JP4042332B2

JP4042332B2 - Process for producing olefin oxide using rhenium-containing catalyst

Info

Publication number: JP4042332B2
Application number: JP2001051555A
Authority: JP
Inventors: 克己仲代
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 2001-02-27
Filing date: 2001-02-27
Publication date: 2008-02-06
Anticipated expiration: 2021-02-27
Also published as: JP2002248351A

Description

【０００１】
【発明の属する技術分野】
本発明はオレフィン、特にエチレンを気相接触酸化してオレフィンオキシドを製造する方法に関するものである。本発明によればオレフィンオキシドを長期間に亘り高選択率で製造することができる。
【０００２】
【従来の技術】
エチレンを気相接触酸化してエチレンオキシドを製造することは大規模に行われている。触媒としては銀を主体とし、これに種々の助触媒成分を添加した担体付触媒が主に用いられている。例えば特開昭４９−３０２８６号公報には、多孔性担体にカリウム、ルビジウム、セシウムなどのアルカリ金属を銀と同時に担持させた触媒が、高い選択率でエチレンオキシドを与えることが記載されている。特開昭５３−１１９１号公報には、銀にナトリウム、カリウム、ルビジウム、セシウムなどを含有させると、触媒の活性及び選択性が向上すると記載されている。アルカリ金属以外の助触媒成分としては、レニウム（特開昭６３−１２６５５２号公報）、モリブデン（特開平２−１３１１４０、２４１５４４号公報）、タングステン（特開平６−２９６８６７、３４３８６４号公報）などが知られている。
【０００３】
また、この反応を行うに際しては、原料ガス中に有機ハロゲン化合物を微量含有させるのが好ましいことが知られており、その含有量の制御方法についても種々検討されている（特開平２−１０４５７９、１０４５８０号公報）。
【０００４】
【発明が解決しようとする課題】
銀を主成分とし、これに上述した種々の助触媒成分を含有させた触媒は、いずれも使用中にその性能が漸次劣化する。公知のエチレンオキシド製造用触媒のなかでも好ましいものの一つとして知られている、銀を主成分とし、レニウム及びアルカリ金属を助触媒成分とする触媒では、この劣化傾向が特に顕著であり、使用中にそのエチレンオキシドの選択率が漸次低下する。この選択率の低下は、エチレンオキシド製造のエチレン原単位を悪化させるので、看過し得ない大きな問題である。従って本発明は、この選択率の低下を抑制して、工業的に有利にオレフィンオキシド、特にエチレンオキシドを製造する方法を提供しようとするものである。
【０００５】
【課題を解決するための手段】
本発明によれば、銀、レニウム及びアルカリ金属を担体に担持させてなる触媒に、オレフィン、酸素及び炭素数１〜３の塩素化炭化水素を含む原料ガスを接触させてオレフィンオキシドを製造する方法において、オレフィンオキシドの選択率が１週間当り０．７％以上低下したならば原料ガス中の塩素化炭化水素の濃度を、塩素分子換算で、１．５体積ｐｐｍを越えない範囲で、０．１５体積ｐｐｍ以上増加させることにより、長期間にわたり高選択率でオレフィンオキシドを製造することができる。
【０００６】
【発明の実施の形態】
本発明では、銀、レニウム及びアルカリ金属の少なくとも三者を担体に担持させた担体付触媒を用いる。担体としては、アルミナ、チタニア、ジルコニア、マグネシア、炭化ケイ素など常用の耐火性担体を用いる。なかでもアルミナ、特にα−アルミナを用いるのが好ましい。担体の比表面積は、０．１〜３．０ｍ²／ｇ、特に０．８〜１．７ｍ²／ｇであるのが好ましい。
【０００７】
銀、レニウム及びアルカリ金属の担体への担持は、常法に従って行うことができる。通常はそれぞれの成分を単独で、又は他の成分との混合溶液として担体に含浸させる。含浸の順序は任意であり、例えば先ず銀を担持させたのち、アルカリ金属及びレニウムを担持させることもできるし、銀と一緒にアルカリ金属やレニウムを担持させることもできる。好ましくは担体にアルカリ金属の溶液を含浸して乾燥させたのち、これに銀及びレニウムを担持させる。銀及びレニウムを担持させる際にアルカリ金属をもう一度担持させるのも好ましい。なお、担体にアルカリ金属の溶液を含浸させたのちの乾燥は、窒素、ヘリウム、アルゴンなどの不活性気体中で行ってもよく、また空気や過熱水蒸気中で行ってもよい。なかでも過熱水蒸気中で行うのが好ましい。乾燥は１２０〜５００℃、特に１２０〜２５０℃で行うのが好ましい。
【０００８】
アルカリ金属としてはセシウム、リチウム、ナトリウムなどのいずれを用いることもできるが、セシウム又はセシウムと他のものとを併用するのが好ましい。通常は水酸化物、ハロゲン化物、硝酸塩、酢酸塩、炭酸塩、重炭酸塩、硫酸塩などを用い、水溶液として担体に含浸させる。レニウムとしては酸化レニウムや過レニウム酸のアンモニウム塩やアルカリ金属塩などを用いればよい。銀としては、通常はアンモニアやアミノ基、カルボニル基、カルボキシル基などを有する化合物と錯体を形成して水や有機溶媒に溶解し、かつ５００℃以下の温度で分解して銀を析出する銀化合物を用いる。なかでも３００℃以下、特に２６０℃以下の温度で分解して銀を析出する銀化合物を用いるのが好ましい。例えば酸化銀、硝酸銀、炭酸銀、硫酸銀、酢酸銀、シュウ酸銀などを用いる。なかでもシュウ酸銀を用いるのが好ましい。錯体形成に用いるアミノ基を有する化合物としては、通常はピリジンや炭素数１〜６のアルキルアミンなどのモノアミン；エチレンジアミン、１，３−ジアミノプロパンなどのポリアミン；エタノールアミン、プロパノールアミンなどのアルカノールアミンなどが用いられる。なかでもエチレンジアミンや１，３−ジアミノプロパンを用いるのが好ましく、両者の混合物を用いるのがより好ましい。またカルボニル基を有する化合物としてはアセチルアセトンなどのβ−ジケトンが、カルボキシル基を有する化合物としてはネオデカン酸などがそれぞれ用いられる。
【０００９】
銀は最終的に生成する触媒の銀の含有量が５〜３０重量％となるように担体に担持させるのが好ましい。またアルカリ金属及びレニウムは、通常は最終的に生成する触媒中の含有量が、それぞれ２０〜１０，０００重量ｐｐｍ、及び１０〜５，０００重量ｐｐｍとなるように担持させる。アルカリ金属及びレニウムの好ましい担持量はそれぞれ１００〜２，０００重量ｐｐｍ及び５０〜１，０００重量ｐｐｍである。銀、レニウム及びアルカリ金属はいずれも溶液として担体に含浸させ、次いで加熱して担体に担持させるのが好ましい。この処理により銀は化合物から金属として析出して担体に担持されるが、加熱による銀の析出は、空気又は窒素、アルゴン、ヘリウムなどの不活性ガス中で１２０〜５００℃で３０分〜２４時間行えばよい。好ましくは０．３〜５ｍ／秒の過熱水蒸気の流通下に、１２０〜３００℃、特に１３０〜２６０℃で、１分〜３時間、特に３分〜３０分間加熱して析出させる。過熱水蒸気を用いると一般に性能の良好な触媒が得られるが、これは触媒中における銀、レニウム、及びアルカリ金属の分布が均一になるためと考えられる。通常は触媒成分を含浸させた担体を、固定床方式又は移動床方式の熱処理装置に収容し、床内に加熱されたガスを流通させることにより触媒の調製を行う。
【００１０】
本発明では、この担体に銀、レニウム及びアルカリ金属を担持させた触媒に、オレフィン、酸素及び微量のハロゲン化合物を含む原料ガスを接触させてオレフィンオキシドを生成させる。オレフィンとしてはブタジエンなども用い得るが通常はエチレンを用いる。エチレンを原料とする場合には、原料ガスの組成はエチレンが１〜４０体積％、酸素が１〜２０体積％であり、残部は窒素、メタンその他の希釈剤である。また、原料ガス中にはハロゲン化合物を１〜５０体積ｐｐｍ程度含有させる。ハロゲン化合物としては通常は塩素化合物、例えば塩素、塩化水素、炭素数１〜５の有機塩素化合物などが用いられる。取扱いの容易な点からして、モノクロロメタン、モノクロロエタン、１，２−ジクロロエタン、モノクロロプロパン、１，２−ジクロロプロパン、１，３−ジクロロプロパン、塩化ビニルなど、炭素数１〜３の塩素化炭化水素を用いるのが好ましい。所望ならば、これらの２種以上を併用してもよい。これらの有機塩素化合物を用いる場合には、原料ガス中のその濃度は、反応初期において０．５〜１０体積ｐｐｍ程度が好ましい。
【００１１】
反応は通常は１８０〜３５０℃、好ましくは２００〜３００℃の温度、０．１〜４ＭＰａの圧力下で行われる。原料ガスの空塔速度（ＧＨＳＶ）は、通常は０℃、１気圧で１，０００〜１０，０００ｈｒ^-1である。
銀、レニウム及びアルカリ金属を含む触媒を用いて上記の条件で反応を行わせると、エチレンオキシドの選択率は、反応開始時から次第に上昇して最高値に達する。この間は原料ガス中のハロゲン化合物の濃度は一定、好ましくは濃度変化が±０．５ｐｐｍの範囲におさまるようにするのが好ましい。エチレンオキシドの選択率が最高値に達した後は、選択率は次第に低下する。本発明では反応生成ガスを分析して選択率の低下を経時的に追跡し、選択率が１週間当り０．７％以上低下したならば、原料ガス中のハロゲン化合物の濃度をハロゲン分子換算で０．１５体積ｐｐｍ以上、好ましくは０．２５体積ｐｐｍ以上増加させる。選択率の低下が小さいうちにハロゲン化合物の濃度を増加させると、選択率が逆に低下するおそれがあるので、選択率の低下が十分に大きくなってからハロゲン化合物の濃度を増加させるのが好ましい。なお、ハロゲン分子換算で０．１５ｐｐｍ以上とは、モノクロロエタンや塩化ビニルのようなモノクロロ有機化合物であれば０．３体積ｐｐｍ以上であり、ジクロロエタンやジクロロプロパンのようなジクロロ有機化合物であれば０．１５体積ｐｐｍ以上であることを意味する。
【００１２】
エチレンオキシドの選択率に１週間当り１．０％以上、特に１．５％以上の低下が認められてからハロゲン化合物の濃度を増加させるのが好ましい。これにより低下した選択率を回復させることができる。なお、１週間当りの選択率の低下とは、エチレンオキシドの空時収率（ＳＴＹ）が一定となるように反応温度などを制御して反応を行った場合に生ずると考えられる選択率の低下であり、反応生成ガスを分析してその選択率を経時的に追跡し、その変化傾向を外挿することにより、一週間当りの選択率の低下を算出することができる。反応生成ガスの分析はガスクロマトグラフィーや質量分析計などで行えばよい。なお、分析精度の問題があるので、少なくとも２日間の分析値に基づいて１週間当りの選択率の低下を算出するのが好ましい。また、選択率の変化を追跡する途中で反応条件を変化させた場合には、経験的に求められるプラント固有の推算式に基づいて、選択率に及ぼす反応条件の変化の影響を補正すればよい。
【００１３】
本発明はエチレンからのエチレンオキシドの製造に特に好適であるが、他のオレフィン、例えばブタジエンのエポキシ化にも適用できる。
【００１４】
【実施例】
以下に実施例により本発明を更に具体的に説明する。なお、実施例で用いた触媒は下記により調製した。
触媒の調製；
α−アルミナ担体（表面積１．０４ｍ²／ｇ、吸収率３２．３％、平均細孔径１．４μｍ、シリカ含有量３．０重量％、外径８ｍｍ、内径３ｍｍ、高さ８ｍｍの筒状）９０ｇを、炭酸リチウム（Ｌｉ₂ＣＯ₃）１．４０ｇと炭酸セシウム（Ｃｓ₂ＣＯ₃）０．１２９ｇが溶解している水溶液１５０ｍＬに投入し、担体に水溶液を含浸させた。担体を取り出し、これに１５０℃の過熱水蒸気を２ｍ／秒で１５分間接触させて乾燥させた。得られた担体のリチウム含有量は５６８重量ｐｐｍであり、セシウム含有量は２２７重量ｐｐｍであった。
【００１５】
硝酸銀（ＡｇＮＯ₃）２２８ｇを１Ｌの水に溶解した水溶液と、シュウ酸カリウム（Ｋ₂Ｃ₂Ｏ₄・Ｈ₂Ｏ）１３５ｇを１Ｌの水に溶解した水溶液を調製し、両溶液を６０℃で徐々に混合してシュウ酸銀の白色沈澱を生成させた。濾過して沈澱を回収し、蒸留水で洗浄してシュウ酸銀の沈澱（Ａｇ₂Ｃ₂ Ｏ₄、含水率２１．２％）を得た。
【００１６】
エチレンジアミン２．０５ｇ、１，３−ジアミノプロパン０．５６２ｇ及び水２．６５ｇから成る混合アミン水溶液に、上記で得たシュウ酸銀の含水沈澱７．３１ｇを徐々に添加して溶解させ、銀アミン錯体溶液を調製した。これに硝酸セシウム（ＣｓＮＯ₃）の５．５４重量％水溶液０．６ｍＬ及び過レニウム酸アンモニウム（ＮＨ₄ＲｅＯ₄）の３．０５重量％水溶液０．６ｍＬを添加して、銀、レニウム及びセシウムを含む溶液を得た。この溶液をエバポレーターに入れ、これに上記で調製したリチウム及びセシウムを担持させた担体３０ｇを加え、減圧下に４０℃で保持して溶液を担体に含浸させた。次いでこの担体を取出し、これに２００℃の過熱水蒸気を２ｍ／秒で１５分間接触させて触媒を調製した。得られた触媒の銀、レニウム、セシウム及びリチウムの担持量は、それぞれ１２重量％、３７０重量ｐｐｍ、６７０重量ｐｐｍ及び４７０重量ｐｐｍであった。この触媒を破砕し、６〜１０メッシュの部分を以下の実験に用いた。
【００１７】
実施例１
内径７．５ｍｍのステンレススチール製反応管に、触媒３ｍＬを充填し、これに原料ガス（エチレン３０体積％、酸素８．５体積％、塩化ビニル１．５体積ｐｐｍ、二酸化炭素６．０体積％、残部窒素）を０℃、１気圧でのＧＨＳＶとして４３００ｈｒ^-1、圧力０．８ＭＰａで供給し、エチレンオキシドの触媒１Ｌ当りの空時収率（ＳＴＹ）が０．１９ｋｇ−エチレンオキシド／ｈｒとなるように反応温度を制御した。反応の経過に伴う反応温度、エチレンオキシドの選択率を表−１に示す。
【００１８】
なお、エチレンオキシドの選択率は４時間間隔で反応生成ガスを分析してエチレンオキシドの選択率を算出し、その１日の平均値をもってその日のエチレンオキシドの選択率とした。塩化ビニル濃度を変化させる操作はその日の分析結果がでてから行った。
【００１９】
【表１】

反応開始から約１８日でエチレンオキシドの選択率が最高値に達し、その後、選択率は低下した。２４日目から２９日目の５日間で選択率が１週間当り２．７％低下したので原料ガス中の塩化ビニル濃度を１．０体積ｐｐｍ増加させ２．５ｐｐｍとしたところ、エチレンオキシドの選択率は３４日目で８８．０％に向上した。その後、選択率がまた低下し、４４日目に１週間当りの選択率の低下が１．０％に達したことが確認されたので、原料ガス中の塩化ビニル濃度を更に０．５体積ｐｐｍ増加させて３．０体積ｐｐｍとしたところ、選択率は４８日目で８７．１％と再び向上した。その後、選択率は６２日目までゆるやかにほぼ直線的に低下したが、１週間当りの選択率の低下は約０．４％であった。この状態で原料ガス中の塩化ビニル濃度を更に０．５体積ｐｐｍ増加させて３．５体積ｐｐｍとしたところ、選択率は逆に低下しはじめた。６６日目に選択率が８３．８％まで低下したので、原料ガス中の塩化ビニル濃度を０．５体積ｐｐｍ減少させて３．０体積ｐｐｍとした。その結果、選択率は向上し、７７日目で８５．９％にまで回復した。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing an olefin oxide by gas phase catalytic oxidation of an olefin, particularly ethylene. According to the present invention, olefin oxide can be produced with high selectivity over a long period of time.
[0002]
[Prior art]
Production of ethylene oxide by vapor-phase catalytic oxidation of ethylene has been carried out on a large scale. As the catalyst, a supported catalyst is mainly used which is mainly composed of silver and to which various promoter components are added. For example, Japanese Patent Application Laid-Open No. 49-30286 describes that a catalyst in which an alkali metal such as potassium, rubidium and cesium is simultaneously supported on silver on a porous carrier gives ethylene oxide with high selectivity. Japanese Patent Application Laid-Open No. 53-1191 describes that the addition of sodium, potassium, rubidium, cesium, or the like to silver improves the activity and selectivity of the catalyst. Examples of promoter components other than alkali metals include rhenium (JP-A 63-126552), molybdenum (JP-A 2-131140, 241544), tungsten (JP-A 6-296867, 343864), and the like. It has been.
[0003]
In conducting this reaction, it is known that a trace amount of an organic halogen compound is preferably contained in the raw material gas, and various methods for controlling the content have been studied (Japanese Patent Laid-Open No. 2-104579, No. 104580).
[0004]
[Problems to be solved by the invention]
The performance of any catalyst containing silver as a main component and containing the various promoter components described above gradually deteriorates during use. This deterioration tendency is particularly remarkable in a catalyst having silver as a main component and rhenium and an alkali metal as a promoter component, which is known as one of preferable catalysts for producing ethylene oxide. The ethylene oxide selectivity gradually decreases. This decrease in selectivity is a serious problem that cannot be overlooked because it deteriorates the ethylene basic unit of ethylene oxide production. Accordingly, the present invention aims to provide a method for producing olefin oxide, particularly ethylene oxide, in an industrially advantageous manner while suppressing the decrease in selectivity.
[0005]
[Means for Solving the Problems]
According to the present invention, a method for producing an olefin oxide by bringing a raw material gas containing olefin, oxygen, and a chlorinated hydrocarbon having 1 to 3 carbon atoms into contact with a catalyst in which silver, rhenium and an alkali metal are supported on a carrier. In this case, if the selectivity of olefin oxide is reduced by 0.7% or more per week, the concentration of chlorinated hydrocarbon in the raw material gas is within a range not exceeding 1.5 vol ppm in terms of chlorine molecules. By increasing it by 15 ppm by volume or more, it is possible to produce olefin oxide with high selectivity over a long period of time.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a supported catalyst in which at least three of silver, rhenium and alkali metal are supported on a support is used. As the carrier, a conventional refractory carrier such as alumina, titania, zirconia, magnesia or silicon carbide is used. Among these, alumina, particularly α-alumina is preferably used. The specific surface area of the carrier is preferably from 0.1 to 3.0 m ² / g, particularly preferably from 0.8 to 1.7 m ² / g.
[0007]
Supporting silver, rhenium and alkali metal on a carrier can be carried out according to a conventional method. Usually, the carrier is impregnated with each component alone or as a mixed solution with other components. The order of impregnation is arbitrary. For example, after silver is first supported, alkali metal and rhenium can be supported, or alkali metal and rhenium can be supported together with silver. Preferably, the support is impregnated with an alkali metal solution and dried, and then silver and rhenium are supported thereon. It is also preferable to support the alkali metal once more when supporting silver and rhenium. The drying after impregnating the support with the alkali metal solution may be performed in an inert gas such as nitrogen, helium, or argon, or may be performed in air or superheated steam. Among these, it is preferable to carry out in superheated steam. Drying is preferably performed at 120 to 500 ° C, particularly 120 to 250 ° C.
[0008]
As the alkali metal, any of cesium, lithium, sodium and the like can be used, but it is preferable to use cesium or cesium in combination with another. Usually, hydroxides, halides, nitrates, acetates, carbonates, bicarbonates, sulfates, etc. are used, and the support is impregnated as an aqueous solution. As rhenium, an ammonium salt or alkali metal salt of rhenium oxide or perrhenic acid may be used. Silver is usually a silver compound that forms a complex with a compound having ammonia, an amino group, a carbonyl group, a carboxyl group, etc., dissolves in water or an organic solvent, and decomposes at a temperature of 500 ° C. or lower to precipitate silver. Is used. Among them, it is preferable to use a silver compound that decomposes at a temperature of 300 ° C. or lower, particularly 260 ° C. or lower to precipitate silver. For example, silver oxide, silver nitrate, silver carbonate, silver sulfate, silver acetate, silver oxalate, or the like is used. Of these, silver oxalate is preferably used. The compound having an amino group used for complex formation is usually a monoamine such as pyridine or an alkylamine having 1 to 6 carbon atoms; a polyamine such as ethylenediamine or 1,3-diaminopropane; an alkanolamine such as ethanolamine or propanolamine. Is used. Of these, ethylenediamine and 1,3-diaminopropane are preferably used, and a mixture of both is more preferably used. Further, β-diketone such as acetylacetone is used as the compound having a carbonyl group, and neodecanoic acid is used as the compound having a carboxyl group.
[0009]
Silver is preferably supported on the support so that the silver content of the finally produced catalyst is 5 to 30% by weight. Further, the alkali metal and rhenium are usually supported so that the content in the finally produced catalyst is 20 to 10,000 ppm by weight and 10 to 5,000 ppm by weight, respectively. The preferred loadings of alkali metal and rhenium are 100 to 2,000 ppm by weight and 50 to 1,000 ppm by weight, respectively. It is preferable that silver, rhenium and alkali metal are all impregnated on the support as a solution and then heated to be supported on the support. Silver is precipitated from the compound as a metal by this treatment and is supported on the support. However, the silver deposition by heating is performed at 120 to 500 ° C. for 30 minutes to 24 hours in air or an inert gas such as nitrogen, argon or helium. Just do it. Precipitation is preferably performed by heating at 120 to 300 ° C., particularly 130 to 260 ° C. for 1 minute to 3 hours, particularly 3 minutes to 30 minutes, under a flow of superheated steam at 0.3 to 5 m / second. When superheated steam is used, a catalyst with good performance is generally obtained. This is considered to be due to the uniform distribution of silver, rhenium, and alkali metal in the catalyst. Usually, a catalyst impregnated with a catalyst component is accommodated in a heat treatment apparatus of a fixed bed type or a moving bed type, and a catalyst is prepared by circulating a heated gas in the bed.
[0010]
In the present invention, a catalyst in which silver, rhenium, and an alkali metal are supported on this carrier is brought into contact with a raw material gas containing olefin, oxygen, and a trace amount of a halogen compound to generate olefin oxide. As the olefin, butadiene or the like can be used, but usually ethylene is used. When ethylene is used as a raw material, the composition of the raw material gas is 1 to 40% by volume of ethylene and 1 to 20% by volume of oxygen, and the balance is nitrogen, methane or other diluents. Moreover, about 1-50 volume ppm of halogen compounds are contained in source gas. As the halogen compound, a chlorine compound such as chlorine, hydrogen chloride, or an organic chlorine compound having 1 to 5 carbon atoms is usually used. Chlorination of 1 to 3 carbon atoms such as monochloromethane, monochloroethane, 1,2-dichloroethane, monochloropropane, 1,2-dichloropropane, 1,3-dichloropropane, vinyl chloride from the viewpoint of easy handling It is preferred to use hydrocarbons. If desired, two or more of these may be used in combination. When these organochlorine compounds are used, the concentration in the raw material gas is preferably about 0.5 to 10 ppm by volume at the beginning of the reaction.
[0011]
The reaction is usually carried out at a temperature of 180 to 350 ° C., preferably 200 to 300 ° C. and a pressure of 0.1 to 4 MPa. The superficial velocity (GHSV) of the source gas is usually 1,000 to 10,000 hr ⁻¹ at 0 ° C. and 1 atm.
When the reaction is carried out under the above conditions using a catalyst containing silver, rhenium and an alkali metal, the selectivity for ethylene oxide gradually increases from the start of the reaction and reaches a maximum value. During this time, the concentration of the halogen compound in the raw material gas is constant, and preferably the concentration change is within the range of ± 0.5 ppm. After the ethylene oxide selectivity reaches a maximum value, the selectivity gradually decreases. In the present invention, the reaction product gas is analyzed to monitor the decrease in selectivity over time, and if the selectivity decreases by 0.7% or more per week, the concentration of the halogen compound in the raw material gas is converted into halogen molecule. Increase by 0.15 ppm by volume or more, preferably by 0.25 ppm by volume or more. If the concentration of the halogen compound is increased while the decrease in the selectivity is small, the selectivity may decrease. Therefore, it is preferable to increase the concentration of the halogen compound after the decrease in the selectivity is sufficiently large. . Note that 0.15 ppm or more in terms of halogen molecule is 0.3 ppm by volume or more for monochloro organic compounds such as monochloroethane and vinyl chloride, and 0 for dichloro organic compounds such as dichloroethane and dichloropropane. .Meaning 15 volume ppm or more.
[0012]
It is preferable to increase the concentration of the halogen compound after a decrease of 1.0% or more, particularly 1.5% or more, is observed in the selectivity of ethylene oxide per week. Thereby, the lowered selectivity can be recovered. The decrease in selectivity per week is a decrease in selectivity that is considered to occur when the reaction is carried out by controlling the reaction temperature so that the space-time yield (STY) of ethylene oxide is constant. Yes, the selectivity reduction per week can be calculated by analyzing the reaction product gas, tracking its selectivity over time, and extrapolating its change tendency. The analysis of the reaction product gas may be performed by gas chromatography, a mass spectrometer or the like. Since there is a problem of analysis accuracy, it is preferable to calculate a decrease in selectivity per week based on at least two days of analysis values. In addition, when the reaction conditions are changed in the course of tracking the change in the selectivity, the influence of the change in the reaction conditions on the selectivity may be corrected based on an empirically obtained plant-specific estimation formula. .
[0013]
The invention is particularly suitable for the production of ethylene oxide from ethylene, but can also be applied to the epoxidation of other olefins such as butadiene.
[0014]
【Example】
The present invention will be described more specifically with reference to the following examples. The catalyst used in the examples was prepared as follows.
Preparation of the catalyst;
α-alumina support (surface area 1.04 m ² / g, absorption rate 32.3%, average pore diameter 1.4 μm, silica content 3.0 wt%, outer diameter 8 mm, inner diameter 3 mm, height 8 mm) 90 g was put into 150 mL of an aqueous solution in which 1.40 g of lithium carbonate (Li ₂ CO ₃ ) and 0.129 g of cesium carbonate (Cs ₂ CO ₃ ) were dissolved, and the support was impregnated with the aqueous solution. The carrier was taken out and dried by contacting with 150 ° C. superheated steam at 2 m / second for 15 minutes. The obtained carrier had a lithium content of 568 ppm by weight and a cesium content of 227 ppm by weight.
[0015]
An aqueous solution in which 228 g of silver nitrate (AgNO ₃ ) was dissolved in 1 L of water and an aqueous solution in which 135 g of potassium oxalate (K ₂ C ₂ O ₄ .H ₂ O) were dissolved in 1 L of water were prepared. Mixing slowly produced a white precipitate of silver oxalate. The precipitate was collected by filtration and washed with distilled water to obtain a silver oxalate precipitate (Ag ₂ C ₂ O ₄ , water content 21.2%).
[0016]
To a mixed amine aqueous solution composed of 2.05 g of ethylenediamine, 0.562 g of 1,3-diaminopropane and 2.65 g of water, 7.31 g of the hydrous precipitate of silver oxalate obtained above was gradually added and dissolved to obtain a silver amine. A complex solution was prepared. To this, 0.6 mL of a 5.54 wt% aqueous solution of cesium nitrate (CsNO ₃ ) and 0.6 mL of a 3.05 wt% aqueous solution of ammonium perrhenate (NH ₄ ReO ₄ ) were added, and silver, rhenium and cesium were added. A solution containing was obtained. This solution was put in an evaporator, and 30 g of the carrier carrying lithium and cesium prepared above was added thereto, and kept at 40 ° C. under reduced pressure to impregnate the carrier with the solution. Next, this support was taken out and contacted with 200 ° C. superheated steam at 2 m / second for 15 minutes to prepare a catalyst. The supported amounts of silver, rhenium, cesium and lithium in the obtained catalyst were 12 wt%, 370 wt ppm, 670 wt ppm and 470 wt ppm, respectively. The catalyst was crushed and the 6-10 mesh portion was used for the following experiments.
[0017]
Example 1
A reaction tube made of stainless steel with an inner diameter of 7.5 mm is filled with 3 mL of catalyst, and raw material gas (ethylene 30 vol%, oxygen 8.5 vol%, vinyl chloride 1.5 vol ppm, carbon dioxide 6.0 vol%). The remaining nitrogen) is supplied as GHSV at 0 ° C. and 1 atm at 4300 hr ⁻¹ and at a pressure of 0.8 MPa, so that the space-time yield (STY) per liter of the ethylene oxide catalyst is 0.19 kg-ethylene oxide / hr. The reaction temperature was controlled. Table 1 shows the reaction temperature and the selectivity of ethylene oxide as the reaction progresses.
[0018]
The ethylene oxide selectivity was calculated by analyzing the reaction product gas at 4-hour intervals to calculate the ethylene oxide selectivity, and the average value for the day was taken as the ethylene oxide selectivity for the day. The operation of changing the vinyl chloride concentration was performed after the analysis result of the day.
[0019]
[Table 1]

About 18 days after the start of the reaction, the selectivity of ethylene oxide reached the maximum value, and then the selectivity decreased. Since the selectivity decreased by 2.7% per week for 5 days from the 24th day to the 29th day, the vinyl chloride concentration in the raw material gas was increased by 1.0 volume ppm to 2.5 ppm. Increased to 88.0% on the 34th day. After that, the selectivity decreased again, and it was confirmed that the decrease in selectivity per week reached 1.0% on the 44th day, so that the vinyl chloride concentration in the raw material gas was further reduced to 0.5 ppm by volume. When the volume was increased to 3.0 ppm by volume, the selectivity improved again to 87.1% on the 48th day. Thereafter, the selectivity gradually decreased almost linearly until the 62nd day, but the decrease in selectivity per week was about 0.4%. In this state, when the vinyl chloride concentration in the raw material gas was further increased by 0.5 volume ppm to 3.5 volume ppm, the selectivity began to decrease conversely. Since the selectivity decreased to 83.8% on the 66th day, the vinyl chloride concentration in the raw material gas was reduced by 0.5 volume ppm to 3.0 volume ppm. As a result, the selectivity improved and recovered to 85.9% on the 77th day.

Claims

Selection of olefin oxide in a method for producing olefin oxide by contacting a raw material gas containing olefin, oxygen and chlorinated hydrocarbons having 1 to 3 carbon atoms with a catalyst in which silver, rhenium and an alkali metal are supported on a carrier if the rate is decreased by more than 0.7% per week, the concentration of chlorinated hydrocarbons in the feed gas, chlorine molecules terms, without exceeding the 1.5 ppm by volume, 0.15 ppm by volume or more increased A process for producing an olefin oxide, characterized by comprising:

The chlorinated hydrocarbon concentration in the raw material gas is increased by 0.15 vol ppm or more in terms of chlorine molecules if the selectivity of olefin oxide is reduced by 1.0% or more per week. The manufacturing method of olefin oxide of description.

The chlorinated hydrocarbon concentration in the raw material gas is increased by 0.15 vol ppm or more in terms of chlorine molecules if the selectivity of olefin oxide is reduced by 1.5% or more per week. The manufacturing method of olefin oxide of description.

The selectivity of olefin oxide is traced over two days or more, and the decrease in selectivity per week is calculated by extrapolating the decrease in selectivity. A method for producing olefin oxide.

The olefin oxide according to any one of claims 1 to 4, wherein the catalyst is obtained by supporting silver, rhenium and an alkali metal on a support having a specific surface area of 0.8 to 1.7 m ² / g. Manufacturing method.

The olefin oxide according to any one of claims 1 to 5, wherein the catalyst is produced through a step of supporting an alkali metal on a carrier and then supporting silver, rhenium and an alkali metal. Production method.

The chlorinated hydrocarbon concentration in the raw material gas is increased by 0.25 volume ppm or more in terms of chlorine molecules if the selectivity of olefin oxide per week decreases by a predetermined value or more. 7. The method for producing an olefin oxide according to any one of items 6 to 6.