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Study on Partial Hydrogenations of Adiponitrile and Benzene

Author: LiaoHongGuang
Tutor: LuoHeAn
School: Xiangtan University
Course: Chemical Engineering and Technology
Keywords: adiponitrile benzene partial hydrogenation ε-caprolactam catalyst 6-aminocapronitrile cyclohexene
CLC: TQ203.2
Type: PhD thesis
Year: 2013
Downloads: 69
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Abstract


ε-Caprolactam is a very important intermediate materials for nylon-6synthesis. Allcurrent commercial ε-caprolactam synthesis processes are main based on the classicaltechnologies, undergoing the cyclohexane oxidation which is a very low efficientprocess with per pass yield of4-5%without catalyst and8-10%catalyzed by cobaltcatalyst. Moreover, the traditional processes involve have several disadvantages such asmulti-step reactions, low atom efficiency, reactor corrosion, environmental pollution andlarge amounts of ammonium sulphate and wastes. To overcome the above-mentionedproblems, it is very attractive to simplify the traditional ε-caprolactam synthesisprocesses and develop the green chemistry method for ε-caprolactam production. Thenovel production routes for caprolactam based on hydrocyanation of butadiene andpartial hydrogenation of benzene avoiding the cyclohexane oxidation have theadvantages of high yield, environmental friendliness and atomic economy. Hence, weprepared and characterized a series of catalysts and their catalytic properties in the keysteps of selective hydrogenation of adiponitrile to6-aminocapronitrile and partialhydrogenation of benzene to cyclohexene were performed.Ni/α-Al2O3and potassium doped Ni/α-Al2O3catalysts with high nickel loadingwere prepared by incipient impregnation method and characterized by nitrogenadsorption-desorption, temperature programmed reduction, hydrogen chemisorption,power X-ray diffraction, transmission electron microscopy, scanning electronmicroscopy and laser particle size analytical technique. It reveals that potassium dopedNi/α-Al2O3has smaller nickel crystal size, higher nickel metallic surface area and betternickel dispersion. The prepared catalysts have been tested in liquid phase hydrogenationof adiponitrile in the absence of ammonia under mild condition. It has been found thatthe Ni/α-Al2O3catalyst doped with potassium and reduced under relatively lowertemperature is favorable to the formation of primary amines. And the Ni-K2O/α-Al2O3catalyst exhibits good performance that the selectivity of6-aminocapronitrile andhexamethylenediamine is99.7%at the adiponitrile conversion of74.1%.A series Ru catalyst supported on ZrO2, TiO2, ZnO, Al2O3, SiO2, CNT, MCM-41and SBA-15were prepared by precipitation method and tested in partial hydrogenationof benzene. The effects of supports’ properties and co-catalysts on cyclohexeneselectivity were discussed. It has been found that Ru/ZrO2with superior hydrophilicity and small specific surface areas and Ru/MCM-41with regular mesoporous structure andbig pore volume exhibit better cyclohexene selectivity than others. The strongerhydrophilicity, relative smaller specific surface areas, regular mesoporous structure andbiger pore volume of the Ru catalyst are beneficial to the desorption of the formedcyclohexene, which inhibits the further hydrogenation of cyclohexene to cyclohexane.Additionally, the promoters of Zn, Fe, La are in favour of improving the catalysthydrophilicity and Ru dispersion and decreasing the Ru activity, which could furtherincrease the cyclohexene selectivity.A mesoporous ZrO2was synthesized by hydrothermal method and characterized viaX-ray Diffraction, N2absorption-desorption technologies. The effects of crystallizationpH, crystallization time and crystallization temperature on the structure of ZrO2wereinvestigated. Ruthenium catalysts supported on the mesoporous ZrO2bydeposition-precipitation method were tested in the selective hydrogenation of benzene. Ithas been demonstrated that the superior hydrophilicity and regular mesoporous ofmesoporous ZrO2are helpful to improve the cyclohexene selectivity. The Ru-Zn catalystsupported on mesoporous ZrO2exhibits better performance than the catalyst supportedon the general ZrO2in partial hydrogenation of benzene.Zirconia, titania and zinc oxide modified mesoporous molecular sieve MCM-41supports were prepared by hydrothermal synthesis method, in situ synthesis method andprecipitation method. Ruthenium promoted by La, Ce, Zn, Fe and Cu catalysts supportedon modified MCM-41were prepared via two solvents impregnation method. Thecatalysts were characterized by X-ray diffraction, Transmission electron microscopy,nitrogen adsorption-desorption and water/benzene static adsorptions techniques. It hasbeen found that Ru-La supported on MCM-41modified with zirconia by hydrothermalsynthesis method （Ru-La/ZrO2-MCM-41-HS） leads to the biggest increase of thehydrophilicity and La shows better dispersity modification to Ru.Ru-La/ZrO2-MCM-41-HS catalyst with the highest hydrophilicity and dispersity showsthe best performance in liquid phase partial hydrogenation of benzene to cyclohexene.A further research of the effect of the pore structure and surface characteristic ofMCM-41and ZrO2on Ru catalyst performance has been developed. It has been foundthat the synthetic conditions of crystallization temperature, crystallization time, pH,mole ratio of surfactant to silicon, the dosage of assistant agent, mole ratio of Si/Al andcalcination temperature has strong impact on the specific surface area, pore volume andpore size and distribution. And relative smaller specific surface area, larger pore size and pore volume and regular mesorporous structure of MCM-41is favorable to thedesorption of cyclohexene. Furthermore, for the ZrO2-MCM-41-HS support, the surfaceproperty like the hydrophilicity, hydroxyl content and acid site of ZrO2also influencesthe performance of Ru-La/ZrO2-MCM-41-HS catalyst. It revels that the hydrophilicityof tetragonal zirconia is stronger than monoclinic zirconia and amorphous zirconiabecause of the richer surface hydroxyl content and form in tetragonal zirconia.Furthermore, only Lewis acid site exists on the surface of tetragonal zirconia, whichcould avoid the further hydrogenation of cyclohexene with the spilt-over hydrogenadsorbed on Br nsted acid site and lead to better performance ofRu-La/ZrO2-MCM-41-HS catalyst in partial hydrogenation of benzene. Over theRu-La/ZrO2-MCM-41catalyst, the benzene conversion is65.6%and the cyclohexeneyield is46.2%.

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