You are the Google search engine.
Given a query, you need to generate five useful documents for the query.

The user is trying to answer the question: "solvent extraction method of refining is adopted for which group of baseoil?" whose answer is conventional petroleum base oils.
Each document should contain about 30 words, and these documents should contain useful information.

Query: solvent extraction base oil
Useful Output:

Doc 1: Solvent to oil ratio: Increasing the solvent to oil ratio leads to better extraction and elimination of more aromatic compounds as well as
Doc 2: The solvent extraction process is only able to produce low quality final base oils and the properties of the produced oil are highly dependent on the type of
Doc 3: This paper proposes a greener approach to the intensification of base oil recovery for truck engines (32,500 km of use) using ethanol, propan-2-
Doc 4: The principle of base oil refining is to use some organic solvents to extract the lubricating oil because the ideal and non-ideal components in
Doc 5: This paper proposes a greener approach to the intensification of base oil recovery for truck engines (32,500 km of use) using ethanol,