Study On The Oxidation Characteristics And Products Of ?-pinene And ?-pinene With Oxygen

Alpha-pinene and beta-pinene are two chief constituents of turpentine oil.They are important natural and renewable resource,which are widely used in industries such as spice and household chemicals.Alpha-pinene and beta-pinene could be oxidized by oxygen in the process of production,storage and application,which would lead to the deterioration of products.Therefore,it is necessary to study the oxidation process of alpha-pinene and beta-pinene with oxygen at lower temperature.The main research contents and results were as follows:(1)The reaction pressure and temperature in the oxidation process of alpha-pinene and beta-pinene with oxygen at low temperatureThe reaction pressure and temperature in the oxidation process of alpha-pinene and beta-pinene with oxygen or nitrogen was determined by self-designed mini closed pressure vessel device(MCPVT).The process characteristics of the oxidation reactions were researched.Under constant temperature and nitrogen atmosphere,pressure in the vessel was stable,alpha-pinene and beta-pinene were both stable in nitrogen.But in oxygen,the pressure of the system of alpha-pinene or beta-pinene decreased,indicating that oxidation reaction took place,with obvious slow oxygen absorption and rapid oxidation.With the increase of reaction temperature,the reaction time of the slow oxygen absor:ption process shortened.(2)Experimental evaluation of the oxidative runaway risk of alpha-pinene and beta-pineneThe MCPVT was used to conduct the pressure-up and temperature rising oxidation experiment of alpha-pinene and beta-pinene,respectively,thus to evaluate the runaway risk in the oxidation reactions of alpha-pinene and beta-pinene.The experiment results indicated that,the rapid oxidation temperature of alpha-pinene was 85 ?.The temperature and pressure mutations occurred under the conditions of alpha-pinene sample mass of 0.87 g,oxygen pressure of 0.5 MPa,heating rate of 1.5 ?·min-1 and system temperature of 116 ?.The abrupt change in temperature was ?T=15 ?,and the abrupt change in pressure rate was 6.87 kPa· min-1.The rapid oxidation temperature of beta-pinene was 70 ?.The reaction explosion would arise under the conditions of beta-pinene sample mass of 0.87 g,oxygen pressure of 1.0 MPa,heating rate of 1.5 0C·min-1 and system temperature of 95 ?.The explosion was characterized by rapid rise in temperature and pressure,the abrupt change in system temperature was AT=32 ?,and the maximum abrupt change in pressure rate was 10.4 MPa·min-1.Along with the explosion,the explosion-proof disc of the reactor was broken down,and the glass sample container was crushed.(3)The peroxide formation in the oxidation reaction of alpha-pinene and beta-pinenePeroxide was measured by iodimetry and thin-layer chromatography(TLC).The results showed that,the peroxide concentration in the oxidation reaction of alpha-pinene with oxygen reached a maximum value of 170.17 mmol·kg-1 when the reaction was carried out at 100 ? for 7 h in atmosphere.At this time,there were at least four kinds of peroxides.And for the beta-pinene,the maximum peroxide concentration was oTbtained of 89.28 mmol· kg-1 at 80 ? for 3 h,and at least 7 kinds of peroxides were formed at this time.Under pressure-up condition,different reaction time and initial oxygen pressure both affected the peroxide concentration of alpha-pinene andbeta-pinene.(4)The oxidation products of alpha-pinene and beta-pineneThe oxidation products of alpha-pinene and beta-pinene was analyzed by gas chromatography mass spectrometry(GC-MS).The main oxidation products of alpha-pinene were 2,3-epoxypinane(6.79%),camphorenal(1.75%),my:rtenal(1.03%),myrtenol(1.56%),verbenenol(9.88%)and verbenone(9.24%)under the reaction conditions of n(O2/pinen)=.0,70 ?and 6.5 h.Compared with the C=C,the oxidation product was more concentrated on the allyl group,and the product selectivity of the secondary hydrocarbon allyl group was significantly higher than that of the primary hydrocarbon allyl group.For beta-pinene,the main oxidation products were composed of 2,10-epoxypinane(0.79%),pinocarvone(4.06%),trans-pinocarveol(4.51%),myrtenal(7.37%)and myrtenol(9.28%).Unlike alpha-pinene,the oxidation products of beta-pinene were more concentrated on the C=C than the propylene group.(5)The oxidation competition of alpha-pinene and beta-p:ineneThe relative activity in the oxidation reaction of alpha-pinene and beta-pinene with oxygen(alpha-pinene reaction amount/beta-pinene reaction amount)=Q was determined by the relative content of alpha-pinene and beta-pinene mixed system and the change of peroxide concentration.The values of Q were all less than 1 under the experimental conditions and were related to temperature.Besides,in different n(alpha-pinene/beta-pinene)ratios,the largest peroxide value was obtained from the beta-pinene excess condition(?-pinene excess>alpha-pinene and beta-pinene equimolar>alpha-pinene excess).The experimental results showed that the reaction activity of beta-pinene with oxygen was higher than that of alpha-pinene.