A comprehensive thermodynamic model for high salinity produced waters

New Process for Na2CO3 Production from Na2SO4 Based on Modeling the Na2SO4-(NH4)2SO4-MEA-MEG-H2O System

Alternative means for soda ash (Na2CO3) production from sodium sulfate (Na2SO4) are needed due to the intensive consumption of energy in the conventional Mirabilite-Solvay process (MSP). We demonstrate a new process to produce soda ash using sodium sulfate as a feed material. The new process relies on the antisolvent crystallization of unreacted Na2SO4 to separate it from soluble (NH4)2SO4 in a mixed monoethanolamine (MEA) and monoethylene glycol (MEG) solution. To develop the process, the solubilities of Na2SO4 and (NH4)2SO4 solids in aqueous mixed MEA-MEG solutions were first measured and then modeled using regressed paired-ion interactions from the electrolyte nonrandom two-liquid (E-NRTL) model. Anhydrous dense soda ash with a bulk density of up to 1146 kg/m3 was obtained when the concentrated Na2SO4 brines reacted with CO2 and NH3.

Comparative Energetics of Various Membrane Distillation Configurations and Guidelines for Design and Operation

This paper presents a comparative performance study of single-stage desalination processes with major configurations of membrane distillation (MD) modules. MD modules covered in this study are (a) direct contact MD (DCMD), (b) vacuum MD (VMD), (c) sweeping gas MD (SGMD), and (d) air gap MD (AGMD). MD-based desalination processes are simulated with rigorous theoretical MD models supported by molecular thermodynamic property models for the accurate calculation of performance metrics. The performance metrics considered in MD systems are permeate flux and energy efficiency, i.e., gained output ratio (GOR). A general criterion is established to determine the critical length of these four MDs (at fixed width) for the feasible operation of desalination in a wide range of feed salinities. The length of DCMD and VMD is restricted by the feed salinity and permeate flux, respectively, while relatively large AGMD and SGMD are allowed. The sensitivity of GOR flux with respect to permeate conditions is investigated for different MD configurations. AGMD outperforms other configurations in terms of energy efficiency, while VMD reveals the highest permeate production. With larger MD modules, utilization of thermal energy supplied by the hot feed for evaporation is in the order of VMD > AGMD > SGMD > DCMD. Simulation results highlight that energy efficiency of the overall desalination process relies on the efficient recovery of spent for evaporation, suggesting potential improvement in energy efficiency for VMD-based desalination.

Geochemistry and Microbiology Predict Environmental Niches With Conditions Favoring Potential Microbial Activity in the Bakken Shale

The Bakken Shale and underlying Three Forks Formation is an important oil and gas reservoir in the United States. The hydrocarbon resources in this region are accessible using unconventional oil and gas extraction methods, including horizontal drilling and hydraulic fracturing. However, the geochemistry and microbiology of this region are not well understood, although they are known to have major implications for productivity and water management. In this study, we analyzed the produced water from 14 unconventional wells in the Bakken Shale using geochemical measurements, quantitative PCR (qPCR), and 16S rRNA gene sequencing with the overall goal of understanding the complex dynamics present in hydraulically fractured wells. Bakken Shale produced waters from this study exhibit high measurements of total dissolved solids (TDS). These conditions inhibit microbial growth, such that all samples had low microbial loads except for one sample (well 11), which had lower TDS concentrations and higher 16S rRNA gene copies. Our produced water samples had elevated chloride concentrations typical of other Bakken waters. However, they also contained a sulfate concentration trend that suggested higher occurrence of sulfate reduction, especially in wells 11 and 18. The unique geochemistry and microbial loads recorded for wells 11 and 18 suggest that the heterogeneous nature of the producing formation can provide environmental niches with conditions conducive for microbial growth. This was supported by strong correlations between the produced water microbial community and the associated geochemical parameters including sodium, chloride, and sulfate concentrations. The produced water microbial community was dominated by 19 bacterial families, all of which have previously been associated with hydrocarbon-reservoirs. These families include Halanaerobiaceae, Pseudomonadaceae, and Desulfohalobiaceae which are often associated with thiosulfate reduction, biofilm production, and sulfate reduction, respectively. Notably, well 11 was dominated by sulfate reducers. Our findings expand the current understanding of microbial life in the Bakken region and provide new insights into how the unique produced water conditions shape microbial communities. Finally, our analysis suggests that produced water chemistry is tightly linked with microbiota in the Bakken Shale and shows that additional research efforts that incorporate coupled microbial and geochemical datasets are necessary to understand this ecosystem.

Potential water recovery during lithium mining from high salinity brines

Lithium extraction from continental brines involves the evaporation of large amounts of water in open air ponds, in order to concentrate the brine. The evaporitic technology implies the evaporation of large water volumes, raising environmental concerns. If we envision the use of desalination processes for the concentration of lithium-rich brines, then fresh water production/recovery becomes a process well integrated with lithium extraction. Here we apply the Pitzer thermodynamic model with effective molality to estimate activity coefficients for 8 different native brines, and for the resulting concentrated solutions produced by a hypothetical advanced desalinization technique. In all cases, rational activity coefficients deviate considerably from unity. We calculate next the least work of separation for a hypothetical desalination process for the 8 different brines. Because of the large total salinity, the calculation shows that the least work of separation ranges from 18 until 42 kJ kg^-1 at nil recovery ratio, and escalating from those numbers as more water is recovered. We can also predict the boiling point elevation, the vapour pressure lowering, and the osmotic pressure. Our calculations show that results are not strictly proportional to the total dissolved solids. Results are strongly dependent with the specific chemical composition of each brine, with the amount of divalent ions (Mg-Ca-SO₄^2-) in particular strongly influencing calculations. Fresh water and lithium minerals production could be part of a single integrated production system.