Propylene Recovery Research Articles

Improving the mass transfer rate in G–L membrane contactors with ionic liquids as absorption medium. Recovery of propylene

The use of membrane contactors for the G–L separation of olefins by means of reactive absorption with ionic liquid silver complexes presents a great potential to intensify the conventional separation process based on cryogenic distillation. Nevertheless, the key issue to be addressed is the high mass transfer resistance offered by the ionic liquid that flows through the shell side of the membrane contactor. It is therefore crucial to improve the fluid dynamics of the system in order to enhance the mass transfer rate in the liquid film. This work reports the analysis of the performance of a gas–liquid transverse flow membrane contactor applied to the reactive absorption of propylene in BMImBF 4–Ag + as reaction media. First the mass transfer phenomena developed in the system in the absence of chemical reactions were assessed; several experiments were carried out at 293 K flowing pure BMImBF 4 at flow rates between 6.42 × 10 −6 m 3 s −1 and 1.19 × 10 −5 m 3 s −1 with propylene as fed gas. Under the operational conditions used in this work, the resistances across the gas film and the microporous membrane are negligible so the overall mass transfer resistance is controlled by the diffusional resistance in the liquid boundary layer. The experimental data were fitted to an empirical correlation, Sh = 1.1 · Re 0.32 Sc 0.33, that allows to calculate the mass transfer rate in the ionic liquid flowing through the shell side of the module at low Reynolds numbers. Moreover it was observed that for the BMImBF 4 flowing at 6.42 × 10 −6 m 3 s −1 and 293 K the improved fluid-dynamics of the transverse flow membrane contactor leads to an overall mass transfer coefficient 17.6 times higher than that reported previously using a parallel-flow contactor. Furthermore, a detailed mathematical model was developed in order to predict and analyze the performance of the system under different operational conditions. This model was applied to simulate the performance of the system under the presence of silver ions in the reaction medium. The reactive absorption of propylene using ionic liquids–silver complexes in the transverse flow membrane contactor has provided promising results, showing a process intensification by a factor of 17.4 in terms of mass transfer per specific area compared to a conventional stirred tank reactor system ( K overall × a(MC)/ K overall × a(CSTR)).

The Study on Effects of Membrane Separation on Compression/Condensation/Membrane Process for Propylene Recovery

Membrane property decay has great effects on propylene yields when compression/condensation/membrane process is applied to recover propylene monomer. There are four types of membrane property decays. The first case is that selectivity keeping constant but membrane flux decreasing, the second case is that selectivity reducing but membrane flux unchanged, the third case is that selectivity reducing but membrane flux increasing, and the last case is that both of them all decreasing. One purpose of this paper is to judge which kind of decay leads to the separation deterioration according to the change of some parameters in the process by simulation. In order to meet target requirement, two operation parameters, membrane pressure and condensation temperature, are regulated. Results indicate that propylene yields decrease when any type of membrane property decay emerges, and the type of membrane property decay can be distinguished by the change trend of propylene yields, the variation of recycle permeate gas flow as well as propylene concentrations in permeate gas. What’s more, membrane pressure is a prior operation parameter to be regulated so as to counteract the effect of membrane property decay to some extent.

FCC Process Role in Propylene Demands

It is widely recognized that naphtha steam crackers are the largest current source of propylene. The yield of propylene from a naphtha cracker is approximately half the yield of ethylene because ethylene has historically averaged a higher market price than propylene. Ethylene producers have primary built naphtha crackers to meet their ethylene demands and recovered propylene as a by-product. The availability of ethane at standard gas prices has attracted a large buildup of ethane-based steam cracker capacity, which produces very little propylene. As a result of buildup of ethane-based crackers, the propylene production rate from steam crackers is anticipated to fall, though the demand for propylene is expected to increase relative to the demand for ethylene. These market dynamics, if proven true, will result is a growing gap between propylene demands and propylene supplied from steam crackers, placing more emphasis and creating more opportunity for fluid catalytic cracking unit (FCC) units. The second largest source of propylene supplied for petrochemical application is from FCC units. The primary function of FCC units has typically been to produce gasoline. However, refiners have been taking advantage of the opportunity to produce and recover more propylene from FCC units by increasing the reaction severity via riser temperature, adding shape-selective catalyst, and installing propylene recovery units (PRUs). In this article propylene production methods are reviewed and comparisons between the methods are made.

Performance Assessment by Simulation of a Gas-Recycle Oxosynthesis Plant with Propylene Recovery

A simulation study of a C4 oxosynthesis plant (gas recycle technology) was performed by using the software package Hysys. The process thermodynamics was described by UNIQUAC property model. An important drawback of this technology is a significant loss of propylene by the purge gas stream. Computer simulations were carried out to evaluate the technical performance and the investment cost of a proposed revamping scheme, allowing an advanced propylene recovery from purge gases. The cost evaluations performed with Aspen Economic Evaluation are indicating that the revamping investment cost is equivalent to the propylene savings during a three years plant running period.

Simulation and energy consumption analysis of a propane plus recovery plant from natural gas

This paper deals with the investigation of a cryogenic plant for the recovery of propane plus compounds from natural gas. The commercially available software ASPEN Plus® has been used to simulate the process, and to investigate the effect of the main operating variables on the efficiency of propane plus recovery and on the energy required by the various pieces of equipment of the plant. With respect to the base case considered, the optimized plant allows to reduce the heat required up to 25%; besides, the refrigeration required can be reduced up to 60%, without significantly affecting the propane plus recovery.

Vacuum Pressure Swing Adsorption to Produce Polymer-Grade Propylene

We have evaluated the Vacuum Pressure Swing Adsorption (VPSA) technology to separate propane–propylene streams to produce polymer-grade propylene. Zeolite 4A is used as kinetic adsorbent since propylene diffuses much faster than propane. A single VPSA process is able to produce propylene with purity higher than 99.6%. However, propylene recovery is only 67% and therefore a second stage is used. In this VPSA unit, zeolite 4A with smaller crystal radius is employed to reduce kinetic limitations. The second VPSA (tail unit) produces purified propane and recovers propylene that is recycled to the feed of the first VPSA (front unit). Linking these two VPSA units allows us to produce polymer-grade propylene (PGP) recovering 95.9% of the propylene. Comparing the performance of this process with distillation, there is a significant decrease in the separation volume. However, further efforts are necessary to reduce the power consumption of VPSA which is still slightly higher than for distillation.

PDMS–silica composite membranes with silane coupling for propylene separation

Polydimethylsiloxane (PDMS) coated membranes on a polysulfone (PSf) support were fabricated for propylene recovery from off-gas stream. PDMS coated membrane, however, showed trade-off trends that permeability and selectivity are inversely proportional to each other. Addition of silica nanoparticles of 12–400 nm size into PDMS matrix enhanced both separation factor and propylene permeance from 5.2 to 7.3 from 31 to 36 GPU, respectively. Silica nanoparticles in composite membrane tended to agglomerate with each other. Coupling of silica nanoparticles with a silane coupling agent modified the silica surface to enhance the compatibility with PDMS. Several coupling agents for silica nanoparticles in the PDMS/organic solvent system were tested and mercapto silane showed the best characteristics as a coupling agent in terms of hydrophobicity and thermal stability. Successful coupling was confirmed by FT-IR, and better dispersion of coupled silica nanoparticles in PDMS matrix was attained. Composite membrane with coupled silica nanoparticles still enhanced separation factor up to 8.5 and propylene permeance up to 42 GPU. Effects of size and amount of the silica nanoparticles were examined by comparing fumed silica and sol–gel silica. Fumed silica enhanced the sorption of propylene into membrane matrix to increase the separation factor maintaining the propylene permeance. Sol–gel silica disrupted chain packing to increase the propylene permeance maintaining the selectivity. Increase of silica content enhanced the separation factor as well as propylene permeance. However, excessive silica loading in PDMS solution caused problems in coating process, and optimum silica nanoparticle content was 15 wt%. This work showed the novelty in preparation of organic–inorganic composite membranes with enhanced permeance and selectivity by properly coupling the silica particles before loading.

Corrosion in Propane Deasphalting Unit in a Lube Producing Refinery: A Case Study

Propane deasphalting is a process of recovery of hydrocarbon distillates from vacuum residue by extracting with liquid propane. A plated tower is used to carry out extraction where extract containing the deasphalted oil and raffinate containing the asphalt are separated. Extract and raffinates are then subject to propane recovery sections wherefrom propane is recovered and reused in extraction. Complete recovery of propane from deasphalted oil is carried out by flashing alone, but recovery from asphalt requires heating in a furnace followed by flashing. Severe corrosion has been observed in the propane condensers, coolers, and the overhead lines of the flashers and stripper columns. Studies have indicated that cracking of asphalt at the prevailing operating temperature and pressure, generating hydrogen sulfide, was the sole reason for corrosion. The problem has been minimized by adjusting the temperature and pressure without affecting the propane recovery efficiency.

SEPARATION OF PROPANE FROM PROPANE/NITROGEN MIXTURES USING PDMS COMPOSITE MEMBRANES BY VAPOUR PERMEATION

This study deals with polydimethylsiloxane (PDMS)/polyvinylidene fluoride (PVDF) composite membranes for propane separation from propane/nitrogen mixtures, which is relevant to the recovery of propane in petroleum and chemical industry. The surface and cross-section morphology of PDMS/PVDF composite membranes was observed by scanning electron microscope (SEM). The surface morphology of PDMS/PVDF composite membranes is very dense. There are three layers, the thin dense top layer, finger-like porous middle layer and sponge-like under layer in the cross-section SEM image of PDMS/PVDF composite membranes. The effects of the types of cross-linking agents and pressure on the membrane permselectivity were investigated. The permeability of nitrogen was independent of feed pressure. However, the permeability of propane increased with the pressure increasing for all membranes. The membrane cured by a tri-functional crosslinker with attached vinyl groups had better performance than the tetra-functional one, in both ...

Modelling and process development for gaseous separation with silicone‐coated polymeric membranes

AbstractThis paper proposes a permeance equation for vapour–permanent gas mixtures in a silicone‐coated polymeric membrane. The equation was derived from the Arrhenius relationship by combining an apparent activation energy and interaction parameter. Accurate values of transmembrane flux were obtained by incorporating this proposed equation, which was dependent on temperature and feed composition. The equation parameters were correlated with the experimental data of eight mixtures consisting of hydrocarbons such as ethylene, ethane, propylene and propane with nitrogen covering a broad range of temperature and concentration. A numerical integration scheme was used for developing a crossflow model utilizing the above equation, which allowed the estimation of product properties including the membrane plasticization cases. The study also reports examples of implementation of this approach in potential industrial applications for the recovery of ethylene and propylene from nitrogen.

Propylene separation from nitrogen by poly(ether block amide) composite membranes

This study deals with poly(ether block amide) (PEBA) composite membranes for propylene separation from nitrogen, which is relevant to the recovery of propylene from the degassing off gas during polypropylene manufacturing. The composite membranes, comprising of a thin layer of PEBA 2533 supported on microporous polysulfone substrate, were initially studied for pure gas permeation to evaluate the effects of pressure and temperature on the membrane permeance, and then they were investigated for the permeation of propylene/nitrogen mixture. It was found that the propylene permeance was affected by the presence of nitrogen, and vice versa, due to interactions between the permeating components. For the separation of propylene/nitrogen gas mixtures, both the permeance of propylene and the propylene/nitrogen selectivity were lower than those based on pure gas permeation. Semi-empirical correlations were developed to relate the permeance of a component in the mixture to the pressures and compositions of the gas on both sides of the membrane, and the performance of the membrane for propylene/nitrogen mixture separation at different operating conditions (e.g., temperature, pressure and feed composition) was analyzed in terms of product purity, recovery and productivity on the basis of cross flow model. Although the model calculations represented a conservative estimate on the separation performance, the results showed that the poly(ether block amide)/polysulfone composite membranes were promising for the separation of propylene from nitrogen.

Propane/Propylene Separation by Pressure Swing Adsorption Using Zeolite 4A

In this work we have studied Pressure Swing Adsorption (PSA) process for separation of propane/propylene mixtures using zeolite 4A extrudates (CECA) as an alternative to distillation. Purified propylene is withdrawn in the blowdown step at 10 kPa because is the most adsorbed compound. The cycle used comprises five steps: pressurization, feed, purge with product, depressurization to intermediate pressure and counter-current blowdown for propylene recovery. Two mixtures with different propylene/propane ratios (54−46 and 85−15 diluted to 50% with nitrogen) corresponding to different sources of propylene production (steam cracking and Fluid Catalytic Cracking) were studied. The effects of the different step times in the performance of the PSA unit were evaluated. PSA performance was also studied using different operating conditions: process temperature and feed pressure. Also, the removal of inert from the process was studied. The simulation of the PSA unit was performed in gPROMS using a bi-LDF approximati...

Propylene Recovery from Propylene/Propane/Nitrogen Mixture by PSA Process

This study is on the process performance (purity, recovery and productivity) of a four-bed bench-scale PSA unit [1000 mm (L) × 25 mm (ID) × 4 beds], with which is applied to enrich propylene from propylene/propane/nitrogen gas mixture (35 mol% propylene, 15 mol% propane, 50 mol% nitrogen). Adsorbent, i.e. AgNO3 impregnated on silica substrate, was prepared and loaded in the above PSA unit. The unit was operated at the pressure of 25–870 mmHg and at the temperature of 10–70∘C. By a four-bed PSA process at 50∘C, the propylene product purity and recovery were 91.9 mol% (7.0 mol% propane, 1.1 mol% nitrogen) and 86.5%, respectively. More than 99% of nitrogen was removed from the feed. The propylene productivity by the process was 0.89 mol/(kg ⋅ hr).

Continuous process for propylene/propane separation by use of silver nitrate carrier and zirconia porous membrane

A continuous isothermal separation process was developed for components of olefin/paraffin mixtures. This process features a combination of two steps: absorption of olefin by silver ion in an aqueous solution at high pressure and isothermal regeneration of the absorbing solution using a ceramic membrane. The process takes advantage of: (1) the specific and reversible interaction between silver ions and olefin molecules; and (2) pressure drop across a ceramic membrane. Silver ions act as a carrier for olefin transport through the porous membrane. The zirconium oxide membrane serves as a depressurizing device for the olefin containing silver nitrate solution, allowing olefin to be released at the low pressure side of the membrane. Silver nitrate solution is recycled to the absorption chamber. Process performance was experimentally evaluated using propylene/propane mixtures in a bench-scale system. The experimental results are: propylene production rates as high as 3.4 cm 3(STP)/(cm 2 min) and a stable continuous separation process with silver utilization efficiency as high as 60% and propylene recovery ratio as high as 80%. This process has features that circumvent previous shortcomings of the pressure-swing adsorption/desorption process for olefin separation.

Recovery of propylene from refinery off-gas using metal incorporated ethylcellulose membranes

Performance of certain modified ethylcellulose (EC) membranes was investigated for the recovery of propylene from a gas mixture, having the same composition as the absorber tail gas (ATG) of a fluid catalytic cracking unit of HPCL refinery, Vishakhapatnam. The mixture contains C 1–C 5 hydrocarbons and non-hydrocarbons such as CO, CO 2, H 2 and N 2. Various metals such as silver, ruthenium, palladium and iridium were incorporated into EC membranes to modify the membrane permeation properties for selectively increasing the propylene flux by facilitating its transport. Ethylcellulose membranes appeared to have good potential for the commercial recovery of propylene from a hydrocarbon rich off-gas mixture containing the olefin as a major constituent. A reasonably high selectivity of 5.1 accompanied by high transport rates was obtained for propylene with respect to propane in the multicomponent mixture. Amongst the metal-incorporated membranes, the best results were obtained with a silver (5 wt.%)-EC membrane which yielded a permeate stream of around 65 mol% propylene. The permeation of the various other hydrocarbon components present in the ATG mixture through the metal incorporated EC membranes was also analyzed. Interaction of the metal ions with the membrane matrix has been explained by characterizing the films with the help of FTIR, WAXD and SEM–EDX techniques.

Automatic Design and Optimization of Natural Gas Plants

A strategy for process configuration design and debottlenecking of natural gas processing plants based on turboexpansion is presented. The approach combines a rigorous process simulation model and a mixed-integer nonlinear programming (MINLP) optimization methodology that embeds different expansion alternatives within a superstructure. A wide range of natural gas mixtures with 6−25% of condensable components is studied in order to determine optimal plant topology and operating parameters under different process conditions. Inlet feed gases with varying CO2 content are also analyzed to evaluate the impact on plant design and operation. Special attention is devoted to an actual gas mixture, currently processed in a large-scale ethane plant in operation. Different turboexpansion configuration designs are further analyzed to explore the possibility of operating in propane recovery mode.

Facilitated Transport Membrane Hybrid Systems for Olefin Purification

Abstract A new membrane system has been developed by BP for refinery and chemical plant olefin purification and recovery. This facilitated transport system, coupled with distillation, offers lower capital and operating costs than conventional distillation alone. Initial results on lab scale hollow fiber devices indicate membrane flux ranging from 8.75×10−6 to 8×10−5 m3/m2/sec (2.5 to 23 scfd/ft2) and selectivities from 150 to 300. Pilot plant experiments on propylene/propane and ethylene purge gas recovery over three to six months duration show membrane stability and product purity of 98.5% or greater using refinery grade propylene feed. Hybrid system optimization data for membranes and distillation indicate that using a side draw from the distillation tower provides advantages in terms of membrane area, purity of feed to the membrane, and low per-pass recovery coupled with high overall propylene recovery. Membrane performance data under various conditions will also be presented. In addition to performance data, economic evaluation and energy savings will be discussed.

Molecular Sieve Sweetening of Propane And Butane

Molecular sieves have been used successfully in sour-gas processing plants in Alberta to sweeten propane and butane products even when plants in Alberta to sweeten propane and butane products even when H2S and COS are present in the feed streams. A system of handling regeneration gas has been devised that minimizes the attention required of the operator and that eliminates pollution problems. Location and Size of Plants Gulf Oil Canada operates seven major gas plants in Alberta, Canada. Three of the plants located at Pincher Creek, Nevis, and Rimbey are sour-gas Pincher Creek, Nevis, and Rimbey are sour-gas plants that yield propane and butane products in plants that yield propane and butane products in addition to sales gas, sulfur, and condensate. Rimbey processes 423 MMcf/D, recovering 8,000 B/D of propane and 5,500 B/D of butanes; Nevis processes propane and 5,500 B/D of butanes; Nevis processes 76 MMcf/D, recovering 1,235 B/D of propane and 788 B/D of butanes; and Pincher Creek processes 100 MMcf /D, recovering 1,050 B/D of propane and 955 B/D of butanes. Gulf Canada's experience with molecular sieve sweetening of propane and butane has been gained over a total of 11 years' operation at the three plants. (Molecular sieve is a granular dry desiccant material manufactured from zeolites to trap particular molecules such as H2S, COS, and mercaptan sulfins, and allow other molecules such as paraffin hydrocarbons to pass through the bed.) Our decision to replace the regenerative caustic sweetening system with the molecular sieve system (Fig. 1) was prompted by common problems related to vapors from regeneration of the caustic system, as well as by pollution, operating, and maintenance problems resulting from disposal of the spent caustic. problems resulting from disposal of the spent caustic. The Rimbey plant, where process gas contains about 1 1/2 percent hydrogen sulfide, was the first to be changed from the regenerative caustic system to the mol sieve system. This was in 1964 when deep cut facilities were installed to increase propane recovery. In 1968, after 4 years of successful operation at Rimbey, a molecular sieve was installed at the Nevis plant, and in 1970 one was installed at the Pincher Creek plant. Sampling and Analysis Method At the Nevis plant, for design purposes, considerable time and money were spent on stream sampling to achieve repeatability of results of tests for carbonyl sulfide (COS), methyl mercaptan, and ethyl mercaptan. At that time there were no local laboratory facilities capable of this analysis, so samples had to be shipped about 2,000 miles to Gulf Canada's Research and Development Center near Toronto, and to the mol sieve manufacturer's laboratory in New York State. Analyses from the two laboratories showed variations in sulfur levels; these we subsequently attributed to reaction with the sample container during the shipping periods, which were sometimes as long as 3 weeks. By sending the containers by air, thus minimizing the reaction time, we were able to improve repeatability. The Gulf Canada Sheridan Park Laboratory used a microcoulometric detector for the mercaptans and COS, and also developed a portable absorption-potentiometric system for on-site analysis of sulfur components. First, the sampling apparatus was connected to the inlet of the mol sieve to determine the level of sulfur compounds entering the bed. Next, the unit was connected to the outlet of the mol sieve to determine the level of remaining sulfur compounds in the product that was leaving. P. 540

The Application of an Electronic Computer to the Calculation of the Recovery of Natural Gasoline by Refrigeration

Abstract A study of the recovery of natural gasoline from natural gas by refrigeration was made with the aid of an IBM 650 computer. A form of the familiar "flash" equation, chosen to minimize calculation time, was employed to determine the natural gasoline recovery. An eight-component system can be solved in about 30 seconds for each pressure and temperature combination. The ranges of the variables studied aregasoline content (isobutane and heavier) of the wet gas, 0.891 to 3.293 gal/Mcf,pressure, 50 psia to 1,000 psia, andtemperature, −20 degrees F to +40 degrees F. For the gases considered the gasoline content of the discharge gas decreases more or less linearly with pressure to about 300 psia and then levels off. For all but the leanest gas, the gasoline content of the discharge gas can be reduced to 0.45 gal/Mcf at 400 psia and 0 degrees F. Under certain conditions of pressure and temperature the gasoline content can be reduced to as low as 0.25 gal/Mcf. In this case a large penalty is paid in the excessive recovery of propane and lighter in the liquid, The extraction efficiency is often a more satisfactory measure of the utility of the process than is the gasoline content of the discharge gas. The extraction efficiency increases more or less linearly to about 300 psia and then levels out beyond 600 psia. For all but the leanest wet-gas the isobutane and heavier extraction efficiency exceed 70 per cent at 400 psia and 0 degrees F. Under certain conditions the efficiency may exceed 90 per cent. At a given pressure and temperature, the richer the wet gas, the higher is the extraction efficiency. Introduction The recovery of natural gasoline from natural gas by refrigeration is a special field processing method. A study was made to establish the area of application of the method. The first step was to determine the ultimate physical recovery of liquid product, and the second step, to determine the economic recovery of liquid product. This paper will deal only with the first step. It describes in some detail the program for solving the flash equation with the aid of the IBM 650 computer and reports the calculated results. A somewhat similar study has been reported by Stamm, McCarty, Allen and Moore, but for a more limited range of wet-gas compositions and operating conditions.