A gas stream (1) contains 18 mol% hexane and remainder nitrogen flows

[TonkaTon]

Summary: Hello, I need some help with this problem since my professor is bad at explaining (he reads a book and repeats everything), there's a problem online similar, but values and what is asked is different.

A gas stream (1) contains 18 mol% (40.2 mass%) hexane and remainder nitrogen flows to a condenser, where its temperature is reduced so that some of the hexane is liquified. The liquid hexane (stream 2) leaves the condenser at a rate of 990g/min (59.4 kg/h). The uncondensed gas stream (3) leaving the condenser now contains 12 mass% hexane. The process operates at a steady rate.

1. What is the flow rate of the stream (3) in kg/h?
2. What is the flow rate of the stream (1) in kmol/h?

I'd really appreciate if you could help me understand this problem, thank you in advance![Moderator's note: Moved from a technical forum and thus no template.]

 

[jrmichler]

I attack these types of problems by starting with a simple flow diagram, on which I write down all relevant information. Then add to the diagram anything that gets you closer to a solution. For example, this problem uses multiple different units (mass%, mol%, g/min, kg/h). Use the information given to calculate the flows in other units, and add that information to the diagram. You will iterate toward the solution.

Most textbooks give the impression that you should just pull the correct formula from the chapter, plug in the numbers, and get the answer. That method works if you can memorize the entire book. Also, if you are doing graded homework or an exam, the diagram shows that you at least understand the problem and how to start solving it. That's usually worth partial credit if you are unable to finish it in time.

 

[Chestermiller]

Let W represent the mass flow rate of stream 1. In terms of W, what is the mass flow rate of hexane and what is the mass flow rate of nitrogen in stream 1? In terms of W, what is the mass flow rate of nitrogen in stream 3?