The Effects of Temperature and Mineral Acids on the

0 downloads 0 Views 644KB Size Report
Dec 17, 2012 - Mineral Acids on the Demineralization Degree of Nallihan Lignite, Energy ... inorganic minerals and elements, such as clay, feldspar, quartz, ...
This article was downloaded by: [Yildiz Teknik University] On: 16 July 2014, At: 22:38 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Energy Sources, Part A: Recovery, Utilization, and Environmental Effects Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ueso20

The Effects of Temperature and Mineral Acids on the Demineralization Degree of Nallihan Lignite a

a

a

J. Gulen , I. Doymaz , S. Piskin & S. Ongen

b

a

Chemical Engineering Department , Yildiz Technical University , Esenler , Istanbul , Turkey b

Geological Engineering Department , Istanbul University , Avcilar , Istanbul , Turkey Published online: 17 Dec 2012.

To cite this article: J. Gulen , I. Doymaz , S. Piskin & S. Ongen (2013) The Effects of Temperature and Mineral Acids on the Demineralization Degree of Nallihan Lignite, Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 35:3, 202-208, DOI: 10.1080/15567036.2012.636725 To link to this article: http://dx.doi.org/10.1080/15567036.2012.636725

PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions

Energy Sources, Part A, 35:202–208, 2013 Copyright © Taylor & Francis Group, LLC ISSN: 1556-7036 print/1556-7230 online DOI: 10.1080/15567036.2012.636725

The Effects of Temperature and Mineral Acids on the Demineralization Degree of Nallıhan Lignite J. Gulen,1 I. Doymaz,1 S. Piskin,1 and S. Ongen2 Downloaded by [Yildiz Teknik University] at 22:38 16 July 2014

1

Chemical Engineering Department, Yildiz Technical University, Esenler, Istanbul, Turkey 2 Geological Engineering Department, Istanbul University, Avcılar, Istanbul, Turkey

Demineralization of lignites from Nallıhan, Turkey, was investigated using various aqueous acids, such as HCl, HNO3 , and H2 SO4 , which were used at the concentrations of 5 and 10 vol%, hydrofluoric acid (HF) acid solutions of 5, 10, 20, 30, and 40 vol%. The experiments were done at 20, 40, 50, and 60ıC temperatures in order to observe the heating effect on the removal yields. The best result was found for the sample being done experimentally with 5% HF. The ash content is decreased from 17.12 to 6.98 wt% and heating value is increased from 16,652 to 23,950 kJ/kg according to the original lignite. The yields are 59.23 and 44%, respectively. Fourier transform infrared and X-ray diffraction were used to observe the leaching effect of the mineral acids on the demineralization degree of Nallıhan lignite. Keywords: demineralization, Fourier transform infrared, lignite, mineral matter, X-ray diffraction

1. INTRODUCTION Coal is an extremely chemically and physically complex and heterogeneous material consisting of organic (carbon) and inorganic (minerals) constituents (Georgakopoulos et al., 2003). The major inorganic minerals and elements, such as clay, feldspar, quartz, anhydride minerals, and Fe, Na, Si, Ca, etc., are commonly found in coals (Vassilev et al., 1997; Bolat et al., 1998; Demirbas, 2002). Coal preparation techniques are important from the point of mineral matters, which have caused difficulty in the utilization processes. So, demineralization treatments increase the coal quality from the points of economy and environment (Culfaz et al., 1996). Although chemical cleaning is more expensive, it is more effective, especially to fine distributed and bound minerals in the structure (Wang and Tomita, 1998). Chemical cleaning of coal with alkali and acid solutions has proved effective in reducing significant amounts of ash-forming minerals (Mukherjee, 2003). In the demineralization process, solutions used are HCl, H2 SO4 , and HNO3 as acidic, NaOH and KOH as basic, and some solutions like H2 O2 and a combination of them (Kusakebe et al., 1989; Karaca and Ceylan, 1997; Kumar and Hari Shankar, 2000; Karaca and Onal, 2003; Seferinoglu et al., 2003; Gulen et al., 2005). Demineralization of coal and lignite by treatment with aqueous sodium or potassium hydroxide alone, or followed by mineral acids has been reported by many investigators. Steel and Patrick (2001) tried hydrofluoric acid (HF) and HF followed by HNO3 acids for the mineral matter of Address correspondence to J. Gulen, Chemical Engineering Department, Yildiz Technical University, Esenler, Istanbul 34210, Turkey. E-mail: [email protected]

202

Downloaded by [Yildiz Teknik University] at 22:38 16 July 2014

DEMINERALIZATION OF NALLIHAN LIGNITE

203

high volatile UK coal. The ash level is decreased from 7.90 to 2.6% with HF and from 2.8 to 0.6% with the successive usage of 3.51 M HF and 1.26 M HNO3 acids. Bolat et al. (1998) demineralized high ash low sulphur bituminous coal of Turkey by treatment with 20% aqueous NaOH followed by 10% mineral acid of HCl, HNO3 , H2 SO4 , and HF. They achieved about 46% demineralization of a high-ash of bituminous coal from Turkey. Mukherjee and Borthakur (2001) leached the mineral matter of Assam coal of India by treatment with 16% NaOH and then 10% HCl at 90ı C. They achieved a 45–50% reduction in ash and around 10% organic sulphur from the Assam coal. Karaca and Onal (2003) removed the mineral matter of some Turkish lignites by using NaOH, HCl, and H2 SO4 solutions. The best results were achieved for Tuncbilek lignite of 3.3% ash with 30% NaOH and 10% HCl usage. Lignite is one of the most important sources of energy in Turkey. However, low calorific value, high ash, and sulphur are general characteristics of Turkish lignites (Yagmur et al., 2005). Hence, they are necessary to demineralize such lignites prior to utilization due to environmental pollution. The present article reports the effect of aqueous various mineral acid solutions and temperature on the demineralization degree of Nallıhan lignite, which has a high ash level.

2. MATERIAL AND METHODS 2.1. Materials The lignite sample used in this study was collected from Nallıhan, Ankara, Turkey. The sample was ground and sieved to pass a 250-m sieve. The proximate analysis of the sample was done by following standard methods (ASTM D 3172). The results of proximate analysis are given in Table 1. Samples were treated with various acids. The acids used were HCl, HNO3 , H2 SO4 of 5 and 10 vol%, and HF of 5, 10, 20, 30, and 40 vol%. The experiments were done at 20, 40, 50, and 60ı C. 2.2. Methods The ground sample (4 g) was stirred with 80 ml of acid solution of various acid concentrations and different temperatures for 20 min. The reaction mixture was cooled, filtered through the blue ribbon filter paper, washed with hot distilled water, and dried in the oven at 105ıC for 4 h. The ash and the calorific values of sample were determined according to the ASTM D 3174 method and IKA calorimeter C4000 apparatus (IKA Werke GmbH&Co., Staufen, Germany) (ASTM D 3286), respectively. TABLE 1 Chemical Analysis Results of Original Sample Analysis Moisture (%) Ash (%) Volatile matter (%) Fixed carbon (%) Sulphur (%) Calorific value (kJ/kg) Dry basis.

Value 11.12 17.12 37.93 26.85 6.98 16,652

204

J. GULEN ET AL.

FTIR spectra and XRD patterns were used to characterize the minerals present in the lignite. The FTIR spectra (A Mattson 1000 spectrometry, Thermo Scientific, Vienna, Austria) were used to characterize the functional groups of the lignite treated. One gram of KBr was mixed with 0.01 g of lignite and taken the spectra with 8 cm 1 resolution scanning 100 parts. X-ray diffractograms were obtained in a Philips PW 1140/00/60 diffractometer (Angstrom Advanced Inc., Braintree, MA) with CuK radiation from 0–50ıC. The mineral groups left in the structure were characterized by X-ray diffractograms.

Downloaded by [Yildiz Teknik University] at 22:38 16 July 2014

3. RESULTS AND DISCUSSION The decrease in the ash amount and the increase in the calorific values are seen in Tables 2–5 after demineralization treatments. The demineralization effect of HCl acid at 20, 40, 50, and 60ıC is seen in Table 2. All the experiments were done in triplicate and the values were averaged. The best result is found for the experiment done at 5 and 10 vol% HCl acid solution at 60ıC. The removal yields are 33.58 and 33.41% for 5 and 10 vol% HCl acids, respectively. The increase in temperature has increased the mineral matter solubility. The calorific values of 20,341 and 21,751 kJ/kg for 5 and 10 vol% HCl acids at 60ı C showed 22 and 31% increases, respectively. Nallıhan lignites were treated with 5 and 10 vol% HNO3 solution at 20, 40, 50, and 60ıC temperatures. The best ash removals are 11.57 and 11.51% for 5 vol% HNO3 at 60ı C and for 10 vol% HNO3 at 50ı C as seen from Table 3. The yields are 32 and 33%, respectively. The calorific values are 20,048 and 20,090 kJ/kg for 5 vol% at 60ı C and 10 vol% at 50ıC. The increase in these values is found to be 20 and 21%, respectively. Nallıhan lignites were leached with 5 and 10 vol% H2 SO4 at the mentioned temperatures. The results are shown in Table 4. The ash amounts are 11.95 and 12.57% for 5 vol% H2 SO4 at 60ıC TABLE 2 Ash and Calorific Values of HCl Treatment Calorific Value, kJ/kg

Ash, % T, ı C 20 40 50 60

5%

10%

5%

10%

13.42 12.94 11.88 11.37

12.51 12.93 11.71 11.40

19,352 20,328 20,136 20,341

20,359 20,492 20,256 21,751

TABLE 3 Ash and Calorific Values of HNO3 Treatments Calorific Value, kJ/kg

Ash, % T, ı C 20 40 50 60

5%

10%

5%

10%

13.24 13.02 12.46 11.57

13.17 11.80 11.51 12.29

19,815 19,877 19,404 20,048

18,620 17,989 20,090 18,092

DEMINERALIZATION OF NALLIHAN LIGNITE

205

TABLE 4 Ash and Calorific Values of H2 SO4 Treatments Calorific Value, kJ/kg

Ash, % T, ı C

Downloaded by [Yildiz Teknik University] at 22:38 16 July 2014

20 40 50 60

5%

10%

5%

10%

14.47 13.43 12.51 11.95

13.64 12.85 12.57 12.84

18,994 19,592 19,449 20,337

18,895 19,856 21,049 19,459

TABLE 5 Ash and Calorific Values of HF Treatments

Concentration, %

Ash, %

Calorific Value, kJ/kg

5 10 20 30 40

6.98 7.97 7.51 7.5 7.45

23,950 22,817 22,929 22,972 23,046

and 10 vol% H2 SO4 at 50ıC, which give 29% yields. The best calorific values found are 20,337 and 21,049 kJ/kg for 5 vol% and 10 vol% H2 SO4 at 60 and 50ı C, respectively. The effect of HF acid is seen in Table 5. The ash amount is decreased from 17.12 to 6.98 wt% and the calorific value increased ranging from 16,652 to 23,950 kJ/kg with the effect of 5 vol% HF. The yields are 59 and 38%, respectively. According to these results, the best result is obtained with the experiment done with HF. The other values are sequenced as HCl, HNO3 , and H2 SO4 acid experiments.

3.1. FTIR Determinations A comparison of the FTIR spectra for the wave number region 400 to 4,000 cm 1 , for the original and treated lignite samples, is presented in Figure 1. The peaks of the original sample at 477, 520, and 604 cm 1 are due to both the mineral matter and aromatic structure of the sample. The 1,033, 1,102, 1,125, 1,140, 1,164, and 1,202 cm 1 bands show C–O stretching. Aromatic CDC and CDO stretching are seen at 1,141 and 1,634 cm 1 . Aliphatic C–H groups give absorbance at 2,861 cm 1 . The peak at 2,930 cm 1 is due to the CH3 and CH2 groups. There is an O– H stretching at 3,435 cm 1 . The peaks seen after 3,500 cm 1 show the clay minerals of the sample. The spectrum gives a shoulder at 1,218 cm 1 after treating with 5% HF (C–O stretching). The sharp peaks at 1,402 and 1,438 cm 1 are increased due to the effect of 5 vol% HF. A shoulder (C–O stretching) is seen at 1,070 cm 1 , when the samples are treated with 5% HCl. The broad peak at 1,630 cm cm 1 is due to CDO stretching.

Downloaded by [Yildiz Teknik University] at 22:38 16 July 2014

206

J. GULEN ET AL.

FIGURE 1 FTIR spectra of Nallıhan lignites: (a) Original, (b) HF, (c) HCl, (d) HNO3 , and (e) H2 SO4 .

There are double peaks at 1,036 and 1,094 cm 1 (C–O stretching) because of the leaching effect of 5 vol% HNO3 . The peak heights shown at 1,198 and 1,627 cm 1 increase representing C–O stretching and CDO stretching, respectively. Some peaks are obvious after reacting in the sample with 5 vol% H2 SO4 . The sharp peak at 1,403 cm 1 and the bands at 1,102, 1,098, and 1,033 cm 1 are due to CDC/CDO stretching and C–O/C–O–C stretching, respectively. 3.2. XRD Determinations Some mineral groups, such as anhydride, feldspar, quartz, calcite, and pyrite, were found in Nallıhan lignites according to the X-ray spectra taken (Figure 2). It can be deduced that major mineral species of original Nallıhan lignite consisted of anhydride (2‚ D 25:34, 31.26, 35.50, 38.50, 40.78, 48.54), feldspar (2‚ D 27:70, 28.00, 30.24), quartz (2‚ D 26:50, 39.40), hematite (2‚ D 33:10, 35.50, 42.50, 49.80), and pyrite (2‚ D 33:10). Some peaks were so close to each other that they were overlapped. For example: 2‚ D 38:50 and 40.78 for anhydride, 2‚ D 27:70 and 28.00 for feldspar. Nallıhan lignites were leached with H2 SO4 acid. Some mineral groups, such as anhydride, were isolated. The peaks at 2‚ D 32:84, 35.34, and 49.26 are due to hematite. The peaks at

Downloaded by [Yildiz Teknik University] at 22:38 16 July 2014

DEMINERALIZATION OF NALLIHAN LIGNITE

207

FIGURE 2 X-Ray spectra of Nallıhan lignites: (a) Original, (b) H2 SO4 , (c) HNO3 , (d) HCl, and (e) HF. Symbols for minerals: A: Anhydride, F: Feldspar, H: Hematite, M: Microcline, P: Pyrite, Q: Quartz.

2‚ D 21:50, 22.60, 23.86, and 27.44 show that microcline is present in the residue. The peaks at 2‚ D 22:60 and 23.86 were overlapped. The peak at 2‚ D 21:26 corresponds to the quartz mineral. Nallıhan lignites were reacted with HNO3 acid. The peak at 2‚ D 33:24, 35.74, and 49.64 represent the hematite group found in the structure. The major peak at 2‚ D 21:84, 23.70, 24.24, 27.70, 28.08, and 30.40 correspond to the feldspar group. The peaks at 2‚ D 23:70, 24.24, and 27.70 and 28.08 were overlapped. Quartz mineral gives a peak at 2‚ D 26:50. Nallıhan lignites were treated with HCl acid. The peak shown at 2‚ D 33:26, 35.76, and 49.60 represent hematite group being in the structure. The peaks at 2‚ D 27:86, 30.24, and 30.44 are due to feldspar mineral. The peaks shown at 2‚ D 30:24 and 30.44 were overlapped. HF acid is used for removing the undesired part of Nallıhan lignites. Most of the mineral groups disappeared with the effect of HF acid. The peak shown at 2‚ D 25:62, 31.58, and 36.00 shows that anhydride is present in the residue.

208

J. GULEN ET AL.

4. CONCLUSIONS The ash values of Nallıhan lignites are decreased and the calorific values are increased with the effect of temperature and various acid solutions. The best result is obtained with the experiments done in HF acid. The other results are sequenced as HCl, HNO3 , and H2 SO4 . By removal of some mineral species from lignite with the effect of acids applied, it is appropriate to determine other minerals found in the structure of lignite. The removal effects of various acid solutions are shown in the X-ray spectra of Nallıhan lignites taken.

Downloaded by [Yildiz Teknik University] at 22:38 16 July 2014

REFERENCES Bolat, E., Saglam, S., and Piskin, S. 1998. Chemical demineralization of a Turkish high ash bituminous coal. Fuel Proc. Technol. 57:93–99. Culfaz, M., Ahmed, M., and Gurkan, S. 1996. Removal of mineral matter and sulfur from lignites by alkali treatment. Fuel Proc. Technol. 47:99–109. Demirbas, A. 2002. Demineralization and desulfurization of coals via column froth flotation and different methods. Energy Convers. Manage. 43:885–895. Georgakopoulos, A., Iordanidis, A., and Kapina, V. 2003. Study of low rank Greek coals using FTIR spectroscopy. Energy Sources 25:995–1005. Gulen, J., Doymaz, I., Piskin, S., and Toprak, S. 2005. Removal of mineral matter from Silopi-Harput asphaltite by various acid treatment. Energy Sources 27:1457–1464. Karaca, H., and Ceylan, K. 1997. Chemical cleaning of Turkish lignites by leaching with aqueous hydrogen peroxide. Fuel Proc. Technol. 50:19–23. Karaca, H., and Onal, Y. 2003. Demineralization of lignites by single and successive pretreatment. Fuel 82:1517–1522. Kumar, M., and Hari Shankar, R. 2000. Removal of ash from Indian Assam coking coal using sodium hydroxide and acid solutions. Energy Sources 22:187–196. Kusakebe, K., Orita, K., Kato, S., Morooka, Y., and Kato, K. 1989. Simultaneous desulphurization and demineralization of coal. Fuel 68:396–399. Murkherjee, S., and Borthakur, P. C. 2001. Chemical demineralization/desulphurization of high sulphur coal using sodium hydroxide and acid solutions. Fuel 80:2037–2040. Mukherjee, S. 2003. Demineralization and desulfurization of high-sulfur Assam coal with alkali treatment. Energy & Fuels 17:559–564. Seferinoglu, M., Paul, M., Sandström, A., Koker, A., Toprak, S., and Paul, J. 2003. Acid leaching of coal and coal-ashes. Fuel 82:1721–1724. Steel, K. M., and Patrick, S. W. 2001. The production of ultra clean coal by chemical demineralization. Fuel 80:2019–2023. Vassilev, S. V., Kitano, K., and Vassileva, C. G. 1997. Relations between ash yield and chemical and mineral composition of coals. Fuel 76:3–8. Wang, Z. Y., and Tomita, A. 1998. Removal of mineral matter from some Australian coals by Ca(OH)2 /HCl leaching. Fuel 77:1747–1753. Yagmur, E., Simsek, E. H., Aktas, Z., and Togrul, T. 2005. Effect of demineralization process on the liquefaction of Turkish coals in tetralin with microwave energy: Determination of particle size distribution and surface area. Fuel 84:2316–2323.