Selective production of chemicals from biomass pyrolysis over metal chlorides supported on zeolite

Direct biomass conversion into chemicals remains a great challenge because of the complexity of the compounds; hence, this process has attracted less attention than conversion into fuel. In this study, we propose a simple one-step method for converting bagasse into furfural (FF) and acetic acid (AC). In this method, bagasse pyrolysis over ZnCl2/HZSM-5 achieved a high FF and AC yield (58.10%) and a 1.01 FF/AC ratio, but a very low yield of medium-boiling point components. However, bagasse pyrolysis using HZSM-5 alone or ZnCl2 alone still remained large amounts of medium-boiling point components or high-boiling point components. The synergistic effect of HZSM-5 and ZnCl2, which combines pyrolysis, zeolite cracking, and Lewis acid-selective catalysis results in highly efficient bagasse conversion into FF and AC. Therefore, our study provides a novel, simple method for directly converting biomass into high-yield useful chemical.

Biohydrogen production from sugarcane bagasse by integrating dark- and photo-fermentation

Hydrogen production from sugarcane bagasse (SCB) by integrating dark-fermentation by Enterobacter aerogenes MTCC 2822 and photo-fermentation by Rhodopseudomonas BHU 01 was investigated. The SCB was hydrolysed by sulphuric acid and the hydrolysate detoxified by passing through adsorbent resin column (Amberlite XAD-4) to remove the inhibitory furfural, and subjected to dark-fermentation. The cellulosic residue from acid hydrolysis was hydrolysed by the new isolate Cellulomonas fimi to release sugars for H2 production by E. aerogenes, through simultaneous saccharification, filtration and fermentation (SSFF). Cumulative H2 production during dark-fermentation and SSFF was 1000 and 613 ml/L, respectively. The spent media of dark-fermentation and SSFF were utilized for photo-fermentation by Rhodopseudomonas BHU 01. The cumulative H2 production was 755 ml/L for dark-fermentation and 351 ml/L for SSFF spent medium.

Catalytic conversion of carbohydrates into 5-hydroxymethylfurfural over cellulose-derived carbonaceous catalyst in ionic liquid

Three environmental-benign and low-cost carbon-based solid acid catalysts containing -SO3H, -COOH and phenolic -OH groups were prepared and used for the conversion of glucose into 5-hydroxymethylfurfural (HMF) in ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl). The results demonstrated that cellulose-derived carbonaceous catalyst (CCC) possessed the highest catalytic activity, which resulted in 46.4% HMF yield at 160°C for only 15 min. In addition, the reaction kinetics for the conversion of glucose into HMF over CCC was fitted with the first-order rate equation. The slightly-deactivated CCC after four successive reaction runs could be easily regenerated by a simple carbonization and sulfonation process. More gratifyingly, the combination of CCC and [BMIM]Cl were confirmed to be suitable for converting other carbohydrates such as fructose, sucrose, maltose, cellobiose, starch and cellulose into HMF. Particularly, a plausible mechanism involving hydrolysis, isomerization and dehydration for the conversion of carbohydrates into HMF was also proposed.

Production of furfural from pentosan-rich biomass: analysis of process parameters during simultaneous furfural stripping

Among the furan-based compounds, furfural (FUR) shows interesting properties as building-block or industrial solvent. It is produced from pentosan-rich biomass via xylose cyclodehydration. The current FUR production makes use of homogeneous catalysts and excessive amounts of steam. The development of greener furfural production and separation techniques implies the use of heterogeneous catalysts and innovative separation processes. This work deals with the conversion of corncobs as xylose source to be dehydrated to furfural. The results reveal differences between the use of direct corncob hydrolysis and dehydration to furfural and the prehydrolysis and dehydration procedures. Moreover, this work focuses on an economical analysis of the main process parameters during N2-stripping and its economical comparison to the current steam-stripping process. The results show a considerable reduction of the annual utility costs due to use of recyclable nitrogen and the reduction of the furfural purification stages.

Effects of Kraft lignin on hydrolysis/dehydration of sugars, cellulosic and lignocellulosic biomass under hot compressed water

The effect of Kraft lignin presenting on the hydrolysis and dehydration of C5 and C6 sugars, cellulose, hemicelluloses and biomass under hot compressed water (HCW) in the presence of H3PO4 catalyst was intensively studied. The lignin strongly inhibited the acid hydrolysis of cellulose and hemicellulose to glucose and xylose, respectively. Interestingly, the admixed lignin markedly promoted the isomerization of glucose to fructose, and dehydration of fructose (except at the low catalyst loading), resulting in high 5-hydroxymethylfurfural yields. Nonetheless, lignin inhibited the hydrolysis of xylan to xylose and dehydration of xylose to furfural. Moreover, the acidity of the system significantly affects the hydrolysis/dehydration of biomass. It was revealed that the presence of lignin strongly interfered the yields of sugars and furans produced from raw corncob, while the delignified corncob provided significant improvement of product yields, confirming the observed role of lignin in the biomass conversion system via sugar platforms.

Immobilizing Cr3+ with SO3H-functionalized solid polymeric ionic liquids as efficient and reusable catalysts for selective transformation of carbohydrates into 5-hydroxymethylfurfural

A series of functional polymeric ionic liquids (FPILs) were prepared by coupling of SO3H-functionalized polymeric ionic liquids with different counterpart anions containing or excluding CrCl3·6H2O, and characterized by SEM, FT-IR, XRD, NH3-TPD, TG, melting point, ICP-AES, and TEM. The catalytic activity of the prepared solid FPILs was investigated for the conversion of biomass including fructose, glucose and cellulose into 5-hydroxymethylfurfural (HMF) with the presence of DMSO-mediated solvents, successively producing moderate to excellent yields of HMF under atmospheric pressure. The FPILs catalysts developed in this study present improved performance on fructose-to-HMF conversion over other solid catalysts, such as functional ionic liquids supported by silica, metal oxides and strong acid ion exchange resin catalysts, and can be very easily recycled at least five times without significant loss of activity. In addition, a kinetic analysis was carried out to illustrate the formation of HMF.

Co-production of furfural and acetic acid from corncob using ZnCl2 through fast pyrolysis in a fluidized bed reactor

Corncob was pyrolyzed using ZnCl2 in a pyrolysis plant equipped with a fluidized bed reactor to co-produce furfural and acetic acid. The effects of reaction conditions, the ZnCl2 content and contacting method of ZnCl2 with corncob on the yields of furfural and acetic acid were investigated. The pyrolysis was performed within the temperature range between 310 and 410°C, and the bio-oil yield were 30-60 wt% of the product. The furfural yield increased up to 8.2 wt%. The acetic acid yield was maximized with a value of 13.1 wt%. A lower feed rate in the presence of ZnCl2 was advantageous for the production of acetic acid. The fast pyrolysis of a smaller corncob sample mechanically mixed with 20 wt% of ZnCl2 gave rise to a distinct increase in furfural. A high selectivity for furfural and acetic acid in bio-oil would make the pyrolysis of corncob with ZnCl2 very economically attractive.

Dilute sulfuric acid pretreatment of corn stover for enzymatic hydrolysis and efficient ethanol production by recombinant Escherichia coli FBR5 without detoxification

A pretreatment strategy for dilute H2SO4 pretreatment of corn stover was developed for the purpose of reducing the generation of inhibitory substances during pretreatment so that a detoxification step is not required prior to fermentation while maximizing sugar yield. The optimal conditions for pretreatment of corn stover (10%, w/v) were: 0.75% H2SO4, 160°C, and 0-5 min holding time. The conditions were chosen based on maximum glucose release after enzymatic hydrolysis, minimum loss of pentose sugars and minimum formation of sugar degradation products such as furfural and hydroxymethyl furfural. The pretreated corn stover after enzymatic saccharification generated 63.2 ± 2.2 and 63.7 ± 2.3 g total sugars per L at 0 and 5 min holding time, respectively. Furfural production was 0.45 ± 0.1 and 0.87 ± 0.4 g/L, respectively. The recombinant Escherichia coli strain FBR5 efficiently fermented non-detoxified corn stover hydrolyzate if the furfural content is <0.5 g/L.

Simultaneous analysis of furfural metabolites from Rehmanniae radix preparata by HPLC-DAD-ESI-MS

A method based on HPLC with diode array detector (DAD) and electrospray ionisation mass spectrometry (ESI-MS) was established for the simultaneous determination of 5-HMF and its derivatives, including a new 5-HMF derivative, in Rehmanniae radix preparata. Validation parameters, such as linearity, limit of detection, limit of quantification, recovery, accuracy, and precision, were successfully obtained. In addition, the efficiencies of diverse extraction methods were compared for the development of a standard analytical method. The verified method was successfully applied to the quantitative determination of four representative metabolites in eighteen R. radix preparata samples from Korea and China. Additionally, the increase in the amount of 5-HMF derivatives was monitored during the processing of three dried R. radix samples. The results showed that a newly isolated diglycosylated 5-HMF derivative, 5-(α-D-galactopyranosyl-(1→6)-α-D-galactopyranosyloxymethyl)-2-furancarboxaldehyde, appeared in concentrations comparable to that of 5-HMF, suggesting its potential to serve as a marker compound in R. radix preparata.

Biotransformation of 5-hydroxymethylfurfural (HMF) by Scheffersomyces stipitis during ethanol fermentation of hydrolysate of the seaweed Gelidium amansii

The seaweed, Gelidium amansii, was fermented to produce bioethanol. Optimal pretreatment condition was determined as 94 mM H2SO4 and 10% (w/v) seaweed slurry at 121°C for 60 min. The mono sugars of 43.5 g/L with 57.4% of conversion from total carbohydrate of 75.8 g/L with G. amansii slurry 100g dcw/L were obtained by thermal acid hydrolysis pretreatment and enzymatic saccharification. G. amansii hydrolysate was used as the substrate for ethanol production by separate hydrolysis and fermentation (SHF). The ethanol concentration of 20.5 g/L was produced by Scheffersomyces stipitis KCTC 7228. The effect of HMF on ethanol production by S. stipitis KCTC 7228 was evaluated and 5-hydroxymethylfurfural (HMF) was converted to 2,5-bis-hydroxymethylfuran. The accumulated 2,5-bis-hydroxymethylfuran in the medium did not affect galactose and glucose uptakes and ethanol production. Biotransformation of HMF to less inhibitory compounds by S. stipitis KCTC 7228 could enhance overall fermentation yields of seaweed hydrolysates to ethanol.

A new correction method for determination on carbohydrates in lignocellulosic biomass

The accurate determination on the key components in lignocellulosic biomass is the premise of pretreatment and bioconversion. Currently, the widely used 72% H2SO4 two-step hydrolysis quantitative saccharification (QS) procedure uses loss coefficient of monosaccharide standards to correct monosaccharide loss in the secondary hydrolysis (SH) of QS and may result in excessive correction. By studying the quantitative relationships of glucose and xylose losses during special hydrolysis conditions and the HMF and furfural productions, a simple correction on the monosaccharide loss from both PH and SH was established by using HMF and furfural as the calibrators. This method was used to the component determination on corn stover, Miscanthus and cotton stalk (raw materials and pretreated) and compared to the NREL method. It has been proved that this method can avoid excessive correction on the samples with high-carbohydrate contents.

High temperature and low acid pretreatment and agarase treatment of agarose for the production of sugar and ethanol from red seaweed biomass

To obtain fermentable sugar from agarose, pretreatment of agarose by using acetic acid was conducted for short durations (10-30 min) at low acid concentrations (1-5% (w/v)) and high temperatures (110-130 °C). On testing the pretreated agarose by using an endo-β-agarase I (DagA), an exo-β-agarase II (Aga50D), and neoagarobiose hydrolase (NABH), we observed that the addition of the endo-type agarase did not increase the sugar yield. Use of the crude enzyme of Vibrio sp. EJY3 in combination with Aga50D and NABH including acetic acid pretreatment resulted in a 1.3-fold increase in the final reducing sugar yield (62.8% of theoretical maximum based on galactose and 3,6-anhydrogalactose in the initial agarose), compared to those obtained using Aga50D and NABH only after acetic acid pretreatment. The simultaneous saccharification and fermentation of pretreated agarose yielded ethanol of 37.1% theoretical maximum yield from galactose contained in the pretreated agarose.

Solid acids as catalysts for the conversion of D-xylose, xylan and lignocellulosics into furfural in ionic liquid

With the aim to develop an ecologically viable catalytic pathway for furfural production without the use of inorganic acids, H3PW12O40, Amberlyst-5 and NKC-9 (macroporous styrene-based sulfonic acid resin) were used as catalysts for producing furfural from xylose, xylan and lignocellulosic biomass in [BMIM]Cl under microwave irradiation at atmospheric pressure. A surprisingly high furfural yield of 93.7% from xylan was obtained by H3PW12O40 at 160 °C in 10 min. The degradation of furfural affected by single addition of [BMIM]Cl and solid acids was also investigated. The IL could be easily recycled and reused with stable solvent capacity for multiple runs (5×) after the product furfural was extracted with ethyl acetate.

Efficient catalytic system for the conversion of fructose into 5-ethoxymethylfurfural

DMSO can improve the selectivity of 5-hydroxymethylfurfural (HMF) in the conversion of carbohydrates. However, one of the bottlenecks in its application is product separation. Thus a one-pot synthesis of 5-ethoxymethylfurfural (EMF) rather than HMF from fructose in ethanol-DMSO was investigated. Phosphotungstic acid was used as an effective catalyst. The yield of EMF can be reached as high as 64% in the mixed solvent system of DMSO and ethanol within 130 min at 140 °C. Ethyl levulinate (LAE) was detected as the main by-product, the yield of which increased with the reaction time, temperature and the amount of catalyst. In addition, the existence of water could significantly reduce the yield of EMF and increased the yield of LAE. Most importantly, it was discovered that EMF could be much more efficiently extracted from the reaction solvent system by some organic solvents than HMF.

Optimization of furfural production from D-xylose with formic acid as catalyst in a reactive extraction system

Furfural is one of the most promising platform chemicals derived from biomass. In this study, response surface methodology (RSM) was utilized to determine four important parameters including reaction temperature (170-210°C), formic acid concentration (5-25 g/L), o-nitrotoluene volume percentage (20-80 vt.%), and residence time (40-200 min). The maximum furfural yield of 74% and selectivity of 86% were achieved at 190°C for 20 g/L formic acid concentration and 75 vt.% o-nitrotoluene by 75 min. The high boiling solvent, o-nitrotoluene, was recommended as extraction solvent in a reactive extraction system to obtain high furfural yield and reduce furfural-solvent separation costs. Although the addition of halides to the xylose solutions enhanced the furfural yield and selectivity, the concentration of halides was not an important factor on the furfural yield and selectivity.

The dehydration of fructose to 5-hydroxymethylfurfural efficiently catalyzed by acidic ion-exchange resin in ionic liquid

The efficient dehydration of fructose to 5-hydroxymethylfurfural (HMF) was developed in ionic liquids (ILs) with acidic ion-exchange resins as catalyst. By screening different resins and ILs respectively, it was found that the structure of resins and ILs had a prominent effect on the dehydration of fructose. In 1-butyl-3-methylimidazolium chloride ([Bmim]Cl), D001-cc resin showed a high activity. And then the effects of reaction temperatures, dosages of D001-cc, and different initial fructose loadings on the dehydration of fructose were studied in detail. The system of D001-cc resin and [Bmim]Cl exhibited a constant activity at 75°C for 20 min and a 86.2% yield of HMF was obtained after seven recycles. At 75°C for 20 min, a 93.0% yield of HMF from the dehydration of fructose was obtained.

Sugarcane bagasse ozonolysis pretreatment: effect on enzymatic digestibility and inhibitory compound formation

Sugarcane bagasse was pretreated with ozone to increase lignocellulosic material digestibility. Bagasse was ozonated in a fixed bed reactor at room temperature, and the effect of the two major parameters, ozone concentration and sample moisture, was studied. Acid insoluble and total lignin decreased whereas acid soluble lignin increased in all experiments. Pretreatment barely attacked carbohydrates, with cellulose and xylan recovery rates being >92%. Ozonolysis increased fermentable carbohydrate release considerably during enzymatic hydrolysis. Glucose and xylose yields increased from 6.64% and 2.05%, for raw bagasse, to 41.79% and 52.44% under the best experimental conditions. Only xylitol, lactic, formic and acetic acid degradation compounds were found, with neither furfural nor HMF (5-hydroxymethylfurfural) being detected. Washing detoxification provided inhibitor removal percentages above 85%, increasing glucose hydrolysis, but decreasing xylose yield by xylan solubilization. SEM analysis showed structural changes after ozonization and washing.

Cyclopentyl methyl ether: a green co-solvent for the selective dehydration of lignocellulosic pentoses to furfural

The effects of cyclopentyl methyl ether (CPME) addition during the aqueous xylose dehydration reaction to furfural are reported here. These investigations were conducted by using pure xylose and Cynara cardunculus (cardoon) lignocellulose as sugar source and H(2)SO(4) as catalyst. The research was also applied to aqueous solutions containing NaCl, since it has been previously demonstrated that NaCl incorporation to these reaction mixtures remarkably increases the furfural formation rate. It has been found that CPME incorporation inhibits the formation of undesired products (resins, condensation products and humins). Thus, cardoon lignocellulosic pentoses were selectively transformed into furfural (near 100%) at the following reaction conditions: 1 wt.% H(2)SO(4), 4 wt.% biomass referred to aqueous solution, 30 min reaction, 443 K, CPME/aqueous phase mass ratio equals to 2.33, and NaCl/aqueous solution mass ratio of 0.4. In contrast, no effect was observed for cellulosic glucose transformation into hydroxymethylfurfural and levulinic acid at identical reaction conditions.

Hydrothermal pentose to furfural conversion and simultaneous extraction with SC-CO2--kinetics and application to biomass hydrolysates

This work explores hydrothermal d-xylose and hemicellulose to furfural conversion coupled with simultaneous furfural extraction by SC-CO(2) and the underlying reaction pathway. A maximum furfural yield of 68% was attained from d-xylose at 230°C and 12MPa. Additionally missing kinetic data for l-arabinose to furfural conversion was provided, showing close similarity to d-xylose. Furfural yields from straw and brewery waste hydrolysates were significantly lower than those obtained from model compounds, indicating side reactions with other hydrolysate components. Simultaneous furfural extraction by SC-CO(2) significantly increased extraction yield in all cases. The results indicate that furfural reacts with intermediates of pentose dehydration. The proposed processing route can be well integrated into existing lignocellulose biorefinery concepts.

FeCl3 and acetic acid co-catalyzed hydrolysis of corncob for improving furfural production and lignin removal from residue

In order to increase furfural yield and lignin removal, both FeCl(3) and acetic acid were used to co-catalyze the hydrolysis of corncob. A series of experiments were carried out to investigate the effects of acetic acid, FeCl(3) concentrations and temperatures on furfural production and residue characteristics. The results showed that high FeCl(3) concentrations caused serious cellulose degradation while acetic acid was more effective for lignin removal. A maximum furfural yield of 67.89% (35.74% higher than that in conventional sulfuric acid-catalyzed process) was obtained at 180°C in the presence of 20mM of FeCl(3) and 3% of acetic acid. Simultaneously, lignin removal reached 54.79%, and 74.29% of the cellulose was remained for further utilization. Acetic acid and FeCl(3) co-catalyzed hydrolysis was not only a high efficiency and environmental friendly technique, but also provided a possibility to utilize the furfural residue for ethanol production and other industries.

Comparison of seven types of thermo-chemical pretreatments on the structural features and anaerobic digestion of sunflower stalks

Sunflower stalks can be used for the production of methane, but their recalcitrant structure requires the use of thermo-chemical pretreatments. Two thermal (55 and 170°C) and five thermo-chemical pretreatments (NaOH, H(2)O(2), Ca(OH)(2), HCl and FeCl(3)) were carried out, followed by anaerobic digestion. The highest methane production (259 ± 6 mL CH(4)g(-1) VS) was achieved after pretreatment at 55°C with 4% NaOH for 24h. Acidic pretreatments at 170°C removed more than 90% of hemicelluloses and uronic acids whereas alkaline and oxidative pretreatments were more effective in dissolving lignin. However, no pretreatment was effective in reducing the crystallinity of cellulose. Methane production rate was positively correlated with the amount of solubilized matter whereas methane potential was negatively correlated with the amount of lignin. Considering that the major challenge is obtaining increased methane potential, alkaline pretreatments can be recommended in order to optimize the anaerobic digestion of lignocellulosic substrates.

[Furfural degradation by filamentous fungus Amorphotheca resinae ZN1]

Some degradation products from lignocellulose pretreatment strongly inhibit the activities of cellulolytic enzymes and ethanol fermentation strains, thus the efficient removal of the inhibitor substances ("detoxification") is the inevitable step for the biotransformation processes. In this study, the biological detoxification of furfural by a newly isolated fungus, Amorphotheca resinae ZN1, was studied and the metabolic pathways of furfural degradation was analyzed. The metabolic pathway of furfural degradation in A. resinae ZN1 was described as follows: first, furfural was quickly converted into the low toxic furfuryl alcohol; then the furfuryl alcohol was gradually converted into furfural again but under the low concentration under aerobic condition, which was not lethal to the growth of the fungi; furfural continued to be oxidized to furoic acid by A. resinae ZN1. It is likely that furoic acid was further degraded in the TCA cycle to complete the biological degradation of furfural. The present study provided the important experimental basis for speeding up the biodetoxification of furfural by A. resinae ZN1 and the rate-limiting step in the lignocellulose biotransformation to ethanol.

Deletion of the PHO13 gene in Saccharomyces cerevisiae improves ethanol production from lignocellulosic hydrolysate in the presence of acetic and formic acids, and furfural

For efficient bioethanol production from lignocellulosic biomass by Saccharomyces cerevisiae, it is necessary to improve cellular tolerance to toxic compounds released during the pretreatment of biomass. The gene encoding p-nitrophenylphosphatase, PHO13, was disrupted in a recombinant xylose-fermenting S. cerevisiae strain, which improved ethanol production from xylose in the presence of three major inhibitors, acetic and formic acids, and furfural. In medium supplemented with 30 mM acetic acid, the ethanol yield obtained by the ΔPHO13 mutant was 0.45 g-ethanol/g-xylose. Notably, the specific ethanol productivity of the mutant in the presence of 90 mM furfural was fourfold higher than that of the control strain. The PHO13-disrupted strain produced ethanol from rice straw hydrolysate obtained by liquid hot-water pretreatment with a greater than fourfold higher xylose consumption rate than the control. Together, our findings demonstrate that PHO13 deletion is a simple, but effective, approach for improving cellulosic bioethanol production by S. cerevisiae.

Conversion of fructose and glucose into 5-hydroxymethylfurfural with lignin-derived carbonaceous catalyst under microwave irradiation in dimethyl sulfoxide-ionic liquid mixtures

5-Hydroxymethylfurfural (5-HMF) was successfully produced by the dehydration of fructose and glucose using lignin-derived solid acid catalyst in DMSO-[BMIM][Cl] (dimethyl sulfoxide and 1-butyl-3-methylimidazolium chloride) mixtures. Six solid acid catalysts were synthesized by carbonization and sulfonation of raw biomass materials, i.e., glucose, fructose, cellulose, lignin, bamboo and Jatropha hulls. It was found that lignin-derived solid acid catalyst (LCC) was the most active one in the dehydration of sugars. LCC coupled with microwave irradiation was used for the 5-HMF production, 84% 5-HMF yield with 98% fructose conversion rate was achieved at 110°C for 10 min. Furthermore, 99% glucose was converted with 68% 5-HMF yield under severer condition (160°C for 50 min). LCC was recycled for five times, 5-HMF yield declined only 7%. Use of LCC combined with DMSO-[BMIM][Cl] solution and microwave irradiation is a novel method for the effective production of 5-HMF.

Synergistic conversion of glucose into 5-hydroxymethylfurfural in ionic liquid-water mixtures

A method for converting glucose into 5-hydroxymethylfurfural (5-HMF) without using chromium-containing catalysts was developed. The method uses ionic liquid-water mixtures with a ZrO(2) catalyst. Addition of a certain amount of water (10-50 wt.%) into the 1,3-dialkylimidazolium chloride ionic liquid promoted the formation of 5-HMF from glucose compared with that in either pure water or in the pure ionic liquid. A 5-HMF yield of 53% was obtained within 10 min at 200 °C in a 50:50 w/w% 1-hexyl-3-methyl imidazolium chloride-water mixture in the presence of ZrO(2). The 1,3-dialkylimidazolium ionic liquids having Cl(-) or HSO(4)(-) anions were effective for promoting 5-HMF formation. Addition of protic solvents such as methanol and ethanol to the ionic liquid had a similar synergistic effect as water and promoted fructose and 5-HMF formation. The results reported in this work can be extended to other fields, where the ratio of ionic liquid and protic solvent can be adjusted to promote the desired reactions.