Green Chemistry/Examples

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Extraction of D-Limonene from orange peel using liquid carbon dioxide

Green Chemistry Principles

Less hazardous chemical synthesis, safer solvents and auxiliaries, design for energy efficiency, safer chemistry and prevention is better than cure.

Super critical CO2 is a very good solvent to extract various natural materials. Since especially designed equipment for supercritical CO2 generation is very expensive and intricate an effective yet affordable alternative in chemistry labs of schools and colleges is liquid CO2. It is useful as a green solvent because it provides environmental and safety advantages. It is nonflammable, relatively non-toxic readily available and environmentally benign. Processing with liquid CO2 also results in minimal liability in the event of unintentional release or residual solvent in the product. Due to solubility properties, less toxicity and ease of removal of CO2 have lead to extraction of various food products, essential oils, decaffeination of coffee etc. Essential oils are organic compounds that are extracted from natural sources and used in many products such as flavoring, fragrance and cleaning products etc. Many o these oils are classified as terpenes and terpenoids(oxygenated derivatives of terpenes).

Conventional method of preparation:

In many organic teaching laboratories, D-Limonene is extracted through a solvent extraction process with pentane or methylene chloride or by steam distillation.

Green method of preparation:

In this experiment the optically active enantiomer D-Limonene is extracted from peel of oranges and other citrus fruits (lemon) using CO2. D-Limonene is the major component of orange oil, which is found in the outer, colored portion of peels of oranges. The greenness of the liquid carbon dioxide extraction can be compared with different extraction procedures through the evaluation of waste, purity, energy used, yield and safety.