Fermentative production of butyric acid from wheat straw: Economic evaluation

Abstract

The economic feasibility of biochemical conversion of wheat straw to butyric acid was studied in this work. Basic process steps included physicochemical pretreatment, enzymatic hydrolysis and saccharification, fermentation with in-situ acids separation by electrodialysis and product purification. Two scenarios (S1 and S2) were examined assuming a plant with an annual capacity of 10,000 tonnes of product installed in India (due to significantly lower feedstock prices). S1 resulted in a product of 89% butyric acid mixed with acetic acid and S2 produced butyric acid of 99% purity. Unit production cost was estimated at 2.75 and 3.31 $ per kg product for S1 and S2 respectively. The main part of production cost was attributed to steam for the purification step and electricity for the in-situ acids separation. This unit production cost combined with an estimated butyric acid selling price (year 2014) at 3.50 and 3.95 $ per kg product (for S1 and S2 respectively) and a plant capacity of 10,000 tonnes indicated an internal rate of return of 14.92% and 12.42 % and payback time of 4.28 and 4.70 Highlights (for review)

Eco-efficient recovery of bio-based volatile C2–6 fatty acids

“…The utilization of extraction in the separation process of fermented product significantly reduces downstream processing costs [47, 48], a major hurdle in bio-product utilization [6, 27, 40, 49]. Separation by the direct distillation of the fermented product requires a large amount of energy due to the low VFAs’ content in water, generally 1–2%.…”

“…Because of the high affinity between water and acetic acid, the second section required more investment cost and more than nine times the utilities costs as compared with the first section, separating high-carbon-number fatty acids. For cost comparison, a similar process for 10,000 ton/year butyric acid production process was used, with investment cost of 8.47 million US dollars, and annual utilities cost of 13.5 million US dollars, at 2014 prices [6]. The costs were only calculated for butyric acid recovery.…”

“…Economic feasibility of the proposed process in commercial application was evaluated with utility cost and solvent loss. The previous studies of VFAs’ production indicated that the separation and purification of the VFAs costed 60–80% of production cost [6, 27]. Therefore, a lot of new separation techniques [6–11] have applied to the VFAs processes, but their operating cost was not low enough to be economical in practical processes.…”

“…Various separation techniques commonly used in chemical process industries have been applied for their separation, but no cost-viable process has yet been introduced with detailed process operation results. The currently suggested procedures include extraction [6], adsorption [7], membrane separation [8], pervaporation [9, 10], and reverse osmosis [11]. Because of the low VFAs’ content, the high operating costs of the suggested techniques limit their wide application for VFA recovery.…”

Pretreatment of wheat straw leads to structural changes and improved enzymatic hydrolysis

“…Approximately 690 ktons of wheat were produced globally in 2009, later reaching 730 million tons in 2014 1 , 2 . As the waste residue of wheat, large mass of wheat straw (WS) has been generated every year and become the most abundant agricultural biomass worldwide after rice straw 3 . However, the usual disposal of WS are discard in the field or burned, result in generating issues of great impact on the economic waste and environmental pollution 4 , 5 .…”