Environ. Sci. Technol. 2005, 39, 5141-5147
Organic Compounds Produced during the Thermal Decomposition of Cotton Fabrics JULIA MOLTO Ä ,* JUAN A. CONESA, RAFAEL FONT, AND I G N A C I O M A R T IÄ N - G U L L O Ä N Chemical Engineering Department, University of Alicante, P.O. Box 99, 03080 Alicante, Spain
Used cotton fabrics, which can be considered a biomass according to its origin, were descomposed thermically in a laboratory scale reactor through a set of runs carried out in inert and air atmospheres, with temperatures between 650 and 1050 °C. More than 90 compounds, including carbon oxides, light hydrocarbons, and PAHs, have been identified and quantified. In the gas phase some of the main components obtained were methane, ethene, and benzene. The main semivolatile compounds detected were styrene, phenol, naphthalene, acenaphthylene, and phenanthrene. Furthermore, analyses of PCDD/Fs in the material tested and in the semivolatile compounds produced during the combustion at 850 °C were also performed, obtaining values of 14.5 (sample) and 7.2 pg I-TEQ/g (combustion). The congener that mostly contributes to the total I-TEQ was 2,3,4,7,8-PeCDF. The results obtained show that this waste could be used as biomass, and in this way, it is a valid alternative to disposal in landfills.
Introduction Textiles are manufactured to perform a wide range of functions. These materials are made up of different types of fibers mixed in varying proportions. While the textile industry has a long history of being thrifty with its resources, a large proportion of unnecessary waste is still produced each year. Textile recycling is one of the oldest forms of recycling. Local thrift stores, charities, churches, and consignment stores are the backbone of clothing recovery and distribution. A minor percentage of the recycled textiles becomes wiping and polishing cloths or is converted into fiber to be used in new textile products (1). Although cotton fabrics are usually recycled in other ways, its thermal valorization can be interesting to some industries that mainly focus on obtaining the potential energy by combustion. Dedicated incineration plants for used cotton fabrics only appear reasonable where sufficient quantities of this waste material can be guaranteed in the long term, which is unusual. The most common option is coincineration, with the advantage that cotton fabrics are not hazardous material, are highly calorific, are easily flammable fuel, and must therefore be mixed well and homogeneized with the other waste. Mueller et al. (2) studied the cocombustion of textile dusts of acrylic fibers, cotton, and wool in a gas firing test * Corresponding author phone: +(34) 96 590 38 67; fax: +(34) 96 590 38 26; e-mail:
[email protected]. 10.1021/es0482435 CCC: $30.25 Published on Web 06/10/2005
2005 American Chemical Society
plant, analyzing the poly aromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/ Fs), and some heavy metals in the initial material, in the ashes formed, and in the flue gas. Some papers concerning the analysis of organic byproducts in pyrolysis and combustion of cellulose and cotton can be found in the literature. Hajaligol et al. (3) studied the formation of aromatic hydrocarbons from pyrolysis of carbohydrate textile materials exposed to conditions of smoldering combustion of the solid carbohydrate substrates. Schwenker et al. (4) pyrolyzed an unmodified cotton fabric at 350-75 °C and obtained a complex mixture of organic acids, aldehydes, ketones, water, and levoglucosan in the aqueous distillate. In the Valencia Region of Spain, the municipal solid waste (MSW) production was estimated to be 1.004.799 Mg/yr in 1999 (5). Textiles represent nearly 4% of MSW. As a consequence, large amounts of this kind of waste is landfilled each year. It is estimated that cotton is the main component of textile waste, since it is the most commonly used natural fiber in the industrial manufacturing sector. Abad et al. (6) carried out a dioxin mass balance in a municipal waste incinerator and analyzed different waste materials (textile, organic, plastic, wood, and paper) finding that textile samples presented the highest values of PCDD/ Fs in the samples themselves and in their combustion. PCCD/ Fs were detected in articles of new cotton clothing at concentrations ranging from low pg/g to high ng/g (7). There is extensive evidence indicating that contaminated textiles are largely responsible for the high concentrations in washing machine effluent (8). Klasmeir and McLachlan (9) developed a screening method for detection of octachlorodibenzo-p-dioxin and octachlorodibenzofuran in textiles, based on the analysis with GC/ECD to develop a rapid and inexpensive method to monitor textiles in order to identify contaminated material. Because exposure of the skin to PCCD/Fs might pose a possible health hazard, Klasmeier et al. (10) measured the transfer of dioxins and furans from contaminated textiles to the outermost layers of the skin of human volunteers and concluded that there is little spatial variability and also little variability among individuals and textiles. A relative small number of data is available for PCDD/F presence and content in textile dyes and pigments. PChloranil is used in the production of dioxazin-dyes, which have a wide application in the dying of cotton. Christmann et al. (11) analyzed eight commercially available tetrachlorbenzoquinones (chloranils), and PCDD/Fs were found in all the samples. Bosˇtjan et al. (12) studied several samples of dyes for PCDD/F content, and they also carried out a mass balance of PCDD/Fs in a dyeing process and concluded that there is strong evidence that PCDD/Fs are formed from precursor compounds in contaminated dyes during textile finishing processes. The aim of this work was to study the evolution of organic compounds produced during the thermal decomposition of used cotton fabrics, specially focusing on those compounds with hazard potential, to know if this kind of waste would be an alternative to use as biomass in combustion processes, in agreement with the environmental regulations.
Material and Experimental Apparatus A used blue T-shirt made of 100% cotton was selected as a used cotton fabrics source in the present study. Prior to the runs, the T-shirt was cut into small pieces with an average size of 1 by 1 cm. VOL. 39, NO. 14, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Characteristics of the Material Used C (wt %) H (wt %) N (wt %) S (wt %) O % by difference (wt %) Cl (wt %) ash content (wt %) net calorific value (kJ/kg)
45.5 6.6 0.3
