Letters

Vapor and Sublimation Pressures of Three Normal Alkanes: C 20 , C 24 , and C 28

Description
Vapor and Sublimation Pressures of Three Normal Alkanes: C 20 , C 24 , and C 28
Categories
Published
of 7
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Share
Transcript
  Subscriber access provided by UNIV CLAUDE BERNARD LYON 1 Journal of Chemical & Engineering Data is published by the American ChemicalSociety. 1155 Sixteenth Street N.W., Washington, DC 20036 Article Vapor and Sublimation Pressures of Three Normal Alkanes: C 20 , C 24 , and C 28 Antonio Razzouk, Ramy Abou Naccoul, Ilham Mokbel, Joseph Saab, and Jacques Jose J. Chem. Eng. Data  , 2009 , 54 (4), 1214-1219• DOI: 10.1021/je800534x • Publication Date (Web): 04 March 2009 Downloaded from http://pubs.acs.org on April 15, 2009 More About This Article Additional resources and features associated with this article are available within the HTML version:•Supporting Information•Access to high resolution figures•Links to articles and content related to this article•Copyright permission to reproduce figures and/or text from this article  Vapor and Sublimation Pressures of Three Normal Alkanes: C 20 , C 24 , and C 28 Antonio Razzouk, † Ramy Abou Naccoul, † Ilham Mokbel,* ,† Joseph Saab, ‡ and Jacques Jose † Laboratoire des Sciences Analytiques, UMR 5180, Universite´ Claude Bernard Lyon1, 43 bd du 11 Novembre 1918, 69642Villeurbanne, France, and De´partement Chimie et Sciences de la Vie, Faculte´ des Sciences et de Ge´nie Informatique, Universite´Saint-Esprit de Kaslik (USEK), Lebanon Vapor and sublimation pressures of three  n -alkanes C 20 , C 24 , and C 28  have been determined using a modifiedgas saturation method. The obtained pressure values range from 10 - 5 Pa to 5.5 Pa. From the temperaturedependence of the vapor pressures, the molar enthalpies of vaporization and sublimation at the meantemperature of the experimental range were derived from the Clausius - Clapeyron equation. From theseresults, the standard enthalpies of vaporization and sublimation at  T   )  298.15 K were calculated. Introduction Vapor pressures of heavy  n -alkanes are of practical impor-tance in the petroleum industry for the characterization of heavypetroleum cut and synthetic fluids. These data are also neededfor thermodynamic calculations and for estimating propertiesof other classes of compounds. Although vapor pressures of normal alkanes up to  n -C 92  are available in the literature, 1 - 9,21 sublimation pressures are practically inexistent.In our previous works, 10,11 vapor pressures of some alkanesup to  n -C 30  were studied. Continuing this research line, the vaporand sublimation pressures of three normal alkanes,  n -C 20 ,  n -C 24 ,and  n -C 28 , have been measured using the gas saturation method.Enthalpy of vaporization ( ∆ vap  H  ) and sublimation ( ∆ sub  H  ) havealso been determined from the vapor and sublimation pressuresand compared with the existing literature data. Experimental Section Chemicals.  The suppliers and the purities of the usedmaterials are as follows: hexadecane,  n -C 16  (Janssen, 99 %);eicosane,  n -C 20 , and tetracosane,  n -C 24  (Aldrich, 99 %); octa-cosane,  n -C 28  (Acros Organics, 99 %).  Apparatus.  The apparatus for the vapor pressure determina-tion was based on the gas saturation method, also known asthe transpiration method. The apparatus allows reliable measure-ments over a large pressure interval ranging from 10 - 5 Pa to10 3 Pa. The detailed description of the saturation apparatus canbe found elsewhere. 11,12 Therefore, we give only the mostsignificant information and modifications made to improve theapparatus. The experimental apparatus, presented in Figure 1,was composed of two parts. The sampling part consisted of anequilibrium oven containing two saturators, which were con-stituted by stainless steel columns filled with a porous gaschromatography support, respectively, impregnated with thesample and the standard compound. The second part was a gaschromatograph equipped with a capillary column and a flameionization detector (FID). When thermal equilibrium wasreached, both compounds were simultaneously swept by the inertgas N 2  into the cold analysis column where they were trapped.To limit adsorption and desorption phenomena, the connectionbetween the saturators and the gas chromatograph was modified.A silica capillary tube (T) was connected to the outlet tube of the saturators in one side, whereas the other end was penetratinginside the analysis column. Under these conditions, the carriergas did not pass through the union tube of fused silica anddesorbed only the compounds trapped in the analysis column.By heating the capillary column, the two compounds were elutedand detected by the FID. The present apparatus is totallyautomatic because all of the valves are controlled by the gaschromatograph output.  Impregnation of the Support.  The impregnation of thesupport by the sample or the standard compound was done bybatch. The compound (0.5 g) was dissolved in an organic solvent(toluene). The chromatographic support (Gas Chrom P (147 to175)  µ m) was added to the solution so as to obtain a “compoundmass/support mass” ratio equal to 0.2. The cell containing themixture was subjected to the action of an oscillating stirrer for24 h before the solvent was totally evaporated using a rotaryevaporator under vacuum. The dry support impregnated withthe compound was finally introduced to the saturation column. Saturation Gas Flow Rate and Purge Time.  A preheatednitrogen steam was passed through the saturators at constant * Corresponding author. E-mail: mokbel@univ-lyon1.fr. † Universite´ Claude Bernard Lyon1. ‡ Universite´ Saint-Esprit de Kaslik (USEK). Table 1. Vapor and Sublimation Pressures of   n -Alkanes,  n -C 20 ,  n -C 24 , and  n -C 28 T P T P K Pa K Pa n -C 20  Solid  n -C 20  Liquid302.37 0.00173 312.76 0.0113304.59 0.00330 322.82 0.0345306.79 0.00459 327.82 0.0601307.86 0.00594 337.82 0.174342.89 0.293373.17 5.45 n -C 24  Solid  n -C 24  Liquid307.74 0.0000589 333.09 0.00458312.83 0.000178 353.20 0.0407317.93 0.000479 373.13 0.268322.94 0.00123 n -C 28  Solid  n -C 28  Liquid323.05 0.0000117 339.02 0.000358326.15 0.0000237 352.98 0.00186329.02 0.0000439 372.85 0.0176392.76 0.114412.72 0.606  J. Chem. Eng. Data  2009,  54,  1214–1219 1214 10.1021/je800534x CCC: $40.75  ©  2009 American Chemical SocietyPublished on Web 03/04/2009  temperature. The flow rates were measured with a relativeuncertainty of 1 % using mass flow meters from Bronkhorstwith a real-time monitoring system. The flow rates wereoptimized to reach the saturation equilibrium of the gas.Therefore, experiments were carried out using flow rates rangingfrom (3 to 8) mL · min - 1 according to the equilibrium temper-ature and the volatility of the compounds. (In this field, the vaporpressures or the sublimation pressures are independent of thegas flow.) The same trap time was applied to both sample andreference compounds. It varies between 30 min and 10 h. Vapor Pressure Determination.  The vapor pressures werecalculated using the following equation, which supposes idealbehavior of the vapor phaseSubscripts  i ) 1 and  i ) 2 refer, respectively, to the standardand the sample,  P i  is the vapor pressure,  A i  is the chromato-graphic peak area,  M  i  is the molar mass,  F  i  is the saturation gasflow rate, and  k   is the relative mass response factor of the FID.For normal alkanes between  n -C 12  and  n -C 38 , the relative massresponse factor,  k  , is equal to unity. It was verified experimen-tally in a previous paper. 11 Figure 2 shows an example of a chromatogram obtained at372.85 K when studying  n -C 28 . In this case,  n -C 24  was thereference compound. The small peaks appearing in the beginningof the chromatogram were due to the impurities contained in n -C 24 . Uncertainty of the Vapor and Sublimation Pressures. Knowing that the uncertainty of the flow rate of the saturationgas is 1 % and the relative uncertainty of the area ratio is 3%, 11 we deduced from eq 1 the relative uncertainty of thepressure ratio, which is about 4 %. In the case of   n -C 20  and n -C 24 , the reference compound (respectively,  n -C 16  and  n -C 20 )is known with good accuracy (1 % uncertainty). By a quadraticcombination with the pressure ratio, the relative uncertainty of the vapor and sublimation pressures for these 2 alkanes is 5 %.In the case of   n -C 28 , the reference compound is  n -C 24 , presenting Figure 1.  Saturation apparatus. A, chemstation acquisition from Agilent; C, analytical nonpolar capillary column (dimethylpolysiloxane), length: 10 m, filmthickness of the stationary phase: 2.65  µ m; F 1 , F 2 , F 3 , mass flow meters from Bronkhorst, flow range (0 to 10) mL · min - 1 , uncertainty 1 %; H, heated zone;S 1 , S 2 , saturation stainless steel column (  L ) 2 m; i.d. ) 2.1 mm) containing Gas Chrom P support (particle diameter: (147 to 175)  µ m); T, capillary silicatube (  L  )  25 cm; i.d.  )  0.32 mm); T 1 , T 2 , T 3 , stainless steel tubing (  L  )  3 m; i.d.  )  0.50 mm) for saturation and carrier gas preheating; V 1 , V 2 , V 3 ,electrovalves controlling gas flow. Figure 2.  Chromatogram obtained at 372.85 K when studying  n -C 28  with  n -C 24  as reference compound (trapping time: 2 h). P 1 P 2 )  k  A 1  A 2  M  2  M  1 F  2 F  1 (1)  Journal of Chemical & Engineering Data, Vol. 54, No. 4, 2009  1215  a relative uncertainty of 5 %. Therefore, the uncertainty of   n -C 28 is estimated to be 7 %. The uncertainty of the temperature is0.02 K. Results and Discussion The vapor and sublimation pressures of   n -C 20  were deter-mined using  n -C 16  as the standard compound (Table 1). Thevalues of the latter were taken from Ruzika and Mayer. 3 Adeviation plot showing differences between the various literaturesources and the fitted experimental results is represented inFigure 3. As can be observed, the present work is in goodagreement with the data reported by Macknick and Prausnitz 6 and Sasse et al., 8 and the deviation is below 10 %. (Our valuesare systematically low.) In the same way, the values reportedby Grenier et al. 7 exhibit a difference of 7 % to 9 % from thepresent data. In this case, our values are systematically above Figure 3.  Relative deviation of the experimental vapor and sublimation pressures of   n -C 20  from values obtained with the Clausius - Clapeyron equation asa function of temperature  T   /K:  ] , solid phase (this work);  [ , liquid phase (this work);  b , Sasse et al.; 8 *, Grenier et al.; 7 × , Piacente et al.; 5 O , Ruzickaand Majer; 3 0 , Macknick and Prausnitz. 6 Figure 4.  Relative deviation of the experimental vapor and sublimation pressures of   n -C 24  from values obtained with the Clausius - Clapeyron equation asa function of temperature  T   /K:  ] , solid phase (this work);  [ , liquid phase (this work);  b , Sasse et al.; 8 *, Grenier et al.; 7 0 , Chickos and Hanshaw. 4 Table 2. Clausius - Clapeyron Equation Parameters,  A  and  B , Standard Deviation,  σ  , Mean Relative Deviation,  d  , and  B  )  ∆ vap  H   ( T  m )/   R  (or  B )  ∆ sub  H   ( T  m )/   R ) with  R  )  8.314 J · K - 1 · mol - 1  a ,  b temperature range  T T  m  ∆ vap  H   ( T  m ) ( σ  )  ∆ sub  H   ( T  m ) ( σ  )alkanes K K  A  ( σ   A )  B  ( σ   B ) 100 d   kJ · mol - 1 kJ · mol - 1 n -C 20  (solid) 302.37 to 307.86 305 62.37 (1.19) 20 784 (365) 0.83 172.8 (3.0) n -C 20  (liquid) 312.76 to 373.17 343 33.72 (0.37) 11 970 (130) 3.7 99.5 (1.1) n -C 24  (solid) 307.74 to 322.94 315 54.74 (0.68) 19 840 (220) 1.8 164.9 (1.8) n -C 24  (liquid) 333.09 to 373.13 353 32.59 (0.16) 12 647 (56) 0.90 105.1 (0.5) n -C 28  (solid) 323.05 to 329.02 326 61.54 (0.83) 23 550 (270) 0.58 195.8 (2.2) n -C 28  (liquid) 339.02 to 412.72 376 33.86 (0.35) 14 160 (140) 4.0 117.4 (1.2) a T  m : mean temperature of the experiments.  b d   ) (1/  n )  ∑  (| P exptl  -  P calcd |)/( P exptl ). 1216  Journal of Chemical & Engineering Data, Vol. 54, No. 4, 2009  those of the authors. Except at (347 and 351) K, where thedeviations are, respectively, 16 % and 11 %, the present studyis in a good agreement with Piacente et al. data. 5 Thecomparison of the experimental vapor pressures with Ruzickaand Majer 3 recommended data shows good agreement exceptat 373 K, where the reported value is lower than the experi-mental measurement by 18 %; nevertheless, the agreement withthe rest of the previously quoted literature values at 373 K isgood.As for  n -C 24 , the used standard compound was the previouslystudied  n -C 20 . The data of the standard compound are from thepresent study and from the values published by Viton et al. 9 The vapor pressures of   n -C 24  were compared with literature data(Figure 4). There is good agreement with Sasse et al. 8 experimental point and with Grenier-Loustalot et al. 7 value. Twocommon points were found with Chickos and Hanshaw 4 valuesat (353.20 and 373.13) K. The relative deviations with thereported data are, respectively, 9 % and 2 %.For  n -C 28  vapor pressure determinations,  n -C 24  was used asthe standard compound (Table 1). The data of   n -C 24  were takenfrom Mokbel et al. 11 for the liquid phase and from the presentstudy for the solid phase. As shown in Figure 5, the agreementwith Chickos and Hanshaw 4 is good. Two common points werefound with Grenier et al. 7 data, at (397.55 and 417.75) K. Therelative deviation with the present study is, respectively,  - 29% and 10 %. No literature data were found with which the solidphase of the studied alkanes could be compared. The pressurevalues below the temperature of fusion of   n -C 24  and  n -C 28 reported by Chickos and Hanshaw 4 were not taken into accountin the present study because they are relative to subcooled liquid.Another way to check the consistency of our data is tocompare the enthalpies obtained in this work with the literaturedata. With this aim, the vapor and sublimation pressures werefitted to the Clausius - Clapeyron equationFrom the fits, the enthalpy of vaporization,  ∆ vap  H  , and theenthalpy of sublimation, ∆ sub  H  , at the mean temperature of the Figure 5.  Relative deviation of the experimental vapor and sublimation pressures of   n -C 28  from values obtained with the Clausius - Clapeyron equation asa function of temperature  T   /K:  ] , solid phase (this work);  [ , liquid phase (this work); *, Grenier et al.; 7 0 , Chickos and Hanshaw. 4 Figure 6.  Clausius - Clapeyron representation (ln  P  versus 1/  T  ) for  n -C 20  ( O , liquid phase;  4 , solid phase), for  n -C 24  ( × , liquid phase;  ] , solid phase), andfor  n -C 28  ( 0 , liquid phase;  + , solid phase). ln  P  /Pa  )  A  -  BT   /K (2)with  B  ) ∆ vap  H  R  or  B  ) ∆ sub  H  R  (3)  Journal of Chemical & Engineering Data, Vol. 54, No. 4, 2009  1217
Search
Similar documents
View more...
Tags
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks
SAVE OUR EARTH

We need your sign to support Project to invent "SMART AND CONTROLLABLE REFLECTIVE BALLOONS" to cover the Sun and Save Our Earth.

More details...

Sign Now!

We are very appreciated for your Prompt Action!

x