Is Butanol Involved in Transesterification Process?

Possibly.

http://pubs.acs.org/cgi-bin/abstract.cgi/iecred/2006/45/i20/abs/ie060536e.html

not commercially

Transesterification is the name given to a class of chemical reactions in which a free alcohol, R'OH, is reacted with an ester. R' represents the organic portion of the alcohol. The alcohol, R'OH, displaces the alcohol portion of the ester to form a new ester. An ester is the reaction product of an organic acid and an alcohol, R''OH, and can be represented as R'''COOR'', where R'' and R''' are organic protions of the molecule. The newly freed up alcohol R''OH is usually removed from the reaction mixture as it is formed in order to drive the tranesterification reaction to completion.

Butanol could be either the alcohol that is reacted with the ester or the alcohol freed up by the tranesterification.

Normally methanol is used as the basis for sodium methoxide. Following transesterification, the products are methyl esters (biodiesel), glycerine, water, and possibly some soaps, so it's quite unlikely butanol is involved. Of course, it's possible there may be a different process that uses butanol in place of methanol that I'm unaware of.

Look at the transesterification synthesis for polybutyenelterephthalate. Similarly, transesterification is simply the reaction of an alcohol (A) with an ester (B) to produce a different ester (D) plus a different alcohol (C). Butanol will undergo transesterification precesses.