Untreated Char Research Articles

Elevating clean energy through sludge: A comprehensive study of hydrothermal carbonization and co-gasification technologies

This study explores the recycling challenges of industrial sludge, owing to its non-recyclable properties and associated environmental problems. To promote sustainable energy utilization, a novel approach combining hydrothermal carbonization and co-gasification was employed to facilitate the conversion from waste to energy. The industrial sludge was pretreated in the batch-type hydrothermal treatment unit at 180–220 °C, followed by co-gasification. The experimental results indicate that pretreating the sludge at the hydrothermal temperature of 200 °C maximized its thermal decomposition, leading to a rougher structure with obvious cracks, eventually transforming into numerous fragmented small particles. At 1100 °C with a blending mass ratio of 1:1, the sludge hydrochar at 200 °C significantly enhanced the reactivity of coal char, exhibiting the gasification reactivity index R0.9 of 1.57 times higher than that of untreated char. Using the in-situ technique with the heating stage microscope, it was first observed that the addition of pretreated sludge coal chars underwent gasification in the shrinking core mode, displaying a significant ash melt flow phenomenon. Based on the in-situ X-ray diffraction, it was discovered that more amorphous structures were formed by the reaction of Fe with other minerals in the sludge-coal blended char after hydrothermal carbonization at 200 °C. With pretreatment at the hydrothermal temperature of 200 °C, the sludge can increase the specific surface area of the blended char and facilitate the cracking of carbon crystals during co-gasification. Its specific surface area and the Raman spectroscopic ratio ID1/IG were 1.76 and 1.17 times that of coal char, respectively. Collectively, this study highlights the potential for energy recovery from industrial sludge, contributing to sustainable waste management in the chemical industry.

Cure characteristics and mechanical properties of natural rubber vulcanizates filled with untreated pyrolytic tire char

AbstractUntreated pyrolytic tire char was used in natural rubber (STR20) composites as single filler at loadings of 30–70 phr and co‐filler with carbon black (N330) at a total loading of 50 phr. The results were compared with rubbers filled with N330 and crumb rubber at 30 phr. The effects of fillers on cure characteristic, crosslink density, filler dispersion in natural rubber vulcanizates and their mechanical properties were investigated. The slight reversions were seen for the cure characteristics of 70 phr‐char‐filled and all co‐filler samples because the sulfur amount in the char together with the added sulfur could shift the vulcanization system from EV to SEV, whereas plateau cure curves were seen for the rest. While the highest tensile strength of char‐filled sample was obtained at 50 phr loading, whose tensile strength was about 88% of the N330 sample at 30 phr, 70‐phr‐char filled sample was superior in surface hardness, abrasion resistance and tear strength to N330 sample at 30 phr. For rubber with co‐fillers, the mechanical properties depended on the mass ratio of N330 to pyrolytic tire char. Therefore, it is possible to use untreated char as reinforcing filler for suitable applications according to their properties.

Development of high-strength and durable coal char-based building bricks

Pyrolysis coal char is a byproduct of the coal industry and causes undesirable environmental issues from conventional coal combustion and gasification. This paper presents a novel approach to utilize coal char for manufacturing new and environmentally friendly building bricks. The effects of sand, silica fume (SF), superplasticizer (SP), air-entraining admixture (AE), and graphene oxide (GO) on the properties of char-based bricks, including heat of hydration, thermogravimetric and differential thermal analysis, microstructures, density, and compressive strength, are investigated. A new treatment method using hydrophobic liquid in a vacuum condition is proposed to improve the durability of char bricks, which is evaluated based on water absorption and freeze-thaw (F-T) cycles. The experimental results indicate that the new bricks with 40% char content have a good compressive strength performance of 49.2–52.5 MPa, which compares favorably to conventional clay bricks with compressive strength of 10–20 MPa. Adding AE and GO slightly increases and decreases the compressive strength at 28 days, respectively. Moreover, the proposed treatment method significantly improves the durability of char bricks. The treated char bricks exhibit a boiling water absorption of ≤2.3%, which is 90% lower than that of untreated char bricks. The untreated and treated char bricks can achieve 22 and 120 F-T cycles, respectively. Overall, this study presents a promising approach to repurpose coal char and produce sustainable building bricks with high compressive strength and durability.

Catalytic steam gasification of food waste using Ni-loaded rice husk derived biochar for hydrogen production

The disposal of food waste (FW) is a major cause of environmental contamination. This study reports an environmentally friendly FW disposal method in the form of catalytic steam gasification using various types of Ni-loaded chars (untreated char, steam-treated char, and ZnCl2-treated char). The results were also compared with the gasification results from the Ni catalysts supported on commercial α-alumina (Ni/α-Al2O3). The Ni/steam-treated char showed the maximum hydrogen generation (0.471 mol/(g feedstock•g cat)) because of the high reducibility, high nickel dispersion, large amount of inherent K and Ca, and moderate surface area. The overall gas and H2 yield were observed in the following order: Ni/steam-treated char > Ni/ZnCl2 treated char > Ni/untreated char > Ni/α-Al2O3. Brunauer-Emmett-Teller analysis of various catalysts showed that the treated chars have a mesoporous structure, and the X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy – energy dispersive spectroscopy showed that the presence of silica in the chars providing the stable support for the Ni loading and prevented coke formation. The chars obtained from biomass pretreatment could be a potential solution for preventing coke formation at high temperatures, thereby increasing the gas yield and enhancing hydrogen generation.

Conversion of chicken feather waste via hydrothermal carbonization: process optimization and the effect of hydrochar on seed germination of Acacia auriculiformis

Using statistical response surface methodology this paper primarily investigates the role of process parameters at different levels (temperature, contact time, and rotation speed) and their influence on yield percentage during the production of chicken feather hydrochar (CFH) as soil amendment. Later, the produced char samples were evaluated before and after washing to assess the phytotoxic effect of seed germination and growth on Acacia auriculiformis through germination index% (GI). The optimized conditions for temperature, contact time, and rotation speed of hydrochar production were 150 °C, 1 h and 105.65 rpm, respectively. The hydrochar yield percentage at optimized conditions was 51.93%. The seed germination test indicated strong phytotoxicity for soil with untreated char, fresh hydrochar extract (FHE) with high doses, and 4 months old hydrochar extract (OHE) but the toxic effect was lower for washed hydrochar extract (WHE). It showed a higher germination rate and growth performance for washed hydrochar extract among all the doses. This study has confirmed the applicability of chicken feather (CF) hydrochar for improving the physical properties of sandy loam soil. Further research into pre-treatment and assessment of hydrochar before field application is required.

Valorization of Char From Biomass Gasification as Catalyst Support in Dry Reforming of Methane

This study responds to the need of finding innovative routes for valorizing char derived from biomass gasification. Char is currently treated as a waste representing an energetic and economic loss for plant owners. However, it displays many similarities to activated carbon (AC) and could replace it in several applications. In this regard, the current work investigates the use of gasification derived char as catalyst support in dry reforming of methane (DRM) reactions. Char collected from a commercial biomass gasifier currently in operation was characterized and employed for the synthesis of cobalt catalysts. The catalysts were characterized and tested in an atmospheric pressure fixed bed reactor operating at 850°C with CH4:CO2 = 1 and a weight hourly space velocity of 6,500 mL g−1 h−1. The effectiveness of the synthesized catalysts was defined based on CO2 and CH4 conversions, the corresponding H2 and CO yields and their stability. Accordingly, catalysts were synthesized with cobalt loading of 10, 15 and 20 wt.% on untreated and HNO3 treated char, and the catalyst with optimum comparative performance was promoted with 2 wt.%MgO. Catalysts prepared using untreated char showed low average conversions of 23 and 17% for CO2 and CH4, yields of 1 and 14% for H2 and CO, and deactivated after few minutes of operation. Higher metal loadings corresponded to lower conversion and yields. Although HNO3 treatment slightly increased conversions and yields and enhanced the stability of the catalyst, the catalyst deactivated again after few minutes. On the contrary, MgO addition boosted the catalyst performances leading to conversions (95 and 94% for CO2 and CH4) and yields (44 and 53% for H2 and CO) similar to what obtained using conventional supports such as Al2O3. Moreover, MgO catalysts proved to be very stable during the whole duration of the test.

Untreated and HNO3-treated pyrolysis char as catalysts for pyrolysis of waste tire: In-depth analysis of tire-derived products and char characterization

The pyrolysis char produced in the pyrolysis of scrap tire rubber has few market outlets, reducing the economic viability. Thus, the char properties was firstly studied in this work, and then untreated and 5M HNO3-treated chars were investigated for their potentials as the catalysts for pyrolysis of waste tire. The product distribution and the quality of tire pyrolysis oil were examined. The gas products were analyzed by using GC/FID whereas the oil products were analyzed by using SIMDIST-GC and GC×GC/TOF-MS. Sulfur and nitrogen contents were determined by using CHNS-analyzer. The catalysts were also characterized by using BET, XRD, XRF, FTIR, FE-SEM, and TG/DTA. The results indicated that the surface area and pore size of treated char were enhanced by the acid treatment. Furthermore, it can be noted that the increase in the total acidity of treated char was caused by the enhancement of carboxyl (-COOH) group on the surface. Additionally, the treatment using 5M HNO3 can demineralize and significantly reduce sulfur content in the char. When employed as a catalyst, the HNO3-treated char increased the gas production due to its enhanced acidity, surface area and pore size, consequently promoting the greater cracking activity. However, both untreated and treated chars dramatically decreased gas oil, light vacuum gas oil, and heavy vacuum gas oil, leading to the drastic enhancement of gasoline and kerosene. Moreover, even though the char catalysts cannot reduce nitrogen content in oil, they can greatly remove sulfur in oil (approximately 26.6–27.3%). Nevertheless, the untreated char that contained a larger content of elements or minerals than the treated one gave significantly higher petrochemical production, which indicates that deminerization by the acid treatment may not always be needed for better activity, especially for petrochemical production.

Adsorptive removal of atmospheric pollutants over Pyropia tenera chars

As a replacement for activated carbon, biochar was synthesized and used for the adsorptive removal of formaldehyde and nitrogen oxide. Biochar was produced from the fast pyrolysis of the red marine macro alga, Pyropia tenera. The P. tenera char was then activated with steam, ammonia and KOH to alter its characteristics. The adsorption of formaldehyde, which is one of the main indoor air pollutants, onto the seaweed char was performed using 1-ppm formaldehyde and the char was activated using a range of methods. The char activated with both the KOH and ammonia treatments showed the highest adsorptive removal efficiency, followed by KOH-treated char, ammonia-treated char, steam-treated char, and non-activated char. The removal of 1000-ppm NO over untreated char, KOH-treated char, and activated carbon was also tested. While the untreated char exhibited little activity, the KOH-treated char removed 80% of the NO at 50°C, which was an even higher NO removal efficiency than that achieved by activated carbon.

Determination of alkylphenols in eluates from pyrolysis solid residues using dispersive liquid–liquid microextraction

Dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–mass spectrometry (GC–MS) was applied for the determination of 11 alkylphenols in eluates of chars produced in the co-pyrolysis of different wastes. The optimized DLLME procedure, 4 mL of sample solution, 15 μL of trichloroethylene as extraction solvent, 1 mL of acetone as dispersion solvent and addition of 15% (w/v) of NaCl, was validated. Under the optimum conditions, the enrichment factors were in the range of 82–180. Calibration curves were constructed for each analyte in pure water in the concentration range of 0.5–8 μg/L with correlation coefficients higher than 0.999. The limits of detection were between 0.07 and 0.17 μg/L. The repeatability of the method was evaluated using water samples fortified with the analyte mixture at two concentration levels: the relative standard deviation (RSD) values were between 3.7% and 8.0% for a concentration of 0.5 μg/L, and between 4.2% and 6.4% for a concentration of 3 μg/L. The recoveries of the analytes evaluated by fortification of real eluate samples were in the range of 67.9–97.9% for eluate 1 (obtained from a decontaminated char) and in the range of 61.9–101.4% for eluate 2 (obtained from the untreated char). o-Methylphenol presented low recoveries for both eluates showing a possible matrix effect. The results obtained show that this method is adequate for the determination of alkylphenols in environmental aqueous samples and presents itself as a fast and inexpensive technique, using minor amounts of organic solvents.

Preparation and characterization of activated carbon derived from the thermo-chemical conversion of chicken manure

Physico-chemical properties of a bioorganic char were modified by pyrolysis in the presence of NaOH, and with subsequent physical activation of carbonaceous species with CO 2 a value-added activated carbon was fabricated. Bioorganic char is produced as a co-product during the production of bio-fuel from the pyrolysis of chicken litter. Untreated char contains ∼37 wt% of C and ∼43–45 wt% of inorganic minerals containing K, Ca, Fe, P, Cu, Mg, and Si. Carbonization and chemical activation of the char at 600 °C in the presence of NaOH in forming gas (4% H 2 balanced with Ar) produced mainly demineralized activated carbon having BET (Brunauer, Emmett, and Teller) surface area of 486 m 2/g and average pore size of 2.8 nm. Further physical activation with CO 2 at 800 °C for 30 min resulted in activated carbon with BET surface area of 788 m 2/g and average pore size of 2.2 nm. The mineral content was 10 wt%. X-ray photoelectron spectroscopy (XPS) indicated that the latter activation process reduced the pyrrolic- and/or pyridonic-N, increased pyridinic-N and formed quaternary-N at the expense of pyrrolic- and/or pyridonic-N found in the untreated char.

Fates of radioactive arsenic, cesium, strontium and organo-chlorine during the gasification of mixed wastes in the presence of organic matter

Radioisotopes of arsenic, cesium, strontium and chlorine were mixed with organic matter to make mixed radioactive/hazardous wastes and gasified to destroy the organic fractions on a macroporous char matrix in a laboratory-scale version of cocurrent flow waste gasification. Except for chlorine, gasified as chlorobenzene on untreated char, essentially all the radionuclides were retained in the gasifier on the char residue. Complete retention of chlorine was obtained by treating the char with sodium hydroxide. Condensate from the gas product and char from a filter used to filter the gas can be recirculated through the system as additional assurance of zero release of radioactive substances. The spent char from the gasifier can be regasified with additional wastes, resulting in a concentration of radioactive substances onto char, which can eventually be converted to a nonleachable slag for ultimate disposal.

石炭ガス化触媒の反応特性の比較

The catalytic properties of three catalysts, potassium, calcium and nickel, in coal char gasification were compared using Blair Athol char devolatilized at 750°C and steam-helium or -hydrogen as the gasifier. The three catalysts behaved differently in reaction pattern, dependence on the amount of the catalyst and composition of the products. In steam-helium, the activities of the calcium and nickel decreased more rapidly than those of the potassium. The catalytic conversion with the nickel was almost proportional to the amount of the nickel, while that with the calcium slightly depended on its amount and this is ascribed to its poor dispersion on char surface. The rate of the nickel-catalyzed gas-ification in steam-hydrogen increased gradually with time until a maximum at about 25% burn-off and then decreased.With a demineralized char, smaller amount of potassium was effective, as compared to the untreated char, probably due to the absence of the deactivating action of mineral matters. In the initial stage of this reaction, carbon monoxide was the main product, whereas carbon dioxide was the main one in the later stage. This is taken to indicate that potassium salt catalyzed the formation of carbon dioxide directly from carbon and steam, under the differential reaction conditions.

Sulphur in char and char desulphurization by acid leaching and hydropyrolysis

Sulphur compounds volatilized during pyrolysis of acid-leached char were measured to determine characteristics of char desulphurization reactions. Pyrolysis of char in a hydrogen atmosphere (hydropyrolysis) produced a much higher concentration of thiophenic organics compared with that produced during pyrolysis in a nitrogen atmosphere. Hydrogen sulphide gas evolution, at progressively increasing pyrolysis temperature in a helium atmosphere, was measured on five char samples: untreated char, hydrochloric acid-leached char, and three model chars: a demineralized char and two demineralized chars incorporated with sulphur via reactions with elemental sulphur. Hydrogen sulphide gas evolution in untreated char and acid-leached char was found to peak in three temperature regions; the maxima are thought to relate to sulphur in different bonding environments. The amounts of hydrogen sulphide volatilized were much higher for acid-leached char than for untreated char. The gas evolved from each of the remaining three samples showed a single peak region corresponding closely to one of the three peak regions observed for the first two chars. The results of this study indicate that elemental sulphur was produced during hydrochloric acid leaching of the untreated char and suggested that the improved rate of desulphurization observed in the char that had been acid-leached before hydropyrolysis was due in part to the conversion of strongly bound mineral sulphur forms to more weakly bound sulphur forms that are predominantly elemental sulphur in character, and are more easily removed by hydrogen.