The performance of two adsorption ice making test units using activated carbon and a carbon composite as adsorbents

The available adsorption working pairs applied to adsorption refrigeration system, which utilize activated carbon as adsorbent, are mainly activated carbon-methanol, activated carbon-ammonia, and composite adsorbent-ammonia. The adsorption properties and refrigeration application of these three types of adsorption working pairs are investigated. For the physical adsorbents, consolidated activated carbon showed best heat transfer performance, and activated carbon-methanol showed the best adsorption property because of the large refrigerant amount that can be adsorbed. For the composite adsorbents, the consolidated composite adsorbent with mass ratio of 4:1 between CaCl₂ and activated carbon, showed the highest cooling density when compared to the granular composite adsorbent and to the merely chemical adsorbent. The physical adsorption icemaker that employs consolidated activated carbon-methanol as working pair had the optimum coefficient of refrigeration performance (COP), volume cooling power density (SCP_v) and specific cooling power per kilogram adsorbent (SCP) of 0.125, 9.25 kW/m³ and 32.6 W/kg, respectively. The composite adsorption system that employs the consolidated composite adsorbent had a maximum COP, SCP_v and SCP of 0.35, 52.68 kW/m³ and 493.2 W/kg, respectively, for ice making mode. These results are improved by 1.8, 4.7 and 14 times, respectively, when compared to the results of the physical adsorption icemaker.     

Production of fibrous activated carbons from natural cellulose (jute, coconut) fibers for water treatment applications

Different fibrous activated carbons were prepared from natural precursors (jute and coconut fibers) by physical and chemical activation. Physical activation consisted of the thermal treatment of raw fibers at 950 °C in an inert atmosphere followed by an activation step with CO₂ at the same temperature. In chemical activation, the raw fibers were impregnated in a solution of phosphoric acid and heated at 900 °C in an inert atmosphere. The characteristics of the fibrous activated carbons were determined in the following terms: elemental analysis, pore characteristics, SEM observation of the porous surface, and surface chemistry. As the objective of this study was the reuse of waste for industrial wastewater treatment, the adsorption properties of the activated carbons were tested towards pollutants representative of industrial effluents: phenol, the dye Acid Red 27 and Cu²⁺ ions. Chemical activation by phosphoric acid seems the most suitable process to produce fibrous activated carbon from cellulose fiber. This method leads to an interesting porosity (S_BET up to 1500 m² g⁻¹), which enables a high adsorption capacity for micropollutants like phenol (reaching 181 mg g⁻¹). Moreover, it produces numerous acidic surface groups, which are involved in the adsorption mechanisms of dyes and metal ions.     

不同驱动温度下间歇性太阳能吸附制冰机的实验研究

设计并搭建了太阳能吸附制冰系统,主要包括制冰机、槽式太阳能集热器及恒温油槽等。通过油槽中的电加热模拟不同太阳能辐射量的工况,得到吸附制冰机在不同驱动热源条件下的运行特性。吸附制冰机采用氯化钙/活性炭复合吸附剂,氨作为制冷工质。实验通过电加热模拟的太阳能驱动温度在110～155℃变化,对应的每天制冰量为10～28kg,计算得到太阳能COP为0.09～0.14。     

A consolidated calcium chloride-expanded graphite compound for use in sorption refrigeration systems

A consolidated composite reactive bed for refrigeration sorption systems made from expanded graphite powder impregnated with CaCl₂ was produced and tested. The composite material was compressed under a pressure of 10 MPa to enhance its heat transfer properties. Experimental results showed that this material could incorporate 0.90 kg of NH₃ per kg of salt and that the agglomeration phenomenon was avoided. The blocks with apparent density of 0.56 g cm⁻³ and 35% of expanded graphite ensured a good refrigerant mass transfer with a negligible pressure drop between the inner and outer part of the blocks. However, the heat transfer still need some improvements, as the temperature difference inside the blocks could reach 15 °C during the decomposition phase. The average specific cooling power during the synthesis phase was 306 and 194 W per kg of salt at the average evaporation temperatures of −2.7 and −18.3 °C, respectively. The calculated coefficient of performance under different generation temperatures and global conversions ranged from 0.28 to 0.46, and it was not very sensitive to the increase of the generation temperature.     

Comparison of the adsorption performance of compound adsorbent in a refrigeration cycle with and without mass recovery

Adsorption and desorption were performed on a compound adsorbent composed of CaCl₂ and activated carbon in cycles both with and without mass recovery and the performances obtained were compared with those of equilibrium adsorption. Experimental results of the cycles without mass recovery carried out on an adsorption refrigeration unit yielded performances that were slightly less than those of equilibrium adsorption. The adsorption performances of the cycle with mass recovery were measured to be much better than those of the cycle without mass recovery. At of evaporating temperature, the cycle adsorption capacity was as high as 0.78 kg/kg for the cycle with mass recovery while it was only 0.55 kg/kg for the cycle without mass recovery. The average adsorption/desorption rate of the cycle with mass recovery, which was 0.031 (kg/kg)/min, has been improved by 47.6% compared with that of the cycle without mass recovery. Research on the cycle adsorption capacity at different evaporating temperatures showed that the improvement of cycle adsorption capacity, with mass recovery, was higher under the condition of lower evaporating temperature. At evaporating temperature, the mass recovery operation had improved the adsorption capacity by 78% compared with the cycle without mass recovery. In addition, refrigeration performances for the cycles with and without mass recovery at an evaporating temperature of were studied. Compared with the results of the cycle without mass recovery, SCP (specific cooling power) and COP (coefficient of refrigeration performance) have been improved by 48.6% and 54.5%, respectively, when mass recovery is performed.     

Performance analysis of activated carbon + HFC-134a adsorption coolers

The purpose of this paper is to present the results of performance analysis of a heat driven continuous vapor adsorption refrigerator with activated carbon as the adsorbent and 1,1,1,2-tetrafluoroethane (HFC-134a) as the refrigerant. A set of four adsorption cells takes on the role of the mechanical compressor in the conventional vapor compression refrigeration (VCR) system. Three specimens of activated charcoal under various packing densities were investigated. A parametric analysis was carried out with several evaporating, condensing/adsorbing and desorbing temperatures which are typical operating conditions catered to by HFC-134a. A new integrated relative performance evaluation scheme is proposed. It uses the maximum cycle uptake difference as a factor against which the coefficient of performance (COP) and exergetic efficiency are evaluated. It is shown that there is an optimal set of operating conditions wherein the exergetic efficiency is the maximum. A major part of the thermal energy input is for sensible heating of the compressor body.     

Electrochemical enhancement of adsorption capacity of activated carbon fibers and their surface physicochemical characterizations

The adsorption of activated carbon fibers (ACFs) and their surface characteristics were investigated before and after electrochemical polarization. The adsorption kinetics of m-cresol showed the dependence on polarized potential, and the adsorption rate constant increased by 77.1%, from 6.38 × 10⁻³ min⁻¹ at open-circuit (OC) to 1.13 × 10⁻² min⁻¹ at polarization of 600 mV. The adsorption isotherms at different potentials were in good agreement with Langmuir isotherm model, and the maximum adsorption capacity increased from 2.28 mmol g⁻¹ at OC to 3.67 mmol g⁻¹ at polarized potential of 600 mV. These indicated that electrochemical polarization could effectively improve the adsorption rate and capacity of ACFs. The surface characteristics of ACFs before and after electrochemical polarization were evaluated by N₂ adsorption-desorption isotherms, scanning electron microscope (SEM), zeta potential and Fourier transform infrared spectroscopy (FTIR). The results showed that the BET specific surface area and pore size increased as the potential rose. However, the surface chemical properties of ACFs hardly changed under electrochemical polarization of less than 600 mV. This study was beneficial to understand the mechanism of electrochemically enhanced adsorption.     

Synthetic carbons activated with phosphoric acid: II. Porous structure

Synthetic activated carbons were prepared by H₃PO₄ activation of a chloromethylated and sulfonated copolymer of styrene and divinylbenzene, using an impregnation weight ratio of 0.75 and carbonization temperatures in the 400-1000 °C range. Other impregnation ratios (0.93 and 1.11) were also used at a carbonization temperature of 800 °C. The porous texture of the resulting carbons was characterized by N₂ adsorption at −196 °C and CO₂ adsorption at 0 °C. All carbons exhibited a multimodal pore size distribution with maxima in the micropore and meso/macropore regions. Maxima in pore volume were attained at 900 °C for micropores and at 500 and 900 °C for mesopores. The mesopore volume was less sensitive than the micropore volume to changes in the impregnation ratio. It is concluded that the porous texture is not a prime factor in determining the outstanding cation exchange capacities of these carbons.     

Adsorption of Hg(II) ions from aqueous chloride solutions using powdered activated carbons

Activated carbons were developed from Casurina equisetifolia leaves, by chemically treating with sulfuric acid (1:1) or zinc chloride (25%), at low (425 °C) and high (825 °C) temperatures. The resulting powdered activated carbons were applied for removing mercuric ions from aqueous solution at different agitation times and mercuric ion concentrations. The equilibrium data fitted well the Langmuir adsorption isotherm. The Langmuir adsorption capacities were 12.3 and 20.3 mg g⁻¹ for low temperature carbons and 43.9 and 38.5 mg g⁻¹ for high temperature carbons impregnated with H₂SO₄ and ZnCl₂, respectively. Studies of the effects of carbon dosage, NaCl concentrations and solution pH values were carried out for the more effective, high temperature carbons. Increasing NaCl concentration resulted in a significant decrease in the adsorption efficiency. Adsorption was high from solutions with low and neutral pH values and lower for solutions with alkaline pH values for the high temperature carbons.     

采用SrCl2-NH4Cl-NH3工质对的二级吸附式冷冻循环性能

吸附式制冷是一种绿色环保节能的制冷技术,在低于100℃的低品位热能如废热能、太阳能等的利用方面具有广阔的发展前景。为了能够利用这部分的能源,提出了由吸附制冷过程与再吸附过程组成的二级吸附式制冷循环。采用SrCl₂-NH₄Cl-NH₃作为工质对,测试不同蒸发温度与冷却温度下吸附剂的吸附与解吸性能。实验测试结果表明：当热源温度为70℃时,二级吸附式制冷也能够实现-25℃下的冷量输出。在测试工况下,氯化锶的最大吸附量达到了理论吸附量的94%。80℃热源、25℃冷源以及-25℃制冷条件下二级吸附式制冷循环的COP和SCP达到了0.250与160 W·kg^-1。这个数值与CaCl₂-BaCl₂-NH₃两级冷冻在85℃驱动热源以及同等的冷源与制冷温度条件下的数据相对比,驱动热源需求降低了5℃,COP提高了4%,SCP提高了10%以上。     

Electrical double-layer characteristics of novel carbide-derived carbon materials

A variety of nanoporous carbide-derived carbon materials possessing improved pore size distributions were synthesised from a mixture of titanium carbide and titanium dioxide. It was observed that TiO₂ caused partial oxidation of the carbon particles created during high-temperature chlorination of the TiC/TiO₂ mixture. The resulting carbon powder is characterised by narrow pore size distribution with a peak pore size of around 8 Å and a noticeably smaller amount of pores below 6-7 Å compared to the carbon derived from pure TiC. Electrochemical and electrical double-layer characteristics of novel carbon materials in the acetonitrile solution of triethylmethylammonium tetrafluoroborate were obtained by using cyclic voltammetry and constant current methods. Carbon electrode materials of this study were tested over the temperature range from −10 °C to +60 °C. Results of this study affirmed a great potential of the synthesised advanced carbide-derived carbon, whose specific double-layer capacitance reaches approximately 90 F cm⁻³ and 125 F g⁻¹.     

Surface chemistry of phosphorus-containing carbons of lignocellulosic origin

Activated carbon adsorbents were prepared by phosphoric acid activation of fruit stones in an argon atmosphere at various temperatures in the 400-1000 °C range and at different acid/precursor impregnation ratios (0.63-1.02). The surface chemistry of the carbons was investigated by elemental analysis, cation exchange capacity (CEC, measured by neutralization of NaOH with acidic surface groups), infrared spectroscopy and potentiometric titration. Porous structure was derived from adsorption isotherms (N₂ at −196 °C and CO₂ at 0 °C). It was demonstrated that all carbons show considerable cation exchange capacity, the maximum (CEC = 2.2 mmol g⁻¹) being attained at 800 °C, which coincides with the maximum contents of phosphorus and oxygen. The cation exchange properties of phosphoric acid activated carbons from fruit stones are chemically stable in very acidic and basic solutions. Proton affinity distributions of all carbons show the presence of three types of surface groups with pK at 2.0-3.3, 4.6-5.9 and 7.6-9.1. These pK ranges were ascribed primarily to: (a) phosphorus-containing and carboxylic groups; (b) lactonic groups, and (c) phenolic groups, respectively. Phosphoric acid activated carbons are microporous with a relatively small contribution of mesopores. A maximum BET surface area of 1740 m² g⁻¹ was attained at 400 °C.     

Synthetic carbons activated with phosphoric acid III. Carbons prepared in air

Synthetic activated carbons were prepared by phosphoric acid activation of a styrene-divinylbenzene copolymer in an air atmosphere at various temperatures in the 400-900 °C interval. The carbons were characterized by elemental analysis, cation-exchange capacity measurement, infrared spectroscopy, potentiometric titration, copper adsorption from solution and physical adsorption of N₂ at −196 °C and CO₂ at 0 °C. It was shown that, similarly to synthetic phosphoric acid activated carbons obtained in argon, the synthetic carbons activated with phosphoric acid in air possess an acidic character and show considerable cation-exchange properties. The contribution of oxygen-containing surface groups along with phosphorus-containing groups to CEC is higher for carbons obtained in air. Three types of surface groups were identified on carbons prepared at temperatures up to 600 °C, and four types on carbons prepared at higher temperatures. These groups were assigned to ‘super-acidic’ (pK<0), phosphorus-containing (pK=1.1-1.2), carboxylic (pK=4.7-6.0) and phenolic (pK=8.1-9.4) groups. The cation-exchange capacity was at a maximum for the carbon prepared at 800 °C. Copper adsorption by synthetic phosphoric acid activated carbons obtained in air at temperatures lower than 800 °C is higher than for similar carbons obtained in argon. The increase is due to additional formation of oxygen-containing surface groups. Calculated copper binding constants revealed the importance of phosphorus-containing and carboxylic groups for adsorption of copper from aqueous solution. All carbons show a multimodal pore size distribution including simultaneously micropores and mesopores, but the porous texture is not a prime factor in determining the cation-exchange capacities of these carbons. Synthetic phosphoric acid activated carbons show a greater development of porosity when obtained in air as compared to carbons carbonized in argon.     

Flue gas treatment by activated carbon obtained from oil-fired fly ash

The treatment of the solid particulates derived from the combustion of heavy oils (that is, oil-fired fly ash) with acidic solutions (HCl and HF) followed by activation at 900 °C with CO₂ and then with O₂ (1%) in N₂ at 800 °C, produces activated carbon having high surface area values (measured both by N₂ adsorption at 77 K and by CO₂ adsorption at 273 K) and surface basic characteristics. This carbon appears to be suitable for SO₂ and NO_X adsorption and hence for industrial flue gas treatment processes. By submitting the activated carbon thus obtained to some adsorption/desorption cycles of gaseous mixtures having a similar composition to that of flue gases, its general characteristics (surface areas, sorbent properties etc.) change as expected of a typical activated carbon. Based on the results obtained, these particulate materials, produced in large amounts by heavy oil combustion, are assumed to be fully exploitable for flue gas treatment.     

热管型船用吸附制冰机的设计

A heat pipe type adsorption ice maker with two adsorbers for fishing boats is designed by using ammonia as refrigerant and compound of activated carbon-CaCl2 as adsorbent. This type of heat pipe adsorber can solve the problem of incompatibility between ammonia, copper, seawater and steel. The working process of the ice maker with 8.7kg adsorbent per bed is simulated. The results show that the optimal semi-cycle time is about 9 min at the evaporating temperature of -15℃, where the corresponding cooling power, specific cooling power per kilogram adsorbent SCP and coefficient of refrigerant performance COP are respectively 3.6kW, 217W·kg-1 and 0.404.     

Removal of elemental mercury by activated carbon impregnated with CeO2

Mercury emission from coal-fired power plants becomes a great environmental concern due to its high toxicity and volatility in particularly for elemental mercury. Activated carbon adsorption is considered to be a potential technology to control elemental mercury emission. In this work, a novel CeO₂/AC (activated carbon impregnated with cerium dioxide) sorbent was studied with an attempt to produce economical and effective sorbent for capturing mercury. The influencing factors researched include loading values changing from 1 wt% to 10 wt% and adsorption temperature changing from 30 to 200 °C. Some physicochemical techniques such as BET and XRD were used to characterize the properties of the sorbents. The adsorption test results show that CeO₂ impregnation significantly enhanced the AC adsorption ability for elemental mercury. When the CeO₂ load was below 3%, Hg⁰ adsorption ability of ameliorated AC enhanced with the increase in the loading value, and then decreased at higher loading. The influence of temperature on the mercury removal efficiency was also studied, the trend of which was similar to the effect of loading value. The maximum removal efficiency was obtained at 100 °C.     

Preparation, characterization and Methylene Blue adsorption of phosphoric acid activated carbons from globe artichoke leaves

Activated carbons were prepared by the pyrolysis of artichoke leaves impregnated with phosphoric acid at 500 °C for different impregnation ratios: 100, 200, 300 wt.%. Materials were characterized for their surface chemistry by elemental analysis, “Boehm titrations”, point of zero charge measurements, infrared spectroscopy, as well as for their porous and morphological structure by Scanning Electron Microscopy and nitrogen adsorption at 77 K. The impregnation ratio was found to govern the porous structure of the prepared activated carbons. Low impregnation ratios (~ 100 wt.%) led to essentially microporous and acidic activated carbons whereas high impregnation ratios (> 100 wt.%) gave essentially microporous-mesoporous carbons with specific surface areas as high as 2038 m²·g^− 1, pore volume as large as 2.47 cm³·g^− 1, and a slightly acidic surface. The prepared activated carbons were studied for their adsorption isotherms of Methylene Blue at pH = 3 and pH = 9. The supermicroporous structure of the material produced at 200 wt.% H₃PO₄ ratio was found to be appropriate for an efficient adsorption of this dye controlled by dispersive and electrostatic interactions depending on the amount of oxygen at the surface.     

Mercury (II) adsorption by activated carbon made from sago waste

The preparation of activated carbon (AC) from sago industry waste is a promising way to produce a useful adsorbent for Hg (II) removal, as well as dispose of sago industry waste. The AC was prepared using sago industry waste with H₂SO₄ and (NH₄)₂S₂O₈ and physico-chemical properties of AC were investigated. Adsorptive removal of mercury (II) from aqueous solution onto AC prepared from sago industry waste has been studied under varying conditions of agitation time, metal ion concentration, adsorbent dose, particle size and pH to assess the kinetic and equilibrium parameters. Adsorption equilibrium was obtained in 105 min for 20 mg l⁻¹ and 120 min for 30, 40, and 50 mg l⁻¹ Hg (II) concentrations. The Langmuir and Freundlich equilibrium isotherm models were found to provide an excellent fitting of the adsorption data, with r² 0.9999 and 0.9839, respectively. The adsorption capacity of Hg (II) (Q_o) obtained from the Langmuir equilibrium isotherm model was found to be 55.6 mg g⁻¹ at pH 5.0 for the particle size range of 125-250 μm. The percent removal increased with an increase in pH from 2 to 10. This adsorbent was found to be effective and economically attractive.     

New acrylic monolithic carbon molecular sieves for O2/N2 and CO2/CH4 separations

The modification of activated carbon fibres prepared from a commercial textile acrylic fibre into materials with monolithic shape using phenolic resin as binder was studied. The molecular sieving properties for the gas separations CO₂/CH₄ and O₂/N₂ were evaluated from the gas uptake volume and selectivity at 100 s contact time taken from the kinetic adsorption curves of the individual gases. The pseudo-first order rate constant was also determined by the application of the LDF model. The samples produced show high CO₂ and O₂ rates of adsorption, in the range 3-35 × 10⁻³ s⁻¹, and in most cases null or very low adsorption of CH₄ and N₂ which make them very promising samples to use in PSA systems, or similar. Although the selectivity was very high, the adsorption capacity was low in certain cases. However, the gas uptake in two samples reached 23 cm³ g⁻¹ for CO₂ and 5 cm³ g⁻¹ for O₂, which can be considered very good. The materials were heat-treated using a microwave furnace, which is a novel and more economic method, when compared with conventional furnaces, to improve the molecular sieves properties.     

Relationship between the nanoporous texture of activated carbons and their capacitance properties in different electrolytes

A series of activated carbons (ACs) with progressively changing nanotextural characteristics was obtained by heat-treatment of a bituminous coal at temperatures ranging from 520 to 1000 °C, and subsequent activation by KOH at 700 °C or 800 °C. As the pre-treatment temperature increases, the total pore volume V_T decreases from 1.28 to 0.30 cm³ g⁻¹, and the BET specific surface area from 3000 to 800 m² g⁻¹. The specific capacitance determined for each series of ACs using symmetric two electrode cells in 6 mol L⁻¹ KOH varies almost linearly with the BET surface area, suggesting that the charge accumulation is controlled primarily by the surface area development. A further analysis of the electrochemical behaviour in different electrolytic media—aqueous and organic—shows that an adequate pore size is more important than a high surface area in order to obtain high values of capacitance. Theoretical values of volumetric capacitance could be evaluated without considering the size of ions, which is always uncertain in solution, and compared with the experimental data as a function of the pore width. The efficiency of pore filling, i.e., of double layer formation, is optimal when the pore size is around 0.7 nm in aqueous media and 0.8 nm in organic electrolyte. A study of the performance of the positive and negative electrodes during the charge/discharge of the capacitor, reveals an additional pseudo-faradaic contribution due to oxygenated functionalities within the working potential window of the negative electrode. This effect is more pronounced for the ACs series obtained at 700 °C, because of their higher oxygen content.