Abstract
Prehydrolysate, a dilute solution consisting mainly of pentoses, hexoses, and lesser quantities of organic acids, furfural and phenolics, is generated in the Kraft dissolving pulp process. An obstacle facing the valorization of the solution in hemicellulose biorefineries, by conversion of the sugars into bioproducts such as furfural, is the low sugar concentration. Membrane filtration is typically proposed in several hemicellulose based biorefineries for concentrating the solution, although they are usually generated using different wood species, pretreatment methods, and operating conditions. However, the chemical composition of the solutions is generally not considered. Also, the combined effect of composition and operating conditions is rarely investigated for biorefinery applications. The purpose of this work was to determine the impact of the prehydrolysate composition and operating parameters on the component separation and permeate flux during membrane filtration. Using model prehydrolysate solutions, two commercial reverse osmosis (RO) membranes were screened, and one was selected for use, based on its higher sugar and acetic acid retention. A Taguchi L18 experimental design array was then applied to determine the dominant parameters and limiting factors. Results showed that the feed pressure and temperature have the highest impact on permeate flux, but the least effect on sugar retention. Further experiments to quantify flux decline, due to fouling and osmotic pressure, showed that furfural has the highest membrane fouling tendency, and can limit the lifetime of the membrane. Regeneration of the membrane by cleaning with a sodium hydroxide solution is also effective for reversing fouling. It has been demonstrated that RO can efficiently and sustainably concentrate wood prehydrolysate.
Highlights
Since the closure of several Kraft pulp mills in the past decade in Canada, efforts to reposition the sector has resulted in a revision of the business model of presently operating mills by transforming them into Integrated Forest Biorefineries (IFBRs) [1]
The cumulative impact that the main chemical compounds found in prehydrolysate solutions from a dissolving pulp mill have on reverse osmosis (RO) membrane filtration was studied using model solutions containing glucose, xylose, acetic acid, furfural, and syringaldehyde
It is important to retain the acetic acid, because it serves as a catalyst for the conversion of pentoses into furfural
Summary
Since the closure of several Kraft pulp mills in the past decade in Canada, efforts to reposition the sector has resulted in a revision of the business model of presently operating mills by transforming them into Integrated Forest Biorefineries (IFBRs) [1]. Kraft dissolving pulping mill include: (i) the existing infrastructure on site can reduce the investment costs for the biorefinery; (ii) skilled manpower with experience in biomass handling and processing is available on site; (iii) the heating and cooling utility requirements can be provided (partially or totally) by the mill. Dissolving Kraft pulp mills are suitable receptors of a sugar platform biorefinery, because the prehydrolysis of the wood chips to remove the hemicellulose fraction is carried out prior to cooking, making hemicellulosic sugars available for new products. The use of hot water is advantageous, because it is a mature, cost-efficient technique, and does not require the use of chemicals
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