Propylene Purity Research Articles

Wood-structured carbon with reassembled pores showing high propylene adsorption rate for efficient separation of propylene/propane

Efficient separation of propylene/propane requires enhancing adsorption rates on adsorbents, while maintaining high adsorption capacity and selectivity, heavily relying on engineering pore structures within the adsorbents. Herein, we have prepared wood-structured carbon with reassembled pores by using wood frameworks incorporated with CuCl2 and a polymer coating. Upon carbonization, the wood framework transforms into microporous carbon, while the polymer coating converts into molecular sieving carbon. Notably, the evaporation of CuCl produced from the in-situ reduction of CuCl2 creates additional micropores in the molecular sieving carbon layer. This wood-structured carbon adsorbent exhibits a propylene diffusion constant of 0.011 min−1 at 0.5 bar, which is 4.1-fold higher than the sample without CuCl2. Additionally, this adsorbent shows a high propylene uptake of 2.38 mmol g−1 and a propylene/propane dynamic selectivity of up to 161 at 298 K and 1 bar. Aspen simulation suggests that a propylene purity of 99.9 % can be achieved with a 70 % recovery using a vacuum swing adsorption process. The enhanced performance is primarily attributed to the unique pore structures of the wood-structured carbon adsorbent.

Polymer-grade propylene production through temperature swing adsorption: Molecular simulation and techno-economic analysis

Producing polymer-grade propylene from the propylene-rich mixtures can be quite challenging since the most commonly employed technology, distillation, requires high-energy input and is expensive. Therefore, identifying less-costly, efficient, and environmentally friendly methods, such as the use of the adsorptive process, is highly desirable. In this regard, six pure silica zeolites (AFV, AST, AVL, IFR, LEV, and SWY) as propane selective adsorbents are investigated for the separation of 10 mol.% propane and 90 mol.% propylene mixture. Molecular simulation Monte Carlo (MC) is used to calculate framework structure parameters such as pore volume, surface area, and framework density of pure silica zeolites. Also, adsorption isotherms, propane selectivity, and working capacity are presented using MC calculations. The Langmuir-Freundlich isotherm model is utilized to calculate isotherm parameters. A system model is implemented in Aspen Adsorption software (version 11) and breakthrough curves are achieved. The Temperature Swing Adsorption (TSA) cycle is simulated and key performance parameters such as propylene purity, recovery, and productivity for all six silica zeolites are calculated. Finally, economic analysis of the TSA process is performed using the Aspen Capital Cost Estimator (version 11) and Aspen Process Economic Analyzer (version 11) and compared with the cost of the conventional distillation process. Results showed that the capital cost and operating cost of temperature swing adsorption are 42.3 % and 91.37 % less than those of distillation, respectively.

Desorbent swing adsorption process using ethylene to separate propane and propylene under isobaric conditions

The separation of olefin and paraffin using adsorption technology remains a significant challenge. This study proposes a novel desorbent swing adsorption (DSA) process using an olefin desorbent with a weaker adsorption affinity (C2: ethylene) to separate a paraffin/olefin mixture with a higher adsorption affinity (C3s: propane and propylene) under isobaric conditions, which is the reverse concept of using a desorbent with a stronger affinity in conventional DSA systems. The proposed DSA process effectively separates the C3 mixture because the deteriorating effects caused by the desorbent is minimized. Based on sequential breakthrough experiments with zeolite 13X DSA using ethylene, the efficient separation of a propylene dehydrogenation product (propane:propylene = 60:40 vol%) to produce polymer-grade propylene is achieved. It is confirmed that ethylene desorbent stream pushes out the adsorbed propylene and regenerates the adsorption bed without changing the pressure. The desorption step plays a key role in the separation performance of the proposed DSA process because the regenerated bed offers favorable conditions when filled with the weaker desorbent after the desorption step. The flowrate of the desorbent strongly affects the efficiency of propylene desorption. After validating the dynamic mathematical model using the experimental results, a two-bed DSA process using a six-step sequence that includes rinse export/import and idle steps is shown to achieve a propylene purity above 99.999 % (desorbent-free basis) with a recovery of 99.39 %, a productivity of 4.21 mol∙kg−1∙hr−1, and an ethylene usage of 7.59 mol∙kg−1∙hr−1. This study offers important insights into the development of adsorptive separation designs for olefin/paraffin separation.

Permylene™ membrane technology: An efficient approach to separate propylene from propane

Permylene™ demonstration system (PDS), a membrane-based pilot unit for olefin/paraffin separation, is designed and fabricated by Imtex Membranes Corp. (Imtex). The PDS, equipped with pilot-scale Permylene™ elements, is capable of treating up to 3 kg/h of olefin/paraffin mixture. The PDS unit is installed in Imtex's testing lab in Mississauga, Ontario, Canada. Various plant-collected and lab-blended olefin/paraffin mixtures involving ethylene/ethane (C2), propylene/propane (C3), and butene/butane (C4) have been assessed on the unit. This paper is focused on the application of PDS for C3 separation, and a series of remarkable performances that have been achieved by the Permylene™ membrane and PDS unit. Propylene purity of over 98.5 vol% in the permeate/product stream has been reached over a wide range of propylene recovery rates, which could offer significant flexibility to meet various industrial operation conditions. Furthermore, the PDS unit demonstrates its stability and efficiency with 1200 hrs of continuous C3 permeation. Finally, a case study of recovering 90 % of propylene from 15,000 kg/h of C3 is performed to estimate energy consumption in commercial applications. The energy consumption of the Permylene™ process is calculated and compared with that of the distillation process. The result indicates that the energy consumption in PDS is extremely low, equal to only 8 % of that required in distillation. The study undeniably validates Permylene™'s remarkable capability for C3 separation, highlighting its potential as a viable and energy-efficient alternative to traditional distillation.

Selective separation of propane from the propylene-propane mixture using pure silica zeolites: A molecular dynamic simulation

Purification of propylene from propylene/propane mixtures which almost have a greater percentage of propylene is always a challenging task, because of using the costly cryogenic distillation process. Therefore, finding less-energy intensive, cleaner, and cheaper methods such as the adsorption process is desirable. In this study, with the purpose of separating an industrial feed stream including 90 mol.% propylene and 10 mol.% propane, a high-throughput screening method based on molecular simulation is used to investigate the most proper zeolite framework for this separation. Grand Canonical Monte Carlo (GCMC) and Molecular Dynamic (MD) simulations of the mixture in all 250 pure silica zeolites in the IZA database have been performed. Since a large mole fraction of this mixture is propylene, it is interesting to find an adsorbent that has a greater tendency to adsorb propane, in order to have a product with a higher purity of propylene. It has been found that the AFV-type framework has the highest propane separation potential (greater than 4 mol/L) and propane uptake capacity (0.76 mol/L).In order to choose the appropriate industrial process for the adsorption-desorption cycle between Pressure Swing Adsorption (PSA) and Temperature Swing Adsorption (TSA) processes, the adsorption isotherms and isobars of the mentioned mixture have been obtained. The results showed that the TSA adsorption process is more favorable due to the effect of increasing the temperature on the molar loading than the reduction of pressure in the PSA adsorption process.

Catalytic Dehydration of Isopropanol to Propylene

Catalytic dehydration of isopropanol to propylene is a common reaction in laboratories to characterize the acid–base properties of catalysts. When acetone is produced, it is the sign of the presence of basic active sites, while propylene is produced on the acid sites. About 2/3rd of the world production of isopropanol is made from propylene, and the other third is made from acetone hydrogenation. Since the surplus acetone available on the market is mainly a coproduct of phenol synthesis, variations in the demand for phenol affect the supply position of acetone and vice versa. High propylene price and low demand for acetone should revive the industrial interest in acetone conversion. In addition, there is an increasing interest in the production of acetone and isopropanol from CO/CO2 via expected more environmentally friendly biochemical conversion routes. To preserve phenol process economics, surplus acetone should be recycled to propylene via the acetone hydrogenation and isopropanol dehydration routes. Some critical impurities present in petrochemical propylene are avoided in the recycling process. In this review, the selection criteria for the isopropanol dehydration catalysts at commercial scale are derived from the patent literature and analyzed with academic literature. The choice of the process conditions, such as pressure, temperature and gas velocity, and the catalysts’ properties such as pore size and acid–base behavior, are critical factors influencing the purity of propylene. Dehydration of isopropanol under pressure facilitates the downstream separation of products and the isolation of propylene to yield a high-purity “polymer grade”. However, it requires to operate at a higher temperature, which is a challenge for the catalyst’s lifetime; whereas operation at near atmospheric pressure, and eventually in a diluted stream, is relevant for applications that would tolerate a lower propylene purity (chemical grade).

Ultramicroporous Hydrogen-Bonded Organic Framework Material with a Thermoregulatory Gating Effect for Record Propylene Separation.

Propane/propylene separation is one of the most challenging and energy-consuming but most important tasks in the petrochemical industry. Herein, a stable hydrogen-bonded organic framework (HOF-FJU-1) was tailor-made for highly efficient propylene separation from binary C3H6/C3H8 and even seven component CH4/C2H4/C2H6/C3H6/C3H8/CO2/H2 mixtures. The temperature-controllable diffusion channels in HOF-FJU-1 have enabled the porous material to completely exclude propane to reach high-performance propylene purification under energy-efficient operation conditions. Single-crystal structural analysis revealed that the well-matched pore aperture of HOF-FJU-1 can exactly accommodate propylene molecules via multiple intermolecular interactions, exhibiting a very high propylene/propane selectivity of 616 at 333 K. The propylene purity and productivity are over 99.5% and 30.2 L kg-1 from the binary C3H6/C3H8 (50/50) mixture at 333 K. Through a follow-up column separation of C3H6/C2H4 at 353 K, not only high-purity propylene (99.5%) but also ethylene (98.3%) can be readily collected from the seven component CH4/C2H4/C2H6/C3H6/C3H8/CO2/H2 (31/10/25/10/10/1/13) cracking gas mixtures. The great potential of HOF-FJU-1 for the industrial propylene separation process has been further supported by the high stability of this porous material under different environments and straightforward processibility and regeneration feasibility.

Large scale synthesis and propylene purification by a high-performance MOF sorbent Y-abtc

Olefin/Paraffin separation, especially propylene purification from propane, is of extreme commercial importance as it produces chemical feedstock for synthetic plastics such as polypropylene. As an alternative to cryogenic distillation commonly used to purify these mixtures, the use of solid porous materials for adsorptive separation offers a more energetically efficient route. Metal-Organic Frameworks (MOFs) have shown great promise as adsorptive separation candidates in recent years. However, reports of these materials for the purification of C3 hydrocarbons exclusively provide insight of their performance in small scale laboratory settings. Single component isotherms and breakthrough curves are typically tested in the milligrams to gram scale. Herein, we present a scale-up, one-pot synthesis of a robust MOF with high propylene/propane selectivity. The organic linker 3,3′,5,5′-azobenzene-tetracarboxylic acid (H4abtc) and its yttrium-based MOF, Y-abtc, are both synthesized at the hundred-gram scale. Furthermore, we perform large-scale breakthrough experiments at the same scale. Our results show that Y-abtc samples synthesized from the one-pot 100 g scale reactions retain high crystallinity and size-exclusion based mechanism for the separation of propane/propylene mixtures. The same polymer-grade purity of propylene (>99.5%) is achieved as in the case of small scale (∼1 g) experiments.

An Ultramicroporous Metal-Organic Framework for High Sieving Separation of Propylene from Propane.

Highly selective adsorptive separation of olefin/paraffin through porous materials can produce high purity olefins in a much more energy-efficient way than the traditional cryogenic distillation. Here we report an ultramicroporous cobalt gallate metal-organic framework (Co-gallate) for the highly selective sieving separation of propylene/propane at ambient conditions. This material possesses optimal pore structure for the exact confinement of propylene molecules while excluding the slightly large propane molecules, as clearly demonstrated in the neutron diffraction crystal structure of Co-gallate⊃0.38C3D6. Its high separation performance has been confirmed by the gas sorption isotherms and column breakthrough experiments to produce the high purity of propylene (97.7%) with a high dynamic separation productivity of 36.4 cm3 cm-3 under ambient conditions. The gas adsorption measurement, pore size distribution, and crystallographic and modeling studies comprehensively support the high sieving C3H6/C3H8 separation in this MOF material. It is stable under different environments, providing its potential for the industrial propylene purification.

Preferential Adsorption of Propylene over Propane on a Ag-Exchanged X-Type Zeolite Membrane.

We investigated the adsorption properties of propylene and propane on an olefin-selective Ag-X membrane and discussed the contribution of adsorption selectivity to propylene/propane separation performance through this membrane. The isotherms of propylene and propane on Ag-X membranes were measured in unary systems at 313 K. The amount of propylene adsorbed on the Ag-X membrane at a lower pressure increased remarkably compared with that on the Na-X membrane. Such a change of adsorption property could induce excellent separation property for the Ag-X membrane. We compared the adsorption properties in a binary system calculated based on the Markham-Benton approach with the results of a permeation test. The molar fractions of propylene in the adsorbed phase in the binary system provided good agreement with propylene purity on the permeation side of the Ag-X membrane. These results clearly show that permeation selectivity of the Ag-X membrane for the propylene/propane mixture is mainly governed by adsorption selectivity.

Techno-economic feasibility study of membrane based propane/propylene separation process

One of the most important issues for developing propylene/propane gas separation membranes is to identify the minimum required membrane performances. Herein, we reported the technical and economic feasibility of facilitated propylene transport membranes containing silver nanoparticles, which produces 99.6% purity of propylene with 97% recovery for 46,000kg/h capacity. In order to suggest minimum specification, the membrane separation process is compared with advanced distillation process employing direct vapor recompression process. The distillation process is optimized using a stochastic solver interfaced with a commercial process simulator. With the distillation process, the energy and total costs are approximately $4.40 and 18.6$ to produce per ton of propylene, respectively. The single-stage membrane processes with various stage-cut conditions were evaluated to meet the same total propylene production cost. Result indicates that required membrane permeance and selectivity ranges between 11.3 to 251.5 GPU (permeance unit, 1 GPU=1×10−6cm3 (STP)/(cm s cmHg)) and 61.9 to 1950 depending on stage-cut. Sensitivity analysis was also performed according to membrane costs, feed flow rates and composition.

Ethane/ethylene and propane/propylene separation in hybrid membrane distillation systems: Optimization and economic analysis

The combination of membrane and distillation processes to form a hybrid separation system is proposed as an alternative design to replace the current distillation technology. The main objective of this work is to scrutinize the feasibility of numerous hybrid membrane distillation (HMD) schemes through simulation. Silver nitrate is used for modeling/simulation as membrane carriers at a concentration of 6 mol L −1. Different configurations are suggested to obtain highest product (ethylene or propylene) purity. These technologies are compared in terms of capital, operating and utility costs with the conventional C2- and C3-splitters. For the ethane/ethylene separation, the membrane cascade system resulted in the highest ethylene purity. However the series configuration is more economical than the membrane cascade system. For propane/propylene separation, the top configuration outperformed the conventional C3-splitter and other HMD configurations in terms of propylene purity.

Carbon Molecular Sieves for Hydrocarbon Separations by Adsorption

The use of vacuum pressure swing adsorption (VSA-PSA) with carbon molecular sieves (CMS) as selective sorbents is evaluated as an alternative technology for methane−nitrogen and propane−propylene separations. The larger molecules, methane and propane, are very low-diffusing species, resulting in processes where nitrogen and propylene are retained in the bed. For the methane−nitrogen separation, a Skarstrom cycle (pressurization, feed, blowdown, and purge) was used with the advantage of recovering methane in the feed step with a low-pressure drop. At ambient temperature, from a mixture with 20% of nitrogen balanced by methane, a purity >93% was obtained. For the propane−propylene mixture, a five-step cycle was usedpressurization, feed, rinse, intermediate depressurization, and countercurrent blowdownwhere purified propylene is obtained as a low-pressure product. Starting with an equimolar mixture at 373 K, the purity of propylene was 83% with a product recovery of 84%.

Propane/Propene Separation by SBA-15 and π-Complexated Ag-SBA-15

Synthesis, characterization and adsorption properties of propane/propylene on mesoporous SBA-15 are reported. This material was also used as high surface area material for silver deposition to enhance propylene adsorption improving selectivity towards the olefin. Two different silver loadings were tested: Ag/SiO2 = 0.5 and Ag/SiO2 = 1.0. With the lower silver content, better selectivity and amount adsorbed was obtained. Preliminary studies were done for the use of this adsorbent in Vacuum-Pressure Swing Adsorption (VSA-PSA) units. With a four-step cycle comprising feed, pressurization, rinse and blowdown recovery of 97% propylene with chemical grade purity (91%) was obtained and also fuel grade HD-5 propane at high pressure. If higher propylene purity is required, a five-step cycle has to be used (pressurization, feed, rinse, co-current depressurization to intermediate pressure and counter-current blowdown). In this case, purity of 99% was obtained with 63% recovery.

The Real-Time Estimation of Propylene Purity Based on Principal Component Analysis and Neural Networks

Abstract Propylene purity is a very significant quality index in the operation and advanced control of propylene/propane splitter. In this paper, the principal component analysis is proposed to select the secondary variables in a soft-sensor and a propylene purity soft-sensing model is established by a BP neural network. The real-time estimation of propylene purity has been implemented in a refinery and the result shows good performance.