Arora M B, Hestekin J A, Snyder S W, St Martin E J, Lin Y J, Donnelly M I, Millard C Sanville
Energy Systems Division, Argonne National Laboratory, Argonne, IL ; Chemical Engineering Division, Argonne National Laboratory, Argonne, IL.
Sep Sci Technol. 2007 Aug;42(11):2519-2538. doi: 10.1080/01496390701477238. Epub 2007 Oct 2.
The replacement of petrochemicals with biobased chemicals requires efficient bioprocesses, biocatalysis, and product recovery. Biocatalysis (e.g., enzyme conversion and fermentation) offers an attractive alternative to chemical processing because biocatalysis utilize renewable feedstocks under benign reaction conditions. One class of chemical products that could be produced in large volumes by biocatalysis is organic acids. However, biocatalytic reactions to produce organic acids typically result in only dilute concentrations of the product because of product inhibition and acidification that drives the reaction pH outside of the optimal range for the biocatalyst. Buffering or neutralization results in formation of the acid salt rather than the acid, which requires further processing to recover the free acid product. To address these barriers to biocatalytic organic acid production, we developed the "separative bioreactor" based on resin wafer electrodeionization, which is an electro-deionization platform that uses resin wafers fabricated from ion exchange resins. The separative bioreactor simultaneously separates the organic acid from the biocatalyst as it is produced, thus it avoids product inhibition enhancing reaction rates. In addition, the separative bioreactor recovers the product in its acid form to avoid neutralization. The instantaneous separation of acid upon formation in the separative bioreactor is one of the first truly one-step systems for producing organic acids. The separative bioreactor was demonstrated with two systems. In the first demonstration, the enzyme glucose fructose oxidoreductase (GFOR) was immobilized in the reactor and later regenerated GFOR produced gluconic acid (in its acid form) continuously for 7 days with production rates up to 1000 mg/L/hr at >99% product recovery and GFOR reactivity >30mg gluconic acid/mg GFOR/hour. In the second demonstration, the E. coli strain CSM1 produced lactic acid for up to 24 hours with a productivity of >200 mg/L/hr and almost 100% product recovery.
用生物基化学品替代石化产品需要高效的生物过程、生物催化和产物回收。生物催化（如酶转化和发酵）为化学加工提供了一种有吸引力的替代方案，因为生物催化在温和的反应条件下利用可再生原料。一类可以通过生物催化大量生产的化学产品是有机酸。然而，由于产物抑制和酸化会使反应pH值超出生物催化剂的最佳范围，生物催化生产有机酸的反应通常只会产生稀浓度的产物。缓冲或中和会导致酸盐而非酸的形成，这需要进一步加工以回收游离酸产物。为了解决生物催化生产有机酸的这些障碍，我们开发了基于树脂片电去离子的“分离式生物反应器”，这是一种使用由离子交换树脂制成的树脂片的电去离子平台。分离式生物反应器在有机酸产生时同时将其与生物催化剂分离，从而避免产物抑制并提高反应速率。此外，分离式生物反应器以酸的形式回收产物以避免中和。在分离式生物反应器中酸形成时的即时分离是首批真正用于生产有机酸的一步式系统之一。分离式生物反应器在两个系统中得到了验证。在首次验证中，葡萄糖果糖氧化还原酶（GFOR）被固定在反应器中，随后进行了再生。GFOR连续7天产生葡萄糖酸（以其酸的形式），产率高达1000 mg/L/小时，产物回收率>99%，GFOR反应活性>30mg葡萄糖酸/mg GFOR/小时。在第二次验证中，大肠杆菌菌株CSM1产生乳酸长达24小时，生产率>200 mg/L/小时，产物回收率几乎达到100%。
