1,721,001 research outputs found
Modelling and Environmental Aspects of Direct or Indirect Dimethyl Ether Synthesis Using Digestate as Feedstock
Full text linkThe conversion of waste and residues towards high added value products has receiving a growing attention, as a reliable strategy to improve sustainability of emergent processes. Anaerobic digestion converts organic waste into biogas and digestate. While biogas may be used for energetic purpose, digestate has limited uses and with a low profitability. In this paper, dimethyl ether (DME) is adopted as target product which may be produced from digestate-derived syngas. Process simulation is carried out for both direct and indirect synthesis of DME and environmental aspects are assessed
Application of nanosized zeolites in methanol conversion processes: A short review
No full textThe effective conversion of methanol toward high-added value molecules, such as dimethyl ether (methanol-to-dimethyl ether process, MTD), olefins (methanol-to-olefins process, MTO), or gasoline-cut hydrocarbons (methanol-to-gasoline process, MTG), is of paramount importance for the transition toward a methanol-based economy. In these processes, zeolites are efficient catalysts owing to their shape selectivity and tuneable acidity. Furthermore, the control of the crystal size of zeolites allows controlling the residence time of the involved species inside the catalytic crystal, with an effect on activity, product distribution, and coke deposition. This work focuses on the recent studies on the application of nanosized zeolites in MTD, MTO, and MTG processes. The results are critically discussed especially in terms of products distribution, coke formation, and deactivation. The methods to prepare the nanosized zeolites are also mentioned, although this aspect is beyond the scope of this review, which is to emphasize the impact of the crystal size on the zeolite-catalyzed methanol conversion reactions
Waste-To-methanol: Direct CO2 emissions assessment for the methanol production from municipal waste-derived syngas
Full text linkThe valorization of municipal waste represents one of the major opportunities for the next future. In particular, the Organic Fraction of Municipal Solid Waste (OFMSW) can be used in anaerobic digesters to produce biogas/biomethane. Furthermore, a fraction of Municipal Solid Waste (e.g. non-recyclable plastics, paper cardboard, etc.) can be converted to Refuse Derived Fuel (RDF). Both biogas/biomethane and RDF may be further converted in syngas (a mixture of H2, CO and CO2) by using several technologies, such as steam reforming for the former, and gasification for the latter. Syngas may be used as fuel in CHP plants or for the production of chemical intermediates and fuel. The digestate derived from anaerobic digestion, as well as CO2 from biogas, can be used as nutrients source to grow microalgae, which are feedstock suitable for supercritical water gasification (SWG). In this paper, an integrated process is proposed, by coupling an anaerobic digestion plant for biomethane production with (i) high-Temperature gasification of RDF and (ii) SWG of algae grown up with digestate and CO2 from biogas. The biomethane is assumed to be converted in syngas by steam reforming. Considering its importance for the chemical industry chain, methanol is considered as a target product. Methanol synthesis is assessed in terms of mass and energy balances and direct CO2 emissions. The results show that high-Temperature endothermic processes require the use of purge gas as a fuel in a burner to sustain itself. The lowest direct CO2 emission value per kg of methanol produced is obtained in the case of high use of RDF, minimum recycling of CO2 to algae production and minimum purge ratio
Process simulation and environmental aspects of dimethyl ether production from digestate-derived syngas
Full text linkThe production of dimethyl ether from renewables or waste is a promising strategy to push towards a sustainable energy transition of alternative eco-friendly diesel fuel. In this work, we simulate the synthesis of dimethyl ether from a syngas (a mixture of CO, CO2 and H2) produced from gasification of digestate. In particular, a thermodynamic analysis was performed to individuate the best process conditions and syngas conditioning processes to maximize yield to dimethyl etehr (DME). Process simulation was carried out by ChemCAD software, and it was particularly focused on the effect of process conditions of both water gas shift and CO2 absorption by Selexol® on the syngas composition, with a direct influence on DME productivity. The final best flowsheet and the best process conditions were evaluated in terms of CO2 equivalent emissions. Results show direct DME synthesis global yield was higher without the WGS section and with a carbon capture equal to 85%. The final environmental impact was found equal to −113 kgCO2/GJ, demonstrating that DME synthesis from digestate may be considered as a suitable strategy for carbon dioxide recycling
Techno-economic assessment of bio-syngas production for methanol synthesis: A focus on the water–gas shift and carbon capture sections
Full text linkThe biomass-to-methanol process may play an important role in introducing renewables in the industry chain for chemical and fuel production. Gasification is a thermochemical process to produce syngas from biomass, but additional steps are requested to obtain a syngas composition suitable for methanol synthesis. The aim of this work is to perform a computer-aided process simulation to produce methanol starting from a syngas produced by oxygen–steam biomass gasification, whose details are reported in the literature. Syngas from biomass gasification was compressed to 80 bar, which may be considered an optimal pressure for methanol synthesis. The simulation was mainly focused on the water–gas shift/carbon capture sections requested to obtain a syngas with a (H2 − CO2)/(CO + CO2) molar ratio of about 2, which is optimal for methanol synthesis. Both capital and operating costs were calculated as a function of the CO conversion in the water–gas shift (WGS) step and CO2 absorption level in the carbon capture (CC) unit (by Selexol® process). The obtained results show the optimal CO conversion is 40% with CO2 capture from the syngas equal to 95%. The effect of the WGS conversion level on methanol production cost was also assessed. For the optimal case, a methanol production cost equal to 0.540 €/kg was calculated
Synthesis and catalytic performances evaluation of FER-based catalysts with different acidity in methanol conversion to DME
No full textIn this work the effect of acidity on catalytic performances of zeolitic catalysts with FER structure in methanol dehydration reaction for DME production is presented. Synthesis condition are tuned in order to obtain a Si/Al ratio in the range of 7-47. NH3-TPD and FT-IR measurements show that aluminum content affect both aluminum incorporation and both strength and distribution of acid sites. Catalytic evaluation suggest that acidity affect methanol conversion while all catalysts exhibit a very high selectivity toward DME suggesting FER structure as a reliable catalyst for DME production
Kinetic analysis of methanol to dimethyl ether reaction over H-MFI catalyst
No full textThis paper reports the kinetic analysis of methanol dehydration to dimethyl ether (DME) on a zeolitic MFI-type catalyst. For this reaction, γ-alumina is the most used catalyst, but the use of a zeolite, such as H-MFI, is gaining greater attention because these materials exhibit a better stability against water presence and can modulate the catalyst acidity acting on different parameters (e.g., Si/Al ratio or postsynthesis treatments). The kinetic analysis of H-MFI is performed by using experimental data of methanol conversion in a differential reactor and in an integral reactor. By including the most important kinetic models proposed in the literature for alumina, kinetic parameters (as a function of temperature) in the case of H-MFI are calculated, and the comparison between different models is also presented and discussed. In addition a new kinetic model is proposed and data fitting is preferable with respect to literature equations: also data of activation energy are in agreement with literature findings
Supercritical water gasification of biomass and agro-food residues: Energy assessment from modelling approach
No full textThe gasification of biomass in supercritical water is a promising technology for hydrogen production and the paper reports a thermodynamic analysis, based on minimization of Gibbs free energy, of the gasification with supercritical water of different biomass and agro-food residues: almond shells, digestate from wastewater treatment, algae and manure sludge. Numerical simulations were performed in order to assess the effect of temperature, pressure and biomass-to-water ratio on gas-phase yield and composition. A partial energy integration was also discussed, by considering the energy recovery from a turbine expansion of the gas-phase stream leaving the gasifier. The proposed thermodynamic approach allows predicting not only gasification efficiency of gasifier but also energy balance on the entire gasification process. Results showed that the dry substrates (almond shells and algae more than digestate and sludge) tend to form more carbon monoxide. Besides, data comparison revealed that the produced hydrogen comes from biomass and water for high process temperature, while when temperature decreases, the thermodynamic path tends to promote water formation from the hydrogen of the dry biomass
Dimethyl ether synthesis via methanol dehydration: Effect of zeolite structure
No full textIn this paper, the effects of either pore size or topology of zeolites were studied in the methanol dehydration to dimethyl ether reaction by comparing catalytic performances of BEA, MFI and FER structures in the temperature range 180 °C-300 °C. The aim of this study was to investigate how the zeolite catalyst characteristics affect the process performances in terms of methanol conversion and DME selectivity. It was found that the largest-pore 3-D framework zeolite (BEA) was very effective in converting methanol but the channel size and topological connection spaces allowed the fast formation of coke precursors that rapidly decreases the catalyst performances at higher temperatures. Even if lower in intensity, the same phenomenon was observed for MFI structure (medium pores 3-D framework) confirming stable performances in the temperature range used in the real processes. On the contrary, the 2-D small pores FER zeolite showed a very good selectivity at high temperature also exhibiting a promising conversion rate for an industrial application. Continuous catalytic tests at 300 °C, followed by coke deposition analysis, confirmed that BEA rapidly deactivates and exhibited the higher coke formation rate, on the contrary, FER structure exhibited a great stability (conversion and selectivity) as well as a reduced coke formation tendency
Valorization of OFMSW digestate-derived syngas toward methanol, hydrogen, or electricity: Process simulation and carbon footprint calculation
Full text linkThis paper explores a possible waste-based economy transition strategy. Digestate from the organic fraction of municipal solid waste (OFMSW) is considered, as well as a low-added value product to be properly valorized. In this regard, air gasification may be used to produce syngas. In this work, the production of methanol, hydrogen, or electricity from digestate-derived syngas was assessed by ChemCAD process simulation software. The process scheme of methanol production comprises the following parts: water gas shift (WGS) with carbon capture and storage units (CCS), methanol synthesis, and methanol purification. In the case of hydrogen production, after WGS-CCS, hydrogen was purified from residual nitrogen by pressure swing absorption (PSA). Finally, for electricity production, the digestate-derived syngas was used as fuel in an internal combustion engine. The main objective of this work is to compare the proposed scenarios in terms of CO2 emission intensity and the effect of CO2 storage. In particular, CCS units were used for methanol or hydrogen production with the aim of obtaining high equilibrium yield toward these products. On the basis of 100 kt/year of digestate, results show that the global CO2 savings were 80, 71, and 69 ktCO2eq/year for electricity, methanol, and hydrogen production, respectively. If carbon storage was considered, savings of about 105 and 99 ktCO2eq/year were achieved with methanol and hydrogen production, respectively. The proposed scenarios may provide an attractive option for transitioning into methanol or hydrogen economy of the future
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