Synthesis of tailored hierarchical ZSM-5 zeolites and aggregates for the catalytic pyrolysis of biomass

Catalytic fast pyrolysis (CFP) is a one-step process for the conversion of lignocellulosic biomass into valuable chemicals and a deoxygenated liquid energy carrier (bio-oil) with improved properties compared to bio-oil from conventional fast pyrolysis. In the process, the vapors produced from the thermal decomposition of biomass react on the surface of a heterogeneous catalyst and are deoxygenated, cracked and converted into more desirable products. Many materials have been investigated as candidate catalysts for CFP, with the most commonly studied one being the ZSM-5 zeolite. ZSM-5 has been found to be a very effective catalyst due to its high acidity and unique micropore structure that is very shape selective for the production of monoaromatic hydrocarbons and the minimization of unwanted coke1. However, bulky oxygenates and oligomers that are formed form the thermal decomposition of biomass cannot diffuse into the micropores of the ZSM-5 and can only react on the limited external surface area of the catalyst. For this reason, the purely micropore structure of the ZSM-5 may not be optimal for the CFP of biomass and recently, there is increasing interest for hierarchical mesoporous zeolites as candidate catalysts for the process. These materials combine the high acidity and shape selectivity of the zeolite microporous structure with the enhanced accessibility that is provided by a secondary mesoporous network. The desilication of conventional zeolites is reportedly one of the most effective, versatile and easily scalable methods available to synthesize hierarchical zeolites2. Hierarchical zeolites synthesized via desilication have been tested for the CFP of biomass in small-scale reactors by several groups3-6. Provided that desilication was carried out at mild conditions, these materials performed better in terms of activity and desirable product formation. At more severe desilication conditions, the performance of the materials deteriorated, most likely due to a collapse of the zeolite structure, macropore formation and severe loss of microporosity and shape-selectivity. In this work, the mild desilication (0.2M NaOH aqueous solution) of a microporous ZSM-5 catalyst (Si/Al = 40) was carried out at variable temperatures (50, 65 and 80 ºC) and contact times (15, 30 and 45 min). The aim was the controlled formation of mesopores in the ZSM-5 catalyst with minimal loss of the micropore structure in order to increase accessibility and preserve shape selectivity, properties that are desirable for the CFP of biomass. Desilication at 50 ºC was found to be effective for the increase of the total and external surface area of the zeolite to levels comparable or higher to those achieved at the higher and more commonly used temperatures of 65 ­­­ºC and 80 ºC, provided enough contact time was allowed (≥ 30 min). Moreover, desilication at the lower temperature of 50 ºC resulted in a zeolite with a markedly narrower mesopore size distribution, between 2-20 nm, compared to desilication at 65 ºC or 80 ºC where wider mesopore size distributions were observed (2-40 nm), as well as some macropore formation (\u3e 50 nm). The smaller mesopore sizes achieved with desilication at 50 ºC may prove to be beneficial for biomass CFP, in which shape-selectivity plays a crucial role to inhibit the formation undesirable byproducts, such as coke. A simple laboratory procedure was developed to prepare the most interesting hierarchical zeolite samples into aggregates with a binder (bentonite) in order to carry out catalyst screening studies in medium-scale fluidized bed reactors with wood biomass. The prepared aggregates were also characterized in depth to identify any interactions between the zeolite and the binder phases. Acknowledgments This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 752941. References 1 J. Jae, G.A. Tompsett, A.J. Foster, at al., J Catal, 2011, 279, 257–268. 2 D. Verboekend and J. Pérez-Ramírez, Catal Sci Technol, 2011, 1, 879–890. 3 S. Stefanidis, K. Kalogiannis, E. F. Iliopoulou, at al., Green Chem, 2013, 15, 1647–1658. 4 D. P. Gamliel, H. J. Cho, W. Fan and J. A. Valla, Appl Catal A-Gen, 2016, 522, 109–119. 5 S. S. Shao, H. Y. Zhang, D. K. Shen and R. Xiao, RSC Adv., 2016, 6, 44313–44320. 6 K. Ding, Z. Zhong, J. Wang, et al., J Anal Appl Pyrol, 2017, 125, 153–161

Techno-economic and uncertainty analysis of Biomass to Liquid (BTL) systems for transport fuel production

This work examines the technical and economic feasibility of Biomass-To-Liquid (BTL) processes for the manufacture of liquid hydrocarbon fuels. Six BTL systems are modelled and evaluated which are based on pressurised oxygen gasification of woody biomass, and specifically on circulating fluidised bed and entrained flow gasification systems. Three fuel synthesis technologies are considered: Fischer-Tropsch synthesis, methanol conversion followed by Methanol to Gasoline (MTG) and the Topsoe Integrated Gasoline (TIGAS) synthesis. Published modelling studies of BTL systems based on gasification have only used deterministic estimates of fuel production costs to assess economic viability without accounting for uncertainties of their model parameters. Unlike other studies, the present techno-economic assessment examines and quantifies the effect of uncertainty of key parameters on the fuel production costs. The results of this analysis show that there is a realistic chance (8–14%) of concepts based on Fischer-Tropsch synthesis meeting the cost of conventional fuels; that this probability could be increased to 50% with moderate tax incentives (an 8% reduction in the tax rate); but that deterministic estimates may be systematically underestimating likely production costs. The overall energy efficiency and production costs of the BTL designs evaluated range from 37.9% to 47.6% LHV and €17.88–25.41 per GJ of produced fuels, respectively. The BTL concept with the lowest production costs incorporates CFB gasification and FT synthesis. The model deterministic estimates of production costs of this design indicate that a BTL process is not yet competitive with conventional refineries since the biofuel production costs are approximately 8% higher than current market prices. Large scale biofuel production may be possible in the long term through subsidies, crude oil price rises and legislation

Slice-selective NMR:a non-invasive method for the analysis of separated pyrolysis fuel samples

Pyrolysis oil has been identified as a possible alternative fuel source, however widespread use is hindered by high acidity and water content. These negative characteristics can be mitigated by blending with, for example, biodiesel, marine gas oil and butanol. These blended samples can be unstable and often separate into two distinct phases. NMR spectroscopy is a well-established spectroscopic technique that is finding increasing application in the analysis of pyrolysis oil and blended fuels derived from it. Here, slice-selective NMR, where the NMR spectrum of only a thin slice of the total sample is acquired, is used to study, non-invasively, how the constituent components of blended biofuel samples are partitioned between the two layers. Understanding the outcome of the phase separation is an important step towards understanding why the blended oil samples separate, and may provide answers to mitigating and eventually solving the problem. The NMR method was successfully used to analyse a number of separated biofuel samples - typically separated into an oil layer, containing marine gas oil and biodiesel, above a bio-oil layer with a high water and butanol content

A techno-economic analysis of energy recovery from organic fraction of municipal solid waste (MSW) by an integrated intermediate pyrolysis and combined heat and power (CHP) plant

The increasing environmental concerns and the significant growth of the waste to energy market calls for innovative and flexible technology that can effectively process and convert municipal solid waste into fuels and power at high efficiencies. To ensure the technical and economic feasibility of new technology, a sound understanding of the characteristics of the integrated energy system is essential. In this work, a comprehensive techno-economic analysis of a waste to power and heat plant based on integrated intermediate pyrolysis and CHP (Pyro-CHP) system was performed. The overall plant CHP efficiency was found to be nearly 60% defined as heat and power output compared to feedstock fuel input. By using an established economic evaluation model, the capital investment of a 5 tonne per hour plant was calculated to be £27.64 million and the Levelised Cost of Electricity was £0.063/kWh. This agrees the range of cost given by the UK government. To maximise project viability, technology developers should endeavour to seek ways to reduce the energy production cost. Particular attention should be given to the factors with the greatest influence on the profitability, such as feedstock cost (or gate fee for waste), maintaining plant availability, improving energy productivity and reducing capital cost

A kinetic reaction model for biomass pyrolysis processes in Aspen Plus

This paper presents a novel kinetic reaction model for biomass pyrolysis processes. The model is based on the three main building blocks of lignocellulosic biomass, cellulose, hemicellulose and lignin and can be readily implemented in Aspen Plus and easily adapted to other process simulation software packages. It uses a set of 149 individual reactions that represent the volatilization, decomposition and recomposition processes of biomass pyrolysis. A linear regression algorithm accounts for the secondary pyrolysis reactions, thus allowing the calculation of slow and intermediate pyrolysis reactions. The bio-oil is modelled with a high level of detail, using up to 33 model compounds, which allows for a comprehensive estimation of the properties of the bio-oil and the prediction of further upgrading reactions. After showing good agreement with existing literature data, our own pyrolysis experiments are reported for validating the reaction model. A beech wood feedstock is subjected to pyrolysis under well-defined conditions at different temperatures and the product yields and compositions are determined. Reproducing the experimental pyrolysis runs with the simulation model, a high coincidence is found for the obtained fraction yields (bio-oil, char and gas), for the water content and for the elemental composition of the pyrolysis products. The kinetic reaction model is found to be suited for predicting pyrolysis yields and product composition for any lignocellulosic biomass feedstock under typical pyrolysis conditions without the need for experimental data

Production of glucose from the acid hydrolysis of anhydrosugars

Acid hydrolysis of levoglucosan and cellobiose as anhydrosugar model compounds was carried out in an autoclave Parr reaction system, using sulphuric acid as catalyst. In addition, acid hydrolysis was carried out using an anhydrosugars mixture from the aqueous fraction of a pyrolysis oil or bio-oil. The bio-oil was obtained from the fast pyrolysis of birch-wood, and the segregated aqueous fraction was found to contain mainly levoglucosan with a concentration of 30 g L-1. Three main hydrolysis parameters including temperature, reaction time, and catalyst to substrate ratios were varied in order to identify their influence towards glucose production. It was found that at hydrolysis conditions of 120 °C, 60 minutes, and a catalyst/substrate ratio of 0.9; glucose yields of 98.55% and 96.56%, and conversion of substrates of 100% and ~92%, were achieved when hydrolysing cellobiose and levoglucosan respectively. An increase in the hydrolysis temperature from 120 °C to 135 °C, resulted in a decrease in the glucose yield and selectivity. Whereas high conversions of substrates (~90%) were maintained for both anhydrosugars. This was attributed to the further dehydration reactions of glucose, possibly yielding HMF or levulinic acid. During the acid hydrolysis of the bio-oil aqueous fraction, a range of hydrolysis conditions suitable to achieve glucose yields higher than 90%, was depicted. It was found that catalyst/substrate molar ratios between 0.17-0.90 and temperatures between 118 °C and 126 °C were suitable conditions to achieve glucose yields ~100% (30 g L-1). Furthermore, glucose concentrations ~117% (35 g L-1) and levoglucosan conversions above 90%, were attained at 135 °C, 20 minutes reaction time and at an estimated catalyst/substrate molar ratio of 0.2 (H2SO4, 0.5 M)

Intermediate pyrolysis of organic fraction of municipal solid waste and rheological study of the pyrolysis oil for potential use as bio-bitumen

This work presents a study on intermediate pyrolysis of the organic fraction of municipal solid waste (OFMSW) and characterisation of organic liquid product (pyrolysis oils) with particular focus on aging and rheological characteristics. The feedstock was a real municipal waste sample received from a local waste treatment plant. Shredded into small particles, it contained a high amount of moisture (51.2%) and ash (17.4%). A pilot-scale intermediate pyrolysis system was used to process the material. The process mass balance showed that the yield pyrolysis oil was 10.6%. GC-MS and FTIR experiments showed that the accelerated aging (80 °C for 24 h) did not cause an obvious change in the liquid chemical composition, but led to a significant reduction in the solids and moisture contents. The dynamic viscosity tests demonstrated that the intermediate pyrolysis oil derived from OFMSW is a non-Newtonian fluid. The dynamic viscosity of the pyrolysis oil reduced with the increase of temperature or shear rate, which can be modelled by WLF function and the Carreau model, respectively. A shear rate-temperature superposition method was proposed to construct the viscosity master curve at a wide range of shear rate, where WLF function was employed to model the shear rate-temperature shift factor. The accelerated aging caused an obvious reduction in dynamic viscosity, resulting from the decomposition of the semisolid organic agglomerates in the solids content during the aging of the OFMSW intermediate pyrolysis oil. The relatively high viscosity and reduced viscosity after aging of the OFMSW pyrolysis oil has indicated its potential for application as a substitute of the light fraction in the bitumen for road construction

Impact of potassium and phosphorus in biomass on the properties of fast Pyrolysis bio-oil

This study investigates fast pyrolysis bio-oils produced from alkali-metal-impregnated biomass (beech wood). The impregnation aim is to study the catalytic cracking of the pyrolysis vapors as a result of potassium or phosphorus. It is recognized that potassium and phosphorus in biomass can have a major impact on the thermal conversion processes. When biomass is pyrolyzed in the presence of alkali metal cations, catalytic cracking of the pyrolysis liquids occurs in the vapor phase, reducing the organic liquids produced and increasing yields of water, char, and gas, resulting in a bio-oil that has a lower calorific value and an increased chance of phase separation. Beech wood was impregnated with potassium or phosphorus (K impregnation and P impregnation, respectively) in the range of 0.10-2.00 wt %. Analytical pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) was used to examine the pyrolysis products during thermal degradation, and thermogravimetric analysis (TGA) was used to examine the distribution of char and volatiles. Both potassium and phosphorus are seen to catalyze the pyrolytic decomposition of biomass and modify the yields of products. 3-Furaldehyde and levoglucosenone become more dominant products upon P impregnation, pointing to rearrangement and dehydration routes during the pyrolysis process. Potassium has a significant influence on cellulose and hemicellulose decomposition, not just on the formation of levoglucosan but also other species, such as 2(5H)-furanone or hydroxymethyl-cyclopentene derivatives. Fast pyrolysis processing has also been undertaken using a laboratory-scale continuously fed bubbling fluidized-bed reactor with a nominal capacity of 1 kg h-1 at the reaction temperature of 525 °C. An increase in the viscosity of the bio-oil during the stability assessment tests was observed with an increasing percentage of impregnation for both additives. This is because bio-oil undergoes polymerization while placed in storage as a result of the inorganic content. The majority of inorganics are concentrated in the char, but small amounts are entrained in the pyrolysis vapors and, therefore, end up in the bio-oil

Processing thermogravimetric analysis data for isoconversional kinetic analysis of lignocellulosic biomass pyrolysis:Case study of corn stalk

Modeling of lignocellulosic biomass pyrolysis processes can be used to determine their key operating and design parameters. This requires significant amount of information about pyrolysis kinetic parameters, in particular the activation energy. Thermogravimetric analysis (TGA) is the most commonly used tool to obtain experimental kinetic data, and isoconversional kinetic analysis is the most effective way for processing TGA data to calculate effective activation energies for lignocellulosic biomass pyrolysis. This paper reviews the overall procedure of processing TGA data for isoconversional kinetic analysis of lignocellulosic biomass pyrolysis by using the Friedman isoconversional method. This includes the removal of “error” data points and dehydration stage from original TGA data, transformation of TGA data to conversion data, differentiation of conversion data and smoothing of derivative conversion data, interpolation of conversion and derivative conversion data, isoconversional calculations, and reconstruction of kinetic process. The detailed isoconversional kinetic analysis of TGA data obtained from the pyrolysis of corn stalk at five heating rates were presented. The results have shown that the effective activation energies of corn stalk pyrolysis vary from 148 to 473 kJ mol−1 when the conversion ranges from 0.05 to 0.85

Physical pretreatment of biogenic-rich trommel fines for fast pyrolysis

Energy from Waste (EfW) technologies such as fluidized bed fast pyrolysis, are beneficial for both energy generation and waste management. Such technologies, however face significant challenges due to the heterogeneous nature, particularly the high ash contents of some municipal solid waste types e.g. trommel fines. A study of the physical/mechanical and thermal characteristics of these complex wastes is important for two main reasons; (a) to inform the design and operation of pyrolysis systems to handle the characteristics of such waste; (b) to control/modify the characteristics of the waste to fit with existing EFW technologies via appropriate feedstock preparation methods. In this study, the preparation and detailed characterisation of a sample of biogenic-rich trommel fines has been carried out with a view to making the feedstock suitable for fast pyrolysis based on an existing fluidized bed reactor. Results indicate that control of feed particle size was very important to prevent problems of dust entrainment in the fluidizing gas as well as to prevent feeder hardware problems caused by large stones and aggregates. After physical separation and size reduction, nearly 70. wt% of the trommel fines was obtained within the size range suitable for energy recovery using the existing fast pyrolysis system. This pyrolyzable fraction could account for about 83% of the energy content of the 'as received' trommel fines sample. Therefore there was no significant differences in the thermochemical properties of the raw and pre-treated feedstocks, indicating that suitably prepared trommel fines samples can be used for energy recovery, with significant reduction in mass and volume of the original waste. Consequently, this can lead to more than 90% reduction in the present costs of disposal of trommel fines in landfills. In addition, the recovered plastics and textile materials could be used as refuse derived fuel