Comparison of the process performances of a tandem 4-zone SMB and a single-cascade 5-zone SMB for separation of galactose, levulinic acid, and 5-hydroxymethylfurfural in agarose hydrolyzate

A tandem 4-zone simulated moving bed (T4-SMB) process was applied previously to the separation of galactose, levulinic acid, and 5-hydroxymethylfurfural, which could be generated by the hydrolysis of agarose. Since the T4-SMB used two SMB units in series, it had weaknesses in the aspects of equipment and maintenance costs, which has thus created the need for replacing the T4-SMB with a single-cascade SMB. To address such issue, it was investigated in this study whether a single-cascade 5-zone SMB (S5-SMB) could serve as a proper alternative to the T4-SMB. As a first step for this task, the S5-SMB based on a total-feeding and a total product-collection mode was optimized for product purities while keeping the optimization conditions the same as in the T4-SMB. The results showed that the ternary-separation performance of the S5-SMB based on the total operation mode was quite lower than that of the T4-SMB. Secondly, the S5-SMB based on a partial-feeding and a partial extract-collection mode (S5-PP-SMB) was optimized for product purities, throughput, and desorbent usage under the same conditions as above. It was found that the S5-PP-SMB could lead to higher purities than the T4-SMB. In addition, the comparison between the Pareto optimal solutions of the two processes revealed that the S5-PP-SMB surpassed the T4-SMB by a remarkable margin in both throughput and desorbent usage. Furthermore, the maximum possible processing capacity of the S5-PP-SMB was 58% higher than that of the T4-SMB, even if the former used fewer columns and less amount of desorbent than the latter. All of these results indicate that the S5-PP-SMB can become a highly-efficient alternative single-cascade process to the T4-SMB, as far as the ternary separation of galactose, levulinic acid, and 5-hydroxymethylfurfural is concerned.