Thermodynamic analysis and experimental verification of a new route for direct diethyl oxalate synthesis
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摘要: 报道新颖的草酸二甲酯(DMO)与乙醇(EtOH)通过酯交换路径一步合成高品质草酸二乙酯(DEO)。采用基团贡献法及Watson公式估算过程中各物质的热力学参数,并通过经典热力学公式计算在常压和温度323−368 K时合成DEO各步反应的焓变、熵变、吉布斯自由能及平衡常数。通过实验测定不同温度和原料比例下DMO转化率、产物组成和反应平衡常数并与理论估算值比较。发现实测DMO转化率与估算值误差在1%内,实测平衡常数与估算值基本一致。经过严格的实验验证,证明经热力学方法估算的热力学参数比较可靠。模拟真实催化精馏条件,以塔釜DEO纯度达99.9%为目标计算353 K时塔釜的初始原料和最终产物组成,当塔釜EtOH含量高于2.59%,初始n(EtOH)/n(DMO)大于2.10时可使DEO纯度达到指标,并显著降低整体工艺能耗,是一个高效绿色的DEO生产工艺。Abstract: The synthesis of high quality diethyl oxalate (DEO) via transesterification of dimethyl oxalate (DMO) and ethanol (EtOH) was reported. The thermodynamic data of each substance involved in the reaction were estimated by Benson and Joback's group contribution method and Watson formula, and the enthalpy change, entropy change, Gibbs free energy and equilibrium constant of each step of DEO synthesis were calculated by classical thermodynamic formula under atmospheric pressure and in the temperature range of 323−368 K. The DMO conversion, product composition and reaction equilibrium constant at different temperatures and raw material ratios were measured by experiments and compared with the theoretical data. It is found that the error between the measured DMO conversion and the estimated value is less than 1%, and the measured equilibrium constant is basically consistent with the estimated value. After strict experimental verification, it is proved that the thermodynamic data estimated by thermodynamic analysis are reliable. The actual catalytic distillation conditions were simulated, and the composition of the initial raw materials and the final products at 353 K was calculated with the hypothesis of 99.9% DEO purity at the bottom. When the content of EtOH in the bottom was higher than 2.59% and the molar ratio of initial EtOH to DMO was higher than 2.10, the purity of DEO could reach the target, and the overall process energy consumption was significantly reduced. It would be an efficient and green route for DEO synthesis.
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表 1 估算标准摩尔生成焓的Benson基团贡献值
Table 1 Group contribution value based on Benson method for standard molar formation enthalpy
Group ni(DMO) ni(MEO) ni(DEO) ${\Delta _f }H_{298}^\Theta$ / (kJ·mol−1) C-(O)(H)3 2 1 0 −42.19 O−(C)(CO) 2 2 2 −180.41 CO−(O)(CO) 2 2 2 −122.65 C−(C)(H)3 0 1 2 −42.19 C−(O)(C)(H)2 0 1 2 −33.91 表 2 Joback估算理想气相比热容的基团贡献值
Table 2 Group contribution value of the specific heat capacity in gas phase derived from Joback method
Group Group contribution value / (J·mol−1·K−1) $\Delta {a_i}$ $\Delta {b_i} \times {10^2}$ $\Delta {c_i} \times {10^4}$ $\Delta {d_i} \times {10^6}$ −CH3 19.5 −0.808 1.53 −0.0967 −CH2− −0.909 9.50 −0.544 0.0119 −OH(alcohol) 25.7 −6.91 1.77 −0.0988 −COO− 24.5 4.02 0.402 −0.0452 表 3 Joback and Reid法估算ΔvHb的基团贡献值
Table 3 Group contribution value of ΔvHb calculatied by Joback and Reid method
Group ni(DMO) ni(MEO) ni(DEO) Δi −CH3 2 2 2 2.373 −CH2− 0 1 2 2.226 −COO− 2 2 2 9.633 表 4 计算的各物质在不同温度下的蒸发焓
Table 4 Vaporization enthalpy values at different temperatures
T/K ΔvHT / (kJ·mol−1) DMO MEO DEO MeOH EtOH 323 47.60 49.89 56.27 36.38 40.55 338 46.44 48.66 54.80 35.26 39.26 353 45.64 47.81 53.78 34.08 37.91 368 44.41 46.92 52.21 32.82 36.47 表 5 计算的各物质在不同温度下的气或液态标准摩尔生成焓和标准熵
Table 5 Calculated standard molar enthalpy of formation and entropy for either gas or liquid phase at different temperatures
T/K DMO MEO DEO MeOH EtOH ${\Delta _f}H_{{\rm{g}},T}^{\Theta}$/
(kJ·mol−1)323 −687.19 −720.51 −753.83 −199.68 −232.99 338 −685.13 −718.07 −751.02 −199.00 −231.94 353 −683.02 −715.57 −748.13 −198.31 −230.86 368 −680.85 −713.00 −745.15 −197.59 −229.74 ${\Delta _f}H_{{\rm{l}},T}^{\Theta}$/
(kJ·mol−1)323 −734.79 −770.40 −810.10 −236.06 −273.54 338 −731.57 −766.73 −805.82 −234.26 −271.20 353 −728.66 −763.38 −801.91 −232.39 −268.77 368 −725.26 −759.92 −797.36 −230.41 −266.21 $S_{{\rm{g}},T}^{\Theta}$ /
(J·mol−1·K−1)323 351.47 400.16 437.33 243.30 286.23 338 357.70 407.53 445.83 245.34 289.40 353 363.83 414.77 454.20 247.36 292.54 368 369.84 421.90 462.45 249.34 295.65 $S_{{\rm{l}},T}^{\Theta}$ /
(J·mol−1·K−1)323 204.10 245.70 263.12 130.67 160.69 338 220.30 263.57 283.70 141.02 173.25 353 234.54 279.33 301.85 150.82 185.15 368 249.16 294.40 320.58 160.16 196.54 表 6 酯交换反应(1)−(4)在不同温度下的ΔrHΘ(kJ/mol)和ΔrSΘJ/(mol·K)
Table 6 Calculated enthalpy ΔrHΘ(kJ/mol)and entropy ΔrSΘJ/(mol·K)values of transesterifications(1)−(4)at different temperatures
T/K Reaction(1) Reaction(2) Reaction(3) Reaction(4) ΔrHΘ ΔrSΘ ΔrHΘ ΔrSΘ ΔrHΘ ΔrSΘ ΔrHΘ ΔrSΘ 323 −0.35 −1.02 1.87 11.58 −2.22 −12.60 −4.09 −24.18 338 −0.37 −1.06 1.78 11.04 −2.15 −12.10 −3.93 −23.14 353 −0.49 −1.35 1.66 10.46 −2.15 −11.81 −3.81 −22.27 368 −0.50 −1.34 1.14 8.86 −1.64 −10.20 −2.78 −19.06 表 7 酯交换反应(1)−(4)在不同温度下的ΔrGΘ(kJ/mol)和KΘ
Table 7 Calculated Gibbs free energy ΔrGΘ(kJ/mol)and equilibrium constant KΘ of reactions(1)−(4)at different temperatures
T/K Reaction(1) Reaction(2) Reaction(3) Reaction(4) ΔrGΘ KΘ ΔrGΘ KΘ ΔrGΘ KΘ ΔrGΘ KΘ 323 −2.054 × 10−2 1.007 −1.870 2.006 1.849 0.502 3.720 0.250 338 −1.172 × 10−2 1.004 −1.952 2.003 1.939 0.502 3.891 0.250 353 −1.345 × 10−2 1.004 −2.032 1.998 2.018 0.503 4.051 0.251 368 −6.880 × 10−3 1.002 −2.120 2.000 2.114 0.501 4.234 0.251 表 8 实验测定的n(DMO)/n(EtOH) = 1/4时各温度下的平衡常数及组成
Table 8 Measured equilibrium constant and composition (initial ratio of n(DMO)/n(EtOH)=1/4)
T/K t/min xDMO
/%sMEO
/%sDEO
/%wMEO
/%wDEO
/%KΘ 323 120 56.79 75.35 24.65 42.79 14.00 180 77.38 63.43 36.57 49.08 28.30 300 82.69 51.63 48.37 42.69 40.00 360 86.35 49.49 50.51 42.73 43.62 480 87.89 47.82 52.18 42.03 45.86 0.96 338 30 55.03 79.93 20.07 43.98 11.04 60 77.67 60.63 39.37 47.09 30.58 120 84.51 51.39 48.61 43.42 41.08 180 86.52 48.92 50.08 42.33 43.33 360 88.15 46.62 52.38 41.10 46.17 1.00 353 30 60.02 77.10 22.90 46.27 13.74 60 80.61 59.80 40.20 48.20 32.04 120 85.46 50.56 49.44 43.21 42.25 180 87.48 49.35 50.65 43.17 44.31 360 88.16 47.65 52.35 42.01 46.15 1.00 表 9 计算的n(DMO)/n(EtOH) = 1/4时各温度下的组成
Table 9 Calculated composition (initial ratio of n(DMO)/n(EtOH) = 1/4) at different temperatures
n(DMO)/
n(EtOH)T/K xDMO
/%sMEO
/%sDEO
/%wMEO
/%wDEO
/%1/4 323 88.95 49.58 50.42 44.10 44.84 338 88.93 49.57 50.43 44.08 44.85 353 88.92 49.52 50.48 44.03 44.89 368 88.92 49.59 50.41 44.10 44.82 表 10 不同物质的量比原料DMO转化率及DEO选择性和产率计算值与实验值比较
Table 10 Comparison between calculated and experimental values of DMO conversion, DEO selectivity and yield of raw materials with different initial molar ratios of reactants
n(DMO)/
n(EtOH)Calculation Experiment xDMO
/%sDEO
/%wDEO
/%xDMO
/%sDEO
/%wDEO
/%KΘ 1/6 93.75 60.00 56.25 93.50 61.75 57.74 1.00 1/12 97.95 75.00 73.46 97.92 75.81 74.23 1.00 1/24 99.40 85.71 85.20 99.38 88.32 87.78 1.01 -
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