Article pubs.acs.org/EF
Autothermal Catalytic Reforming of Pine-Wood-Derived Fast Pyrolysis Oil in a 1.5 kg/h Pilot Installation: Performance of Monolithic Catalysts Evert J. Leijenhorst,*,†,‡ William Wolters,† Bert van de Beld,† and Wolter Prins‡ †
BTG Biomass Technology Group B.V., Josink Esweg 34, 7545 PN Enschede, The Netherlands Department of Biosystems Engineering, Ghent University, Coupure links 653, 9000 Ghent, Belgium
‡
ABSTRACT: The autothermal catalytic reforming of pyrolysis oil for the production of syngas has been studied in a 1.5 kg/h pilot unit. The influence of the feed ratio’s air-fuel-steam and the catalyst amount on the product gas quality were determined. While using a combination of nickel and platinum group metal (PGM) catalysts in monolithic form, a nearly tar- and methanefree product gas could be produced. The maximum syngas yield was obtained at an equivalence ratio of 0.36 and a space time of 1.3 s. These conditions resulted in the production of 47 mol syngas per kg of pyrolysis oil, which corresponds to 97% of the theoretical maximum. The total syngas production decreased at lower equivalence ratios primarily due to increased formation of carbonaceous solids. Incomplete conversion of methane at lower equivalence ratios had a smaller impact on the syngas production. Decreasing the space time to 0.7 s increased both the methane and tar concentrations in the product gas. Tar concentrations remained below 6 mg/Nm3 in all experiments, showing the tar conversion activity of the catalyst combination to be very good. The progress of the methane steam reforming over the individual catalysts was followed by gas sampling upstream from, in-between, and downstream from the catalysts. It appeared that, in the lower temperature range (780−880 °C), the methane reforming activity of the PGM catalyst is higher than that of the nickel catalysts. Above 880 °C, however, the reforming activity is quite similar. In conclusion, the route from pyrolysis oil to syngas via autothermal catalytic reforming, and without using any external energy sources, seems attractive.
1. INTRODUCTION Biomass is a renewable resource; the carbon content of biomass originates primarily from carbon dioxide captured from air via photosynthesis during plant growth. Therefore, the combustion of biomass gives no net carbon emissions, so biomass can be regarded as a carbon-neutral resource.1 The conversion of biomass to fuels and/or chemicals that are currently produced from fossil resources is highly desired for various reasons, including security of supply and environmental considerations. For further information on biomass classification, composition and the use of biomass, the work of Vassilev et al.2 is a good starting point. To overcome certain difficulties associated with biomass collection, storage, and processing, the conversion of biomass into pyrolysis oil by fast pyrolysis can be advantageous.3 One of the proposed routes in producing fuels and/or chemicals from biomass or biomass-derived intermediates is via gasification. Even though significant successes4 have been achieved in recent decades by the efforts of many researchers, engineers, and supporting staff in the process development activities, biomass gasification is not yet a widely implemented technology. Difficulties in implementing biomass gasification systems lie among others in the contamination of the product gas by tars. Tar is a common name for a range of heavy hydrocarbons; typical compounds include, for example, naphthalene and acenaphthalene. Worldwide, research on tar analysis and removal is ongoing. In a recent overview,5 results from over 15 years of work performed by the Energy Research Centrum of The Netherlands (ECN) on tars have been published. Tars can be removed within the gasifier system using © 2014 American Chemical Society
so-called primary measures, while secondary measures indicate tars are removed or converted downstream the gasifier.6 One of the most promising techniques, which can be applied both in and downstream from the gasifier, is to convert tars catalytically. A recent review on catalytic tar removal is published by Shen and Yoshikawa.7 The elimination of tars by steam reforming reactions are known to be kinetically limited,7 so the reaction rates can be increased by increasing the temperature and/or by using a catalyst. In gasification systems, often small solid particles are present in the produced gas (char/ash, soot, and dust from bed materials). When a catalyst is applied, the system must be suitable to deal with these particles, preferably with as little requirement for regeneration as possible. Fixed-bed catalysts have the tendency to become plugged after time. While utilization of a catalytic fluidized bed poses a solution to process streams that contain these small particles, other difficulties, such as maintaining adequate fluidization behavior and preventing attrition of the catalyst, can be encountered. Monolithic catalysts are believed to be a potential solution to typical problems encountered with fixed-bed and fluidized-bed catalysts. The open structure of monolithic catalyst allows fine particles to pass the catalyst without blocking the surface of the catalyst and without generating a pressure drop over the catalyst bed. Furthermore, the open structure is expected to decrease the temperature gradient over the catalyst bed, Received: June 4, 2014 Revised: July 18, 2014 Published: July 28, 2014 5212
dx.doi.org/10.1021/ef501261y | Energy Fuels 2014, 28, 5212−5221
Energy & Fuels
Article
Table 1. Pyrolysis Oil Composition and Process Conditions Applied for the Three Experimental Series oil name % H2O (a.r.) % ash (a.r.) % solids (a.r.) % C (a.r.) % H (a.r.) % O (a.r.) % N (a.r.) kinematic viscosity MCRT (a.r.) τ ER S/C
Series 1
Series 2
Series 3
oil A 25.6 0.03 0.12 42.7 7.1 50.2
