinyl chloride monomer was not recovered in the step (2), but unreacted vinyl chloride monomer was recovered only in the step (1). The vinyl monomer was recovered.
[0074]
Table 2 shows the residual vinyl chloride monomer concentration and the foaming state of the obtained aqueous dispersion of vinyl chloride polymer after the recovery of the unreacted vinyl chloride monomer.
[0075]
The vinyl chloride monomer concentration remaining in the obtained aqueous dispersion of vinyl chloride polymer was high.
[0076]
Comparative Example 2
Except that the recirculation of the bottom liquid obtained in the step (2) was not carried out at the time of collecting the unreacted vinyl chloride monomer in the step (2), the unreacted vinyl chloride monomer was obtained in the same manner as in Example 1. The monomer was recovered.
[0077]
Table 2 shows the residual vinyl chloride monomer concentration and the foaming state of the obtained aqueous dispersion of vinyl chloride polymer after the recovery of the unreacted vinyl chloride monomer.
[0078]
When unreacted vinyl chloride monomer was recovered, no bubbling was observed in the vacuum evaporation tower, but the concentration of vinyl chloride monomer remaining in the obtained aqueous dispersion of vinyl chloride polymer was high. .
[0079]
Comparative Example 3
When the unreacted vinyl chloride monomer is recovered in the step (2), the bottom liquid obtained in the step (2) is not circulated and re-sprayed, and the temperature of the outer jacket of the vacuum evaporation tower used in the step (2) is reduced to 65. An attempt was made to recover the unreacted vinyl chloride monomer in the same manner as in Example 1 except that the operation was performed after adjusting the temperature to 0 ° C., but foaming in the vacuum evaporation tower became severe during the operation in the step (2). As a result, bubbles were scattered to the vacuum pump side, the vacuum pressure could not be adjusted to the set pressure, and the operation was stopped.
[0080]
Comparative Example 4
Example 1 Example 1 except that the liquid temperature of the bottom liquid to be circulated and re-sprayed was adjusted to 55 ° C. instead of the liquid temperature of the bottom liquid 65 ° C. obtained in the step (2). The unreacted vinyl chloride monomer was recovered in the same manner as described above.
[0081]
Table 2 shows the residual vinyl chloride monomer concentration and the foaming state of the obtained aqueous dispersion of vinyl chloride polymer after the recovery of the unreacted vinyl chloride monomer.
[0082]
No foaming was observed in the vacuum evaporation tower, but the concentration of the vinyl chloride monomer remaining in the obtained aqueous dispersion of vinyl chloride polymer was high.
[0083]
Comparative Example 5
(1) An empty cone-type spray nozzle having a spray nozzle with a spray angle of 120 ° for spraying the aqueous vinyl chloride polymer dispersion obtained in Synthesis Example 2 into the vacuum evaporation tower in the step (the spray liquid is the inner wall surface of the vacuum evaporation tower) ), Except that a fan-type spray nozzle having a spray angle of 120 ° (the spray liquid has not reached the inner wall surface of the vacuum evaporator) was installed in place of the unreacted vinyl chloride monomer in the same manner as in Example 1. However, in each process, foaming in the vacuum evaporator tower became intense from the beginning of operation and foam was scattered to the vacuum pump side, the vacuum pressure could not be adjusted to the set pressure, and the operation was stopped. did.
[0084]
Comparative Example 6
An empty cone type having a spray nozzle with a spray angle of 120 ° installed at the top of the step (2) for spraying the bottom liquid which is the aqueous vinyl chloride polymer dispersion obtained in the step (1) into the vacuum evaporation tower in the step (1) An empty cone type spray nozzle having a spray nozzle (spray liquid reaches the inner wall surface of the vacuum evaporation tower) and a spray nozzle having a spray angle of 120 ° for circulating and respraying the bottom liquid obtained in the step (2) (the spray liquid is a vacuum evaporation tower Instead of using a fan-type spray nozzle with a spray angle of 120 ° (spray liquid has not reached the inner wall surface of the vacuum evaporator) instead of spray nozzles, the same method as in Example 1 was used. An attempt was made to recover the reacted vinyl chloride monomer. However, foaming in the vacuum evaporation tower became intense from the beginning of the operation in step (2), and bubbles were scattered to the vacuum pump side, and the vacuum pressure was reduced to the set pressure. Can not be adjusted, it was discontinued operation.
[0085]
Comparative Example 7
(1) An empty cone-type spray nozzle having a spray nozzle with a spray angle of 120 ° for spraying the aqueous vinyl chloride polymer dispersion obtained in Synthesis Example 2 into the vacuum evaporation tower in the step (the spray liquid is the inner wall surface of the vacuum evaporation tower) ), But recovery of unreacted vinyl chloride monomer was attempted in the same manner as in Example 1, except that a charged conical spray nozzle having a spray angle of 120 ° was installed as the spray nozzle. Foaming in the vacuum evaporation tower became more intense, foam was scattered to the vacuum pump side, the vacuum pressure could not be adjusted to the set pressure, and the operation was stopped.
[0086]
Comparative Example 8
An empty cone type having a spray nozzle with a spray angle of 120 ° installed at the top of the step (2) for spraying the bottom liquid which is the aqueous vinyl chloride polymer dispersion obtained in the step (1) into the vacuum evaporation tower in the step (1) An empty cone type spray nozzle having a spray nozzle (spray liquid reaches the inner wall surface of the vacuum evaporation tower) and a spray nozzle having a spray angle of 120 ° for circulating and respraying the bottom liquid obtained in the step (2) (the spray liquid is a vacuum evaporation tower Instead of using an unreacted vinyl chloride monomer in the same manner as in Example 1, except that a vacuum evaporation tower equipped with a charged conical spray nozzle having a spray angle of 120 ° was used as the spray nozzle instead of the inner wall). However, during the operation in the step (2), foaming in the vacuum evaporation tower became intense during the operation in the step (2), and bubbles were scattered to the vacuum pump side, and the vacuum pressure could not be adjusted to the set pressure. It was discontinued operation.
[0087]
[Table 1]
In the method for recovering an unreacted vinyl chloride monomer of the present invention, foaming is suppressed, and the unreacted vinyl chloride monomer can be recovered stably and efficiently from an aqueous dispersion of a vinyl chloride polymer. And so on.
[Brief description of the drawings]
FIG. 1 shows an example of an apparatus for recovering unreacted vinyl chloride monomers that can be used for carrying out the present invention.
[Explanation of symbols]
1 Inlet of aqueous dispersion of vinyl chloride polymer into vacuum evaporation tower in step (1)
2 Exit of unreacted vinyl chloride monomer recovered in step (1)
3 pump
4 Vacuum evaporator in step (1)
5 (1) Vacuum evaporation tower heating device
6 Empty cone type spray nozzle
7 heat exchanger
8 Flow meter
9 Thermometer
10 Pressure gauge
11 Flow control valve
12 Circulation pump
13 Heat exchanger
14 Inlet of the bottom liquid obtained in step (1) to the vacuum evaporation tower in step (2)
15 (2) Exit of unreacted vinyl chloride monomer recovered in step
16 outlet of aqueous vinyl chloride polymer dispersion from which unreacted vinyl chloride monomer is recovered
17 (2) Process vacuum evaporation tower
18 Vacuum evaporator heating device in step (2)
19 Empty cone type spray nozzle
20 empty cone spray nozzle
21 Heat exchanger
22 Circulation line
23 Circulation pump
24 heat exchanger
25 Flow meter
26 Thermometer
27 Pressure gauge
28 flow meter
29 thermometer
30 Flow control valve
31 Flow control valve
32 Flow control valve
33 Circulation pump
34 heat exchanger
Claims (6)
（１）工程：塩化ビニル系重合体水性分散液を真空蒸発塔の塔頂部に設置した空円錐型スプレーノズルにて、その噴霧液到達外周径が真空蒸発塔内周径より大きくなるように噴霧し、未反応塩化ビニル系単量体を回収する工程
（２）工程：（１）工程により得られたボトム液を真空蒸発塔の塔頂部に設置された空円錐型スプレーノズルにて真空蒸発塔内に噴霧し、且つ該塔頂部より噴霧される（１）工程により得られたボトム液の噴霧液量に対して３〜３０倍量の流量で該（２）工程により得られるボトム液を真空蒸発塔内飽和水蒸気温度以上の温度で真空蒸発塔内へ空円錐型スプレーノズルを用いて循環再噴霧し未反応塩化ビニル系単量体を回収する工程The unreacted vinyl chloride monomer is recovered from the aqueous dispersion of the vinyl chloride polymer obtained by polymerizing the vinyl chloride monomer in an aqueous medium in the presence of a surfactant and a polymerization initiator using a vacuum evaporation tower. A method for recovering an unreacted vinyl chloride-based monomer from an aqueous dispersion of a vinyl chloride-based polymer, at least through the following steps (1) and (2).
Step (1): The aqueous dispersion of the vinyl chloride polymer is sprayed with an empty cone spray nozzle installed at the top of the vacuum evaporation tower so that the outer diameter of the spray reaches the inner diameter of the vacuum evaporation tower. Step (2) of recovering the unreacted vinyl chloride-based monomer: The bottom liquid obtained in the step (1) is vacuum-evaporated by an empty cone spray nozzle installed at the top of the vacuum evaporation tower. The bottom liquid obtained in the step (2) is sprayed at a flow rate of 3 to 30 times the sprayed liquid amount of the bottom liquid obtained in the step (1) and sprayed from the top of the tower. A process of recovering unreacted vinyl chloride monomer by circulating and re-spraying into the vacuum evaporator tower at a temperature higher than the saturated steam temperature in the evaporator tower using an empty cone spray nozzle
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007217626A (en) * | 2006-02-20 | 2007-08-30 | Tosoh Corp | Seed particle latex for seeded polymerization, and method for producing paste vinyl chloride-based resin using it |
| WO2015183006A1 (en) * | 2014-05-28 | 2015-12-03 | 주식회사 엘지화학 | Stripping apparatus |
| US10570223B2 (en) | 2014-05-28 | 2020-02-25 | Lg Chem, Ltd. | Stripping apparatus |
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2002
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007217626A (en) * | 2006-02-20 | 2007-08-30 | Tosoh Corp | Seed particle latex for seeded polymerization, and method for producing paste vinyl chloride-based resin using it |
| WO2015183006A1 (en) * | 2014-05-28 | 2015-12-03 | 주식회사 엘지화학 | Stripping apparatus |
| US10570223B2 (en) | 2014-05-28 | 2020-02-25 | Lg Chem, Ltd. | Stripping apparatus |
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| JP4120383B2 (en) | 2008-07-16 |
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