Trace Analysis of Carbazole in Commercial Diesel by using Adsorption on Activated Biochar from Rice Husk Pyrolysis
Abstract
The valorization of rice husk biochar obtained by pyrolysis was studied by production high quality activated carbon. Activated carbon (AC) chemically treated by K2CO3, was used as sorbent phase in bar adsorptive microextraction followed by comprehensive two-dimensional gas chromatography coupled to a quadrupole mass spectrometer analysis (BAµE/GC×GC-qMS) for trace analysis of carbazole in commercial diesel. The prepared AC was characterized by N2 adsorption, SEM-EDS and pHPZC. Assays of nitrogen adsorption isotherm demonstrated that the AC presented microporosity and the Density Functional Theory Calculation was applied to obtain information concerning the micropore size distribution. The BET surface area and total pore volume were 1850 m2 g -1 and 0.83 cm3 g -1 , respectively. AC from rice huskpyrolysis (RH) showed an acceptable adsorption capacity for Carbazole in diesel matrices allowed us to obtain average recoveries of 91.0 % and convenient analytical parameters. From the data obtained, the proposed methodology proved to be a suitable sorption-based static microextraction alternative for monitoring trace levels of carbazole in commercial diesel.
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Introduction
In the last year, there was a growing interest in using low-cost and abundantly available waste materials as precursors of carbon materials. Actually, any carbonaceous material with high carbon content can be used as raw material for the preparation of activated carbons (ACs) [1]. This is the case of t agricultural solid wastes [2] , such as, cotton stalk [3,4], tobacco stem [5], rice husk [6], cork [7], bamboo [8], waste tea [9, 10], coconut shell [11], oil palm fiber [12], durian shell [13], wood [14], sisal [15] and many others.
In South Brazil, rice processing is an important agro-industrial sector, giving rise to large amounts of rice husk (about 2.5 million metric tons per year) produced as agricultural waste. Fast pyrolysis is an interesting option for the reducing the environmental impact and to valorize rice husk, as shown in a previous study [16]. The production of AC from rice husk is achieved through chemical or physical activation [17].
Chemical activation is a widely used method to obtain AC with a very large surface area and great micropore volume and is usually performed using NaOH/KOH [18-21], H3PO4 [22] or ZnCl2[20, 23]. K2CO3 is an alternative to KOH with the advantage that carbonate mediated activation is less extensive, as well as being a more environmental friendly activating agent when compared to the most commonly reported chemical activating agents above mentioned. In fact, K2CO3 is nontoxic (can be used as food additives), is easy removed by water washing, has weak corrosion thus allowing good operating conditions. The uses of K2CO3 as activating agent have been reported by several authors [3, 7, 15, 24-29] resulting in the preparation of ACs with high surface area [13] and developed microporosity.
Conclusion
Rice husk biochar may be converted into a cost-effective adsorbent to remove compounds with the use of chemical activation, being a good alternative to be used in adsorption-based technologies. Considering there is an urgent need to explore new applications of the rice husk, an important agro-industrial waste in South Brazil, and solve the environmental problems, both in relation to use of agricultural waste such as emissions of nitrogen from fuel, this study showed good answers to these challenges.
In the present study, a microextraction technique and a sensitive method using BAµE-LD/GC×GC-qMS were applied for the first time for trace analysis of carbazole in diesel oil sample. The potential for the carbazole removal in diesel oil of low-cost ACs, obtained from rice husk pyrolysis and prepared by chemical activation was also investigated. Overall results indicate that it is possible to add value to thesebiochars. Besides the appearance of the micropores, which is generally promoted by the chemical activation, the present values of surface areas are much larger than those obtained after silica removal during the washings. Therefore, it is noteworthy that the results of this study point to the potential of producing high quality AC with surface area 1850 m2 g -1 , with satisfactory adsorbent proprieties, using rice husk as starting material and K2CO3 as activating agent.
The sorbent tested demonstrated a good stability, robustness and microextraction efficiency. Furthermore, the enhanced peak capacity of comprehensive two-dimensional GC and the great identification capacity of mass spectrometry allow in the same analysis the accurate identification and quantification of carbazole. Therefore, this is a valid analytical technique with good selectivity and high sensitivity for the detection of compounds with very strong interference from the matrix.For the first time, a cost-effective and environmentally friendly method for extraction and detection of nitrogen compound in commercial diesel is reported.