Effects of Wheat Straw Pretreatments on Preparation of Superabsorbent Resins
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Abstract:
Pretreatments of wheat straw are necessary before preparation of superabsorbent resins(SAR).Both the effects on wheat straw and the superabsorbent resins were analyzed and compared after acid hydrolysis,dipping in sodium hydroxide solution or ammonia,alkali cooking and their united pretreatments.Besides,the morphology and chemical structure of wheat straw and the chemical structure of SAR were confirmed by metallurgical microscope and IR spectra before and after the pretreatments.The results showed that the appropriate pretreatments were alkali cooking(water solution of w(NaOH)=14%,150 ℃,0.6 MPa,30 min)followed by hydrolysis with 1 mol/L nitric acid at 100 ℃ for 30 min,or dipping in w(NH_3·H_2O)=10% ammonia for 48 h at room temperature followed by hydrolysis with 1 mol/L nitric acid at 100 ℃ for 45 min.SAR prepared with the wheat straw after the two pretreatments can absorb distilled water of 405 g and 294 g per 1 g respectively,and can absorb the water solution(w(compound fertilizer) = 0.1% in which w(N)=w(P)=w(K)=10%,N existing in urea,P existing in single superphosphate and K existing in KCl) of 124 g and 84 g per 1 g,respectively.Keywords:
Nitric acid
Sodium hydroxide
Distilled water
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Background/Objectives: Sodium hydroxide (NaOH) pretreatment was used to determine the effect of pretreatment on chemical composition of pretreated rice straw. The experiment was designed to measure the effects in terms of NaOH concentration and pretreatment time mainly on the total carbohydrate content (TOC) and lignin content of pretreated rice straw. Methods/Statistical analysis: Compositional characterization was performed based on the National Renewable Energy Laboratory (NREL) laboratory analysis protocols. Rice straw obtained from Sekinchan, Selangor Malaysia was dried to reduce the moisture content (<15%) and ground to 2 mm particle size. Rice straw was pretreated with different concentration of NaOH (2%w/v, 6%w/v and 12%w/v) and pretreatment time of 1 and 3 hours, while temperature was kept constant at 55°C. Findings: Rice straw sample pretreated with 12%w/v NaOH for 1 hour gave the highest glucan content, an increase of 85.6% from the native untreated rice straw. This condition also yielded the best delignification effect which reduced the lignin composition up to 79.6%, while sample pretreated with 2%w/v for 3 hours gave the highest composition on total carbohydrate content of 79.16% for which included glucan, xylan and arabinan. Hence, the pretreatment condition of 2%w/v NaOH concentration for 3 hours was the best condition in order to obtain high total carbohydrate content while severe pretreatment condition of 12%w/v NaOH concentration for 1 hours was best to give the delignification effect to the rice straw. Application/Improvements: The results from this work can be used for further evaluation of pretreated rice straw using NAOH particularly for enzymatic hydrolysis. Keywords: Sodium hydroxide, pretreatment, rice straw, composition
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Rice straw
Hemicellulose
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This paper presents a comprehensive study of wheat straw that was alkali-pretreated with NaOH loadings from 60 to 220 mg NaOH/g dry straw and a 0.5% anthraquinone (AQ) loading at 90 °C for 1, 2, and 3 h. Images of the residual solids were taken with a scanning electron microscope. A full compositional analysis of the raw material and residual solids, yield of compounds dissolved in the black liquor (BL), and molecular weight (Mw) after the different pretreatments were presented to track the dissolution process of lignin and carbohydrates. The ratio of the lignin fraction to carbohydrates dissolved in the BL was used for an analysis of the reaction selectivity. The cellulose retained 90% of the carbohydrates in the pretreated straw, while 75% of the lignin was dissolved in the BL gradually with an intermediate value of Mw. Low-molecular weight lignin (Mw ~ 1800 and degree of polymerization ~ 1.05) was dissolved out with the 60 mg NaOH/g dry straw loading. When the NaOH loading was increased to 220 mg NaOH/g dry straw, the Mw of the lignin was 4300 to 4700.
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Hemicellulose
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Enzymatic Hydrolysis
Hemicellulose
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Hemicellulose
Enzymatic Hydrolysis
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The effects of alkaline pretreatment with NaOH, KOH, Ca(OH)2, and NaOCl at varying temperatures and concentrations on the production of sugars, changes in the morphological structure, and the chemical composition of rice straw were evaluated. Enzymatic saccharification of 2% (w/v) KOH-treated rice straw with autoclaving at 121 °C, 15 psi, 20 min, gave a maximum yield of 59.90 g/L of reducing sugars, which was slightly higher than that of NaOH (55.48 g/L) with the same conditions. Chemical composition analysis of the rice straw showed that the cellulose content was increased to 71% and 66% after pretreatments with NaOH and KOH, respectively. Fourier Transform Infrared (FTIR) spectroscopy revealed that solubilization and removal of the lignin component also took place. The scanning electron microscope (SEM) analysis showed a marked change in the morphological structure of the treated rice straw compared to the untreated rice straw. These results suggested that pretreatment of rice straw with either 2% (w/v) NaOH or KOH at high temperature could be a promising pretreatment method for sugars production.
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Acetylation of cellulose fiber extracted by methylbenzene/ethanol (2/1), sodium chlorite solution, and sodium hydroxide from raw wheat straw (RWS) was studied to examine its potential as an oil-spill adsorbent. Wheat straw cellulosic sorbent was produced by using acetic anhydride as an acetylating reagent and N-bromosuccinimide (NBS) as a catalyst. Effects of the volume ratio of acetic anhydride (from 6.25% to 57.5%), catalyst concentration (from 10 to 60 mM NBS), reaction temperature (from 50 to 120 °C), and reaction time (from 0.5 to 3 h) on oil-sorption properties were evaluated. The best oil absorbencies for diesel fuel, diesel oil slick, corn oil, and corn oil slick treatments were 24.21 ± 0.76, 22.39 ± 0.77, 25.61 ± 2.13, and 24.73 ± 1.19 g/g, respectively. Chemical composition and morphologic structure of RWS before and after acetylation were investigated and compared. Oil-absorption capacity, oil-retention ability, recyclability, and selectivity of RWS, pretreated wheat straw, and acetylated wheat straw were also discussed. The acetylated wheat straw demonstrated good potential for the utilization of agricultural residues as natural sorbents in oil cleanup.
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Dilute solutions of H2SO4,NaOH,ammonia and H2O2 were evaluated as pretreatment reagents for improving the enzymatic saccharification of rice straw at room temperature (28 ℃). The highest saccharification rate was achieved in the case of rice straw pretreated with 2% NaOH. Mild alkali pretreatment resulted in a majority removal of lignin,but higher than half of hemicellulose was remained in the material. The compound enzyme produced by T. koningii QF-02 was more suitable for the hydrolysis of pretreated rice straw than the mixture of two commercial cellulases. The optimum temperature and pH for the hydrolysis of pretreated rice straw of the compound enzyme was 50℃ and 4.8 respectively. For the hydrolysis of alkali pretreated rice straw by the compound enzyme,the optimal hydrolysis time,enzyme loading and substrate concentration were determined as 48 h,10 FPU/g biomass and 8% (w/v),respectively.
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Article investigates the influence of different pretreatment methods on sugar conversion and bioethanol production. Different dilute acid and alkaline pretreatment methods are compared to determine the best pretreatment method to give the highest glucose and ethanol yields under the mild operating conditions. Wheat straw is used as a raw material as it is the most widely grown cereal in Europe. Dilute sulfuric acid, hydrochloric acid, nitric acid and potassium hydroxide solutions are used for pretreatment in combination with enzymatic hydrolysis. Results indicate that the highest cellulose-to-glucose conversion rate of 316.7 g kg -1 of biomass is achieved by the pretreatment with nitric acid. The lowest glucose concentration of 221.3 g kg -1 is achieved by hydrochloric acid. In the wheat straw samples pretreated with sulfuric acid and KOH, two different approaches are used. Solid phase of half the samples is rinsed with water before adding enzymes, and the rest of the samples are not. The rinsed samples pretreated with KOH solution give the highest ethanol yield of 104.3 g kg -1 , while the lowest ethanol yield is 67.7 g kg -1 from samples pretreated with HCl solution. Unrinsed samples and rinsed samples pretreated with sulfuric acid give an ethanol yield of 78.7 g kg -1 and 92.0 g kg -1 , respectively. These results indicate that rinsing the solid phase of the samples with distilled water before hydrolysis removes most of the inhibitory compounds formed during the pretreatment with dilute acid and increases fermentation efficiency by approximately 12%.
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Potassium hydroxide
Hydrochloric acid
Distilled water
Enzymatic Hydrolysis
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