Bioeconomy aims to substitute fossil resources with renewable feedstocks derived from biomass, residues, or waste streams. Using biotechnological conversions, these feedstocks can be converted into valuable platform chemicals such as alcohols, carboxylic acids, and amines. Despite its potential, industrial implementation of such processes remains challenging due to the complex and often energy-intensive downstream processing required to recover products from aqueous media. In this context, energy- and resource-efficient separation processes are required to establish economically attractive process routes. Separation processes must address the following challenges: aqueous product streams with low concentrations of mainly low-boiling products, biotechnological conversions often limited by product inhibition or unfavorable equilibria, frequent need for pH adjustment resulting in saline waste, foam formation, and fluctuating process conditions. In this contribution, case studies on downstream processes based on solvent extraction are presented that aim to lower energy demand, increase productivity and yield, or reduce waste generation, thereby enhancing the competitiveness of processes based on renewable feedstocks. [1]
Diols can be produced by microbial fermentation, where the first step in downstream separation is usually energy-intensive distillation. An example of conventional separation by distillation is 2,3-butanediol (2,3-BDO), a high-boiling component relative to water, which is therefore obtained as the bottom product of the distillation column. By using solvent extraction with high-boiling solvents, 2,3-BDO can be recovered as a low-boiling distillate. Hydrophobic, high-boiling terpenoids have recently been proposed as promising solvents. Terpenoids exhibit excellent distribution coefficients and selectivities compared to conventional high-boiling solvents. The technical feasibility of separating 2,3-BDO from water using terpenoids has been demonstrated in a countercurrent extraction column. Based on process simulations, it can be shown that the exergy demand for this extraction-distillation sequence with terpenoids is lower compared to processes using conventional solvents. [2, 3]
The microbial production of carboxylic acids is often limited by product inhibition. To address this, in situ product removal (ISPR) by reactive solvent extraction has been applied for the separation of itaconic acid directly from the fermentation broth. This technique can enable fermentation in continuous operation mode, resulting in lower substrate consumption and improved space-time yields. Typically, pH control during carboxylic acid fermentation and separation requires the addition of equimolar amounts of acids and bases, resulting in high amounts of salt waste. Electrochemical water splitting provides the required protons and hydroxide ions directly, without the need for auxiliary materials, offering a sustainable, wastefree alternative for pH management in carboxylic acid production and separation. [4–8]
Amino alcohols are used as starting materials for the synthesis of a wide range of products. Metaraminol, a pharmaceutical precursor, can be produced via enzymatic transamination. However, this biocatalytic process is limited by an unfavorable reaction equilibrium. This limitation
can be effectively overcome by applying in situ product removal (ISPR) by solvent extraction, leading to enhanced product yields. [9]
The microbial production of bio-based detergents can lead to operational challenges such as foam formation, as the products are surface-active. A novel multiphase loop reactor (MPLR) addresses this problem by combining fermentation and solvent extraction in a single device, reducing foam formation by continuously removing the surface-active products. [10, 11]
Fluctuating concentrations of products and fluctuating amounts of by-products and salts in biotechnological processes can impact the operation of extraction equipment such as mixersettlers or columns and potentially lead to reduced separation efficiency or flooding. For this purpose, we have developed an advanced online monitoring system for crucial fluid dynamic parameters such as Sauter mean diameter, droplet sedimentation velocity, and dispersed phase hold-up. This system enables the early detection of critical operating conditions of an extraction column. In addition, the tool includes a detailed extraction column model that will serve as the basis for real-time optimization of the separation performance. Ultimately, we are striving for autonomous and optimal column operation with minimal solvent consumption at
maximum load, capable of handling the fluctuating conditions typical of biotechnological processes. [12–14]
The case studies presented will demonstrate that solvent extraction, when tailored to specific challenges and combined with innovative strategies for process intensification and monitoring, can reduce energy demand or waste generation, while overcoming equilibrium limitations,
product inhibition, foam formation or fluctuations, thereby representing an essential contribution to a sustainable bioeconomy.