Garakuta Reijou ga Tensai Renkinjutshi no Saiai ni Naru made

https://mechacomic.jp/books/290636

"Marry me, Lilia." -- Lilia, an alchemist who was looked down upon as a "junk lady" at her family home and banished to a remote island after her engagement was broken off. But instead of being sad, she is overjoyed at the prospect of "being able to research to her heart's content!" when Kai, the super-elite and overly confident head of the Alchemy Guild, shows up! Witnessing Lilia's extraordinary genius, Kai confidently proposes to her in order to fulfill his long-held dream of research. However, Lilia's answer to this seemingly perfect man is unexpected --!?