91Ó°ÊÓ

In the production of soybean oil, dried and flaked soybeans are brought into contact with a solvent (often hexane) that extracts the oil and leaves behind the residual solids and a small amount of oil. (a) Draw a flowchart of the process, labeling the two feed streams (beans and solvent) and the leaving streams (solids and extract). (b) The soybeans contain 18.5 wt\% oil and the remainder insoluble solids, and the hexane is fed at a rate corresponding to \(2.0 \mathrm{kg}\) hexane per \(\mathrm{kg}\) beans. The residual solids leaving the extraction unit contain 35.0 wt\% hexane, all of the non-oil solids that entered with the beans, and \(1.0 \%\) of the oil that entered with the beans. For a feed rate of \(1000 \mathrm{kg} / \mathrm{h}\) of dried flaked soybeans, calculate the mass flow rates of the extract and residual solids, and the composition of the extract. (c) The product soybean oil must now be separated from the extract. Sketch a flowchart with two units, the extraction unit from Parts (a) and (b) and the unit separating soybean oil from hexane. Propose a use for the recovered hexane.

Step by step solution

01

Flowchart Creation (a)

Producing a flowchart for the extraction process includes indicating the soybeans and solvent as entering streams, and solids and extract as exiting streams. This diagram serves as a visual aid for understanding the process and simplifying the mass balance equations used in the calculations.

02

Mass Balances and Calculations (b)

Assuming steady-state operation, mass balances around the extraction unit can be written. First, the total material balance is given by \( \text{{input}} = \text{{output}} \), which translates into: F = E + R, where F represents the total input mass flowrate, E is the total extract flowrate, and R is the total residuals flowrate. The mass balance equation for each component (soybean, oil and hexane) are constructed using the provided composition information. Solving the set of equations yields the flowrate for extract and residuals as well as the composition of the extract.

03

Flowchart Completion and Proposal (c)

The flowchart from part (a) is enhanced in part (c) to add the separation unit, which separates hexane (to be reused in the process or in other industrial applications) from soybean oil. The recovered hexane can be proposed to be used in the same process again or in other industrial applications where a solvent is needed.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Flowchart Creation

Creating a flowchart is a vital step in understanding a chemical process. This visual tool helps us to delineate the sequence of operations, inputs, and outputs of a system more clearly. In our soybean oil extraction case, the flowchart should clearly display:

• Two feed streams, which are the soybeans and the hexane solvent.
• Two leaving streams, which are the residual solids (a mixture of residual oil, solids, and hexane) and the desired oil-rich extract.

Visualizing these streams and their interactions allows us to better structure the subsequent calculations. By labeling each stream, you can simplify complex mass balance equations. Imagine the flowchart as a map that guides you through the chemical process, ensuring that every step is covered quantitatively and qualitatively.

Chemical Process Calculations

Chemical process calculations are the backbone of process engineering. They help determine the flow rates and compositions of streams in chemical processes. In this scenario, we use mass balances to calculate these parameters. The key equation is the total material balance: \(\text{input} = \text{output}\). This principle applies to the entire process and to individual components, like soybeans, oil, and hexane.
To perform these calculations, we need to:

• Define variables for each stream's flow rate and composition.
• Set up equations based on the mass balances for these streams and components.
• Solve the equations to find unknown values, like the extract and residuals flow rate, or the composition of the extract.

This step essentially provides a mathematical confirmation of what the flowchart visually represents, ensuring that all assumptions are validated, and the process is feasible.

Extraction and Separation Techniques

Extraction and separation techniques play a crucial role in isolating desired components in chemical processes. In this exercise, the primary goal is to separate the soybean oil from the other constituents, primarily using hexane as the extraction solvent. This technique relies on the principle that different substances have different solubilities in a solvent.
Once the oil is extracted, separating the hexane and oil becomes the focus. This can be accomplished using units like distillation columns or evaporators, which take advantage of differing boiling points or volatilities. The hexane, being volatile, can be recovered and reused. This not only makes the process more cost-effective but also environmentally friendlier by reducing waste.
Proposing a use for recovered hexane also demonstrates an understanding of the importance of recycling and sustainability in industry. The hexane might be reintroduced into the extraction cycle or employed in other solvent-involved processes, showcasing the versatility and resource efficiency.