Papers by Stylianos D Stefanidis
Catalyst hydrothermal deactivation and metal contamination during the in situ catalytic pyrolysis of biomass
Catal. Sci. Technol., 2016
Optimization of bio-oil yields by demineralization of low quality biomass
Biomass and Bioenergy, 2015
Pyrolysis of lignin with 2DGC quantification of lignin oil: Effect of lignin type, process temperature and ZSM-5 in situ upgrading
Journal of Analytical and Applied Pyrolysis, 2015
Waste and Biomass Valorization, 2015
One of the main constraints and the most costly step in the production of lignocellulosic ethanol... more One of the main constraints and the most costly step in the production of lignocellulosic ethanol is the biomass pretreatment step that aims at liberating the cellulose by dissolving the lignin and the hemicellulose fractions. For this reason, several pretreatment methods have been developed that aim at dissolving biomass lignin and hydrolysing the cellulosic part in order to maximize fermentation yields towards ethanol. In this work, delignification of a forestry residue was carried out via a Milox treatment and its variations. Formic acid (FA) with hydrogen peroxide (HP) was used as the delignifying agent and the effects of temperature and HP concentration were investigated. Hydrolysis of untreated and delignified biomass samples with hot water (HW) was also carried out to depolymerize the solid feed.
Catalytic and thermal pyrolysis of polycarbonate in a fixed-bed reactor: The effect of catalysts on products yields and composition
Polymer Degradation and Stability, 2014
ABSTRACT A meaningful and advanced method concerning the management of waste electrical and elect... more ABSTRACT A meaningful and advanced method concerning the management of waste electrical and electronic equipment (WEEE) becomes a necessity, mainly due to their increased production, applications and their short life. Thermal methods have been an attractive option and for this reason the investigation of pyrolysis and catalytic pyrolysis as a potential method for the recycling of polycarbonate (PC) based plastics has been the aim of the current study. Nine different catalysts with variations in properties (such as porosity and acidity/basicity) were introduced in a bench scale pyrolysis system together with the polycarbonate polymeric material and the pyrolysis fractions were collected and analyzed. The liquid product consisted mainly of phenols and substituted phenols as well as the original monomer and, due to the commercial value of these products in the chemical industry, it is expected to enhance the economic viability of the process. Results showed a reduction in the degradation temperature in the presence of all catalytic materials, depending on the pore characteristics and the acidic nature of the solid. It seems that in the presence of the basic catalysts, PC degradation leads to lower molecular weight compounds and high phenolic fractions in the liquid produced. In terms of reduction in the production of the monomer, pore size rather than acidity appears to be the determining factor.
Pyrolysis and catalytic pyrolysis as a recycling method of waste CDs originating from polycarbonate and HIPS
Waste Management, 2014
Pyrolysis appears to be a promising recycling process since it could convert the disposed polymer... more Pyrolysis appears to be a promising recycling process since it could convert the disposed polymers to hydrocarbon based fuels or various useful chemicals. In the current study, two model polymers found in WEEEs, namely polycarbonate (PC) and high impact polystyrene (HIPS) and their counterparts found in waste commercial Compact Discs (CDs) were pyrolysed in a bench scale reactor. Both, thermal pyrolysis and pyrolysis in the presence of two catalytic materials (basic MgO and acidic ZSM-5 zeolite) was performed for all four types of polymers. Results have shown significant recovery of the monomers and valuable chemicals (phenols in the case of PC and aromatic hydrocarbons in the case of HIPS), while catalysts seem to decrease the selectivity towards the monomers and enhance the selectivity towards other desirable compounds.
Journal of Chromatography A, 2014
Thermal and catalytic pyrolysis are efficient processes for the transformation of biomass to bio-... more Thermal and catalytic pyrolysis are efficient processes for the transformation of biomass to bio-oil, a liquid energy carrier and a general source of chemicals. The elucidation of the bio-oil's composition is essential for a rational design of both its production and utilization process. However, the complex composition of bio-oils hinders their complete qualitative and quantitative analysis, and conventional chromatographic techniques lack the necessary separation power. Two-dimensional gas chromatography with time-offlight mass spectrometry (GC × GC-ToFMS) is considered a suitable technique for bio-oil analysis due to its increased separation and resolution capacity. This work presents the tentative qualitative and quantitative analysis of bio-oils resulting from the thermal and catalytic pyrolysis of standard xylan, cellulose, lignin and their mixture by GC × GC-ToFMS. Emphasis is placed on the development of the quantitative method using phenol-d 6 as internal standard. During the method development, a standard solution of 39 compounds was used for the determination of the respective Relative Response Factors (RRF) employing statistical methods, ANOVA and WLSLR, for verification of the data. The developed method was applied to the above mentioned bio-oils and their detailed analysis is presented. The different compounds produced and their diverse concentration allows for an elucidation of the pyrolysis mechanism and highlight the effect of the catalyst.
Journal of Analytical and Applied Pyrolysis, 2014
In this study, thermogravimetric (TG) analyses, along with thermal and catalytic fast pyrolysis e... more In this study, thermogravimetric (TG) analyses, along with thermal and catalytic fast pyrolysis experiments of cellulose, hemicellulose, lignin and their mixtures were carried out in order to investigate their pyrolysis products and whether the prediction of the pyrolysis behavior of a certain lignocellulosic biomass feedstock is possible, when its content in these three constituents is known. We were able to accurately predict the final solid residue of mixed component samples in the TG analyses but the differential thermogravimetric (DTG) curves indicated limited heat transfer when more than one component was present in the pyrolyzed sample. The limited heat transfer did not have a significant effect on the TG curves but it affected the product distribution in the fast pyrolysis experiments, which resulted in inaccurate calculation of the product yields, when using a simple additive law. In addition, the pyrolysis products of each biomass constituent were characterized in order to study their contribution to the yield and composition of the products from whole biomass pyrolysis. An investigation into the pyrolysis reaction pathways of each component was also carried out, using the bio-oil characterization data from this study and data found in the literature. pathways alternative and renewable energy source that can be converted via the biomass fast pyrolysis process into a liquid product, known as bio-oil, which is considered to be a promising biofuel/bioenergy carrier. The bio-oil is a complex mixture of oxygenated compounds and its composition and quality is heavily dependent on the composition of the biomass feedstock. Lignocellulosic biomass is composed mainly of three basic structural components; cellulose, hemicellulose and lignin. The content of these components in biomass varies depending on the biomass type. Woody plant species have tightly bound fibers and are richer in lignin while herbaceous plants have more loosely bound fibers, a fact that indicates lower lignin content. Usually, cellulose, hemicellulose and lignin constitute 40-50 wt.%, 20-40 wt.% and 10-40 wt.% of the plant material respectively . In addition to these components, lignocellulosic biomass also contains a small amount of inorganic material (ash) and extractives.
Green Chemistry, 2013
Mesopore-modified Mordenite zeolitic materials with different Si/Al ratios have been prepared and... more Mesopore-modified Mordenite zeolitic materials with different Si/Al ratios have been prepared and tested in the biomass pyrolysis and catalytic cracking of vacuum gasoil.
Green Chemistry, 2014
The main objective of the present work was the evaluation of commercial ZSM-5 catalysts (diluted ... more The main objective of the present work was the evaluation of commercial ZSM-5 catalysts (diluted with silica-alumina matrix) in the in situ upgrading of lignocellulosic biomass pyrolysis vapours and the validation of their bench-scale reactor performance in a pilot scale circulating fluidized bed (CFB) pyrolysis reactor. The ZSM-5 based catalysts were tested both fresh and at equilibrium state, and were further promoted with cobalt (Co, 5% wt.%) using conventional wet impregnation techniques. All tested catalysts had a significant effect on product yields and bio-oil composition, both at bench-scale and pilot scale experiments, producing less bio-oil but of better quality. Incorporation of Co exhibited no additional effect on water or coke production induced by ZSM-5, compared to non-catalytic fast pyrolysis. On the other hand, Co addition significantly increased the formation of CO 2 compared to the CO increase which was favored by the use of ZSM-5 alone. These changes in CO 2 /CO yields are indicative of the different decarbonylation/decarboxylation mechanism that applies for Co 3 O 4 compared to ZSM-5 zeolite, due to the differences in their acidic properties (mainly type of acid sites). Co-promoted ZSM-5 catalysts simultaneously enhanced production of aromatics and phenols with a more pronounced performance in the pilot-scale experiments resulting in the formation of a three phase bio-oil, rather than the usual two phase catalytic pyrolysis oil (aqueous and organic phases). The third phase produced is even lighter than the aqueous phase and consists mainly of aromatic hydrocarbons and phenolic compounds. Addition of Co in ZSM-5 is thus suggested to strongly enhance aromatization reactions that result in selectivity increase towards aromatics in the bio-oil produced. Possible routes of catalyst deactivation in the pilot plant continuous operation process have been suggested and are related to pore blocking and masking of acid sites by formed coke (reversible deactivation), partial framework dealumination of the fresh zeoltic catalyst, and accumulative ash deposition on the catalyst that depends on the nature of biomass (content of ash).
Bioresource Technology, 2012
This study evaluates an integrated process for the production of platform chemicals and diesel mi... more This study evaluates an integrated process for the production of platform chemicals and diesel miscible biofuels. An energy crop (Miscanthus) was treated hydrothermally to produce levulinic acid (LA). Temperatures ranging between 150 and 200°C, sulfuric acid concentrations 1-5 wt% and treatment times 1-12 hours were applied to give different combined severity factors.
Second-generation biofuels by co-processing catalytic pyrolysis oil in FCC units
Applied Catalysis B: Environmental, 2014
ABSTRACT Previous research showed that hydrodeoxygenated (HDO) pyrolysis-oils could successfully ... more ABSTRACT Previous research showed that hydrodeoxygenated (HDO) pyrolysis-oils could successfully be co-processed with vacuum gasoil (VGO) in a labscale fluid catalytic cracking (FCC) unit to bio-fuels. Typically the hydrodeoxygenation step takes place at ∼300 °C under 200–300 bar of hydrogen. Eliminating or replacing this step by a less energy demanding upgrading step would largely benefit the FCC co-processing of pyrolysis oils to bio-fuels. In this paper a bio-oil that has been produced by catalytic pyrolysis (catalytic pyrolysis oil or CPO) is used directly, without further upgrading, in catalytic cracking co-processing mode with VGO. The results are compared to the co-processing of upgraded (via HDO) thermal pyrolysis oil. Though small but significant differences in the product distribution and quality have been observed between the co-processing of either HDO or CPO, they could be corrected by further catalyst development (pyrolysis and/or FCC), which would eliminate the need for an up-stream hydrodeoxygenation step. Moreover, the organic yield of the catalytic pyrolysis route is estimated at approximately 30 wt.% compared to an overall yield for the thermal pyrolysis followed by a hydrodeoxygenation step of 24 wt.%.
Applied Catalysis B: Environmental, 2012
The main objective of the present work was the study of different ZSM-5 catalytic formulations fo... more The main objective of the present work was the study of different ZSM-5 catalytic formulations for the in situ upgrading of biomass pyrolysis vapours. An equilibrium, commercial diluted ZSM-5 catalyst was used as the base case, in comparison with a series of nickel (Ni) and cobalt (Co) modified variants at varying metal loading (1-10 wt. %). The product yields and the composition of the produced bio-oil were significantly affected by the use of all ZSM-5 catalytic materials, compared to the non-catalytic flash pyrolysis, producing less bio-oil but of better quality. Incorporation of transition metals (Ni or Co) in the commercial equilibrium/diluted ZSM-5 catalyst had an additional effect on the performance of the parent ZSM-5 catalyst, with respect to product yields and bio-oil composition, with the NiO modified catalysts being more reactive towards decreasing the organic phase and increasing the gaseous products, compared to the Co 2 O 3 supported catalysts. However, all the metal-modified catalysts exhibited limited reactivity towards water production, while simultaneously enhancing the production of aromatics and phenols. An interesting observation was the in situ reduction of the supported metal oxides during the pyrolysis reaction that eventually led to the formation of metallic Ni and Co species on the catalysts after reaction, which was verified by detailed XRD and HRTEM analysis of the used catalysts. The Co 2 O 3 supported ZSM-5 catalysts exhibited also a promising performance in lowering the oxygen content of the organic phase of bio-oil.
Wiley Interdisciplinary Reviews: Energy and Environment, 2012
Application of heterogeneous catalysis in biomass pyrolysis seems to be one of the most promising... more Application of heterogeneous catalysis in biomass pyrolysis seems to be one of the most promising methods to improve bio--oil quality by minimizing its undesirable properties (high viscosity, corrosivity, instability, etc.) and producing renewable crude (bio--crude). This bio--crude could finally lead to transportation fuels using existing refinery processes (like hydro--treating). A plethora of catalytic materials have been investigated in the literature as catalysts for the biomass catalytic pyrolysis process. Among them micro--(zeolitic) or meso--porous (Al--MCM--41) acid materials have been tested, either promoted or not with several transition metals. Lately basic materials are also suggested. For this process a circulating fluid bed reactor seems to be the most effective technology since it offers continuous catalyst regeneration. The research till today shows that catalysts based on ZSM--5 are the most promising. With these catalysts bio--oil yield up to about 30 wt. % (on dry biomass) with about 21 wt. % oxygen can be produced. However, tailoring of catalyst properties like acidity/basicity and porosity characteristics is still needed to develop an optimized catalyst.
Catalytic upgrading of lignocellulosic biomass pyrolysis vapours: Effect of hydrothermal pre-treatment of biomass
Catalysis Today, Jan 1, 2011
... doi:10.1016/j.cattod.2010.12.049 | How to Cite or Link Using DOI Copyright © 2011 Elsevier BV... more ... doi:10.1016/j.cattod.2010.12.049 | How to Cite or Link Using DOI Copyright © 2011 Elsevier BV All rights reserved. Permissions & Reprints. Catalytic upgrading of lignocellulosic biomasspyrolysis vapours: Effect of hydrothermal pre-treatment of biomass. ...
Bioresource …, Jan 1, 2011
In-situ catalytic upgrading of biomass fast pyrolysis vapors was performed in a fixed bed bench-s... more In-situ catalytic upgrading of biomass fast pyrolysis vapors was performed in a fixed bed bench-scale reactor at 500 °C, for catalyst screening purposes. The catalytic materials tested include a commercial equilibrium FCC catalyst (E-cat), various commercial ZSM-5 formulations, magnesium oxide and alumina materials with varying specific surface areas, nickel monoxide, zirconia/titania, tetragonal zirconia, titania and silica alumina. The bio-oil was characterized measuring its water content, the carbonhydrogen-oxygen (by difference) content and the chemical composition of its organic fraction. Each catalytic material displayed different catalytic effects. High surface area alumina catalysts displayed the highest selectivity towards hydrocarbons, yielding however low organic liquid products. Zirconia/titania exhibited good selectivity towards desired compounds, yielding higher organic liquid product than the alumina catalysts.
Applied Thermal …, Jan 1, 2009
This paper evaluates nine types of electrical energy generation options with regard to seven crit... more This paper evaluates nine types of electrical energy generation options with regard to seven criteria. The options use natural gas or hydrogen as a fuel. The Analytic Hierarchy Process was used to perform the evaluation, which allows decision-making when single or multiple criteria are considered.
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Papers by Stylianos D Stefanidis