Final answer:
The two main types of liquid biofuels are bioethanol and biodiesel, produced from plant sources such as sugar cane and corn for bioethanol and vegetable oils for biodiesel. These biofuels have environmental and social impacts due to their production and use.
Step-by-step explanation:
The two main types of liquid biofuels currently produced are bioethanol and biodiesel. Bioethanol is commonly produced from the fermentation of sugar cane juice in places like Brazil, or from the fermentation of corn starch in the United States. Biodiesel is manufactured from vegetable oils, including recycled cooking oil, and crops like soybeans and sunflowers. Considering the social and environmental impacts, it's important to note the competition between land for fuel and food production, which can lead to higher food prices and deforestation. However, biofuels can also be derived from non-food parts of plants, potentially reducing these negative impacts. Compared to their petroleum counterparts, bioethanol and biodiesel burn cleaner but can have other environmental effects such as increased evaporative emissions.