Production of hemicellulosic sugars and glucose from residual corrugated cardboard
Introduction
Cellulosic biomass is a widespread and renewable resource. Agricultural residues, fruit and vegetables wastes, woods, urban lignocellulosic wastes (ULW), residues from pulp and paper industry and others are of cellulosic nature [1]. The benefit of cellulosic raw materials is receiving attention due to their large availability and immense potential.
In comparison with alternative feedstocks (such agricultural byproducts like straw or bagasse), the urban lignocellulosic wastes show several advantages, including: (i) large availability and non-seasonal character, (ii) zero or negative cost (if disposal is considered), (iii) collection and transportation facilitated by the increasing cooperation of consumers, and (iv) in some cases, improved susceptibility towards chemical and/or enzymatic processing caused by previous chemical treatments [2].
Corrugated cardboard, one of the main components of ULW, is usually manufactured by kraft pulping pine wood, a technology that results in partial removal of hemicelluloses and lignin [3]. The polysaccharide content of corrugated cardboard is about 75% of its dry weight, and its enzymic digestibility (without further chemical processing) is near 50% of the theoretical value [4]. The remarkable extent of the enzymic hydrolysis can be ascribed to the morphological effects caused by lignin removal during the kraft pulping, which results in an increased susceptibility to enzymic attack [5]. As corrugated cardboard is manufactured from softwoods, hemicelluloses are mainly made up of mannose units, whereas xylose, arabinose and galactose also appear as hemicellulosic sugars [6].
The separate production of hemicellulosic sugars and glucose allows a desirable flexibility in the processing of cellulosic materials, because each fraction can be used for a specific product application.
When the utilisation of the cellulosic fraction of raw materials is carried out by enzymic processing, the presence of lignin and hemicelluloses hinders the access of enzymes to cellulose, thus reducing the efficiency of the hydrolysis. A number of pretreatments (including physical, physico-chemical, chemical and biological processes) has been applied to several cellulosic materials to enhance their enzymatic digestibility [7].
Prehydrolysis of lignocellulosics (carried out with dilute strong acids) enables the selective solubilisation of hemicelluloses, leaving a solid phase mainly made up of cellulose and lignin more susceptible towards enzymic hydrolysis. When prehydrolysed solids are subjected to enzymic saccharification, the resulting sugar solutions can be employed as fermentation media suitable for the manufacture of a variety of chemicals. Katzen and Fowler [8] applied a prehydrolysis stage to waste paper mixtures achieving an almost quantitative hemicellulose removal and a solid suitable for the manufacture of ethanol by simultaneous saccharification and fermentation. Prehydrolysis has been applied as a pretreatment for enzymatic hydrolysis of cellulose owing to the structural alteration caused in native feedstocks [9], [10], [11].
This work deals with the saccharification of both hemicelluloses and cellulose contained in corrugated cardboard by performing successive stages of acid prehydrolysis and enzymic hydrolysis of prehydrolysed solids, which lead to separate streams containing hemicellulosic sugars and glucose, respectively. Mathematical models assessing the effects of the operational conditions on both the prehydrolysis stage and the susceptibility of substrates towards enzymic hydrolysis have been developed.
Section snippets
Raw material
Cardboard samples were randomly collected in local public containers of urban solid wastes and cut in pieces, suspended in water at 60 °C for 30 min at a solid concentration of 55 g/l and defibered for 30 s using an Ultraturrax T-50 device. Defibered samples were filtered, air dried and mixed in a single lot. Aliquots of the homogenised lot were employed in experiments.
Acid prehydrolysis
In prehydrolysis assays, water and H2SO4 were mixed at a liquor/solid ratio of 10 g/g and treated in an autoclave at 130 °C for the
Composition of the raw material
Table 1 shows the chemical composition of the homogeneized cardboard lot. In HPLC analysis, mannose, galactose and xylose are eluted in a single peak. The joint concentrations of these compounds and arabinose are reported as hemicelluloses. Experimental results show that about 75% of the oven-dry cardboard weight corresponds to polysaccharides, a proportion higher than the ones reported for woods of Eucalyptus globulus (62.3%) [14], or Pinus pinaster (59.6%) [15].
Chemical processing of the raw material
Removal of hemicelluloses
Generalisation of models
In order to obtain generalized models useful for predicting the effects caused by both reaction time and catalyst concentration employed in the prehydrolysis step on the dependent variables studied (composition of solids and liquors coming from prehydrolysis and concentrations of hemicellulosic sugars and glucose in enzymic hydrolysates), the regression parameters listed in Table 3, Table 4 were assumed to be a linear function of the catalyst concentration. Table 5 lists the corresponding
Conclusions
Corrugated cardboard samples were subjected to two-step processing consisting of an acid prehydrolysis step (able to cause the hydrolytic degradation of hemicelluloses) and a subsequent enzymic hydrolysis with commercial enzyme concentrates (to achieve the saccharification of cellulose). Up to 78.2% of initial hemicelluloses were solubilized in treatments, leading to liquors containing up to 10 g hemicellulosic sugars/l and 9.2 g glucose/l, and to a solid phase with enhanced cellulose content (up
Acknowledgements
Authors are grateful to “Xunta de Galicia” for the financial support of this work (Research Project reference PGIDT00PXI38301PR).
References (18)
- et al.
Fermentation of lignocellulosic hydrolysates for ethanol production
Enzyme Microb. Technol.
(1996) - et al.
Hydrolysis of lignocellulosic material for ethanol production: a review
Biores. Technol.
(2002) - et al.
Modeling and optimisation of the dilute-sulfuric-acid pre-treatment of corn stover, poplar and switchgrass
Biores. Technol.
(1997) - et al.
On the behaviour of lignin and hemicelluloses during the acetosolv processing of wood
Biores. Technol.
(1993) - et al.
Delignification and swelling of Eucalyptus wood ahead of enzymatic hydrolysis of the cellulosic fraction
Proc. Biochem.
(1995) - et al.
Kinetics of Eucalyptus wood fraction in acetic acid–HCl–water media
Biores. Technol.
(1995) - et al.
Optimzation of simultaneous saccharification and fermentation for the production of ethanol from lignocellulosic biomass
J. Agric. Food Chem.
(2000) - Alonso JL, Yañez R, Abad S, Moldes AB. Procesos Biotecnológicos para la Obtención de Productos de Alto Valor a partir...
- et al.
Factors affecting the enzymatic hydrolysis of municipal-solid-waste components
Biotechnol. Bioeng.
(1988)
Cited by (42)
Investigation of mechanisms and approaches for improving hydrophobicity of molded pulp biocomposites produced from apple pomace
2022, Food and Bioproducts ProcessingCitation Excerpt :Hemicellulose may be removed under chemical treatment, which are typical during CF production (Zambrano et al., 2021). Previous studies reported CF hemicellulose content of 13.8% (Yáñez et al., 2004) and NF of 15.33% (Mohamed et al., 2015) or 16.4–40% (Chen et al., 2015). AP typically has a hemicellulose content of 4.26–24.40% (Dhillon et al., 2013), while rhubarb was found to have 12.7% hemicellulose (Salo and Suomi, 1972).
Characterization of bio-oil and biochar from pyrolysis of waste corrugated cardboard
2020, Journal of Analytical and Applied PyrolysisDevelopment of a biobased superabsorbent polymer from recycled cellulose for diapers applications
2019, European Polymer JournalLignocellulosic bioethanol: Current status and future perspectives
2019, Biomass, Biofuels, Biochemicals: Biofuels: Alternative Feedstocks and Conversion Processes for the Production of Liquid and Gaseous BiofuelsEfficient conversion of municipal solid waste to biofuel by simultaneous dilute-acid hydrolysis of starch and pretreatment of lignocelluloses
2018, Energy Conversion and ManagementCitation Excerpt :Food and household wastes [13,14], two major parts of MSW, was used for ethanol production with a yield of 25 g/L ethanol per 100 g/L food residues using Saccharomyces cerevisiae [14]. Corrugated cardboard, another component of MSW, was also used for ethanol production after dilute-acid prehydrolysis and enzymatic hydrolysis [15]. As lignocelluloses are a dominant part of MSW and due to their recalcitrant structure, a pretreatment is necessary to improve the production of ethanol and biogas from MSW [16,17].