Seperation prcoesses fundamentals module

[christo7]

Hi I am curently doing my degree in chemical engineering and I'm finding the separation processes module a bit rough, mainly because of interuption to lectures and the lecturer not being there most of the time.

Anyway I've got an exam coming very soon and need some help, getting desperate! A question below is a sample one which I'm truly stuck with.


1 Batches of 12,000 kg of crushed sugar cane containing 15 wt% sucrose, 20 wt%
fibre and 65 wt% water is to be leached with water in a two-stage cascade
leaching system where equal amounts of fresh water are added to each stage.
Assume that all sucrose is extracted into solution. If 3 kg of solution is entrained
with every kg of fibre:
(a) How much sucrose is extracted into the combined overflows if 8000 kg of
water is used in each stage? [8]
(b) How much water is required in each stage to extract 90 wt% of the sucrose
into the combined overflows [9]
(c) Describe how the leaching system could be improved to extract 95 wt% of
the sucrose. [3]

Can anone help me out?
Thanks
Kristian

 

[Navin A S]

a) 8000 kg of water is used in each stage, so the total amount of water used is 16000 kg. Since 15 wt% of the sugar cane is sucrose, this means that 12000 kg of sugar cane contains 1800 kg of sucrose. If 90% of the sucrose is extracted into the combined overflows, this means that 1620 kg of sucrose is extracted. b) To extract 90 wt% of the sucrose, you would need to use a total of 15600 kg of water; 8000 kg in the first stage and 7600 kg in the second stage. c) To extract 95 wt% of the sucrose, you could improve the leaching system by increasing the amount of water used in the second stage, and/or increasing the residence time of the solution in each stage. You could also use a different solvent, such as ethanol, that is better at extracting sucrose from the sugar cane.

 

[oswaler]

Hello Kristian,

I understand that you are facing some challenges with the separation processes module and are in need of assistance with a specific question. I would like to offer some guidance and suggestions to help you better understand this topic.

Firstly, it is important to have a clear understanding of the basic principles of leaching. Leaching is a separation process in which a solid material is dissolved in a liquid, usually in order to extract a desired component. In your case, the solid material is crushed sugar cane and the desired component is sucrose.

Now, let's break down the question into smaller parts to make it easier to understand.

Part (a): Here, we are given the initial conditions of the leaching process - 12,000 kg of crushed sugar cane containing 15 wt% sucrose, 20 wt% fibre, and 65 wt% water. We are also told that equal amounts of fresh water (8000 kg) are added to each stage. The question asks for the amount of sucrose extracted into the combined overflows. To solve this, we need to use the mass balance equation: Mass of sucrose in feed = Mass of sucrose in overflow + Mass of sucrose in underflow. Since all sucrose is extracted into solution, the mass of sucrose in feed is equal to the mass of sucrose in the combined overflows. Using this equation, we can calculate the amount of sucrose extracted into the combined overflows.

Part (b): In this part, we are asked to calculate the amount of water required in each stage to extract 90 wt% of the sucrose into the combined overflows. This means that 90% of the sucrose needs to be in the overflow and the remaining 10% in the underflow. Again, we can use the mass balance equation to solve this question. We know that the total amount of water used in each stage is 8000 kg. Using this information and the mass balance equation, we can determine the amount of water needed to extract 90% of the sucrose into the combined overflows.

Part (c): Finally, we are asked to describe how the leaching system could be improved to extract 95 wt% of the sucrose. To achieve this, we can make some changes to the leaching process, such as increasing the residence time, using a different solvent, or adjusting the temperature and pressure. These changes can help improve the efficiency