Production Of Carboxylic Acids Research Articles

Regulation on C2-C8 carboxylic acid biosynthesis from anaerobic CO2 fermentation.

Bioconversion of CO2 into liquid fuels or chemicals, preferred medium chain carboxylic acids (caproic and caprylic acid), is an attractive CO2 utilization technology. The present study aims to investigate the effects of different ratios of H2/CO2 on regulating the distribution of C2-C8 carboxylic acid products, while the headspace pressure of 1.5bar was set to amplify the effect of different ratios. The H2/CO2 ratio of 4:1 was more suitable for preparing acetic acid, where the highest acetic acid yield was 17.5g/L. And the H2/CO2 ratio of 2:1 showed excellent chain elongation ability with the highest n-caprylic yield of 2.4g/L. Additionally, the actual H2/CO2 ratios of 4:1 reactors were higher than that in 2:1 may be course chain elongation often accompanied by H2 production. The 16S rRNA genes analysis shows that the genus Terrisporobacter and Coriobacteriales may be related to acetic acid production enriched in H2/CO2 ratio 4:1 reactors, and the genus Clostridium and Paenibacillaceae may associate with the chain elongation pathway were enriched in H2/CO2 ratio 2:1 reactors.

Deciphering the role and mechanism of nano zero-valent iron on medium chain fatty acids production from CO2 via chain elongation in microbial electrosynthesis

The integrated system of microbial electrosynthesis (MES) coupled with chain elongation has been considered a promising platform for carboxylic acids production. However, this biotechnology is still in its infancy, and many limitations are needed to be transcended, such as low electron transfer efficiency between cathode and microbes. In this study, nano zero-valent iron (NZVI) was employed to improve carboxylic acid production in the integrated system, and the promotion mechanisms were revealed. Results suggested that the highest production concentrations of acetate, butyrate, and caproate were observed at 7.5 g/L optimized NZVI dosage, increasing the total yield and coulomb efficiency by 23.7 % and 40.3 % compared to the control. Mechanism studies indicated that the hydrogen and electron released by the anaerobic corrosion of NZVI could be used as additional reducing equivalents, thereby enhancing the electron transfer performance. Besides, NZVI was also proven to facilitate the formation of electroactive biofilms according to the results of biofilm characterization and total DNA. In functional microbes' respect, the moderate NZVI enriched the chain elongator in biofilm, like Clostridium_sensu-stricto_12, and upregulated the activities of key enzymes of homoacetogenesis and chain elongation metabolic pathways, like carbon-monoxide dehydrogenase and hydroxyacyl-CoA dehydratase. This study provided the evidence and revealed how NZVI assisted carboxylic acid production from CO2 via chain elongation in MES.

Bio-refinery of xylose processing wastes for green polymalic acid production and l-malic acid recovery by engineered Aureobasidium pullulans in a non-waste-disposal system

Commercial carboxylic acid fermentation is susceptible to CaSO4 solid waste pollution owing to the heavy use of neutralizer CaCO3. Polymalic acid (PMA), a biodegradable polyester generated from the fungus Aureobasidium pullulans, has attracted attention in the bioplastic and biomedical fields and is easily hydrolyzed to release the monomer l-malic acid (L-MA). This study evaluated the feasibility of using waste xylose-containing mother liquor (WXML) for efficient PMA fermentation under low pH control and L-MA recovery in a non-waste-disposal system. Herein, the multi-adaptive evolution of A. pullulans under high concentrations of WXML, coupled with low pH, was demonstrated. Subsequently, an engineered calcineurin signaling pathway overexpressing the exogenous cnb gene from Beauveria bassiana was employed to further regulate cell tolerance. A mutant strain AE-59 was obtained, and a comparable PMA titer of 49.47 ± 0.48 g/L and a yield of 0.33 g/g at low pH control with Na2CO3 in a 5-L fermenter were achieved. Finally, the direct-aqueous-phase-crystal method was employed to obtain 78.55 % of the total L-MA (with a purity of 95.4 %) from the acidic downstream broth using a low dosage of sulfuric acid for acid hydrolysis. This result showed the feasibility of L-MA production in the low-pH control mode with Na2CO3 without solid waste CaSO4. In conclusion, this study overcomes the major obstacles of calcium waste pollution for future industrial fermentative L-MA production and provides a green and sustainable route from lignocellulosic biorefinery for the production of future biopolymers and carboxylic acids.

Oxidation of Phenolic Aldehydes by Ozone and Hydroxyl Radicals at the Air-Solid Interface.

Biomass burning emissions contain abundant phenolic aldehydes (e.g., syringaldehyde, vanillin, and 4-hydroxybenaldehyde) that are oxidized during atmospheric transport, altering the physicochemical properties of particulates. Herein, the oxidative processing of thin films made of syringaldehyde, vanillin, and 4-hydroxybenaldehyde is studied at the air-solid interface under a variable O3(g) molar ratio (410 ppbv-800 ppmv) and relative humidity (0-90%). Experiments monitored the absorption changes of C=C, C=O, and -COOH vibration changes during the oxidation of thin films by transmission Fourier transform infrared spectroscopy (FTIR). Selected spectroscopic features of aromatic ring cleavage by O3(g) revealed the production of carboxylic acids. Instead, monitoring O-H stretching provided a comparison of a hydroxylation channel from in situ produced hydroxyl radical. The overall oxidation reactivity trend syringaldehyde > vanillin > 4-hydroxybenzladehyde can be explained based on the additional electron density from methoxide substituents to the ring. The reactive uptake coefficient of O3(g) increases for higher relative humidity, e.g., for syringaldehyde by 18 and 215 times at 74% and 90% relative humidity (RH), respectively, as compared to dry conditions. A Langmuir-Hinshelwood mechanism fits well the kinetics of oxidation under a variable O3(g) molar ratio at 74% RH, providing useful information that should be included in atmospheric chemistry models.

CO2 Chemisorption Behavior in Conjugated Carbanion-Derived Ionic Liquids via Carboxylic Acid Formation.

Superbase-derived task-specific ionic liquids (STSILs) represent one of the most attractive and extensively studied systems in carbon capture via chemisorption, in which the obtained CO2 uptake capacity has a strong relationship with the basicity of the anions. High energy input in desorption and side reactions caused by the strong basicity of the anions are still unsolved issues. The development of other customized STSILs leveraging an alternative driving force to achieve efficient CO2 chemisorption/desorption is highly desirable yet challenging. In this work, carbanion-derived STSILs were developed for efficient CO2 chemisorption via a carboxylic acid formation pathway. The STSIL with the deprotonated malononitrile molecule ([MN]) as the anion exhibited much higher CO2 uptake capacity than the one derived from 2-methylmalononitrile ([MMN]). Notably, this trend was opposite to their basicity ([MN] < [MMN]). Detailed characterization of the products, supported by density functional theory simulations of spectra and calculations of the reaction energetics, demonstrated that carboxylic acid was formed upon reacting with CO2 via proton transfer in [MN]-derived STSILs but not in the case of [MMN] due to lack of an α-H. The preference of the carboxylic acid product over carboxylate formation was driven by the extended conjugation among the central sp2 carbon, the as-formed carboxylic acid, and the two nitrile groups. The achievements made in this work provide an alternative design principle of STSILs by leveraging the extended conjugation in the CO2-integrated product.

Scaling up carboxylic acid production from cheese whey and brewery wastewater via methane-arrested anaerobic digestion

In a circular economy, organic waste streams are valuable resources for sustainably producing chemicals and fuels. This study investigates a new methane-arrested anaerobic digestion (MAAD) process that converts high-strength cheese whey and brewery wastewater into carboxylic acids. The process was developed and optimized under various bench-scale semi-continuous (fed-batch) operating conditions (e.g., retention time, organic loading rate, pH, and feed/harvest frequency). The MAAD responses to various control-failure scenarios were also systematically investigated. The highest total acid productivity was 26 g/(Lliq⋅d) with a substrate conversion of 0.79 g CODdigested/g CODfed at a hydraulic retention time (HRT) of approximately 2 d in a 14-L digester. The most stable conditions for digester operation (HRT 3 d at pH 6.0 and 40 °C) were selected for process scale-up to 100 gal (∼380 L). Semi-continuous, pilot-scale MAAD successfully produced a total acid concentration of 40.6 ± 1.1 g/L with 8.1 % acetic acid, 45.1 % butyric acid, and 44.5 % lactic acid. The links between wastewater characteristics, operation mode, digester scale, and microbial community structure were statistically analyzed. The results show genera Sporolactobacillus and Clostridium positively correlate with butyric acid production (Pearson correlation coefficient >0.5). Moreover, four kinetic models were developed and fit to batch MAAD experimental datasets (R2 > 95 %) and were successfully applied to predict the total acid production in both bench- and pilot-scale semi-continuous MAADs. This study shows MAAD has the potential for industrial-scale applications and is a robust platform to valorize low- or negative-value waste streams into high-value bioproducts.

In vitro metabolic fate of the synthetic cannabinoid receptor agonists (quinolin-8-yl 4-methyl-3-(morpholine-4-sulfonyl)benzoate [QMMSB]) and (quinolin-8-yl 4-methyl-3-((propan-2-yl)sulfamoyl)benzoate [QMiPSB]) including isozyme mapping and carboxylesterases activity testing.

The synthetic cannabinoid receptor agonists (SCRAs) (quinolin-8-yl 4-methyl-3-(morpholine-4-sulfonyl)benzoate [QMMSB]) and (quinolin-8-yl 4-methyl-3-((propan-2-yl)sulfamoyl)benzoate [QMiPSB], also known as SGT-46) are based on the structure of quinolin-8-yl 4-methyl-3-(piperidine-1-sulfonyl)benzoate (QMPSB) that has been identified on seized plant material in 2011. In clinical toxicology, knowledge of the metabolic fate is important for their identification in biosamples. Therefore, the aim of this study was the identification of in vitro Phase I and II metabolites of QMMSB and QMiPSB in pooled human liver S9 fraction (pHLS9) incubations for use as screening targets. In addition, the involvement of human monooxygenases and human carboxylesterases (hCES) was examined. Analyses were performed by liquid chromatography coupled with high-resolution tandem mass spectrometry. Ester hydrolysis was found to be an important step in the Phase I metabolism of both SCRAs, with the carboxylic acid product being found only in negative ionization mode. Monohydroxy and N-dealkyl metabolites of the ester hydrolysis products were detected as well as glucuronides. CYP2C8, CYP2C9, CYP3A4, and CYP3A5 were involved in hydroxylation. Whereas enzymatic ester hydrolysis of QMiPSB was mainly catalyzed by hCES1 isoforms, nonenzymatic ester hydrolysis was also observed. The results suggest that ester hydrolysis products of QMMSB and QMiPSB and their glucuronides are suitable targets for toxicological screenings. The additional use of the negative ionization mode is recommended to increase detectability of analytes. Different cytochrome P450 (CYP) isozymes were involved in the metabolism; thus, the probability of drug-drug interactions due to CYP inhibition can be assessed as low.

Extraction performance evaluation of amide-based deep eutectic solvents for carboxylic acid: Molecular dynamics simulations and a mini-pilot study

Carboxylic acids are important precursors of chemical raw materials produced from the bioconversion of renewable feedstocks. In these processes, the separation of carboxylic acid products from fermentation broth is of great significance and challenge. In this research, the extraction performance of carboxylic acid using novel hydrophobic deep eutectic solvents (DESs) composed of amides and geraniol was studied. Molecular dynamics (MD) simulations have also been adopted to understand the extraction mechanism. Radial and combined distribution functions analysis shows that hydrogen bond-induced geraniol-carboxylic acid and amide-carboxylic acid multi-molecular assembly drives the separation of carboxylic acids from fermentation broth. Thermodynamics and mean square displacement calculations show that increasing temperature breaks the hydrogen bond networks, and the hydrophobic DESs can be recycled. Finally, a mini-pilot experiment for lactic acid recovery from fermentation broth verified the effectiveness of the amide-based DESs and their application to practice. These findings provide references for industrial-scale production of carboxylic acid separation.

Highly selective butyric acid production by coupled acidogenesis and ion substitution electrodialysis

Selective production of carboxylic acids (CAs) from mixed culture fermentation remains a difficult task in organic waste valorization. Herein, we developed a facile and sustainable carbon loop strategy to regulate the fermentation micro-environment and steer acidogenesis towards selective butyric acid production. This new ion substitution electrodialysis-anaerobic membrane bioreactor (ISED-AnMBR) integrated system demonstrated a high butyric acid production at 11.19 g/L with a mass fraction of 76.05%. In comparison, only 1.04 g/L with a mass fraction of 30.56% was observed in the uncoupled control reactor. The carbon recovery reached a maximum of 96.09% with the assistance of ISED. Inorganic carbon assimilation was believed to be an important contributor, which was verified by 13C isotopic tracing. Microbial community structure shows the dominance of Clostridia (80.16%) in the unique micro-environment (e.g., pH 4.80–5.50) controlled by ISED, which is believed beneficial to the growth of such fermentative bacteria with main products of butyric acid and acetic acid. In addition, the emergence of chain elongators such as Clostridium sensu stricto 12 was observed to have a great influence on butyric acid production. This work provides a new approach to generate tailored longer chain carboxylic acids from organic waste with high titer thus contributing to a circular economy.

Ultrasound-sodium percarbonate effectively promotes short-chain carboxylic acids production from sewage sludge through anaerobic fermentation

Short-chain carboxylic acids (SCCAs) production from sewage sludge via anaerobic fermentation is usually restricted by low substrates availability and rapid products consumption. Therefore, the ultrasound (US)-sodium percarbonate (SPC) technique was proposed to effectively break the bottlenecks. Results showed the total SCCAs yield, acetate yield and particulate organics reduction respectively attained 392.8 mg COD/g VSS, 204.6 mg COD/g VSS and 47.4 % under the optimal condition. Mechanistic explorations disclosed that US + SPC largely reduced biodegradation resistances of particulate organics and improved sludge biodegradability. The destruction of spatial structure was the inherent mechanisms for initial solubilization and further degradation of solid-phase sludge. Besides, US + SCP up-regulated hydrolytic and SCCAs-forming enzymes, but downregulated the key enzyme for methanation. Meanwhile, US + SPC altered the microbial structure and stimulated functional microorganism enrichment, well correlated with substrate biotransformation and products output. Overall, this strategy could effectively enhance SCCAs production from WAS and reduce the environmental risk for subsequent sludge disposal.

Predicting the performance of medium-chain carboxylic acid (MCCA) production using machine learning algorithms and microbial community data

The carboxylate platform-based bioprocess for medium-chain carboxylic acid (MCCA) production from waste biomass via mixed culture has been the subject of extensive research because of the high economic value of MCCA and potential environmental benefits. However, modeling the conversion process using mechanistic models is challenging due to the complex and unclear interactions and metabolic pathways of the system. Herein, four data-driven machine learning (ML) algorithms, including random forest (RF), extreme gradient boosting (Xgboost), k-nearest neighbor (KNN), and artificial neural network (ANN), were employed to predict the MCCA concentration and production rate based on data (environmental and operational parameters and corresponding genomic data) collected under 94 experiment conditions from 8 research groups. It was found that all selected ML algorithms achieved prediction accuracy higher than 0.7 using operational parameters only. A significant improvement in the predictive efficacy (ranging from 0.83 to 0.87) was observed when incorporating the genomic data with environmental and operational parameters. The prediction of MCCA production by the random forest (RF) model had the highest prediction accuracy of 0.83, 0.87, and 0.89 when the operational parameters, genomic data, and combined dataset were used as input parameters, respectively. Hydraulic retention time (HRT) and organic loading rate (OLR) were identified as the dominant operational parameters that affect the MCCA concentration and rate based on the feature importance generated by RF. The key microbes that affected the MCCA concentration and MCCA production rate were different. Bacteroidales and Coriobacteriales were the only orders sensitive to both the MCCA concentration and rate, with feature importance weights of 6.71% and 6.97%, respectively, and could be potential universal biomarkers for process monitoring. The results demonstrated that the proposed ML models could be used as a means of simulating the carboxylate platform for MCCA production from waste feedstock, enhancing the understanding of the behavior of microorganisms in the process, and providing guidance for further optimization.

Enhancing the production of small molecular products from pubescens via stepwise pyrolysis process

Pyrolysis of pubescens pretreated by torrefaction was investigated by one-step and stepwise processes. The cumulative yield of small molecular compounds reached up to 19.6 wt% via stepwise processing, yielding monosaccharides (1.49 wt%), carboxylic acids (5.20 wt%), furans (3.97 wt%) and monophenols (8.94 wt%), which is higher than the corresponding value of 12.39 wt%, with 0.65 wt%, 6.15 wt%, 1.05 wt% and 4.54 wt% of the four kinds of species obtained respectively, from one-step pyrolysis. Production of carboxylic acids could be enhanced in the temperature range of 200–320 °C via dehydration of holocellulose and cleavage of acetyl group in lignin, while the acquisition of furans could be promoted in the range of 240–360 °C via further dehydration of the units of holocellulose. In the temperature range of 240–440 °C, the cleavage of β-1,4-glycosidic linkages in cellulose and glycosidic bonds in hemicellulose enhanced the yield of monosaccharides. Furthermore, the formation of monophenols from the decomposition of H, G, and S units of lignin was enhanced via cleavage of C1-Cα, Cα-Cβ, Cβ-Cγ, Cα-OH, C-O-H(R), etc. in saturated and unsaturated regions, accompanied by elimination, dehydration reactions. With stepwise processing, the corresponding carbon content in the pyrolyzed residue was enriched, resembling the elemental composition of Bituminous coal. Moreover, the relationship between small molecular weight compounds and oligomers has been probed.

In Vitro Metabolic Fate of the Synthetic Cannabinoid Receptor Agonists 2F-QMPSB and SGT-233 Including Isozyme Mapping and Carboxylesterases Activity Testing.

Quinolin-8-yl 3-(4,4-difluoropiperidine-1-sulfonyl)-4-methylbenzoate (2F-QMPSB) and 3-(4,4-difluoropiperidine-1-sulfonyl)-4-methyl-N-(2-phenylpropan-2-yl)benzamide (SGT-233) belong to a new group of synthetic cannabinoid receptor agonists containing a sulfamoyl benzoate or sulfamoyl benzamide core structure. 2F-QMPSB was identified in herbal material seized in Europe in 2018. The aims of this study were the identification of in vitro Phase I and II metabolites of 2F-QMPSB and SGT-233 to find analytical targets for toxicological screenings. Furthermore, the contribution of different monooxygenases and human carboxylesterases to Phase I metabolism was investigated. Liquid chromatography coupled to high-resolution tandem mass spectrometry was used for analysis. Ester hydrolysis was found to be an important step in the metabolism of 2F-QMPSB, which was catalyzed mainly by human carboxylesterases (hCES)1 isoforms. Additionally, nonenzymatic ester hydrolysis was observed in case of 2F-QMPSB. Notably, the carboxylic acid product derived from ester hydrolysis and metabolites thereof were only detectable in negative ionization mode. In case of SGT-233, mono- and dihydroxy metabolites were identified, as well as glucuronides. The cytochrome P450 (CYP) isozymes CYP2C8, CYP2C9, CYP2C19, CYP3A4 and CYP3A5 were found to be involved in the hydroxylation of both compounds. The results of these in vitro experiments suggest that the ester hydrolysis products of 2F-QMPSB and their glucuronides are suitable targets for toxicological screenings. In the case of SGT-233, the mono- and dihydroxy metabolites were identified as suitable screening targets. The involvement of various CYP isoforms in the metabolism of both substances reduces the likelihood of drug-drug interactions due to CYP inhibition.

Surface Oxidation of Phenolic Aldehydes: Fragmentation, Functionalization, and Coupling Reactions.

Substantial amounts of phenolic aldehydes, represented by the structures of syringaldehyde, vanillin, and 4-hydroxybenzaldehyde, are emitted to the atmosphere during biomass burning. The oxidative transformation of phenolic aldehydes during atmospheric transport has the potential to modify the physicochemical properties of particulates, which play a vital role in Earth's climate and human health. Herein, thin solid films made of syringaldehyde, vanillin, and 4-hydroxybenzaldehyde are oxidized in contact with O3(g) under a relative humidity of 74% representative of average global conditions. New physical insights into the surface reactions are achieved by analyzing isopropanol-extracted films before and during oxidation by multiple techniques. Changes in electronic transitions at 220, 310, and 350-400 nm registered by UV-vis spectroscopy show that the oxidized films have enhanced mass absorption coefficients at λ > 300 nm. Electrospray ionization (ESI) mass spectrometry (MS) and ion chromatography with conductivity and MS detection of extracted oxidized films confirm aromatic ring cleavage of syringaldehyde and vanillin by O3(g) with the production of carboxylic acids. Carboxylic acids were observed as anions ([M - H]-) at m/z 45 (formic acid), 73 (glyoxylic acid), 75 (glycolic acid), 89 (oxalic acid), 115 (maleic acid), 117 (mesoxalic acid), 119 (tartronic acid), and 129 (maleic acid monomethyl ester), while other polyfunctional products were registered by ultrahigh-pressure liquid chromatography with UV-vis and MS detection. In situ production of hydroxyl radicals is confirmed by demethoxylation products and ipso attack at the C1 ring position holding the -C(H)═O group. The order of reactivity increased with the number of methoxy substituents that donate electron density to the aromatic ring. Combined oxidation mechanisms for the three compounds are proposed based on all of the experimental observations and explain the contribution of aged biomass burning material to secondary organic aerosol formation.

Effect of metals on the regulation of acidogenic metabolism enhancing biohydrogen and carboxylic acids production from brewery spent grains: Microbial dynamics and biochemical analysis.

The present study reports the mixed culture acidogenic production of biohydrogen and carboxylic acids (CA) from brewery spent grains (BSG) in the presence of high concentrations of cobalt, iron, nickel, and zinc. The metals enhanced biohydrogen output by 2.39 times along with CA biosynthesis by 1.73 times. Cobalt and iron promoted the acetate and butyrate pathways, leading to the accumulation of 5.14 gCOD/L of acetic and 11.36 gCOD/L of butyric acid. The production of solvents (ethanol + butanol) was higher with zinc (4.68 gCOD/L) and cobalt (4.45 gCOD/L). A combination of all four metals further enhanced CA accumulation to 42.98 gCOD/L, thus surpassing the benefits accrued from supplementation with individual metals. Additionally, 0.36 and 0.31 mol green ammonium were obtained from protein‐rich brewery spent grain upon supplementation with iron and cobalt, respectively. Metagenomic analysis revealed the high relative abundance of Firmicutes (>90%), of which 85.02% were Clostridium, in mixed metal‐containing reactors. Finally, a significant correlation of dehydrogenase activity with CA and biohydrogen evolution was observed upon metal addition.

Valorizing prickly pear cladodes via methane-arrested anaerobic digestion for carboxylic acid production.

To address climate change, liquid biofuels are an essential alternative to fossil fuels, especially for transportation. The carboxylate platform uses methane-arrested anaerobic digestion (MAAD) to ferment biomass to carboxylic acids, which can be chemically converted to liquid fuels via the carboxylate platform. Most biomass sources require expensive pretreatments to remove lignin; however, prickly pear (Opuntia ficus-indica) cladodes have low lignin content and therefore do not require pretreatment. Furthermore, this sugar-rich feedstock is readily digested to high concentrations of carboxylic acids. At various substrate concentrations, batch MAAD of prickly pear cladodes yielded primarily acetic, butyric, and caproic acids. From these batch data, continuum particle distribution modeling (CPDM) simulated four-stage countercurrent digestion. At a non-acid volatile solid (NAVS) concentration of 100 g/Lliq , CPDM predicts a high total acid concentration of 93 g/L and conversion of 0.93 g NAVSdigested /NAVSfed at a volatile solid loading rate of 6g/(Lliq ·d) and liquid retention time of 35 days. Without chemical pretreatment, co-digestion, or in situ product removal, prickly pear produced high yields, biomass conversion, product concentration, and selectivity compared to previously studied lignocellulosic feedstocks.

Production of medium-chain carboxylic acids using sewage sludge pretreated by combined Fenton and persulfate oxidation

Medium chain carboxylates (MCCs) production from sewage sludge (SS) is an economically and environmentally feasible technology for recovering value-added chemicals from SS. To improve MCCs production from SS, Fe (II)-mediated advanced oxidation processes (AOPs) including Fenton oxidation (FO), persulfate oxidation (PO), and combined Fenton-persulfate oxidation (CFP) were adopted to examine their effect on fermentation. Highest total MCCs concentration of 3445.85 mg COD/L was achieved in CFP treated group, followed by PO treated group (2678.78 mg COD/L), control group (2367.72 mg COD/L) and FO treated group (2294.14 mg COD/L). MCCs produced in all groups were dominated by caproate, and all three AOPs treatment promoted longer-chain MCCs (i.e. heptylate and caprylate) production. Microbial analysis showed that genus Romboutsia, Paraclostridium, Clostridium_sensu_stricto_1, norank_f_Anaerolineaceae and Acetobacterium that were positively correlated with MCCs production were significantly enriched in CFP treated group, which contributed to the highest MCCs production in CFP treated group. The functional enzymes analysis showed that both PO and CFO treatment promoted MCCs production by strengthening the fatty acid biosynthesis pathway during the chain elongation (CE) process.

Hydrogen Production and Storage: Analysing Integration of Photoelectrolysis, Electron Harvesting Lignocellulose, and Atmospheric Carbon Dioxide-Fixing Biosynthesis

Green hydrogen from photocatalytic water-splitting and photocatalytic lignocellulosic reforming is a significant proposition for renewable energy storage in global net-zero policies and strategies. Although photocatalytic water-splitting and photocatalytic lignocellulosic reforming have been investigated, their integration is novel. Furthermore, biosynthesis can store the evolved hydrogen and fix the atmospheric carbon dioxide in a biocathode chamber. The biocathode chamber is coupled to the combined photocatalytic water-splitting and lignocellulose oxidation in an anode chamber. This integrated system of anode and biocathode mimics a (bio)electrosynthesis system. A visible solar radiation-driven novel hybrid system comprising photocatalytic water-splitting, lignocellulose oxidation, and atmospheric CO2 fixation is, thus, investigated. It must be noted that there is no technology for reducing atmospheric CO2 concentration. Thus, our novel intensified technology enables renewable and sustainable hydrogen economy and direct CO2 capture from air to confront climate change impact. The photocatalytic anode considered is CdS nanocomposites that give a low absorption onset (200 nm), high absorbance range (200–800 nm), and narrow bandgap (1.58–2.4 V). The biocathode considered is Ralstonia eutropha H16 interfaced with photocatalytic lignocellulosic oxidation and a water-splitting anode. The biocathode undergoes autotrophic metabolism fixing atmospheric CO2 and hydrogen to poly(3-hydroxybutyrate) biosynthesis. As the hydrogen evolved can be readily stored, the electron–hole pair can be separated, increasing the hydrogen evolution efficiency. Although there are many experimental studies, this study for the first time sets the maximum theoretical efficiency target from mechanistic deductions of practical insights. Compared to physical/physicochemical absorption with solvent recovery to capture CO2, the photosynthetic CO2 capture efficiency is 51%. The maximum solar-to-hydrogen generation efficiency is 33%. Lignocelluloses participate in hydrogen evolution by (1–4)-glycosidic bond decomposition, releasing accessible sugar monomers or monosaccharides forming a Cd–O–R bond with the CdS/CdOx nanocomposite surface used as a photocatalyst/semiconductor, leading to CO32− in oxidised carboxylic acid products. Lignocellulose dosing as an oxidising agent can increase the extent of water-splitting. The mechanistic analyses affirm the criticality of lignocellulose oxidation in photocatalytic hydrogen evolution. The critical conditions for success are increasing the alcohol neutralising agent’s strength, increasing the selective (ligno)cellulose dosing, broadening the hybrid nanostructure of the photocatalyst/semiconductor, enhancing the visible-light range absorbance, and increasing the solar energy utilisation efficiency.

Experimental investigation on recovery of bio‐based protocatechuic acid using ionic liquids

AbstractBACKGROUNDThe production of protocatechuic acid (PCA) (which has significant applications in organic intermediates, chemical reagents, pharmaceuticals, dye synthesis, etc.) by fermentation is a potential replacement to the conventional petrochemical routes of carboxylic acid production. However, the extraction processes of these carboxylic acids from fermentation broths and dilute waste water using organic solvents imply additional environment hazards. Ionic liquids (ILs) have come to the focus because of their superior properties as well as environmentally friendly nature, and are being intensively used for separation processes. The equilibrium extraction efficiency for bio PCA using two imidazolium ILs – 1‐butyl‐3‐methylimidazolium tetrafluoroborate (bmimBF4) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate (bmim‐PF6) – was investigated under isothermal conditions in diluent octanol. The distribution coefficient and extraction efficiency were determined to be much greater than those obtained with traditional extractants and diluents.RESULTSThis work is the first of its type to use ILs for PCA isolation. From the equilibrium extraction experiments conducted it was observed, in octanol, that the average distribution coefficients (KD) values for bmimBF4 and bmim‐PF6 were 5.3 and 5.36, respectively, with average extraction efficiencies of 83.84% and 84.08% at a lower IL concentration of 10% by volume, and the findings may be utilised to develop an extraction purification system for PCA separation from aqueous streams. Multiple stages of separation may lead to almost 100% recovery.CONCLUSIONPCA was efficiently extracted from aqueous solutions using bmimBF4 and bmim‐PF6 in octanol, providing preliminary practical information and theoretical support for PCA separation, purification and recovery. © 2022 Society of Chemical Industry (SCI).

Enhancing semi-continuous carboxylic acid production from methane-arrested anaerobic digestion of cellulosic biomass by in-situ product removal with CO2-sustained anion-exchange resin adsorption

Methane-arrested anaerobic digestion (MAAD) provides a sustainable route for cleaner production of carboxylic acids from renewable biomass. However, low acid productivity and high product recovery costs have restricted widespread industrial implementation of this technology. This study enhances carboxylic acid (C2 to C8) production from cellulosic biomass using a newly developed integrated digestion-separation system. Using a mixed culture of marine microorganisms grown under mesophilic conditions (40 °C), paper and chicken manure were co-digested to produce carboxylic acids through semi-continuous four-stage countercurrent MAAD. During digestion, multi-stage CO2-sustained anion-exchange resin (Amberlite IRA-67) adsorption was applied for in-situ recovery of inhibitory acid products from the digestion medium. Efficiency was enhanced by supplying 1-atm CO2 during the in-situ adsorption process. Compared with stand-alone digestion (control), biomass conversion and acid yield in the integrated MAAD system significantly increased by 2.28 and 2.09 times, respectively. The integrated system also increased the mass fractions of longer-chain carboxylic acids (C5 and C6) in liquid products. With various amounts of resin, the optimal normalized resin loadings for biomass conversion and acid yield were 10.9 and 14.6 g wet resin/(Lliq·d), respectively. This work demonstrates countercurrent digestion coupled with in-situ product separation via CO2-sustained anion-exchange resin is highly effective at recovering carboxylic acids from cellulosic biomass.