Hydro-Pyrolysis of Biomass and Online Catalytic Vapor Upgrading with Ni-ZSM‑5 and Ni-MCM-41 F. Melligan, M. H. B. Hayes, W. Kwapinski, and J. J. Leahy* Carbolea Research Group, Department of Chemical and Environmental Sciences, University of Limerick, Ireland ABSTRACT: A catalyst reactor coupled with analytical pyrolysis gas chromatography/mass spectroscopy (Py-GC/MS) was used to carry out online analysis of the product vapors from the fast pyrolysis of Miscanthus x giganteus, Scots pine, and mahogany. Pyrolysis was carried out in both an inert atmosphere of He gas and in a highly reducing atmosphere of H 2 . Significant changes in the vapor compositions were achieved with the use of H 2 as the carrier gas. The most notable of these were the increases in the hydrocarbon compositions. The roles of ZSM-5, Ni/ZSM-5, MCM-41, and of Ni/MCM-41 catalysts on the compositions of the pyrolysis vapors were investigated. Lower amounts of the higher molecular weight phenolic compounds and larger amounts of the lighter phenols were observed in the presence of Ni supported on ZSM-5 and MCM-41. This effect was more evident for the 10% than for the 2.5% Ni loadings. Overall, the results both from the use of H 2 as the carrier gas and from all the catalysts demonstrates significant improvements in the composition of the vapors. However, this resulted in the lowering of the quantities of condensable products. 1.1. INTRODUCTION Bio-oil, an important product from biomass pyrolysis, can be regarded in its crude state as a low grade fuel. Many pyrolysis process parameters, such as temperature, pressure, heating rate, reactor configuration, biomass type, and particle size have been extensively studied 1-3 and summarized. 4-6 The majority of studies have used inert gas, usually N 2 at ambient pressure. Bio- oil from this process possesses many undesirable properties, such as high quantities of carboxylic acids, water, and oxygen- ated molecules; furthermore, the H/C ratio is low. Thus, there is a very limited demand for the product. To meet the requirements for a fuel-oil, bio-oil produced by this method must undergo extensive and, in most cases, expensive upgrading processes. To achieve a better quality fuel, the process used must remove oxygen, convert carboxylic acids and other reactive species to more benign products, and also add hydrogen to the bio-oil. To date, the methods that have provided the most useful products are hydrodeoxygenation of the bio-oil and catalytic processing of the pyrolysis vapors. Neither method is without major problems. Bridgwater et al. 7 has reported that it is possible to obtain hydrocarbon yields of up to 58% by weight of liquid bio-oil through hydrodeoxyge- nation. However, this process can be expensive and slow. Elliott et al. 8 have shown that single stage hydrotreating is an inappro- priate method, due to the formation of large quantities of both coke and tar, causing rapid catalyst deactivation and reactor clogging. To combat these problems, a multi stage process was developed, involving initially the stabilization of the bio-oil, followed by a more aggressive hydrotreatment. 8 Similar issues, such as catalytic deactivation have been en- countered with catalytic upgrading of pyrolysis vapors. 9 Also, biomass is hydrogen deficient, 10 and further hydrogen deple- tion takes place during catalytic upgrading of the vapors because oxygen is usually removed as H 2 O. When supplementary hydrogen is present during the pyrol- ysis process, very reactive H• radicals are generated. These react readily, adding hydrogen to biomass fragments, while simultaneously removing oxygen and capping free radicals, thereby increasing hydrocarbon production and yielding an improved product. However, until recently, there have been limited reports on the use of ‘active’ gases such as H 2 for pyrolysis. Thangalazhy et al. 11 studied the production of hydrocarbon fuels from biomass pyrolysis using ZSM-5 as a catalyst under both He and H 2 environment. Zhang et al. 12 carried out a more detailed study, where N 2 , CO, CH 4 , and H 2 were used as gases for the pyrolysis of corncobs. Other studies involving active carrier gases were carried out by Minkova et al. 13 and Jindarom et al. 14 All studies concluded that the type of carrier gas plays an important role in both the product distribution and composition. The higher heating value (HHV) of the bio-oil obtained under N 2 was 17.8 MJ/kg, while that from H 2 was 24.4 MJ/kg. 15 Although use of atmospheric pressure pyrolysis with H 2 results in an increase in HHV, some of the inherent problems associated with crude bio-oil still remain, such as thermal instability and immiscibility with crude-oil-based fuels, requiring further catalytic treatment. 15 To date, zeolite and modified zeolite catalysts have received the majority of attention as materials for the catalytic upgrading of pyrolysis vapors. Several researchers have investigated the use of the zeolite based ZSM-5 and modified ZSM-5 catalysts for producing improved products. 16-19 Pyrolysis vapors when passed over an acidic zeolite catalyst can become deoxyge- nated through simultaneous dehydration and decarboxylation reactions. An extensive study of zeolite catalysts, particularly modified ZSM-5, was carried out by French et al. 20 They investigated 40 different catalysts and observed that the highest hydrocarbon yield was obtained from the Ni/ZSM-5 catalysts. The incorporation of transition metals, such as nickel, was Received: July 25, 2012 Revised: September 17, 2012 Published: September 18, 2012 Article pubs.acs.org/EF © 2012 American Chemical Society 6080 dx.doi.org/10.1021/ef301244h | Energy Fuels 2012, 26, 6080-6090