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Hi guys newbie here. Was hoping for help with a process engineering mass balance using the douglas approach. Got to the input and output flow diagram but now im stuck on the balance. Please help.

The question sheet is attached via a word document

My work so far is attached via a word document pleas help me!
Need help with q 7 of the worksheet

Attached Files

•  process.doc   34KB   172 downloads
•  Problem.doc   26KB   126 downloads

[Art Montemayor]

latkan:

I am going to try to give you a hand with this assignment because I think you need it – and not only in arriving at the “correct” answer(s). Bear in mind that some answers are subjective in nature – based on experienced engineering. I am going to be very candid and I hope you pick up the suggestions and hints I offer:

• Do not assume that Chemical Engineers outside of the U.K. would know what “the douglas approach” is. I never heard of Mr. Douglas, but I assume it is a recent method to facilitate a manner of making a mass balance.
• The manner that you present your basic data and engineering information - especially calculations - can be much improved if you did it in a spreadsheet format, rather than in a word processor. Business majors and secreteries employ word processors; engineers, however, employ spreadsheets. Note the method that I employ in the attached engineering spreadsheet. Spreadsheets were developed for making calculations and presents graphics and that is what engineers do.
• Please correct the mistakes you make in presenting equations. Note that your equations:
  Benzene/mol Styrene = 0.333x-0:215x^2+2.547x^3
  Toluene/mol Styrene = 0:084x-0:264x^2+2:638x^3
  are not expressed correctly. Compare them with my version in the spreadsheet.
• Take your problem seriously and do some research – especially on the Internet. Look at my workbook and see some of the background that I found right here in our Website. From this research you can readily see the complete flow diagram of the industrial process described in your problem. From the flow diagram I give you, you can see that your answers are not correct – at least not according to the common, industrial, engineering manner of producing styrene. Your problem tells you to think as an engineer and the engineering answers do not concur with yours. You state: “The process should be batch given the production requirements (100mol/hr ≈ 91 tonnes/yr which is below the 500 tonnes/yr the upper boundary for batch operation). [Check the calculation]”. There is no calculation given. Additionally, how are you to compete with other manufacturers if you intend to make the process batch? You won’t be able to compete economically. I would make the process continuous – just as in the flow diagram.
• In my opinion, the conversion to be expected is around 60 – 65% - just as the research indicates.
• I also don’t think you need any feed purification – mainly because I assume that the EB and Steam feeds can be assumed as basically pure.
• As the flow diagram clearly points out there is no hydrogen recycle. All gaseous byproducts are produced as probably fuel or feedstock for other processes (not “purged”).
• The number of product streams (4) are seen in the flow diagram. This is a “no-brainer”.
• Using the flow diagram given, you should easily calculate the mass balance using the equations given and the process description. A simple, conventional and logical mass balance will do – although if you want to do it Mr. Douglas’ way, then go at it.

I hope this helps.

Attached Files

•  Styrene Monomer Produciton.xls   70KB   204 downloads