The text is for questions 13 - 16.

    Biodiesel is a clean burning substitute for petroleum based diesel fuel. Biodiesel is made of vegetable oil.

    To make or manufacture Biodiesel, you must first start with raw materials. The raw materials needed in the production of Biodiesel are a small amount of methanol and a ready supply of vegetable product. One of the most common vegetables used in the production of Biodiesel is corn, although depending on the geographic location of the manufacturing facility many other plants are used as well (rapeseed, soybeans, flaxseed, etc.). The first step is to use the raw vegetable product to make vegetable oil. Vegetable oil by itself will not be what you need to power a car, from here it has to be processed into Biodiesel.

    The process for converting vegetable oil into Biodiesel is sometimes called ester interchange. To complete this process the vegetable oil has to be combined with a smaller amount of methanol and then put in the presence of a small quantity of an alkaline catalyst (for example, 5% to 1% sodium hydroxide). Vegetable oil is made up of so-called triglycerides, which is a compound of the trivalent alcohol glycerin with three fatty acids. The goal of ester interchange is to separate the glycerin molecule from the three fatty acids and replace it with three methanol molecules. This process then yields roughly 90% Biodiesel and 10% of a glycerin byproduct. The glycerin byproduct can be used in a number of other chemical processes for different industries.

14. What is interchanged in the process of ester interchange?