• Clean Technology
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• v.20 no.1
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• pp.64-71
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• 2014

We have investigated the effects of various additives on Eco coal gasification under $CO_2$ atmosphere. The temperature ranges from $750{\sim}900^{\circ}C$ and the gasification experimental was carried out with Eco coal adding 7 wt% $K_2CO_3$, $Na_2CO_3$, $CaCO_3$, Dolomite, and non-additive under $N_2$ and $CO_2$ gas mixture. At $850^{\circ}C$, we observed that the reaction rate increased when the concentration of $CO_2$ increased. However, we also observed that the increment of reaction rate was small at more than 70% of the concentration of $CO_2$. The additives activity was ranked as 7 wt% $Na_2CO_3$ > 7 wt% $K_2CO_3$ > non-additive > 7 wt% Dolomite > 7 wt% $CaCO_3$ at $850^{\circ}C$. At the temperatures of $750^{\circ}C$, $800^{\circ}C$, $850^{\circ}C$, and $900^{\circ}C$, when the temperature increased, the gasification rate increased. The gasification was suitably described by the volumetric reaction model. Using volumetric reaction model, the activation energy of Eco coal including 7 wt% $Na_2CO_3$ gasification was 83 kJ/mol, which was the lowest value among all the alkaline additives.

• Resources Recycling
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• v.17 no.6
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• pp.68-78
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• 2008

Using a Pinus koraiensis and Pinus rigida which are normally being discarded in South Korea, optimal conditions of producing activated carbons have been studied to recycle as a higher value-added product. This study consists of two processes, the production process of charcoals from waste timbers by low temperature pyrolysis and the production process of activated carbons from the charcoals by chemical activation reaction. This paper deals with the production process of activated carbons from the charcoals by chemical activation reaction. As an alkali has been generally used as an activating agent, KOH and NaOH which react well with a carbon were used in this study. As a result of the experiments, it is confirmed that activated carbons made with KOH treatment had superior values in physicochemical properties to NaOH, showing that there was no remain of KOH at the surface of the charcoals while there was $3{\sim}4%$ of NaOH remaining after the experiments. Thus, it is concluded that KOH reacted more actively with a charcoal than NaOH. Moreover, it was also found that values in physicochemical properties when using a Pinus koraiensis are superior to the ones when using a Pinus rigida. The optimal mixing ratio of an activating agent to a charcoal was 400 wt.%. To improve the physicochemical properties, activated carbons were washed out by distilled water after neutralization with SM hydrochloric acid solution. When activated carbons were produced from a Pinus koraiensis in this optimal conditions, value of BET surface area was found to be approx. $2400\;m^2/g$.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.589-594
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• 2006

The recycling of industrial wastes in the concrete manufacturing is of increasing interest worldwide, due to the high environmental impact of the cement and concrete industries and to the rising demand of infrastructures, both in industrialized and developing countries. The production of municipal wastes in the South Korea is estimated at about 49,902 ton per day and only 14.5% of these are incinerated and principally disposed of in landfill. These quantities will increase considerably with the growth of municipal waste production, the progressive closing of landfill, so the disposal of municipal solid waste incinerator(MSWI) ashes has become a continuous and significant issue facing society, both environmentally and economically. MSWI ash is the residue from waste combustion processes at temperature between $850^{\circ}C\;and\;1,000^{\circ}C$. And the main components of MSWI ash are $SiO_2,\;CaO\;and\;Al_2O_3$. The aim of this study is to find a way to useful application of MSWI ash(after treatment) as a structural material and to investigates the hydraulic activity, compressive strength development composition variation of such alkali-activated MSWI ashes concrete. And it was found that early cement hydration, followed by the breakdown and dissolving of the MSWI-ashes, enhanced the formation of calcium silicate hydrates(C-S-H). The XRD and SEM-EDS results indicate that, both the hydration degree and strength development are closely connected with a curing condition and a alkali-activator. Compressive strengths with values in the 40.5 MPa were obtained after curing the activated MSWI ashes with NaOH+water glass at $90^{\circ}C$.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.593-600
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• 2016

The paper presented investigates the effects of kaolinite on strength properties of alkali-activated multi-component cement. The binders of this study was blended of ground granulated blast furnace slag (GGBFS), fly ash (FA), silica fume (SF) and kaolinite (KA). In this study, the specimens of combination of 20%~70% GGBFS, 10%~60% FA, 10% SF (constant ratio) and 10%~50% KA binder were used for strength properties tests. The water/binder ratio was 0.5. The binders (GGBFS + FA + SF + KA) was activated by sodium hydroxide (NaOH) and sodium silicate ($Na_2SiO_3$) was 10% by total binder weight (10% NaOH + 10% $Na_2SiO_3$). The research carried out is on the compressive strength, water absorption, ultrasonic pulse velocity (UPV) and X-ray diffraction (XRD). The compressive strength decreased as the contents of KA increase. One of the major reason for this is the low reactivity of KA compared with other raw materials used as precursors such as GGBFS or FA. The presence of remaining KA indicates that the initially used quantity has not fully reacted during hydration. Moreover, the results have indicated that increased of KA contents decreased UPV under all experimental conditions. The drying shrinkage and water absorption increased as the content of KA increase. Test result clearly showed that the strength development of multi-component blended cement were significantly dependent on the content of KA and GGBFS.

• Journal of the Korea Concrete Institute
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• v.18 no.4 s.94
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• pp.449-458
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• 2006

The discharge of fly ash that is produced by coal-fired electric power plants is rapidly increasing in Korea. The utilization of fly ash in the raw materials would contribute to the elimination of an environmental problem and to the development of new high-performance materials. So it is needed to study the binder obtained by chemically activation of pozzolanic materials by means of a substitute for the cement. Fly ash consists of a glass phase. As it is produced from high temperature, it is a chemically stable material. Fly ash mostly consists of $SiO_2\;and\;Al_2O_3$, and it assumes the form of an oxide in the inside of fly ash. Because this reaction has not broken out by itself, it is need to supply it with additional $OH^-$ through alkali activators. Alkali activators were used for supplying it with additional $OH^-$. This paper concentrated on the strength development according to the kind of chemical activators, the curing temperature, the heat curing time. Also, according to scanning electron microscopy and X-Ray diffraction, the main reaction product in the alkali activated fly ash mortar is Zeolite of $Na_6-(AlO_2)_6-(SiO_2)_{10}-12H_2O$ type.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.601-607
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• 2012

The alkali-activation reaction of two types of typical kaolin calcined at various lower temperatures was investigated at room temperature and at elevated temperatures. For the assessment of the reactivity, the temperature increase and the setting time of pastes prepared with calcined kaolin and sodium/potassium hydroxide solution were measured. Unlike raw kaolin, calcined kaolin samples prepared at various temperature showed an alkali-activation reaction according to the different aspects of the changes in the mineral phases. The reactivity with alkaline solutions was exceedingly activated in the samples calcined at $600-650^{\circ}C$, but the reactivity gradually decreased as the temperature increased in a higher temperature range, most likely due to the changes in the crystal structure of the dehydrated kaolin. The activation effect of the calcination treatment was achieved at reaction temperatures that exceeded $60^{\circ}C$ and was enhanced as the temperature increased. The reactivity of the calcined kaolin with an alkaline solution was more enhanced with the solution of a higher concentration and with a solution prepared from sodium hydroxide rather than potassium hydroxide.

• Clean Technology
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• v.28 no.2
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• pp.131-137
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• 2022

The semiconductor process currently emits various by-products and unused gases. Emissions containing pollutants are generally classified into categories such as organic, acid, alkali, thermal, and cabinet exhaust. They are discharged after treatment in an atmospheric prevention facility suitable for each exhaust type. The main components of organic exhaust are volatile organic compounds (VOC), which is a generic term for oxygen-containing hydrocarbons, sulfur-containing hydrocarbons, and volatile hydrocarbons, while the main components of alkali exhaust include ammonia and tetramethylammonium hydroxide. The purpose of this study was to determine the combustion characteristics and analyze the NO_X reduction rate by maintaining a direct combustion and temperature to process organic and alkaline exhaust gases simultaneously. Acetone, isopropyl alcohol (IPA), and propylene glycol methyl ether acetate (PGMEA) were used as VOCs and ammonia was used as an alkali exhaust material. Independent and VOC-ammonia mixture combustion tests were conducted for each material. The combustion tests for the VOCs confirmed that complete combustion occurred at an equivalence ratio of 1.4. In the ammonia combustion test, the NO_X concentration decreased at a lower equivalence ratio. In the co-combustion of VOC and ammonia, NO was dominant in the NO_X emission while NO₂ was detected at approximately 10 ppm. Overall, the concentration of nitrogen oxide decreased due to the activation of the oxidation reaction as the reaction temperature increased. On the other hand, the concentration of carbon dioxide increased. Flameless combustion with an electric heat source achieved successful combustion of VOC and ammonia. This technology is expected to have advantages in cost and compactness compared to existing organic and alkaline treatment systems applied separately.

• Korean Chemical Engineering Research
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• v.48 no.3
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• pp.322-326
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• 2010

Stability of sodium borohydride solution during storage was studied. In order to enhance the $NaBH_4$ stability, NaOH and KOH were added to the $NaBH_4$ solution. The effect of concentration of the borohydride and alkaline solution, temperature and materials of storage vessels on the rate of borohydride hydrolysis was investigated. The rate of hydrogen evolution decreased as the concentration of alkaline increased due to increase of $NaBH_4$ stability in the solution. The stability of $NaBH_4$ solution decreased when the borohydride concentration raised from 10 to 15 wt% and then increased when the $NaBH_4$ concentration increased above 15 wt% due to increase in the pH of the concentrated solution. The activity coefficient of hydrolysis of $NaBH_4$ solution(NaOH 3.0 wt%, $NaBH_4$ 25 wt%) was 115.1 kJ/mol and this value was 1.5~4.0 times higher than that of hydrolysis of $NaBH_4$ solution with catalyst. The borohydride solutions in glass and stainless-steel vessel were more stable than the solution in plastic(PE) vessel.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.6
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• pp.415-421
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• 2013

To increase specific surface property of activated carbon fiber(ACF), chemical activation(CA) using alkali metals and surface treatment(ST) using oxidant was widely used. The CA and ST process developed micro-pore on the surface of ACF by chemical reaction of the alkali metals and oxidative of oxidant, respectively. To improve the efficiency of CA process for developing micro-pores on the surface of ACF, the ST process was adopted as an pre-treatment method. After treatment of ST process, ACF properties was investigated depending on the ST pre-treatment process. FT-IR, TG and elemental analysis of the ACF are carried out, and an adsorption property of ACF was also evaluated using toluene(which in typical volatile organic matter). Once the single CA process is used, the surface area and adsorption capacity of ACF were increased from 1,483 to 1,988 $m^2/g$ and from 0.22 to 0.27 $g_{-Tol.}/g_{-ACF}$, respectively. On the other hands, once the ST and CA processes are used successively, the surface area and adsorption capacity of ACF are greatly increase(where the surface area is 2,743 $m^2/g$ and the adsorption capacity is 0.37 $g_{-Tol.}/g_{-ACF}$). It indicates that the combined process of ST and CA can improve the surface process properties of ACF.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.315-322
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• 2012

Alkali-activated slag (AAS) is the most obvious alternative materials that can replace OPC. But, AAS industrial usage as a structural material should be evaluated for its durability. Carbonation resistance is one of the most important factors in durability evaluation. Test results for 18 slag-based mortars activated by sodium silicate and 6 OPC mortars were obtained in this study to verify the carbonation property. Main variables considered in the study were flow, compressive strength before and after carbonation, and carbonation depth. Mineralogical and micro-structural analysis of OPC and AAS specimens prior to and after carbonation was conducted using XRD, TGA, FTIR FE-SEM. Test results showed that CHS was major hydration products of AAS and, unlike OPC, no other hydration products were found. After carbonation, CSH of hydration product in AAS turned into an amorphous silica gel, and alumina compounds was not detected. From the analysis of the results, it was estimated that the micro-structures of CSH in AAS easily collapsed during carbonation. Also, the results showed that this collapse of chemical chain of CSH lowered the compressive strength of concrete after carbonation. By increasing the dosage of activators, carbonation resistance and compressive strength were effectively improved.