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The Catalytic Oxidation Of Isobutane To Produce Tert-butyl Hydroperoxide

Posted on:2013-06-05Degree:MasterType:Thesis
Country:ChinaCandidate:Q FengFull Text:PDF
GTID:2251330401950743Subject:Chemical Engineering and Technology
Abstract/Summary:PDF Full Text Request
Tert-butyl hydroperoxide (TBHP), one kind of important organic peroxide oroxidant of co-oxidation process to prepare propylene oxide, has been frequently usedas alkyl hydroperoxides for the radical reaction or polymerization initiator.Nowadays, there are mainly three industrial methods to produce TBHP:oxidation of tert-butanol, oxidation of isobutylene by hydroperoxide, and oxidation ofisobutane, etc. The first method is widely applied in the domestic industry because ofits low investment cost. However, the discharge in the process has a side effect on theenvironment. The use of oxidation of isobutylene by hydroperoxide is limited by theinconvenience of raw material storage and harsh operating conditions. In theoxidation of isobutene method, that is Arco process, the conversion of isobutane is36.9%; the selectivity of TBHP and TBA (mole fraction) is53.4%and40.2%,respectively, at the condition of137oC and3.15MPa. Although this method isenvironmental friendly, the cost of equipment investment is expensive as the processrequires high temperature and pressure. Also, TBHP is instable at75oC or higher, andwill decompose above90oC, which will cause the potential safety harzard. Besides,there is a longer induce time exist before reaction, which will also lead to lowproductivity.In order to overcome the drawbacks of the high reaction temperature andpressure in the industrial application, and maximize the selectivity towards TBHPwithout making too great a sacrifice on the rate and conversion, it is necessary toconstruct a novel catalytic system, and make a systematic research on the optimalcondition and the mechanism of the reaction to achieve this goal.This thesis developes a novel catalytic system to catalyze isobutane with O2using N-hydroxyphthalimide (NHPI) as catalyst under mild condition. Afterinvestigated the effect of parameters such as catalyst dosage, mole ratio of rawmaterials, temperature, reaction time, amount of solvent, etc. on the reaction, theoptimal condition is confirmed. The results of orthogonal experimental show that inthe condition of NHPI dosage of2.72wt%, molar ration of n(isobutane):n(O2)=1.75,reaction temperature85oC, reaction time7h, the amount of acetonitrile (as solvent)20mL, the reaction can get a better result. The conversion of isobutane reaches28.76%,the selectivity of tert-butyl hydroperoxide and tert-butanol are64.94%and33.45%, respectively. With the addition of a small amount of α-α’-azoic-isobutyronitrile(AIBN),the conversion of isobutane is33.32%, the selectivity of tert-butyl hydroperoxide andtert-butanol are52.23%and44.47%, respectively. All of these indexes close to theArco process. Furthermore, the addition of ditert butyl peroxide, TBHP andanthraquinone can improve the selectivity of tert-butyl hydroperoxide.The possible reaction mechanism is proposed based on the oxidation productswith GC-MS analysis. The main side-products are: methanol, acetone, tert-butylmethyl ether, ditert butyl peroxide, et al. The methanol and acetone are the products ofthe side reaction of isobutane reacts with O2, tert-butyl methyl ether forms as a resultof tert butanol reacts with isobutane, while the ditert butyl peroxide is the product oftert-butanol reacts with TBHP in the metal-clave. The further study shows that thereaction mechanism is as follows. The active free radical PINO is generated whenNHPI is heated and the PINO takes the hydrogen atom from O-H of isobutene. Thelatter forms the terti-butyl radical, captures O2, and forms the radical C-O-O, whichcombines with the hydrogen atom from tert-butal of isobutane, then gives TBHP. Thereuse of catalyst is accomplished by centrifugal separation after cooling down thesystem, and the recovery of NHPI is80%or so. The activity of recovery NHPIdeclines, whereas the results of UV and IR characterizations demonstrate that there isno obvious difference between the fresh catalyst and the recycled catalyst in structure.With the help of GC-MS analysis, the possible reason is the thermal decomposition ofNHPI to non-activity products, such as phthalic anhydride, phthalimide and phthalicacid, et al.
Keywords/Search Tags:Isobutane, Catalytic oxidation, Tert-butyl peroxide(TBHP), Tert-butanol, N-hydroxyphthalimide(NHPI)
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