Longjiaxin  Zhong1,  Erica  Gunn  Ph.D.2,  Jillian  L.  Goldfarb  Ph.D.3  1.  Department  of  Chemistry,  Boston  University,  590  Commonwealth  Ave,  Boston  MA  02215  

 2.  Department  of  Chemistry,  Simmons  College,  300  The  Fenway,  Boston,  MA  02115    3.  Department  of  Mechanical  Engineering  ,  Division  of  Materials  Science  &  Engineering,  Boston  University,  110  Cummington  Mall,  Boston  MA  02215  

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Image  Munich  city  lantern  ward  Wilhelm  Schuepfer  lights  a  gas  street  light  in  July,  1961.  RED  GRANDY/STARS  AND  STRIPES\    

Fluorene  +  Acenaphthene  

Eutec7c  Behavior  of  Binary    Polycyclic  Aroma7c  Hydrocarbon  Mixtures  

U n i n t e n d e d  c o n s e q u e n c e s   o f  industrializa2on:   PAH  abound   at   the   former  manu f a c t u r e d   g a s  plants  that  lit  the  way  to  our   modern   society.  

Eutec7c  Systems  • Phase  diagram  at  low  temperatures  

dominated  by  a  two-­‐phase  field  of  two  

different  solid  structures,  one  enriched  in  

component  A,  other  in  component  B  

• Stable,  intermediate  mixtures  form  between  

the  extremes  of  pure  component  A  and  pure  

component  B  

Solid&A&+&B&

Melt&

Tme&

TmA&TmB&

TA+B!&AB&

Melt&+&A&

Melt&&+&B&

100%&A&& &&&&&&&&&&&&&&&&&&&&&100%&B&

Abstract  Polycyclic  aromahc  hydrocarbons  (PAH)  are  byproducts  of  incomplete  combushon.  Despite  their  ubiquitous  environmental  and  industrial  posihoning,  likle  is  known  about  the  phase  behavior  of  PAH  mixtures,  which  is  important  in  predichng  their  fate  and  transport,  and  in  industrial  crystallizahon  processes.  These  compounds  precipitate  during  hydrocracking,  underscoring  the  need  to  fully  understand  their  solid-­‐liquid  equilibrium  behavior  and  the  intermolecular  forces  at  play.  Phase  diagrams  of  binary  polycyclic  aromahc  hydrocarbon  (PAH)  mixtures  display  single  and  mulhple  eutechc  points  depending  on  the  compounds.  We  studied  the  behavior  of  acenaphthene-­‐fluorene  and  fluorene-­‐phenanthrene  mixtures  of  varying  composihon  using  differenhal  scanning  calorimetry  to  measure  their  melhng  points  and  fusion  enthalpies.  As  is  omen  the  case  with  interachng  components,  the  enthalpies  of  fusion  of  these  eutechc  mixtures  are  lower  than  those  calculated  by  an  ideal  mixture  of  the  sum  of  the  individual  components.  

Fluorene  +  Phenanthrene  

Degrees  of  Devia7on  from  Ideal  Mixtures  and  Future  Work  

Ideal  Mixtures  •  If  there  were  no  intermolecular  

interachons  in  a  mixture,  we  

expect  the  enthalpy  of  fusion  to  be  

sum  of  its  individual  components  

 

• Eutechc  enthalpies  of  fusion  omen  

considerably  lower  than  ideal  

predichons  due  to  an  interachon  

energy  between  the  compounds  

Materials  &  Methods  • Compounds  from  TCI  America  at  minimum  purity  of  98%;  frachonally  sublimed  to  

remove  impurihes    

• Mixtures  fabricated  by  weighing  on  microbalance,  melted  together  on  hot  plate  at  

2°C  above  lowest  melhng  point  

• Melhng  points  and  enthalpies  of  fusion  of  pure  components  and  mixtures  

determined  on  a  TA  Instruments  Q2000  Differenhal  Scanning  Calorimeter  (DSC)  

using  hermehcally  sealed  aluminum  pans  

he ability of a binary mixture to form an ideal solution stems from the constituents’ molecular sizes and, more importantly in the case of these similar sized PAH, specific intermolecular interactions between the components (Dorset et al. 1989). In an ideal solution, we would expect the liquidous curve to follow the Schröder equation for freezing point depression, representing the melting point of the mixture, T, as

!" !! = −∆!!!!1! −

1!!,!

(1)

where R is the universal gas constant; x1 is the mole fraction of component 1 (e.g. the solvent); ΔHf1 its corresponding enthalpy of fusion at an absolute temperature of Tm,1. The same relation would hold for component 2 as in the binary mixture x2 = 1 – x1. The eutectic temperature, Te, of an ideal binary mixture is found by setting x1 = xe and T=Te (Hsu and Johnson 1974).

In a similar vein, if there were no intermolecular interactions, one might expect the enthalpy of fusion of a mixture to be the sum of the individual components, such that:

∆!!!"#,!"#$% = !!∆!!! + !!∆!!! (5)

However, this if often not the case; the enthalpies of fusion of eutectic mixtures are often considerably lower than those calculated by equation (5), attributed to an interaction energy between the compounds, equal to the difference between the measured and mixing law prediction (Gupta et al. 2012).

xi  =  Mole  frachon  of  component  i  ΔHfi  =    Enthalpy  of  fusion  component  I  

n, if there were no intermolecular interactions, one might expect the enthalpy of fusion of a mixture to be the sum of the individual components, such that:

∆!!!"#,!"#$% = !!∆!!! + !!∆!!! (5)

However, this if often not the case; the enthalpies of fusion of eutectic mixtures are often considerably lower than those calculated by equation (5), attributed to an interaction energy between the compounds, equal to the difference between the measured and mixing law prediction (Gupta et al. 2012).

∆!!"#$%&'#!(" = ∆!!!"#,!"#$%&"' − ∆!!!"#,!"#$% (6)

Sample Calculation (Acenaphthene-fluorene mixture in 50:50):

[Not pretty sure how to use this equation]

66.55℃ = 339.7!K

Fluorene  C13H10  Molecular  Weight:  166.2185        Acenaphthene  C12H10  Molecular  Weight:  154.2078  g/mol  

Heat/Cool  Thermal  cycle  at  5°C/min,  50wt%  (0.14mol%)  Fluorene  

69.5°C                                    64.3°C                                  56.5°C                          51.5°C          49.3°C                                46.0°C                            44.5°C  

48.5°C                                    50.5.3°C                            55.3°C                              51.5°C          67.5°C                                72.0°C                            72.8°C  

Cooling  and  reheahng  of  mixture.  Some  evidence  of  low  temperature  phase  growing  back  in  at  low  temperature,  and  then  re-­‐converhng  as  the  sample  is  heated.  

RT# 50.8#°#C# 55.0#°#C#

55.5#°#C#(b)#

66.0°#C# 67.0#°#C#(b)#

Sample  quenched  from  melt  between  coverslips.  (b)  Images  taken  between  crossed  polarizers;  crystalline  material  appears  bright,  melt  appears  dark.  Appearance  changes  with  temperature,  but  sample  remains  crystalline.  Changes  very  possibly  due  to  solid-­‐solid  phase  transformahon,  which  completes  around  66°C.  

1mm  

Mixtures  of  40-­‐60wt%  (46-­‐63mol%)  acenapthene  in  fluorene  show  single  melhng  points  across  composihon  range    

Mixtures  of  40-­‐60wt%  (46-­‐63mol%)  acenapthene  in  fluorene  have  enthalpies  of  fusion  similar  to  

that  predicted  by  an  ideal  mixture.  Outside  of  this  range,  we  find  negahve  interachon  enthalpies.  

 

Fluorene  C13H10  Molecular  Weight:  166.2185        Phenanthrene  C14H10  Molecular  Weight:  178..2292    

Conclusions  &  Implica7ons  

Mixtures  with  more  than  20wt%  of  either  compound  show  single  melhng  points  

Enthalpies  of  fusion  are  fairly  close  to  ideal  mixture  

predichons  

Fluorene  +  Phenanthrene  mixtures  show  considerably  lower  enthalpies  of  interachon  than  Fluorene  +  Acenaphthene  mixtures  

The degree to which a mixture deviates from ideal behavior can also be described by excess functions for enthalpy (ΔHE), Gibbs free energy (ΔGE), and entropy (ΔSE).

∆!! = −!!! !!!"#!!!" + !!

!"#!!!"

(7)

∆!! = !" !!!"!! + !!!"!! (8)

∆!! = −! !!!"!! + !!!"!!+!!!!"#!!!" + !!!

!"#!!!"

(9)

!

*Explain ΔGE minimization at eutectic!

The  degree  to  which  a  mixture  deviates  from  ideal  behavior  can  also  be  described  by  excess  funchons  for  enthalpy  (ΔHE),  Gibbs  free  energy  (ΔGE),  and  entropy  (ΔSE).  

We  will  explore  the  degree  to  which  deviahons  from  ideality  stem  from  entropic  versus  enthalpic  contribuhons  based  on  Gibbs  minimizahon  at  the  eutechc  

The  acenaphthene-­‐fluorene  system  exhibits  both  single  and  double  melhng  peaks  from  low  mass  frachon  to  high  mass  frachon.  The  fluorene-­‐phenanthrene  mixture  goes  from  eutechc  to  non-­‐eutechc  and  then  going  back  to  eutechc  behavior.  As  a  result,  the  range  of  acenaphthene’s  mass  frachon  across  the  single  phase  melhng  for  the  acenaphthene-­‐fluorene  mixture  was  between  44.6  and  64.3%,  and  the  range  of  temperature  of  the  eutechcs  was  between  67.5  and  66.6  °C.  The  range  of  fluorene’s  mass  frachon  to  achieve  this  eutechc  for  the  fluorene-­‐phenanthrene  mixture  is  between  5.27  to  54.89%  and  79.89  to  95.06%,  and  the  eutechcs  formed  for  these  mass  frachons  between  97.98  and  114.85  °C.  The  fluorene-­‐phenanthrene  system  has  a  considerably  broader  eutechc.  As  is  omen  the  case  with  interachng  components,  the  enthalpies  of  fusion  of  these  eutechc  mixtures  are  lower  than  those  calculated  by  an  ideal  mixture  of  the  sum  of  the  individual  components.