How Green Is My Orange Biology Essay

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Many fruits and vegetables contain essential oils, which are water repellent or hydrophobic liquids that give the fruit or vegetable its distinctive fragrance. These essential oils are often extracted for use in perfume, cosmetics, food, medicine and house cleaning products. Many of these essential oils are extracted through liquid chemical extraction using dangerous chemical solvents, such as methylene chloride. Conventional methods used to extract essential oils include steam distillation or liquid chemical extraction. Steam distillation requires high energy input as energy is required to boil water to produce steam. The energy used combined with the dangers of heating large amounts of matter on an industrial level means that this process does not adhere to the principles of green chemistry. This is an important component of teaching students about green chemistry as Green Chemistry is not just a concept used in the lab but a concept meant to be used on an industrial scale to make products which are useful to the world. Steam distillation may seem like a benign process until it is evaluated against the 12 principles on an industrial scale.

Scientists have discovered the use of supercritical carbon dioxide (CO2) at high pressure is an alternative method of extracting essential oils and that is the process which you will discover with your students through this activity.

It is important to note that the use of supercritical CO2 for extraction does not affect the net amount of CO2 in the environment, thus using supercritical CO2 for essential oil extraction is not considered to affect climate change in any way. Instead, the use of supercritical CO2 is considered a greener way of essential oil extraction since it reduces the amount of energy input and eliminates the need for dangerous solvents. Because supercritical CO2 does not have high reactivity with essential oils, which can lead to the breakdown of the essential oil, its use in essential oil extraction is gaining popularity. Currently, supercritical CO2 is used to remove caffeine from coffee beans to produce decaffeinated coffee and as a replacement for perchloroethlyene in dry cleaning applications.

In this experiment, students will extract the essential oil d-limonene from the rind (skin) of orange peels using both a steam distillation or simple distillation method and the method of using supercritical CO2. They will analyze the difference between the two methods and make connections between the laboratory activities they do in the classroom and the industrial chemical processes that are used to make products. D-limonene gives oranges, lemons and limes their citrus-like scent.

Please refer to additional teacher background info and safety considerations at the end of this lesson.

* The steam distillation as a demo lab and the supercritical CO2 as a hands on students lab if you feel that you only have one class period to cover this material.

Educational Goal: To understand chemical, steam and CO2 extraction methods and their relationship to green and industrial chemistry practices.

Student Objectives: Students will …

Extract essential oils from oranges using steam distillation

Extract essential oils from oranges using supercritical CO2

Compute the use of energy in both extractions.

Compare the use of energy in both extractions

Compare the use of hazardous chemicals in both extractions

Learn about phase changes of CO2

Materials: (per lab group -3 students)

Steam Distillation

Watt's up meter (optional)

Orange

Food grater

Scale

Weigh boat or weigh paper

Spatula

De-ionized water (DI H2O)

Distillation apparatus

2 ring stands with clamps

Heat source (i.e. hot plate, bunsen burner)

Distilling flask

Condenser

Joint adapters

Thermometer

Collection beaker or flask

Cold water source

Tubing

CO2 Extraction

3 pairs of gloves

2 oranges

1 coil trap (copper wire net to contain the orange peel) (18-22 gauge copper or aluminum wire bent into a tapered coil shape, wire can be found at arts and crafts stores)

1 zester or orange peel grater -medium grade

two weighing boats

one spatula

one pair of forceps

5 x 15 mL polypropylene centrifuge tubes with caps (Corning Catalog #430052)

1 transparent polycarbonate plastic cylinder on base (a plastic soda bottle works fine)

An 8 inch water bath heated to 65oC

20 oC to 100oC alcohol thermometer

1 lb dry ice crushed dry ice

analytical balance

Time Required: 2 x 60 minute class period

National Standards Met: National: S1, S2, S5, S6

MA Standards: C1, C6

Green Chemistry Principles Addressed: 5, 6, 11, 12

Teacher Prep:

Crush the dry ice into a fine powder

You may want to let students do this part but if you want to prepare these before class, follow the directions below:

Prepare coil traps prior to the lesson (you can have the students do this step if you feel that you have enough class time) - one per students following the directions below

Cut the 18-22 gauge copper wire into 10 inch long pieces.

Coil the piece of copper wire around so the it creates a bowl-like structure that will fit into the bottom of the test tube and provide a catcher for the orange peel once it is inserted into the test tube.

Replace the test tube cap.

Prepare 3-4 large beakers of water and heat to 50-60 degrees at the front of the class.

Procedure:

Day 1

Show the PowerPoint Slides 1-5 for this lesson to give the background information to the students.

Explain to the students that they will now extract orange oil, limonene from an orange using steam distillation.

Hand out the student lab sheet and have the students review the information.

Check for understanding and answer any questions.

Instruct the students to begin the lab activity for steam distillation.

When all students have finished debrief the students data sheet questions, paying special attention to the analysis of the process against the 12 principles of green chemistry.

Day 2

Optional: dress up as Supercritical CO2 girl for the day!

Review essential oil extraction from the last class period.

Now show PowerPoint slides 5 - 9

Instruct the students to begin the second part of the lab.

During the lab, monitor the water to ensure a constant temperature.

When students are ready transfer the 50ËšC-60ËšC water from the beaker on the hot plate into the polycarbonate plastic bottle. Fill the water up to 2/3 of the bottle. Add more water to the beaker on the hot plate, and maintain the temperature of that water to 50-60ËšC.

Have students stand at least a foot away from the experiment after they have dropped their test tubes into the water and have them watch from the side as tops can sometimes pop off due to pressure.

After the lab is complete have the students fill out the student lab sheet.

Show Powerpoint slide #10

Hand out the 12 principles comparison student table. Have students work in groups to complete the table and then discuss their answers as a class.

This lesson plan was based on a laboratory experiment McKenzie, Lallie C.; Thompson, John E.; Sullivan, Randy; Hutchison, James E. Green chemical processing in the teaching laboratory: a convenient liquid CO2 extraction of natural products. Green Chemistry (2004), 6(8), 355-358.

Steam Distillation Orange Oil Extraction

Student Lab Procedure

Many fruits and vegetables contain essential oils, which are water repellent or hydrophobic liquids that give the fruit or vegetable its distinctive fragrance. These essential oils are often extracted for use in perfume, cosmetics, food, medicine and house cleaning products.

You will use the lab directions below to extract essential oils from an orange using steam distillation. This essential oil is called d-limonene and is represented by the chemical structure shown below:

Chemical structure of d-limonene

Steam Distillation:

Steam distillation is a technique used to isolate or extract compounds at temperatures below their boiling points. Some compounds, such as essential oils, tend to decompose at their boiling temperature. By adding water or steam to the compound, the boiling point of the compound is reduced, allowing it to evaporate at a lower temperature so as to avoid decomposition during extraction.

The evaporated compounds are in their gaseous phase once heated, but condense back into their liquid phase upon contact with a cold surface (such as a condenser with cold water surrounding it). The compound in liquid form is then collected into a receiving flask. The diagram below shows the distillation set-up.

Procedure:

1. Collect the following apparatus from the supply area:

Orange

Food grater

Watt's Up Meter (optional)

Scale

Weigh boat or weigh paper

Spatula

Deionized water (DI H2O)

Distillation apparatus

2 ring stands with clamps

1 hot plate

Distilling flask

Condenser

Joint adapters

Thermometer

Collection beaker or flask

Cold water source

Tubing

Review the data sheet below to ensure that youa re recording data at certain phases of the experiment.

Set up the distillation equipment as shown in the diagram attaching the Watt's Up Meter to the hot plate.

Determine the mass of the receiving flask and record it on the student data sheet.

Use the grater at the medium grating side to grate off the outside peel of the orange.

Place 25 g of the orange rind in the distilling flask.

Add 25 mL DI H2O into the distilling flask.

Place the distilling flask in an oil bath over a hot plate.

Turn on the hot plate and allow the flask to heat up. Monitor the temperature at which the water in the distilling flask begins to boil.

Collect the essential oil distillate in the receiving flask.

Allow the contents in the distilling flask to boil until approximately 20 mL of the distillate is collected.

Determine the mass of the essential oil collected.

Calculate the percent recovery of the essential oil compared to the mass of the rind.

Complete the student data sheet for steam distillation and answer all questions in full.

Supercritical CO2 Orange Oil Extraction

Student Lab Procedure

Scientists have discovered the use of supercritical carbon dioxide (CO2) at high pressure as an alternative method of extracting essential oils. CO2 is the gas exhaled by humans during respiration, is consumed by plants during photosynthesis and exists in the environment in abundance from human activity such as fossil fuel combustion.

Supercritical CO2 is considered an alternative way of essential oil extraction. Because supercritical CO2 does not have high reactivity with essential oils, which can lead to the breakdown of the essential oil, its use in essential oil extraction is gaining popularity. Currently, supercritical CO2 is used to remove caffeine from coffee beans to produce decaffeinated coffee and as replacement for perchloroethlyene in dry cleaning applications.

Procedure:

Collect the following apparatus from the supply area:

1 Orange

Safety glasses

Gloves (latex or nitrile)

Hot pads/oven mitt for handling dry ice

Food grater

Weigh boat

Spatula

Scale or triple beam balance

Forceps or tweezers

1 test tube full of crushed dry ice (you will go and get this when you are ready for this step)

1 solid trap

18-22 gauge copper wire

15 mL polypropylene centrifuge tubes with caps (one per person in your group)

500 ml plastic cylinder

500 mL beaker

Put on safety gloves and glasses.

Using the medium grate opening on a food grater, grate only the colored part of the orange peel.

Using the scale, spatula and boat, measure 2.5 g of orange peel and set it aside.

Find the mass of the centrifuge tube and cap and record it on the students data sheet

Refer to the Tube Preparation page for images of the coil and the following steps.

Take the piece of copper wire and create a trap for the orange peel as shown in the picture below: Prepare a trap to hold the orange rind in by obtaining copper wire and forming 5-6 tight coils around the bottom of the tube. Hold one end of the wire against the narrow end of the tube while wrapping and forming the 5-6 tight coils. The wire will need to fit into the tapered end of the centrifuge tube. At the very bottom, the diameter of the coil is smallest, and gradually enlarges to the same inner diameter of the largest part of the centrifuge tube by the 5-6th coil. Leave a long end of the wire available as a stem.

Place the trap into the centrifuge tube with the tapered end in first. The long stem of the trap should sit just below the rim of the centrifuge tube.

Place 2.5 g of orange peel into the tube so that it sits on the coiled part of the trap. Tap the bottom of the tube against the lab bench to ensure all orange peel is off of walls. Very important: do not pack the orange peel in tightly.

Wear the cryogenic gloves (these gloves should be worn every time dry ice is handled).

Using a mortar and pestle or a hammer, crush the dry ice into small pieces. The smaller the pieces, the better. Use right away or the dry ice will sublime (melt).

Fill the centrifuge tube with crushed dry ice all the way to the top. Tap the bottom of the tube against the lab bench to pack as much dry ice in as possible.

Place the cap on the centrifuge tube. Tighten the cap, but do not over tighten so that you over screw the cap and go from tight to loose.

Transfer the tube to the prewarmed pastic bottle at the front of the class that is being monitored by your teacher.

STAND BACK FROM THE EXPERIMENT AS TOPS CAN POP OFF.

Allow the centrifuge tube to sit in the bottle. You may hear the hissing sound of CO2 gas escaping, which is expected.

When the level of dry ice (solid CO2) has lowered, meaning the solid CO2 has been converted to gaseous and liquid CO2, remove the tube from the water and slowly uncap it. Always point the tube away from your face and body.

Add more crushed dry ice a few times until you can see a liquid at the bottom tip of the centrifuge tube. This pale yellow liquid is the essential oil d-limonene.

The yellow oil should be in the tip of the tube when the extraction is complete.

Carefully remove the trap by pulling the copper stem with tweezers. If any solid remains in the tube, remove it with a spatula. NOTE: Keep the tube upright to avoid any loss of the oil. There should be nothing in the tube at this point except for the essential oil collected in the tip of the tube.

Dry the outside of the tube with a paper towel, weigh the tube, and determine the mass of the product. Calculate percentage recovery based upon the yield of the product compared to the mass of rind used.

Tube Preparation

Loosely pack the tube with 2.5 g orange rind

Tube with copper trap inserted

Trap: copper wire with tapered coiled end

Tube with

cap removed

Dry, empty clean centrifuge tube (15 mL polypropylene with a screw cap)

Pack the rest of the tube with crushed dry ice

Place the tube in the plastic container (which is filled 2/3 of the way with 50ËšC - 60ËšC water). Always point the tube away from the face and body to avoid injury.

Tightly screw the cap on the tube

How Green is my Orange

Student Data Sheet - Steam Distillation

What is the mass of the dry, empty receiving flask?____________________grams

What is the mass of receiving flask with essential oil distillate? __________grams

What is the mass of the essential oil collected?__________________________grams

What is the volume of the essential oil collected?_________________________mL

What is the mass of the orange rind placed into distilling flask? _________grams

What is the temperature at which the water in the distilling flask boils?______ËšC

What is the color of the essential oil you have created?_________________________

What was the percent recovery of the essential oil compared to the mass of the rind used with the steam distillation extraction?

To calculate the percent recovery:

(mass of essential oil/mass of rind) x 100

________________________________________________________________________________________________________________________________________________________

How many minutes does it take to collect approximately 20 mL of the distillate?

______________________________________________________________________________

In a brief paragraph, consider the properties of the essential oil you have created - paying special attention to the toxicity and impact on the environment of the d-limonene.

_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

In a brief paragraph, analyze this process against the 12 principles of green chemistry. Which principles does this process not adhere to and why?

______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

_________________________________________________________________________________

Draw the chemical structure of the D-limonene you have created below:

How Green is My Orange

Student Data Sheet - Supercritical CO2

What is the mass of the essential oil collected?__________________________grams

What is the volume of the essential oil collected?_________________________mL

What is the mass of the orange rind placed into distilling flask? _________grams

What is the temperature of the water used in the process?______ËšC

What is the color of the essential oil you have created?_________________________

What was the percent recovery of the essential oil compared to the mass of the rind used with the steam distillation extraction?

To calculate the percent recovery:

(mass of essential oil/mass of rind) x 100

________________________________________________________________________________________________________________________________________________________

How many minutes does it take to collect approximately 20 mL of the distillate?

In a brief paragraph, consider the properties of the essential oil you have created - paying special attention to the toxicity and impact on the environment of the d-limonene.

_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Comparison of Orange Oil Extraction Methods

Not all principles will apply to this process - put N/A (not applicable) in any cells that do not apply to this process.

REMEMBER: think about all of these processes both on a laboratory level and as an industrial process where large quantities of product need to be produced.

USE: the information that you gathered using the laboratory data sheets to inform your decision on this grid.

Principle

Traditional Solvent Extraction

Steam Distillation Extraction

Supercritical CO2 extraction

#1 Pollution prevention

#2 Atom Economy

#3 Less hazardous synthesis

#4 Design safer chemicals

#5 Safer solvents and auxilaries

#6 Energy efficiency

#7 Renewable feedstocks

#8 Reduce Derivatives

#9 Cataylsis

#10 Design for degradation

#11 Real-time analysis

#12 Accident prevention

Additional Teacher Background Information and Safety Considerations

Safety concerns

The most serious safety concerns in this experiment involve the possibilities of cap discharge (most common occurrence) or vessel rupture (rarely observed). During the testing phase of this experiment, caps blew off during approximately 4% of the extractions. All caps were directed upward by the containment cylinders. Caps remained on during all extractions when students 1) tightened the cap as tightly as possible and 2) did not use caps that were stripped. If the cap cannot be completely tightened and continues to turn, the stripped cap should be discarded and replaced. Due to variations in the centrifuge tubes and caps, a tight seal is not always formed at their junction. In this case, the CO2 does not liquefy, and retightening of the cap or replacement of the cap or tube may be required. Although many modifications of the sealing process have been proposed, such as the use of Teflon tape or parafilm on the threads, it is important that the cap seal well enough to induce liquefaction but not so tightly that the gas cannot escape. The cap must allow the gaseous CO2 to escape slowly during the extraction and also must function as a safety valve. During experiment development, attempts were made to observe the transition from the liquid to the solid phase by opening the cap while the CO2 was liquid. In two of these cases, the centrifuge tube ruptured, and plastic shards were propelled several feet from the demonstrator. Although no injuries occurred, it is recommended that the tubes always remain in containment cylinders during liquefaction. It is important to note that in our experience vessel rupture only occurred while attempting to release the pressure from the vessel when liquid CO2 was present.

Industrial methods for obtaining D-limonene.

Traditionally essential oils have been extracted through the use of steam distillation or organic solvent extraction. During the past two decades, great strides have been made in technology that uses supercritical or liquid carbon dioxide in place of organic solvents. Carbon dioxide (CO2) is useful as a green alternative solvent because it provides environmental and safety advantages; it is nonflammable, relatively nontoxic, readily available, and environmentally benign. Processing with CO2 also results in minimal liability in the event of unintentional release or residual solvent in the product. Although CO2 is a greenhouse gas, when used as a solvent it is captured from the atmosphere, not generated, resulting in no net environmental harm. Large-scale CO2 processing has had commercial success in many separation and extraction processes. The tunable solubility properties, low toxicity, and ease of removal of CO2 have led to well established CO2 technology for the extraction of various food products, including essential oils and hops, and for the decaffeination of coffee and tea.

Another major benefit of using carbon dioxide as a solvent is its accessible phase changes. Unlike other gases, relatively low temperatures and pressures can be used to form liquid and supercritical CO2. As shown on the phase diagram in Figure 2, CO2 sublimes (goes directly from a solid to a gas) at normal atmospheric pressure of 1.01 bar. The triple point of CO2, where solid, liquid, and gas phases coexist in equilibrium, is achieved at 5.2 bar and -56.6 C. At or near this point, dry ice melts, forming liquid carbon dioxide. If the temperature and pressure are increased to the critical point (73.8 bar and 31.0 C), the CO2 exists as a supercritical fluid and has no distinct liquid or vapor phase but properties that are similar to both.

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