【作者】 杨运泉；

【导师】 罗和安；

【作者基本信息】 湘潭大学 ， 化学工程， 2008， 博士

【摘要】 铜系氧化物及其金属单质负载型催化剂在石油化工领域的芳烃催化重整、烯烃和烷烃的催化脱氢过程以及在精细化工领域的醇类催化脱氢制取相应的酮、醛、酸等过程中有着重要的应用价值和广泛的工业应用前景。从20世纪50年代起,有关该催化剂的制备技术开发及其工业应用研究就一直受到世界各国的广泛关注并成为化工热点问题之一,经过科学家们的不断探索和创新,已经取得了一系列令人瞩目的研究进展和成就。本文在大量文献调研和深入的催化剂设计与制备理论分析基础上,采用氧化锆为载体,铜为活性组分,以硝酸铜、氧氯化锆为原料,利用氢氧化钠为共沉淀剂,通过调控催化剂制备过程的主要工艺参数,在实验室制备出了同时适合于氨基醇和环己醇脱氢的活泼金属铜-负载型Cu-ZrO₂催化剂。运用多种现代测试手段对所制备的催化剂前驱体及成品进行了理化表征。结果表明:所制备的Cu-ZrO₂催化剂比表面积达到116.53m²/g;催化剂前驱体及其成品均为单一四方晶型载体结构,当载体中含有其他结构的氧化锆混晶时催化剂性能下降;共沉淀过程的中和终止pH值以及前驱体焙烧温度对形成的锆氧化物晶体结构有明显影响。所制备的Cu-ZrO₂催化剂粒度约为2.0³.0μm,活性组分在载体表面的分布比较均匀。理论计算表明:催化剂前驱体中锆氧化物晶体颗粒几乎以单晶单层的结构形式存在。催化剂活性组分前驱体氧化铜在227℃有很强的还原峰,低于其纯氧化物的最高还原峰值320℃;TG和外观分析表明:具有较高活性的自制Cu-ZrO₂催化剂在宏观上表现为催化剂前驱体（铜锆氢氧化物）的密度较大（>1.70g/ cm³ ） ,色泽鲜亮;在微观上表现为铜锆氢氧化物的热失重温度范围较窄（150⁵30℃）。采用正交和单因素实验方法,对影响催化剂在氨基醇和环己醇脱氢过程反应性能（选择性,转化率,失活率和失活速率）的主要制备工艺条件和因素进行了考察评价,得出了制备过程关键因素对反应性能的影响规律,获得了优化的催化剂制备工艺参数。结果表明:在一定的制备条件范围内,Cu-ZrO₂催化剂对于氨基醇和环己醇的催化脱氢具有比较优良和稳定的反应选择性;制备条件对催化剂在氨基醇脱氢过程的反应选择性影响大小顺序为:共沉淀终点pH值>n（Zr） /n （Cu）>锆盐初始浓度>还原时间>焙烧时间;对转化率的影响大小顺序为:共沉淀终点pH值>还原时间>锆铜原子比>焙烧时间>锆盐初始浓度。而在环己醇脱氢过程中其对反应选择性影响的大小顺序为n（Zr） /n （Cu）>共沉淀终点pH>焙烧时间>焙烧温度>锆盐初始浓度;对反应转化率影响的大小顺序为n（Zr） /n （Cu）>共沉淀终点pH>锆盐初始浓度>焙烧时间>焙烧温度。适宜的催化剂制备实验条件为:顺加料共沉淀方法,锆铜原子比为2,共沉淀终点pH值为12,共沉淀锆盐初始浓度为0.2⁰.3 mol/L,500℃下焙烧4h,230℃下用氢气与氮气混合还原4h。将此条件下制备的Cu-ZrO₂催化剂用于二乙醇胺催化脱氢,其最高反应选择性为99.60%;用于环己醇催化脱氢,其最高反应选择性为99.46 %。实验还考察了催化剂制备过程中n（Zr） /n （Cu）原子比、微量过渡金属元素引入、共沉淀终点pH值、锆盐初始浓度、催化剂前驱体的焙烧时间和焙烧温度等工艺条件参数对催化剂在氨基醇和环己醇的催化脱氢活性的单因素影响规律。总体来说,（1）共沉淀过程的终点pH值越高,得到的催化剂其反应选择性和脱氢产物收率越高;（2）在锆铜原子比为2.0⁶.0的范围内,催化剂对于氨基醇和环己醇脱氢的目标产物收率随该比例的减小而升高;（3）共沉淀过程锆盐初始浓度在0.1～0.4mol/L范围内变化时,所制备的催化剂对脱氢反应过程的收率和选择性影响均不大;（4）前驱体氢氧化物在500℃下焙烧所得的催化剂反应性能最好,高于500℃时反应性能有所下降;铜锆氢氧化物焙烧分解的彻底程度、氧化物晶体形成的完整性以及氧化铜活性组分在载体表面的烧结或团聚现象都与焙烧温度的高低或焙烧时间的长短有关; （5）催化剂前驱体氧化物的还原时间过长,反应产物的收率和催化剂反应选择性将有所下降,但选择性的下降幅度要小于反应产物收率的下降幅度。原因可能是催化剂前驱体氧化物的还原程度过深,造成催化剂表面的两种不同价态形式活性中心Cu⁰、Cu⁺的比例失调或是催化剂中的铜微晶发生团聚而导致催化剂的性能变差;（6）在催化剂中引入部分其它过渡金属元素氧化物后,会导致催化剂中毒,使得环己醇脱氢的反应选择性较单纯负载铜时有所下降。此外,实验还对氨基醇和环己醇催化脱氢过程的反应工艺条件（反应温度、压力和加入体系的NaOH碱浓度和总量等）与脱氢产物收率及催化剂反应性能的关系进行了研究。（1）对于氨基醇的催化脱氢,由于过程属于放热可逆反应,因此温度的升高有利于该反应的动力学而不利于该反应的热力学,转化率（产物收率）随温度呈现先升后降的变化趋势;反应体系的（氢气）压力变化对反应选择性影响较小,但其对反应转化率（产物收率）的影响较明显,呈现先升后降的变化规律;反应过程中NaOH碱浓度基本不影响催化剂的选择性,而反应转化率（产物收率）受化学平衡移动的影响,呈现先随碱浓度上升而上升然后基本维持不变的规律。实验结果表明,氨基醇脱氢反应的适宜工艺条件为:反应温度165℃,压力1.60MPa,浓度为30%wt的NaOH碱加入量为理论量的105%。（2）对于环己醇脱氢生成环己酮的反应,由于过程属于吸热可逆反应,因此,采用较高的反应温度既有利于环己酮动力学也有利于环己醇的热力学。实验表明:在温度为200℃左右Cu-ZrO₂催化剂就对环己醇的脱氢显示出较好活性,但温度高于280℃时副反应加剧,产物中有环己基环己酮及一些未知杂质生成;该反应属于体积增加的过程,因此降低压力有利于反应朝着提高转化率的方向进行。综合考虑到反应体系需要保持的氢气还原气氛,以保障Cu-ZrO₂催化剂的良好活性,因此整个反应较适宜的工艺条件选择为:反应温度240℃,压力2.50MPa。通过对氨基醇脱氢过程反应物分子在Cu-ZrO₂催化剂颗粒上的扩散计算,结果表明:该反应过程主要受普通分子扩散的影响,而反应物在催化剂内孔中的Knudsen扩散影响很小,两者的扩散系数之比为D_B/D_K =1/188.3;该反应过程φ_S,R很小(=1.536×10^-8),催化剂的内表面利用率接近100%,反应属于大孔慢反应类型。因此可以进一步减小催化剂的孔径d ,以获得高的反应速率;扩散计算结果还表明,在氨基醇的催化脱氢反应中,采用淤浆式搅拌反应器进行液相脱氢方式,有利于增加反应体系液体的湍流程度,降低反应物流体在催化剂表面附着的层流底层厚度,从而可以同时消除该过程反应物分子在催化剂颗粒表面上和在催化剂内孔中的分子扩散和Knudsen扩散传质阻力,由此获得更加接近于该过程化学反应步骤控制的本征动力学模型,所采用的这种液相脱氢方式和反应器形式对于该脱氢反应过程是比较适合的。分析、提出了采用Cu-ZrO₂作催化剂、在碱性和有水条件下使氨基醇催化脱氢生成氨基酸（钠盐）的过程反应机理,该机理符合有关文献提出的反应历程假说。其中,氨基醛自身分子间发生亲核加成生成氨基酸和氨基醇的歧化反应过程（即康尼查罗S.Cannizzaro反应）是极快反应步骤,过程的控制步骤是氨基醇脱氢生成氨基醛的反应;氨基醇的脱氢反应基本上不存在副反应的影响。实验结果表明,该化学反应呈一级动力学形式,其反应的活化能Ea=147.80kJ/mol,反应速度常数k与温度T的关系为:k=6.8111×10¹⁵exp（-147.80×10³/RT）。最后,实验考察了脱氢过程回收的Cu-ZrO₂催化剂的重复使用后的活性稳定情况。在二乙醇胺的催化脱氢反应中,该催化剂重复使用9次后的平均反应选择性、转化率和产物收率分别为97.90%, 89.60%和87.80%,以选择性表示的催化剂平均单批失活率η_deac和平均失活速率v_deac分别为0.51%/批和0.16%/hr,以转化率表示的催化剂平均单批失活率ηdXeac和平均失活速率v dXeac分别为1.93%/批和0.62%/hr;在环己醇脱氢反应中该催化剂重复使用9次后其平均反应选择性、转化率和产物的收率分别为96.82%,80.17%和77.69%。η_deac为0.68%/批, v_deac为0.22%/hr;η_deac为1.06%/批, v_deac为0.36%/hr。该催化剂对环己醇脱氢过程的催化活性略低于其对氨基醇脱氢过程的催化活性。相对于转化率受反应条件的影响程度而言,其选择性受反应条件的影响较小。因此,Cu-ZrO₂催化剂对于氨基醇和环己醇的脱氢都表现出了较高的反应选择性和活性稳定性。转化率下降较快的原因可能是催化剂的回收操作中缺乏有效的隔氧保护措施,导致其暴露于空气中的时间过长,使催化剂表面的部分Cu0或Cu+1被空气中O₂氧化成Cu+2所致。从反应转化率（收率）来看,该催化剂对氨基醇脱氢反应更为有效和适用,主要原因可能是由于化学平衡对环己醇脱氢过程的抑制影响较其对氨基醇脱氢过程的抑制影响更为显著所致。相比于工业上现有的一些其他醇类脱氢传统催化剂而言,总体来说Cu-ZrO₂仍不失为一种性能优良稳定、制备简易、成本低廉、用途广泛的醇类脱氢新型催化剂。更多还原

【Abstract】 The supported catalysts of copper oxide and elementary metal copper have been widely used in petrochemical industry for the catalytic reforming of aromatic hydrocarbons and catalytic dehydrogenation of alkane and alkene. They are also widely used in fine chemical industry for the preparation of derived ketone, aldehyde and organic acid from their original alcohols. Since the middle of the 20th century, the R & D of the catalysts preparation technologies and their industrial applications has been received a wide range of attentions from all over the world and it has been become one of the hot-spot issues of chemical science and technology. With the continuous exploring and innovation of the scientists, a series of significant progresses and achievements have been made in the past decades towards the frontier issue.Based on a wide range of literature investigations and a solid theoretical analysis on the catalyst design and preparation, a supported active elementary metal copper catalyst Cu-ZrO₂ which applies to the dehydrogenation of amino-alcohols and cyclohexanol were successfully prepared in a laboratory scale in the present study, using ZrO₂ as the supporter and metal copper as the active component, by the co-precipitation of Cu（NO3）2 and ZrOCl2·8H2O with the addition of NaOH, through the controlling and adjusting of the key process parameters during the preparation of the catalyst.Several modern material testing methods were applied to the characterization of the physical and chemical properties of the catalyst. The results show that the Cu-ZrO₂ catalyst has a BET surface area of 116.53 m2/g, the final product and the precursors of the catalyst each has a unique ZrO₂ square crystal structure, the reactivity of the catalyst decrease while the ZrO₂ supporter contains the mixture of other ZrO₂ crystal morphology, the terminal pH of the co-precipitation and the calcinations temperature of the precursor each plays an important role in the formation of the ZrO₂ crystal structures, the particle size of the Cu-ZrO₂ catalyst prepared in the experiment is about 2.0³.0μm and the distribution of the active component on the ZrO₂ supporter surface is of uniformity. Theoretical calculation reveals that the ZrO₂ crystal particles exist in the precursor of the catalyst almost in the form of mono-layer crystal. The CuO in the precursor of the catalyst appears a strong reduction peak at 227℃by TPR, whereas the pure copper oxide appears the peak at about 320℃. The analysis results from TG and the appearances of the catalyst indicate that a high reactivity Cu-ZrO₂ catalyst will have a significant mixtures density of copper hydroxyl and zirconium hydroxyl precursors （which is greater than 1.70g/cm³） with a brilliant color macroscopically, whereas the thermal gravity-lost（TG） temperature range of the hydroxyl compounds is very narrow （from 150℃to 530℃） microscopically.By the methods of orthogonal and single-factor experimental design, the key technical conditions and the main factors which affect the dehydrogenation activity （such as selectivity, conversion, de-activation rate, etc） of amino-alcohols and cyclohexanol during the catalyst preparation were investigated and evaluated. The influence rules of the key factors to the reactivity of the catalyst were studied and the optimal parameters for the preparation of the catalyst were obtained. The results show that in a certain range of the preparation conditions, the Cu-ZrO₂ catalyst can maintain a good and stable high selectivity during the catalytic dehydrogenation of amino-alcohols and cyclohexanol. The influence factors order of the preparation conditions in terms of selectivity of the catalyst during the dehydrogenation of amino-alcohols is: terminal pH of co-precipitation>ratio of n（Zr） /n（Cu） >initial concentration of ZrOCl2·8H2O>reduction time>calcinations time, whereas in terms of the conversion, the influence order is: terminal pH of co-precipitation> reduction time> ratio of n（Zr） /n（Cu） >calcinations time>initial concentration of ZrOCl2·8H2O. On the other hand, in the dehydrogenation of cyclohexanol the influence order for the preparation conditions in terms of the selectivitywas found to be: ratio of n（Zr） /n（Cu） > terminal pH of co-precipitation>calcinations time > calcinations temperature>initial concentration of ZrOCl2·8H2O, and, of the conversion, this order is shown as the follows: ratio of n（Zr）/n（Cu）>terminal pH of co-precipitation>initial concentration of ZrOCl2·8H2O> calcinations time > calcinations temperature. The optimal conditions for the preparation of the catalyst are: 2:1 of the n（Zr）/n（Cu） atomic ratio, 12.0 of the terminal pH of the co-precipitation by direct addition of NaOH, 0.2⁰.3 mol/L of the initial concentration of ZrOCl2·8H2O, 4 hours of the calcinations time at 500℃of calcinations temperature, 4 hours of reduction time at 230℃in the mixture of H2 and N2. By using the catalyst prepared under the above conditions to the dehydrogenation of diethanolamine, a highest selectivity of 99.60% has been obtained, whereas to the dehydrogenation of cyclohexanol, the highest selectivity is 99.46 %.The single-factor effect of the n（Zr）/n（Cu） atomic ratio, the introducing of trace transition metal elements, the terminal pH of co-precipitation, the initial concentration of ZrOCl2·8H2O, the calcinations time and temperature of the precursor during the preparation of the catalyst on the reactivity each was also approached in the dehydrogenation of amino-alcohols and cyclohexanol. Summarily, （a） the selectivity of the prepared catalyst and the product yields of dehydrogenation increase with the increase of the terminal pH of co-precipitation; （b） in the range of 2.0⁶.0 of the n（Zr）/n（Cu） atomic ratio, the product yields of the dehydrogenation from amino-alcohols and cyclohexanol decrease with the increase of the ratio;（c） in the range of 0.1⁰.4 mol/L of the initial concentration of ZrOCl2·8H2O, the influences of the concentration to the selectivity and the yields of the dehydrogenation of the reactants are very small;（d） the reactivity of the catalyst prepared from the hydroxyl precursors which calcined at 500℃reaches to its highest activity. The reactivity decreases when the calcinations temperature of the hydroxyl precursors is over 500℃. The completion degrees for calcinations and decomposition of the hydroxyl precursors, the integrity for the formation of the ZrO2 and CuO crystals and the degree for sintering or agglomeration of the active component CuO on the surface of the ZrO2 supporter is each correlated to the calcinations time and temperature; （e） by overtime reduction of the copper oxide precursor, the selectivity of the catalyst and the product yields of the dehydrogenation will decrease. However, the decreasing degree for the selectivity is a little less than that for the product yields. The over-reduction of the precursors might be one of the key causes of the phenomena, and which could lead to the maladjustment or the unbalance of the activation sites ratio of Cu0 and Cu+ and to the agglomeration of the microcrystal of metal copper on the catalyst supporter surface. （f） the introducing of some trace transition metal elements to the catalyst will lead to the poisoning and de-activation of the Cu0 and Cu+ active components, which finally lead to the decrease of the selectivity in the dehydrogenation of cyclohexanol, compared to the single pure copper oxide usee as the active component to the catalyst.Furthermore, the relationship between the reaction conditions （reaction temperature and pressure, addition amount and concentration of NaOH to the reaction system, etc） and the product yields or the reactivity of the catalyst was established experimentally in the catalytic dehydrogenation of amino-alcohols and cyclohexanol.（a）because the catalytic dehydrogenation of amino-alcohols is an exothermic reversible reaction, the increase of reaction temperature is of advantages to the reaction kinetically whereas is of disadvantages thermodynymically. The conversion and the product yield increase with the increase of the reaction temperature at first and then will decrease with the further increasing of the temperature. The effect of reaction system pressure to the selectivity of the catalyst is very small. However, it is a little distinct to the conversion and the product yields of the reaction, the rules of which are similar to that of reaction temperature effect on the conversion and the yields. The concentration of NaOH has very little effect on the selectivity. Influenced by the reversible reaction equilibrium effect, the conversion of amino-alcohols increases with the increasing of NaOH concentration at first and then it will approaches to a stable value with the further increasing of the NaOH concentration. A set of feasible reaction parameters has been worked out for the dehydrogenation of amino-alcohols with 165℃of reaction temperature, 1.6Mpa of reaction pressure and 1.05 times of NaOH amount by theoretical demanded with 30%wt of NaOH concentration. （b） the dehydrogenation of cyclohexanol is endothermic and reversible, therefore a high reaction temperature is favorable both kinetically and thermodynamically. It has been observed by experiments that even if with a low reaction temperature of 200℃, the Cu-ZrO2 catalyst can still show a good reactivity to the dehydrogenation of cyclohexanol. However, some side reactions will occur seriously when the temperature exceeds 280℃and cyclohexyl-cyclohexanone and some other unknown by-products or impurities will hence produced. With the decrease of the system pressure, the reaction goes along with the promotion of the conversion because of the equilibrium effect of volume enlargement reaction for the process. For the sake of maintaining a good reduction atmosphere in the reaction system and a stable catalyst activity to the reaction, the suitable parameters for the reaction process has been determined as a reaction temperature of 240℃and reaction pressure of 2.50MPa.According to the result from the calculation of diffusion effects of the reactant molecules on the Cu-ZrO₂ catalyst in the dehydrogenation of amino-alcohol, it reveals that the reaction is mainly subjected to the effect from ordinary molecular diffusion rather than that from Knudsen diffusion in the porous catalyst. The ratio of the two diffusion coefficient DB/DK is 1: 188.3, the Thiele ModulusφS,R of the reaction is very small （ about 1.536×10-8） and the utility of the inner surface area of the catalyst is close to 100%. The reaction is of the characteristics of a macro-porous slow reaction pattern. A higher reaction rate can be available by a further decreasing of the particle diameters and the porous sizes of the catalyst. The calculation results also show that by using slurry stirred reactor to the catalytic dehydrogenation of amino alcohols in the liquid-solid phase, it has the advantages of increasing the turbulent degree of the reactant liquid and deminishing the thickness of the laminar flow layer of the reactant on the catalyst surfaces, which will lead to the eliminations of the resistances of molecular diffusion outside the catalyst surface and Knudsen diffusion inner the porous catalyst simultaneously, and to obtain a more real and intrinsic kinetical model which can describe the control of the true chemical reaction step much accurately. The reactor type and the operation pattern used for the reaction are compatible.Combined with the literatures reports and some theoretical investigations, the dehydrogenation mechanism of amino-alcohols to amino-acids by Cu-ZrO₂ catalyst with the existence of water and alkali in the reaction system was proposed in the paper. The results reveal that during the catalytic reaction, the rate for the formation of amino-acid by nucleophilic addition which occurs between amino-aldehyde molecules and the rate for the disproportionation or S Cannizzaro reaction of amino-alcohols each is extremely fast, the overall reaction rate in the process is controlled by the step of the formation of amino- aldehyde which produced by the dehydrogenation of amino-alcohols. Very few side-reactions occur in the dehydrogenation of amino-alcohols. The investigations indicate that the reaction kinetics equation is a 1st-order mode, the activation energy Ea for the catalytic dehydrogenation of diethanolamine to iminodiactic-acid is 147.80kJ/mol and the relationship between the rate constant and the reaction temperature can be summarized as follows: k=6.8111×10¹⁵exp（-147.80×10³/RT）.Finally, the stability of the catalyst reactivity was studied by recovering Cu-ZrO₂ catalyst from the dehydrogenation of amino-alcohols and cyclohexanol. In the catalytic dehydrogenation of diethanolamine, after 9 recycles in the reactions, the average selectivity, the conversion and the product yield of the catalyst is 97.90%, 89.60% and 87.80% respectively. The average de-activity per batch (η_deac) and de-activity rate ( v_Seac) of the catalyst in terms of selectivity is 0.51%/batch and 0.16%/hr, respectively. Whereas in terms of conversion,ηdXeacand v dXeac is 1.93%/batch and 0.62%/hr, respectively. For the dehydrogenation of cyclohexanol, the average selectivity, the conversion and the product yield of the catalyst is 96.82%,80.17% and 77.69%, respectively.ηdSeac, v dSeac,ηdXeac and Xv deacis 0.68%/batch, 0.22%/hr, 1.06%/batch and 0.36%/hr, respectively. The activity of the catalyst in dehydrogenation of cyclohexanol is a little lower than it in dehydrogenation of amino-alcohols. Compared to the influence degree of the reaction conditions on the conversion, the influences of the reaction conditions to the selectivity is a little slight. Hence the Cu-ZrO₂ catalyst shows a high and good selectivity and a stable activity for the dehydrogenation from both amino-alcohols to amino-acid and cyclohexanol to cyclohexanone. The reason for the rapid conversion declining in dehydrogenation might be caused by the long-time exposure of the catalyst in the air and the lack of effective oxygen isolation during the recovering of the catalyst, which results in the oxidation of Cu0 and Cu+1 to Cu+2 by the air. From the view of the conversion, it seems that the novel Cu-ZrO₂ catalyst is more favorable to the dehydrogenation of amino-alcohols. The reason might be resulted from the greater inhibiting effect of chemical equilibrium on the dehydrogenation of cyclohexanol rather than that of amino-alcohols. Compared to some other conventional industrial catalysts used for the dehydrogenation of alcohols, the novel Cu-ZrO₂ catalyst has the advantages and characteristics of good and stable reactivity, easily manufacture, low production cost and wide ranges of industrial applications.更多还原