Efficient oxidation of p-xylene to terephthalic acid by using N,N-dihydroxypyromellitimide in conjunction with Co-benzenetricarb.pdf

1、Applied Catalysis A,General 599(2020)117569 Contents lists available at ScienceDirect Applied Catalysis A,General ELSEVIER journal homepage: Efficient oxidation of p-xylene to terephthalic acid by using N,Ndihydroxypyromellitimide in conjunction with Co-benzenetricarboxylate Luo Xua Dawei Chena Haor

2、an Jianga Xia Yuana,b,.,a College of Chemical Engineering,Xiangtan University,Xiangtan,411105,China b National&Local United Engineering Research Centre for Chemical Process Simulation and Intensification,Xiangtan,411105,China ART I CLE INFO A BSTRA CT Keywords:p-Xylene oxidation Terephthalic acid Co

3、-benzenetricarboxylate NDHPI Metal-0rganic framework The MOF Co-BTC(BTC=benzenetricarboxylate)has been synthesized by a hydrothermal method,and characterized by means of N2 physical adsorption,X-ray diffraction,scanning electron microscope,thermogravimetric analysis,and X-ray photoelectron spectrosc

4、opy.The material has multiple crevices,as opposed to a pore structure,and shows high thermal stability,with Co in the divalent state.It has been used in conjunction with N,N-dihydroxypyromellitimide to catalyze the oxidation of p-xylene to terephthalic acid,the reaction conditions for which have bee

5、n investigated and optimized.At 150 C,with acetonitrile as solvent instead of acetic acid and in the absence of corrosive bromine,the conversion of p-xylene reached 100%and the selectivity for terephthalic acid exceeded 97%.Under the optimized conditions,Co-BTC exhibits stronger catalytic activity t

6、han cobalt(II)acetate,and maintains excellent stability during the reaction.The reaction mechanism has been deduced,and the roles of N,N-dihydroxypyromellitimide and Co-BTC as synergistic catalysts in the reaction have been clarified.1.Introduction In the polyester industry,terephthalic acid(TA)is a

7、n important raw material used primarily in the manufacture of non-toxic polyethylene terephthalate(PET),which accounts for about 20%of the polyester market.PET is mainly used in machinery parts,fiber materials,and packaging for foods and medicines.Oxidation of p-xylene(PX)is the main route for obtai

8、ning TA.This process is shown in Scheme 1,and is consistent with a mechanism of hydrocarbon radical oxidation.In general,the difficulty of hydrocarbon oxidation lies mainly in the initiation step,that is,the formation of hydrocarbon radicals by the removal of hydrogen from alkyl groups 1-4.However,i

9、n the oxidation of PX,p-methyl benzyl radical and pTA will also be present 5,which are resistant to oxidation.Due to the difficult oxidation characteristics of PX,current industrial production of TA mainly relies on the harsh Amoco process,using cobalt(II)acetate,manganese(II)acetate,and bromine as

10、catalysts,and acetic acid as solvent,which is conducted at high temperature(about 200 C)and high pressure(1.5-3.0 MPa).The selectivity for TA is over 95%.Under the high-temperature operating conditions,corrosive bromine acts as a co-catalyst,resulting in high production and equipment costs.Therefore

11、,the quest for an efficient and mild catalyzed route for PX oxidation,leading to TA without the need for acid and bromine,has become a hot topic of research.N-Hydroxyphthalimide(NHPI)and its derivatives are effective catalysts for the oxidation of organic compounds by molecular oxygen under mild con

12、ditions 6,and are widely used as initiators for the oxidation of hydrocarbons.Tashiro et al.7 used NHPI/Co(OAc)z/Mn(OAc)z as a catalyst and acetic acid as a solvent to oxidize PX at 100 C.The yield of TA reached 82%after 14 h of reaction;when the temperature was raised to 150 C,the yield of TA reach

13、ed 84%after 3 h.Koshino et al.found that the PINO formed by the-NO-H cleavage of NHPI is more likely to capture a proton from the alkyl group on the alkyl aromatic hydrocarbon in acetonitrile(MeCN)than in acetic acid;during the oxidation of PX,the effect of N,N-dihydroxypyromellitimide(NDHPI)as an i

14、nitiator is superior to that of NHPI because it bears two-NOH groups 8.Heterogeneous catalysts have also been used to catalyze the oxidation of PX 9.Ratnasamy et al.loaded cobalt manganese oxide into a zeolite to catalyze the oxidation of PX at high temperature(473 K)and an air pressure of 550 psi.T

15、he conversion of PX was 100%,and the selectivity for TA was over 98%,but corrosive bromine was still needed as a co-catalyst to capture hydrogen from the methyl group 10.Deka et al.prepared porous Ce02 as a catalyst to catalyze the oxidation of PX to TA.Using only water as a solvent under extremely

16、mild conditions(70 C,1 bar 02),the conversion of PX reached 100%and the Corresponding author at:College of Chemical Engineering,Xiangtan University,Xiangtan,411105,Hunan,China.E-mail address:(X.Yuan).https:/doi.org/10.1016/j.apcata.2020.117569 Received 21 December 2019;Received in revised form 6 Apr

17、il 2020;Accepted 14 April 2020 Available online 07 May 2020 0926-860X/2020 Elsevier B.V.All rights reserved.L.Xu,et aL p-toluladehyde(p-T ALD)4-carbox)benzaldehyde(4-CBA)0.0 5 Scheme 1.Oxidation of PX to TA.0.5 Relative Pressure(P/Po)Fig.1.N2 adsorption/desorption of Co-BTC.10 15 20-Fresh 25 2Theta-

18、Cycle 1 30 35 Fig.2.XRD of Co-BTC.40 I 1.0 45 selectivity for TA exceeded 99%11.Guo et al.used a metalloporphyrin(T(p-Cl)PPMnCl)as a catalyst to catalyze the oxidation of PX with acetic acid as a solvent,although its concentration was as high as 20%.Under these operating conditions(3.5 h,180 C,2.0 M

19、Pa),the conversion rate of PX was 41.8%,the selectivity for p-TA is 82.1%,but the selectivity for TA was only 12.4%12.Porous metal-organic frameworks(MOFs),due to their variable combinations of metals and organic ligands,offer great diversity in their structures and properties,making them suitable f

20、or adsorbing drugs 13 and harmful substances 14,15 as well as gas absorption 16-18 and storage 19.They also have broad prospects and value in 2 100 90 80;?.70 t 60 50 40 30 815-Wt,%-DTG,%Applied Catalysis A,General 599(2020)117569-0.02-0.04-0.06:?.-0 08 Cl-0.10-0.12-=-0.14 L.-0.16 100 810 200 300 40

21、0 500 600 700 800 Temperature,Fig.3.TGA of Co-BTC.805 800 795 Binding energy,eV 790 781.8 785 780 Fig.4.XPS spectrum of Co-BTC with peak fittings.the field of catalysis 18,20,19,20,21,22,23.To date,MOFs have been studied as heterogeneous catalysts in the selective oxidation of some hydrocarbons,such

22、 as cyclohexane 24-27,cyclooctane 28,olefins 27,29-32,alcohols,27,33-35,and so on.Wang et al.used a CuMOF as a catalyst to catalyze the oxidation of PX to 4-hydroxymethylbenzoic acid under a mild conditions 36.To the best of our knowledge,however,no MOFs have hitherto been used in the oxidation of P

23、X to TA.In this study,Co-BTC(BTC=benzenetricarboxylate)has been used as a catalyst for the first time in the oxidation of PX to TA.It has been used in conjunction with NDHPI instead of corrosive bromine as an initiator for PX oxidation in the non-acidic solvent MeCN.The catalytic properties of Co-BT

24、C and cobalt(II)acetate have also been compared.Through suitably designed experiments,the mode of action of NDHPI and Co-BTC in PX oxidation has been investigated.Furthermore,the stability of Co-BTC in the oxidation of PX has been studied.2.Materials and methods 2.1.Materials and reagents MeCN(AR),P

25、X(AR),Co(OAch-4H2O(AR),Co(NO3h-6H2O(AR),trimesic acid(H3BTC,AR),NDHPI(AR),dimethyl sulfoxide(DMSO,AR),and ethanol(AR)were purchased from Macklin.Water was purified and deionized in our laboratory.2.2.Synthetic procedure Co-BTC was synthesized according to a method in the literature 37,with some modi

26、fications.The specific process was as follows:Co L.Xu,et aL Applied Catalysis A,General 599(2020)117569 Fig.5.SEM images of Co-BTC.Table 1 Study of catalytic performance.NDHPI Co-BTC Conversion Selectivity/%/g/g/%p-TALD p-TA 4-CBA TA la 0.1 0 0 0 0 0 0 2a 0 0.1 0 0 0 0 0 3a 0.1 0.1 57.0 3.6 89.4 1.6

27、 5.4 4b 0.372 0 93.5 0 30 2.5 67.5 5b 0 0.05 3.1 97 3 0 0 5b 0.372 0.02 100 0 2.5 1.3 96.2 7 0.372 0 100 0 10 0.9 89.1 a Reaction carried out at 100 C for 12h,10g PX,20g MeCN,3.0MPa 02 b Reaction carried out at 150 C for 12 h,0.54 g PX,25 g MeCN,3.0 MPa 02 c Reaction carried out at 150 C for 12 h,0.

28、54 g PX,25 g MeCN,3.0 MPa 02;0.025 g Co(0Acz-6H20 was added.(N03h-6H20(4.8 g)was dissolved in deionized water(20 mL),and H3BTC(2.0 g)was dissolved in absolute ethanol(130 mL).When the two materials had completely dissolved,the two solutions were mixed,and the mixture was transferred to a 200 mL Tefl

29、on crystallization vessel.After agitation in an ultrasonicator for 20 min,the mixture was transferred to an incubator for crystallization by programmed temperature control.First,the temperature was quickly raised to 140 C within 22 min and maintained at this level for 24 h;it was then uniformly lowe

30、red to 120 C in 200 min.After 5 h,the temperature was steadily reduced to 100 C over a period of 200 min and maintained at this level for 5 h.Finally,the mixture was cooled to room temperature.The vessel was removed from the incubator,the supernatant was decanted,and the solid was collected by sucti

31、on filtration and washed with absolute ethanol until the washings were colorless and transparent.Thereafter,the solid was placed in a vacuum oven at 80 C for 24 h.The dark-blue solid product was designated as Co-BTC.2.3.Catalysis and product analysis All reactions were carried out in an autoclave eq

32、uipped with a 100 mL quartz vessel and operated at a stirring speed of 1000 rpm.In a representative reaction process,combined catalyst(0.372 g NDHPI,0.05 g Co-BTC),raw material(0.54 g PX),and solvent(25 g 3 acetonitrile)were combined in the quartz vessel.The autoclave was then closed,and the inside

33、of the reactor was flushed twice with oxygen through a valve.The reactor was finally supplied with oxygen(3 MPa,room temperature),then heated to 150 C,and the reaction was allowed to proceed for 12 h.Thereafter,the product was taken up in DMSO and analyzed by high-performance liquid chromatography 38.2.4.Characterization The specific surface areas and pore structures of samples were measured by N2