Study On Thermal Dimerization Of Cracking C₅ Fraction

Cracking C₅ fraction was the byproduct of ethene device and with the increasing of ethene production, the amount of it would be much more. C₅ fraction was compose of active olefins and dienes, of which dienes especially cyclopentadiene (CPD), isoprene(IP) and 1,3-pentadiene (PD) were valuable resources in chemical production because of their active chemical properties. But in our country, most C₅ fraction was directly used as fuel, and only little as chemical raw material. So the there dienes's separating technology was the important aspect of making the best of C₅ resources. C₅ separating technology was based on the technology that CPD was tend to dimerize and dicyclopentadiene(DCPD) was easy to separated from C₅ fraction. So by thermal dimerization CPD could be separated. Although reference materials about C₅ fraction thermal dimerization had been reported, their conclusions weren't coincident because of different C₅ compositions and experiment conditions. Reference materials about IP and PD reaction behaviors were few, and the influence of inhibitor putted in former process when C4 fraction was isolated was very little. So study on dimerization reaction was essential. The C₅ fraction samples were offered by Yangtse Ltd. Co. and its thermal dimerization were investigated by seal-tube method. Details were as follow: 1 Foundation of C₅ fraction's analysis method Because C₅ fraction contains lots of components and their boiling points range was wide, qualitative and quantitative analysis was hard. In this dissertation, the analysis method was as follows: (1) In SE-30 capillary collum, two-stage programmed heating method was used. So as the beginning temperature was set up 20 ℃, C₅ fraction could be preferably separated. C₅ hydrocarbons and dimers all had peaks in gas chromatogram, but trimers didn't. (2) DCPD's relative mass correction factor was determined using n-pentane as reference matter. By corrected area normalization method, the contents of components in C5 raw material or dimerization compound which had peaks were gained. Basing on the principle of inert component's content wasn't change, trimer's content could be computed, and then the contents of components which had peaks were all corrected. 2 Study on dimerization reaction C5 fraction's thermal dimerization was investigated by seal-tube method. Results indicated that: (1) Temperature and time were the key parameters in dimerization reaction. When temperature was heated up or time was expanded, the conversions of CPD, IP, PD and 1,3-butadiene(BD) all increased and the yield of DCPD rised in initial stage and then declined, the selectivity of CPD appeared downtrend and the contents of unkown dimmers and trimers severally increased. In the thermal dimerization, except high CPD conversion and DCPD yield were expected, the consumption of IP and PD, meanwhile the contents of unknown dimers and trimbers were as low as possible. So temperature 115 ℃and time 2³ h were recommended. In above conditions, CPD conversion could reach 90% and DCPD yield could greater than 75%, IP and PD conversions were 7%¹0% and 2.5%⁴% respectively, and about 14% BD reacted. Meanwhile mass fractions of unknown dimers and trimers were about 2.5 % and 3.0%. (2) The influence of micro inhibitor content on thermal dimerization.It had no apparent influence on CPD conversion and on generating quantity of unknown dimers. On high temperature, inhibitor could reduce conversions of IP, PD and BD. The generating quantities of trimers were also reduced. DCPD yield were slightly increased. When the inhibitor mass fraction in C5 fraction was 100×10-6 and tempreture and reaction time were set 115 ℃and 3h, CPD conversion would reach about 92 % and DCPD yield would reach about 78%. The consumptions of IP and PD were probably 8% and 3%, meanwhile about 11% BD was used up and the mass fractions of dimers and trimers all were nearly 2.6%. (3) Study on CPD content variation. CPD conversion and DCPD yield would reduce as the CPD content reduced, But conversions of IP, PD and BD would belower. Accordingly generating quantities of unknown dimers and trimers were a little low. Low content of cyclopentendiene in raw material caused that CPD reaction rate slowed up, and consumptions of IP and PD accordingly decreased because codimers content reduced. 3 Dynamic model foundation of C5 fraction sample thermal dimerizatin On consideration of dienes reaction behaviors in thermal dimerization, a dynamic model was established, and then model parameters were gained by a optimization method. The verified result indicated that except IP's content calculated value was higher than experimental value, others dienes's well coincided. The recommended optimal dimerazation conditions were that temperature was 110 ℃and reaction time was 3 h. In above conditions, CPD conversion could reach 90% and DCPD yield would reach about 80%. Conversion of PD, IP and BD would reach round about 2%, 6%⁸% and 9%¹1%.