Number Of Acidic Functional Groups Research Articles

Chemical properties of biochars prepared from corn and wheat straw at different temperatures

In this study, biochar produced by anaerobic combustion of wheat straw and corn straw in Henan Province at 300 ℃, 500 ℃ and 700 ℃ was used. The chemical properties of wheat biochar and corn biochar, such as pH and infrared spectra, were studied with the increase of temperature. The chemical properties of wheat and corn biochars were compared based on the related literatures.It was found that the pH of biochar from wheat straw and corn straw combustion increased with the increase of temperature. Through the analysis of infrared spectra, it was found that the pH change of the two biochars may be related to the content of functional groups in the biochars themselves. With the increase of temperature, the spectra showed that the functional groups of the two biochars, such as hydroxyl and carboxyl,The main reason is that the chemical bonds of the above functional groups are broken with the increase of temperature. Resulting in a decrease in the number of acidic functional groups and an increase in the alkalinity of the biochar.

Quantifying the bioaccumulation of Pb to Chlorella vulgaris in the presence of dissolved organic matters with different molecular weights.

Dissolved organic matter (DOM) is ubiquitous in natural waters which exhibits obvious effects on the toxicity of heavy metals. However, information on the toxicity of heavy metals in the presence of DOMs with different molecular weights (MWs) was still unclear. In this study, Suwannee river humic acid (SRHA) and algae-derived organic matter (ADOM) were selected as typical terrestrial and microbial DOMs, with the bulk DOMs fractionating into high MW (HMW-, 1kDa ~ 0.45μm) and low MW (LMW-, < 1kDa) fractions to explore the MW-dependent heterogeneities in the bioaccumulation of Pb to Chlorella vulgaris. Results showed that, regardless of DOM types, the LMW fraction exhibited more acidic groups and humic-like substances than the HMW counterparts. Presence of bulk DOM can decrease the bioaccumulation of Pb, while the specific effects were MW- and type-dependent. The LMW-SRHA enhanced the bioaccumulation of Pb while the HMW counterpart alleviated the effects. However, both the HMW- and LMW-ADOM can reduce the bioaccumulation of Pb to C. vulgaris. Moreover, the correlation analysis showed a significant positive correlation between the content of phenolic-OH and the adsorbed/internalized amounts of Pb, demonstrating that the phenolic-OH played a critical role in altering the bioaccumulation of Pb. The results obtained in this study suggest that distribution of MWs, number of acidic functional groups, and metal complexation capacity within DOM pool should be considered for the eco-environmental risk assessment of heavy metals in aquatic environments.

Identification of the Physicochemical Factors Involved in the Dye Separation via Methionine‐Functionalized Mesoporous Carbons

AbstractSynthetic dyes in the wastewater from different industries have adverse effects on human and animal health and cause disturbance of the environmental equilibrium. Functional porous materials have provided significant progress in the removal of dyes from wastewater using adsorption methods. Yet, the correlation and deeper understanding of the physicochemical properties of the porous materials and the dye remains a great challenge. Although ordered mesoporous carbons (OMCs) have unique beneficial features for dye separation, such as high surface area, uniform pore size, good mechanical and thermal stability, so far no report explores OMCs for selective dye adsorption from mixtures. Herein, OMCs of different morphologies and structures are synthesized via nanocasting and modification with methionine amino acid as new adsorbents for rhodamine B and sunset yellow FCF dyes. The results confirm that the obtained carbon materials have a significantly better affinity to rhodamine B than to sunset yellow FCF, which is related to the presence of a high number of acidic functional groups on their surface. In addition, the morphology of materials plays also an important role in the adsorption process. Carbon spheres with wrinkled walls are more efficient in the removal of both dyes than carbon particles with worm‐like shapes.

Adsorption of ampicillin sodium on activated carbons with different surface chemistries

BACKGROUND: The adsorption of ampicillin from aqueous solution by three types of activated carbon was investigated. The first was a commercial activated carbon (AC), the second (AAC) was AC modified by HNO3 oxidation and the third (HAAC) was AAC modified through thermal treatment. The surface properties of the activated carbon samples were characterized and the effects of pH and contact time on the adsorption were determined. The adsorption isotherms, adsorption kinetics and adsorption mechanism are discussed. RESULTS: Compared to AC, HNO3 oxidation increased the number of acid functional groups on the surface of AAC, which hindered the adsorption of ampicillin. For HAAC, thermal treatment removed surface oxygen groups and then improved the adsorption ability. The adsorption processes was greatly affected by pH and acidic conditions were favorable for adsorption. With an initial ampicillin sodium concentration of 200 mg/L, 9 h was needed for adsorption to reach equilibrium. The Langmuir isotherm provides a better fit for the adsorption than the Freundlich isotherm and the maximum adsorption capacities for AC, AAC and HAAC were 90.6, 59.8, 140.9 mg/g, respectively. The sorption kinetics can be described by a pseudo-second order model. CONCLUSION: The functional groups on activated carbon greatly affect its adsorption ability. The adsorption of ampicillin can be improved by increasing the number of basic functional groups on the activated carbon. Chemisorption was the dominant adsorption process and pH was an important factor affecting ampicillin adsorption.

Chemically engineered biochar – Effect of concentration and type of modifier on sorption and structural properties of biochar from wood waste

The main aim of study was a) preparation of biochars (BCs) engineered chemically with various reagents including base (NaOH), as well as mineral (HCl, HNO3, H2SO4) and organic (CH3COOH) acids, b) determination of type and concentration effect of the modifier on surface properties of the BCs, and c) assessment of optimal modification conditions regarding environmental aspects. Results showed that modifiers used at the lowest concentration (0.001 M and 0.01 M) changed the BCs properties insignificantly. Modification with 0.1–1.0 M NaOH caused increase of value of surface area (by 21–82%) and volume of pores from 5 to 40 nm (by 109–239%). Acidic modifiers at 0.1–1.0 M enhanced the number of acidic functional groups, mainly lactonic ones. The best effect was obtained for BCs treated with CH3COOH and H2SO4, revealing an elevation of acidic structures by 13–17% and by 9–15%, respectively. The largest enhancement of basic groups occurred for the BCs treated with increasing concentration of NaOH (by 21–154%) and CH3COOH (by 2–50%). The pH of the modified BCs was drastically reduced/elevated after treating with the highest acid/base concentrations, which suggests considering compromise between the best chemical properties of BC and its safe use, e.g. selection of the BC modified with 0.1 M modifier.

Changes in the Composition of Humic Acids with Mechanochemical Impact on Peat and Coal

The analysis of the mechanochemical transformations of humic acids (HAs) in caustobioliths of different genesis (peat, brown coal, and oxidized coal) was carried out. It was found that the greatest changes in the peripheral carbohydrate fragments and the aromatic framework of a HA macromolecule occurred upon the mechanical activation of less transformed peats. The mechanochemical solid-phase alkaline hydrolysis of HAs was performed. Changes in the composition of HAs in the process of mechanical activation, which consist in an increase in the number of acid functional groups and in the degree of oxidation of aromatic and aliphatic fragments and in a decrease in the aromaticity of macromolecules, were detected.

Effect of hydrothermal carbonization temperature on pH, dissociation constants, and acidic functional groups on hydrochar from cellulose and wood

The aims of this work were to quantify chemical states associated with the pH, dissociation constants, and pH at point of zero charge (pHPZC) of hydrochar and to quantify the acidic functional groups on hydrochar surface. Hydrochars from cellulose and wood treated at 180, 220, and 260 °C with 30 min residence time were produced. Boehm titration was applied to analyze acidic functional groups and dissociation constants on hydrochar surfaces. FTIR spectroscopy was used to identify the functional groups qualitatively. The results of this study indicate that hydrochar becomes more acidic due to a larger number of acidic functional groups on the hydrochar surface with the increase of hydrothermal carbonization (HTC) temperature. The total number of acidic functional groups increased from 20.5 ± 0.3 μmol/g to 1267.9 ± 22.5 μmol/g and 576.6 ± 7.8 μmol/g to 680.8 ± 18.8 μmol/g for cellulose and wood, respectively.

Preparation and Characterization of Chemically-Modified Biomaterials and Their Application as Adsorbents of Penicillin G

The prevalence of antibiotics in water creates microbial resistance and has a negative impact on the ecosystem. Biomaterials such as spent tea leaves are rich in functional groups and are suitable for chemical modification for diverse applications. This research proposes the use of spent tea leaves of chamomile (CM), green tea (GT), and peppermint (PM) as structural scaffolds for the incorporation of carboxyl, sulfonyl, and thiol groups to improve the adsorption of Penicillin G (Pe). Adsorbents characterization reported a higher number of acidic functional groups, mainly in thiolated products. Scanning electron microscopy (SEM) analysis showed changes on the surfaces of the adsorbents due to reaction conditions, with a stronger effect on thiolated and sulfonated adsorbents. Elemental analysis by Energy dispersive X-ray spectrophotometry (EDS) corroborated the chemical modification by the presence of sulfur atoms and the increase in oxygen/carbon ratios. Batch experiments at different pH shows a strong pH-dependence with a high adsorption at pH 8 for all the adsorbents. The adsorption follows the trend CMs &gt; GTs &gt; PMs. Thiolation and sulfonation reported higher adsorptions, which is most likely due to the sulfur bridge formation, reaching adsorption percentages of 25%. These results create a new mindset in the use of spent tea leaves and their chemical modifications for the bioremediation of antibiotics.

The copper complexation ability of a synthetic humic-like acid formed by an abiotic humification process and the effect of experimental factors on its copper complexation ability.

Humic acids have an important impact on the distribution, toxicity, and bioavailability of hazardous metals in the environment. In this study, a synthetic humic-like acid (SHLA) was prepared by an abiotic humification process using catechol and glycine as humic precursors and a MnO2 catalyst. The effect of physico-chemical conditions (ionic strength from 0.01 to 0.5M NaNO3, pH from 4 to 8, temperature from 25 to 45°C, and humic acid concentration from 5 to 100mg/L) on the complexation ability of SHLA for Cu2+ were investigated. A commercial humic acid (CHA, CAS: 1415-93-6) from Sigma-Aldrich was also studied for comparison. The results showed that for pH4 to 8, the conditional stability constants (log K) of SHLA and CHA were in the range 5.63-8.62 and 4.87-6.23, respectively, and complexation capacities (CC) were 1.34-2.61 and 1.42-2.31mmol/g, respectively. The Cu complexation ability of SHLA was higher than that of the CHA due to its higher number of acidic functional groups (SHLA 19.19mmol/g; CHA 3.87mmol/g), extent of humification and aromaticity (AL/AR: 0.333 (SHLA); 1.554 (CHA)), and O-alkyl functional groups (SHLA15.56%; CHA 3.45%). The log K and complexation efficiency (fraction of metal bound to SHLA) of SHLA were higher at higher pH, lower ionic strength, higher temperature, and higher SHLA concentration. Overall, SHLA was a good and promising complexation agent for copper in both soil washing of copper contaminated soil and the treatment of copper-containing wastewater.

Nanocellulose: Abundant Biopolymer Membranes for Next-Generation Low-Cost Fuel Cells

Nafion has been the industry standard membrane for polymer electrolyte membrane fuel cells (PEFCs) for decades due to its high conductivity, mechanical stability and durability. However, it has several drawbacks such as poor performance at high temperatures / low humidity, use of harmful fluorine in its production, and as its high price. Therefore research into new membrane materials is necessary. Basic requirements for next-generation fuel cell membranes are sufficiently high proton conductivity, high mechanical strength, good hydrogen gas barrier, and low cost. Nanocellulose is a biopolymer produced in bulk from abundant cheap cellulosic materials such as wood or cotton. Depending on its source, nanocellulose fiber dimensions can range from a few to several tens of nanometers in diameter, and are several micrometers in length. Nanocellulose paper with high mechanical strength and thermal stability up to 150°C has been reported.1,2 Previously, we showed that the hydrogen barrier of nanocellulose membranes is approximately 1000 times higher than Nafion.3 In addition, reasonable proton conductivity at high temperature (~5 mS/cm at 120°C) was shown by impedance spectroscopy. Based on these results we fabricated the world’s first nanocellulose “paper fuel cells” and successfully operated them as hydrogen fuel cells. The performance was stable, with no degradation over 24 hours. Here, in order to increase the proton conductivity, we perform chemical modification of nanocellulose fibers. This chemical treatment resulted in an increase in the number of acidic functional groups, as well as modifying the microstructure. A strong increase in the proton conductivity was observed, with an associated increase in fuel cell performance. In addition, nanocellulose was composited with more established ionomer materials and the resulting membranes were investigated for their fuel cell properties.

Effect of Temperature on the Structural and Physicochemical Properties of Biochar with Apple Tree Branches as Feedstock Material

The objective of this study was to study the structure and physicochemical properties of biochar derived from apple tree branches (ATBs), whose valorization is crucial for the sustainable development of the apple industry. ATBs were collected from apple orchards located on the Weibei upland of the Loess Plateau and pyrolyzed at 300, 400, 500 and 600 °C (BC300, BC400, BC500 and BC600), respectively. Different analytical techniques were used for the characterization of the different biochars. In particular, proximate and element analyses were performed. Furthermore, the morphological, and textural properties were investigated using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, Boehm titration and nitrogen manometry. In addition, the thermal stability of biochars was also studied by thermogravimetric analysis. The results indicated that the increasing temperature increased the content of fixed carbon (C), the C content and inorganic minerals (K, P, Fe, Zn, Ca, Mg), while the yield, the content of volatile matter (VM), O and H, cation exchange capacity, and the ratios of O/C and H/C decreased. Comparison between the different samples show that highest pH and ash content were observed in BC500. The number of acidic functional groups decreased as a function of pyrolysis temperature, especially for the carboxylic functional groups. In contrast, a reverse trend was found for the basic functional groups. At a higher temperature, the brunauer–emmett–teller (BET) surface area and pore volume are higher mostly due to the increase of the micropore surface area and micropore volume. In addition, the thermal stability of biochars also increased with the increasing temperature. Hence, pyrolysis temperature has a strong effect on biochar properties, and therefore biochars can be produced by changing pyrolysis temperature in order to better meet their applications.

Role of surface chemistry and morphology in the reactive adsorption of H₂S on iron (hydr)oxide/graphite oxide composites.

Composites of magnetite and two-line ferrihydrite with graphite oxide (GO) were synthesized and tested as hydrogen sulfide adsorbents. Exhausted and initial composites were characterized by the adsorption of nitrogen, X-ray diffraction, potentiometric titration, thermal analysis, and FTIR. The addition of GO increased the surface area of the composites due to the formation of new micropores. The extent of the increase depended on the nature of the iron (hydr)oxide and the content of GO. The addition of GO did not considerably change the crystal structure but increased the number of acidic functional groups. While for the magnetite composites an increase in the H2S adsorption capacity after GO addition was found, the opposite effect was recorded for the ferrihydrite composites. That increase in the adsorption capacity was linked to the affinity of the composites to adsorb water in mesopores of specific sizes in which the reaction with basic surface groups takes place. Elemental sulfur and ferric and ferrous sulfates were detected on the surface of the exhausted samples. A redox reactive adsorption mechanism is proposed to govern the retention of hydrogen sulfide on the surface of the composites. The incorporation of GO enhances the chemical retention of H2S due to the incorporation of OH reactive groups and an increase in surface heterogeneity.

Characterization of Modified Biochars Derived from Bamboo Pyrolysis and Their Utilization for Target Component (Furfural) Adsorption

Biochar (BC) derived from bamboo pyrolysis and its modified forms were treated with chemical methods (oxidation either by KMnO4 or HNO3 and base treatment with NaOH) and heat method. BC and modified BCs were investigated as adsorbents for target component (furfural) removal from aqueous solution. The samples were characterized to assess the effects of different treatments on structure and surface chemistry of BCs. The results show that chemical treatments increase the hydrophilicity of BC, whereas heat treatment causes the opposite effect. Oxidation treatment leads to the introduction of a large number of acidic functional groups on the BC surface, with HNO3 being more effective than KMnO4. In contrast, NaOH treatment and heat treatment increase the basicity of BC. Pore structures of BCs are also significantly changed after these modifications. Furfural adsorption capacity of BCs increases with the increase of basic surface group content, which can be attributed to the enhancement of dispersion interactions. The higher hydrophilicity of BC is, the lower the furfural uptake capacity is. The heat-treated samples demonstrate the highest capacity for furfural adsorption, with a removal efficiency of up to 100% at a furfural concentration of 10 g/L. However, all chemical treatments reduce furfural removal capacity. The Ho’s pseudo-second-order model, intraparticle diffusion model, and Langmuir isotherm fit the adsorption data well.

Influence of heating temperature and holding time on biochars derived from rubber wood sawdust via slow pyrolysis

Biochar samples were produced from rubber wood sawdust (RWSD), which is a by-product from sawmills, via slow pyrolysis. Biochar is a potential additive for agricultural soil as a soil amendment and for agronomics. The approach proposed in the current study considers the effects of heating temperature and holding time on the surface functional groups and morphologies of RWSD-derived biochars. The pyrolysis was performed in a vertical tube furnace heated at 5°C/min from room temperature to maximum heating temperatures of 300°C, 400°C, 500°C and 700°C under nitrogen gas purging at a rate of 30ml/min. Two sets of biochars were produced with holding times of (i) 1h and (ii) 3h. Proximate and ultimate analyses were performed on the raw RWSD using thermogravimetric analysis (TGA) and carbon–hydrogen–nitrogen (CHN) elemental analysis. The influence of heating temperature and holding time on biochar surface functional groups and porosities was investigated using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Boehm titration, pH alkalinity, Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy (SEM) and SEM with energy-dispersive X-ray (SEM–EDX) spectrocopy. The FT-IR spectra indicated the presence of acidic functional groups, such as carboxylic, phenolic and lactonic groups, and these groups were quantified by Boehm titration. The number of acidic functional groups decreased as the heating temperature and holding time increased. The maximum amount of acidic functional groups was determined to be 1.9mmol/g at 300°C for a 1-h holding time compared to 1.3mmol/g for a 3-h holding time and 1.0mmol/g with a 1-h holding time at 700°C. All of the biochars produced at heating temperatures above 400°C were alkaline, and the pH value increased as the heating temperature and holding time increased. The biochar produced at 300°C with a 1-h holding time had a pH of 6.72 and the sample produced with a 3-h holding time had a pH of 7.67. In addition, the sample produced when the temperature was increased to 700°C with a 1-h holding time had a pH of 11.44. The BET surface area analysis reported maximum values of 5.49m2/g, and the total pore volume was 0.0097cm3/g at a heating temperature of 700°C with a 3-h holding time. SEM micrographs clearly showed the development of well-defined pores in the biochars, and the SEM–EDX spectra indicated localised carbon and oxygen content in all the samples. The results indicated that biochars produced from RWSD are potentially beneficial as soil amendments. However, an extensive study of biochar sustainability is worth investigating.

Adsorption of Copper Acetate onto Pretreated Activated Carbons over a Wide Concentration Range

The commercially available microporous activated carbon Kuraray GC was pretreated in two different ways: one was heated to 950 °C in 5% hydrogen and the other boiled in nitric acid for 5 h. BET surface area measurements and Boehm titrations were done to find the surface area and the numbers of surface functional groups for each carbon. A large range of linearly varying concentrations of aqueous copper acetate solutions was made and stirred with each sample of pretreated carbon. Atomic absorption spectroscopy, titrations, and weight measurements were employed to measure the amount of copper acetate actually adsorbed onto the respective carbon samples. The number of acidic functional groups on the carbon surface as determined by Boehm titrations in the case of the hydrogen treated sample and the nitric acid treated sample do not match with the usual Langmuir parameters both at low and high concentrations. Two distinct isotherm fittings have been obtained for both carbons; double Langmuir isotherms for the hydrogen-treated sample, and a low concentration Langmuir isotherm combined with a high concentration Freundlich isotherm for the nitric acid treated sample. The results have also been compared with the results for untreated Kuraray GC.

Characteristics and turnover of exopolymeric substances in a hypersaline microbial mat

The properties and microbial turnover of exopolymeric substances (EPS) were measured in a hypersaline nonlithifying microbial mat (Eleuthera, Bahamas) to investigate their potential role in calcium carbonate (CaCO(3)) precipitation. Depth profiles of EPS abundance and enzyme activities indicated that c. 80% of the EPS were turned over in the upper 15-20 mm. Oxic and anoxic mat homogenates amended with low-molecular-weight (LMW) organic carbon, sugar monomers, and different types of EPS revealed rapid consumption of all substrates. When comparing the consumption of EPS with that of other substrates, only marginally longer lag times and lower rates were observed. EPS (5-8%) were readily consumed during the conversion of labile to refractory EPS. This coincided with a decrease in glucosidase activity and a decrease in the number of acidic functional groups on the EPS. Approximately half of the calcium bound to the EPS remained after 10 dialyses steps. This tightly bound calcium was readily available to precipitate as CaCO(3). We present a conceptual model in which LMW organic carbon complexed with the tightly bound calcium is released upon enzyme activity. This increases alkalinity and creates binding sites for carbonate and allows CaCO(3) to precipitate. Therefore, this model explains interactions between EPS and CaCO(3) precipitation, and underscores the critical role of aerobic and anaerobic microorganisms in early diagenesis and lithification processes.

Use of soft hydrothermal processing to improve and recycle bedding for laboratory animals

Cage bedding for laboratory rodents can influence animal wellbeing and thus the experimental data. In addition, a large amount of used bedding containing excrement is discharged as medical waste from life science institutes and breeding companies. We developed a ground-breaking system to improve fresh bedding and recycle used bedding by applying a soft hydrothermal process with high-temperature and high-pressure dry steam. The system removes both harmful organic components and aromatic hydrocarbons that can affect animals' metabolism. The purpose of the present study was to evaluate the chemical and physical properties of the improved fresh bedding and the recycled used bedding treated by the system. The results showed that 68-99% of the predominant aromatic hydrocarbons were removed from fresh bedding treated at 0.35 MPa and 140 degrees C for 120 min ('improved bedding'). In addition, 59.4-99.0% of predominant harmful organic compounds derived from excrement were removed from used bedding treated at 0.45 MPa and 150 degrees C for 60 min ('recycled bedding'). The soft hydrothermal treatment increased the number of acidic functional groups on the bedding surface and gave it the high adsorptive efficiency of ammonia gas. Harmful substances such as microorganisms, heavy metals and pesticides decreased below the detection limit. The results clearly showed that the improved and recycled bedding is safer for laboratory rodents and has the potential to ameliorate conditions in primary and secondary enclosures (e.g. cages and animal rooms) used for maintaining laboratory animals. This process may be one of the most advanced techniques in providing an alternative to softwood and other bedding, economizing through the recycling of used bedding and reducing bedding waste from animal facilities.

A comparison of the properties of polyurethane immobilised Sphagnum moss, seaweed, sunflower waste and maize for the biosorption of Cu, Pb, Zn and Ni in continuous flow packed columns

The biosorption of Cu, Pb, Zn and Ni from a mixed solution of the metals was investigated in continuous flow packed columns containing polyurethane immobilised biomass. The characteristics and biosorption properties of Sphagnum moss, the brown seaweed Ascophyllum nodosum, waste biomass from the preparation of sunflower oil, and whole plant maize were compared. All the biomass types showed a preference for the sequestration of Pb followed by Cu, with Ni and Zn having roughly equal affinity. With continuous metal loading to the column there was an initial binding of all metals and then a displacement of the lower affinity metals by those with a high affinity. This led to a chromatographic effect in the column with breakthrough concentrations for low-affinity metals higher than the concentration in the feed. A similar phenomenon was found on desorption using acidic solutions where low-affinity metals were desorbed preferentially. The results also indicated that despite competitive displacement of one metal species by another the biomass appeared to succeed in retaining some low-affinity metal species indicating that there may be selective sites present with different affinity characteristics. When using a multi-metal solution with Cu, Pb, Zn and Ni at equal 10 mg l −1 concentrations as column influent, the total quantities of metal sequestered were: seaweed, 117.3 mg g −1; sunflower waste, 33.2 mg g −1; Sphagnum moss, 32.5 mg g −1; and maize, 2.3 mg g −1. The use of an acid base potentiometric titration showed a relationship between the number of acid functional groups and biosorption capacity, although this was not proportional for the biomass types studied. It can, however, be used in conjunction with a simple classification of metals into high and low-affinity bands to make a preliminary assessment of a biosorption system.

04/01713 Development of the meso- and macroporous structure of coals with rank as analysed with small angle neutron scattering and adsorption experiments: Prinz, D. et al. Fuel, 2004, 83, (4–5), 547–556

Brown coals have a considerable number of acidic functional groups of which the main component is carboxyl groups, and the acidity has a wide distribution. In this paper, changes of the acidity distribution were examined by aqueous titration when brown coal was heat-treated to control its acidity distribution. For Loy Yang brown coal from Australia dried at 50 °C under vacuum (LY50), the acid dissociation constant, Ka, was distributed over a wide pKa range between 2 and 9. Then, using Gaussian functions, the acidity distribution was divided into four groups, which were characterized by average pKa values: average pKa value of 3.8 (hereafter referred to as Group A), 5.2 (Group B), 6.8 (Group C), and 8.3 (Group D). Among them, Groups A, B, and C were assigned to carboxyl groups. From the changes of the number of carboxyl groups when brown coal was heat-treated up to 400 °C, it was found that the way of decrease was different among these acidic groups. The decrease of the amount of carboxyl groups in Group C was significant, and at 325 °C most of them disappeared. On the other hand, the carboxyl groups in Group A remained even at a high temperature of 400 °C. We estimated approximately the structures around carboxyl groups for LY50 and their structural changes by heat treatment using the known pKa values for simple carboxylic acids and the pKa values calculated by the MOPAC program for complicated carboxylic acids.

Acidity distribution of carboxyl groups in Loy Yang brown coal: its analysis and the change by heat treatment

Brown coals have a considerable number of acidic functional groups of which the main component is carboxyl groups, and the acidity has a wide distribution. In this paper, changes of the acidity distribution were examined by aqueous titration when brown coal was heat-treated to control its acidity distribution. For Loy Yang brown coal from Australia dried at 50 °C under vacuum (LY50), the acid dissociation constant, Ka, was distributed over a wide p Ka range between 2 and 9. Then, using Gaussian functions, the acidity distribution was divided into four groups, which were characterized by average p Ka values: average p Ka value of 3.8 (hereafter referred to as Group A), 5.2 (Group B), 6.8 (Group C), and 8.3 (Group D). Among them, Groups A, B, and C were assigned to carboxyl groups. From the changes of the number of carboxyl groups when brown coal was heat-treated up to 400 °C, it was found that the way of decrease was different among these acidic groups. The decrease of the amount of carboxyl groups in Group C was significant, and at 325 °C most of them disappeared. On the other hand, the carboxyl groups in Group A remained even at a high temperature of 400 °C. We estimated approximately the structures around carboxyl groups for LY50 and their structural changes by heat treatment using the known p Ka values for simple carboxylic acids and the p Ka values calculated by the MOPAC program for complicated carboxylic acids.