Scientific publications

Sorption-enhanced gasification (SEG) is a promising technology for producing renewable feedstock gas to be used in biofuel synthesis processes, especially in dimethyl ether (DME) synthesis. To adopt the technology on a commercial scale, it is necessary to acquire knowledge about the related operational characteristics. The SEG process is carried out at lower temperatures than those employed in conventional gasifiers. A typical operating range is from 600 °C to 800 °C. Fuel decomposition experiments have shown distribution of the decomposition products to vary by the process temperature in this operating range, and thus, it is important to adapt this phenomenon for modelling the SEG process. To model the temperature dependence of the decomposition products, a fuel model was developed. Fuel decomposition experiments were conducted to obtain the boundary conditions for the fuel model. The developed fuel model was implemented to an SEG model frame, and the model prediction was compared against data from a 200 dual fluidised bed facility. The model gave satisfactory predictions for producer composition and temperature trends. Furthermore, the main balances of the model were in agreement with typical trends of the SEG process. The conducted simulations improved our understanding of material balances in SEG reactors. Knowledge from physical operations governing the process is of value in further development of the technology.

Steam adsorption enhanced reaction processes are a promising process intensification for many types of reactions, where water is formed as a byproduct. To assess the potential of these processes, adequate models are required that accurately describe water adsorption, particularly under the desired elevated temperatures and pressures. In this work, an adsorption isotherm is presented for H2O adsorption at 200–350 °C and 0.05–4.5 bar partial pressure on molecular sieve (LTA) 3A. The isotherm has been developed on the basis of experimental data obtained from a thermogravimetric analysis and integrated breakthrough curves. The experimental data at lower steam partial pressures can be described with a Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm, whereas at higher steam partial pressures the experimental data can be adequately captured by capillary condensation. Based on the characteristics of the adsorbent particles, a linear driving force relation has been derived for the adsorption mass transfer rate and the apparent micropore diffusivity is determined. The isotherm and mass transport model presented here prove to be adequate for modelling and improved evaluation of steam adsorption enhanced reaction processes.

In this work, we study the direct synthesis of DME using CO2 -rich syngas, with a CO2/CO ratio similar to that obtained from the gasification of biomass, i.e. , 1.9. We used catalytic beds consisting of physical mixtures of the benchmark catalysts used for the synthesis of methanol from syngas and for methanol dehydration to DME, namely Cu/ZnO/Al2O3 and 𝛾-Al2O3 , respectively. Our results show that the ratio between each catalytic phase determines the productivity and selectivity to DME, as well CO and CO2 conversions. Thus, higher total carbon conversions were obtained with the catalytic bed with the highest content of the Cu/Zn/Al2O3 phase. The presence of 𝛾-Al2O3 allows to exceed the equilibrium conversion of CO for the syngas to methanol synthesis. The highest DME productivity is obtained with the catalytic bed containing equal amounts of both catalytic phases. In addition, we also show that other reaction variables such as temperature, pressure, and contact time also play an important role in terms of DME productivity. The presence of a high fraction of CO2 in the syngas results in a high production of H2O, which after long times on stream result in the deactivation of the Cu/ZnO/Al2O3 catalytic phase due to the sintering of the copper particles. The in situ removal of H2O via the addition of an H2O sorbent, zeolite 3A, into the catalytic bed, results in a significant enhancement of both carbon conversion and DME productivity.

Sorption enhanced dimethyl ether synthesis (SEDMES) is a novel DME production route from CO2-rich feedstocks. In situ water removal by adsorption results in high single-pass conversions, thereby circumventing the disadvantages of conventional routes, such as low carbon efficiency, energy intensive downstream separation and large recycling. The first-time demonstration of pressure swing regeneration with 80% single-pass carbon selectivity to DME allows for an enormous increase in productivity. Already a factor four increase compared to temperature swing regeneration is achieved, unlocking the potential of SEDMES as a carbon utilisation technology.

The direct synthesis of dimethyl ether (DME) from biomass-derived syngas is a topic of great interest in the field of biofuels. The process takes place in one reactor combining two catalytic functions, Cu/ZnO/Al2O3(CZA) for the synthesis of methanol and an acid catalyst (typicallyg-Al2O3) for methanol dehydration to DME. However, the catalytic performance of those catalysts is negatively affected by the high CO2/CO ratio in the bio-syngas, resulting in low methanol and DME production rates. In this work, we show that promoters such as zirconium and gallium oxides increase the CO fraction in the syngas. However, the production of H2O is also increased, leading to the deactivation of both CZA and g-Al2O3. The addition of a water sorbent (zeolite 3A) in the reaction medium alleviates the detrimental effect of H2O in the direct synthesis of DME from CO2-rich syngas. Thus, DME production over the CZA/g-Al2O3 catalytic bed increases from ca.8.7% to 70% when a zeolite 3A is placed in the reaction medium. In fact, carbon conversions higher than conventional equilibrium conversions are achieved. This work demonstrates that the sorption enhanced synthesis of DME is a suitable strategy to increase DME production from biomass-derived syngas.

The direct synthesis of dimethyl ether (DME) from syngas is an exothermic process, which requires two different catalyst functions in the same reactor: methanol (MeOH) synthesis and dehydration to DME. The two functions can be intimately mixed in hybrid pellets, located on separated pellets or coupled in core@shell-engineered pellets. In this work, a multitubular fixed-bed reactor, loaded with the catalyst configurations mentioned above, has been investigated by mathematical modeling. It is shown that the different spatial distribution of the active phases has a drastic impact on reactor performance. Using the mechanical mixture of separated pellets, the DME yield is hindered by intraparticle diffusion limitations. The hybrid catalyst, minimizing the diffusion length between methanol synthesis and dehydration catalyst functions, provides better DME yield performances but higher hotspot temperatures and can suffer from deactivation issues due to the detrimental interaction between the two catalytic functions. The MeOH@DME configuration, which allows for a limited contact between the catalyst active phases, guarantees DME yields comparable to those of hybrid pellets while moderating the hotspot temperature.

Dimethyl ether (DME) is an advanced second-generation biofuel produced via methanol dehydration over acid catalysts such as γ-Al2O3, at temperatures above 240 °C and pressures above 10 bar. Heteropolyacids such as tungstosilicic acid (HSiW) are Brønsted acid catalysts with higher DME production rates than γ-Al2O3, especially at low temperatures (140–180 °C). In this work, we show that the performance of supported HSiW for the production of DME is strongly affected by the nature of the support. TiO2 and SiO2 supported HSiW display the highest DME production rates of ca. 50 mmolDME/h/ gHSiW. Characterization of acid sites via 1H-NMR, NH3-isotherms and NH3-adsrobed DRIFT reveal that HSiW/X have Brønsted acid sites, HSiW/TiO2 showing more and stronger sites, being the most active catalyst. Methanol production increases with T until 200 °C where a rapid decay in methanol conversion is observed. This effect is not irreversible, and methanol conversion increases to ca. 90% by increasing reaction pressure to 10 bar, with DME being the only product detected at all reaction conditions studied in this work. The loss of catalytic activity with the increasing temperature and its increasing with reaction pressure accounts to the degree of contribution of the pseudo-liquid catalysis under the reaction.

Sorption Enhanced DiMethyl Ether Synthesis (SEDMES) is a promising option to overcome thermodynamic limitations of conventional DME production processes. In this work a 2D + 1D heterogeneous dynamic model of the reaction/adsorption step in a tube of an externally cooled multitubular fixed bed SEDMES reactor is developed in order to investigate the effect of design and operating parameters on thermal behavior and DME yield performances of the reactor. The model is validated by comparison with experimental results from a bench scale unit, including the dynamics of the outlet composition and the temperature trajectories in different points alongthe axial coordinate. Simulations with the validated model address the effect of the CO/CO2 ratio in the feed. The results confirm that, thanks to the effective in-situ H2O removal, the DME yield performances (65–70% in this work) of SEDMES are poorly sensitive on the CO/CO2 ratio. Accordingly, on increasing the CO2 content in thefeed, SEDMES provides larger advantages with respect to conventional DME direct synthesis. Calculations of maximum temperatures achieved along the axial coordinate show that catalyst thermal stress in the hottest inlet zone of the SEDMES reactor slightly increases with the CO content in the feed due to faster kinetics of the DME production reactions. However, thanks to the dilution effect provided by the adsorption material, maximum bed temperature keeps∼20–30 K below the catalyst stability limit reported in the literature (573 K). Accordingly, larger tube diameters (up to 46.6 mm) than in conventional reactors for the direct synthesis of DME can be adopted with less than 2% loss in DME yield.

Sorption-enhanced gasification (SEG) is a promising indirect gasification route for the production of synthetic fuels since it allows the H2, CO and CO2 content of the resulting syngas to be adjusted. This SEG process has been successfully demonstrated at pilot scale for lignocellulosic biomass and other agricultural and forest waste products, mainly focusing on H2-rich gas production. Within this work, the potential application of the SEG process to a material derived from municipal solid waste (MSW) as feedstock is experimentally demonstrated in a 30 kWth bubbling fluidised-bed (BFB) gasifier. The influence of the sorbent-to-biomass ratio, steam excess and gasification temperature has been carefully analysed in order to understand their effect on SEG performance. Moreover, main conditions able to affect the resulting syngas composition, specifically in terms of H2, CO and CO2 content, have been indicated. Gasification temperature turned out to be the variable that most influenced syngas composition due to the limiting mechanisms associated with the carbonation of the CaO used as bed material. This operating variable also determined biomass conversion, together with solids residence time in the gasifier, resulting in a wide variation of fixed carbon conversion under the studied conditions. Finally, tar yield and composition were evaluated as a function of temperature and the sorbent-to-biomass ratio used, resulting in tar contents as low as 7 g/Nm3 (dry gas), consisting mainly of 1-ring aromatic compounds.

Dimethyl ether is one of the most promising alternative fuels under consideration worldwide. Both the conventional indirect DME synthesis and the improved direct DME synthesis process are constrained by thermodynamics, which results in limited product yield, extensive separations and large recycle streams. Sorption enhanced DME synthesis is a novel process for the production of DME. The in situ removal of H2O ensures that the oxygen surplus of the feed no longer ends up in CO2 as is the case for direct DME synthesis. As a result CO2 can be converted directly to DME with high carbon efficiency, rather than being the main byproduct of DME production. The sorption enhanced DME synthesis process is a promising intensification, already achieving over 80 % single-pass CO2 conversion for a non-optimized system. The increased single-pass conversion requires less downstream separation and smaller recycle streams, especially for a CO2-rich feed. A key optimization parameter for the process performance is the adsorption capacity of the system. This capacity can be improved by optimizing the reactive adsorption conditions and the regeneration procedure. In this work, a detailed modelling study is performed to investigate the impact of various process parameters on the operating window and the interaction between different steps in a complete sorption enhanced DME synthesis cycle, and to compare its performance to other direct DME synthesis processes. The development of sorption enhanced DME synthesis, with its high efficiency carbon conversion, could play a significant role in the energy transition in which the carbon conversion will become leading.

Synthetic fuel production from renewable energy sources like biomass is gaining importance driven by the ambitious targets for reducing greenhouse gas emissions worldwide. Sorption enhanced gasification (SEG)
proposes carrying out the gasification of biomass in the presence of a CO2 sorbent, which allows producing a syngas with a suitable composition for a subsequent synthetic fuel production step. This study aims at analysing the effect of different operating parameters (e.g. steam-to-carbon (S/C) ratio, CO2 sorption capacity and sorbent-to-biomass ratio) in the syngas composition and char conversion obtained in a 30 kWth bubbling fluidized bed gasifier, using grape seeds as feedstock. The importance of reducing the formation of higher hydrocarbons through a high steam-to-carbon ratio and using a CO2 sorbent with high sorption capacity is assessed. C3-C4 and unsaturated C2 hydrocarbons contents below 1%vol. (in dry and N2 free basis) can be achieved when working with S/C ratios of 1.5 at gasification temperatures from 700 to 740 °C. Varying the amount of the CO2 separated in the gasifier (by modifying the temperature or the CO2 sorption capacity of the sorbent) the content of H2, CO and CO2 in the syngas produced can be greatly modified, resulting in a module M=(H2-CO2)/(CO+CO2) that ranges from 1.2 to almost 3.

Enhancement by steam separation is a promising process intensification for many types of reactions in which water is formed as a byproduct. For this, two main technologies are reactive vapor permeation (membrane technology) and reactive adsorption. Both can achieve significant conversion enhancement of equilibrium limited reactions by in situ removal of the by-product steam, while additionally it may help protecting catalysts from steam-induced deactivation.
In general, reactive permeation or reactive adsorption would be preferable for distinctly different process conditions and requirements. However, although some advantages of reactive steam separation are readily apparent from a theoretical, thermodynamic point of view, the developments in several research lines make clear that the feasibility of in situ steam removal should be addressed case specifically and not only from a theoretical point of view. This includes the hydrothermal stability of the membranes and their permselectivity for reactive steam permeation, whereas high-temperature working capacities and heat management are crucial aspects for reactive steam adsorption. Together, these developments can accelerate further discovery, innovation and the rollout of steam separation enhanced reaction processes.

Acidic γ-Al2O3 is an active catalyst for the dehydration of methanol to dimethyl ether (DME). However, the produced steam reduces the activity. In this work, the influence of the exposure of γ-Al2O3 to steam on the catalytic activity for methanol dehydration has been determined. At 250 °C and increasing stream partial pressure the conversion of γ-Al2O3 into γ-AlO(OH) is observed at a p(H2O) of 13–14 bar. As a consequence, the catalytic activity decreases, reducing the rate of methanol dehydration to around 25%. However, this conversion is reversible and under reaction conditions γ-AlO(OH) converts back to γ-Al2O3, recovering its catalytic activity.

A novel sorption enhanced dimethyl ether synthesis (SEDMES) process is presented using a solid adsorbent to remove produced water in situ. SEDMES experiments from feed mixtures of H₂, CO, and CO₂ have shown an increased yield of DME, an improved selectivity to DME over methanol, and a strongly reduced CO₂ content in the product. Consequently, SEDMES will reduce the downstream separation effort and minimise the recycle streams. Within the European Horizon 2020 project FLEDGED, synthesis gas from biomass gasification will be used as feedstock for the separation enhanced DME-synthesis.

A flexible sorption enhanced gasification (SEG) process is assessed in this work, where CaO-based material circulating between gasifier and combustor reactors is adjusted for fulfilling the syngas composition requirements according to the downstream fuel synthesis process. A case study of a synthetic natural gas (SNG) production plant based on this SEG process is presented, which has been analysed under different conditions of gasification temperature or solid circulation. A possible integration of this plant with an electrolysis system for power-to-gas application for balancing the electric grid is also proposed and assessed. SNG production efficiencies as high as 62% (LHV-based) have been found for the production of SNG with final CH4 content of 98%. Excess energy recovered from the process streams can be used for producing electricity in a steam turbine, covering the electric demand in the plant. If credits associated to electricity production are considered, equivalent SNG production efficiencies higher than 70% have been calculated. Efficiencies reported in this work are in the upper limit of the range found in the literature for non-SEG concepts, which require an intermediate conditioning step of WGS and CO2 removal. When coupled with an electrolyser, power-to-gas efficiencies of about 60% have been calculated, in line with stand-alone power to gas methanation systems.

The indirect steam gasification in circulating fluidized bed reactors was studied by modelling. The object of study was a coupled 12 MWth gasifier-combustor system, which was fired by woody biomass. The heat for the steam-blown gasifier was produced in the air-blown combustor and transported by circulating solids between the interconnected reactors. The system was modelled by a semi-empirical three-dimensional model, which simulated the fluid dynamics, reactions, and heat transfer in the coupled process. The studied cases included different temperature levels, which were controlled by the amount of additional fuel feed to the combustor. The model concept can be later applied to study sorption enhanced gasification, which is a promising method for sustainable production of transport fuels to substitute fossil based fuels.