工业粒度Fe-ZSM-5分子筛上N_2O一步氧化苯制苯酚工艺条件研究

为实现N_2O一步氧化苯制备苯酚的工业化生产,基于自制的Fe-ZSM-5分子筛(粒度?1.5 mm×1 mm),在等温固定床积分反应器中,以单因素实验和正交实验[L_9(3~4)]相结合的方式,系统考察了温度(375~475℃)、空速(2 500~10 500 h~(-1))和苯与N_2O的物质的量比(6:1~14:1)等操作条件对N_2O一步氧化苯制苯酚反应过程规律及产物分布的影响。结果表明,实验所用Fe-ZSM-5分子筛对N_2O一步氧化苯制苯酚具有良好的催化活性和选择性;该反应过程存在催化剂起始活性高但失活速率快的特点,适宜操作条件域的选取对催化剂性能的发挥至关重要;基于正交实验分析最终确定的相对适宜工艺条件操作域为:温度425~450℃、空速4 500~5 500 h~(-1)和苯与N_2O的物质的量比8:1~10:1,在此条件下苯酚收率可达60%以上。     

苯直接氧化制苯酚Fe-ZSM-5催化剂研究新进展

介绍了以N2O作为氧化剂苯直接催化氧化制备苯酚Fe-ZSM-5催化剂的研究新进展,综述了Fe-ZSM-5改性来提高苯转化率、苯酚收率和催化剂稳定性的一些方法,旨在为其应用于苯直接催化氧化反应提供理论参考。     

N2O一步氧化苯制苯酚FeZSM-5分子筛的失活与再生

将离子交换法制备并经水热处理的FeZSM-5分子筛应用于N2O一步氧化苯制苯酚反应中.在固定床反应器上研究了导致催化剂失活的原因,考察了失活催化剂的再生条件,并采用热重-差热综合热分析法(TG-DTA)、N2吸附比表面测定法(BET)和程序升温氧化法(TPO)等对失活前后的催化剂进行了表征.结果表明,FeZSM-5分子筛催化剂在N2O一步氧化苯制苯酚反应中具有较高的初始活性,但失括较快.失活催化剂上存在两种形式的积炭,C与H比不同的低温炭和高温炭是催化剂失活的主要原因.再生实验结果表明,失活催化剂在450℃下,在N2O气氛中烧炭再生处理40 min后,催化剂的活性可完全恢复,此时催化剂表面的积炭率仍保持在30%左右.     

固定流化床中N_2O一步氧化苯制苯酚的工艺条件研究

采用固定流化床反应器,研究了工艺条件对N20一步氧化苯制苯酚反应及Fe-ZSM-5分子筛催化剂性能的影响.在固定流化床反应器性能考察的基础上,以单因素实验法系统考察了温度(300～500℃)、原料苯/N_2O物质的量比(4:1～16:1)和操作气速(0.040～0.072 m/s)等对反应过程的影响;并基于单因素实验结果,采用L9(34)正交实验设计,综合考察了温度、原料苯/N_2O物质的量之比和操作气速对N_2O一步氧化苯制苯酚反应过程规律及产物分布的影响.以苯酚收率最大为目标函数最终确定的相对适宜工艺条件为:温度430℃,原料苯/N_2O摩尔物质的量之比9:1,操作气速0.050 m/s.在此条件下,苯酚的收率可达71.32%.     

N2O-步氧化苯制苯酚FeZSM-5分子筛的失活与再生

将离子交换法制备并经水热处理的FeZSM-5分子筛应用于N2O-步氧化苯制苯酚反应中。在固定床反应器上研究了导致催化剂失活的原因,考察了失活催化剂的再生条件,并采用热重-差热综合热分析法（TG-DTA）、N2吸附比表面测定法（BET）和程序升温氧化法（TPO）等对失活前后的催化剂进行了表征。结果表明,FeZSM-5分子筛催化剂在N2O-步氧化苯制苯酚反应中具有较高的初始活性,但失活较快。失活催化剂上存在两种形式的积炭,c与H比不同的低温炭和高温炭是催化剂失活的主要原因。再生实验结果表明,失活催化剂在450℃下,在N2O气氛中烧炭再生处理40min后,催化剂的活性可完全恢复,此时催化剂表面的积炭率仍保持在30％左右。     

AF—5分子筛催化剂上苯气相乙基化反应失活动力学研究…

根据前文的实验结果，提出了苯和乙烯在ＡＦ－５分子筛催化剂上进行烷基化反应的失活动力学模型，乙烯引起的失活，芳烃引起的失活可按独立失活处理。通过理论分析和数据拟合确定了动力学参数和失活参数，得到了如下失活动力学模型。动力学方程（－ｒｅ）＝ｄｃｅ／ｄτ＝－５６．３７ｅｘｐ（－２４．２／ＲＴ）┿ｅ＾１＾．＾１ψ（ｍｏｌ／ｋｇｃａｔ·ｓ）活性程（－ｒψ）＝ｄψ／ｄｔ＝－［２．０２×１０＾－＾４ｅｘｐ（－１     

苯一步法制苯酚反应中TS-1催化剂失活研究

考察了TS-1催化剂在过氧化氢氧化苯一步法制苯酚反应中的催化效果,研究表明在反应初期TS-1具有较高的反应活性,但易失活;采用XRD、SEM、微结构分析、TG-DTA多种方法分析反应前后TS-1的性质,表明反应前后其骨架结构未发生变化,失活催化剂晶型晶貌未发生明显改变,在TG由线中320℃附近有失重;失活催化荆可通过焙烧再生,其活性基本得到恢复,表明反应中催化剂的失活是由羽产物积碳所导致的暂时性失活.     

一步氧化法苯制苯酚的研究进展

苯酚作为重要的化工中间体,目前最主要的工业化生产采用的是异丙苯法,但其存在能耗高、反应条件苛刻以及苯酚收率低等局限性。因此,开发经济性高、可持续且绿色的合成苯酚方法十分必要。本文介绍了苯直接氧化合成苯酚的三大主要途径,为一步氧化法苯制苯酚的催化剂设计提供参考。     

Fe-ZSM-5分子筛催化剂催化降解高浓度含酚废水

以不同Si/Al比的H-ZSM-5分子筛制备了Fe-ZSM-5分子筛催化剂,研究了废水pH值、反应温度、催化剂用量、H2O2用量、反应时间、搅拌转速和Si/Al比对Fe-ZSM-5催化H2O2氧化降解高浓度含酚废水的影响,确定了较佳的工艺条件,苯酚的降解率可达99%以上,CODcr去除率达88%. Si/Al比高的催化剂活性较高,催化剂酸强度对反应影响显著,酸强度越高越有利于苯酚降解. Fe-ZSM-5分子筛催化剂经过多次重复使用,催化活性基本没有降低,使用寿命长. Fe-ZSM-5分子筛催化剂与Fenton试剂比较发现,Fe-ZSM-5非均相体系废水中的Fe离子浓度低于1′10-6 g/L,无二次污染,克服了Fenton试剂体系中存在大量Fe离子的缺陷.     

AF—5分子筛催化剂上苯气相乙基化反应的失活动力学研究…

在绝热固定床实验反应器中对苯和乙烯在ＡＦ－５分子筛催化剂上进行的烷基化反应的失活动力学作了研究。初步考察表明乙烯和苯都会引起失活，但乙烯引起的失活是主要的。在和工业反应器类似的操作条件下系统测定了由催化剂失活引起的乙烯转化率随操作时间的变化，所得数据将用于建立失活动力学模型。     

Benzene Selective Oxidation with N2O on Fe/MFI Catalysts: Role of Zeolite and Iron Sites on the Deactivation Mechanism

The catalytic performances of Fe-zeolites having MFI structures and in which the Fe introduced either by ion exchange or during the hydrothermal synthesis has undergone partial framework to extra-framework migration induced by controlled heat treatment are reported. In particular, the catalytic behavior as function of time-on-stream and the formation of carbonaceous species were studied. The results suggest that only a small fraction of the iron is active in the selective oxidation of benzene to phenol in the presence of N₂O. It is suggested that the active fraction is formed by isolated iron ions in a pseudo-octahedral configuration with the sites positioned in hydroxyl nests (defects) of the zeolite and is selective in phenol formation as a result of in situ reduction during the catalytic tests. Two possible pathways of carbonaceous species were identified, the first through the intermediate further hydroxylation of phenol and the second through the coupling of phenol with benzene or another phenol molecule. This second pathway is the dominant mechanism of formation of carbonaceous species, although the relative rate of the two pathways depends on the zeolite characteristics and iron loading. It is also suggested that the second pathway depends on the strong chemisorption of phenol, probably on Lewis acid sites, which hinders the fast back-desorption of phenol out from the zeolite channels and thus favors the formation of carbonaceous species. Catalysts prepared by hydrothermal treatment show a lower rate of deactivation than those prepared by ion exchange, although the latter show a comparable productivity to phenol for amounts of iron in extra-framework positions around 20 to 30 times lower. The results also indicate that the presence of Al in the zeolite framework is beneficial for reducing the rate of deactivation as compared to that of Fe-silicalite samples.     

电氧化N_2O_4制备N_2O_5工艺研究

以N2O4和HNO3为原料,通过电氧化法制备了新型绿色硝化剂N2O5,并研究了电解氧化法制备N2O5工艺的影响因素,主要讨论了电解反应时间、电流密度和反应温度对该工艺的影响。在反应时间为4～5h,电流密度为0.09～0.10A/cm2,反应温度为5～10℃时,可得到质量分数较高的N2O5阳极液。     

Cluster Model DFT Study of the Intermediates of Benzene to Phenol Oxidation by N2O on FeZSM-5 Zeolites

An Fe(II) ion at an -cation exchange position of ZSM-5 zeolite (Fe/Z) was taken as a model for the active site in the nitrous oxide decomposition and in the selective oxidation of phenol with nitrous oxide. The oxygen deposited by decomposition of N₂O is commonly referred to as -oxygen (OFe/Z). Cluster model DFT calculations show that the interaction of the OFe/Z center with benzene resulted easily in arene oxide formation. The results indicate a rather low activation energy for this step. Possible transformations of the adsorbed arene oxide are considered and the experimental evidence for the absence of the kinetic H/D isotope effect in phenol formation is discussed. It is concluded that the rate-limiting step for the in situ oxidation of benzene to phenol is the desorption of the product.     

Possible role of nitrite/nitrate redox cycles in N2O decomposition and light-off over Fe-ZSM-5

Surface nitrite/nitrate redox cycles were proposed to explain light-off behavior that was observed during the decomposition of N₂O over Fe-ZSM-5. Further study has demonstrated that while the nitrite/nitrate model can explain the original observations as an isothermal, mechanistic phenomenon, the light-off behavior is thermal, and not a mechanistic effect. Nonetheless, a pathway involving nitrite/nitrate redox cycles appears to be more consistent with experimental observation than the simple two-step pathway involving cation redox cycles. In particular, the nitrite/nitrate pathway can explain the effect of added NO upon the reaction kinetics and the reported isotopic product composition when unlabeled N₂O reacts over an oxygen-labeled catalyst. Further, a nitrite/nitrate pathway is consistent with the steady-state kinetics as well as published thermal desorption and infrared spectroscopic results.     

金属改性的FSM-16分子筛催化苯与过氧化氢合成苯酚

研究了金属改性的FSM-16分子筛在催化苯与过氧化氢合成苯酚反应中的应用,其中钒改性的FSM-16分子筛显示了较好的活性和高的选择性。当温度为323 K,反应时间为10 h,n(H2O2)∶n(C6H6)=1∶1,乙酸作溶剂,在催化剂V-FSM-16上得到苯的转化率为5.8%,苯酚的选择性为98.8%。催化剂的红外光谱和XRD的表征表明,钒进入了分子筛的骨架中。     

The Effect of Different Active Sites on the Catalytic Activity of Fe-ZSM-5 Zeolite for N2O Direct Decomposition

Fe-modified ZSM-5 zeolites (Si/Al = 25) were prepared by adopting the liquid ion-exchange method with nitrate and oxalate of iron as Fe precursors and their catalytic performance was studied in the N₂O decomposition reaction. The results of FT-IR and H₂-TPR investigations indicated that (i) part of the iron ions could replace Brönsted acid protons at the straight channel wall (α sites), intersection of straight and sinusoidal channels (β sites), and sinusoidal channel wall (γ sites) within the ZSM-5 zeolite; and (ii) different Fe precursors gave rise to various distributions of α, β, and γ sites. We observed that the Fe-ZSM-5 catalyst prepared with iron oxalate as Fe precursor outperformed the ones prepared with iron nitrate as Fe precursor in the direct decomposition of N₂O. Furthermore, the catalytic activity of iron ions located at the α sites was higher than those of iron ions located at the β and γ sites.     

N2O decomposition over wet- and solid-exchanged Fe-ZSM-5 catalysts

The N₂O decomposition activity of Fe-ZSM-5 strongly depends on the iron content and the preparation methods, including wet (WIE) and solid state ion exchanges (SSIE). The state of Fe species formed on the surface of a series of Fe-ZSM-5 catalysts containing a variety of Fe contents with respect to the preparation method and their role for N₂O decomposition activity have been systematically examined. The general trend for the decomposition activity of Fe-ZSM-5-SSIE is higher than that of Fe-ZSM-5-WIE, indicating the formation of a distinctive local structure of Fe on the catalyst surface during the course of the ion-exchange procedure. Based upon the Fourier transformed Fe K-edge EXAFS spectra for the series of Fe-ZSM-5-SSIE and -WIE catalysts, most of the Fe species on the surface of Fe-ZSM-5-SSIE with high Fe loading are well dispersed in the form of oxygen-bridged binuclear Fe species. The turnover frequency (TOF) for N₂O decomposition under dry and wet conditions has been confirmed assuming that Fe-ZSM-5-SSIE samples with Fe/Al = 0.20 and Fe/Al = 0.65 only contain mononuclear and binuclear Fe species, respectively, as active reaction species on their surface. The high performance of Fe-ZSM-5-SSIE may be mainly due to the formation of the binuclear Fe species onto its surface during the preparation of the catalyst.