Article pubs.acs.org/EF
Polycyclic Aromatic Hydrocarbons in Birch Wood Slow Pyrolysis Products Leena Fagernas̈ ,* Eeva Kuoppala, and Pekka Simell VTT Technical Research Centre of Finland, P.O. Box 1000, 02044 VTT, Espoo, Finland ABSTRACT: The products from slow pyrolysis of birch hardwood are promising to be used for various purposes, in addition to conventional charcoal. To evaluate their utilization, knowledge about their polycyclic aromatic hydrocarbons (PAHs) is needed. The content and distribution of the PAHs in the different products were determined in a test run with a typical slow pyrolysis carbonization retort. The PAH compositions of gases, and distillates including aqueous phases and tars, were followed in terms of time and retort temperature. Also, other compounds in gases and aqueous phases through the test run were analyzed. PAHs were found in all the products, but were mostly concentrated in the tars. Because of the results, the PAH contents in the tars has to be considered. In contrast, very low PAH concentrations were found for the tar-free aqueous phases. Because of low PAH and also low benzene contents, the aqueous phases are promising to be utilized in various applications, for example as biodegradable pesticides. Due to high proportions of combustible gases, such as carbon monoxide, methane, and hydrogen, the gases could be utilized as a fuel gas for energy. In addition to barbecue charcoal, the charcoal might have potential to be used as biochar as a soil amendment. The PAH results can be exploited when planning the utilization of the products and for registration purposes needed in the commercialization.
■
INTRODUCTION Polycyclic aromatic hydrocarbons (PAHs) are organic substances containing two or more fused aromatic rings made up of carbon and hydrogen atoms. They are hydrophobic, stable, and sparingly soluble in water. Hundreds of individual PAHs are known. Many PAHs are carcinogenic and mutagenic and form a risk for human health. Hence occupational exposure to PAHs can lead to body burdens to the workers.1−3 PAHs are widely distributed contaminants in the environment. They are formed during the incomplete combustion or pyrolysis of organic material. They originate mostly from industry, traffic and energy production. Industrial processes that involve the pyrolysis or combustion of coal and the production and use of coal-derived products are major sources of PAHs. In nature, they are formed in forest fires and volcanic eruptions. They are found in air, water, soils, and sediments, generally at trace levels except near their sources. They are also present in some foods, for example, in smoked and grilled food.1−3 PAHs of particular toxicological and environmental concern are monitored and controlled. International Agency for Research on Cancer (IARC) has classified PAHs into five groups according to their carcinogenicity.1 Compounds that are listed as carcinogenic, probably carcinogenic or possibly carcinogenic to humans are as follows: benzo[a]pyrene, benzo[a]anthracene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, chrysene, dibenzo[a,h]anthracene, dibenzo[a,h]pyrene, dibenzo[a,i]pyrene, dibenzo[a,l]pyrene, indeno[1,2,3-cd]pyrene, 5-methylchrysene, and naphthalene. The list of priority PAHs varies in different countries. In the United States, the U.S. Environmental Protection Agency (EPA) has defined 16 PAHs as priority pollutants being hazardous to the environment.4 In the European Union (EU), legislation concerning PAHs includes monitoring of ambient air, water, emissions from incineration plants, food, and primary smoke products. 5 Threshold values and exposure limits for certain © 2012 American Chemical Society
Table 1. Properties of Birch Wood Feedstock in the Slow Pyrolysis Retort Test Run
a
analysis
concentration
moisture content, wt % ash content, wt % of dry wood volatile matter, wt % of dry wood carbon (C), wt % of dry wood hydrogen (H), wt % of dry wood nitrogen (N), wt % of dry wood sulfur (S), wt % of dry wood oxygen (O),a wt % of dry wood
14.7 0.6 84.5 49.7 6.1 0.1 0.01 44
By difference: 100% − (CHNS + ash).
compounds and for total PAH content in different matrices have been given. Benzo[a]pyrene is often used as a marker for total PAHs.1 Limits for other PAH compounds are currently also under planning. At present, generally more attention is being paid to the PAHs and their effects. The European Commission’s Scientific Committee on Food (SCF) has identified 15 PAHs as of major concern for human health.3 In 2005 the EU recommended research on the occurrence of these PAHs in food and in 2006 expanded the list to the 15 + 1 EU priority PAHs. The PAH contents of smoke flavorings based on the aqueous phase of condensed smoke (smoke condensate, originated often from slow pyrolysis), have been controlled by Commission Regulations.6,7 The maximum permitted concentrations have been given for benzo[a]pyrene (10 μg/kg) and benzo[a]anthracene (20 μg/kg). In the chemical analysis of PAHs, different separation and quantification methods are used and standardized for various Received: June 21, 2012 Revised: October 18, 2012 Published: October 24, 2012 6960
dx.doi.org/10.1021/ef3010515 | Energy Fuels 2012, 26, 6960−6970
Energy & Fuels
Article
Figure 1. Decomposition behavior of birch hardwood feedstock material (dust, d
