Chemical desalination Is there a way to remove salt from water, even just partially, using chemical or filtration methods prior to a reverse osmosis?

The problems is that salt is very hard on a reverse osmosis membrane which is expensive. Is there some way to attract some of the salt out of the water before using the membrane?

One possibility I have heard of is decanoic acid which can be used to sequester salt.
The method you mentioned is known as directional solvent extraction and seems quite straight forward and efficient. It is a relatively new method of desalination. Soybean oil, hexanoic acid, decanoic acid, and octanoic acid can be used (the last two are most effective) [ source: https://dspace.mit.edu/handle/1721.1/78539 ]. This video shows the setup used.