Multi-objective optimization for the economic production of d-psicose using simulated moving bed chromatography

• Model-based design for SMB separation of rare sugar d-psicose from d-fructose.
• Experimental validation of the proposed design strategy.
• Temperature was analyzed as key variable during Pareto optimization.
• Highest PR and lowest DR achieved for d-fructose/d-psicose separation using SMB.

The biocatalytic production of rare carbohydrates from available sugar sources rapidly gains interest as a route to acquire industrial amounts of rare sugars for food and fine chemical applications. Here we present a multi-objective optimization procedure for a simulated moving bed (SMB) process for the production of the rare sugar d-psicose from enzymatically produced mixtures with its epimer d-fructose. First, model parameters were determined using the inverse method and experimentally validated on a 2-2-2-2 lab-scale SMB plant. The obtained experimental purities (PUs) were in excellent agreement with the simulated data derived from a transport-dispersive true-moving bed model demonstrating the feasibility of the proposed design. In the second part the performance of the separation was investigated in a multi-objective optimization study addressing the cost-contributing performance parameters productivity (PR) and desorbent requirement (DR) as a function of temperature. While rare sugar SMB operation under conditions of low desorbent consumption was found to be widely unaffected by temperature, SMB operation focusing on increased PR significantly benefited from high temperatures, with possible productivities increasing from 3.4 kg (L day)−1 at 20 °C to 5 kg (L day)−1 at 70 °C, indicating that decreased selectivity at higher temperatures could be fully compensated for by the higher mass transfer rates, as they translate into reduced switch times and hence higher PR. A DR/PR Pareto optimization suggested a similar but even more pronounced trend also under relaxed PU requirements, with the PR increasing from 4.3 kg (L day)−1 to a maximum of 7.8 kg (L day)−1 for SMB operation at 50 °C when the PU of the non-product stream was reduced from 99.5% to 90%. Based on the in silico optimization results experimental SMB runs were performed yielding considerable PRs of 1.9 (30 °C), 2.4 (50 °C) and 2.6 kg (L day)−1 (70 °C) with rather low DR (27 L per kg of rare sugar produced) on a lab-scale SMB installation.