In accordance with the teachings of the present invention, a system and method converting biomass into useful chemicals are provided. In a particular embodiment, the method includes fermenting biomass in one or more fermentors to produce a fermentation broth comprising ammonium carboxylate salts, the fermentors containing an ammonium carbonate or ammonium bicarbonate buffer. The method further includes reacting the ammonium carboxylate salts from the fermentors with a high-molecular-weight amine to produce amine carboxylate salt, and thermally cracking the amine carboxylate salt to produce carboxylic acid. In another embodiment, the ammonium carboxylate salts from the fermentors may be reacted with a low-molecular-weight amine to produce a low-molecular-weight-amine carboxylate salt. The low-molecular-weight amine in the low-molecular-weight-amine carboxylate salt may then be switched with a high-molecular-weight amine to form a high-molecular-weight-amine carboxylate salt, which is then thermally cracked to produce carboxylic acid.