Characterization of a High-Performance Biosorbent for Natural Gas Dehydration

Abstract

Dehydration of gases is crucial in industry. Current dehydration methods have concerns about high energy consumption and environmental pollution. In this work, natural gas, an important energy source, was selected as a model gas to investigate dehydration using a cost-effective biosorbent in a pressure swing adsorption process. The biosorbent was developed from flax shives, a byproduct of the flax industry, and are representative of renewable cellulose materials. The morphology, surface functional groups, and thermal stability of the biosorbent were investigated by FE-SEM, XPS, and TGA. The biosorbent has higher water adsorption capacity (up to 0.9 g/g) and higher water selectivity compared to those of conventional adsorbents. Adsorption of the main component of natural gas, i.e., nonpolar methane, was negligible. In addition, the most significant operation factors and interaction among them were determined with regards to their effects on water adsorption capacity. The water adsorption equilibrium data was simulated well by the Redhead and Fowler–Guggenhein (F-G) models. On the basis of the Redhead modeling results, the surface area was determined for water adsorption. The F-G modeling results indicated the adsorbed water molecules on the surface of the biosorbent were attracted to one another; however, the interaction was weak. The length of mass transfer zone under various operating conditions was also calculated. Furthermore, the water-saturated biosorbent was regenerated at room temperature at a fast rate. The biosorbent was used for 70 adsorption–desorption cycles without deterioration. The TGA results showed that the biosorbent was stable at temperatures up to 200 °C even though the dehydration process effectively operated at room temperature in this work. The results indicate that the biosorbent or similar can be used in a pressure swing adsorption process for dehydration of natural gas and other nonpolar gases in industry.

Dynamic Simulation and Mass Transfer Study of Carbon Dioxide Capture Using Biochar and MgO-Impregnated Activated Carbon in a Swing Adsorption Process

“…A value of 10.32 J/mol was obtained for the CO 2 interaction forces, which shows attraction among the molecules. Ghanbari et al reported values of 6.4 and 8.33 J/mol at 35 and 50 °C, respectively, for the interaction forces among water molecules adsorbed on the surface of a flax-shive-based biosorbent . These forces are much weaker than van der Waals weak forces (400–4000 J/mol) and hydrogen bonds, such as HO–H···OH 3 + (18 000 J/mol) .…”

“…Because only CO 2 was adsorbed by the adsorbent (helium carrier gas), we remove the subscript i from the rate of adsorption term (this term is assumed to be 0 for the carrier gas). The LDF is one of the most common expressions used for the rate of adsorption term in the equation, which takes the following form: where q * is the biosorbent loading at equilibrium with the gas phase and k LDF is the effective mass transfer coefficient (s –1 ).…”

“…In this work, TSA and VSA processes were simulated using ASPEN Adsim. All of the experimental data used in the simulation were experimentally obtained and reported in the previous works by Shahkarami et al ,,, Gas-phase energy balance includes thermal conduction, convection of energy, accumulation of heat, compression, and heat transfer from gas to solid. These terms are shown in the governing partial differential equation as follows: where k ga is the effective axial gas-phase thermal conductivity (MW m –1 K –1 ), T g is the gas-phase temperature (K), C vg is the specific gas-phase heat capacity at a constant volume (MJ kmol –1 K –1 ), ρ g is the gas-phase molar density (kmol/m 3 ), P is the pressure (bar), v g is superficial velocity (m/s), r p is the particle radius (m), HTC is the gas–solid heat transfer coefficient (MJ/m 2 /s), and T s is the solid-phase temperature (K).…”

“…43 In this work, TSA and VSA processes were simulated using ASPEN Adsim. All of the experimental data used in the simulation were experimentally obtained and reported in the previous works by Shahkarami et al 17,32,36,37 Gas-phase energy balance includes thermal conduction, convection of energy, accumulation of heat, compression, and heat transfer from gas to solid. These terms are shown in the governing partial differential equation as follows: 43 1) HTC( )…”

“…Without any micro-/mesopore volume, other small molecules in the gas, i.e., methane in biogas/natural gas or nitrogen and oxygen in flue gas, cannot be adsorbed according to the micropore diffusional activation force principle, while surface functional groups can selectively adsorb CO 2 from a gas mixture. Ghanbari et al reported a similar scenario for gas dehydration using biosorbents that were 100% selective to water vapor and did not adsorb nonpolar gases, such as nitrogen and methane. − Their experimental and modeling results showed that the biosorbents had negligible micro-/mesopore volume and abundant hydroxyl and carboxyl functional groups on the surface that selectively adsorbed moisture from gas. Amine functional groups showed potential for CO 2 adsorption, which are further discussed in the next paragraph.…”