BackgroundIn the kraft-based dissolving pulp production process, pre-hydrolysis liquor (PHL) is produced, which contains hemicelluloses, lignin, furfural and acetic acid. PHL is currently burned in the recovery boiler of the kraft pulping process, but it can be utilized for the generation of high-valued products, such as xylitol and xylanase, via fermentation processes. However, some PHL constituents, e.g., furfural and lignin, are contaminants for fermentation processes and they must be eliminated for production of value-added products.ResultsIn this work, a process is introduced for removing contaminants of PHL. Ca(OH)2 treatment is the first step of this process, which removed 41.2% of lignin and negligible amount of sugars. In this step, a notable increase in the concentration of acetic acid was achieved (ranging from 6.2 to 11.7 g/L). In the second step, the implementation of adsorption using activated carbon (AC) at 1 wt% dosage led to additional 32% lignin and 5.9% xylosugar removals. In addition, laccase assisted activated carbon treatment led to further removal of lignin via accelerating lignin polymerization and adsorption on AC (i.e., removal from PHL). Overall, 90.7% of lignin, 100% of furfural, 5.7% of xylose, and 12% of xylan were removed from PHL, while the concentration of acetic acid became twofolds in the PHL.ConclusionsThis study reports an attractive process for purifying sugars and acetic acid of PHL. This process may be implemented for producing sugar-based value-added products from PHL. It also discusses the mechanism of Ca(OH)2 treatment, AC adsorption and laccase assisted activated carbon treatment for lignin removal.
Efficient selective separation of oils or organic pollutants from water is important for ecological, environmental conservation and sustainable development. Various absorption methods have emerged; the majority of them still suffer from defects including low removal efficiency, a complicated preparation process, and high cost. Herein, we present a highly porous and mechanical resilient bacterial cellulose (BC) carbon aerogel directly from BC hydrogel via facile directional freeze-drying and high-temperature carbonization. The resultant BC carbon aerogel showed excellent mechanical compressibility (maximal height compression ∼99.5%) and elastic recovery due to the porous structure. Taking advantages of the high thermal stability and superhydrophobicity, the BC carbon aerogel was directly used as a versatile adsorbent for oil/water separation. The result demonstrated that the BC carbon aerogel showed super oil/water separation selectivity with the oil absorption capacity as high as 132−274 g g −1 . More importantly, the BC carbon aerogel adsorbent can be reused by a simple absorption/ combustion method and still keep high-efficiency oil absorption capacity and excellent superhydrophobicity after 20 absorption/ combustion cycles, displaying recyclability and robust stability. In sum, the BC carbon aerogel introduced here is easy to fabricate, ecofriendly, highly scalable, low cost, mechanically robust, and reusable; all of these features make it highly attractive for oil/water separation application.
Even
though compressible carbon aerogels are widely studied for
oil/organic solvent recovery, it is challenging to simultaneously
achieve excellent mechanical performance and recovery efficiency due
to the brittleness of the carbon skeleton. Here a novel strategy is
proposed to efficiently fabricate a 3D elastic reduced graphene oxide
(RGO)-cross-linked carbon aerogel. Notably, cellulose nanocrystals
(CNCs) isolated from plant pulp act as an essential component, and
prehydrolysis liquor (PHL), an industrial byproduct in the plant pulping
process, serves as the adhesion promoter to achieve enhancement of
the strength and flexibility of the carbon aerogel. For the first
time, all components (pulp and PHL) of the tree were fully exploited
to design a carbon aerogel. The formation of wavy carbon layers with
springboard elastic supporting microstructure enables mechanical stretch
and shrink as well as avoids interfacial collapse during compression.
Benefiting from the unique wavy layer structure and strong interaction,
the carbon aerogels are ultralight (4.98 mg cm–3) and exhibit supercompression (undergoing extreme strain of 95%)
and superelasticity (about 100% height retention after 500 cycles
at a strain of 50%). Particularly, the carbon aerogel can selectively
and quickly adsorb various oily contaminants, exhibiting high oil/organic
solvents absorption capacity (reaches up to 276 g g–1 for carbon tetrachloride) and good recyclability. Finally, practical
applications of the carbon aerogel in oil-cleanup and pollution-remediation
devices are exhibited. Hence, this versatile and robust functionalized
carbon aerogel has promising potential in oil cleanup and pollution
remediation.
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