Stylianos D. Stefanidis

In-situ upgrading of biomass pyrolysis vapors: Catalyst screening on a fixed bed reactor

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 carbon-hydrogen-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. The ZSM-5 formulation with the highest surface area displayed the most balanced performance having a moderate selectivity towards hydrocarbons, reducing undesirable compounds and producing organic liquid products at acceptable yields.

Pilot-scale validation of Co-ZSM-5 catalyst performance in the catalytic upgrading of biomass pyrolysis vapours

The main objective of the present work was the evaluation of commercial ZSM-5 catalysts (diluted with a 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 the equilibrium state, and were further promoted with cobalt (Co, 5% wt%) using conventional wet impregnation techniques. All the 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 CO2 compared to the CO increase which was favored by the use of ZSM-5 alone. These changes in CO2/CO yields are indicative of the different decarbonylation/decarboxylation mechanism that applies for Co3O4 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 the 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 plants 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 zeolitic catalyst, and accumulative ash deposition on the catalyst that depends on the nature of biomass (content of ash).

Quantitative and qualitative analysis of hemicellulose, cellulose and lignin bio-oils by comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry.

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-oils 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-of-flight 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-d6 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.

Mesopore-modified mordenites as catalysts for catalytic pyrolysis of biomass and cracking of vacuum gasoil processes

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. Alkaline treatment was carried out to generate mesoporosity. Severity of alkaline treatment was found to be of paramount importance to tune the generated mesoporosity, while it significantly affected the crystallinity of treated mordenites. It was moreover observed that the alkaline treatment selectively extracted Si decreasing the Si/Al ratio of treated samples. Catalytic activity of parent and alkaline treated mordenites was studied in the pyrolysis of biomass. All zeolitic based materials produced less amounts of bio-oil but of better quality (lowering the oxygen content from ∼40% to as much as 21%) as compared to the non-catalytic pyrolysis experiments. On the other hand, it was found that the combination of mesopore formation and high surface area after alkaline treatment of the mordenite with a high Si/Al ratio resulted in the enhancement of its catalytic activity, despite the reduction of its acidity. The increment of the decarboxylation and dehydration reactions, combined with a reduction of carbon deposition on the catalyst, resulted in a remarkable decrease in the oxygen content in the organic fraction and therefore, resulted in a superior quality liquid product. Alkaline treated mordenites were additionally acid treated targeting dealumination and removal of the extra framework debris, thus generating mesopore-modified mordenite samples with stronger acid sites and higher total acidity, as candidate catalysts for catalytic cracking of vacuum gasoil. Desilicated and especially desilicated and dealuminated mordenites exhibited the highest activity and selectivity towards LCO with the best olefinicity in gases and higher bottoms conversion. Therefore, an optimized desilicated–dealuminated mordenite additive could be an interesting candidate as a component of the FCC catalyst for a high LCO yield.

An integrated process for the production of platform chemicals and diesel miscible fuels by acid-catalyzed hydrolysis and downstream upgrading of the acid hydrolysis residues with thermal and catalytic pyrolysis.

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 h were applied to give different combined severity factors. Temperatures of 175 and 200 °C and acid concentration of 5 wt.% were found to be necessary to achieve good yield (17 wt.%) and selectivities of LA while treatment time did not have an effect. The acid hydrolysis residues were characterized for their elemental, cellulose, hemicellulose and lignin contents, and then tested in a small-scale pyrolyzer using silica sand and a commercial ZSM-5 catalyst. Milder pretreatment yielded more oil (43 wt.%) and oil O(2) (37%) while harsher pretreatment and catalysis led to more coke production (up to 58 wt.%), less oil (12 wt.%) and less oil O(2) (18 wt.%).

Catalyst hydrothermal deactivation and metal contamination during the in situ catalytic pyrolysis of biomass

Lignocellulosic biomass contains small amounts of alkali and alkaline earth metals, which may volatilize during the in situ catalytic pyrolysis of biomass and deposit on the catalyst, affecting its properties. In addition, due to the presence of steam in the process and exposure of the catalyst to high temperatures, hydrothermal deactivation also plays a key role to the catalysts life span. In this work we studied the effect of hydrothermal deactivation and deactivation by metal contamination of commercial ZSM-5 zeolite based catalyst formulations using two techniques. In the first technique, biomass metal nitrates were spray impregnated on the catalyst at different levels, followed by hydrothermal deactivation of the samples and characterization. In the second technique, hydrothermal deactivation and metal contamination were decoupled by using a hydrothermally stable ZSM-5 sample as a parent material for the preparation of catalyst samples that were exposed to different biomass amounts by carrying out biomass catalytic pyrolysis reaction–regeneration cycles in a bubbling fluidized bed reactor. During spray impregnation, the different metals accumulated on the catalyst at the same rate and increasing metal loading resulted in gradual loss of the surface area and pore volume of the catalyst, eventually leading to complete destruction of the zeolite after a certain threshold. During catalytic pyrolysis however, the biomass metals accumulated at different rates. Potassium accumulated very selectively on the catalyst, while sodium and calcium were less selective. Accumulation of magnesium and iron was not found to increase with increasing exposure to biomass. Cross section examination of the catalyst particles revealed that potassium was deposited evenly throughout the particles, while magnesium and calcium were only detected on the outer surface. Evaluation of the catalyst in pyrolysis tests showed that the presence of biomass metals on the catalyst altered the catalysts functionality, likely by introduction of some basic sites, which led to the deterioration of its catalytic performance.