Assessing the Viability of Recovery of Hydroxycinnamic Acids from Lignocellulosic Biorefinery Alkaline Pretreatment Waste Streams

Abstract

The hydroxycinnamic acids p‐coumaric acid (pCA) and ferulic acid (FA) add diversity to the portfolio of products produced by using grass‐fed lignocellulosic biorefineries. The level of lignin‐bound pCA in Zea mays was modified by the alteration of p‐coumaroyl‐CoA monolignol transferase expression. The biomass was processed in a lab‐scale alkaline‐pretreatment biorefinery process and the data were used for a baseline technoeconomic analysis to determine where to direct future research efforts to couple plant design to biomass utilization processes. It is concluded that future plant engineering efforts should focus on strategies that ramp up accumulation of one type of hydroxycinnamate (pCA or FA) predominantly and suppress that of the other. Technoeconomic analysis indicates that target extraction titers of one hydroxycinnamic acid need to be >50 g kg−1 biomass, at least five times higher than observed titers for the impure pCA/FA product mixture from wild‐type maize. The technical challenge for process engineers is to develop a viable process that requires more than 80 % reduction of the isolation costs.

Accessing p‐Hydroxycinnamic Acids: Chemical Synthesis, Biomass Recovery, or Engineered Microbial Production?

“…Even if absorption on various supports is highly popular, [72,75,80,91,93–97] the absorption/desorption process suffers from important drawbacks such as low selectivity of absorption, [64,75,91,93,96] high consumption of chemicals (salt and/or solvent) for desorption, and generation of solid waste due to resin aging. Moreover, the use of solvents has to be reflected taking into account the energy consumption necessary for their recycling (evaporation/condensation), which can highly impact the total process cost [34] . The same issues will be encountered using solvent extraction or ethanol washing.…”

“…Over the past 10 years, this scientific output has doubled. Although a very recent technoeconomic analysis reported a potential $5.05 per kg for purified p ‐HCAs ( p‐ CA and FA) from maize biorefinery, [34] they still exhibit high prices (Table 1), and their availability remains limited.…”

Strategies for the production of biochemicals in bioenergy crops

“…Expression of these transferases in Arabidopsis and poplar resulted in increases of cell wall-bound pCA, which is otherwise found in low amounts in these two eudicots plants [80,81]. Recently, overexpression of the maize PMT gene in maize led to a ~ 40% increase in lignin-bound pCA, which was released from biomass upon alkaline treatment [82]. Interestingly, higher amount of pCA attached to lignins in Arabidopsis resulted in increased lignin solubility under alkaline treatment of biomass [81].…”

“…These observations are relevant considering that base-catalyzed depolymerization liquors generated from biomass are rich in pCA and other aromatic compounds that are suitable for microbial conversion [83,84]. Alternatively, pCA can be recovered and purified as coproduct from the alkaline pretreatment stream after ethanol separation and precipitation under acidic conditions [82]. For such a biorefinery concept, a techno-economic analysis indicates that pCA content in plant biomass should be at least 5% DW in order to be economically attractive at current pCA market price [82].…”

“…Alternatively, pCA can be recovered and purified as coproduct from the alkaline pretreatment stream after ethanol separation and precipitation under acidic conditions [82]. For such a biorefinery concept, a techno-economic analysis indicates that pCA content in plant biomass should be at least 5% DW in order to be economically attractive at current pCA market price [82]. Other purification methods potentially involve membrane fractionation [85] or ultrafiltration coupled to affinity adsorption [86].…”