H2S Loading Research Articles

A case Study of Fat and Release of Hydrogen in Sewage Sulfide During the Management of Sewage Projects

During sewage projects, management appears Hydrogen sulfide (H2S) emission-related odours have been a problem in sewage project networks for decades. One of the gases that directly harms employees and network infrastructure is hydrogen sulfide gas. Using the TOXCHEM software, the network of the Al-Hur project in Karbala, south of the Iraqi capital, Baghdad, was simulated for three main lines of different diameters 630, 315, and 1000 mm, each with a diameter of 1000 meters, they are connected to a main manhole by drop structure, and then to the lift station. Samples for these diameters were collected for two seasons (summer and winter) with all the necessary parameters of this network to be included in the model. The model was validated for the two seasons, and the results were very close to reality after being examined in a statistical way, where the results of R and RMSE were (0.821 and 0.821) and (0.000462 and 0.000184) for Summer and Winter, respectively. Sensitivity analysis studied wastewater characteristics with different levels of H2S loading rate, flow rate, suspended solid concentration, oil/grease concentration, and temperature. The results showed that all emissions in these networks are dangerous, especially in the summer when the emissions concentrations for pipe 315, pipe 630, pipe 1000, drop 315, drop 630 and the lift station were 7.6, 6.2, 2.5, 8.01, 3.78 and 6.06 ppm, respectively. By utilizing a TOXCHEM model, the study helped to understand the fate and emission of hydrogen sulfide gas in all parts of the networks.

Hybrid Filtration Process for Gas Desulfurization

A hybrid desulfurization process combining a physical filtration stage on cellular concrete (CC abiotic filter, called CCAF) and a biotrickling filter (called BTF) filled with expanded schist as packing material was used to remove high H2S concentrations from a synthetic gas containing dinitrogen (N2), dioxygen (O2) and H2S without the addition of a nutritive solution. Provided that small amounts of oxygen are present in the gas (1.2 ± 0.1% in volume), the global removal efficiency was 100%, and the global removal capacity reached 35 ± 2 gH2S m−3 h−1 for a total empty bed residence time (EBRT) of 120 s (CCAF + BTF). The resilience of the desulfurization process was demonstrated by applying severe changes in the H2S concentrations, from 160 to 1150 ± 20 mg m−3 for an EBRT = 120 s. According to the performances of the abiotic filter, which can decline over time due to the lifetime of the cellular concrete (137 days), the biotrickling filter reacted either as a refining system or as an efficient system able to treat significant H2S loading rates (up to 45 ± 3 gH2S m−3 h−1). Depending on the operating conditions, the increase in the pressure drops of the biotrickling filter (from 45 ± 3 to 234 ± 8 Pa m−1) highlighted biomass accumulation, especially extremophilic Acidithiobacillus sp. Considering the cellular concrete abiotic filter alone, removal capacities of up to 56 ± 3 gH2S m−3 h−1 were recorded for an EBRT of 60 s, demonstrating that gases such as landfill biogas or household biogas could be efficiently treated using this simple technique.

Simultaneous removal of H2S and particulate matter by a multistage dual-flow sieve plate scrubber

In this work, an experimental study has been conducted in a newly designed and developed dual-flow scrubber with three sieve plates for simultaneous removal of hydrogen sulphide and particulate matter (fly-ash) from syngas produced in a gasifier as these impurities of syngas destroy and decrease the efficiency of the downstream processing equipment. The performance of the scrubber at different gas and liquid flow rates in the range of 16.59 × 10−4- 27.65 × 10−4 Nm3/s 20.649 × 10−6-48.183 × 10−6 m3/s has been observed for both the particulate matter and hydrogen sulphide removal along with the effect of inlet particulate loading (15 × 10−3- 25 × 10−3 kg/Nm3) and 100–300 ppm inlet H2S loading. The H2S removal efficiency in the dual-flow wet scrubber increased from 78.88% to 87.45% when the particulate matter loading was increased from zero to 25 × 10−3 kg/Nm3 at 300 ppm inlet H2S concentration for 48.183 × 10−6 m3/s liquid flow rate and 27.65 × 10−4 Nm3/s gas flow rate. The efficiency of the particulate matter is similar to that of the particulate scrubbing in absence of the H2S.

Polysulfide Concentration and Chain Length in the Biological Desulfurization Process: Effect of Biomass Concentration and the Sulfide Loading Rate.

Removal of hydrogen sulfide (H2S) can be achieved using the sustainable biological desulfurization process, where H2S is converted to elemental sulfur using sulfide-oxidizing bacteria (SOB). A dual-bioreactor process was recently developed where an anaerobic (sulfidic) bioreactor was used between the absorber column and micro-oxic bioreactor. In the absorber column and sulfidic bioreactor, polysulfides (Sx2-) are formed due to the chemical equilibrium between H2S and sulfur (S8). Sx2- is thought to be the intermediate for SOB to produce sulfur via H2S oxidation. In this study, we quantify Sx2-, determine their chain-length distribution under high H2S loading rates, and elucidate the relationship between biomass and the observed biological removal of sulfides under anaerobic conditions. A linear relationship was observed between Sx2- concentration and H2S loading rates at a constant biomass concentration. Increasing biomass concentrations resulted in a lower measured Sx2- concentration at similar H2S loading rates in the sulfidic bioreactor. Sx2- of chain length 6 (S62-) showed a substantial decrease at higher biomass concentrations. Identifying Sx2- concentrations and their chain lengths as a function of biomass concentration and the sulfide loading rate is key in understanding and controlling sulfide uptake by the SOB. This knowledge will contribute to a better understanding of how to reach and maintain a high selectivity for S8 formation in the dual-reactor biological desulfurization process.

Rate-based modeling and energy optimization of acid gas removal from natural gas stream using various amine solutions

Reduction in energy consumption of industrial plants is always an essential need due to high cost, CO2 emissions and global warming caused by energy supply from fossil fuels for boilers and electricity consumers. Iran has been struggling to compensate the lack of gas supply for domestic and industrial demands in winter within the past decade despite of having large natural gas resources. One of the most economical methods to decrease energy requirements in hydrocarbon plants is process improvement and revamping by changing existing solvents. There are already 44 identical acid gas removal units under operation in the South Pars Gas Complex (located in Iran) with the same feed composition. The gas-sweetening unit in the Phase 12, operating with the solution of 45.5 wt% methyldiethanolamine (MDEA), was modeled by Aspen Plus for acid gas removal (CO2 and H2S) as a rate-based model with the application of electrolyte non–random two–liquid (E-NRTL) activity model and Peng–Robinson equation of state in addition to the actual characteristics of the absorber and regenerator, and the operational conditions of the gas and liquid streams. After validation of the model by the real data from the plant, the incumbent amine solution was replaced with five proposed amine solutions – one single and four blended amine mixtures – in the same mass concentration to select the most efficient alternative from the aspects of outlet acid gas concentration, H2S content in the treated flash gas, required total power, reboiler power supply, and regeneration heat duty. The simulation results revealed that H2S was sharply absorbed on the top of the column, while CO2 was smoothly removed from the gas phase to the MDEA and blended solutions along the absorber and it occurred at the bottom of the column for the DEA solution. The blended amine solution of 1.5 wt% sulfolane + 44 wt% MDEA (Sulfinol-M) has shown to be the most appropriate option instead of the solution of MDEA compared to other suggested absorbents, with several advantages such as higher selectivity of H2S over CO2, low temperature bulge, highest H2S loading, and outlet sweet gas flow rate while required total power, reboiler power supply, and regeneration heat duty were reduced by 21.19%, 21.26%, and 23.54% respectively. The operational conditions of the unit with the application of the Sulfinol-M solution were optimized to achieve three specifications (constraints) and the minimum required total power (objective function) through a sensitivity analysis and optimization using a genetic algorithm to assure the reliability of values for three independent parameters, namely, amine solution temperature, amine solution flow rate, and gas temperature. The optimum limits and values of these parameters were 47–50 °C, 220 – 240 ton/h, and 34 °C respectively.

Performance and Characterization of Bi-Metal Compound on Activated Carbon for Hydrogen Sulfide Removal in Biogas.

This study reports on the synthesis of bi-metal compound (BMC) adsorbents based on commercial coconut activated carbon (CAC), surface-modified with metal acetate (ZnAc2), metal oxide (ZnO), and the basic compounds potassium hydroxide (KOH) and sodium hydroxide (NaOH). The adsorbents were then characterized by scanning electron microscopy and elemental analysis, microporosity analysis through Brunauer-Emmett-Teller (BET) analysis, and thermal stability via thermogravimetric analysis. Adsorption-desorption test was conducted to determine the adsorption capacity of H2S via 1 L adsorber and 1000 ppm H2S balanced 49.95% for N2 and CO2. Characterization results revealed that the impregnated solution homogeneously covered the adsorbent surface, morphology, and properties. The adsorption test result reveals that the ZnAc2/ZnO/CAC_B had a higher H2S breakthrough adsorption capacity and performed at larger than 90% capability compared with a single modified adsorbent (ZnAc2/CAC). Therefore, the synthesized BMC adsorbents have a high H2S loading, and the abundance and low cost of CAC may lead to favorable adsorbents in H2S captured.

Graphene/Rh-doped SnO2 nanocomposites synthesized by electrochemical exfoliation and flame spray pyrolysis for H2S sensing

In this study, flame-made Rh-doped SnO2/electrochemically exfoliated graphene hybrid materials were developed and systematically investigated for gas sensing towards H2S. Structural characterizations by various microscopic and spectroscopic techniques demonstrated the dispersion of graphene sheets on Rh-substituted polycrystalline SnO2 nanoparticles with improved specific surface area. The effects of Rh dopants and graphene on gas-sensing behaviors of the hybrid sensors were systematically evaluated towards H2S, H2, CH4, C2H2, C2H4, CH3SH, CO2, C2H5OH, C3H6O and NO2 at 200–400 °C in dry and humidified air with 20–80% RH. It was found that Rh doping at the optimal amount of 0.5 wt% considerably enhances the response and selectivity of flame-made SnO2 nanoparticles toward H2S and additional graphene loading further increases the H2S-sensing performance with the optimum graphene content of 0.5 wt%. Accordingly, the 0.5 wt% graphene-loaded 0.5 wt% Rh-doped SnO2 sensor provided the highest responses of ∼439 and the shortest response time of 6.5 s to 10 ppm H2S with high selectivity against CH3SH, H2, CH4, C2H2, C2H4, CO2, C2H5OH, C3H6O and NO2 at the optimal working temperature of 350 °C. The mechanisms of H2S response enhancement were described by the combinative effects of catalytic p-type substitutional Rh dopants and active graphene–Rh-doped SnO2 junctions.

A Two-Stage Biogas Desulfurization Process Using Cellular Concrete Filtration and an Anoxic Biotrickling Filter

A two-stage desulfurization process including an abiotic filtration using cellular concrete waste (first stage) and an anoxic biotrickling filter filling with an inoculated expanded schist material (second stage) was investigated to remove H2S in mimic biogas with limited O2 amount (ranged from 0.5 to 0.8%). The two-stage process was able to satisfactorily remove H2S for all experimental conditions (RE > 97%; H2S concentration = 1500 mg m−3; total Empty Bed Residence Time (EBRT) = 200 s; removal capacity (RC) = 26 g m−3 h−1). Moreover, at a total EBRT = 360 s (i.e., 180 s for each stage), the H2S loading rate (LR) was almost treated by the bed of cellular concrete alone, indicating that abiotic filtration could be applied to satisfactorily remove H2S contained in the gas. According to the H2S concentration entering the biotrickling filter, the majority end-product was either elemental sulfur (S0) or sulfate (SO42−). Thus, the ability of the abiotic filter to remove a significant part of H2S would avoid the clogging of the biotrickling filter due to the deposit of S0. Consequently, this two-stage desulfurization process is a promising technology for efficient and economical biogas cleaning adapted to biogas containing limited O2 amounts, such as landfill biogas.

Model-based design and operation of biotrickling filters for foul air H2S removal at wastewater networks

Biotrickling filters (BTFs) are odour control technologies that utilise the action of sulfur oxidising bacteria to treat foul air contaminated with H2S. BTFs are complex systems where an immobilised biofilm is allowed to grow on a supportive solid media, while the foul air flows counter-currently with a stream of trickling liquid. In this work, a mechanistic model is developed, based on first principles where applicable, that describes the interphase mass transfer and biological oxidation kinetics. The model also focuses on the spatial discretisation of a BTF bed and describes the competition between sulfur oxidising bacteria (SOB) and aerobic heterotrophs growing within different niches of the bed. The model successfully produced concentration profiles over time and space of all relevant chemical and biological species within the bed. The model was then used to theoretically investigate the effect of design and operating parameters on the bed performance. It was found that the optimum liquid rate could vary significantly based on other factors such as bed size and inlet H2S concentrations but a typical value lies between 0.3 and 1.3 m/hr, with a larger bed and/or higher H2S loads requiring higher loading rates to achieve the same treatment levels. The model also predicted that bed shape has no significant impact on H2S removal, provided all other conditions are the same. The model successfully allowed for more detailed design of industrial BTF units in terms of both sizing and tuning of operational parameters.

Analyses of deodorization performance of mixotrophic biotrickling filter reactor using different industrial and agricultural wastes as packing material

In this study, to efficiently remove malodorous gas and reduce secondary pollution under mixotrophic conditions, pine bark, coal cinder, straw and mobile bed biofilm reactor (MBBR) fillers were used as packing materials in a biological trickling filter (BTF) to simultaneously treat high-concentration H2S and NH3. The results showed that the removal rate of BTF-A filled with pine bark was the highest, which was 86.31% and 94.06% under the H2S and NH3 loading rates of 53.59 g/m³·h while the empty bed residence time (EBRT) was 40.5 s. The theoretical maximum load was obtained by fitting the kinetic curve, and the value were 90.09 g H2S m-³·h−1 and 172.41 g NH3 m-³·h−1. Meanwhile, after treating with 720 ppm of NH3, the average concentration of NO3- in the BTF circulating fluid was only 127.58 mg/L, indicating the better performance of secondary pollutants control. Microbiological analysis showed that Dokdonella, Micropruina, Candidatus_Alysiosphaera, Nakamurella and Thiobacillus possessed high abundance at the genus level, and their entire percentage in four BTF reactors were 62.87%, 46.32%, 47.98%, and 57.35% respectively. It is worthwhile that the genera Comamonas and Trichococcus with heterotrophic nitrification and aerobic denitrification capabilities and proportion of 3.66%, 1.45%, 5.43%, and 3.23% were observed in four reactors.

Impact of an anoxic desulfurization process on methane content of the purified biogas

This study showed the impact of an anoxic desulfurization process on the CH4 and CO2 content of the purified biogas. The desulfurization system was implemented in an anoxic bioscrubber, which supported H2S removal efficiencies ranging from 92 ± 8 to 97 ± 6% for H2S loading rates between 28.3 and 37.8 g S mliquid-3h−1. CO2 absorption during the desulfurization process mediated a slight reduction in the CO2 concentration from 39.5% in the raw biogas to 36.5–38.2% in the purified biogas. Such reduction in the CO2 concentration was proportional to the increase of CH4 concentration recorded, passing from 60.0% in the raw biogas to 61.7–63.5% in the purified biogas. Bacterial community characterization by means of 16S rRNA high-throughput sequencing revealed the consistent presence of both methanotrophs (Methylibium, Methylomonas and Methylosinus genera) and methanol-oxidizing denitrifiers (Simplicispira and Methyloversatilis genera), which suggested that methane oxidation indeed occurred. The quantification of a potential CH4 uptake in the desulfurization process was hindered by the CO2 absorption observed, however, strategies for quantifying biological CH4 consumption in anoxic desulfurization systems are proposed and discussed, based on the results herein obtained.

Development of an H2S emission model for wastewater treatment plants

ABSTRACT Modeling and prediction of H2S emission from wastewater are important since gaseous H2S will induce significant corrosion and odor problems. Most previous studies focused on H2S emission of wastewater in pipeline systems, which may not be fit for H2S emission in wastewater treatment plants (WWTPs). This study provided a two-phase mass transfer model for prediction of H2S emission concentrations. The model is based on the mass transfer rate equation of the mass transfer impetus, expressed by the concentration difference. The main parameters of the model are the mass transfer coefficient, the carrier gas flow rate and the concentration of H2S in liquid phase. The results showed that the model can simulate and predict H2S emission concentrations of various processes in WWTPs. Moreover, the model can analyze and predict the influences of different pH values, mass transfer coefficients and carrier gas flow rates on H2S emission concentrations and loads. Therefore, the model provides theoretical guidance for design of WWTPs regarding H2S emissions. Implications: Modeling and prediction of H2S emission from wastewater are quite important since gaseous H2S will induce significant corrosion and odor problems. Most of previous studies are focused on H2S emission from wastewater in pipeline system, which may not be fit for H2S emission in wastewater treatment plants (WWTPs). Thus in this study, a model for predicting H2S emission from typical units of WWTPs is established and verified. Moreover, the influences of pH values, mass transfer coefficients and carrier gas flow rates on H2S emission are analyzed. The model can be a useful tool to predict the H2S concentration in odor gas collection system of WWTP and understand the behaviors of H2S emission under different WWTPs operating conditions.

Effects of H2S Loading Rate on the Performance of Reactive Absorption with Electrochemical Oxidation

The odor released from environmental facilities is recognized as a major problem in environmental industries. In this study, reactive absorption, using an electrolyzed water solution (electrolyzed water scrubber, EWS), was developed to treat the odorous gases H2S and NH3, which are representative odorous substances. In addition, a numerical model composed of mass transfer coefficients and zero-order kinetic constants was established to predict the performance of EWS. The model was verified through experiments and data fittings. In the experiments, the concentration of H2S varied from 500 to 2000 ppm, while NH3 was fixed at 500 ppm. The results revealed that the H2S removal rate varied depending on the inlet H2S concentration, but no changes were observed for NH3. The numerical model appropriately described the experimental results to further predict the performance of EWS. The model prediction results for the shock loading of H2S indicated that a 100% removal rate can be achieved by increasing the current density to 70 mA cm−2 or higher. Finally, the EWS can be used to reduce the odor, owing to its flexible operation that responds to fluctuating loading rates.

H2S oxidation coupled to nitrate reduction in a two-stage bioreactor: Targeting H2S-rich biogas desulfurization

A two-stage bioreactor operated under anoxic denitrifying conditions was evaluated for desulfurization of synthetic biogas laden with H2S concentrations between 2500 and 10,000 ppmv. H2S removal efficiencies higher than 95% were achieved for H2S loads ranging from 16.2 to 51.9 gS mliquid−3h−1. Average H2S oxidation performance (fraction of S-SO42− produced per gram of S-H2S absorbed) ranged between 8.2 ± 1.2 and 18.7 ± 5.3% under continuous liquid operation. Nitrogen mass balance showed that only 2–6% of the N-NO3− consumed was directed to biomass growth and the rest was directed to denitrification. Significant changes in the bacterial community composition did not hinder the H2S removal efficiency. The bioreactor configuration proposed avoided clogging issues due to elemental sulfur accumulation as commonly occurs in packed bed bioreactors devoted to H2S-rich biogas desulfurization.

Modelling of hydrogen sulfide fate and emissions in extended aeration sewage treatment plant using TOXCHEM simulations

Odors due to the emission of hydrogen sulfide (H2S) have been a concern in the sewage treatment plants over the last decades. H2S fate and emissions from extended aeration activated sludge (EAAS) system in Muharram Aisha-sewage treatment plant (MA-STP) were studied using TOXCHEM model. Sensitivity analysis at different aeration flowrate, H2S loading rate, wastewater pH, wastewater temperature and wind speed were studied. The predicted data were validated against actual results, where all the data were validated within the limits, and the statistical evaluation of normalized mean square error (NMSE), geometric variance (VG), and correlation coefficient (R) were close to the ideal fit. The results showed that the major processes occurring in the system were degradation and emission. During summer (27 °C) and winter (12 °C), about 25 and 23%, 1 and 2%, 2 and 2%, and 72 and 73% were fated as emitted to air, discharged with effluent, sorbed to sludge, and biodegraded, respectively. At summer and winter, the total emitted concentrations of H2S were 6.403 and 5.614 ppm, respectively. The sensitivity results indicated that aeration flowrate, H2S loading rate and wastewater pH highly influenced the emission and degradation of H2S processes compared to wastewater temperature and wind speed. To conclude, TOXCHEM model successfully predicted the H2S fate and emissions in EAAS system.

A high efficient absorbent for the separation of H2S from low partial pressure coke oven gas.

To high efficiently remove H2S from low partial pressure coke oven gas (COG), a novel activator (tetramethylammonium arginine, [N1111][Arg]) was used to blend with N-methyldiethanolamine (MDEA) for the absorption of H2S. High concentrated [N1111][Arg]-MDEA aqueous solution was used as absorbent. Thermodynamic properties including absorption amount and H2S loading values were measured, then the kinetic apparent absorption rate was calculated based on the change of absorption amount with time. The removal efficiency of H2S in simulated COG was verified in tray towers. Compared with monoethanolamine (MEA)-MDEA and tetramethylammonium glycinate ([N1111][Gly])-MDEA aqueous solutions, [N1111][Arg]-MDEA aqueous solution takes advantages of higher absorption capacity, absorption rate and removal efficiency. Our results showed that the proposed absorbent has good industrial application prospect in coke oven gas desulfurization, because it achieved 100% removal of H2S in the tray tower containing only 4 sieve plates under high concentrated condition (water content < 45%), which may significantly decrease the energy consumption.

Stoichiometry-driven heuristic feedforward control for oxygen supply in a biological gas desulfurization process

In this work, a stoichiometry-driven heuristic feedforward control strategy is proposed for controlling the oxygen supply to a biological gas desulfurization process that treats biogas, landfill, and high-pressure natural gas containing H2S and volatile organic sulfur compounds (VOSC). Traditionally, PI or PID feedback control is used when the feed gas contains H2S only. Because the oxidation–reduction potential (ORP) is mostly dominated by the dissolved sulfide concentration, the feedback controller maintains a constant sulfide concentration in the bioreactor by maintaining an ORP setpoint value through controlling the oxygen supply. However, when the feed gas also contains VOSCs, e.g., thiols, it appears from our research that controlling ORP at a fixed value does not lead to stable process performance. Hence, an alternative control strategy is proposed, which controls the O2/H2S supply ratio based on the stoichiometry of the dominant chemical reaction and experimental experience. The heuristic feedforward control strategy was validated by a fluctuating supply of H2S (26.5 to 126.5 mM S day−1) in the absence and presence of ethanethiol (0.8 to 1.16 mM S day−1). A sulfur selectivity above 95 mol%, and complete removal of H2S, was achieved at an O2/H2S supply ratio of about 0.63 mol mol−1 compared to 56 mol% when a PI/PID controller was used at a randomly varying, stepwise H2S dosing rate This work shows that fluctuations in the H2S loading rate and presence of ethanethiol in the feed gas of full-scale systems can be controlled by applying the heuristic feedforward control strategy. However, online measurements of the H2S concentration in the feed gas are required to implement the proposed strategy in full-scale installations successfully.

H2S removal from sour water in a combination system of trickling biofilter and biofilter

Desulfurization of sour water was investigated in a combination system of trickling biofilter (BTF) and biofilter (BF) filled with ceramic packing materials. A critical elimination capacity (EC) of 251.93 g S m−3 h−1 was obtained for the BTF/BF system during a stepwise increase of sulfide concentration from 10 to 60 g S m−3. This stepwise increment of loading rate also led to critical ECs of 176.21 and 478.88 g S m−3 h−1 for BTF and BF, respectively. A dynamic model describing biological H2S removal from sour water in the BTF/BF was developed and calibrated by a set of experimental data. The model includes the main processes occurring in the BTF/BF such as mass transfer between phases, diffusion and biological reaction inside the biofilm. The model also considers the intermediate (elemental sulfur) production/consumption and sulfate formation through the different oxidation pathways. The model validation was performed under a starvation period and a dynamic H2S loading period. A sensitivity analysis was carried out to evaluate the relative importance of the key parameters on the performance of the BTF/BF system. Sensitivity analysis showed that the BTF performance is more affected by the parameters related to H2S mass transfer.

Enhancing the removal of H2S from biogas through refluxing of outlet gas in biological bubble-column

Biological bubble-column (BBC) is beneficial for elemental sulfur recycle from H2S, but it’s difficult to remove high concentration of H2S in biogas efficiently due to the mass transfer limitation of H2S from gas to liquid. In this study, a novel method with refluxing outlet gas in BBC was investigated. The results showed that gas reflux greatly enhanced the removal of high concentration of H2S (about 5000 ppmv) from biogas. The removal efficiency of H2S was 88.0 ± 4.1% with the reflux ratio at 1.0, which was higher than those without gas reflux (58.4 ± 1.0%), when the inlet H2S loading was 143.1 ± 4.5 g/(m3·h). Moreover, the removal capacity of H2S improved significantly with the increase of the reflux ratios from 1.0 to 4.0 and achieved the maximum at 271.8 ± 2.4 g/(m3·h). This might mainly be attributed to longer residence time and enhanced the mass transfer of O2 and H2S from gas to liquid through gas reflux.

Modeling H2S solubility in aqueous N-methyldiethanolamine solution using a new ePC_SAFT-MB equation of state

Perturbed chain statistical associating fluid theory (PC-SAFT) equation of state (EoS), mean spherical approximation (MSA) term and Born term are combined and proposed as a new electrolyte equation of state (ePC_SAFT-MB EoS) to model the solubility of H2S in aqueous N-methyldiethanolamine (MDEA) solutions in a wide range of temperature, pressure, MDEA concentration, and H2S loading. In order to find the best association schemes (2B, 3B and 4C) for H2O, MDEA and H2S in PC-SAFT EoS, different association schemes are considered for each one of the components in the wide range of temperature and pure parameters are determined. The binary interaction parameters (BIP) for H2O + H2S and MDEA + H2O binary systems are adjusted in the VLE calculation for different association schemes. The best result with minimum average absolute relative deviation percent (AAD%) of 2.21 and 2.72 are obtained with considering the 4C, 4C and 3B association schemes for MDEA, water and H2S, respectively. By using the obtained BIPs, 277 data points of the bubble pressure for H2O + MDEA + H2S system are predicted by PC-SAFT EoS with the AAD% of 25.5. To improve the accuracy of PC-SAFT EoS, the Born and MSA terms are added to PC-SAFT EoS. The BIPs between the ion-ion and molecules-ions are adjusted by the bubble pressure calculation algorithm using 277 experimental data points. Very good results with the AAD% of 18.6 are obtained by adjusting the binary parameters (MDEAH+−MDEA,MDEAH+−H2O,MDEAH+–H2S and MDEAH+−HS−) in H2O + MDEA + H2S ternary system. Finally, to investigate the predictive ability of the proposed ePC_SAFT-MB EoS, it is employed to model the selected 44 solubility data points of H2O + MDEA + H2S system without further adjustment for model parameters. The value of AADs% is obtained about 30.0 for the H2 S partial pressure, which shows the predictive ability of the proposed model.