Integrated process design for sorption-enhanced steam reforming of biogas and sorption-enhanced DME synthesis: a techno-economic study

1 Introduction

The transition towards a low-carbon energy system and economy has stimulated interest in converting carbon-containing feedstocks into clean fuels and value-added chemicals. Biogas utilisation to produce advanced fuels, such as methanol and dimethyl ether (DME), is of utmost significance in pursuing sustainable energy solutions (Fedeli et al., 2023). Dimethyl ether has the potential to exert a large societal impact compared to other liquid organic hydrogen carriers (LOHCs), especially when integrated into technological chains of CO₂ sequestration and utilization (Catizzone et al., 2021). DME is a non-toxic, low-emission fuel that can be handled similarly to conventional liquefied petroleum gas (LPG), making it a promising alternative to diesel in compression ignition engines. Its use can reduce combustion-related emissions, while its properties also enable it to serve as a hydrogen carrier (Boon et al., 2019; Schühle et al., 2023).

Methanol and DME synthesis from biogas begins with the production of bio-syngas via reforming (Fedeli et al., 2023). The sorption-enhanced steam reforming (SESR) process has recently emerged as a promising technology for producing high-purity hydrogen from biogas (Capa et al., 2023a; Capa et al., 2020; Capa et al., 2023b). Other biomass-derived feedstocks, such as ethanol, glycerol, bio-oil, and syngas, have also been explored (Dewoolkar and Vaidya, 2016; Dang et al., 2016; Fermoso et al., 2012; Esteban-Díez et al., 2016; Gil et al., 2015; Rodríguez et al., 2022; Vega et al., 2025). In SESR, methane steam reforming (SR) (Equation 1), which coexists with the water-gas shift reaction (Equation 2), is combined with in situ CO₂ capture (Equation 3). By integrating these reactions into a single step using a reactor bed containing both the reforming catalyst (typically Ni-based) and the CO₂ sorbent (typically CaO-based), the equilibrium limitations of the reforming reaction are overcome. As a result, hydrogen productivity and selectivity are significantly enhanced.

CH 4 + H 2 O ⇌ CO + 3 H 2 Δ H r 0 = + 206 kJ mol ‐ 1 (1)

CO + H 2 O ⇌ CO 2 + H 2 Δ H r 0 = ‐ 41 kJ mol ‐ 1 (2)

CaO + CO 2 ⇌ CaCO 3 Δ H r 0 = ‐ 178 kJ mol ‐ 1 (3)

Downstream, DME synthesis can be performed via different routes: indirect production (two reactors), direct production (single reactor), and the novel sorption-enhanced route, known as sorption-enhanced DME synthesis (SEDMES) (Van Kampen et al., 2020a). In the synthesis of DME from carbon sources such as syngas or captured CO₂, methanol is first synthesised (Equations 4, 5) and subsequently dehydrated to DME (Equation 7). SEDMES has emerged as a novel process in which water is removed in situ using a solid adsorbent to intensify the reaction and improve the carbon and hydrogen conversion (Boon et al., 2019; Van Kampen et al., 2020a; Liuzzi et al., 2020; Van Kampen et al., 2020b; Peinado et al., 2020; Guffanti et al., 2021; Peinado et al., 2024). Process intensification using membranes has also been explored in the literature (Poto et al., 2023a; Poto et al., 2023b). However, the use of adsorbents is more suitable since low water partial pressure must be reached in the reactor, and water removal in the membrane is effective only with a consistent partial pressure gradient (indicatively >1bar) (Guffanti et al., 2021). As in the SESR process, the concept is based on Le Chatelier’s principle. The complete set of reactions involved is presented in Equations 4–7:

Methanol synthesis

CO 2 + 3 H 2 ⇌ CH 3 OH + H 2 O Δ H r 0 = − 49 kJ mol − 1 (4)

CO + 2 H 2 ⇌ CH 3 OH Δ H r 0 = − 90 kJ mol − 1 (5)

Water-gas shift

CO + H 2 O ⇌ CO 2 + H 2 Δ H r 0 = − 41 kJ mol − 1 (6)

Methanol dehydration

2 CH 3 OH ⇌ CH 3 OCH 3 + H 2 O Δ H r 0 = − 24 kJ mol − 1 (7)

DME production using SEDMES technology has recently been demonstrated for the first time using a multi-column test rig at TNO (Petten, the Netherlands) and optimised for operation with pure CO₂ and renewable H₂ feedstocks. Multi-column experiments showed continuous DME production with high CO₂ conversion in a single step, achieving a carbon yield up to 95%, while recent modelling studies demonstrated the flexibility of the process for different industrial applications (Van Kampen et al., 2023; Tyraskis et al., 2025; Tyraskis et al., 2026). According to a recent study, the impact on the levelised cost of fuel (LCOF) is significant for two-stage DME synthesis systems due to higher hydrogen consumption in these indirect routes (Kofler et al., 2024). Therefore, SEDMES represents a promising technology for reducing the cost of sustainable DME production. To qualify as an advanced biofuel, DME should be produced entirely from secondary biomass feedstock, and to qualify as a renewable fuel of non-biologic origin, it should use renewable H₂ as feedstock. When proton exchange membrane (PEM) electrolysers are used for hydrogen production, the main cost contributions are related to the electrolyser itself (Skorikova et al., 2020). Consequently, alternative routes have been proposed, such as the direct synthesis of DME from landfill gas (Merkouri et al., 2022; Fedeli et al., 2022).

Process simulations of bio-DME synthesis from biogas have been reported by Saebea et al., who evaluated suitable operating conditions by coupling biogas tri-reforming with a single-step DME synthesis reactor (Saebea et al., 2019). Similar simulation studies, including both direct and indirect DME synthesis routes, have also been reported by other authors (Kumar et al., 2026; Fedeli et al., 2024). The BIGSQUID technology, consisting of a portable and flexible module for converting biogas into valuable compounds (i.e., bio-methanol and bio-DME), has been validated at an industrial scale of 0.15 MWe (Negri et al., 2022). In addition, several techno-economic analysis studies addressing the conversion of biogas to advanced biofuels such as bio-DME have been published (Kofler et al., 2024; Merkouri et al., 2022; Fedeli et al., 2022; Baena-Moreno et al., 2021). Reported payback times are typically around 10 years, with revenues mainly derived from DME sales (Merkouri et al., 2022; Fedeli et al., 2022). Additionally, Baena-Moreno et al. concluded that profitability would only be achievable under scenarios with high DME market prices (1983-5566 €/tDME) or with feed-in tariff support, reaching up to 95.22 €/MWh in the most favorable case (Baena-Moreno et al., 2021). Other biomass feedstocks have also been investigated. Thus, Fornell et al. analyzed the co-production of bio-DME and bio-ethanol from softwood via black liquor, showing that an annuity below 0.15 can provide a positive business case at a DME selling price of 600 €/tDME (Fornell et al., 2013). Clausen et al. estimated the cost of producing bio-DME from gasifying torrefied wood pellets followed by DME synthesis (Clausen et al., 2010). Their analysis indicated production costs of 320 €/tDME for a recycle configuration and 347 €/tDME for a once-through setup. While the production of value-added compounds from CO₂ is of great importance for the energy transition, further efforts are needed to develop economically attractive green processes (Baena-Moreno et al., 2021). Life-cycle assessment studies have also highlighted the potential of energy-dense fuels derived from biogas, such as biomethane, Fischer-Tropsch fuels, methanol, and DME, to replace fossil-based fuels for transportation and energy production, while emphasizing the strong influence of process configuration on the reported environmental performance (Ravindran et al., 2025).

To the best of the authors’ knowledge, the integration of the two intensified processes, i.e., SESR and SEDMES, for DME production from biogas to improve the efficiency of bio-DME production has not been previously investigated. In this study, the hydrogen produced via SESR and a fraction of the CO₂ released during regeneration of the SESR sorbent are directly utilised in the subsequent SEDMES process. The main objective is to identify efficient integration strategies between biogas SESR and SEDMES by exploiting synergies between the two processes and to assess the profitability of the resulting bio-DME plant through a techno-economic evaluation.

2 Methodology

2.1 Model development

The bio-DME plant was simulated under steady-state conditions using Aspen Plus V11. The system integrates a biogas SESR unit with a hydrogen production capacity of 40 MW, coupled with a SEDMES unit for producing bio-DME. A simplified scheme of the process is shown in Figure 1.

Biogas and water are fed into the sorption-enhanced biogas reforming unit, producing H₂-rich and CO₂-rich streams. In the SESR reactor, steam reforming is coupled with in situ CO₂ capture, which is typically performed using CaO-based sorbents whose regeneration is highly endothermic. Therefore, a calcination reactor (REG) is included, where sorbent regeneration takes place.

Biogas and steam are fed to the reformer at a steam-to-methane (S/CH₄) ratio of 5. The reformer operates at 675 °C and 5 bar(a), corresponding to the optimal conditions identified in a previous optimisation study of the SESR process (Capa et al., 2023b). The spent sorbent is separated from the H₂-rich gas and sent to regeneration, where CaO is recovered to enable continuous SESR operation. During sorbent regeneration via the calcination reaction (reverse of Equation 3) at 900 °C and 1 bar(a), CO₂ is released.

The intensified reformer (SESR) and the calciner (REG) were modelled using RGibbs reactor blocks, assuming thermodynamic equilibrium and neglecting kinetic limitations. For SESR, experimental studies have shown that operation under favourable conditions can achieve performances close to those of thermodynamic equilibrium, supporting the use of an equilibrium approach for conceptual design (Capa et al., 2020; García et al., 2021). In addition, based on experimentally reported CaO carbonation conversions, it is reasonable to assume an average carbonation conversion of approximately 50% under SESR operating conditions (Broda et al., 2013; Di Giuliano et al., 2019). Such performance can be sustained through the continuous replacement of spent sorbent. Similar assumptions have previously been employed in SESR simulation studies (Yan et al., 2020). A heat exchanger network (HEN) was designed to recover available heat for preheating inlet streams and generating steam. The efficiency of the sorption-enhanced biogas reforming step is improved by recovering excess heat from the exothermic reforming reactions. In this study, the energy required for sorbent regeneration in the REG unit is supplied by indirect heating from an external burner, in which biogas is combusted in an air atmosphere.

Bio-DME is subsequently produced in the SEDMES reactor and purified downstream through a distillation train to meet the DME product specifications. The H₂-rich gas produced in SESR and part of the CO₂ generated in the calciner are used as feedstocks for the SEDMES unit. These gases are conditioned to match the SEDMES operating conditions, i.e., 20-50 bar(a) and 250 °C. The H₂-to-CO_x ratio in the SEDMES feed is defined using the M-module, which is used as a reference parameter to control the stoichiometry. The M-module is calculated by Equation 8, where F _*i* is the molar flow rate of species i (kmol hr^-1). A target value of 2 is selected, corresponding to stoichiometric proportions of CO_x and H₂ (Van Kampen et al., 2020a).

M ‐ module = F H 2 reformer gas − F CO 2 reformer gas F CO reformer gas + F CO 2 reformer gas (8)

The SEDMES unit was modelled using three blocks: (i) a stoichiometric reactor, (ii) a water separator, and (iii) an RGibbs reactor. Using these three blocks, one can mimic the sorption-enhanced operation to achieve the main objective of this study, i.e., to integrate SESR and SEDMES, identify synergies between these processes to improve the efficiency of the integration, and assess the profitability of the resulting bio-DME plant.

In the first block, the stoichiometric reactor is used to estimate the theoretical upper limit of CO and CO₂ conversion to DME and calculate the maximum amount of H₂O produced. In the separator block, H₂O is removed to simulate the H₂O adsorption by the zeolite sorbent. The fraction of H₂O removed is treated as a design parameter. Previous experimental studies have demonstrated the stable cyclic SEDMES operation using zeolite 3A and pressure swing regeneration, supporting the practical feasibility of maintaining high water removal performance. Nevertheless, in practice, it depends on the adsorbent regeneration strategy and cycle design (Van Kampen et al., 2021a; Van Kampen et al., 2019; Van Kampen et al., 2021b). A sensitivity analysis was performed to determine the amount of water that needs to be removed to obtain a DME product composition consistent with that reported in the literature. Details of this analysis are provided below in the model assumptions section. It should be noted that the model does not account for heat and mass transfer phenomena within the catalyst-adsorbent bed. In practice, inadequate heat management could reduce the thermodynamic benefit associated with in situ water removal. Indeed, temperature control has been reported as a key challenge in SEDMES operation, as the reactor must simultaneously accommodate the exothermic nature of DME synthesis and water adsorption. Consequently, insufficient heat removal may lead to unfavourable thermodynamic conditions, reducing process performance and potentially accelerating catalyst deactivation, as reported in the literature (Guffanti et al., 2021). These effects are beyond the scope of the present assessment. The final block of the SEDMES model is an RGibbs reactor, which estimates the equilibrium composition after H₂O removal. In this block, CH₄, C₂H₄, C₂H₆, and solid C are treated as inert and therefore neither formed nor consumed.

Finally, a distillation train is added to purify the DME to the required specifications (DME purity >98.5%). For this purpose, the output stream from the SEDMES unit is sent to a first distillation column where light components (e.g., H₂, CO, CO₂) are separated from the DME/methanol mixture. The heavy components from the first distillation column are sent to a second column, where methanol is separated from the DME to reach a DME purity of at least 98.5%, in accordance with ISO standards (i.e., ISO-16861-2015). As explained below, the main parameters of the distillation columns were initially determined using shortcut models and subsequently implemented in rigorous RadFrac column models.

2.2 Model assumptions

The assumptions applied to the biogas SESR unit are summarised in Table 1. These values rely on a previous study in which the biogas SESR process was optimised (Capa et al., 2023b).

TABLE 1. Thermodynamic and operational assumptions adopted for the biogas SESR unit.

Table 2 summarises the assumptions used for the SEDMES unit. The operating temperature was set at 250 °C (Van Kampen et al., 2021a), and a pressure of 50 bar(a) was selected, as reported in previous studies in the literature (Merkouri et al., 2022). Regarding the water removal percentage, experimental studies in the literature reported that the CO/CO₂ ratio in the outlet gas should be approximately 2 (Van Kampen et al., 2023). To determine the required water removal to achieve this ratio, a sensitivity analysis was performed. The results are presented in the (Supplementary Table S1). With 98.7% of H₂O removed, the desired ratio CO/CO₂ of 2 is achieved at the reactor outlet, and, hence, this value was selected.

TABLE 2. Modelling assumptions adopted for the SEDMES unit.

As mentioned earlier, the first distillation column (D1) separates light components such as H₂, CO, CH₄, and CO₂ from the DME/methanol mixture. The separation of CO₂ from DME is the most energy-consuming step in the purification train (Skorikova et al., 2020). A product specification limiting the CO₂ concentration in the heavy (DME-rich) fraction to below 0.1 wt% was therefore imposed. Likewise, the operating pressure was reduced to 30 bar(a) to minimize the reflux ratio needed to achieve the targeted CO₂ separation in this column, improving the energy efficiency (duty requirement). The final operating parameters of the first distillation column are listed in Table 3.

TABLE 3. Final design parameters of the first distillation column in the DME purification train.

The bottom stream from the first column is the feed to a second distillation column (D2), where methanol (and any remaining water) is separated from DME to meet the final product specifications. The reflux ratio was defined to achieve a methanol content below 0.05 wt% while minimising the column duty. The operating pressure was set to 5 bar(a), consistent with values reported in the literature (Merkouri et al., 2022). The final parameters of the second distillation column are shown in Table 4.

TABLE 4. Final design parameters of the second distillation column in the DME purification train.

2.3 Technical evaluation

Different key performance indicators (KPIs) were defined to evaluate and discuss the performance of the integrated system, including the biogas SESR and SEDMES units. The fuel consumption associated with sorbent regeneration in the SESR unit is calculated using Equation 9:where F_{BIOG, fuel} is the biogas molar flow rate used as fuel for sorbent regeneration, and F_{BIOG, feedstock} is the biogas molar flow rate fed to the SESR unit.

Fuel consumption % = F BIOG , fuel F BIOG , fuel + F BIOG , feedstock · 100 (9)

The cold gas efficiency (CGE) and net efficiency (NE) are used to evaluate the overall efficiency of the system and are defined by Equation 10 and Equation 11, respectively: where F_DME,out is the molar flow rate of DME produced, LHV_DME is the lower heating value of DME, F_{CH4,feedstock} is the methane molar flow rate in the biogas feed, F_CH4,fuel is the methane molar flow rate fuel for sorbent regeneration, LHV_CH4 is the lower heating value of methane. In Equation 11, the auxiliary electricity consumption (P_e), represents the electrical utility demand, assuming a thermal-to-electric conversion efficiency, η elect, of 50%.

CGE % = F DME , out · LH V DME F CH 4 , feedstock + F CH 4 , fuel · LH V C H 4 · 100 (10)

NE % = F DME , out · LH V DME F CH 4 , feedstock + F CH 4 , fuel · LH V C H 4 + P e η elect · 100 (11)

The overall process yield is determined using Equation 12, which quantifies the conversion of biogas (CH₄ and CO₂) into DME. This parameter, referred to as the global mass yield (GMY), has been adopted in previous state-of-the-art studies and is applied here to facilitate results comparison (Fedeli et al., 2022).

GMY % = Mass of purified DME kg / h Mass of biogas feedstock kg / h · 100 (12)

The purity of the produced DME is evaluated using Equation 13 as the molar flow rate of DME produced (F_DME,out) to the total molar flow (F_total) of the stream leaving the top of the second distillation column (light ends):

DME purity % = 100 · F DME , out / F total (13)

Finally, a carbon balance was performed to determine the distribution of carbon among the different output streams. The utilised C fraction, calculated using Equation 14, represents the carbon captured and converted into DME. The sequestered C fraction, calculated using Equation 15, corresponds to carbon that is captured as CO₂ but not used for DME synthesis due to the M-module = 2 constraint. The vented C fraction, defined by Equation 16, includes carbon released in the flue gas and/or by-products streams that is neither utilised nor stored. where F_C,DME is the molar flow rate of carbon contained in the produced DME, F_C,storage is the molar flow rate of carbon sent to CO₂ storage, and F_{C,flue gas/by-products} is the molar flow rate of carbon released in the flue gas and other by-product streams. F_{total C,in} represents the total molar carbon input to the system, accounting for carbon in both CH₄ and CO₂ in the biogas feed.

Utilised C % = 100 · F C , DME / F total C , in (14)

Sequestered C % = 100 · F C , storage / F total C , in (15)

Unretained C % = 100 · F C , flue gas / by ‐ products / F total C , in (16)

2.4 Economic evaluation

To evaluate the cost of producing bio-DME using the proposed process, the levelised cost of DME (LCODME) was calculated. The concept of levelised cost, originally introduced for electricity generation as the levelised cost of electricity (LCOE), represents the total cost of constructing and operating a plant over its lifetime, normalised by the net product output (IEAGHG, 2013). This approach integrates technical inputs (i.e., process modelling) with economic and financial parameters to enable a robust economic assessment. In this work, the LCODME is used as the primary economic performance indicator and is calculated using Equation 17:where TOC is the total overnight capital cost, including direct and indirect capital expenditures; FOM is the fixed operating and maintenance cost; VOM is the variable operating and maintenance cost excluding fuel; FC is the fuel cost; CF is the capacity factor; HR is the net plant heat rate; and FCF is the fixed charge factor.

LCODME = TOC × FCF + FOM CF × 8760 + FC × HR + VOM (17)

The fixed charge factor, FCF, is defined in Equation 18, where t is the plant economic lifetime and r is the discount rate. Consistent with previous studies, a plant lifetime of 25 years and a discount rate of 12% were assumed (Skorikova et al., 2020; Yan et al., 2020).

FCF = r · 1 + r t 1 + r t ‐ 1 (18)

Capital and operational costs were estimated using the chemical plant cost methodology proposed by Sinnott et al. (Sinnott, 1993) Capital costs include both direct costs associated with major equipment (e.g., reactors and compressors) and indirect costs. Direct equipment costs were primarily estimated from reference units reported in the literature and normalised to a common base year (2024). This normalisation was performed using the Chemical Engineering Plant Cost Index (CEPCI) and capacity scaling relationships, as shown in Equation 19:where C_A and C_B are the costs of the scaled and base equipment, respectively; CI_A and CI_B are the annual index factors (CEPCI) for years A and B, respectively; S_A and S_B are the capacities of the new and base equipment, respectively; and x is the scaling exponent, assumed to be 0.6 according to the six-tenths rule.

C A = C I A C I B · C B · S A S B x (19)

The cost of compressors was estimated using the widely applied correlation proposed by Douglas, given in Equation 20 (Luyben, 2018; Douglas, 1988):

Compressor cost $ = 5840 · kW 0.82 (20)

The main parameters and assumptions used in the economic evaluation are summarised in Table 5. Cost values were taken as originally reported in the literature (€, £), converted to euros using average annual exchange rates, and subsequently updated to the reference year using CEPCI.

TABLE 5. Key parameters and assumptions used in the economic evaluation.

(*) An equivalent sorbent lifetime of 500 h was assumed for estimating the annual cost of sorbent replacement.

To assess the economic performance of the proposed bio-DME plant, key economic drivers were identified, and a sensitivity analysis was conducted to account for associated uncertainties. In addition, the profitability of the plant was evaluated by the calculation of the net present value (NPV), defined in Equation 21, where NCF_*n* is the net cash flow in year n.

NPV = ∑ n = 1 t NCF n 1 + r n (21)

It was assumed that the first 2 years of the project are dedicated to plant construction and that, during the first year of operation, the plant operates at 50% of its nominal capacity (Merkouri et al., 2022). From the second year of operation onward, the plant is assumed to run at full capacity.

3 Results and discussion

3.1 SESR and SEDMES integration

The main objective of this work is to integrate biogas SESR with SEDMES to enable the production of bio-DME. The configuration, including the integration synergies, is shown in Supplementary Figure S1. The base-case configuration, without any integration synergies, is shown in Figure 1 and the Aspen Plus flowsheet of the base-case is shown in Supplementary Figure S2. In the base case, approximately 7 t/h of biogas is consumed as feedstock, producing 4.4 t/h of bio-DME. In addition, around 4.2 t/h of biogas is required as fuel for the regeneration of the sorbent used in the SESR unit. A summary of the overall mass balance for the base case is provided in Supplementary Table S2.

Regarding utilities, the main cooling, heating, and compressing duties for the base-case configuration are shown in Figure 2. For this reference design, a CGE of 64% is obtained, with a global mass yield of 39%. When external utilities are accounted for, the overall process efficiency decreases to a NE value of approximately 47%.

To increase the overall efficiency of the integrated SESR-SEDMES system, several process synergies were identified and systematically evaluated. These synergies aim to reduce energy consumption, improve resource utilisation, and maximise DME yield by exploiting interactions between the two units. The integration strategies considered are summarised below:

• - Synergy 1: Heat integration. Heat recovery between the two units (see Supplementary Figure S3).
• - Synergy 2: By-products integration. Recycling by-products from the SEDMES unit (i.e., H₂, CO) as fuel in the external burner that supplies heat to the SESR calciner (see Supplementary Figure S4).
• - Synergy 3: Steam integration. A stream containing steam at 250 °C and 1 bar produced during the SEDMES purge step is recycled from SEDMES to SESR (see Supplementary Figure S5).

3.1.1 Heat integration

As shown in Figure 2a, a significant portion of the cooling demand arises from the temperature mismatch between the reforming section and the DME synthesis unit, accounting for approximately 62% of the total cooling duty. Specifically, the H₂-rich stream exiting the SESR unit is at 675 °C, while the CO₂ stream from the calciner leaves at 900 °C. When these streams mix upstream of the SEDMES unit, their temperature remains significantly higher than the SEDMES operating temperature of 250 °C. Consequently, substantial cooling is required, representing a major source of energy inefficiency in the base-case configuration.

A second important contribution to the cooling demand is associated with the first distillation column in the DME purification train, especially the first cryogenic separation. This unit is particularly energy-intensive, as its primary objective is to separate unconverted CO₂ from the DME-rich product stream. In the base case, the feed to the first distillation column is cooled to approximately 10 °C, accounting for nearly 25% of the total cooling duty.

Together, these two cooling steps account for approximately 87% of the total cooling demand, making them key targets for thermal integration. Accordingly, the first integration strategy explored was optimising the heat exchanger network (HEN) to recover excess thermal energy and improve the overall energy efficiency of the system.

In this configuration, the cooler used to match the temperatures between SESR and SEDMES is replaced with a heat exchanger, allowing recovery of thermal energy for steam generation in the SESR unit. Furthermore, the cooling step upstream of the first distillation column is replaced by a second heat exchanger, which also contributes to steam production for the SESR unit. This dual heat-integration strategy follows pinch analysis principles to minimise external utility requirements and maximise internal heat recovery. A total cooling duty of 3.5 MW is integrated. As a result, CGE increases by approximately 3 percentage points, while the global mass yield improves by about 2 percentage points. These improvements are mainly driven by a reduction in the biogas required for sorbent regeneration in the SESR unit, from 37.5% to 34.3%, with part of the regeneration duty supplied by recovered process heat.

3.1.2 By-products integration

In addition to heat integration, another synergy was explored to reduce further biogas consumption for sorbent regeneration in the SESR unit. The unconverted gases exiting the SEDMES unit at the top and bottom of the first and second distillation columns can be recycled and used as fuel in the external combustor, supplying heat to the SESR calciner. This by-product stream is rich in hydrogen and can therefore be effectively utilised for energy recovery, as previously explored by Fedeli et al. (Fedeli et al., 2022). The main reaction occurring in the external combustor is hydrogen oxidation, as shown in Equation 22:

H 2 + 1 2 O 2 → H 2 O (22)

Implementing this integration strategy reduces biogas consumption as fuel by approximately 4 percentage points, further improving overall plant efficiency. As a consequence, the CGE increases by 4.3 percentage points, reflecting a more effective conversion of biogas into DME. The global DME yield increases to 43.5%, mainly due to the reduced biogas consumption as fuel.

Although a temperature mismatch exists between the by-product streams and the external combustor, the net efficiency analysis shows that the fuel savings outweigh the additional utility requirements for heating the recycled streams. As a result, the NE improves from 54% (heat integration only) to 56% when by-product recycling is included. All KPI values reported in this section refer to the combined effect of both synergies, i.e., heat integration and by-product recycling, demonstrating their cumulative contribution to achieving an efficient configuration.

3.1.3 Steam integration

The final integration strategy investigated is steam integration. The SEDMES process can serve as a steam source, as water is adsorbed during intensified DME synthesis, shifting the equilibrium toward DME formation. To restore the adsorbent capacity, a regeneration step is required before the next adsorption cycle. During regeneration, water is desorbed at approximately 250 °C, the same temperature as in the SEDMES process due to its PSA-like nature, producing low-pressure steam. Although this steam is of relatively low quality, it can partially meet the SESR unit’s steam demand. Reusing this steam reduces the heat required to generate it, allowing recovered energy to preheat other process streams. This results in lower biogas fuel consumption and improved overall plant efficiency.

The implementation of this third synergy yields the best overall performance among all configurations studied, achieving a CGE of 74.1% and a global DME yield of 45.3%. In addition, water consumption is reduced by approximately 38%, which is an increasingly important consideration in CCU processes (Kätelhön et al., 2019). The full benefit of this integration is achieved when biogas feedstock is used as the purge gas in the SEDMES unit, acting as a dry gas to desorb water from the sorbent. In this configuration, the purge gas and desorbed water can be directly recycled to the SESR unit, eliminating the need for condensation and separation steps. As a result, the energy penalty associated with the latent heat of steam production is partially avoided.

Conversely, when the feedstock is not used as the purge gas, only water savings contribute to efficiency improvement, as the steam must first be condensed and separated from the purge gas stream before it can be reused in the SESR unit. Table 6 shows the efficiencies and global DME yields for the different integration strategies.

TABLE 6. Performance indicators for the three integration synergies, expressed as efficiencies and global bio-DME yield, for the integrated biogas SESR-SEDMES system.

As shown in Figure 3, the carbon balance also improves significantly with increasing integration, with nearly 54% of the total carbon ending up as utilised carbon in the form of DME. It should be noted that these results are mainly driven by the reduction in the flue gas carbon from the external combustor. Although this increases the relative share of utilised and sequestered carbon, their absolute values remain essentially constant.

Beyond the synergies explored for reducing unretained carbon, CO₂ storage requirements could be further reduced by adjusting the CO₂ capture degree in the SESR unit, aiming to match the producer-gas composition to the M-module requirements of the SEDMES unit and thereby increase carbon utilisation. The results indicate that, for conventional biogas compositions (60/40 vol% CH₄/CO₂), the target M-module value of 2 can be achieved by limiting the CaO input in the reformer to approximately 30% of the stoichiometric requirement (Supplementary Figure S6a). However, reducing the CaO content leads to a significant amount of unconverted CH₄ in the product gas (Supplementary Figure S6b). Because methane behaves as an inert species in the SEDMES process, it escapes with the unconverted gases, leading to carbon losses. In this context, and consistent with the findings of the Bio-ReFuel project, CO₂ that would otherwise require storage could instead be utilised by supplying additional H₂ produced in a small electrolyser (International Energy Agency, 2020).

3.2 Economic evaluation

Beyond technical performance, an economic evaluation is essential to assess the feasibility and competitiveness of the proposed process. Following the methodology described above, an economic assessment of the bio-DME plant was conducted. The configuration with the highest efficiency, i.e., the case including all identified synergies, was selected as the basis for the economic analysis.

Table 7 summarises the main contributors to capital and operational costs. These results are complemented by Figure 4, which shows the relative contributions expressed as percentages. In terms of CAPEX, the equipment associated with hydrogen production accounts for the largest share of the total investment (38%), followed by the equipment associated with DME synthesis (24%). Regarding OPEX, biogas cost (including both feedstock and fuel) is the dominant contributor, accounting for approximately 49%.

TABLE 7. Main results of the economic analysis of the bio-DME plant.

Based on these assumptions, the levelised cost of DME is estimated at approximately 1 €/kg, with the contribution of individual cost components illustrated in Figure 5. The results show that the overall cost is largely dominated by the fuel and feedstock component (biogas in this work), while CAPEX and other operating costs contribute to a lesser extent. This reflects the strong influence of the biogas price on the overall economics.

The estimated LCODME obtained in this study (∼1 €/kg DME) is lower than values reported for power-to-X-derived (PtX) DME, which are around 1.3 €/kg DME (Skorikova et al., 2020). To quantify the influence of the main cost drivers, a sensitivity analysis was performed, focusing on biogas and electricity prices, total capital cost and discount rate.

The results of the sensitivity analysis (Figure 6) show that the LCODME varies approximately between 0.8 and 1.25 €/kg DME across ±50% variations of the key economic parameters. The cost of biogas has the largest impact on the levelized cost followed by a moderate impact of the capital cost and discount rate. The electricity price shows a comparatively smaller influence.

Comparison with the literature shows that when the cost of the carbon source is negligible (i.e., biogas treated as a waste stream rather than a commodity), when alternatives such as direct air capture are considered, or when hydrogen is produced via electrolysis, the system becomes less feedstock-driven. In those cases, the cost structure shifts towards a greater influence of CAPEX and/or electricity costs (Skorikova et al., 2020; Merkouri et al., 2022; D’Adamo et al., 2024).

To evaluate the profitability of the bio-DME plant, a discounted cash flow analysis was carried out to calculate the net present value (NPV) over the plant’s lifetime. This analysis provides insight into both the investment requirements and the timing of revenue generation. Different DME selling prices, ranging from 860 to 1500 €/t, were considered to assess the plant profitability under various market scenarios (Figure 7). As expected, the DME selling price plays a crucial role in determining economic viability. At a selling price of 860 €/t, the plant does not achieve a positive NPV. When the DME selling price increases to approximately 1000 €/t, the plant becomes profitable after year 15 of operation. The payback time can be reduced to approximately 5 years when the DME selling price reaches 1500 €/t. Compared with literature values, which report break-even DME prices in the range of 1900-5000 €/t, the results obtained in this study are considerably less demanding (Baena-Moreno et al., 2021). This suggests that the proposed bio-DME configuration, where both hydrogen production and DME synthesis are intensified, can be economically more attractive than systems based on the integration of conventional technologies.

3.3 Opportunities and challenges for deployment

Based on previous studies, several additional strategies could be explored to further improve plant profitability. In some cases, biogas is considered a cost-free feedstock, which would significantly reduce operating costs, as biogas is one of the main cost drivers. This assumption may apply when biogas is derived from landfill gas and treated as a waste stream rather than a commercial commodity (Merkouri et al., 2022). Further research could also explore the use of alternative renewable waste streams as feedstock for synthetic DME production. In addition, future work could explore the use of an electrified calciner to eliminate the main flue gas stream identified in this work, assessing its impact not only on the carbon balance but also on process economics (Jacob et al., 2023; Jacob and Tokheim, 2023). Other studies have proposed increasing the DME selling price or introducing incentives for biogas utilisation, which are already implemented in many EU countries for green energy production (Baena-Moreno et al., 2021). Additionally, carbon pricing mechanisms could enhance profitability, as suggested for other CCU processes (Yan et al., 2020), since the proposed bio-DME plant operates with non-upgraded biogas and enables the avoidance of CO₂ emissions. Contributions to European targets for carbon dioxide removal (CDR) and bioenergy with CCS (BECCS) could therefore further strengthen the economic case for the proposed system.

From a broader perspective, the proposed SESR-SEDMES concept presents significant strengths, including process intensification, improved carbon utilisation, reduced water consumption, and competitive production costs compared with other reported processes. However, process complexity and the long-term performance of materials remain potential challenges for large-scale implementation. At the same time, the growing interest in advanced biofuels, CCU technologies, and carbon management policies creates important opportunities for future deployment, although market uncertainties associated with DME prices and future regulatory frameworks may influence commercial uptake.

4 Conclusion

This study investigates an integrated process that combines sorption-enhanced steam reforming (SESR) of biogas with sorption-enhanced dimethyl ether synthesis (SEDMES) to efficiently produce bio-DME. The results demonstrate that coupling both technologies enables the valorisation of biogas without prior upgrading, avoiding CO₂ emissions associated with conventional upgrading while directly utilising CO₂ to produce an energy-dense renewable fuel, i.e., bio-DME. Three integration synergies were identified and exploited to improve the efficiency of the DME plant: heat recovery between units, energetic use of SEDMES by-products, and steam reuse from SEDMES adsorbent regeneration. As a result, the cold gas efficiency increased from 64% to 74%, while the global DME yield improved from 39% to 45%. From an economic perspective, the optimised bio-DME plant achieves a levelised cost of DME (LCODME) of approximately 1 €/kg, which is competitive and lower than values reported in the literature for power-to-X routes. Net present value (NPV) analysis indicates that the plant becomes profitable at DME selling prices above approximately 1000 €/t, suggesting favourable economic prospects under suitable market conditions. Overall, this work shows that integrating biogas SESR and SEDMES processes provides an efficient, economically attractive route to producing bio-DME from biogas. The proposed configuration offers opportunities for decentralised, carbon-efficient DME production that could contribute to future renewable fuel and chemical value chains.

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fceng.2026.1915733/full#supplementary-material

Supplementary material Supplementary material at the source

Footnotes

Edited by: Vincenzo Russo, University of Naples Federico II, Italy

Reviewed by: Raffaele Cucciniello, University of Salerno, Italy

Jhulimar Castro, University of Canterbury, New Zealand