Jump to content



Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Vertical Tank Selection

New Blog Entry

Low Flow in Pipes- posted in Ankur's blog

Melting Point Of Lpg


This topic has been archived. This means that you cannot reply to this topic.
14 replies to this topic
Share this topic:
| More

#1 MrShorty

MrShorty

    Gold Member

  • ChE Plus Subscriber
  • 517 posts

Posted 26 February 2015 - 01:43 PM

This is more out of professional curiosity than for any practical purpose. Does anyone know the melting point of lpg type mixtures? Obviously pure component melting points (like 85 K for propane, 130 K for butane, 90 K for methane and ethane) are easy enough to look up, but how do the mixtures behave? Simple eutectics? Solid solutions where the melting points are intermediate between the pure component melting points? Other?



#2 gegio1960

gegio1960

    Gold Member

  • Members
  • 517 posts

Posted 27 February 2015 - 04:21 AM

It should be "the second you told"... "Solid solutions where the melting points are intermediate between the pure component melting points"



#3 MrShorty

MrShorty

    Gold Member

  • ChE Plus Subscriber
  • 517 posts

Posted 27 October 2015 - 03:13 PM

Sorry to resurrect an old thread, but this continues to pique my professional curiosity. Is there any evidence for the claim that they form solid solutions with melting points in between the melting points of the pure component?



#4 P.K.Rao

P.K.Rao

    Gold Member

  • Members
  • 265 posts

Posted 28 October 2015 - 12:42 AM

There is no specific melting point for mixtures of hydrocarbons. LPG is a mixture of hydrocarbons. As the temperature is lowered, the component having highest melting point will separate out first followed by next as in the case of kerosene/diesel etc. In case of LPG, n-pentane (if LPG contains n-pentane) will separate out  first followed by isopentane, n-butane,etc as per the melting point of pure components. Please note that LPG may contain butenes and propenes also. Please also note that the separation may be influenced by the manner in which the mixture is cooled.  


Edited by P.K.Rao, 28 October 2015 - 12:43 AM.


#5 Arunkannan

Arunkannan

    Brand New Member

  • Members
  • 4 posts

Posted 28 October 2015 - 05:07 AM

hi 

 

Kindly attached the LPG or BIogas Plant ,the Basic details and Calculation 

 

And give the detail how to calculate Diesel Generator composition ratio.



#6 P.K.Rao

P.K.Rao

    Gold Member

  • Members
  • 265 posts

Posted 28 October 2015 - 05:44 AM

Please be clear. What is meant by LPG and BioGas plant details and diesel generator composition?



#7 Neelakantan

Neelakantan

    Gold Member

  • Members
  • 124 posts

Posted 28 October 2015 - 05:57 AM

LPG is a mixture of HC alkanes. (predominantly c3/c4); both are gases at normal ambient temp (15 deg C) at atmospheric pressure and are liquids only in compressed state; hence the name.

 

we talk about melting point when we move from a solid to liquid, we should be looking at freezing point (as we may be moving from liquid to solid).

 

now assuming we have a block of solidified LPG(atmospheric pressure?) ; in that the I-propane component is the last melting component; propane would start melting earlier, but it wont separate, but will dissolve butanes. thereby arriving at a different meting point (in other words, the melting point will move up from the propane's individual melting point. similarly, considering freezing the isobutane (and probably some pentanes) will start freezing out first.

 

it would be interesting to see the material specification: see the sample from TOTAL INDIA

 

http://www.total.co....cification.html

 

the quoted freezing point is -47 deg C

 

2 PHYSICAL & CHEMICAL DATA:   Boiling range :-42oC to 2oC Physical state : Gas @ 15oC & 1 atm. Appearance : Colourless     Vapor pressure @ 35oC :120 psi @ 38oC Odour :Ethyl Mercaptan added for odour warning   Melting / freezing point : - 47oC

 

regards

neelakantanr

There is no specific melting point for mixtures of hydrocarbons. LPG is a mixture of hydrocarbons. As the temperature is lowered, the component having highest melting point will separate out first followed by next as in the case of kerosene/diesel etc. In case of LPG, n-pentane (if LPG contains n-pentane) will separate out  first followed by isopentane, n-butane,etc as per the melting point of pure components. Please note that LPG may contain butenes and propenes also. Please also note that the separation may be influenced by the manner in which the mixture is cooled.  



#8 MrShorty

MrShorty

    Gold Member

  • ChE Plus Subscriber
  • 517 posts

Posted 28 October 2015 - 10:08 AM

we talk about melting point when we move from a solid to liquid, we should be looking at freezing point (as we may be moving from liquid to solid).
You are, of course, correct. We can talk about both freezing point curves and melting point curves, and, for mixtures, they are not necessarily the same. In many ways, I don't think I care whether we want to talk about melting point curve or freezing point curve, ultimately I think my question is about what these phase diagrams look like (qualitatively).

 

For those looking for more details about the mixture, I don't really have a specific mixture or plant sample or what have you in mind. Examples that I might throw out there:

 

1) Methane and ethane both freeze/'melt at about 90 K, What is the freezing point and/or melting point of a 50:50 mix of methane:ethane? Will mixtures of methane/ethane also freeze/melt at about 90 K, or will the sytem form a eutectic that freezes/melts colder than either pure component (possibly even colder than propane)?

 

2) How about a mix of propane (mp 85 K) and ethane (mp 90 K)? Are the melting/freezing points all in between 85 and 90 K, or does this system form a eutectic or exhibit other interesting behavior?

 

3) What about pairs that have a wider difference in melting points? methane + n-butane or propane + n-pentane?

 

4) I find it interesting that Neelakantan's LPG mix has a specified freezing point of 226 K for a mix that is essentially 40% propane (mp 85 K) : 20% isobutane (mp 114 K): 40% n butane (mp 135 K). I would guess that this freezing point is really due to unspecified impurities (water or heavy hydrocarbons) rather than the real mixture listed. If we could assume a perfectly clean ternary mix like this, would it really freeze at a temperature 100 K higher than any of its consituents? If not, what would the melting/freezing point temperatures/curves look like?



#9 Art Montemayor

Art Montemayor

    Gold Member

  • Admin
  • 5,779 posts

Posted 28 October 2015 - 07:51 PM

Shorty:

 

Your positive and constructive responses and contributions to our Forums through the years is something that is well-known among our senior members.  That, and the fact the topic you bring up is not only intriguing - but also illusive - are reasons why I am injecting myself into this topic.

 

Since the quantitative composition of LPG varies according to source, location, and definition, the physical and chemical properties useful and needed for design and processing use have always been difficult to obtain, estimate, or nail down.  Throughout my 54 years as an engineer I had to resort to various techniques when I need to obtain LPG properties.  I resorted to the “faithful” “Handbook of Butane-Propane Gases” (Chilton Company; Los Angeles, CA), “The Properties of Gases and Liquids” (Reid & Sherwood; McGraw-Hill), or in the near past to “Phase Equilibria in Chemical Engineering” (Stanley Walas; Butterworth Publishers).  Perry’s Handbook always lacked any useful information.  But I have never found any detailed information on solid LPG.  All I have recently found is the following (and you probably already know this):

 

Source: http://pubchem.ncbi....ne#section=Odor

1) Butane Melting Point = -138.3 oC (-216.94 oF = 134.85 K)
Source: Haynes, W.M. (ed.).  CRC Handbook of Chemistry and Physics. 94th Edition.  CRC Press LLC, Boca Raton: FL 2013-2014, p. 3-76

2) Propane Melting Point = -187.6 oC (-305.68 oF = 85.55 K)
Source: O'Neil, M.J. (ed.).  The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. 13th Edition, Whitehouse Station, NJ: Merck and Co., Inc., 2001., p. 1397

 

I believe that the reason for the scarce work done on identifying specific properties on LPG is for the following reasons:

  • There is little or no industrial or academic interest in the solid state;
  • The variety of different LPG compositions makes for very laborious and expensive experimental laboratory procedures;
  • The need applications of LPG are limited to a few: domestic heating and only a few more.

Therefore, it isn’t surprising to google through the internet and get weird results like the posting of TOTAL-India who in their website, http://www.total.co....cification.html, state that the LPG Melting/freezing point: - 47 oC (-52.6 oF = 226.15 K.  This sounds ridiculous; it doesn't make sense.

 

Cameo Chemicals is more candid and truthful at their website, cameochemicals.noaa.gov/chris/LPG.pdf by simply stating “Freezing Point: Not pertinent”.  And I believe this is where the current scientific and engineering feeling are vis-a-vis LPG 

 

I wish I could lend some useful advice on your basic query simply because it is a valid and very interesting topic that harbors the dilemma facing all chemical engineers - which is confronting the real-life applications that are composed of chemical mixtures and not pure components - something that was a subject totally avoided in chemical engineering during my university time.

 

Good luck on your search and let us all know if you find a reliable and detailed answer to your query - especially if you find a source for detailed LPG physical liquid data.



#10 Neelakantan

Neelakantan

    Gold Member

  • Members
  • 124 posts

Posted 29 October 2015 - 09:10 AM

ART

 

you are  forthright to use the word "ridiculous", while i used "interesting"

 

i really donot feel the temperature is an experiemental result; it may be worth wrting to TOTAL how they arrived at it!

 

regards

neelakantan


Therefore, it isn’t surprising to google through the internet and get weird results like the posting of TOTAL-India who in their website, http://www.total.co....cification.html, state that the LPG Melting/freezing point: - 47 oC (-52.6 oF = 226.15 K.  This sounds ridiculous; it doesn't make sense.

 

Cameo Chemicals is more candid and truthful at their website, cameochemicals.noaa.gov/chris/LPG.pdf by simply stating “Freezing Point: Not pertinent”.  And I believe this is where the current scientific and engineering feeling are vis-a-vis LPG 

 



#11 MrShorty

MrShorty

    Gold Member

  • ChE Plus Subscriber
  • 517 posts

Posted 29 October 2015 - 11:16 AM

I realized that I should probably apologize for being "loose" with terminology. I have been using the term LPG to refer to both LPG and LNG type mixtures. As noted above, LPG usually refers to light hydrocarbon mixtures that have littel to no methane in them, where LNG refers to mixtures that are rich in methane.

 

I have come across some data from Kuebler and McKinley (back in the '70's I believe) reporting "solubilities" (aka freezing points) of n-pentane and n-butane in methane, which is interesting. Of course, data along the freezing point curve don't tell us anything about the melt curve. Shall we assume, as PKRao suggests in post 4, that the butane/pentane is freezing out as pure butane/pentane, or is the methane crystallizing out with it? The data do not extend low enough to see if there is a eutectic (if there is, the eutectic composition is likely nearly all methane, and the freezing point of the eutectic is close the the freezing point of pure methane). As Art says, it is a question that may not have any practical application, but it makes for interesting theoretical work.

 

(I know, we became engineers rather than theoretical scientists because we wanted to use the science in practical, useful ways rather than sit around all day performing "thought experiments" that have no meaning -- no offense intended towards the theoretical scientists out there. I find myself occasionally dabbling in this kind of theorizing, just the same).

 

Art mentioned Stanley Walas's excellent text. In Figure 5.22 (f), he shows a diagram for the 2,2-dimethylbutane + 2,3-dimethylbutane mixture that shows some very interesting freeze/melt behavior. His data (taken from Fink et al JACS vol 69 from 1947) show a maximum and a minimum in the freeze/melt curves and alleges the existence of an intermolecular compound. If these two hexanes can exhibit this kind of complex behavior, is it possible that other hydrocarbons exhibit something other than "simply freezing out as the pure hydrocarbon".

 

As suggested, maybe not of practical interest, but I do sometimes find such theoretical speculation interesting.



#12 Bobby Strain

Bobby Strain

    Gold Member

  • Members
  • 3,526 posts

Posted 30 October 2015 - 11:44 AM

One of the sources for such data might be found at Brigham Young (I think) through work by professor Grady Wilson. He worked on the issue in late '69 and  '70s.  All of the LNG players have developed data for use in their LNG process. Here is a small bit of information.

    http://webwormcpt.bl...mit-in-lng.html

 

Bobby



#13 P.K.Rao

P.K.Rao

    Gold Member

  • Members
  • 265 posts

Posted 31 October 2015 - 01:13 AM

Please refer to the document of TOTAL (MSDS of LPG)

Melting point/Freezing point : Minus 470 C

Boiling Range: minus 42 to +2 deg C

There is very small difference between melting point (freezing point) (minus 47 deg C) and minimum boiling point (minus 42  deg C). This is somewhat surprising.

Material Safety Data Sheet (MSDS) may not provide actual data. It provides data for safety purposes only. Please refer to standard reference text books for the actual data. (you may also write to TOTAL for clarifications). As you said earlier above, when a material is heated from a lower temperature to higher temperature, it passes through solid to liquid to vapor. On the reverse, when a vapor is cooled, it passes through states of vapor to liquid to solid. Data of LPG components is given in the attachment.

Please note that all substances have vapor pressures at all temperatures. So depending on the vapor pressures of the components of a mixture, the composition of the vapor at a specific temperature can vary.

Freeing points/melting point can behave in a similar way. Freezing point/melting point is also used to separate the components  of the mixture similar to use of vapor pressure for separating the components. The components are purified by repeated crystallization wherever and if required

Finally, if you can carry out some studies on your thoughts and publish the results, it would be much appreciated.

The freezing points and boiling points of LPG components are given in the attachment


Edited by P.K.Rao, 31 October 2015 - 01:16 AM.


#14 P.K.Rao

P.K.Rao

    Gold Member

  • Members
  • 265 posts

Posted 31 October 2015 - 02:14 AM

   Attachment               

 

                    Chemical Technology of Petroleum

                                Gruse and Stevens

                                Second Edition 1942

 

Hydrocarbon                      Boiling Point deg C           Freezing Point deg C

 

Propane                               minus 42.1                          minus 188

Butane                                 minus 0.5                             minus 138

Iso butane                          minus 11.7                          minus 159.4

Propylene                           minus 47.7                          minus 185.3

Butene-1                             minus 6.5                             ---

Butene-2 cis                       3,7                                          minus 139.3

Butene-2 Trans                 0.3                                          minus 105.8


Edited by P.K.Rao, 31 October 2015 - 02:16 AM.


#15 MrShorty

MrShorty

    Gold Member

  • ChE Plus Subscriber
  • 517 posts

Posted 11 January 2016 - 10:16 AM

One possible piece of this puzzle. I found a paper that references freezing point data for methane + ethane from D. W. Moran's PhD thesis (University of London, 1959). These data suggest a simple eutectic type system with the eutectic at ~70% methane and ~73 K.






Similar Topics