双酯加氢制备二醇的新型Cu基催化剂的合成及催化性能研究

【作者】 陈梁锋；

【导师】 范康年；

【作者基本信息】 复旦大学 ， 物理化学， 2009， 博士

【摘要】 1,4-丁二醇（BDO）的用途十分广泛,以其为原料合成的聚酯或聚氨酯比由乙二醇或丙二醇为原料合成的聚合物具有较均衡的物理性能。1,4-丁二醇的主要下游产品四氢呋喃（THF）、γ-丁内酯（GBL）和PBT（聚丁烯对苯二甲酯）树脂都是重要的化工产品,在医药中间体、家电行业等众多领域有着广泛的应用。随着科学生产技术的发展,BDO的生产也由最初的操作危险的Reppe工艺演变到马来酸酐（或酯）的选择性加氢工艺,后者也因初原料——正丁烷的经济易得而极具发展前景。调变催化剂或反应条件,还可以由马来酸酐（或酯）选择性制备GBL或THF,增强了该工艺路线的市场弹性。乙二醇（EG）也是一种重要的化工原料,主要用于聚酯纤维、塑料、橡胶、聚酯漆、胶黏剂、表面活性剂和炸药等,也大量用作溶剂、润滑剂、增塑剂和防冻剂等。自从七十年代石油危机以来,人们清醒的意识到不能再过分的依赖传统的从石油化工下游产品（环氧乙烷）出发的制备路线。因此,从合成气出发经由草酸酯制备乙二醇的路线日益引起人们的重视。草酸酯法合成乙二醇分CO氧化偶联合成草酸酯和草酸酯催化加氢制乙二醇两步,第二步为草酸酯法合成乙二醇实现工业化的关键。公开文献中对于马来酸酯和草酸酯加氢的报道多限于专利,而系统研究催化剂载体、制备条件等对于马来酸酯及草酸酯加氢催化剂活性组分的种类、分散度、价态等的影响,并通过比较这两种底物加氢的反应结果,总结出决定双酯加氢活性的关键因素。另一方面,介孔材料由于其具有较大的孔径、较高的比表面积及高的热稳定性,常常用来作为催化剂载体。与普通载体相比,介孔材料负载的催化剂由于其能更好的分散和稳定活性物种,因此常常具有较高的活性、选择性以及稳定性。在本论文中,我们以Cu/ZnO/Al₂O₃和Cu/SiO₂为催化剂,研究了马来酸二甲酯（DMM）和草酸二甲酯（DMO）加氢分别制备1,4-丁二醇和乙二醇,研究了Cu/ZnO/Al₂O₃催化剂上酸性对于DMM加氢的影响;载体SiO₂的种类、Cu/SiO₂（包括介孔SiO₂）中Cu的负载量、制备方法等对于DMM及DMO加氢活性的影响,并总结出了决定双酯加氢催化活性的关键因素。具体如下:1.Cu/ZnO/Al₂O₃催化剂上DMM催化加氢的研究为了调节催化剂的加氢和脱水能力以便得到较高的BDO得率,我们首先用共沉淀法制备了不同Zn:Al比例（Cu的含量固定为50 wt%）的Cu/ZnO/Al₂O₃催化剂,发现在Al含量较多的时候,还原前后CuO、Cu的晶粒均比较小且结晶度较差,而Zn含量较多时则结晶度好,颗粒也比较大。TPR则发现当Al的含量比较高时,催化剂的还原峰变得很宽,且向高温方向移动。这说明Al含量较高的催化剂能够促进CuO的分散,但是CuO也会与Al₂O₃产生较强的相互作用,使得催化剂难于还原。而Cu和ZnO间的相互作用却能够促进Cu的还原提高Cu表面积。CZA-81（Zn:Al=8:1）Cu表面积高达12.9 m²/gcat,而CZA-18却只有4.1 m²/gcat。这导致CZA-18的低温活性较差,在180℃的时候,双键加氢产物DMS不能完全转化。另外,BDO的选择性随着Zn:Al的增加而增加,并在CZA-41上最高,在180℃反应时,BDO的得率达73%。而THF的选择性则随着Zn:Al的比例的下降而逐渐增加,并在CZA-14上最高,在220℃反应时,THF的得率达96%。这是因为随着Al含量的增加,催化剂上的酸中心的量也随之增加,这导致了BDO脱水生成THF的反应更容易进行。为了进一步验证酸中心对于BDO脱水反应的促进作用,并了解不同酸中心种类对于脱水产物的分布的影响,在上述共沉淀制备的CZA-14催化剂上我们用浸渍的方法修饰了0.5～2 wt%的K,结果发现K的加入使得催化剂的还原峰往高温方向移动,降低了低温活性和脱水产物的选择性,提高了BDO的选择性。K的修饰还改变了脱水产物的分布,尤其是在高温和K修饰量较高（1.5和2wt%）的时候丁醇（BL）成为主要的脱水产物。这可能是由于K的修饰主要覆盖了B酸位,而BL可能是BDO在L酸位上脱水产生的。2.Cu/介孔SiO₂催化剂上DMM催化加氢的研究首先用Cu（NO₃）₂的水溶液直接浸渍MCM-41载体,制备了负载量为10～80wt%的Cu/MCM-41催化剂,XRD表征发现介孔MCM-41的长程有序结构被明显的破坏,而且CuO的颗粒较大,为60 nm左右,这表明部分CuO以较大的颗粒分布在载体的外表面。将这些Cu/MCM-41催化剂用于DMM加氢,发现60 wt%的Cu/MCM-41催化剂的活性和BDO的选择性最佳,在240℃、5 MPa、H₂/E=200以及DMM LHSV=0.36 ml/gcat.h的时候,BDO的得率为55.5%。由于Cu/MCM-41催化剂DMM加氢低温活性比较低,CuO颗粒不能很好的分散,且MCM-41的长程有序结构有明显的破坏,因此一方面我们使用水热稳定性更高的SBA-15作为载体,另一方面我们改进了浸渍方法,使用醋酸铜的乙醇溶液来浸渍。这种方法浸渍的Cu/SBA-15能够很好的保持长程有序性,XRD测出的CuO的颗粒的大小为20 nm左右,在低负载量（5,10wt%）时TEM上能观察到有较多的CuO以较小的颗粒分散与SBA-15的孔道中。与Cu/MCM-41催化相比,Cu/SBA-15催化剂在较低的负载量时就有较高的DMM加氢活性,在10 wt%负载量时催化活性最高,在220℃时BDO得率达56.4%。为了进一步研究Cu的分散和价态对于DMM加氢反应活性的影响,我们用不同方法制备的Cu/SBA-15催化剂,包括等体积浸渍法（IWI）、沉积沉淀法（DP）、均匀沉积沉淀法（HDP）和嫁接法（Grafting）,负载量均为10 wt%。TEM发现IWI方法不能很好的分散Cu物种,而其他三种方法则能很好的分散Cu物种,而且这三种方法制备的催化剂还原前后TEM中均未发现CuO或Cu的颗粒,XRD也未检测出CuO或者Cu的衍射峰,但是EDX却证实了Cu元素的存在,这说明CuO或Cu可能是以TEM不能检测出来的颗粒均匀分布在孔壁上。另外,通过小角XRD和TEM发现HDP方法制备的Cu/SBA-15催化剂中载体的长程有序结构被部分的破坏,这是由于HDP过程中载体SBA-15部分溶解并与Cu物种反应生成页硅酸铜的缘故,这在FTIR和N₂吸脱附等温线上得到了证实。虽然HDP法得到的Cu/SBA-15结构有部分的破坏,但是其催化活性在四种催化剂中最高,且活性顺序与Cu⁰表面积的顺序一致。但Grafting得到的Cu/SBA-15催化剂的Cu比表面虽然比较低（1.6 m²/g）,但是其催化活性仍然与Cu表面要高的多的DP得到的Cu/SBA-15催化剂（3.8 m²/g）相当,这是由于还原后其表面的Cu主要是以Cu⁺的形式存在,且在反应过程中没有明显的改变,这被XPS-Auger所证实。这说明了Cu⁺在马来酸二甲酯加氢中也具有十分重要的作用,因此我们认为是Cu⁰/Cu⁺的协同作用决定了该反应的催化活性。3.Cu/SiO₂催化剂上DMO加氢的研究首先我们以硅溶胶作为硅源、用蒸氨法制备了Cu/SiO₂催化剂,我们通过改变蒸氨温度来研究Cu物种的分散及其与载体的相互作用,并研究了这些对于DMO加氢催化活性的影响。我们发现在蒸氨温度较低的时候（333 K、343 K）,Cu物种与载体SiO₂的作用力较弱,且Cu物种的分散性较差,XRD能检测出尖锐的CuO的衍射峰。而蒸氨温度比较高的时候（353 K、363 K、373 K）时,Cu物种和载体作用力则比较强,XRD谱图上未检测出CuO的衍射峰,且发现FTIR在663 cm^-1有δ-OH的振动峰存在;N₂吸附谱图上3 nm附近产生新的孔径分布;TEM上更是观察到了无规则分布的针状物。这些都表明较高蒸氨温度制备的催化剂上有铜页硅酸盐的存在,而且通过比较663 cm^-1的页硅酸盐的δ_OH峰和800cm^-1附近的SiO₂的振动峰的强度比值,我们发现363 K制备的催化剂（CuSi-363）上页硅酸盐的量最多,另外该催化剂的XPS谱图上Cu 2p_3/2的结合能最高,这说明363 K制备的催化剂中Cu物种和载体SiO₂的作用力最强,因此还原以后Cu⁺的含量也是最高的。将这一系列的Cu/SiO₂催化剂用于DMO加氢反应后发现,CuSi-363的DMO加氢活性最高,在优化条件下,EG得率达98%。而且我们发现蒸氨温度较低时催化剂的活性与Cu⁰表面积成正比,而蒸氨温度较高时则与Cu⁺表面积成正比。这说明在DMO加氢反应中也是Cu⁺/Cu⁰的协同作用决定这催化剂的催化活性。为了更好的研究Cu⁺/Cu⁰的协同作用,我们用浸渍法（WI）、蒸氨法（AE）和化学吸附水解法（CH）制备了Cu/SiO₂催化剂,这三种方法制备的催化剂中Cu和载体相互作用的强弱顺序为AE＞CH＞WI。研究发现浸渍法不能很好的分散Cu物种,催化剂还原前后CuO和Cu的颗粒大小分别为25.6 nm和36.5 nm,因此其催化活性也最差。而AE和CH方法则能较好的分散Cu物种,在350℃还原后,Cu颗粒大小仅为3 nm左右。H₂-TPR中,Cu/SiO₂-AE的还原峰温比Cu/SiO₂-CH的高,这表明前者Cu物种与载体的作用力强。XPS-AES分峰结果显示还原后的催化剂中AE法的Cu⁺占28.0%,而CH和WI法的分别占19.3%和5.6%,但是由于Cu/SiO₂-CH的Cu⁰表面积比Cu/SiO₂-AE的要高,因此计算出CH法和AE法的Cu⁺的表面积类似。DMO加氢活性结果显示Cu/SiO₂-CH的活性最高,表明在Cu⁺表面积相近时,催化剂的活性由Cu⁰表面积决定。为了进一步提高催化剂的活性,我们将CH方法的Cu的理论负载量加倍,但ICP-AES测定Cu的负载量并未因此增加,而且Cu表面积和DMO加氢活性还因此稍有下降,这表明CH方法制备的催化剂的Cu负载量仅取决于载体本身的性质。4.Cu/介孔SiO₂催化剂上双酯加氢的研究由于CH方法制备的Cu催化剂的负载量与载体相关,因此我们选用不同的介孔材料作为载体,包括SBA-15、MCM-41、MCF和HMS,用CH方法制备了一系列催化剂。ICP-AES结果表明,Cu/介孔SiO₂的Cu负载量均在23 wt%左右,这比普通SiO₂作为载体时的Cu的负载量提高了将近一倍。XRD显示还原前后Cu物种能够很好的分散在介孔SiO₂上,还原前后的TEM也证实了这一点。但TEM和小角XRD表征发现Cu/MCM-CH、Cu/MCF-CH和Cu/HMS-CH的长程有序结构有部分的破坏。还原以后XPS-AES显示Cu/介孔SiO₂催化剂上Cu物种主要以Cu⁰的形式存在,且Cu颗粒均在3 nm左右,Cu⁰表面积顺序为Cu/MCM-CH＞Cu/SBA-CH＞Cu/HMS-CH＞Cu/MCF-CH,但均在11 m²/g左右。DMO加氢活性顺序却与上述顺序不一样,为Cu/SBA-CH＞Cu/MCM-CH＞Cu/MCF-CH＞Cu/HMS-CH,这可能是由于Cu/MCM-CH和Cu/HMS-CH的孔径和Cu颗粒大小相近,从而导致孔道阻塞和传质困难,因此使得反应活性较低。在Cu/SBA-CH催化剂上,我们优选了反应条件,发现该催化剂在200℃,2.5MPa,H₂/E=50,DMO LHSV=1.5 h^-1时,EG得率为96.2%。而时空得率高达0.758 g（h.gcat）,这高于所有文献值。对于SBA-15载体的制备过程,我们做了一些改变,将除去模板剂的过程由500℃空气中焙烧改为冰水浴中用Fenton方法除去,希望能够提高SBA-15表面的硅羟基的密度,从而提高Cu负载量,最终提高催化活性。但是ICP结果显示Fenton方法除模板剂并未提高Cu的负载量,而且活性甚至有所下降,N₂吸附脱附和小角XRD结果显示SBA-15的长程有序结构有所破坏,这可能与Fenton法处理SBA-15反应比较剧烈,瞬间产生大量气体,以及使用过量强酸来除去Fe（OH）₃有关。因此,我们还是使用焙烧法来除去模板剂P123。如此制得的上述Cu/SBA-CH催化剂在优选的反应条件下,在500h的反应时间内能够保持平均约96%的EG得率,显示了极高的EG时空得率和很高的稳定性。我们将Cu/SBA-CH催化剂继续用于DMM加氢中,结果发现其活性比HDP方法制备的催化剂高,优选条件为T=200℃、p=5.0 MPa、H₂/DMM=300(molmol^-1)和DMM LHSV=0.36 ml/（gcat·h）,此时BDO的得率为74.6%。这表明Cu/SBA-CH催化剂在DMO和DMM加氢中均具有优异的催化活性,因此具有很大的工业应用潜力。更多还原

【Abstract】 Great interest has been aroused due to the steadily growing demand for 1,4-butanediol（BDO） which is widely used as a starting material for polymers and solvents.The polybutylene terephthalate（PBT） and other polyurethances produced from BDO had superior properties as structural and engineering plastics,and play an important role in many fields.Tetrahydrofuran（THF）,obtained through the dehydration of BDO,is an indispensable solvent for many polymers and a monomer in the manufacture of polytetramethylene ether glycol（PBT）,etc.At present,Davy process has showed great advantage for producing BDO not only the lower operation pressure,but also because well-established fixed-bed reactor technology could be utilized.Moreover,the products distribution could be regulated to fit the market demand using dialkyl maleate as reactant.Ethylene glycol is also an important chemical used in polyesters manufacture or as antifreeze.The catalytic hydrogenation of dimethyl oxalate（DMO） to ethylene glycol（EG） is the second step of indirect synthesis of glycol from syngas,which is a new chemical process including the oxidative coupling reaction of carbon monoxide to diaikyl oxalate and the catalytic hydrogenation of dialkyl oxalate to glycol.In this work,catalytic hydrogenation of dimethyl maleate and dimethyl oxalate has been studied in details.The optimum copper-based catalysts were prepared by changing carriers,adding promoters as well as improving preparation methods.By means of N₂-adsorption,XRD,XPS&AES, SEM,TEM,TPR,FTIR,UV-Vis techniques,the elects of bulk structure and surface component of catalysts on the catalytic performance were investigated.The main contents of this paper are as follows:1.DMM hydrogenation over Cu/ZnO/Al₂O₃ catalystFor the purpose of obtaining higher yield of BDO,we adjusting the hydrogenation and dehydrogenation ability by preparation of Cu/ZnO/Al₂O₃ catalysts of different Zn:Al molar ratio.It is found that when Zn:Al is higher,the crystallinity of Cu species is also higher and the crystallite size larger,but its reduction temperature is smaller than the one with lower Zn:Al ratio,which is because of the promotion effect of ZnO to the reduction of CuO.When Zn:Al is lower,Cu species can be well dispersed,resulting in smaller CuO and Cu particles.However,because of the strong interaction between Cu species and Al₂O₃,the Cu species are reduced at higher temperatures and the catalysts display a lower Cu⁰ surface area and DMO hydrogenation activity;and also because of its higher acidic Al₂O₃ content,THF selectivity is higher over the catalysts with lower Zn:Al ratio.At a reaction temperature of 220℃,THF selectivity reaches 96%at CZA-14.On the contrary, higher Zn:Al ratio favor the selectivity of BDO.At 180℃,BDO selectivity reaches 73%over CZA-41.For the confirmation of the effect of acid center on BDO dehydration to THF,a small amount of K is added to CZA-14 catalyst by impregnation.It is found that K adding hinders reduction of Cu species,decreases both hydrogenation and dehydration activity and increases BDO selectivity.Moreover,the dehydration product distribution has been substantially changed after K modification.At higher reaction temperatures and higher K loadings,butanol becomes the main dehydration product,which may be because of the preferential covering of Br（o｜¨）nsted acid by K₂O, leaving Lewis acid uncovered.2.DMM hydrogenation over Cu/mesoporous SiO₂ catalyst10～80 wt%Cu was loaded on mesoporous MCM-41 by impregnation method. It was found that the long range ordered structure of MCM-41 was obviously deteriorated during impregnation,and Cu species could not be well dispersed.When this series of catalysts was used in DMO hydrogenation,it was found that 60Cu/MCM-41 catalyst showed the best catalytic performaces,with a BDO yield of 55.5%at a reaction temperature of 240℃.In order to increase copper dispersion and better retention of mesoporous structure,SBA-15 instead of MCM-41 is used as catalyst support and the method of impregnation is improved.It was found that over thus prepared Cu/SBA-15 catalyst, Cu species can be better dispersed yet not better enough,because an average CuO particle size of around 20 nm was detected over 20Cu/SBA-15.Compared with Cu/MCM-41 catalysts,DMO hydrogenation activity maximizes at a much lower Cu loading of 10 wt%over Cu/SBA-15.At 220℃,over 10Cu/SBA-15,a BDO yield of 56.4%was obtained.For the purpose of better understanding of the influence of Cu dispersion and valence state to DMM hydrogenation,Cu/SBA-15 prepared by different methods was carefully characterized and was related with DMM hydrogenation activity.It was found that deposition-precipitation（DP）,homogeneous deposition-precipitation（HDP） and Grafting method can well disperse copper species before and after reduction, while incipient wetness impregnation（IWI） method can not.Small angle XRD pattern and N₂ adsorption-desorption data indicate that partial structure collapse was found over Cu/SBA-15 catalyst prepared by HDP method,however,the HDP catalyst shows the best DMM hydrogenation activity and the activity was found to be linearly correlated with the Cu⁰ surface area except for DP and Grafting Cu/SBA-15.The DMM hydrogenation activity of Grafting Cu/SBA-15 catalyst is comparable with DP Cu/SBA-15,while its Cu⁰ surface area was much lower.XPS-AES spectra indicate that after reduction and reaction,Cu⁺ predominates over Grafting Cu/SBA-15,while over other catalysts,Cu⁰ predominates.Combining the XPS-AES results,Cu⁰ surface areas and the catalytic performances,it can be deduced that Cu⁺ plays an important role in DMM hydrogenation.We suppose that it is Cu⁺/Cu⁰ cooperation that determines DMM hydrogenation activity.3.DMO hydrogenation over Cu/commercial SiO₂ catalystThe influence of ammonia evaporation temperature(T_AE) to the structure and DMO hydrogenation activity was studied over Cu/SiO2 catalysts prepared by ammonia evaporation（AE） method.It was found that a lower T_AE（333 K and 343 K） resulted in poor Cu dispersion and a weaker Cu-support interaction,while it was the opposite over Cu/SiO₂ catalysts prepared with higher T_AE.When T_AE was higher（353 K,363 K and 373 K）,TEM,FTIR and N₂ adsorption results suggest the existence of copper phyllosilicate,whose amout maximized at T_AE of 363 K and XPS indicates a strongest Cu-support interaction in CuSiO-363 catalyst.As a result,after reduction, CuSi-363 contains the highest amour of Cu⁺.At lower T_AE,DMO hydrogenation activity was found to be linearly correlated with Cu⁰ surface area,while at higher T_AE, the activity was linearly correlated with Cu⁺ surface area,which means that Cu+ also plays an important role over DMO hydrogenation.So we also make a conclusion that Cu⁺/Cu⁰ cooperation determines the activity of DMO hydrogenation.Cu/SiO₂ catalysts was prepared by different methods including wetness impregnation（WI）,chemisorption-hydrolysis（CH） and ammonia evaporation（AE）, which will result in different Cu-support interactions,in order to better understand Cu⁺/Cu⁰ interaction.It was found that WI can not well disperse Cu species,thus resulted in lowest DMO hydrogenation activity.XPS-AES and N₂O titration results shows that although a higher Cu⁺/Cu⁰ ratio was found over CuSi-AE catalyst,Cu⁺ surface area was almost the same with that of CuSi-CH,however,a much larger Cu⁰ surface area was found over CuSi-CH catalyst,which resulted in a better DMO hydrogenation activity.It was also found that the Cu loading of the CH Cu/SiO₂ catalyst was determined by the SiO₂ support,further increase of Cu nominal loading could not increase the actually Cu loading.4.Di-ester hydrogenation over Cu/mesoporous SiO₂ catalystWe choose different mesoporous SiO₂ as support in order to increase Cu loading and DMO hydrogenation activity of CH CuSiO₂ catalyst.ICP-AES results show that Cu loading was substantially increased over Cu/mesoporous SiO₂ catalysts.Among SBA-15,MCM-41,MCF and HMS,it was SBA-15 supported Cu catalyst that shows the best DMO catalytic activity and the catalyst also best retains the mesoporous structure.Under optimized reaction conditions,an EG yield of 96.2%was obtained. The space time yield was calculated to be 0.758 g/（h·gcat）,which was the highest among all the values reported by open literatures.Fenton method was used to remove the P123 surfacant in order to reduce the loss of suface silanols induced by calcination.However,it was found that when the Fenton SBA-15 was used as support,Cu loading and Cu⁰ surface area was not substantially increased when compared with calcined SBA-15,which may be because of the deterioration of SBA-15 support during Fenton and subsequentant CH process. Thus,calcined SBA-15 was again used as support for the preparation of CH Cu/SBA-15 catalyst and the catalyst was subjected to a stability test of 500 h under the optimized conditions.An average EG yield of 96%was obtained over 500 h time on stream,which proves the superior DMO hydrogenation activity and EG selectivity as well as stability of the CH Cu/SBA-15 catalyst.The CH Cu/SBA-15 catalyst was also used in DMM hydrogenation and it was found that it shows higher activity and BDO selectivity than HDP Cu/SBA-15 catalyst. A BDO yield of 74.6%was obtained under optimized conditions.These results indicate that CH Cu/SBA-15 shows superior catalytic performances in both DMO and DMM hydrogenation and is a very promising catalyst for industrial purpose.更多还原