The Oxidation And Safety Of Cinnamaldehyde And Three Phenylpropene Compounds

Cinnamon oil is a kind of characteristic plant resource in Guangxi.The main components include cinnamaldehyde,cinnamyl alcohol and cinnamic acid.It is widely used in food,medicine and other industries.It is prone to oxidation or polymerization when exposed on light or heat due to the double bond structure.And it brings two negative effects:poor quality of products and potential safety hazards during production,transportation,storage,and usage.Therefore,it is necessary to study the oxidation characteristics and safety of cinnamaldehyde and three phenylpropene compounds.The research on the reactive activity and oxidation risk of cinnamaldehyde,1-propenylbenzene,cinnamyl alcohol and cinnamic acid has the important theoretical significance and application value for the safe production of cinnamon oil and its four derivatives.The main contents and results are as follows:（1）The oxidation of cinnamaldehyde and its riskIn view of the characteristics of cinnamaldehyde carbon-carbon double bond（C=C）and aldehyde group（-CHO）prone to oxidation,a mini closed pressure vessel test（MCPVT）device was designed to track cinnamaldehyde oxidation.The temperature and pressure behaviors of cinnamaldehyde were measured by MCPVT under nitrogen and oxygen atmosphere to investigate the thermal stability,oxidation characteristics and hazardous of oxidation process.The results show the chemical reaction of cinnamaldehyde is not observed under nitrogen atmosphere.It has a good thermal stability.However,cinnamaldehyde is easy to be oxidized under oxygen atmosphere.The initial oxidation temperature is 271.25 K（-1.90°C）,and the accelerated oxidation temperature is300.38 K.The stable oxidation temperature is 304.13 K,and the thermal runaway temperature is 345.15 K.Under continuous heating and isothermal modes,the oxidation kinetics of cinnamaldehyde was discussed respectively.Both are second-order reaction,and the activation energy is 22.26 k J·mol^-1 and18.57 k J·mol^-1,respectively.The peroxide concentration was measured with iodometry method and the reaction products were analyzed by GC-MS.According to the results of MCPVT and oxidation products,the cinnamaldehyde oxidation pathway was proposed.It includes three stages:firstly,cinnamaldehyde reacts with oxygen to form peroxides;secondly,the rapid oxidation of cinnamaldehyde is initiated by thermal decomposition of peroxides;finally,further thermal decomposition of oxidation products leads to a thermal runaway reaction.（2）The oxidation of 1-propenylbenzene and its safetyThe oxidation and its safety were investigated by MCPVT under the continuous heating mode.The results show that 1-propenylbenzene has a good stability without any chemical reactions under nitrogen atmosphere.And1-propenylbenzene is oxidized under oxygen atmosphere.The temperatures of initial oxidation,rapid oxidation and stable oxidation are 328.13 K,357.91 K,and 363.75 K,respectively.The temperature of exothermic reaction is 347.65 K,which has a potential danger.The oxidation kinetic reaction is second-order,and the activation energy is 29.67 k J·mol^-1.The oxidation products were determined by iodometry and GC-MS,and the oxidation pathway of 1-propenyl benzene was proposed as follows:a.1-propenyl benzene reacted slowly with oxygen to form peroxides;b.thermal decomposition of peroxides lead to a deep oxidation reaction;c.the oxides further decomposed to release heat.（3）The oxidation of cinnamyl alcohol and cinnamic acid and their riskThe thermal stability and oxidation risk were evaluated by MCPVT.The reaction activity and risk of cinnamaldehyde,1-propenylbenzene,cinnamyl alcohol and cinnamic acid were comprehensively assessed.The results show that both cinnamyl alcohol and cinnamic acid are stable without chemical reactions under nitrogen atmosphere.Under oxygen atmosphere,the cinnamyl alcohol reaction temperatures of initial oxidation,accelerated oxidation and stable oxidation are 292.37 K,332.75 K,and 346.50 K respectively.And cinnamic acid’s is 363.88 K,385.35 K,and 403.38 K respectively.The oxidation kinetics of cinnamyl alcohol and cinnamic acid are second-order,and the activation energy is 25.70 k J·mol^-1and 32.21 k J·mol^-1,respectively.The peroxide concentration was measured by iodometry.The results show that the peroxide concentration of cinnamyl alcohol reaches the maximum of 118.53mmol·kg^-1 at 328 K,16 h.The peroxide concentration is 3.29 mmol·kg^-1at378 K,6 h.The experiment on oxidation hazards shows that cinnamyl alcohol occurrs thermal runaway and explosion.The temperature and pressure of the system rise rapidly.The thermal runaway temperature is 398.75 K;and the maximum rate of temperature rise is 1.88 K·s^-1;and the maximum rate of pressure rise is 12.97 MPa·s^-1.And cinnamic acid oxidation is relatively safe.Cinnamyl alcohol oxidation process can be divided into three stages:firstly,cinnamyl alcohol reacts with oxygen to form peroxides;secondly,the thermal decomposition of peroxides leads to the deep oxidation reaction;finally,further thermal decomposition of the oxide leads to thermal runaway reaction.And the oxidation of cinnamic acid can be divided into two stages:firstly,cinnamic acid reacts with oxygen to form peroxides;secondly,the thermal decomposition of peroxides leads to the deep oxidation reaction.The sequence of oxidation activity and its risk of cinnamaldehyde and three phenylpropene compounds are cinnamaldehyde（highest）,cinnamyl alcohol,1-propenylbenzene,cinnamic acid（lowest）.The oxidation products were determined by GC-MS.The C=C bond of cinnamaldehyde and three phenylpropene compounds was involved in reactions.The main products are benzaldehyde,benzoic acid and epoxides.The allylic groups of cinnamyl alcohol,cinnamaldehyde,and 1-propenylbenzene also participate in reactions,and the products are corresponding acids and aldehydes.The carboxyl group of cinnamic acid is stable without oxidation reactions.（4）Thermal stability and risk of the mixture of cinnamaldehyde and benzaldehydeIt is found that both benzaldehyde and benzoic acid existed in the oxidation products of cinnamaldehyde and three phenylpropene compounds.So the thermal stability of benzaldehyde or benzoic acid was investigated separately,and then thermal stability and risk of the mixture system of cinnamaldehyde and benzaldehyde were discussed.The results show that benzoic acid has good stability under nitrogen and oxygen atmosphere below 420 K.Benzaldehyde and the mixture of cinnamaldehyde and benzaldehyde are stable under nitrogen atmosphere and easy to be oxidized under oxygen atmosphere.Benzaldehyde reaction temperatures of initial oxidation,accelerated oxidation and stable oxidation are 272.25 K,300.88 K,and 307.50 K respectively.And the mixture’s is 270.88 K,300.59 K,and 307.35 K respectively.MCPVT monitored the exothermic reaction in oxidation process of benzaldehyde and the mixture cinnamaldehyde and benzaldehyde.And their initial exothermic temperatures were 306.88 K and 313.88 K,respectively.Benzaldehyde increases the explosion risk of the mixture.The oxidation kinetic of benzaldehyde is second-order,and activation energy is 23.26 k J·mol^-1.The peroxide concentration of benzaldehyde was determined by iodimetry,and the peroxide concentration of benzaldehyde reached the maximum value of 118.53 mmol·kg^-1 at 328 K.The oxidation of benzaldehyde includes three stages:firstly,oxidation induction stage:benzaldehyde reacts with oxygen to form peroxide;secondly,Self-heating oxidation stage:peroxide is decomposed into free radicals by heating,and free radicals initiate deep oxidation reaction;finally,thermal degradation stage of oxidation products:thermal degradation of benzaldehyde oxides forms small molecular compounds.（5）The risk of cinnamon oil oxidationAccording to the complex composition of cinnamon oil,the thermal stability and oxidation characteristics of cinnamon oil were discussed by tracking and measuring the temperature and pressure behaviors during the oxidation process.And the simulation experiment of runaway reaction was carried out on this basis.The results show that cinnamon oil is stable without chemical reactions under nitrogen atmosphere.The cinnamon oil is easy to be oxidized under oxygen atmosphere and exothermic reaction is monitored.The initial oxidation temperature of cinnamon oil is 300.13 K,the accelerated oxidation temperature is 324.63 K,the stable oxidation temperature is 330.15 K,and the initial exothermic temperature is 327.75 K.The simulation experiment of oxidation runaway was carried out with1.48 g cinnamon oil under the oxygen pressure of 0.90 MPa in a 50 m L high-pressure reactor.When high-pressure reactor was heated to 356.50 K,the thermal runaway of oxidation was occurred.The system temperature and pressure increased rapidly.The sample was burned and its glass container was broken into slag.The explosion-proof device was cracked and sparked.