不同形貌纳米氧化锌的制备及其对有机催化反应活性的影响研究进展

纳米氧化锌是沿C轴具有较强极性的极性晶体,改变外部反应条件可以制备出棒状、层状、球状、花状等形貌多样的纳米级氧化锌晶体。近年来很多文献报道不同形貌的纳米氧化锌作为催化剂对甲醇合成、甲醇水蒸气重整制氢、乙醇水蒸气重整制氢等有机催化反应的活性不同。本文综述了反应溶剂、锌源、表面活性剂和pH值等反应条件对纳米氧化锌形貌影响的研究进展以及不同形貌的纳米氧化锌作为催化剂载体或催化剂活性组分对有机催化反应活性的影响。     

乙炔氢氯化制氯乙烯反应中水蒸汽对铜铋催化剂活性组分的稳定作用

通过引入水蒸汽改进乙炔氢氯化反应中铜铋催化剂的再生性能,将催化剂多次循环反应评价其稳定性. 结果表明,与传统的空气再生法6 h循环再生造成近95%以上催化剂活性组分流失相比,引入水蒸汽可将催化剂表面在反应过程中形成的易升华的BiCl3转化为具有很好热稳定性的BiPO4,提高了催化剂的稳定性,经15 h循环再生后活性组分Bi仅损失20%,且可保持初始反应活性,使催化剂的工业化成为可能.     

苯乙烯-异戊二烯-苯乙烯嵌段共聚物选择性催化加氢

苯乙烯-异戊二烯-苯乙烯嵌段共聚物(SIS)通过催化加氢可提高物理化学性能,使其更广泛地应用于工业中。以氯铂酸、尿素为原料,通过简单的浸渍还原法制备了Pt/g-C_3N_4催化剂并应用于SIS非均相催化加氢反应。采用XRD、TEM、~1HNMR和DSC对催化剂及产物进行了结构表征,考察了催化剂组成、Pt负载量、反应条件等因素对SIS加氢性能的影响。结果表明,以环己烷作溶剂,SIS用量是催化剂质量的2.3倍,在140℃、2 MPa条件下反应2 h,催化剂具有很好的活性和选择性,SIS加氢度为85%,对聚异戊二烯段碳碳双键选择性高达95%。     

固体碱催化剂用于油脂甲醇酯交换反应制备生物柴油

固体碱催化剂用于酯交换反应制备生物柴油有易分离、流程简单的优点。通过金属氧化物活性筛选,发现氧化钙具有很好的酯交换反应活性。将乙酸钙溶液等体积浸渍负载于碱性载体MgO上,并煅烧得到了氧化钙负载量为16.5％(质量)的CaO/MgO混合氧化物催化剂,其在油脂甲醇酯交换反应制备生物柴油的过程中具有高的反应活性。在64.5℃、醇油比18∶1 、催化剂用量2%、反应3.5 h条件下,油脂转化率为92%,接近传统的液体强碱NaOH的催化能力。用XRD、AAS、XPS、CO2 -TPD等对制得的系列催化剂进行了表征,发现催化剂的碱强度对酯交换反应有着重要的影响。通过选择合适的载体、含钙前驱体和氧化钙负载量可以增加负载型氧化钙催化剂的强碱性位,提高催化剂的反应活性。     

连续催化酯化-精馏联合过程合成乙酸正丙酯的研究

在一连续酯化-精馏装置中,对以固体酸为催化剂、乙酸与正丙醇为原料合成乙酸正丙酯的酯化反应进行了研究.结果表明催化剂在反应条件下有很高的活性,运行300小时后仍具有很好的稳定性和寿命,酯化率达96%以上.     

草酸二甲酯气相法加氢制乙二醇催化剂研究进展

草酸二甲酯的气相加氢具有高水平的活性,采用共沉淀法制备需要不同特性规格的沉淀剂,催化剂的组合和反应条件都对乙二醇的合成性质具有明显的性能影响。通过采用独特的吸附方法表征制备的催化剂,以及通过试验获得的值表明草酸二甲酯的独特氢化反应与铜离子的独特活性状态密切相关。此外,通过气相催化得到的乙二醇,草酸二甲酯的比转化率可超过97%;乙二醇的选择性特征高达85%;制备的催化剂突出了最佳的稳定性能。     

低压法甲醇合成催化剂

低压法合成甲醇催化剂现在使用较多的是CuO-ZnO-A l2O3为主要组成的铜基催化剂。在合成甲醇时,一氧化碳在铜催化剂表面的吸附率相当高,而对氢的吸附则比一氧化碳慢得多;氧化锌是很好的氢化剂,使氢吸附和活化,可提高铜基催化剂的转化率。催化剂还原后才具有活性,因此使用前必须先进行还原。介绍了铜基催化剂还原过程中的注意事项。     

TS-1分子筛光催化氧化降解氧化乐果

以TS-1分子筛为光催化剂,H2O2为氧化剂,紫外灯为光源,对农药氧化乐果进行光催化氧化降解研究。详细考察了催化剂添加质量浓度,H2O2添加体积分数和光照时间对氧化乐果降解率的影响。实验结果表明,TS-1分子筛催化剂对氧化乐果具有很好的催化降解活性。氧化乐果可以降解为CO2,NH3,SO42-,PO43-等。最佳反应条件:催化剂质量浓度5 g/L,H2O2体积分数30 mL/L,光照时间90 min,氧化乐果降解率高达96%。此反应为一级动力学反应。三次再生后,TS-1分子筛对氧化乐果的光催化活性没有明显降低。     

高水热稳定性加氢脱氧Ni-Mo复合氧化物催化剂的制备

以动植物油脂为原料加氢脱氧生产生物柴油的关键是开发具有优异加氢脱氧活性和稳定性的新型催化剂。今采用溶胶凝胶法制备了本体型Ni-Mo复合氧化物加氢脱氧催化剂,并对其进行了XRD、BET等表征,以含20%小桐子油的正辛烷溶液为原料,在连续固定床反应装置上考察了催化剂的活性和水热稳定性。结果表明:溶胶凝胶法可制备出具有优异活性的钼镍复合氧化物催化剂,水热处理后催化剂的比表面积和孔容减小以及形成了部分Ni Mo O4新相,前者使催化剂的活性下降,后者使催化剂的活性增加,二者的综合作用使水热处理催化剂的活性下降。提高催化剂的焙烧温度或添加镁铝尖晶石等方法可有效改善催化剂的水热稳定性和调控小桐子油的加氢脱氧反应路径。在330℃、2~5 h-1和310℃、2 h-1条件下,小桐子油在700℃焙烧、水热处理前后的催化剂上的脱氧率均高达99.0%以上。与在水热处理前催化剂上的反应结果相比,小桐子油在水热处理后催化剂上的脱羧基、脱羰基反应产物增加了15%。     

载体结构对钙钛矿氨分解催化活性的影响

采用溶胶凝胶法,制备了负载型镍基钙钛矿型催化剂,并在常压微反应装置上对其氨分解催化活性进行了评价。采用BET、XRD、TPR、TEM等方法对催化剂进行表征。研究结果表明,以MCM-41分子筛为载体的催化剂,由于其较大的比表面积和规整的介孔结构,使活性组分能够很好地分散在载体表面,有利于增加有效活性位,提高活性组分的反应能力,表现出很好的氨分解催化活性。以NiO计,负载量为20%的LaNiO₃/MCM-41具有比非负载的LaNiO₃更好的催化活性,这样不仅提高了催化活性,还大大地减少了活性组分用量,降低了生产成本,从而具有很好的应用前景。     

Supported solid and heteropoly acid catalysts for production of biodiesel

Biodiesel has developed attraction of most researchers recently because of its renewable resources and environmental benefits. Transesterification process in the presence of catalysts is the most common way, which is used for biodiesel production. Heterogeneous acid catalysts are considered more reliable than any other catalysts to carry out most vital reactions related to green chemistry (biodiesel production), because the production of biodiesel from solid acid catalysts is considered economically favorable. Nowadays, biodiesel is preparing from low quality feedstock by using solid acids catalysts in many research laboratory throughout the world. This article discusses how much catalyst shapes affect the efficiency of catalyst during catalysis. Different types of supports (zinc oxide, alumina, zirconia, and silica) are used to increase the efficiency of catalysts. Supported Lewis acid, Brønsted acid, and heteropoly acid catalysts show good efficiency for the catalytic transesterification of oil with alcohol. Heteropoly acid catalysts are tremendous and environment friendly acid catalyst and have ability to tolerate contaminations of oil resources such as water contents and free fatty acids (FFAs) contents. Keggin-type heteropoly acids are easily available and having stable structure while Wells–Dawson-type heteropoly acids are included in super acid class, due to these reasons heteropoly acids are considered as best acidic catalysts for biodiesel production by catalytic transesterification process. Therefore, this review also focused on the deactivation, regeneration and advantages of supported solid acid catalysts used for the catalytic production of biodiesel through transesterification.     

Transesterification of karanja (Pongamia pinnata) oil by solid basic catalysts

The transesterification of karanja oil with methanol was carried out using solid basic catalysts. Alkali metal‐impregnated calcium oxide catalysts, due to their strong basicity, catalyze the transesterification of triacylglycerols. The alkali metal (Li, Na, K)‐doped calcium oxide catalysts were prepared and used for the transesterification of karanja oil containing 0.48–5.75% of free fatty acids (FFA). The reaction conditions, such as catalyst concentration, reaction temperature and molar ratio of methanol/oil, were optimized with the solid basic Li/CaO catalyst. This catalyst, at a concentration of 2 wt‐%, resulted in 94.9 wt‐% of methyl esters in 8 h at a reaction temperature of 65 °C and a 12 : 1 molar ratio of methanol to oil, during methanolysis of karanja oil having 1.45% FFA. The yield of methyl esters decreased from 94.9 to 90.3 wt‐% when the FFA content of karanja oil was increased from 0.48 to 5.75%. The performance of this catalyst was not significantly affected in the presence of a high FFA content up to 5.75%. The catalytic activities of Na/CaO and K/CaO were also studied at the optimized reaction conditions. In these two cases, the reaction initially proceeds slowly, however, leading to similar yields as in the case of Li/CaO after 8 h of reaction time. The purified karanja methyl esters have an acid value of 0.36 mg KOH/g and an ester content of 98.6 wt‐%, which satisfy the American as well as the European specifications for biodiesel in terms of acid value and ester content.     

Cordierite Honeycomb Monoliths Coated with Zirconia and Its Modified Forms for Biodiesel Synthesis from Pongamia glabra

This study investigates the use of cordierite honeycomb monoliths coated with solid acids such as zirconia, Mo(VI)/ZrO₂ and Pt‐SO₄^2?/ZrO₂ and solid bases like zirconia–calcia, zirconia–magnesia mixed oxides in the synthesis of biodiesel from oil (PG‐oil). Solid acids were used for the esterification of free fatty acids in PG‐oil with methanol to reduce the percentage of free fatty acids in the oil followed by transesterification of PG‐oil over solid bases to synthesize biodiesel. The oxide catalysts were coated on honeycombs by an impregnation technique and characterized for their surface acidity/basicity, crystallinity and morphology. The effect of the molar ratio of PG‐oil/methanol in esterification and transesterification was studied. Reactivation and reusability of both solid acid and solid base catalysts was investigated. The catalysts were also prepared in their powder forms and their activity was compared with that of honeycomb coated forms. A twofold increase in the yield of biodiesel was obtained when the catalysts were used in honeycomb coated forms. The results revealed that the honeycombs coated with mixed oxides such as zirconia–calcia and zirconia–magnesia were economical, efficient and eco‐friendly (3e concept) for biodiesel production with ~95 % yield.     

MnO and TiO solid catalysts with low-grade feedstocks for biodiesel production

Manganese (II) oxide (MnO) and titanium (II) oxide (TiO) solid catalysts were found to be robust catalysts for both the transesterification of triglycerides and esterification of free fatty acids. These metal oxides were shown to exhibit long life with little loss of activity. The ability to esterify free fatty acids (FFA) and handle high levels of water illustrates the potential of these catalysts to produce biodiesel from low quality feedstocks without the pretreatment operations required with the traditional process. Some soaps were produced in the presence of free fatty acids, but soaps were within tolerable levels and formed at concentrations that were orders of magnitude lower than the traditional process. This results in significant reductions in product washing. By utilizing a 2-stage process, high quality fuel (meeting ASTM specifications) and glycerol were produced.     

Oil transesterification over calcium oxides modified with lanthanum

Investigations were conducted on a series of calcium and lanthanum oxides catalyst for biodiesel production. Mixed oxides catalyst showed a superior transesterification activity over pure calcium or pure lanthanum oxide catalysts. The catalyst activity was correlated with surface basicity and specific surface areas. The effects of water and free fatty acids (FFA) levels in oil feedstock, water and CO₂ in air, mass ratio of catalyst, molar ratio of oil to methanol, and reaction temperature on fatty acid methyl ester (FAME) yield were investigated. Under optimal conditions, FAME yields reached 94.3% within 60 min at 58 °C. Mixed CaO-La₂O₃ catalyst showed a high tolerance to water and FFA, and could be used for converting pure or diluted unrefined/waste oils to biodiesel.     

Biodiesel production from waste animal fats using pyrolysis method

It is necessary to utilize waste cooking oil as a raw material of biodiesel because the land area available for cultivation in Japan is limited. Waste cooking oil also includes long-chain saturated compounds and free fatty acids derived from animal fats. The former has a high freezing point and the latter forms a soap with the alkali catalyst typically used in biodiesel production, reducing the yield. To make waste cooking oil available for biodiesel production, pyrolysis of the waste oil was attempted. The resulting triacylglycerols were found to decompose at 360 to 390 °C, fatty acids were generated by cleavage of the ester bond, and short-chain hydrocarbons and short-chain fatty acids were generated by cleavage of the unsaturated bonds in the hydrocarbon chain. When the retention time was extended with a reaction temperature of 420 °C, light-oil hydrocarbons were generated by decarboxylation of the fatty acids. By adding palladium supported by activated carbon (Pd/C) as a catalyst, decarboxylation was promoted, and hydrocarbons comparable to light oil were selectively obtained in high yield at 85 wt.%. Compared to the biodiesel obtained by transesterification, the biodiesel obtained by pyrolysis showed improvement of about − 5 °C in the pseudo-cold filter plugging point.     

Biodiesel Production from Soybean Oil Catalyzed by Li<Subscript>2</Subscript>CO<Subscript>3</Subscript>

In the present study, we synthesized biodiesel from soybean oil through a transesterification reaction catalyzed by lithium carbonate. Under the optimal reaction conditions of methanol/oil molar ratio 32:1, 12 % (wt/wt oil) catalyst amount, and a reaction temperature of 65 °C for 2 h, there was a 97.2 % conversion to biodiesel from soybean oil. The present study also evaluated the effects of methanol/oil ratio, catalyst amount, and reaction time on conversion. The catalytic activity of solid base catalysts was insensitive to exposure to air prior to use in the transesterification reaction. Results from ICP-OES exhibited non-significant leaching of the Li₂CO₃ active species into the reaction medium, and reusability of the catalyst was tested successfully in ten subsequent cycles. Free fatty acid in the feedstock for biodiesel production should not be higher than 0.12 % to afford a product that passes the EN biodiesel standard. Product quality, ester content, free glycerol, total glycerol, density, flash point, sulfur content, kinematic viscosity, copper corrosion, cetane number, iodine value, and acid value fulfilled ASTM and EN standards. Commercially available Li₂CO₃ is suitable for direct use in biodiesel production without further drying or thermal pretreatment, avoiding the usual solid catalyst need for activation at high temperature.     

Biodiesel production from vegetable oil using heterogenous acid and alkali catalyst

Zanthoxylum bungeanum seed oil (ZSO) with high free fatty acids (FFA) can be used for biodiesel production by ferric sulfate-catalyzed esterification followed by transesterification using calcium oxide (CaO) as an alkaline catalyst. Acid value of ZSO with high FFA can be reduced to less than 2 mg KOH/g by one-step esterification with methanol-to-FFA molar ratio 40.91:1, ferric sulfate 9.75% (based on the weight of FFA), reaction temperature 95 °C and reaction time 2 h, which satisfies transesterification using an alkaline catalyst. The response surface methodology (RSM) was used to optimize the conditions for ZSO biodiesel production using CaO as a catalyst. A quadratic polynomial equation was obtained for biodiesel conversion by multiple regression analysis and verification experiments confirmed the validity of the predicted model. The optimum combination for transesterification was methanol-to-oil molar ratio 11.69:1, catalyst amount 2.52%, and reaction time 2.45 h. At this optimum condition, the conversion to biodiesel reached above 96%. This study provided a practical method to biodiesel production from raw feedstocks with high FFA with high reaction rate, less corrosion, less toxicity, and less environmental problems.     

Biodiesel synthesis combining pre-esterification with alkali catalyzed process from rapeseed oil deodorizer distillate

A two-step technique combining pre-esterification catalyzed by cation exchange resin with transesterification catalyzed by base alkali was developed to produce biodiesel from rapeseed oil deodorizer distillate (RDOD). The free fatty acids (FFAs) in the feedstock were converted to methyl esters in the pre-esterification step using a column reactor packed with cation exchange resin. The acid value of oil was reduced from the initial 97.60 mg-KOH g^? 1 oil to 1.12 mg-KOH g^? 1 oil under the conditions of cation exchange resin D002 catalyst packed dosage 18 wt.% (based on oil weight), oil to methanol molar ratio 1:9, reaction temperature 60 °C, and reaction time 4 h. The biodiesel yield by transesterification was 97.4% in 1.5 h using 0.8 wt.% KOH as catalyst and a molar ratio of oil to methanol 1:4 at 60 °C. The properties of RDOD biodiesel production in a packed column reactor followed by KOH catalyzed transesterification were measured up the standards of EN14214 and ASTM6751-03.     

Synthesis of Phytosteryl Esters by Using Alumina-Supported Zinc Oxide (ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) from Esterification Production of Phytosterol with Fatty Acid

The feasibility of zinc oxide-catalyzed esterification of natural phytosterols with oleic acid was investigated well by a chemical process. The influences of various reaction parameters were evaluated. Basic solid zinc oxide is the most desirable catalyst due to its high selectivity (more than 90%), reusability, activity and less corrosivity, whereas sterol selectivity with other catalysts, such as H₂SO₄, NaHSO₄ and NaOMe, did not exceed 80%. Further results showed that during zinc oxide-catalyzed synthesis, the nature of the acyl donor was of paramount importance with direct esterification with fatty acids, which gives better results with higher conversion rate selectivity and more mild reaction conditions than transesterification with methyl esters. The substrate molar ratio of 2:1 (oleic acid/phytosterol) was optimal. Other parameters such as optimal catalyst load (0.5%) and temperature (170 °C) showed a maximum production of steryl esters close to 98% after 8 h. It was also found that the amount of trans fatty acid formed in esterification was low, and the trans fatty acid content (%) in the phytosterol oleate ester fraction (3.26%) was much lower than that in free oleic oil (7.35%), which suggested that fatty acids in esters were more stable than free fatty acids regarding the combination with sterol. Immobilized ZnO could be a promising catalyst for replacing homogeneous and corrosive catalysts for esterification reactions of sterol.