John Adjaye

Production of hydrocarbons by catalytic upgrading of a fast pyrolysis bio-oil. Part I: Conversion over various catalysts

The upgrading of a fast pyrolysis bio-oil was studied with different catalysts in a fixed bed micro-reactor. The catalysts were HZSM-5 (average pore size, 0.54 nm), H-Y (0.74 nm), H-mordenite (0.67 nm), silicalite (0.54 nm) and silica-alumina (3.15 nm). The experiments were carried out at atmospheric pressure, 1.8 and 3.6 weight hourly space velocity, and a temperature range of 290–410°C. The products were char, coke, gas, tar, residue, water and an organic distillate fraction (ODF). The objective was to obtain high yields of hydrocarbons in the ODF. The yields of hydrocarbons (based on the amount of bio-oil fed) were 27.9 wt% with HZSM-5, 14.1 wt% with H-Y, 4.4 wt% with H-mordenite, 5 wt% with silicalite and 13.2 wt% with silica-alumina. It was interesting to note that whereas HZSM-5 and H-mordenite produced more aromatic than aliphatic hydrocarbons, H-Y, silicalite and silica-alumina produced more aliphatic than aromatic hydrocarbons. The main aromatic hydrocarbons were toluene, xylenes and trimethylbenzenes. The liquid aliphatic hydrocarbon content consisted mostly of C6-C9 hydrocarbons. Alkylated cyclopentene, cyclopropane, pentane and hexene were the main aliphatic hydrocarbons. In most of the runs, doubling the space velocity from 1.8 to 3.6 h−1 resulted in decreased coke, char and gas formation and increased ODF yields. On the other hand, deoxygenation and hydrocarbon formation decreased.

Production of hydrocarbons by catalytic upgrading of a fast pyrolysis bio-oil. Part II: Comparative catalyst performance and reaction pathways

Abstract Catalysts, namely, HZSM-5, H-mordenite H-Y, silicalite and silica-alumina which were used for the upgrading of Pyrolysis bio-oil in Part I of this study were examined for their relative performance in the production of organic distillate fraction (ODF), hydrocarbon formation and minimization of char, coke and tar formation. A catalyst effectiveness criterion based on yield and selectivity for each product was defined and correlated with the performance of each catalyst. Amongst the five catalysts studied, HZSM-5 was the most effective catalyst for the production of ODF, overall hydrocarbons and aromatic hydrocarbons. Also, it provided the least coke formation. Silica-alumina catalyst was most effective for minimizing the char formation and H-Y catalyst was superior in minimizing tar formation as well as maximizing the production of aliphatic hydrocarbon. Reaction pathways were proposed for the conversion of bio-oil. It was postulated that bio-oil conversion proceeded as a result of thermal effects followed by thermocatalytic effects. The thermal effects produced separation of bio-oil to light organics and heavy organics and polymerization of bio-oil to char. The thermocatalytic effects produced coke, tar, gas, water and the desired organic distillate fraction. Deoxygenation, cracking, cyclization, aromatization, isomerization and polymerization were the main thermocatalytic reactions.

Catalytic conversion of a biofuel to hydrocarbons: effect of mixtures of HZSM-5 and silica-alumina catalysts on product distribution

Abstract The potential for producing hydrocarbons from the conversion of biofuels has been the focus of attention in recent years. In a preliminary study, we observed that it was possible to produce various types of liquid hydrocarbons and also to dramatically change the hydrocarbon content from aromatic to aliphatic by mixing silica-alumina and HZSM-5 catalysts in different proportions. In the present work, an in-depth study was undertaken in order to investigate the effect of various mixture compositions of silica-alumina and HZSM-5 on the yield and selectivity for liquid hydrocarbons. The biofuel used in the present study was produced by the rapid thermal processing of maple wood. The runs were performed in a fixed-bed microreactor operating at atmospheric pressure, 1.8–7.2 WHSV and 330–410°C. It was interesting to observe that for all catalyst mixtures, the optimum yields of organic liquid product (OLP) and total hydrocarbons were obtained at 370°C. The HZSM-5 content ( H f ) of the catalyst mixtures ranged between 0 and 40 wt.%. The catalysts were thoroughly characterized by the following techniques: X-ray powder diffraction, temperature-programmed desorption with ammonia, FT-IR and NMR spectroscopy and measurement of their BET and pore sizes. The yield of OLP increased with H f and ranged between 13 and 27 wt.% of the biofuel feed. Aliphatic hydrocarbons were the main products (37–77 wt.% of OLP), followed by aromatic hydrocarbons (2–38 wt.% of OLP). At low H f (below 10 wt.%), the main effect of HZSM-5 was to increase the extent of cracking and thereby increase the aliphatic hydrocarbon production. At H f > 10, a combination of cracking followed by shape selectivity resulted in the production of aromatic hydrocarbons at the expense of aliphatic hydrocarbons. The results were analyzed statistically in order to determine which factors (namely HZSM-5 content in the catalyst ( H f ), space velocity, temperature and their interactions) were mainly responsible for the formation of OLP and its hydrocarbon content. The results showed that all three factors affected the OLP yields rather significantly. However, the aliphatic hydrocarbon yield was mostly affected by the space velocity and H f , and the aromatic hydrocarbon yield was significantly affected by temperature and H f . A regression surface response model was used to relate the yields of these products with the above-mentioned factors.

Characterization and stability analysis of wood-derived bio-oil

Abstract The stability characteristics of a bio-oil, produced by the high pressure liquefaction of aspen wood were studied by observing the changes in its physical properties, composition and distillation characteristics with time. Distillation characteristics of the fresh bio-oil showed that maximum amount of organic distillate was obtained at 172 Pa and 200°C. This distillate fraction mainly consisted of aromatic, aliphatic and naphthenic hydrocarbons and oxygenated compounds such as phenols, furans, alcohols, acids, ethers, aldehydes and ketones. The bio-oil viscosity, and chemical composition were found to change substantially over time probably due to polymerization of some components. Upon storage, the concentration of aromatic hydrocarbons and phenols decreased while the concentration of aldehydes and ketones increased. Also, the oxygen content of the distillate decreased from 22.7 wt% for the fresh bio-oil to 18.8 wt% after 31 days. However, when the bio-oil was mixed with tetralin it was observed that the properties of the mixture remained unchanged with time. Tetralin was found to donate hydrogen leading to the improvement in bio-oil stability. A free radical mechanism is proposed to explain the effect of tetralin.

Catalytic conversion of wood derived bio-oil to fuels and chemicals

Abstract A bio-oil, produced by high pressure liquefaction of aspen wood, was upgraded over HZSM-5 in a fixed bed micro-reactor at atmospheric pressure and in the temperature range 250-450°C. The oil was co-processed with tetralin and in addition, steam was co-fed in some runs. The products were the desired organic distillate, gas, aqueous phase and residue. The amount of organic distillate was at maximum 59 wt.% of bio-oil at 390°C and contained 65 wt.% aromatic hydrocarbons. With steam co-feeding, the maximum amount of distillate increased to 65 wt.% at 390°C although the maximum aromatic concentration dropped to 59 wt.% of distillate. Also, the amount of coke decreased from 10 wt.% (without steam) to 6 wt.% (with steam). Model compound studies indicated that cracking, deoxygenation, aromatization and isomerisation probably were the main reactions which occurred in bio-oil upgrading.

Simulation of a Two-Stage Micro Trickle-Bed Hydrotreating Reactor using Athabasca Bitumen-Derived Heavy Gas Oil over Commercial NiMo/Al2O3 Catalyst: Effect of H2S on Hydrodesulfurization and Hydrodenitrogenation

A two-stage, micro trickle-bed reactor (for studies of the effects of hydrogen sulfide on hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of Athabasca bitumen-derived heavy gas oil over commercial NiMo/Al2O3 catalyst) has been simulated. One dimensional homogeneous mass transfer and a two dimensional heat transfer models were developed. The essence of the simulation was to enhance the understanding of the effects of hydrogen sulfide in the hydrotreating catalyst bed in a two-stage mode and also to predict the catalyst requirements for deep HDS and HDN processes. The kinetic model used in the simulation was based on the Langmuir-Hingshelwood method of rate determination. Adsorption constants were estimated by non-linear least squares method. The kinetic models were tested on independent set of data and found to predict the experimental data satisfactorily. The mass transfer simulation considered the effects of variables such as temperature and catalyst loading or liquid hourly space velocity (LHSV) on the trends of hydrogen sulfide generation and, sulfur and nitrogen conversions along the catalyst bed. The model was numerically solved using a fourth-order Runge-Kutta technique. The 1:3 wt/wt catalyst loading with inter-stage hydrogen sulfide removal was found to give the best HDN and HDS activities. Simulated results showed that doubling the present catalyst mass and operating at 653 °C with inter-stage hydrogen sulfide removal would give 6 and 179 ppm product sulfur and nitrogen, respectively. On the other hand, without hydrogen sulfide removal, only 49 and 302 ppm product sulfur and nitrogen could be attained, respectively. The heat transfer simulation compared temperature profiles in the two-stage process to a single stage process for the 1:3 wt/wt catalyst loading at 653 K. The temperature regime in Stage II was found to be more uniform unlike Stage I and the single stage. Crank Nicholson algorithm was used to solve the 2-D partial differential equations.

Hydrotreating of light gas oil using a NiMo catalyst supported on activated carbon produced from fluid petroleum coke

Nitric acid functionalized steam activated carbon (NAFSAC) was prepared from waste fluid petroleum coke (FPC) and used as a support material for the synthesis of a NiMo catalyst (2.5 wt-% Ni and 13 wt-% Mo). The catalyst was then used for the hydrotreatment of light gas oil. The support and catalysts were characterized by Brunauer-Emmett-Teller (BET) gas adsorption method, X-ray diffraction, H2-temperature programmed reduction, NH3-temperature programmed desorption, CO-chemisorption, mass spetrography, scanning electron microscopy (SEM), Boehm titration, and Fourier transform infrared spectroscopy (FTIR). The SEM results showed that the carbon material retained a needle like structure after functionalization with HNO3. The Boehm titration, FTIR, and BET results confirmed that the HNO3 functionalized material had moderate acidity, surface functional groups, and mesoporosity respectively. The produced NAFSAC had an inert nature, exhibited the sink effect and few metal support interactions, and contained functional groups. All of which make it a suitable support material for the preparation of a NiMo hydrotreating catalyst. Hydrotreating activity studies of the NiMo/NAFSAC catalyst were carried out under industrial operating conditions in a laboratory trickle bed reactor using coker light gas oil as the feedstock. A parallel study was performed on the hydrotreating activity of NiMo/γ-Al2O3 as a reference catalyst. The hydrodesulfurization and hydrodenitrogenation activities of the NiMo/NAFSAC catalyst were 62% and 30%, respectively.

Catalytic Conversion of Canola Oil in a Fluidized Bed Reactor

Studies were conducted in a fluidized-bed reactor at atmospheric pressure, reaction temperatures in the range 400–500°C and fluidizing gas flow rates ranging from 175–275 mL/min to study the product distribution obtained from the conversion of canola oil over HZSM-5, silica-alumina and HS-Mix (a physical mixture containing 20 wt% HZSM-5 and 80 wt% silica-alumina).

Catalytic Upgrading of Wood Derived Bio-Oil over HZSM-5 Catalyst: Effect of Co-Feeding Steam

A bio-oil was produced from high pressure liquefaction of aspen poplar wood, mixed with tetralin in a 2:1 weight ratio and processed with HZSM-5 catalyst in the presence of steam. Experiments were carried out in a 12.7 mm ID fixed bed micro-reactor at 3.6 WHSV, 1 atm and a temperature range of 290–410 °C. Fractions collected were coke, gas, residue, unconverted oil and an organic distillate fraction. The objective was to optimize the organic distillate yield and minimize coke formation. The results were calculated on steam and tetralin-free basis. Amount of the organic distillate was maximum at 65 wt% of the bio-oil at 370 °C and contained about 59 wt% aromatic hydrocarbons. The coke increased with temperature from 0.3 wt% at 290 °C to 7 wt% at 410 °C. On the other hand, treating the bio-oil-tetralin mixture in the absence of steam resulted in an organic distillate fraction maximum of 58 wt% at 390 °C. Also, coke increased from 1.2 wt% at 290 to 12 wt% at 410 °C. These results indicated that catalytic treatment in the presence of steam resulted in a higher organic distillate yield as well as a significant reduction in the formation of coke. Competitive adsorption processes, cracking, deoxygenation and aromatization were probably the main reactions by which the final products were obtained.