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Sustainable biomaterial binders developed from lignin plus collagen have offered effective binder systems for the fabrication of specialty graphites and graphite electrodes. To further chronicle collagen's synergistic effects and benefits, the authors appraised the formation and evolution of the chars pyrolyzed from lignin, collagen and their blends. Following pyrolysis in a vertical tube furnace at 1000 °C, the lignin-collagen blend yielded more char than did mere lignin or mere collagen. Elemental analysis indicated that along with the release of the oxygenated, nitrogenated, and hydrogen-containing gases, the collagen's presence facilitated carbon-enriched chars with more oxygenated polyaromatic structures. Collagen yielded an aryl (aromatic) carbon source in the aromatic condensation reactions, leading to the continuous cross-linking and growth of the lignin aromatic rings. Per Fourier-transform infrared spectroscopy (FTIR), during pyrolysis, collagen enhanced the hydrogen aromaticity index, and reduced the extent of aromatic substitution. The collagen presence facilitated more removal of functional groups, as indicated by bonded O–H stretching, symmetric CH3 stretching in O–CH3, and aliphatic C–H stretching. Scanning electron microscope (SEM) revealed that collagen served as a thermoplastic bio-binder that formed a thermally-fused framework with lignin. Thus, collagen induced significant differences in solidification behaviors and surface morphologies.

A morphological study of lignin-bound anthracite briquettes was carried out to understand the mechanisms that hold together anthracite fines and silicon grains at elevated temperatures and high abrasion conditions. Lab-scale briquettes were prepared from anthracite fines, lignin, collagen, silicon, and other additives; and then pyrolyzed at 800 °C, 1400 °C and 1600 °C under nitrogen atmosphere to simulate the conditions inside a foundry cupola. The pyrolyzed samples were analyzed by reflected light microscopy, electron microscopy and x-ray diffraction. These analyses gave information on the transformations that lignin-bound anthracite briquettes may undergo in a cupola furnace. Lignin and collagen melted and formed an amorphous carbon phase that linked anthracite and silicon grains. Silicon carbide (SiC) nanowires coated in silicon oxide were formed at 1400 °C, and at 1600 °C most of the silicon was converted to SiC. Silicon carbide nanowires filled the interstitial voids left by volatilization of lignin and collagen. These findings support the idea that lignin and collagen hold anthracite fines at low temperature regimes. Silicon carbide nanowires contribute to briquette strength at high temperature conditions, acting as reinforcing filler and prevent collapse of the lignin-collagen matrix surrounding the anthracite grains.

Sustainable biomaterial binders were developed from lignin and collagen to replace the conventional petroleum pitch and coal tar pitch binders that have been used when making specialty graphites and graphite electrodes. The team prepared lab-scale graphite electrodes by first creating green composites, by hot-pressing together the lignin, collagen, petroleum coke, and other additives, followed by carbonization and graphitization. Response Surface Methodology (RSM) experimental design was employed, based on Box-Behnken Design (BBD). This was employed to optimize the recipes and processing protocols for the green composite hot-pressing of 3.5 cm diameter × 19 cm long cylinder specimens. Relative to density, the apparent optimum conditions occurred with 13.0% lignin, 3.6% collagen, 27.4% petroleum coke fines, and the balance of petroleum coke particles plus some additives. The green hot-pressing protocol employed 30 MPa pressure at 400 °C for 2 h. Baking peaked at 800 °C, ramped up and down over 13 days. This baked product hosted an apparent density of 1.67 g/mL, and exhibited 6.2% puffing. Another baked product hosted 1.56 g/mL and 1.67% puffing. After the baked product was graphitized, we achieved an apparent density of 1.51 g/mL and resistance of 25–30 μΩm. These results approached the specifications for specialty graphites.

Construction of large-scale atomistic representations of activated carbon aids exploration of structure–property relationships. The construction approaches for existing structures are limited in the control over the distribution of structural features. Here, an initial atomistic representation of a lignite-based activated carbon was constructed using a construction strategy that allows control over the distributions of stacking, degree of orientation, and pore size. Fringe3D was used to produce a collection of 42 molecules within 25 stacks comprised of graphene sheets with control over their length, orientation, and stack height. Vol3D populated the specified 100 × 100 × 100 A cuboid volume with an assumed Gaussian distribution of stack width, without changing orientation and thus retaining regional organization. Eight of these were combined to create a large-scale structure. The pore size distribution was captured due to smaller microporosity caused by packing inefficiencies of the stacks and by inclusion of additional desired porosity. To demonstrate the control over the extent of curvature, three 200 × 200 × 200 A structures overall were constructed with varying extent of curvature. The construction protocols were efficient producing large-scale structures (∼330,000 atoms) constructed far more rapidly than traditional strategies using a personal computer.

A novel method has been developed for immobilizing (tailoring) polypyrrole (PPy) into activated carbon (AC) in a manner that facilitates the removal of sulfate, and then electrochemically regenerating the tailored activated carbon. This tailoring was achieved by sorbing pyrrole into AC pores, then oxidizing the pyrrole by means of either a FeCl 3 oxidant or electrochemical oxidation. The resultant oxidized PPy hosted a positive charge that sorbed sulfate from acid mine drainage (AMD) water. Next, the spent AC/PPy was electrochemically reduced such that the nitrogen functionality became neutrally charged, and released the sorbed sulfate. This AC/PPy was then electrochemically oxidized such that it regained a positive charge, and again sorbed sulfate. When processing rapid small scale column tests (RSSCTs) with AMD water that contained 773 mg/L SO 4 2− the media processed 23 bed volumes before breakthrough occurred. Subsequent to these RSSCTs, electrochemical reduction at −2.0 V (vs Ag/AgCl) released 95% of this sorbed sulfate, and subsequent oxidation at 0.4 V yielded a media that had restored 61.5% of its initial sulfate-sorption capacity.

Positively charged nitrogen functional groups were introduced onto the surface of granular activated carbon (GAC), and these increased perchlorate anion removal from drinking water sources. Nitrogen functionalization involved three treatment steps: (1) introducing oxygen groups onto the GAC, (2) incorporating nitrogen groups by thermal treatment in ammonia flow to replace O with N, and (3) quaternerizing pyridine-like groups to create positively charged pyridinium-like groups. Functionalized bituminous GAC provided 6 times more perchlorate removal than its predecessor, pristine bituminous GAC. The conversion of pyridine-like groups (after step 2) to pyridinium-like groups by quaternization (step 3) was confirmed by analysis of the XPS N 1s signals and surface charge analysis. Redox peaks, observed during cyclic voltammetry analysis of the functionalized GAC, evidenced that these nitrogen functional groups were electrochemically active, so that they sorbed perchlorate when they were oxidized, and then desorbed perchlorate when reduced. Moreover, after sorbing perchlorate onto pyridinium-GAC in RSSCTs, the GAC media could be regenerated by electrochemical reduction, and its capacity for perchlorate adsorption was mostly restored. This tailored functionality and redox regeneration of a relatively inexpensive media such as activated carbon could offer novel opportunity to the adsorption industry.

A novel method of removing sulfate from acid mine drainage (AMD) water was developed by depositing polypyrrole into the pores of wood-based activated carbon (RGC) using in situ chemical oxidative polarization. This polypyrrole-tailored activated carbon hosted positively charged polypyrrole functionality that offered sorption capacity for sulfate. Specifically, in batch tests, the polypyrrole-grafted RGC achieved a sulfate loading of 48 mg/g, this being 8 times higher than for pristine RGC. Rapid Small Scale Column Tests appraised the polypyrrole-tailored RGC for removing 773 mg/L sulfate from AMD water. The more favorably tailored carbon removed sulfate to half-breakthrough at 24 bed volumes (BV). This compared to 1.5 BV for pristine activated carbon. Per mass and charge balance, 9% of the nitrogen in the polypyrrole functionality was active for capturing sulfate. On this tailored carbon, the nitrogen content was 12.9%, as characterized by X-ray photoelectron spectroscopy. With this polypyrrole tailoring, the carbon’s pore volume distributions diminished to one-third, as characterized by argon adsorption.

The current study uses nuclear magnetic resonance, Fourier-transform infrared spectroscopy and Raman spectroscopy to investigate the evolution of refined softwood and hardwood lignins under various pyrolytic exposures. Little chemical change occurred at pyrolysis temperatures of 250 and 300 °C, whereas significant mass loss and chemical change was observed at 400 and 500 °C. These losses were mainly attributed to evolution of methoxyl, hydroxyl, and propyl groups. Mass loss plateaued following pyrolysis at 500 °C, but rearrangements continued to occur at higher temperatures, resulting in char that became increasingly polyaromatic in nature. Following brief pyrolytic exposures at 500 and 600 °C, the refined hardwood and softwood lignins yielded coal-like products. Lignin pyrolyzed at higher temperatures yielded chars with greater order, similar in composition to coke. These coal and coke-like products are called “lignin-based carbon” (LBC). The polyaromatic nature of the LBC after high temperature pyrolysis was perceived as the result of radical formation and recombination, leading to fused aromatic structures, which occurs more readily at higher temperatures.

A novel method has been developed for anchoring quaternary ammonium/epoxide-forming compounds (QAE) within bituminous and wood based granular activated carbons (GACs). This QAE-anchored GAC was then used to enhance perchlorate removal from perchlorate-spiked natural groundwater. Specifically, for the bituminous based carbon, while processing natural groundwater that had been spiked with 30–35 ppb perchlorate, and passing this water through rapid small scale column tests, the bed volumes (BV) to 2 ppb perchlorate breakthrough increased from 870 BV for pristine GAC up to 21,000 BV for the corresponding GAC that had been pre-anchored with QUAB360 (360 Da). However, the wood based GAC that had been anchored with this QUAB360 achieved only 3000 BV. None of the QAE leached out of these GACs during the column tests. The bituminous GAC that had been pre-anchored with QAE hosted more positive surface charge at pH 7.5 than did the wood based QAE–GAC. Per X-ray photoelectron spectroscopy, the QAE anchored into the GACs increased their N-content by 1–1.3%. By means of multiple analyses, the authors surmised that the active quaternary ammonium sites within the tailored bituminous-based GAC were more exposed and thus more accessible for perchlorate adsorption than those within wood based GAC.

Thermal reactivation with CO2 or NH3 at temperatures higher than 700 °C effectively restored the perchlorate adsorption capacity of ammonia-tailored carbon. In contrast, steam regeneration restored only a portion of the perchlorate adsorption capacity, and these distinctions were attributed to the change in surface chemistry that was induced by regeneration. After perchlorate loading, regenerating the ammonia-tailored GAC via CO2 or NH3 preserved the nitrogen content and positive surface charge density of the initial ammonia-tailored activated carbon. In contrast, steam regeneration caused a decrease in nitrogen content and positive surface charge. Perchlorate breakthrough was monitored in rapid small-scale column test (RSSCT) operations with either CO2 or NH3 regeneration. 4000–4500 bed volumes of perchlorate adsorption life could be achieved through at least three cycles of RSSCT operation and regeneration. This compared favorably to the 4500 bed volumes that had been achieved when using the initial ammonia-tailored carbon.

Water contact pH experiments employing several reactivated granular activated carbons (GAC) showed that reactivated carbons exhibit pH excursions (i.e., pH > 8.5) when wetted. Moreover, when the water contact pH was predicted based on the log of the quantity of calcium that leached out of the GAC during the pH experiments, good agreement was obtained with the measured water contact pH for reactivated GACs that contained a range of calcium content, typically 0–1% wt. Ca.

Thermal tailoring of a bituminous granular activated carbon (GAC) by ammonia gas at 500–800 °C for 60 min achieved as much as 4-fold improvement in perchlorate adsorption as determined by rapid small-scale column tests (RSSCTs). When treating natural groundwater that contained 70–78 ppb perchlorate, the bed volumes to 4 ppb perchlorate breakthrough increased from 1100 bed volumes for commercial bituminous carbon up to 4400 bed volumes for carbon that was tailored in ammonia at 700 °C. Increased perchlorate adsorption corresponded to increased positive surface charges with R2 0.956. The increase in positive surface charge was closely related to the increase in nitrogen content after ammonia tailoring. The ammonia-tailored activated carbons also exhibited a moderate increase in TOC removal and higher selectivity for erchlorate. The work herein interfaces with a companion paper by the same authors in which the ammonia-tailored carbon surfaces are characterized relative to physical–chemical features [1] .

A commercially available bituminous granular activated carbon (GAC) was subjected to thermal treatment with ammonia for 60 min at temperatures of 500–800 °C. The effect of this treatment on the physical and chemical characteristics of carbon was studied in detail. Comparison of virgin and NH3-tailored carbons relative to pore volume distribution and argon-BET surface area indicated that ammonia acted as an activating agent under these conditions. Micropore volume increased with increasing treatment temperature up to 700 °C; and then declined at 800 °C. Elemental analysis results showed that nitrogen was incorporated into the carbon matrix during the thermal treatment as proven by an increase in N-content from 0.64% for virgin GAC up to 1.61–1.63% for all the tailored samples. The ammonia treatment caused an increase in positive surface charge density over a broad pH range; and this was reflected in a higher pHpzc and pHIEP. This was attributed to the more basic nature of the carbon surface after its treatment in ammonia.

Thermal treatment by steam or by methane plus steam altered the physicochemical properties of a commercial lignite-based activated carbon; and improved the carbon’s sorption capacity for the odorant 2-methylisoborneol (MIB). Rapid small scale column tests (RSSCTs) revealed that favorable thermal treatment allowed an activated carbon to remove this odorant for up to six times longer before initial MIB breakthrough than did its commercial lignite counterpart. For these RSSCTs (135 ppt), clarified water from a water treatment plant (2.07 mg/L TOC) was spiked with 14 C-MIB; and liquid scintillation protocols facilitated 14 C-MIB detection at 1–3 ppt. The more favorable thermal treatment at 1000 °C increased pore volumes with 5–400 A widths by twofold; and the bed volume to initial MIB breakthrough correlated fairly well ( R 2 = 0.9) with pore volume in the range of 5–60 or 5–400 A. Thermal tailoring altered the carbon’s apparent point of zero charge: from pH 6.5 for the commercial lignite carbon, to pH 9.2 for tailored carbon. When methane and steam were used together, the C, H, N and O contents were virtually the same as for the commercial lignite. In contrast, when steam was employed alone, the percent of oxygen increased, and the percent of H, C and N therefore decreased slightly.

During full-scale water treatment operation at the Richard Miller water treatment plant (Cincinnati, Ohio) we frequently evaluated the changes in pore volume distributions of a reactivated (F-400) granular activated carbon (GAC), as compared with that of its virgin counterpart. The reactivated GAC had experienced six cycles of water treatment and thermal reactivation. The reactivated GAC was slightly more effective at removing TOC (total organic carbon) than was the virgin GAC during the first half-year of service. Yet, the pore size distributions of the two GACs were very different. The virgin GAC was mostly microporous, with less mesopores. Conversely, the reactivated GAC was mostly mesoporous, with less micropores. For the virgin GAC, adsorption changed the volume of pores below 50 A in width most significantly, and there was minor change in pores larger than 50 A. In contrast, the reactivated GAC showed the greatest volumetric change in pores that were 100 to 500 A in width.

In order to overcome the deleterious effects of calcium catalysis during thermal reactivation, the authors have developed a methodology for first steam-curing spent GAC at 548–748 K, and then ramping the furnace temperature to 1023–1223 K while exposing the GAC to flowing N2. In this article, the authors evaluated the influence of an array of parameters on the steam-curing plus ramped-temperature protocol that included curing time, curing temperature, ramped-to temperature and steam flow rate. Pore size distribution (PSD) measurements employed the density functional theory (DFT), and these revealed that the steam-curing time had the greatest influence on pore size distribution: increasing the steam-curing time from 15 to 60 min increased the

The objective of this research was to describe equilibrium between volatile organic compounds and granular activated carbon (GAC) during adsorption and desorption processes occurring in carbon beds used for air pollution control. A thermogravimetric analyzer measured the adsorption of methylisobutylketone (MIBK) onto a coconut based GAC at concentrations ranging from 55 to 10 300 ppmv and temperatures ranging from 25 to 105°C. The equilibrium adsorption data was first modeled by the two-parameter isotherms of Langmuir, Brunauer–Emmett and Teller, and Freundlich as well as the three-parameter isotherm of Dubinin–Astakhov. Also, a new three-parameter isotherm, created by adding a concentration-dependent term to the Freundlich equation, was introduced as the modified Freundlich isotherm. In both three-parameter isotherms, proper choice of the extra parameter allowed for a more accurate fit of the isotherm than did any of the two-parameter isotherms. Moreover, the authors have constructed a modified Freundlich polytherm and a Dubinin–Astakhov polytherm that properly described adsorption and desorption over the full range of test temperatures and concentrations.

This research evaluates adsorption equations for argon, nitrogen, and volatile organic compound adsorption onto several commercially available activated carbons that represented a broad range of pore volume character, from predominantly microporous to predominantly mesoporous. For all these carbons, both the recently introduced (Paulson PD, Cannon FS, submitted to Carbon) Modified Freundlich equation and the Dubinin–Astakhov equation accurately characterized adsorption behavior in the relative pressure range of 1.0×10−5 to 0.1 for argon adsorption onto six different activated carbons and for nitrogen adsorption onto two different activated carbons. In particular, the Modified Freundlich equation offered a slightly better fit to the experimental data for mesoporous carbons in the full relative pressure range, and to all activated carbons in the relative pressure range of 10−2.5 to 0.1. Micromeritics’ density functional analysis software further used this argon and nitrogen adsorption data to characterize these activated carbons by their pore volume distribution. The Modified Freundlich’s v0MF term correlated best to the cumulative pore volume up to 60 A and the Dubinin–Astakhov’s v0DA term correlated best to the cumulative pore volume up to 30 A as determined via density functional theory. In addition, the research herein identified a consistency in the adsorption behavior of methylisobutylketone, m-xylene, and argon at their respective boiling points.

In response to proposed EPA regulations governing disinfection by-products the water treatment industry may need to remove natural organic matter (NOM) more extensively prior to chlorination. Unit processes such as granular activated carbon (GAC) adsorption and enhanced coagulation can be used to achieve conformance with these proposed regulations; and the water treatment industry actively seeks means to reduce the cost of these unit processes. One of the cost-saving steps in GAC use pertains to its reactivation; however the buildup of calcium within GAC pores can deleteriously alter the micropores of the GAC during thermal reactivation and affect its performance. Thus, it is proposed that by reducing the buildup of calcium within GAC during water treatment service, a utility could improve its reactivation effectiveness. The purpose of this paper is to explore how iron coagulation and competitive complexation with NOM can limit calcium accumulation within GAC, and therefore contribute to favorable reactivation. Research conducted by the authors has shown that iron addition and coagulation prior to GAC treatment is capable of the following favorable effects: (1) promoting complexation between Fe and NOM, preventing Ca-NOM complexes from forming, and thus limiting calcium accumulation in complexed form onto GAC; and (2) removing substantial fractions of NOM ahead of the GAC beds such that subsequent GAC bed life increases considerably. By minimizing calcium accumulation, less destruction of micropores occurs during reactivation. Furthermore, reactivation becomes less frequent when bed life is increased. Both high (20 mg L−1) and moderate (5 mg L−1) iron (as Fe) dosages were found to be effective at preventing calcium accumulation. Also, tests determined that a pH 6.0 or lower was better than a pH of 7.0 or 8.0 when attempting to achieve calcium exclusion.

The Pennsylvania State University is researching an advanced oxidation system, which includes an air-phase photolytic chamber, an air/water stripping tower, and granular activated carbon (GAC) beds, for controlling volatile organic compounds (VOCs). A laboratory-scale experimental procedure has been employed that simulated certain aspects of several full-scale installations. The apparatus has been used to characterize the loading capacity and mass transfer zone of selected VOCs on coconut shell GAC. The GAC bed has then been placed in series with an ultraviolet reactor, which generates ozone and advanced oxidants in order to regenerate the loaded GAC at intensities of advanced oxidants that were higher than full-scale installations. VOC loading tests revealed that the adsorption of methyl isobutyl ketone (MIBK) was characterized by a well-defined mass transfer zone. Upon exposure to UV/O3, desorption and/or destruction of the MIBK and other VOCs occurred most prominently within the first inch of the GAC bed. This correlated with the penetration of advanced oxidants into the GAC bed, which also occurred most significantly in the bed's first inch. However, the amount of oxidant penetration increased with time. The removal of oxidants from air by GAC was accompanied by a decrease in mass of the GAC. The ability of oxidants to penetrate a GAC bed was altered when the bed was loaded with a VOC.

Thermal regenerations were conducted on a spent granular activated carbon (GAC) that had served in a water treatment plant for about four years and contained 1.8% calcium. Oxidation was conducted in steam, CO2, or steam plus CO2, at 650–950°C. As described earlier, when steam and CO2 were employed together, the regenerated product's pore structure maintained greater micropore volume at high temperatures ( > 800°C) than at low temperatures (