This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy J. Anal. Appl. Pyrolysis 82 (2008) 140–144 Contents lists available at ScienceDirect Journal of Analytical and Applied Pyrolysis journal homepage: www.elsevier.com/locate/jaap Understanding the pyrolysis of CCA-treated wood Part II. Effect of phosphoric acid Qirong Fu, Dimitris S. Argyropoulos *, David C. Tilotta, Lucian A. Lucia Organic Chemistry of Wood Components Laboratory, Department of Forest Biomaterials Science & Engineering, North Carolina State University, Raleigh, NC 27695-8005, USA ARTICLE INFO ABSTRACT Article history: The pyrolysis process of chromated copper arsenate-treated wood impregnated with phosphoric acid (2– Received 15 February 2007 6 wt.%) has been investigated using a Kugelrohr short-path distillation apparatus. The presence of Accepted 22 February 2008 phosphoric acid is shown to change the overall pyrolysis kinetics and yields of products resulting in a Available online 7 March 2008 decrease in the amount of volatile products and an increase in the char formation. The yield of levoglucosan was found to decrease in the presence of relatively higher concentrations of phosphoric Keywords: acid, while the yield of levoglucosenone increased. The pyrolysis of chromated copper arsenate-treated CCA-treated wood wood in the presence of phosphoric acid gave rise to 22% (on water-free tar basis) levoglucosenone. Such Pyrolysis Levoglucosenone data demonstrates the potential for a new pathway toward the rational utilization of chromated copper Phosphoric acid arsenate-treated wood waste. ß 2008 Elsevier B.V. All rights reserved. 1. Introduction be considered: chemical composition of cellulosic materials, the addition of inorganic catalysts, and the conditions of pretreatment Waterborne chromated copper arsenate (CCA) has been used to and pyrolysis. preserve wood against fungi and insects for many years [1]. CCA- Various additives have been investigated to change the treated wood is usually used for outdoor applications, such as pyrolysis product distribution and convert cellulosic materials telephone poles, decks, fence posts, boat docks, and wooden to valuable added products. Acid catalysts are known to promote playgrounds. In recent years, CCA-treated wood has been phased dehydration reactions and favor the formation of LGO. Phosphoric out for any residential use due to the potential health risks acid has proved to be an efficient catalyst to enhance the yield of associated from the leaching of arsenic-laced preservatives. LGO from the pyrolysis of cellulosic materials [13–15]. In industrial Environmental friendly recovery and/or disposal technologies materials, phosphoric compounds are used as flame retardants for for CCA-treated wood have been developed [2–5]. Low-tempera- wood, textile finish and polymeric fibers in order to reduce ture pyrolysis has shown to be a promising approach to this flammability and smoke generation by lowering their weight loss growing disposal problem [2], with the purpose of minimizing rate and increasing their char yield [16,17]. Since LGO was detected metal release and maximizing production of pyrolysis oils. through the thermal degradation of cellulose in the presence of Pyrolysis oils can be used as a source of valuable chemical acidic additives such as phosphoric acid in the 1970s [8], this products [6,7], such as levoglucosan (LG), levoglucosenone (LGO), research area has attracted much interest. Phosphoric acid has hydroxyacetone, hydroxyacetaldehyde, isoeugenol, guaiacol, etc. specific effects on cellulose. Phosphoric acid is known to induce Both LG and LGO are carbohydrate thermal decomposition less catalytic degradation to cellulose than other mineral acids [13] products. LGO is a highly functionalized compound owing to its and it has lower volatility than that of sulfuric acid or hydrochloric carbon–carbon double bond, the ketone group and the glycosidic acid [18]. It is also well known for its swelling property resulting in anhydro linkage. LG is also an optically active compound. Thus, LG easy penetration into interfibrillar reaction centers [19]. Thus, and LGO are attractive chiral raw materials for application in phosphoric acid promotes diffusion and chemical processes. organic synthesis and the pharmaceutical industry. There have During pyrolysis, phosphoric acid can change the depolymeriza- been many studies on the formation mechanisms of LG and LGO tion and dehydration mechanisms of cellulose. It has been [8–12]. To obtain high yields of LG and LGO, various factors need to observed [20–25] that the presence of phosphoric acid in cellulosic materials lowered decomposition temperatures, suppressed vola- tiles production and increased char yields. * Corresponding author. Tel.: +1 919 515 7708; fax: +1 919 515 6302. The objective of the present study is to investigate LGO and LG E-mail address: [email protected] (D.S. Argyropoulos). formation from pyrolysis of CCA-treated wood that has been 0165-2370/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jaap.2008.02.007 Author's personal copy Q. Fu et al. / J. Anal. Appl. Pyrolysis 82 (2008) 140–144 141 pretreated with phosphoric acid, with the purpose of developing a 2.4. Analytical methods new pathway in the rational utilization of CCA-treated wood waste. In addition, thermogravimetric analytical (TGA) data of 2.4.1. GC/FID analysis pretreated wood samples is also provided. Quantitative tar analysis was performed on a Hewlett Packard HP6890 series GC system, using a DB-1701 (J&W) capillary column 2. Experimental (60 m  0.25 mm i.d. and 0.25-mm film thickness). The tempera- ture program was an isothermal temperature profile at 45 8C for 2.1. Materials the first 4 min, followed by a 3 8C/min temperature gradient to 270 8C and finally an isothermal period at 270 8C for 7 min. Helium Southern pine wood and its CCA-treated equivalent (Type C) was used as a carrier gas, with a split ratio of 1:20 and a constant were used in this study. The active ingredients in this CCA flow of 1.0 mL/min. The temperature of the detector and injector preservative are 47.5% CrO3, 18.5% CuO, and 34.0% As2O5 (based on were maintained at 280 8C and 250 8C, respectively. For the sample a 100% oxide). The wood was milled to a powder that had a particle preparation, 70 mg of tar was weighed and dissolved in 5 mL of size of 0.1–0.2 mm, and the moisture content was 8%. Chemically acetone. Fluoranthene was used as an internal standard. Detailed pure 85% phosphoric acid was used for impregnation. signal assignments of the emerging gas chromatograms of the obtained pyrolysis tars can be located in Ref. [26]. 2.2. Impregnation with phosphoric acid 2.4.2. Metal analysis Solutions of phosphoric acid (2 wt.%, 4 wt.%, 5 wt.%, 6 wt.% The chromium and copper content of pyrolysis char were based on dry wood) in methanol were mixed with untreated wood determined by atomic absorption spectrometer PerkinElmer 2380. and CCA-treated wood (wood/acid solution = 1:5). Methanol was Analytical wavelengths were 357.9 nm for chromium and 324.8 nm evaporated under vacuum and the impregnated wood powders for copper. The arsenic content of pyrolysis char was determined by were dried over a phosphorous pentoxide desiccator under inductively coupled plasma (ICP) spectrometer, using a PerkinElmer vacuum. Optima 2000DV. The samples for metal analysis were prepared according to the reflux method provided by Helsen et al. [27]. This 2.3. Pyrolysis methodology causes the complete sample dissolution in nitric acid without loss of any material. 0.1 g of pyrolysis char was placed into a The pyrolysis of pretreated wood samples was carried out conical flask equipped with a reflux condenser, followed by the under heat in a Kugelrohr short-path distillation apparatus (Fig. 1). addition of 10 mL of 65% HNO3. Then the flask was heated on a The sample weight was 3 g for each trial. The vacuum pressure was heating plate under reflux until the sample dissolved completely controlled at 7 mmHg. The thermal treatment was carried out at (approximately 2 h). The concentration of chromium, copper and 350 8C for 30 min. The end product—char was collected in the first arsenic in pyrolysis char from the CCA-treated wood pretreated with flask, whereas the tar was collected in two consequently connected 4% H3PO4 were 82.7%, 87.5% and 74.5%, respectively. receiving flasks (B in Fig. 1) and condensed with ice water (0 8C) for further analyses. The volatiles were condensed with dry ice– 2.4.3. Thermogravimetric analysis acetone at À70 8C in the first trap (E in Fig. 1). TGA was carried out using a TA Q500 Instrument. The wood powder sample, approximately 10–15 mg in weight, was intro- duced into a platinum sample pan and heated from room temperature to 600 8C at a heating rate of 50 8C/min under a nitrogen flow of 60 mL/min. 3. Results and discussion 3.1. Quantitative analysis of tar products Yields of pyrolysis fractions (at 350 8C) of untreated wood and CCA-treated wood pretreated with phosphoric acid are shown in Table 1. The total recovery (the sum of the yields of char, tar and volatiles) from pyrolysis was around 90%.