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Author Topic: Chemical process calculations - problem. (Pls Help)  (Read 491 times)

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euphoria97

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Chemical process calculations - problem. (Pls Help)
« on: November 04, 2017, 09:05:15 AM »

Q. The average gasoline tank in an automobile has a 50 L capacity. Every time the gas tank is filled, the vapor space in the tank is displaced to the environment. Since all forms of hydrocarbons in the atmosphere contribute to the formation of ozone and need to be controlled, this problem attempts to quantify some of these emissions. Assume the automobile tank vapor space, the air, and the gasoline supply is all at 20 degrees C. The vapor space is saturated with gasoline. The vapor-phase mole fraction of gasoline under these conditions is approximately 0.4. The lost vapor has a molecular weight of about 70 g/gmol and a liquid specific gravity of 0.62.
a) Calculate the amount of gasoline (in gallons of liquid) that is lost to the air during a 35 L fill.
b) How much is lost annually from 50 million cars filled once each week with 35 L of gasoline.

Please help with this problem. I'm really stuck.
I would really appreciate it if you could provide the solution to this.
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billnotgatez

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Re: Chemical process calculations - problem. (Pls Help)
« Reply #1 on: November 04, 2017, 09:11:09 AM »

You have to show your attempts or thoughts at solving the question to receive help.
This is a forum policy.
Click on the link near the top center of the forum page.
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http://www.chemicalforums.com/index.php?topic=65859.0
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euphoria97

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Re: Chemical process calculations - problem. (Pls Help)
« Reply #2 on: November 04, 2017, 08:50:12 PM »

Okay so I've got the basic idea here.
You need to use the properties of the gasoline vapor to determine how much liquid gasoline is in vapor form when the tank has 15L of liquid in it in order to answer part A. You can use the vapor-phase mole fraction to determine a molar concentration in air and convert that to a liquid volume using molecular weight and specific gravity (density).
Part B is a simple dimensional analysis, converting part A's L/fill to L/year based on a given number of fills and vehicles.

But still I'm unclear on how to go ahead with this approach. Any help would be really appreciated.
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Borek

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Re: Chemical process calculations - problem. (Pls Help)
« Reply #3 on: November 04, 2017, 10:43:13 PM »

The approach you have outlined looks OK, hard to tell what stops you from going ahead. Just try to express amount of gasoline lost during filling the tank with the gas volume and amount of vapor in the gas, then see what you can plug into the formula you got.
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euphoria97

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Re: Chemical process calculations - problem. (Pls Help)
« Reply #4 on: November 06, 2017, 02:45:41 AM »

Okay I've tried to solve the problem. You can look at it here. Can you please look at it and just verify if you think its correct? Thanks. https://www.photobox.co.uk/0x1ef7031c7e0278e7b146fd4466cb6406/album/temporary
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sjb

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Re: Chemical process calculations - problem. (Pls Help)
« Reply #5 on: November 06, 2017, 04:42:22 AM »

Any chance you could type this out to help search functionality?

At a glance, I'm not sure you've converted your volume from litres to gallons correctly at the very least.
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Enthalpy

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Re: Chemical process calculations - problem. (Pls Help)
« Reply #6 on: November 13, 2017, 04:56:31 AM »

The given molecular weight and liquid specific gravity of gasoline are wrong, so don't keep them in your mind. Though it's very possible that the given molecular mass corresponds to the lighter fraction of gasoline that evaporates preferentially.
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