Effect of Alkali and 1,4-Butanediol Contents on the Extraction of Lignin and Lignin-Based Activated Carbon.

In the process of lignin extraction by the organic solvent method, the amount of alkali and the content of 1,4-butanediol are important conditions that affect lignin yield. The effects of alkali and alcohol contents on lignin recovery, removal rate, and structure were studied. In this reaction system, the removal rate of lignin increased with the increase of alkali content but decreased with the increase of alcohol content. Fourier transform infrared (FT-IR) analysis showed that the phenol hydroxyl group and the ether bond in lignin had different trends in different alkali and 1,4-butanediol environments, and four different infrared parameters in lignin had an obvious linear relationship. Gel permeation chromatography (GPC) results showed that high alkali content and high 1,4-butanediol content could lead to the fragmentation of lignin. In addition, lignin extracted from alkali-quantity factor series was selected to prepare activated carbon, CaCl2 was selected as the activator, and its effects were studied. Results showed that in the process of extracting lignin, on the one hand, NaOH content affects the functional groups of activated carbon by affecting the aromatic structure of lignin; on the other hand, the NaOH content affects the graphitization degree and specific surface area of activated carbon by affecting the removal rate and the molecular weight of lignin.

Selective removal of lignin with sodium chlorite to improve the quality and antioxidant activity of xylo-oligosaccharides from lignocellulosic biomass.

As a key anti-degradation barrier that restricts the biotransformation of lignocellulose, the presence of lignin usually severely affects the quality of the extracted xylo-oligosaccharides (XOS). Herein, this study proposed a practical route to improve the quality and antioxidant activity of XOS extracted from lignocellulosic biomass via selective removal of lignin. The highest delignification of 92.6% was successfully achieved with 8% sodium chlorite at 75°C for 2 h. An ideal hemicellulose sample with a purity of 86.1% was obtained by selective removal of lignin. A high-quality XOS sample with a purity of 96.3%, a yield of 77.4%, and a color value of 814 was obtained by separating and purifying the enzymatic hydrolysate. Antioxidant activity assay showed that the highest radical scavenging activity of XOS was 87.3%. Importantly, this study provide a feasible and effective route for the lignocellulosic biomass utilization strategy based on the selective removal of lignin.

Preparation of Syringaldehyde from Lignin by Catalytic Oxidation of Perovskite-Type Oxides.

The influence of different reaction conditions on the yield of syringaldehyde was studied by using perovskite oxide as the catalyst. The optimal reaction conditions are as follows: 0.60 g of dealkali lignin, 0.60 g of 5 wt % theta ring-loaded LaFe0.2Cu0.8O3 catalyst, 30 mL of 1.0 mol/L NaOH solution, 160 °C reaction temperature, 0.80 MPa O2 pressure, and 2.5 h reaction time. Under these conditions, the highest syringaldehyde yield was 10.00%. The recycling performance of the catalyst was studied. It was found by XRD analysis that the catalyst maintained high catalytic activity after four times of use.

Selective removal of lignin to enhance the process of preparing fermentable sugars and platform chemicals from lignocellulosic biomass.

The economic dependency on fossil fuels and the resulting effects on climate and environment have put more focus on finding alternative renewable sources (e.g. lignocellulose) for the production of fuels and chemicals. Nevertheless, the yield and quality of fermentable sugar and platform chemical produced by directly degradation of lignocellulose are severely restricted owing to the presence of lignin and its derivatives. Therefore, the present study was aimed to selective removal of lignin to enhance the process of preparing fermentable sugars and platform chemicals from lignocellulosic biomass. The results showed that the highest degree of delignification was 92.01%. Reducing sugar obtained by enzymatic hydrolysis of lignocellulose was suitable for L-lactic acid fermentation without appreciable inhibition. The highest cellulose digestibility and yield of 5-HMF were 90.67% and 61.02%, respectively. SO42-/ZrO2 could be reused at least 5 times without appreciable loss of catalytic performance, which shows an industrial application prospects in biorefinery.

Investigating desorption during ethanol elution to improve the quality and antioxidant activity of xylo-oligosaccharides from corn stalk.

As the most representative of lignocellulosic materials, corn stalk (CS) will be a great candidate to produce xylo-oligosaccharides (XOS). Owing to the high impurity content of the XOS produced by directly enzymatic hydrolysis of xylan extracted from CS, subsequent refining steps are essential. The present study was aimed to investigate desorption during ethanol elution to improve the quality and antioxidant activity of XOS from CS. The desorption was systematically investigated after optimizing the elution conditions. The results showed that it had an elution watershed when the volume ratio was 2:1. More interestingly, XOS had a obvious priorities of desorption during ethanol gradient elution. The highest purity of XOS was 98.12% from 30% ethanol eluate. Antioxidant activity assay showed that the highest radical scavenging activity of XOS was 89.89% obtained from 70% ethanol eluate at a concentration of 3 mg/mL, which could be used in antioxidant food, feed additives.

Removal of chromophore in enzymatic hydrolysis by acid precipitation to improve the quality of xylo-oligosaccharides from corn stalk.

As the most representative functional sugar, the application areas and market demands of xylo-oligosaccharides (XOS) have been expanding year by year. Owing to the complex structure of corn stalk (CS), XOS obtained from CS are accompanied by problems such as low purity and high color value, which degrade the product. To improve the quality of XOS from CS, the enzymatic hydrolysis was precipitated by acid; then, the ethanol elution concentration was systematically investigated after optimizing the adsorption conditions. The results showed that the purity of XOS was increased to 87.28% from 67.31%, and the color value was decreased to 1050 from 4682 when the acid precipitation pH was 2. On the basis of acid precipitation, if the corresponding optimal conditions of XOS adsorption and elution were used, the highest purity of XOS was 97.87% obtained, with the lowest color value, 780, which reached the standard of the commercial XOS.

Changes on structural properties of biomass pretreated by combined deacetylation with liquid hot water and its effect on enzymatic hydrolysis.

A novel combined pretreatment of deacetylation and liquid hot water (LHW) was invented which has been proved to be effective in increasing enzymatic hydrolysis yield of biomass. In order to further understand the effect of this new pretreatment process on biomass, the variation on structural properties including cellulose crystallinity index (CrI), specific surface area (SSA) and degree of polymerization (DP) before/after pretreatment and how these properties affected the enzymatic hydrolysis of biomass were explored. The improvement of pretreatment severity (PS) could increase CrI, SSA and reduce DP. Whereas the enhancement of degree of deacetylation could decrease SSA and DP. An optimal formula (E12Y=0.347(100-CrI)(-0.375)×(SSA)(0.203)×(1700-DP)(0.281)) was achieved to express the correlation between structural properties and enzymatic hydrolysis after 12h. The enzymatic yield was more sensitive to CrI than to SSA and DP.

One-pot conversion of disaccharide into 5-hydroxymethylfurfural catalyzed by imidazole ionic liquid.

Conversion of carbohydrate into 5-hydroxymethylfurfural (5- HMF), a versatile, key renewable platform compound is regarded as an important transformation in biomass-derived carbohydrate chemistry. A variety of ILs, not only acidic but also alkaline ILs, were synthesized and used as catalyst in the production of 5-HMF from disaccharide. Several factors including reaction temperature, IL dosage, solvent and reaction time,were found to influence the yield of 5-HMF from cellobiose. Of the ILs tested, hydroxy-functionalized ionic liquid (IL), 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ([AEMIM]BF4) showed the highest catalytic activity and selectivity. 5-HMF yield of 68.71% from sucrose was obtained after 6 hrs at 160 °C. At the same condition with cellobiose as substrate, 5-HMF yield was 24.73%. In addition, 5-HMF also exhibited good stablity in this reaction system. Moreover, a kinetic analysis was carried out in both acidic and alkaline IL-catalyzed system, suggesting main side reaction in the conversion of fructose catalyzed by acidic and alkaline IL was polymerization of fructose and 5-HMF degradation, respectively.

Microwave irradiation--A green and efficient way to pretreat biomass.

As a non-traditional heating way, microwave irradiation (MWI) has long been used for lignocellulose pretreatment with the advent of commercial microwave oven since the 1970s. MWI pretreatment using MWI as heating source is similar to other pretreatment methods. Although MWI pretreatment solves some problems caused by other pretreatment methods, such as low heating rate and thermal efficiency, uneven heating, it brings some new challenges such as reaction vessel selection and pretreatment process design. Over 30 years of development, researchers have achieved good pretreatment performance with MWI which has been applied gradually from laboratory scale to pilot-scale. It should be noted that MWI pretreatment is facing some problems: high cost of pretreatment, short of large-scale equipment, the non-thermal effects in pretreatment is still controversial. If MWI pretreatment reaction mechanism could be further clarified and large-scale industrialized reactor be designed, MWI pretreatment might be widely used in biorefinery.

Comparison on structural modification of industrial lignin by wet ball milling and ionic liquid pretreatment.

As the most abundant aromatic compounds, lignin is still underutilized due to its relatively low quality. In order to improve its quality, two pretreatment technologies, wet ball milling (WBM) and ionic liquid pretreatment (ILP) were tested on the industrial lignin and evaluated on the average molecular weight and polydispersity, surface morphology, and functional groups changes. The results showed that the lignin pretreated by the WBM with phosphoric acid presented dramatic decrease of polydipersity (23%) and increase of phenolic hydroxyl content (9%). While, the ILP treated samples exhibited the significant reduction of the average molecular weight and polydispersity. The decrease on the particle size and the emergence of the porous structure were found when treated with [Emim][OAc]. In addition, the remarkable reduction of the methoxy groups were observed to be 50% and 45% after treated with [Bmim]Cl and [Emim][OAc], respectively.

[Pretreatment of industrial lignin and catalytic conversion into phenol].

Recent concerns about the gradual depletion of conventional fossil resources and the pressure from global climate change have accentuated the need for new alternative feedstock. As one of the main components in biomass, lignin is the second most abundant natural polymer after cellulose, and has the potential to serve as a sustainable source of energy and organic carbon to replace petroleum-based chemicals. Efficient conversion of lignin into high value-added chemicals is crucial to improve the economic feasibility of biomass refinery. In the present study, several pretreatment technologies on industrial lignin were carried out to enhance phenol production. A microwave irradiation assisted biphasic reaction system was used to convert pretreated industrial lignin into phenolic compounds. Lignin conversion, reaction temperature, time and pretreatment method, were optimized. The highest phenol yield was 8.14% obtained from lignin pretreated by 1-ethyl-3-methylimidazolium acetate at 400 W for 60 min in a biophasic system catalyze by 1-aminoethyl-3-methylimidazolium tetrafluoroborate.

Microwave-assisted conversion of microcrystalline cellulose to 5-hydroxymethylfurfural catalyzed by ionic liquids.

Ionic liquid (IL) has been widely investigated in 5-HMF production from biomass. However, most of studies employed IL as reaction solvent which requires a large amount of IL. In the present study, IL was utilized as catalyst in the conversion of microcrystalline cellulose (MCC) to 5-HMF under microwave irradiation (MI) in N,N-dimethylacetamide (DMAc) containing LiCl. 1,1,3,3-tetramethylguanidine (TMG)-based ILs, including 1,1,3,3-tetramethylguanidine tetrafluoroborate ([TMG][BF4]) and 1,1,3,3-tetramethylguanidine lactate ([TMG]L) which were commonly used in the absorption of SO2 and CO2 from flue gas, were synthesized and applied in the conversion of MCC to 5-HMF for the first time. Of the catalysts employed, [TMG]BF4 showed high catalytic activity in 5-HMF production from MCC. The condition including the ratio of IL to MCC, temperature and time for MCC conversion was optimized using Central Composite Design (CCD) and Response Surface Methodology (RSM). The highest 5-HMF yield of 28.63% was achieved with the optimal condition.

Efficient dehydration of glucose to 5-hydroxymethylfurfural catalyzed by the ionic liquid,1-hydroxyethyl-3-methylimidazolium tetrafluoroborate.

The dehydration of fructose or glucose to 5-hydroxymethylfurfural (5-HMF) using room temperature ionic liquids (ILs) as a solvent is a promising method for producing liquid fuels from renewable resources. The IL, 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ([C(2)OHMIM]BF(4)), was used a catalyst-rather than as a solvent-in the conversion of fructose or glucose to 5-HMF. With glucose, the yield of 5-HMF reached as high as 67.3% after 1h at 180°C in dimethylsulfoxide (DMSO) as solvent. The catalyst was separated from the reaction mixture by distilling solvent and reused six times without loss of activity. Furthermore, a kinetic analysis was carried out to illustrate the formation of 5-HMF, and the values of the activation energy and the pre-exponential factor for the reaction were 55.77 kJ mol(-1) and 1.6 × 10(4)min(-1) respectively.

Efficient dehydration of fructose to 5-hydroxymethylfurfural catalyzed by a recyclable sulfonated organic heteropolyacid salt.

The dehydration of fructose to 5-hydroxymethylfurfural (5-HMF) with room temperature ionic liquids (ILs) is a way of producing liquid fuels from renewable resources, but separation of products and IL is energy intensive. In this work, a heteropolyacid salt of an IL-forming cation functionalized with a propanesulfonate group, 1-(3-sulfonicacid)propyl-3-methyl imidazolium phosphotungstate ([MIMPS](3)PW(12)O(40)), was used as a catalyst-rather than as a solvent-in the conversion of fructose to 5-HMF. The maximum yield of 5-HMF was 99.1% at 120°C after 2h using sec-butanol as solvent, and the catalyst was separated from the reaction mixture by a simple process at the end of the reaction and reused six times without loss of activity.