(470d) Solid Phase Reactive Simulated Moving Bed Chromatographic Separation System for Biofuel and Biochemical Production

Efforts to produce new cleaner and more sustainable liquid fuels and chemicals from lignocellulosic biomass have created the incentive to develop efficient and cost-effective processes for pretreatment of this type of biomass. Hydrolysis of lignocellulosic materials for sugar production can proceed via different pretreatment and hydrolysis technologies. Two well-known classes of hydrolysis technology are enzymatic and acid hydrolysis. Hydrolysis by both diluted and concentrated acid media has been reported having a faster rate of reaction compared to the enzymatic hydrolysis pathway¹, but has drawbacks both in terms of byproduct formation and the cost of disposal of the acid streams after hydrolysis. In the diluted acid hydrolysis process, a high operating temperature is required to break down the structure of the material. These severe conditions cause sugar decomposition and generate side products such as furfural, HMF, acetic acid, and levulinic acid which can inhibit the fermentation process for bioethanol production raising overall capital and operating costs. In the concentrated acid hydrolysis process, a smaller amount of sugar degradation is reported due to lower operating temperatures. Nevertheless, the main drawbacks are the expensive process equipment to prevent corrosion and a significant cost of acid recovery.²The synthesis of a new process for acid hydrolysis that avoids these two drawbacks is our research goal.

Considerable effort has been made to improve both the reactor designs and the separation process to achieve higher sugar yield and productivity. Several reactor designs have been proposed for acid hydrolysis of lignocellulosic materials such as batch, plug flow, and percolation reactors. A percolation reactor is a packed-bed-flow reactor where the sugar is removed as it formed; therefore, sugar concentration increases with smaller byproduct formation compared to the batch and plug flow reactors.³ Another reactor configuration is a counter-current reactor with a reverse flow between a biomass and a liquid stream was investigated and found to have a significant improvement of sugar yield due to the shorter time of sugar decomposition.⁴ However, the movement of a solid stream in this process increases the complexity of the design and operation of the reactor. Therefore, a  progressing batch reactor (PBR) design has been proposed to mimic the countercurrent flow of diluted acid and biomass.⁵ The key principle of this reactor configuration is the movement of the feed location of the acid to different percolation reactors arranged in series. The main advantage of this configuration is the realization of countercurrent scheme while maintaining its simplicity of percolation reactor operation. For the separation process, simulated moving bed (SMB) chromatography has gained interest to separate the acid from sugars in the hydrolyzate.^6,7 The underlying principle of the SMB, similar to the PBR, is that the fluid is in contacted with the solid phase where the feed and outlet streams switch to simulate the movement of solid phase to achieve a countercurrent flows.⁸

The disadvantages of the acid hydrolysis reaction motivate this work to develop reactive separation in which reaction and separation are integrated to avoid byproduct formation, improve sugar yield, and reduce recycle cost. Previous studies have explored the reactive separation principle with the simulated moving bed chromatography which has been applied to both liquid gas phase reactions.⁹However, no previous work has been considered a combination of SMB and reactor where the reactants are in the solid and liquid phase.

This work proposes a new reactive separation process system termed solid-phase reactive separation system (SPRSS) which integrates the PBR and SMB units and aims to apply this to the acid hydrolysis of lignocellulosic materials for sugar production before fermentation to produce bioethanol. Both PBR and SMB have similar principles of the movement of the liquid feed to imitate the countercurrent movement of solid and liquid phase. The overarching goal is to improve the sugar yield and sugar product concentration while minimizing the sugar decomposition reaction and undesired product formation. Moreover, the acid consumption is expected to be further reduced and therefore decrease the cost of acid recycle. Optimization strategy using a superstructure formulation will be applied to find the optimal process parameters and process configurations of SPRSS to maximize both of the sugar concentration and the sugar yield while minimizing the byproduct formation.

Reference

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(5)        Wright, J. D.; Bergeron, P. W.; Werdene, P. J. Progressing Batch Hydrolysis Reactor. Ind Eng Chem Res 1987, 26(4), 699-705.

(6)        Heinonen, J.; Tamminen, A.; Uusitalo, J.; Sainio, T. Ethanol production from wood via concentrated acid hydrolysis, chromatographic separation, and fermentation. J Chem Technol Biot 2012, 87(5), 689-696.

(7)        Xie, Y.; Chin, C. Y.; Phelps, D. S. C.; Lee, C. H.; Lee, K. B.; Mun, S.; Wang, N. H. L. A five-zone simulated moving bed for the isolation of six sugars from biomass hydrolyzate. Ind Eng Chem Res 2005, 44(26), 9904-9920.

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