Sodium Carbonate Pretreatment Research Articles

High efficient ethanol production from corn stover by modified mild alkaline pretreatment

Sodium carbonate pretreatment, an environmentally-friendly and efficient pretreatment, was used to improve solid-state ethanol production from corn stover (CS). To further enhance ethanol yield from the pretreated CS, especially at low enzyme loadings, a combined pretreatment, including steam and sodium carbonate pretreatments, was developed. The removal/modification of lignin by sodium carbonate pretreatment (at 100 °C for 3 h) helped to obtain high ethanol titer at high solids and low enzymes loadings. The maximum ethanol concentration was about 44 g/L, obtained after 72 h simultaneous saccharification and fermentation (SSF) of CS pretreated with sodium carbonate without mixing and prehydrolysis at 30% solid and 15 FPU/g enzyme loadings. Applying prehydrolysis and increasing the SSF time to 120 h improved ethanol concentration to 59 and 67 g/L, respectively. Steam pretreatment at 190 °C for 10 min before sodium carbonate pretreatment led to 76% increase in ethanol concentration. At the enzyme loading of only 5 FPU/g substrate, the modified pretreatment increased the ethanol concentration from 24 g/L to 41 g/L, compared with that of sodium carbonate pretreatment. The results showed that hemicellulose removal and delignification by steam and sodium carbonate pretreatment, respectively, considerably improved ethanol concentration at high solids and low enzyme loadings.

Bioconversion of Glycyrrhiza glabra residue to ethanol by sodium carbonate pretreatment and separate hydrolysis and fermentation using Mucor hiemalis

The non-valuable non-edible Glycyrrhiza glabra residue (GGR) was efficiently subjected to inexpensive sodium carbonate pretreatment for enhanced enzymatic hydrolysis and ethanol production. The process included sodium carbonate pretreatment at different concentrations (0.5 and 1 M), temperatures (60, 100 and 120 °C), and retention times (3, 5 and 8 h), followed by separate hydrolysis and fermentation using a rarely-reported fungus Mucor hiemalis. The GGR pretreated with 0.5 M sodium carbonate solution at 120 °C for 3 h exhibited the maximum digestibility yield of 94.6% which was 6.2-fold higher than that observed for the untreated GGR. Consequently, fermentation of GGR hydrolyzates by M. hiemalis led to a maximum ethanol production yield of over 94%. Composition analysis of the biomass indicated that the process could substantially remove the majority of lignin part but left the cellulose relatively intact. Moreover, in-depth analyses of the materials by rapid semi-quantitative methods (e.g., Simons’ stain) as well as FTIR, XRD, and FE-SEM investigations revealed that sodium carbonate pretreatment could not only modify biomass composition, but also expanded cellulosic surface area, increased surface hydrophilicity, enlarged the pores, and improved morphological quality of GGR; thereby, rendered it more accessible to the cellulase. The implication of the study may potentially provide the first insight into commercial utilization of GGR for large-scale bioethanol production in a biorefinery framework.

Process development for sodium carbonate pretreatment and enzymatic saccharification of rice straw for bioethanol production

Optimization of pretreatment of rice straw was carried out with sodium carbonate. Initially, sodium carbonate pretreatment of rice straw followed by saccharification using partially purified cellulolytic enzymes of thermophilic mould Myceliophthora thermophila BJTLRMDU3 (20 U/g) at 60 °C and pH 5.0 after 6 h, released about 3-fold more reducing sugars with autoclaving (154.93 mg/g substrate) as compared to room temperature (51.01 mg/g substrate). Further optimization was carried out using statistical tools by response surface methodology (RSM) selecting three variables i.e., sodium carbonate concentration, substrate concentration and autoclaving time. Statistical optimization has resulted in enhanced liberation of reducing sugars i.e., 531.2 mg/g substrate using 5% rice straw, 1.25% sodium carbonate and autoclave time of 30 min after saccharification for 6 h. Furthermore, maximum liberation of reducing sugars (728.45 mg/g substrate) from pretreated rice straw was recorded after 48 h. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) data clearly confirmed the breakdown of cellulose and hemicellulose, removal of lignin and morphological changes in pretreated rice straw. Fermentation of enzymatic hydrolysate (20%) was carried out by Saccharomyces cerevisiae at 30 °C, pH 6.0, 150 rpm that resulted in 18.07 g/L ethanol after 72 h.

Improvement of dry simultaneous saccharification and fermentation of rice straw to high concentration ethanol by sodium carbonate pretreatment

Ethanol at high concentration was produced from rice straw pretreated with sodium carbonate through dry simultaneous saccharification and fermentation (DSSF). A high concentration of ethanol was obtained without mechanical mixing, an increase in fermentation time, and pre-hydrolysis. The most important influencing factors, including pretreatment time (3–10 h), enzyme loading (5–40 FPU/g substrate), solid loading (15–30 wt %), and DSSF reaction time (48–120 h), were investigated on dry hydrolysis and DSSF. An increase in pretreatment time from 3 to 10 h improved ethanol concentration from 55.1 to 67.7 g/L, obtained through DSSF at 20% solid loading and 10 FPU/g substrate. A glucose concentration as high as 124.6 g/L was obtained from the hydrolysis of the straw treated for 5 h. The highest total sugar and ethanol concentration were 137.3 g/L and 83.1 g/L for the treated straw, while they were 65.2 g/L and 38.6 g/L for the untreated ones, respectively, obtained by hydrolysis and DSSF at 30% solid loading. Changes associated with pretreatment, i.e., composition, crystallinity, and microscopic structure of untreated and treated straws, were investigated to find the reason for the improved hydrolysis and DSSF.

Effect of sodium carbonate solution pretreatment on drying kinetics, antioxidant capacity changes, and final quality of wolfberry (Lycium barbarum) during drying

Wolfberry is an important medicinal and edible plant in China that is difficult to dehydrate owing to its dense pulp and epicuticular wax. Sodium carbonate (SC) pretreatment is an efficient low-cost technology that can help improve the wolfberry drying rate. To determine the effect of SC pretreatment on drying kinetics and quality changes during hot-air drying (AD), wolfberries were dried using AD at different temperatures (40, 50, and 60 °C) with or without SC pretreatment. SC pretreatment was found to increase the effective diffusivity (Deff) and reduce the total drying time by 22–28%. SC pretreatment and low-temperature AD (40 and 50 °C) helped improve wolfberry quality and increased its total phenolic content (TPC), total flavonoid content (TFC), antioxidant activity, carotenoids content, and betaine content by 10–17%, 9–24%, 21–25%, 14–22%, 3–23%, and 17–42%, respectively. Samples dried with or without SC pretreatment showed the same trends, but a different moisture content inflexion point in the drying kinetics and different antioxidant attributes. In all drying processes, the Deff initially increased and then decreased, while the TPC, TFC, and antioxidant capacity initially decreased and then increased.

Effects of Green Liquor (GL) and Sodium Carbonate (SC) Pretreatment on Structural Characteristics of Wheat Stem Lignin

The content and structure of lignin have been considered as important factors that affect both pretreatment and enzymatic hydrolysis of lignocellulosic biomass. In this work, wheat stems (WS) were pretreated using mild alkali including green liquor (GL) and sodium carbonate (SC). The results indicate that GL pretreatment exhibits better delignification selectivity and higher enzymatic digestibility than SC pretreatment. Analysis of 1H–13C HSQC NMR and FTIR on cellulolytic enzyme lignin (CEL) preparations isolated from untreated and pretreated WS also proves that a certain amount of lignin degrades which leads to a decrease of β-O-4′ linkages. Under mild alkaline conditions, more guaiacyl units in lignin are removed than syringyl units, which results in a higher condensation degree and S/G ratio of CELs isolated from GL- and SC-pretreated stems. Compared with p-coumarate structures, ferulates in lignin are more stable under mild alkaline conditions.

Structural and health functionality of dried goji berries as affected by coupled dewaxing pre-treatment and hybrid drying methods

ABSTRACTCoupled effects of sodium carbonate (SC) pre-treatment and hybrid drying methods (freeze-drying (FD)-instant controlled pressure drop drying (DIC), hot air drying (HAD)-DIC) on the microstructure, physicochemical, nutritional, and antioxidant properties of goji berries were investigated. Dewaxing pre-treatment by SC could decrease drying time and improve quality. A substantial increase in pore size of goji was found after SC pre-treatment coupled with hybrid drying. Although the best colour was found in FD products, goji dried by hybrid methods (especially FD-DIC) showed better overall quality than that dried by HAD or FD alone. FD-DIC products exhibited the lowest moisture content (127 g/kg), the best crispness (21), the highest glass transition temperature (27.82ºC), higher contents of total Lycium barbarum polysaccharide (139.8 g/kg), total carotenoids (2.43 g/kg) as well as ABTS+ radical scavenging activity (57.55 μmol TE/g). FD-DIC could be an alternative drying method for processing valuable agro-products.

Silica Removal from Rice Straw To Improve its Hydrolysis and Ethanol Production

Rice straw has high silica content compared with other lignocelluloses. Presence of silica in the outer layer of rice straw reduces enzymatic hydrolysis and ethanol production yield. In this study, silica removal from rice straw was investigated through various alkali treatments. The results showed that sodium carbonate could effectively remove silica from the straw (>91%). To investigate only the effects of silica removal and eliminate the effect of lignin removal on enzymatic hydrolysis, organosolv followed by sodium carbonate pretreatment was conducted. Organosolv pretreatment removed most of the straw lignin, while silica was not separated. Organosolv pretreatment of rice straw improved the glucose and ethanol yield from 34.4% and 39.3% for the untreated straw to only 52.9% and 51.6%, respectively, whereas further treatment with sodium carbonate increased the yields up to 94.8% and 78.7%. The results indicated that the protecting effect of silica layer was greater than that of lignin in rice straw.

Recent progress on the pretreatment and fractionation of lignocelluloses for biorefinery at QIBEBT

Pretreatment or fractionation is one of the key steps for the conversion of lignocelluloses to sustainable biofuels, biomaterials or biochemicals, because pretreatment/fractionation can break the natural recalcitrance of lignocelluloses, improving the conversion efficiency of downstream processes. This paper will review the recent progress on pretreatment and fractionation of lignocelluloses for biorefinery in Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT). Main technologies introduced were alkaline twin-screw extrusion pretreatment, modified alkali pretreatment, hydrogen peroxide-assisted sodium carbonate pretreatment, fractionation with formic acid, as well as the two-step fractionation by hot water treatment coupling ammonium sulfite treatment. With the development of these technologies, a pilot scale platform of pretreatment and saccharification was established in the pilot plant of QIBEBT.

Combination of Gamma Irradiation and Sodium Carbonate Pretreatment on Oil Palm Empty Fruit Bunch (EFB) for High Acidic Hydrolysis Yield

Oil palm empty fruit bunch (EFB) fibres were pretreated by gamma irradiation followed by sodium carbonate (Na2CO3) before the acid hydrolysis process to produce reducing sugars using diluted sulphuric acid (H2SO4). In this study, EFB fibres were irradiated at different doses, i.e. 0, 100 and 200 kGy. Meanwhile, the gamma irradiated sample were then subjected to Na2CO3 pretreatment with 0 and 5% total titratable alkali (TTA). The effect of the pretreatment using gamma irradiation and Na2CO3 on the physical and chemical properties of the EFB fibres and the yield of the reducing sugar obtained from the acid hydrolysis process was investigated. The obtained results showed that the content of holocellulose was increased significantly with the increase of irradiation doses combined with Na2CO3 pretreatment, whereas lignin content of the EFB was decreased. The gamma irradiation and Na2CO3 pretreatment resulted in structure breakage and removal of silica of EFB fibres which can be due to the swelling of the fibres. A synergistic effect between gamma irradiation and Na2CO3 was observed, in which the yield of reducing sugars was increased by combining the gamma irradiation and Na2CO3 pretreatment.

Reducing biomass recalcitrance via mild sodium carbonate pretreatment

This study examined the effects of mild sodium carbonate (Na2CO3) pretreatment on enzymatic hydrolysis of different feedstocks (i.e., corn stover, Miscanthus, and switchgrass). The results showed that sodium carbonate pretreatment markedly enhanced the sugar yields of the tested biomass feedstocks. The pretreated corn stover, Miscanthus, and switchgrass gave the glucose yields of 95.1%, 62.3%, and 81.3%, respectively, after enzymatic hydrolysis. The above glucose yields of pretreated feedstocks were 2–4 times that of untreated ones. The pretreatment also enhanced the xylose yields, 4 times for corn stover and 20 times for both Miscanthus and switchgrass. Sodium carbonate pretreatment removed 40–59% lignin from the tested feedstocks while preserving most of cellulose (<5% cellulose loss). Corn stover appeared to be least resistant to breakdown by Na2CO3 and enzymatic hydrolysis. Our study indicated that mild sodium carbonate pretreatment was effective for reducing biomass recalcitrance and subsequently improving the digestibility of lignocellulosic biomass.

Hydrogen Peroxide-Assisted Sodium Carbonate Pretreatment for the Enhancement of Enzymatic Saccharification of Corn Stover

In this work, the effectiveness of hydrogen peroxide-assisted sodium carbonate (HSC) pretreatment of corn stover to produce fermentable sugars was investigated. It was found that the addition of H2O2 (a green oxidative agent) in Na2CO3 pretreatment could enhance the lignin removal and increase the hydrophilicity of the residual lignin, leading to the improved enzymatic digestibility and the yield of fermentable sugars. Also, results showed that lignin removal (in the range of 12-65%) was positively and linearly correlated with final total sugar yields. Post PFI refining could further improve the enzyme accessibility by increasing porosity of substrates. After HSC pretreatment (40 wt % Na2CO3 and 15 wt % H2O2 120 degrees C for 60 min) and enzymatic hydrolysis, the final total sugar yield could achieve 79%, which was about 10% higher in comparison with the conventional Na2CO3 pretreatment under the same conditions. HSC pretreatment will have less environmental impact and less barriers for large scale production.

Ethanol production from rice straw by sodium carbonate pretreatment and Mucor hiemalis fermentation

Rice straw, one of the most abundant and mainly unused lignocellulosic wastes, is a promising substrate for ethanol production. To improve ethanol production yield from the straw, pretreatment with sodium carbonate at mild conditions followed by fermentation using zygomycetes fungus Mucor hiemalis was performed. The sodium carbonate treatment was conducted at different concentrations, time intervals, and solid loadings. The highest glucose and ethanol production yields were obtained after the pretreatment with 0.5M sodium carbonate at 100°C and 1:20g/g solid loading for 3h. This pretreatment removed more than 90% of silica from the straw and improved the enzymatic hydrolysis yield from 35% to 100%. Afterward, ethanol was produced by simultaneous saccharification and fermentation (SSF) from the pretreated straw at 37°C using M. hiemalis, and the results were compared with SSF using Saccharomyces cerevisiae. The results showed that ethanol yield was improved by more than 40% under the optimum conditions and the yield was higher using M. hiemalis. Thus, the fungus could be a suitable alternative to S. cerevisiae for ethanol production from lignocellulosic wastes.

Sodium carbonate pretreatment: an approach towards desilication of paddy straw and enhancement in biogas production

Lignocellulosic biomass is a useful but an inconvenient form of energy, and paddy straw (PS) is one of the most abundant lignocellulosic wastes on the earth. Lignocellulosics generally have a high content of cellulose having combustion energy of 15 kJ/g which, when converted to methane, have a combustible energy of 50 kJ/g. But lignin and silica are the main deterrents for the microbial action on the cellulose/hemi-cellulose component of PS. In order to break the protective shield made by lignin and silica and to enhance the PS digestibility, the PS was pretreated with different concentrations (2, 4, 6, 8 and 10 %) of sodium carbonate by soaking the PS in sodium carbonate solution for the periods of 24 and 48 h and simultaneously irradiating the other set with microwaves (power 720 W, temperature 180 °C) for 30 and 60 min. The change in chemical composition of PS was the factor determining the enhancement in PS digestibility. Sodium carbonate (4 %) + microwave (60 min) pretreatment was found to be the best amongst the other pretreatments with 84.9 % desilication of PS and 44.3 and 54.4 % increase in cellulose and biogas production, respectively.

Enhanced glucose yield and structural characterization of corn stover by sodium carbonate pretreatment

Na2CO3 was employed as an efficient yet cheap alkaline catalyst for the pretreatment of corn stover. To systematically obtain an optimal condition, the effects of critical pretreatment parameters including Na2CO3 concentration (2-6%), temperature (120-160 °C), and reaction time (10-30 min) on glucose yield were evaluated in lab-scale using response surface methodology. The best conditions were found to be Na2CO3 of 4.1%, temperature of 142.6 °C, and reaction time of 18.0 min, under which glucose yield reached to 267.5 g/kg biomass. Physical properties, based on scanning electron microscopy (SEM) imagery, surface area, pore volume and size, and crystallinity of pretreated corn stover, were examined. The Na2CO3 pretreatment apparently damaged the surface and altered structural features of corn stover, which resulted in the enhancement of enzymatic of hydrolysis. These results evidently support that Na2CO3 is indeed a robust and feasible catalyst for pretreating lignocellulosic biomass.

Comparison of sodium carbonate pretreatment for enzymatic hydrolysis of wheat straw stem and leaf to produce fermentable sugars

The specific characteristics of biomass structure and chemical composition of straw stem and leaf may result in different behavior of pretreatment and enzymatic hydrolysis. In this work, sodium carbonate (SC) was employed as a pretreatment to improve the enzymatic digestibility of wheat straw. The chemical composition and enzymatic hydrolysis of wheat straw stem and leaf (sheath included) were investigated comparatively. Most of the polysaccharides are kept in the solid fractions after SC pretreatment, while the stem has better delignification selectivity than leaf at high temperature. The enzymatic hydrolysis efficiency of wheat straw leaf is significantly higher than that of stem. The maximum total sugar yield from SC pretreated leaf was about 16% higher than stem. The results show that sodium carbonate is of great potential to be used as a pretreatment for the production of bioethanol from straw handling waste in a straw pulp mill with a low feedstock cost.

Efficient Conversion of Rice Straw to Bioethanol Using Sodium Carbonate Pretreatment

In this study, rice straw was treated with sodium carbonate prior to enzymatic hydrolysis and fermentation. All pretreatments were performed in a high-pressure reactor at 90, 120, 150, and 180 °C by 0.25, 0.5, and 1 M sodium carbonate (Na2CO3) solution. The reactor was designed to inject the straw to the reactor at a desired temperature without any preheating effects. The reactor content was continuously mixed, and samples were taken at different time periods. Afterward, enzymatic hydrolysis of the untreated and all treated straws were conducted at 45 °C for 72 h with enzyme loading of 20 FPU cellulase and 30 IU β-glucosidase per gram of substrate. The best pretreatment conditions were obtained to be 0.5 M Na2CO3 at 180 °C for 120 min. This pretreatment improved the released glucose from 9.5 g/L for the untreated straw to 43.5 g/L for the treated one. On the other hand, the treatment showed significant improvement on ethanol production from rice straw applying simultaneous saccharification and fermentation. Ethanol production was enhanced from 90.2 to 351.4 g/L by the treatment. The analysis showed that the treatment with sodium carbonate at elevated temperature can significantly reduce the lignin and xylan contents and the cellulose crystallinity and also convert cellulose type I to type II, which is more amenable for enzymatic hydrolysis.

Effects of sodium carbonate pretreatment on the chemical compositions and enzymatic saccharification of rice straw

The effects of sodium carbonate (Na2CO3) pretreatment on the chemical compositions and enzymatic saccharification of rice straw were investigated. The enzymatic digestibility of rice straw is enhanced after pretreatment since pretreated solids show significant delignification with high sugar availability. During pretreatment, an increasing temperature and Na2CO3 charge leads to enhanced delignification, whereas an increased degradation of polysaccharides as well, of which xylan acts more susceptible than glucan. The sugar recovery of enzymatic hydrolysis goes up rapidly with the total titratable alkali (TTA) increasing from 0% to 8%, and then it reaches a plateau. The highest sugar recovery of rice straw after pretreatment, 71.7%, 73.2%, and 76.1% for total sugar, glucan, and xylan, respectively, is obtained at 140°C, TTA 8% and cellulase loading of 20FPU/g-cellulose. In this condition, the corresponding delignification ratio of pretreated solid is 41.8%, while 95% of glucan and 76% of xylan are conserved.