Microwave-assisted Hydrolysis Research Articles

Microwave-Assisted Hydrolysis of Robusta Coffee Skin Waste as a Reducing Sugar Feedstock

Microwave-Assisted Hydrolysis of Robusta Coffee Skin Waste as a Reducing Sugar Feedstock

Optimization of Ulva sp. Decomposition using H2SO4 with Microwave-Assisted Hydrolysis Method as Feedstock of Bioethanol

<p class="StyleE-JOURNALAbstrakKeywordsBold">Bioethanol is a renewable energy used to reduce dependence on fossil fuels, which have negative impacts on the environment. Furthermore, Ulva sp. contains high levels of carbohydrates, making it potentially suitable as a raw material for bioethanol production. Therefore, this study aims to determine the optimal decomposition process using the microwave-assisted hydrolysis method with an acid solvent (H<sub>2</sub>SO<sub>4</sub>), by examining the effects of acid concentration, hydrolysis time, and microwave power. Optimization was carried out using several parameters such as hydrolysis time, microwave power, and the ratio of raw materials to solvents. The ANOVA test results showed that the hydrolysis variable parameter had a significant effect on the reducing sugar content obtained, evidenced by the R<sup>2</sup> value of 0.9892. The highest reducing sugar content of 19.71 mg/mL was produced under the operating conditions of 15 min hydrolysis time, 450 W microwave power, and 0.065 g/mL ratio of raw material to solvents.</p>

β-Ketoadipic acid production from poly(ethylene terephthalate) waste via chemobiological upcycling.

The upcycling of poly(ethylene terephthalate) (PET) waste can simultaneously produce value-added chemicals and reduce the growing environmental impact of plastic waste. In this study, we designed a chemobiological system to convert terephthalic acid (TPA), an aromatic monomer of PET, to β-ketoadipic acid (βKA), a C6 keto-diacid that functions as a building block for nylon-6,6 analogs. Using microwave-assisted hydrolysis in a neutral aqueous system, PET was converted to TPA with Amberlyst-15, a conventional catalyst with high conversion efficiency and reusability. The bioconversion process of TPA into βKA used a recombinant Escherichia coli βKA expressing two conversion modules for TPA degradation (tphAabc and tphB) and βKA synthesis (aroY, catABC, and pcaD). To improve bioconversion, the formation of acetic acid, a deleterious factor for TPA conversion in flask cultivation, was efficiently regulated by deleting the poxB gene along with operating the bioreactor to supply oxygen. By applying two-stage fermentation consisting of the growth phase in pH 7 followed by the production phase in pH 5.5, a total of 13.61 mM βKA was successfully produced with 96% conversion efficiency. This efficient chemobiological PET upcycling system provides a promising approach for the circular economy to acquire various chemicals from PET waste.

Synthesis, Characterization, and the Potential for Closed Loop Recycling of Plant Oil-Based PA X.19 Polyamides

We report on plant oil-based linear aliphatic polyamides from 1.19-nonadecanedioic acid and aliphatic diamines of different chain lengths. Their thermal, mechanical, and rheological properties as well as the water uptake and crystalline structures were analyzed. The polyamides were synthesized with high molecular weights of 26 000 to 52 000. All polyamides showed high thermal stability with T5% of >400 °C as well as high crystallinities of ∼50%. Injection molding of the plant-oil-based polyamides was successfully performed to produce tensile test specimens. Chemical recycling of the polyamides was demonstrated by microwave-assisted hydrolysis, with a recovery of 99% for 1.19-nonadecanedioic acid. Melt polycondensation using the recovered monomer was successfully performed to synthesize recycled polyamide in similar quality, which underlines its potential for closed loop recycling.

Amino Acid Fingerprinting of Authentic Nonfat Dry Milk and Skim Milk Powder and Effects of Spiking with Selected Potential Adulterants.

A collaborative study was undertaken in which five international laboratories participated to determine amino acid fingerprints in 39 authentic nonfat dry milk (NFDM)/skim milk powder (SMP) samples. A rapid method of amino acid analysis involving microwave-assisted hydrolysis followed by ultra-high performance liquid chromatography-ultraviolet detection (UHPLC-UV) was used for quantitation of amino acids and to calculate their distribution. The performance of this rapid method of analysis was evaluated and was used to determine the amino acid fingerprint of authentic milk powders. The distribution of different amino acids and their predictable upper and lower tolerance limits in authentic NFDM/SMP samples were established as a reference. Amino acid fingerprints of NFDM/SMP were compared with selected proteins and nitrogen rich compounds (proteins from pea, soy, rice, wheat, whey, and fish gelatin) which can be potential economically motivated adulterants (EMA). The amino acid fingerprints of NFDM/SMP were found to be affected by spiking with pea, soy, rice, whey, fish gelatin and arginine among the investigated adulterants but not by wheat protein and melamine. The study results establish an amino acid fingerprint of authentic NFDM/SMP and demonstrate the utility of this method as a tool in verifying the authenticity of milk powders and detecting their adulteration.

Microwave-assisted synthesis of ternary Li-M-Al LDHs (M = Mg, Co, Ni, Cu, Zn, and Cd) and examining their use in phenol oxidation

It remained challenging to synthesize Li and Al-containing ternary Li-M-Al layered double hydroxides (LDH) because LiI and other metal ions (MII or MIV) prefer different atomic positions, consequently making traditional methods such as co-precipitation or hydrothermal method fail. In the present work, several transition (Co, Ni, Cu) and non-transition (Mg, Zn, Cd) metal ions incorporated ternary Li-M-Al LDHs were synthesized by reacting LiAlH4 and different divalent metal nitrates under microwave-assisted hydrolysis reaction. The layer arrangement formation was verified from powder X-ray diffraction and SEM images, while the presence of three cations in all these samples was confirmed from ICP-AES measurements. FTIR and Raman spectra of these samples confirmed the nitrate anion's (majorly) presence in the interlayer space and the fingerprint bands due to the hydroxide units. The thermal traces contained a two-step dehydroxylation, suggestive of the existence of three cations in the hydroxide layers. Isothermal magnetization of ternary LDH containing Co, Ni, and Cu showed paramagnetic behavior at room temperature. On calcination, α-LiAlO2 and other metal oxides were formed. All the ternary Li-M-Al LDHs (M = Mg, Co, Ni, Cu, Zn, and Cd) were examined as catalysts for the oxidative degradation of phenol, a well-known toxic pollutant. Only Li-Cu-Al LDH displayed high catalytic activity for phenol oxidation. p-benzoquinone formed from phenol initially (60 min) and degraded completely into oxalic acid, maleic acid, and fumaric acid after 120 min, as determined by UV–visible and GC-HRMS measurements.

Abstract 2324: Small-scale microwave-assisted acid hydrolysis method for glycogen determination and turnover in tumors using Stable Isotope Resolved Metabolomics

Abstract Introduction: Glycogen is a readily deployed intracellular energy storage macromolecule composed of branched chains of glucose. Although glycogen primarily occurs in the liver and muscle, it can be found in most tissues throughout the body, and its metabolism has been shown to be important in cancers and immune cells. Robust analysis of glycogen turnover requires stable isotope tracing plus a reliable means of quantifying total and labeled glycogen derived from precursors such as 13C6-glucose. Current methods for analyzing glycogen are time- and sample-consuming, at best semi-quantitative, and unable to measure stable isotope enrichment. Methods: We have developed a microscale method for quantifying both intact and acid-hydrolyzed glycogen by ultra-high-resolution Fourier transform mass spectrometric (UHR-FTMS) and/or NMR analysis in stable isotope resolved metabolomics (SIRM) studies. Polar metabolites, including intact glycogen and their 13C positional isotopomer distributions were first measured in crude biological extracts by high resolution NMR, followed by rapid and efficient acid hydrolysis to glucose in 1 N HCl for 10 minutes at 110 °C under a N2 atmosphere in a microwave-assisted synthesis reactor. The resulting glucose and its 13C isotopologues were then analyzed by UHR-FTMS and/or NMR. Results: We optimized the microwave digestion time, temperature, and oxygen purging in terms of recovery versus degradation and found 10 minutes at 110-115 °C to give > 90% recovery. The method was applied to track the fate of 13C6-glucose in primary human lung BEAS-2B cells, human macrophages, murine liver and patient-derived tumor xenograft (PDTX) in vivo, and the fate of 2H7-glucose in ex vivo lung organotypic tissue cultures of a lung cancer patient. We showed the incorporation of 13C6-glucose into glycogen and its metabolic intermediates, UDP-Glucose and glucose-1-phosphate, both in terms of the 13C levels and fractional enrichment, thereby demonstrating the utility of the method in tracing glycogen turnover in cells and tissues. Conclusions: The method offers a quantitative, sensitive, and convenient means to analyze glycogen turnover in mg amounts of complex biological materials. Keywords: glycogen turnover; 13C6-glucose, stable isotope resolved metabolomics (SIRM); microwave-assisted hydrolysis. Citation Format: Andrew N. Lane, Timothy L. Scott, Juan Zhu, Teresa A. Cassel, Sara Vicente-Munoz, Penghui Lin, Richard M. Higashi, Teresa W-M Fan. Small-scale microwave-assisted acid hydrolysis method for glycogen determination and turnover in tumors using Stable Isotope Resolved Metabolomics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2324.

Spectroscopic Probing Of Mn-Doped ZnO Nanowires Synthesized via a Microwave-Assisted Route

Dilute magnetic semiconductors such as transition-metal-doped ZnO are potential candidates for spintronic applications. Transition metals such as Mn, Fe, and Cu when doped in ZnO enable spin magnetic properties to conventional semiconductors. Although several techniques such as wet chemical and vapor deposition methods are employed to achieve homogeneous doping in ZnO, these methods have limits pertaining to solubility levels of dopant ion, morphology, competition between intrinsic and extrinsic defects and localization of the defect species. This manuscript is an addition to the vast knowledge of methods and protocols that present the synthesis of transition-metal-doped ZnO. In this report, manganese-doped ZnO is synthesized via a microwave-assisted hydrolysis technique. The defect structure of Mn-doped ZnO wires is investigated via electron paramagnetic resonance and photoluminescence techniques. The analysis indicates that Mn2+ substitutes the Zn ion and dominates the intrinsic defect species in ZnO.

Microwave-assisted enzymatic hydrolysis to produce xylooligosaccharides from rice husk alkali-soluble arabinoxylan

The prebiotic properties of xylooligosaccharides (XOS) and arabino-xylooligosaccharides (AXOS) produced from rice husk (RH) using microwave treatment combined with enzymatic hydrolysis were evaluated. The RH was subjected to microwave pretreatment at 140, 160 and 180 °C for 5, 10 and 15 min to obtain crude arabinoxylan (AX). Increasing microwave pretreatment time increased sugar content. Crude AX was extracted with 2% (w/v) sodium hydroxide at 25 °C for 24 h and used as a substrate for XOS production by commercial xylanases. Results showed that oligosaccharides produced by Pentopan Mono BG and Ultraflo Max provided xylobiose and xylotriose as the main products. AXOS was also present in the oligosaccharides that promoted growth of Lactobacillus spp. and resisted degradation by over 70% after exposure to simulated human digestion.

Microwave-Assisted Hydrolysis of Hemicellulose over Sulfonated Catalysts

Sulfonated catalysts based on zirconia (SO3H-ZrO2), silica (SO3H-SBA-15) and zeolite (SO3H-ZSM-5) were studied in the catalytic hydrolysis reaction of hemicellulose in a microwave reactor. The prepared catalysts were characterized by various techniques (XRD, N2 physisorption at 77 K, SEM, TEM and NH3-TPD). The obtained results reveal that despite the differences in their structural and textural properties, the ZrO2, Al-SBA-15 and H-ZSM-5 supports show similar conversions. Doping supports with sulfonate species created hydrogen bonds between SO3H groups and increased the amount of weak acid sites, which enhanced the hydrolysis of hemicellulose. SO3H- ZSM-5 showed the highest catalytic activity followed by SO3H-SBA-15 while SO3H-ZrO2 exhibited a poor conversion. Furthermore, the catalytic hydrolysis of the hemicellulose leads to several interesting products, such as formic acid, acetic acid, lactic acid and xylan. The correlation between the catalytic performances and the acidic properties of the different samples indicates that the best catalytic performances were obtained with the least acidic solids and especially when the density of strong acid sites decreases.

NANOSTRUCTURED IRON OXIDE POWDERS BY MICROWAVE ASSISTED SYNTHESIS

A range of nanostructured oxides with excellent properties is used in technology and science for applications in several fields: catalysis, gas detection, biomedical applications. The most studied forms of oxides are hematite, maghemite and magnetite. In this study, microwave-assisted hydrolytic synthesis and microwave-assisted coprecipitation synthesis are described for the preparation of undoped and doped iron oxide powders using iron (III) chloride (FeCl3), potassium chloride (KCl) as precursors and sodium hydroxide (NaOH) solution as a hydrolysis agent. Microwave-assisted hydrolysis was performed at different concentrations of FeCl3 precursor: 0.1 M, 0.4 M, 0.7 M to which a constant concentration of hydrolysis agent was added, and the synthesis to obtain potassium-doped powders consisted of co-precipitation of 0.1M FeCl3 and 0.025M KCl precursor solutions in the presence of 2M NaOH hydrolysis agent. The developed powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The novelty is the use of potassium as a doping element for iron oxide, for potential application as catalyst. Hematite doped with 5% K was obtained by microwave-assisted coprecipitation synthesis. The presence of K was evidenced by EDS, while XRD spectra indicate successful doping of iron oxide with potassium, either interstitially or by substitution. By microwave synthesis, an increase in particle size was observed with increasing calcination temperature. The formation of the crystalline hematite phase was not obtained in the microwave heating process but following calcination of the powder

A comparative investigation of non-catalysed versus catalysed microwave-assisted hydrolysis of common North and South European seaweeds to produce biochemicals

Using a circular economy approach, this study investigated microwave assisted non-catalysed (water only), acid catalysed (H2SO4), and metal cation catalysed (PbII and AlIII) hydrolysis of brown and red seaweed biomass prior to and following extraction of high value products. Results show a wide variety of organic acid products is attained following each hydrolytic method, which are heavily depending on initial quantity and type of carbohydrates in seaweed as well as process conditions, such microwave reactor temperature and catalyst properties. The best results were achieved with extracted Gracilaria gracilis residues, which resulted in 20.1% w.t. levulinic acid, produced at 180 °C after 10 min with an overall carbohydrates conversion rate over 95%. Metal ion catalysed hydrolysis of the same extracted seaweed also yielded interesting quantities of lactic acid (5% w.t. at 240 °C), 5-HMF (6% w.t. at 220 °C) with Pb(II) and propionic acid (5% w.t. at 220–240 °C) with Al(III), bringing seaweed residues closer to full bioresource valorisation.

Third-generation L-Lactic acid production by the microwave-assisted hydrolysis of red macroalgae Eucheuma denticulatum extract

The development of an efficient third-generation L-lactic acid (L-LA) production process from Eucheuma denticulatum extract (EDE) was achieved in this study. Microwave-assisted dilute acid hydrolysis (MADAH) and microwave-assisted hydrothermal hydrolysis (MAHTH) were chosen as the hydrolysis of EDE for the objective of increasing galactose yield. Single-factor optimization of hydrolysis of the EDE was studied, MADAH had high performance in galactose production relative to MAHTH, in which the yield and optimal conditions for both processes were 50.7% (0.1 M H2SO4, 120 °C for 25 min) and 47.8% (0 M H2SO4,160 °C for 35 min), respectively. For fermentation, the optimal L-LA yield was achieved at the inoculum cell density of 4% (w/w) Bacillus coagulans ATCC 7050 with 89.4% and 6% (w/w) Lactobacillus acidophilus LA-14 with 87.6%. In addition, lipid-extracted Chlorella vulgaris residues (CVRs) as co-nutrient supplementation increased the relative abundance of B. coagulans ATCC 7050, thus benefiting L-LA production.

Swelling and microwave-assisted hydrolysis of animal keratin in ionic liquids

Four kinds of acidic ionic liquids (ILs) were synthesized to hydrolyze keratin with microwave radiation for the first time, among which 1-propylsulfonic-3-methylimidazolium hydrogensulfate ([PSmim]HSO4) presented the best performance for the sample of wool. Then the effects of ionic liquid concentration, solid–liquid ratio, duration, and microwave power on the hydrolysis rate of wool were investigated. After that, the optimum hydrolysis conditions for keratin were determined as: 2 mol/L [PSmim]HSO4, radiation time of 3 h, solid–liquid ratio of wool to ionic liquid at 1:10, microwave power of 300 W, and the final hydrolysis rate of wool was more than 98%; besides that, the swelling effect and kinetics of related processes were also explored, and the hydrolysates were characterized by infrared spectra (IR) and thermalgravimetric analysis (TGA), which were further compared with the product hydrolyzed by traditional volatile strong acid. Furthermore, this IL-catalyzed microwave-assisted method was also applied to hydrolyze a series of feathers and hairs with the comprehensive comparison on the antioxidant activity, free amino acid concentration, and molecular distribution of hydrolysates. The recovered ionic liquid by resin was not changed from its original status obviously, which could be reused and improve the economy of the whole process. Compared with conventional ways, higher hydrolysis degree can be obtained by the developed method, which was a high-efficient, low consumption and environmentally friendly technique.

Quantification of advanced glycation end products and amino acid cross-links in foods by high-resolution mass spectrometry: Applicability of acid hydrolysis

An analytical method was developed and validated for simultaneous identification and quantification of advanced glycation end products (AGEs), amino acid cross-links, lysine and arginine in foodstuffs based on acid hydrolysis, hydrophilic interaction chromatography and high-resolution mass spectrometry. The method proved to be sensitive, reproducible and accurate for furosine, N-Ɛ-(carboxymethyl)lysine, N-Ɛ-(carboxyethyl)lysine, methylglyoxal and glyoxal-derived hydroimidazolones (MG-H and GO-H isomers, respectively), glyoxal lysine dimer, lysinoalanine, lanthionine, lysine and arginine. LOD and LOQ values in water were found to be 0.9–15.5 ng/mL and 2.8–47 ng/mL, respectively, and increased to 1.4–60 ng/mL and 4.4–182 ng/mL in liquid infant formula. Recovery values ranged from 76 to 118% in four different food matrices. Microwave-assisted hydrolysis for 11 min had similar efficiency as conventional hydrolysis, which requires overnight incubation. Acid stability of each compound was determined during microwave and conventional hydrolysis, and showed that the MG-H1 isomer is partially converted to the MG-H3 isomer during acid hydrolysis.

Integrated cascade biorefinery processes for the production of single cell oil by Lipomyces starkeyi from Arundo donax L. hydrolysates

Giant reed (Arundo donax L.) is a promising source of carbohydrates that can be converted into single cell oil (SCO) by oleaginous yeasts. Microbial conversion of both hemicellulose and cellulose fractions represents the key step for increasing the economic sustainability for SCO production. Lipomyces starkeyi DSM 70,296 was cultivated in two xylose-rich hydrolysates, obtained by the microwave-assisted hydrolysis of hemicellulose catalysed by FeCl3 or Amberlyst-70, and in two glucose-rich hydrolysates obtained by the enzymatic hydrolysis of cellulose. L. starkeyi grew on both undetoxified and partially-detoxified hydrolysates, achieving the lipid content of 30 wt% and yield values in the range 15–24 wt%. For both integrated cascade processes the final production of about 8 g SCO from 100 g biomass was achieved. SCO production through integrated hydrolysis cascade processes represents a promising solution for the effective exploitation of lignocellulosic feedstock from perennial grasses towards new generation biodiesel and other valuable bio-based products.

Chemical Recycling of Aliphatic Polyamides by Microwave-Assisted Hydrolysis for Efficient Monomer Recovery.

We report on a simple and efficient chemical recycling process for aliphatic polyamides (PA 66, PA 1010, PA 11, and PA 12), whereby PAs are converted exclusively into their constituent monomers even in the presence of reinforcement additives, such as carbon- and glass-fibers. In this process, the rate of PA hydrolysis reaction, performed under microwave irradiation in the presence of HCl as an acid catalyst, depends on the PA type, the HCl/amide mole ratio, and the type and amount of reinforcement additives. PA 66 is completely converted into the constituent monomers at 200 °C and a 1.25 HCl/amide mole ratio in 10 min. Long-chain PAs (PA 11, PA 12, and PA 1010) and PAs containing glass- or carbon-fiber reinforcement additives need at the same experimental conditions longer reaction times. Alternatively, they can be completely hydrolyzed at 200 °C within a comparable reaction time at a higher HCl/amide mole ratio of 2.5. Complete and straightforward conversion of PAs into the constituent monomers in the absence of side reactions simplifies the isolation and purification of monomers and reinforcement additives, which have been recovered in high yields and quality comparable to those of commercially available chemicals.

Microwave-assisted alkali hydrolysis for cellulose isolation from wheat straw: Influence of reaction conditions and non-thermal effects of microwave

Microwave-assisted hydrolysis has been widely studied for cellulose fiber isolation, but the influence of reaction conditions and the microwave non-thermal effect are not well clarified. In this study, a series of well-designed experiments were carried out to measure the effects of reaction conditions including temperature, duration and alkali concentration. Compared to the other parameters, temperature was more relevant to the cellulose content in fiber. It could reach the maximum purity of 90.66 % when the temperature was up to 140 °C. Moreover, the existence of non-thermal effect of microwave has been confirmed through extensive determination and characterization of the fibers obtained from parallel controlled experiments conducted with or without microwave assistance. Approximately 50 %–75 % reduction in reaction time or 67 % of that in chemical costs would be realized under microwave with respect to traditional heating hydrolysis. Therefore, this work provides both deep insight and efficiency strategy into the microwave-assisted cellulose isolation.

Microwave-Assisted Hydrolysis of Cellulose in Towel and Wheat Straw Using Freeze-Thawing with NaOH

The aim of this study was to produce a high yield of direct hydrolysis of glucose from a cotton towel and wheat straw by microwave-assisted (MW) treatment. To this effect, a freeze-thawing with 3% NaOH was added before MW treatment. Multiple MW parameters were tested. For the towel, the highest glucose yield of 42.4% based on freeze-thawing with 3% NaOH-treated sample was observed after MW treatment at 200 °C for 30 s with 2% sulfuric acid as a catalyst. This corresponded to a 44.4% yield based on the cellulose content of treated samples, which was 1.3-fold higher than that of samples treated only by MW at 200 °C for 7 min with 1% sulfuric acid as a catalyst (maximum glucose yield in our previous report). For wheat straw, the highest glucose yield of 27.0% based on freeze-thawing with 3% NaOH-treated sample, and 41.9% based on the treated sample cellulose content were observed after MW treatment at 200 °C for 3 min with 0.5% sulfuric acid as a catalyst. Under the optimum conditions, the glucose yield was 40.5% from raw towel and 14.7% from wheat straw. Combined severity parameter analysis revealed that the addition of freeze-thawing with NaOH before the MW treatment increased the glucose yield and reduced the severity of the treatment conditions. In conclusion, freeze-thawing using 3% NaOH before MW treatment is effective for the direct hydrolysis of glucose from towels and wheat straw.

Microwave-assisted pretreatment of harmful algal blooms for microbial oil-centered biorefinery approach

Utilization of harmful algal blooms (HABs) for the cultivation of oleaginous microorganisms can provide dual benefits of mitigating the toxicity from the aquatic reservoirs and generation of copious media for biodiesel production. In the present investigation, microwave-assisted dilute alkali-freeze pretreatment was optimized to develop a low-cost growth medium from HAB dried biomass. The electron micrographs along with the elemental analysis confirmed the efficient breakage of HABs after the microwave-assisted hydrolysis treatment as compared with the acid hydrolysis. Moreover, the sugar analysis revealed ~ 46% higher carbohydrate content in microwave-assisted hydrolysate as compared with acid hydrolysate. The microwave-assisted hydrolysate and conventional dilute acid hydrolysate were then used to cultivate microalga (Chlorella minutissima) and yeast (Trichosporon cutaneum) for biomass and lipid accumulation and compared to artificial media. Microalga showed ~ 1.3- and 2-fold higher dry cell weight (DCW) and lipid content, respectively, while the yeast growth increased by ~ 27% with lipid content of 30%. The fatty acid profiles and biodiesel properties were also amenable to the international biodiesel standards. Hence, the present study provides a proof-of-concept of utilizing HAB hydrolysate for culturing oleaginous microorganisms for potential biodiesel production.