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The 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. [ABSTRACT FROM AUTHOR]

The 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. [ABSTRACT FROM AUTHOR]

• A combined method for supply chain network and a process design optimization is proposed. • Lignocellulosic biorefineries to produce ethanol, ethyl levulinate and electricity are modelled. • A wheat straw supply network is economically feasible in Germany with four biorefineries. • The environmental margin of the wheat straw supply network is about 4 Mt of CO 2 per year. A supply chain network MILP model, developed by means of AIMMS software, and a process plant simulation model, developed by means of Aspen Plus®, are combined for the optimization of a biorefinery network. Optimization of the supply chain network is initially addressed using literature process and economic data. The results are used as input in the Aspen Plus ® model where the technical and economic performance of the biorefineries is calculated rigorously. The two computational tools are iteratively executed until convergence on number, locations and size of the biorefineries and on process yield to products and total costs is achieved. The final results are used to perform the Economic Value and Environmental Impact (EVEI) analysis of the overall biorefinery network. The methodology is applied to a case study concerning the deployment of cereal straw in Germany to produce ethanol, ethyl levulinate and electricity. Optimization results reveal that the wheat straw supply network with four biorefineries is economically feasible and determines an environmental margin in terms of equivalent emissions savings of about 4 Mt of CO 2 per year. [ABSTRACT FROM AUTHOR]

This 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. [ABSTRACT FROM AUTHOR]