張振華,王 博,秦 越,馬 輝,呂 劍
(西安近代化學(xué)研究所,陜西 西安 710065)
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綜述與展望
氣相催化合成氫氟烴和氫氟烯烴催化劑研究進(jìn)展
張振華,王博,秦越,馬輝,呂劍*
(西安近代化學(xué)研究所,陜西 西安 710065)
摘要:隨著氯氟烴(CFCs)制冷劑逐步被淘汰,市場(chǎng)上使用的制冷劑主要是以氫氟烴(HFCs)和氫氟烯烴(HFOs)為主要成分的單一或混合產(chǎn)品,氣相催化法具有可連續(xù)操作和催化劑與產(chǎn)品易于分離等特點(diǎn),是工業(yè)合成氫氟烴和氫氟烯烴的主要方法。介紹了氟氯交換反應(yīng)、加氫脫氯反應(yīng)和脫鹵化氫反應(yīng)等常見(jiàn)的氣相催化合成氫氟烴和氫氟烯烴的反應(yīng)類(lèi)型,概括其反應(yīng)原理以及影響催化劑活性的主要因素,并綜述了氣相催化劑在氫氟烴和氫氟烯烴合成中的應(yīng)用,建議開(kāi)發(fā)高活性的低溫、無(wú)鉻或低鉻催化劑。
關(guān)鍵詞:有機(jī)化學(xué)工程;氣相催化;氫氟烴;氫氟烯烴;氣相催化劑
CLC number:TQ222.4+23;TQ426.94Document code: AArticle ID: 1008-1143(2016)05-0008-05
氟利昂曾長(zhǎng)期作為制冷劑在我國(guó)制冷工業(yè)領(lǐng)域發(fā)揮重要作用,但該類(lèi)物質(zhì)對(duì)臭氧層破壞大,是引起氣候變暖的主要因素之一。氫氟烴和氫氟烯烴類(lèi)制冷劑溫室效應(yīng)潛值低,是理想的氟利昂替代品,目前市場(chǎng)上使用的制冷劑產(chǎn)品主要是以氫氟烴和氫氟烯烴為主要成分的單一或混合產(chǎn)品。氣相催化是工業(yè)合成氫氟烴和氫氟烯烴的主要方法,具有可連續(xù)操作和催化劑與產(chǎn)品易于分離等特點(diǎn)[1-3]。
合成氫氟烴和氫氟烯烴的主要反應(yīng)類(lèi)型有氟氯交換法、脫鹵化氫法、加氫脫氯法和異構(gòu)化反應(yīng)等[4-6]。本文對(duì)合成氫氟烴和氫氟烯烴常見(jiàn)的幾種反應(yīng)類(lèi)型所用催化劑進(jìn)行綜述,以期對(duì)氫氟烴和氫氟烯烴合成中催化劑的研究開(kāi)發(fā)有所借鑒。
1氣相氟氯交換反應(yīng)
氣相氟氯交換反應(yīng)是典型的親核取代反應(yīng),一般采用HF為氟源。氟氯交換反應(yīng)機(jī)理及其影響因素是催化劑制備的理論基礎(chǔ),對(duì)催化劑活性物種的選擇、助劑的添加以及催化劑活化方法等有很好的指導(dǎo)意義,一直是研究的重點(diǎn)。
相關(guān)研究表明,只有催化劑表面具有特殊的缺陷構(gòu)型才能顯示其氟氯交換活性,而這種構(gòu)型與催化劑表面L酸性位點(diǎn)和不穩(wěn)定鹵素原子的存在相關(guān)[7],例如以L(fǎng)酸性較強(qiáng)的AlF3為催化劑,發(fā)生如下反應(yīng):
(1)
(2)
Lee Hyunjoo等[8]在Cr-Mg催化劑存在下,以1-氯-2,2,2-三氟乙烷(HCFC-133a)氟化制備1,1,1,2-四氟乙烷(HFC-134a)為研究對(duì)象,通過(guò)嘧啶吸附實(shí)驗(yàn)驗(yàn)證此催化劑擁有L酸性位點(diǎn),在催化劑失活過(guò)程中催化劑酸性逐漸減弱,當(dāng)催化劑經(jīng)堿金屬鹽LiCl和KF浸泡后,催化活性大大降低,表明氟氯交換活性中心是L酸性位點(diǎn)。Kemnitz E等[9]用鎂逐步代替鋁研究催化劑AlF3-x(OH)x在氟氯交換反應(yīng)中的活性,結(jié)果表明,在鎂添加量為10%時(shí),催化劑活性最高,繼續(xù)提高鎂含量,由于L酸性減弱,催化劑活性越來(lái)越差。
Chung Y S等[10]研究表明,氟氯交換反應(yīng)的關(guān)鍵在于非穩(wěn)態(tài)F-的存在,在以HF為氟源的氟氯交換反應(yīng)中,首先HF分子化學(xué)吸附在催化劑表面的電子空缺位點(diǎn)上,催化劑的電子云向HF分子方向轉(zhuǎn)移,使H—F鍵斷裂,形成催化劑表面的不穩(wěn)定氟離子。
Scott J D等[11]采用浸漬法制備Zn/Al2O3催化劑,用于HCFC-133a與氟化氫氣相氟氯交換生成HFC-134a的反應(yīng),并添加Ni、Co、Mn和Fe等助劑考察催化劑活性,結(jié)果表明,添加Fe后催化劑活性最高,且有益于催化劑再生。Elsheikh M Y等[12]以1-氯-1,1-二氟乙烷(HCFC-142b)與HF取代生成1,1,1-三氟乙烷(HFC-143a)為探針?lè)磻?yīng),選用Sb/C為催化劑,在反應(yīng)溫度100℃,接觸時(shí)間(26~32) s和n(HF)∶n(HCFC-142b)=1.15~2條件下,HFC-142b轉(zhuǎn)化率大于99.9%,HFC-143a選擇性為100%;對(duì)此催化劑進(jìn)行壽命實(shí)驗(yàn),結(jié)果顯示,運(yùn)行330 h后,HCFC-142b轉(zhuǎn)化率仍大于99%,HFC-143a選擇性為100%,表明該催化劑對(duì)氣相氟氯交換反應(yīng)合成HFC-134a具有高的活性。Elsheikh M Y等[13]還以HF處理的活性炭為載體,浸漬法制備SbCl5/AC催化劑,在反應(yīng)溫度110℃、n(HF)∶n(HCFC-142b)=7.9和接觸時(shí)間3.5 s條件下,HCFC-142b轉(zhuǎn)化率90%,HFC-143a選擇性100%。Elsheikh M Y等[14]還研究了以SnCl4/C為催化劑氣相氟化1,1-二氯乙烷合成1,1-二氟乙烷(HFC-152a)反應(yīng),在75℃和n(HF)∶n(CH3CHCl2)=2條件下,CH3CHCl2轉(zhuǎn)化率為78.3%,HFC-152a選擇性為74.5%。
Yasuo H等[15-16]對(duì)氣相催化氟化1,1,1,3,3-五氯丙烷合成HFC-245fa進(jìn)行研究,以活性炭為載體,分別制備了以Ti、Mo、Sn、Nb、Ta和Sb為活性組分的催化劑用于此反應(yīng),發(fā)現(xiàn)在最佳反應(yīng)條件下,Sb/C催化劑催化活性最高,1,1,1,3,3-五氯丙烷轉(zhuǎn)化率為91.6%,HFC-245fa選擇性80.1%。
王博[17]以自制CaF2為載體,通過(guò)浸漬法制備以Cu、Ni、Fe和Cr等為活性組分的11種催化劑,以HCFC-1233zd與HF氣相氟化制備HFO-1234ze為探針?lè)磻?yīng),對(duì)制備的催化劑進(jìn)行評(píng)價(jià),結(jié)果表明,以Fe為活性組分的催化劑活性最高,反應(yīng)產(chǎn)物中HFO-1234ze質(zhì)量分?jǐn)?shù)達(dá)27.8%,其次是添加Cr和Zn的催化劑活性較高,反應(yīng)產(chǎn)物中HFO-1234ze質(zhì)量分?jǐn)?shù)分別達(dá)15.9%和15.2%,而負(fù)載Co、Ag和Zr等的催化劑活性較差。
2加氫脫氯反應(yīng)
加氫脫氯反應(yīng)是在催化條件下將含氯有機(jī)物分子中氯原子脫去并引入氫原子,把對(duì)環(huán)境有害的含氯有機(jī)物轉(zhuǎn)化為不含氯或低氯的產(chǎn)物,該方法可以將含氯烯烴轉(zhuǎn)化為氫氟烯烴或?qū)⒙确鸁N轉(zhuǎn)化為合成氫氟烯烴的中間體等。
加氫脫氯反應(yīng)常見(jiàn)的催化劑活性組分有Pt、Pd、Ir和Rh等,Makkee M等[18]制備一系列活性炭負(fù)載型貴金屬催化劑用于CCl2F2(CFC-12)加氫脫氯制備CH2F2(HFC-32),結(jié)果表明,負(fù)載Pd的催化劑催化性能最好。
Coq B等[19-20]分別研究了金屬氧化物和氟化物負(fù)載的Pd催化劑對(duì)CCl2F2加氫脫氯反應(yīng)的催化性能,結(jié)果表明,以金屬氟化物為載體,催化性能明顯優(yōu)于金屬氧化物,認(rèn)為金屬氧化物載體可與HCl等反應(yīng),水的生成逐漸降低催化劑活性,而金屬氟化物載體具有吸電子效應(yīng)改變了Pd原子d電子云密度,利于氟化卡賓脫附,使催化劑表面反應(yīng)副產(chǎn)物減少,提高了目標(biāo)產(chǎn)物選擇性。研究表明[21-22],金屬氟化物在酸性介質(zhì)中是一種相對(duì)穩(wěn)定的載體,以金屬氧化物為載體,隨著加氫脫氯產(chǎn)生的Cl、F離子進(jìn)入載體相,氧化物載體表面積減小,引起活性組分團(tuán)聚,催化劑逐漸失活。
朱偉東等[23]報(bào)道了一種HFC-12加氫脫氯制備HFC-32的方法,以Pd為活性組分,Bi為助劑,活性炭為載體,采用浸漬法制備催化劑,在最優(yōu)條件下,HFC-12轉(zhuǎn)化率大于90%,HFC-32選擇性大于80%,催化劑壽命超過(guò)1 200 h。
一些助劑可以與Pd原子相互作用改變其原子外層電子云密度,有利于卡賓基團(tuán)的脫附,提高目標(biāo)產(chǎn)物選擇性。Morikawa S等[24]提出添加鑭、鑭系稀土金屬和錸作為助劑對(duì)Pd/C進(jìn)行改性,可以提高催化劑的活性和穩(wěn)定性。
Malinowski Artur等[25]研究了MgF2負(fù)載Pd和Ru催化劑對(duì)CCl2F2的加氫脫氯作用,實(shí)驗(yàn)結(jié)果表明,Pd在此加氫脫氯反應(yīng)中顯示出較好的活性,在Pd/MgF2中添加Au后,CH2F2選擇性由72%提高至86%。
納帕 M J等[26]報(bào)道了以2,3-二氯-1,1,1,4,4,4-六氟-2-丁烯(CFC-1316mxx)加氫脫氯生成1,1,1,4,4,4-六氟-2-丁烯(HFC-1336mzz)的方法,催化劑為酸洗過(guò)的炭或氟化鈣負(fù)載的Cu、Ni、Cr及混合金屬組分,以酸洗過(guò)的活性炭負(fù)載CuNi合金作為催化劑,在350℃、接觸時(shí)間30 s、H2與CFC-1316mxx物質(zhì)的量比為7.5∶1條件下,CFC-1316mxx轉(zhuǎn)化率達(dá)100%,HFC-1336mzz選擇性為66.84%。
3脫鹵化氫反應(yīng)
鹵代烷烴脫鹵化氫反應(yīng)生成含氟烯烴屬于β-脫去反應(yīng),鹵代烷烴消去反應(yīng)有E1、E1cB和E2三種機(jī)理[27-28]:
鹵化烷烴脫鹵化氫是制備含氟烯烴的常用方法,氣相催化脫鹵化烴具有工藝簡(jiǎn)單和目標(biāo)產(chǎn)物選擇性高等優(yōu)點(diǎn),工業(yè)應(yīng)用最為廣泛,催化劑的應(yīng)用在氣相催化中具有核心地位,目前文獻(xiàn)報(bào)道的催化劑多為金屬催化劑,一般將其負(fù)載在活性炭或氧化鋁等載體上,這些載體對(duì)某些反應(yīng)活性較高,也可以單獨(dú)作為催化劑使用。某些金屬氟化物催化劑具有較好的脫鹵化氫活性,Li、Mg等堿金屬和堿土金屬氟化物催化劑具有較好的脫HCl性能,而Al、Cr等3價(jià)或高價(jià)金屬氟化物催化劑則更易脫HF[29-33]。
Miller R N等[34]研究了單獨(dú)采用活性炭催化1,1,1,3,3-五氟丙烷(HFC-245fa)氣相脫HF制備1,1,1,3-四氟丙烯(HFO-1234ze)的反應(yīng),在最佳反應(yīng)條件下,HFC-245fa轉(zhuǎn)化率為38%,HFO-1234ze選擇性達(dá)96%。Mukhopadhyay S等[35]比較了未處理活性炭和酸洗后活性炭對(duì)HFC-245fa脫HF制備HFO-1234ze的催化性能,在最佳反應(yīng)條件下,酸洗處理可使活性炭的活性由88%提高至100%。
Sakyu F等[36]用活性炭浸漬法制備了系列金屬催化劑,經(jīng)HF氣體處理后,用于HFC-245fa脫HF制備HFO-1234ze,在反應(yīng)溫度350℃時(shí),各催化劑對(duì)HFO-1234ze選擇性均大于96%,其中,5%MoCl5/AC顯示出較好的催化性能,轉(zhuǎn)化率達(dá)58%。
Tung H S等[37]采用活性炭負(fù)載FeCl3為催化劑,HFC-245fa氣相脫HF制備HFO-1234ze,HFC-245fa轉(zhuǎn)化率為85.0%,HFO-1234ze選擇性為95.0%。
Puy M V D等[38]以氟化的Zr/Al2O3為催化劑用于HFC-245fa脫HF制備HFO-1234ze,在反應(yīng)溫度300℃時(shí),HFC-245fa轉(zhuǎn)化率和HFO-1234ze選擇性大于94%。
Miller R N等[39]用氟化后的氧化鋁催化HFC-245fa脫HF制備HFO-1234ze,在反應(yīng)溫度375℃和接觸時(shí)間30 s條件下,HFC-245fa轉(zhuǎn)化率為84.8%,目標(biāo)產(chǎn)物HFO-1234ze選擇性98.5%。
Wang H等[40]制備了一系列金屬氟化物催化劑用于HCFC-244fa脫鹵化氫反應(yīng),結(jié)果表明,LiF和MgF2等堿金屬或堿土金屬催化劑具有較好的脫HCl性能,而AlF3等3價(jià)金屬氟化物催化劑更適合脫HF反應(yīng),具有更高活性。
Mukhopadhyay S等[41]考察了3種類(lèi)型活性炭及其負(fù)載的鈀和鉑催化劑對(duì)1,1,1,2,2-五氟丙烷(HFC-245cb)氣相脫HF制備HFO-1234yf的催化活性,負(fù)載貴金屬后,催化劑反應(yīng)活性提高,但HFO-1234yf選擇性下降。
Miller R N等[42]報(bào)道了以活性炭為催化劑,在反應(yīng)溫度400℃和接觸時(shí)間120 s時(shí),HFC-245cb轉(zhuǎn)化率為23.6%,HFO-1234yf選擇性高達(dá)97%。
Tung Hsuehsung等[43]研究了以1-氯-3,3,3-三氟丙烯(HCFC-1233zd)為原料兩步氣相反應(yīng)合成HFO-1234ze的方法,首先將HCFC-1233zd與HF反應(yīng)生成1-氯-1,3,3,3-四氟丙烷(HCFC-244fa)和HFC-245fa,然后將兩種產(chǎn)物分離后分別脫HCl和HF得目標(biāo)產(chǎn)物,其中,脫鹵化氫優(yōu)選的催化劑有負(fù)載或本體的FeCl3、NiCl2和CoCl2等,其中以負(fù)載在活性炭上的FeCl3為催化劑,在反應(yīng)溫度250℃時(shí),HCFC-244fa脫HCl,HFO-1234ze選擇性為98.0%,HCFC-244fa單程轉(zhuǎn)化率為95.0%;同樣條件下,HFC-245fa脫HF,HFO-1234ze選擇性及HCFC-244fa單程轉(zhuǎn)化率分別為95%和85%,表明HCFC-244fa較易脫HCl制備HFO-1234ze。
Wang H等[44]以MgF2為催化劑,對(duì)HCFC-244bb進(jìn)行脫HCl反應(yīng)合成HFO-1234yf,并考察添加Cs、Fe和Co等一系列助催化劑對(duì)催化劑性能的影響,結(jié)果表明,添加10%的Cs可使催化劑對(duì)HFO-1234yf選擇性由86%提高到97%。
4結(jié)語(yǔ)
工業(yè)上氣相催化合成氫氟烴和氫氟烯烴工藝比較成熟,各類(lèi)催化劑應(yīng)用也較穩(wěn)定,但仍有許多不足之處,例如一些加氫脫氯催化劑活性組分容易流失,需要改進(jìn)制備方法,氟氯交換和脫鹵化氫反應(yīng)一般反應(yīng)溫度較高,催化劑容易結(jié)焦失活,需要開(kāi)發(fā)低溫高活性催化劑,延長(zhǎng)催化劑壽命。目前工業(yè)上氟氯交換和脫鹵化氫反應(yīng)使用的催化劑多為含鉻催化劑,帶來(lái)諸多環(huán)境問(wèn)題,因此,開(kāi)發(fā)高活性無(wú)鉻催化劑是該領(lǐng)域今后研究的熱點(diǎn)。
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Research advance in the catalysts for gas phase catalytic synthesis of hydrofluorocarbons and hydrofluoroolefins
Zhang Zhenhua, Wang Bo, Qin Yue, Ma Hui, Lü Jian*
(Xi’an Modern Chemistry Research Institute,Xi’an 710065, Shaanxi, China)
Abstract:With gradually elimination of chlorofluorocarbons(CFCs) as refrigerants,the refrigerants used in the market are the single or mixed products with hydrofluorocarbons(HFCs) and hydrofluoroolefins(HFOs) as the main components.The gas phase catalytic synthesis,which has the advantages of continuous operation and easy separation of the catalyst from the product,is the main method for the synthesis of HFCs and HFOs.The common reaction types for gas phase catalytic synthesis of hydrofluorocarbons and hydrofluoroolefins,including F/Cl exchange reaction,hydrodechlorination reaction and dehydrohalogenation,were introduced.The reaction principles and the main factors affecting catalyst activity were summarized.The application of gas phase catalysts in synthesis of hydrofluorocarbons and hydrofluoroolefins was reviewed.It is suggested that low-temperature,chromium-free and low chromium fluorination catalysts with high activity should be developed.
Key words:organic chemical engineering; gas phase catalysis; hydrofluorocarbon; hydrofluoroolefins; gas phase catalyst
收稿日期:2015-10-19;修回日期:2016-04-28
作者簡(jiǎn)介:張振華,1985年生,男,碩士,從事氟利昂替代品的合成及其催化劑開(kāi)發(fā)研究。
doi:10.3969/j.issn.1008-1143.2016.05.002 10.3969/j.issn.1008-1143.2016.05.002
中圖分類(lèi)號(hào):TQ222.4+23;TQ426.94
文獻(xiàn)標(biāo)識(shí)碼:A
文章編號(hào):1008-1143(2016)05-0008-05
通訊聯(lián)系人:呂劍,1963年生,研究員,博士研究生導(dǎo)師,從事氟化工及催化技術(shù)研究。