Production of cellulosic ethanol and value-added products from corn fiber

Abstract

Corn fiber, a by-product from the corn processing industry, mainly composed of residual starch, cellulose, and hemicelluloses, is a promising raw material for producing cellulosic ethanol and value-added products due to its abundant reserves and low costs of collection and transportation. Now, several technologies for the production of cellulosic ethanol from corn fiber have been reported, such as the D3MAX process, Cellerate™ process, etc., and part of the technologies have also been used in industrial production in the United States. The ethanol yields range from 64 to 91% of the theoretical maximum, depending on different production processes. Because of the multicomponent of corn fiber and the complex structures highly substituted by a variety of side chains in hemicelluloses of corn fiber, however, there are many challenges in cellulosic ethanol production from corn fiber, such as the low conversion of hemicelluloses to fermentable sugars in enzymatic hydrolysis, high production of inhibitors during pretreatment, etc. Some technologies, including an effective pretreatment process for minimizing inhibitors production and maximizing fermentable sugars recovery, production of enzyme preparations with suitable protein compositions, and the engineering of microorganisms capable of fermenting hexose and pentose in hydrolysates and inhibitors tolerance, etc., need to be further developed. The process integration of cellulosic ethanol and value-added products also needs to be developed to improve the economic benefits of the whole process. This review summarizes the status and progresses of cellulosic ethanol production and potential value-added products from corn fiber and presents some challenges in this field at present.

Keywords: Cellulosic ethanol; Corn fiber; Production; Structure and chemical compositions; Value-added products.

Fig. 1

Biorefining of corn fiber to produce fuel and other value-added products

Fig. 2

Schematic structure of the sugar moiety of heteroxylans from corn fiber (Saha 2003)

Fig. 3

Xylose fermentation in S. cerevisiae. The fungal pathway uses xylose reductase (XR) and xylitol dehydrogenase (XDH), whereas the bacterial pathway uses xylose isomerase (XI). Both pathways produce d-xylulose which is converted to d-xylulose-5P by endogenous xylulokinase (XK). d-Xylulose-5P then enters the pentose phosphate pathway (PPP), where it is further metabolized to form ethanol under appropriate conditions. Arrows indicate the direction of the chemical reactions (Moysés et al. 2016)

Fig. 4

Entner–Doudoroff (ED) pathway for ethanol fermentation in Z. mobilis. ADH alcohol dehydrogenase; EDA 2-keto-3-deoxy-gluconate aldolase; EDD 6-phosphogluconate (Xia et al. 2019)

Fig. 5

Feedstock mass balance of cellulosic ethanol production from corn fiber. The steps of pre-saccharification, biodetoxification and SSCF were carried out in the same reactor, which were considered as continuous process (Zhang et al. 2021)