Effect of the Previous Composting on Volatiles Production during Biomass Pyrolysis † Agustı ´n G. Barneto,* José Ariza Carmona, and M. Jesús Díaz Blanco Chemical Engineering Department, Campus El Carmen, UniVersity of HuelVa, 21071 HuelVa, Spain ReceiVed: April 30, 2009; ReVised Manuscript ReceiVed: June 1, 2009 Composting is a biological process of decomposition of organic materials in an aerobic environment, which modifies the chemical composition and the thermal behavior of biomass. During composting, fungi and bacteria promote the decomposition of hemicellulosic and cellulosic fractions, increasing the lignin proportion. Its product, compost, is usually used as an amendment to soil; however, its physicochemical characteristics turn it into an interesting feedstock in pyrolysis or gasification facilities. The changes that composting produces on biomass pyrolysis can be explained using an autocatalytic kinetic model (Prout-Tompkins). Thus, by means of a similar set of kinetic parameters for both the biomass and compost, it is possible to simulate the thermogravimetric analysis data (TG and DTG curves) of the materials as a sum of thermal degradations of its main pseudocomponents, hemicellulose, cellulose, lignin, and extractives. TG analysis coupled to mass spectrometry (MS) allows monitoring of the gas production during pyrolysis. Water and carbon oxide MS profiles can be simulated by an optimized linear combination of previously calculated DTG curves of pseudocomponents; however, in order to simulate the hydrogen MS signal, it is necessary to consider the char obtained in the course of the volatilization process. During pyrolysis, hydrogen production has two origins, volatilization of biomass pseudocomponents and charring. The last mechanism explains ∼75% of the hydrogen obtained from compost. The pseudocomponent that produces more hydrogen by weight unit is lignin, showing a specific hydrogen production much higher than carbohydrates (3:1:8 for hemicellulose/ cellulose/lignin). This fact, together with the greater lignin content in compost, explains the positive effect of composting on hydrogen production. 1. Introduction Usually, biomass is a term used for all organic material that stems from plants. 1 Main components of biomass are cellulose, hemicellulose, lignin, and extractives. Its respective proportions change according to the type of biomass. For example, wood plants (hardwoods and softwoods) contain 20-30% hemicel- lulose, 35-50% cellulose, 20-30% lignin, and 5-10% extrac- tives. Herbaceous plants and grasses contain less lignin but more hemicellulose than wood plants. 1,2 Historically, biomass has played a relevant role as a renewable energy source at low scale. However, nowadays, the contribution of biomass to future global energy supply is uncertain. 3 On average, biomass contributes to about 9-13% of the total energy supplies in industrialized countries, 5 but only 3.0 to 3.5% of the yearly produced biomass is used in applications not related to foodstuff. 4 Although energy production from biomass for power generation or transport fuels is increasing, a large part has noncommercial use. In order to increase the future utilization of biomass as fuel feedstock, it is necessary to improve the present technologies and avoid competition between alimentary and energetic uses of biomass. Fast-growing species such as tagasaste (Chamaecytisus palmensis) or leucaena (Leucaena leucocephala), capable of growing in large amounts on arid soils, could be an alternative to the use of traditional feedstocks. In recent years, several technologies of thermochemical biomass conversion have been developed. As alternative to traditional incineration, gasification and pyrolysis have shown their capacity to recover the energy stored in plants by the photosynthetic process. These thermal processes provide an efficient, environmentally acceptable, and cost-effective method for providing a sustainable energy source. 4,6,7 Modern integrated gas-steam combined cycles (IGCC) are capable of achieving high thermodynamic efficiencies. 8 Pyrolysis consists of thermal degradation of biomass in the absence of oxidizing agents. Reaction products can be divided into three groups, permanent gases (mainly CO, CO 2 ,H 2 O, H 2 , and hydrocarbons), bio-oil (pyrolytic liquid), and char (carbon- aceous solid). Their respective proportions depend on several factors, mainly pressure and heating rate. Slow pyrolysis favors char production; however, short processing times are adequate to obtain liquid products in high yield. Bio-oil and char can be used as renewable fuels. 9,10 Gasification is the thermochemical conversion of a solid biomass into a gaseous fuel by heating with a gasification agent (i.e., air, oxygen, steam, hydrogen, CO 2 , or mixtures of these gases). The obtained gas is easier and more versatile to employ than the original biomass, making it possible to use it in power gas engines and gas turbines or to produce liquid fuels. 11-13 In biomass gasification facilities, feedstock pretreatments (basically drying and size reduction) 8 have influence on the physical characteristics of the biomass but do not affect its chemical properties. In this sense, it is necessary to take into account some studies which show that the chemical character- istics of biomass have influence on its thermochemical behavior. 14-16 For instance, it has been shown that the char yield is favored by the presence of some mineral elements in the biomass. 17 Another example is the effect of the composting on the hydrogen production during biomass gasification. 18 Using composting as pretreatment during biomass (leucaena and † Part of the special issue “Green Chemistry in Energy Production Symposium”. * Tel.: +34 959 219982. Fax: +34 959 219983. E-mail: agustin.garcia@ diq.uhu.es. J. Phys. Chem. A 2010, 114, 3756–3763 3756 10.1021/jp903994p  2010 American Chemical Society Published on Web 07/31/2009