Abstract
Vanillin is an important building block for the chemical, pharmaceutical and food industries, with potential to become a key intermediate for bio-polymers. Vanillin nowadays is mostly produced from non-renewable petro-based resources as raw materials. A plausible process design to recover vanillin from an acidic oxidation of Kraft lignin in an hydroalcoholic mixture is available from recent literature, but it has yet to be improved before becoming a competitive one capable of substituting the petrochemical route. The alcohol used in the reaction is methanol. Following the reaction step, the process requires a flash drum and five distillation columns, most of the energy consumption being due to methanol recovery and recycle for which three distillation columns are employed. The first aim of the present study is to simulate and quantify the energetic costs and environmental impact of the proposed process design, while studying possible improvements to the principal energetic hotspots identified in the literature.Through rigorous simulations, it is shown that this base case design can be improved and the train of distillation columns simplified. Through the use of alternative designs, one of the distillation columns used to separate methanol from water coming from the vapour phase of the flash drum can be eliminated. An energy consumption of only 43 % relative to the base case scenario is achieved this way. The second aim of this work is to perform simulations of suitable solvents used for liquid-liquid extraction of vanillin from the main stream, taking into account both the energetic efficiency and the environmental impact of each one, and to classify them accordingly. Specific emphasis is put on the study of the performance of aliphatic alcohols such as hexanol, as their physicochemical properties allow for the elimination of the acidification operation in the pre-reactor feed preparation stage. This is important because it avoids the technological problems related to lignoacid precipitation that follows an acidification step and has the potential to reduce energy consumption greatly, as fewer columns would be needed. Rigorous simulations show that an energetic consumption reduction of 78 % relative to the base case design is achieved when using hexanol as the solvent in an aliphatic-alcohol-specific process design, improving the energy efficiency of both the currently used industrial methods and the commonly studied alternatives based on non-aliphatic alcohol solvents.
