Isobaric Molar Heat Capacity of Ethyl Octanoate and Ethyl Decanoate

Article pubs.acs.org/jced

Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Isobaric Molar Heat Capacity of Ethyl Octanoate and Ethyl Decanoate at Pressures up to 24 MPa Chao Su, Chenyang Zhu, Feng Yang, Zheng Ye, Xiangyang Liu, and Maogang He* Key Laboratory of Thermo-Fluid Science and Engineering, Ministry of Education, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, People’s Republic of China ABSTRACT: The isobaric molar heat capacities of ethyl octanoate and ethyl decanoate were determined at T = 294−354 K and p = 0.1−24 MPa. The measurements were conducted by a flow calorimeter. The measured results were in good agreements with several available experimental data at atmosphere pressure and the calculated results at high pressure in literatures. Furthermore, a fitting equation was presented to calculate the Cp of ethyl octanoate and ethyl decanoate. The maximum absolute relative deviations between experimental results and calculated data are lower than 0.4%.

1. INTRODUCTION Because of detrimental environmental influence of fossil fuels utilization and their limited storage, many countries show great interests in alternative energy sources.1 Biodiesel fuel is considered as one of promising alternative energy sources, which is produced with methanol or ethyl alcohol added to rapeseed, soybean, and palm oils, resulting in a mixture of fatty acid esters. Owing to the unique properties such as high flash point, miscible with fossil fuels and low sulfur contents, biodiesel has been extensively used as lubricant, plasticizer, solvent, and so forth.2−4 Biodiesel consists of kinds of fatty acid ester with different carbon atom numbers, so it is feasible to study the properties of each pure component to predict the thermophysical properties of biodiesels. In addition, the thermophysical properties of pure components are important for the diesel engine design by conducting the behavior combustion systems and fuel injection process. One of the important thermodynamic properties is isobaric molar heat capacity (Cp), which is the fundamental property for predicting other properties and required in industry calculation.5−9 Many measurements have been carried out to determine the Cp of pure fatty acid methyl or ethyl ester (FAME or FAEE), but most data were obtained at atmosphere pressure. Pauly et al.10 have measured the Cp of kinds of FAMEs at atmosphere by microdifferential scanning calorimetry. Dzida et al.11 have determined the experimental Cp of ethyl decanoate and ethyl octanoate at atmosphere pressure and calculated the Cp at pressures up to 100 MPa by an acoustic method. Zaitsau et al.12 have measured the Cp of ethyl decanoate at T = 5−370 K at atmosphere. Mohamed et al.13 have determined the Cp of methyl laurate, ethyl laurate, ethyl myristate, and ethyl oleate at atmosphere. Bogatishcheva et al.14 have measured the Cp of five FAEEs (CnH2n−1O2C2H5, n = 10, 11, 12, 14, 16) at atmosphere. © XXXX American Chemical Society

Our group has made many efforts to study the Cp of FAME and FAEE at high pressure, such as methyl laurate, methyl decanoate, ethyl cinnamate, and ethyl heptanoate to 16.3 MPa and methyl decanoate and methyl laurate to 4.25 MPa by using a flow calorimeter.15−17 But the effect of carbon chain length of fatty acid esters on the Cp change at high pressure is still not well understood because there is not enough experimental data. In this work, we report new experimental values for the Cp of ethyl octanoate and ethyl decanoate at T = 294−354 K and p = 0.1−24 MPa. In addition, we investigated the influence of temperature, pressure and carbon chain length on the Cp of fatty acid esters. A fitting equation was also presented to calculate the Cp of ethyl octanoate and ethyl decanoate.

2. EXPERIMENTAL SECTION 2.1. Material. Ethyl octanoate and ethyl decanoate were provided by Aladdin and used without further purification. The detailed chemical information is provided in Table 1. Table 1. Chemicals Used in This Work

Received: March 14, 2018 Accepted: May 23, 2018

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DOI: 10.1021/acs.jced.8b00199 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 2. Isobaric Molar Heat Capacities Cp of Ethyl Octanoatea

2.2. Experimental Method. The experimental system for measuring the Cp of ethyl octanoate and ethyl decanoate was based on the flow method, which has been described in our previous papers.18−20 For a constant pressure system, when the sample fluid absorbs heat from the heater, the Cp can be measured by the following equation when the heat loss is ignored. Cp(T , p) =

PM qm ·ΔT

(1)

where P is the quantity of heat obtained from the heater, M is the sample liquid molar mass, qm is the mass flow rate, and ΔT is the temperature increment. In actual situations, the heat loss cannot be ignored. So eq 1 can be rewritten as following Cp(T , p) =

PM PM − 0 qm ·ΔT qm ·ΔT

(2)

where P0 is the heat loss. From eq 2, when increasing the qm, the effect of heat loss can be reduced until it is negligible.21−23 The expanded uncertainty of temperature is lower than 0.02 K and that of pressure is lower than 5 kPa with coverage factor k = 2. The uncertainty caused by the impurity is nonnegligible, so the standard uncertainty caused by purity, which is 0.99, should be24 u(i) =

(1 − 0.99) ≈ 0.006 3

(3)

When taking the impurity of chemicals into account, the relative expanded uncertainty of Cp is estimated to be lower than 1.2% (k = 2).

3. RESULTS AND DISCUSSION The Cp of ethyl octanoate and ethyl decanoate were determined at T = 294−354 K and p = 0.1−24 MPa. The experimental results are presented in Tables 2 and 3. We compared our experimental values for Cp of ethyl octanoate with those reported by Dzida et al.11 and Cp of ethyl decanoate reported by Dzida et al.,11 Zaitsau et al.,12 and Bogatishcheva et al.14 at atmospheric pressure because there is no experimental data under high pressure. As shown in Figures 1 and 2, there is a good consistency between our experimental data and the values from literatures. Figures 3 and 4 show the Cp of ethyl octanoate and ethyl decanoate at different temperatures as a function of pressure. From Figure 3 and 4, we can conclude that the Cp of ethyl octanoate and ethyl decanoate decreases with pressure increasing and increases with temperature increasing. Additionally, it is clear to observe that the Cp of ethyl octanoate and ethyl decanoate is not sensitive with temperature and pressure changes. For ethyl octanoate, when the pressure increased with 3 MPa or the temperature increased with 10 K, the Cp reduced to lower than 0.14% or increased to lower than 1.7%, respectively. For ethyl decanoate, lower than 0.15% and 1.8% reduction in Cp with 3 MPa increment in pressure and 10 K decrement in temperature, respectively, was found. This is because the intermolecular free length decreases when temperature drops or pressure increases.13 Figure 5 shows the Cp of ethyl heptanoate,15 ethyl octanoate, and ethyl decanoate at T = 354 K and p = 0.1−24 MPa. The Cp of ethyl heptanoate is lower than those of ethyl octanoate and ethyl decanoate while the slopes are almost the same, which indicates that the carbon atoms number in fatty acid group have a great effect on

T/K

p/MPa

Cp/(J·mol−1·K−1)

T/K

p/MPa


294.0 294.0 294.1 294.1 294.1 294.1 294.1 294.1 294.1 305.6 303.7 303.7 303.8 303.8 303.9 304.0 304.0 304.0 314.3 314.3 314.3 314.4 314.4 314.4 314.5 314.5 314.5 323.8 323.8 323.8 323.9 323.9

0.16 3.02 5.96 9.04 12.02 14.98 17.99 21.06 23.98 0.16 2.94 6.07 8.95 12.02 15.04 18.13 21.05 24.03 0.17 3.14 6.13 9.11 12.10 15.03 18.31 20.91 24.10 0.13 3.03 6.16 9.30 12.12

339.59 339.17 338.74 338.30 337.90 337.54 337.13 336.71 336.29 344.76 344.30 343.83 343.35 342.90 342.50 342.09 341.67 341.18 350.60 350.17 349.71 349.29 348.89 348.53 348.11 347.72 347.25 355.82 355.40 354.96 354.54 354.09

323.9 323.9 323.8 323.9 333.7 333.7 333.7 333.8 333.8 333.8 333.8 333.9 333.9 343.5 343.5 343.5 343.5 343.6 343.7 343.8 343.8 343.8 353.6 353.6 353.6 353.7 353.7 353.8 353.9 354.0 354.0

15.23 18.11 21.03 24.10 0.11 3.06 6.01 9.11 11.92 15.07 18.08 21.12 24.00 0.13 2.95 6.04 8.99 12.07 15.05 18.07 21.01 24.09 0.13 3.03 6.06 8.99 11.90 15.04 18.02 20.96 24.11

353.71 353.28 352.89 352.47 360.49 360.06 359.65 359.17 358.75 358.37 357.90 357.47 357.06 365.32 364.93 364.48 364.02 363.60 363.15 362.70 362.30 361.84 370.06 369.66 369.24 368.80 368.40 367.99 367.57 367.14 366.72

a Expanded uncertainties U are U(T) = 0.02 K, U(p) = 5.0 kPa (0.95 level of confidence), U(i) = 0.012, and the relative expanded uncertainties Ur (Cp) = 1.2% (k = 2).

the Cp but has a slight effect on the slope of Cp as a function of pressure. Figure 6 shows the Cp of ethyl heptanoate, ethyl octanoate, and ethyl decanoate at p = 12 MPa from T = 294− 385 K. The Cp of these three compounds also have a similar slope as a function of temperature. For FAME, Pauly et al. have concluded that the length of the molecule does not seem to affect the slope value of Cp versus the temperature.10 The same conclusion can be drawn for FAEE from our results. It should be noted that the substantial growth of Cp with an increase in the number of carbon atoms in the acid part of each ester molecule was primarily due to the differences in molecular packing and the greater molecular mass.14,25 From Figures 3 and 4, we concluded that the Cp of ethyl octanoate and ethyl decanoate have a linear relation with temperature and pressure. So the Cp of ethyl octanoate and ethyl decanoate can be determined as Cp/J·mol−1·K−1 = a1 + a 2 ·T /K + a3·p /MPa

(4)

where a1, a2, and a3 are fitting parameters. For ethyl octanoate, a1, a2, and a3 are 188.955 J·mol−1·K−1, 0.513 J·mol−1·K−2, and −0.144 J·mol−1·K−1·MPa−1, respectively. For ethyl decanoate, a1, a2, and a3 are 227.009 J·mol−1·K−1, 0.589 J·mol−1·K−2, and −0.168 J·mol−1·K−1·MPa−1, respectively. Figure 7 shows the Cp B



Article

Table 3. Isobaric Molar Heat Capacities Cp of Ethyl Decanoatea T/K

p/MPa


T/K

p/MPa


294.0 294.0 294.0 294.0 294.0 294.1 294.1 294.1 294.1 304.0 304.0 304.0 304.0 304.0 304.0 304.0 304.1 304.1 313.9 313.9 313.9 313.9 314.0 314.0 314.0 314.0 314.0 323.8 323.9 323.9 323.9 323.9

0.10 3.08 6.09 8.97 12.12 14.87 17.91 21.09 24.04 0.13 3.03 6.16 9.03 11.95 15.09 17.87 21.10 24.05 0.11 2.92 5.99 9.08 11.91 15.03 18.09 21.08 24.11 0.15 3.04 5.93 9.07 11.98

400.39 399.98 399.53 399.07 398.72 398.28 397.82 397.38 396.93 406.09 405.62 405.12 404.66 404.19 403.69 403.23 402.75 402.24 411.45 410.92 410.45 409.95 409.43 408.93 408.41 407.89 407.34 416.54 416.03 415.53 415.03 414.54

323.9 324.0 324.0 324.0 333.8 333.8 333.8 333.8 333.9 333.9 333.9 333.9 334.0 343.7 343.7 343.7 343.8 343.8 343.8 343.8 343.8 343.9 353.7 353.7 353.7 353.7 353.8 353.8 353.8 353.8 353.9

15.05 18.05 21.21 24.03 0.12 2.96 5.99 9.04 12.03 14.94 18.05 21.10 24.05 0.15 3.00 6.19 8.99 12.10 14.91 17.99 21.01 23.97 0.11 2.98 6.02 8.99 11.92 14.94 17.96 21.07 23.98

414.03 413.54 413.06 412.57 423.19 422.70 422.28 421.77 421.17 420.66 420.15 419.65 419.11 429.52 429.02 428.50 427.96 427.46 426.93 426.40 426.07 425.54 435.96 435.41 434.91 434.40 433.87 433.36 432.85 432.33 431.81

Figure 2. Isobaric molar heat capacity of ethyl decanoate from different authors at atmosphere pressure. ■, this work; ○, Dzida et al.;11 △, Zaitsau et al.;12 ◇, Bogatishcheva et al.;14 Error bars: ±1%.

Figure 3. Isobaric molar heat capacity of ethyl octanoate at different temperatures as a function of pressure. ◆, 294 K; ◇, 304 K; ▲, 314 K; △, 324 K; ●, 334 K; ○, 344 K; ■, 354 K.

a

Expanded uncertainties U are U(T) = 0.02 K, U(p) = 5.0 kPa (0.95 level of confidence), U(i) = 0.012, and the relative expanded uncertainties Ur (Cp) = 1.2% (k = 2).

Figure 4. Isobaric molar heat capacity of ethyl decanoate at different temperatures as a function of pressure. ◆, 294 K; ◇, 304 K; ▲, 314 K; △, 324 K; ●, 334 K; ○, 344 K; ■, 354 K.

Figure 1. Isobaric molar heat capacity of ethyl octanoate from different authors at atmosphere pressure. ■, this work; ○, Dzida et al.;11 Error bars: ±1%.

4. CONCLUSIONS In this work, we measured the Cp of ethyl octanoate and ethyl decanoate at T = 294−354 K and p = 0.1−24 MPa. The effects of temperature, pressure and carbon atoms number on the Cp of FAEE were also investigated. The Cp decrease with increasing pressure or decreasing temperature. With the carbon chain length in fatty acid alkyl ester increasing, Cp will also increase. However, the change of carbon chain length has a slight effect on the Cp change as a function of temperature. A

deviations between the experimental results and calculated values from eq 4. The maximum absolute relative deviation (MARD) which was calculated from eq 5 is less than 0.4. ⎛ Cpi exp − Cpi cal MARD = Max⎜⎜100 Cpi exp ⎝

⎞ ⎟ ⎟ ⎠

(5) C



Article

Funding

This work was supported by the National Science Fund for Distinguished Young Scholars of China (No. 51525604), Foundation for Innovative Research Groups of the National Natural Science Foundation of China (No. 51721004), and Natural Science Basic Research Plan in Shaanxi Province of China (No. 2017JQ5053). Notes

The authors declare no competing financial interest.

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Figure 5. Isobaric molar heat capacities of ethyl ester at T = 354 K as a function of pressure. ◆, ethyl heptanoate;15 □, ethyl octanoate (this work); △, ethyl decanoate (this work).

Figure 6. Isobaric heat capacities of ethyl ester at p = 12 MPa as a function of temperature. ◆, ethyl heptanoate;15 □, ethyl octanoate (this work); △, ethyl decanoate (this work).

Figure 7. Deviations between the experimental data and calculations from eq 3 for the isobaric molar heat capacities. △, ethyl octanoate; ◇, ethyl decanoate.

fitting equation with high accuracy was also proposed to calculate the Cp of ethyl octanoate and ethyl decanoate.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*Tel: 86-29-82663863. E-mail:[email protected]. ORCID

Maogang He: 0000-0002-2364-2140 D



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Isobaric Molar Heat Capacity of Ethyl Octanoate and Ethyl Decanoate

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