Abstract: A layered structure can be formed having immobilized or segregated pH buffering groups that can be used to separate carbon dioxide or other gases. The pH buffering groups can be immobilized within a matrix, confined within a gel, or segregated by a semi-permeable membrane. The pH buffering groups can be configured to increase the efficiency of the system by maintaining a desirable pH profile within the cell and to permit the flow of the carbon-containing ions within the system while controlling diffusion of protons and/or hydroxyl ions.

Abstract: A multi-stage membrane process for the removal of carbon dioxide from syngas streams containing at least about 5 volume percent carbon dioxide. The syngas is preferably obtained by the gasification of a biomass feedstock.

Abstract: A membrane for gas separation includes a porous support layer and a separation layer. The separation layer comprises a mixture of one or more saccharide derivatives and one or more homopolymers. The saccharide derivative(s) may have a cyclic structure with five or six ring atoms, or a linear structure, or may include monosaccharide derivatives which are bound via glycoside bonds, and the number of monosaccharides bound in this manner may be 2 to 1,000. A membrane can be produced by preparing a homogeneous solution which comprises a saccharide derivative and a homopolymer in a solvent; and pouring the homogenous solution onto a support layer. The membrane may be used in a gas separation module the operation of which makes use of the membrane.

Abstract: A gas separation process for treating flue gases from combustion processes, and combustion processes including such gas separation. The invention involves flowing the flue gas stream to be treated across the feed side of a membrane, flowing a sweep gas stream, usually air, across the permeate side, then passing the permeate/sweep gas to the combustor.

Abstract: A process for the production of a carbon membrane comprising: (i) reacting a mixture of cellulose and hemicellulose with an acid; (ii) casting the mixture to form a film, (iii) drying said film; and (iv) carbonizing said film.

Abstract: New ionic liquid-solid-polymer mixed matrix membranes were proposed for gas separations such as CO2 removal from natural gas or N2. For the new mixed matrix membranes, the solids such as carbon molecular sieves, microporous molecular sieves, MCM-41 type of mesoporous molecular sieves, or polymer of intrinsic microporosity (PIM) are coated (or impregnated) with ionic liquids such as 1-butyl-3-methyl imidazolium bis[trifluoromethylsulfonyl]amide. The ionic liquids coated or impregnated solids are then dispersed in the continuous polymer matrix to form mixed matrix membranes. These hybrid mixed matrix membranes will combine the properties of the continuous polymer phase, the ionic liquids, and the dispersed ionic liquids coated or impregnated solids phase, which will possibly open up new opportunities for gas separation processes such as CO2 separation from natural gas or flue gas.

Abstract: Ionic liquids can be immobilized in a membrane by, for example, bonding to a support such as a matrix, or by inclusion within a gel. Immobilized ionic liquids can be used in a number of applications, such as separation of carbon dioxide or other gases from gas streams. Membranes can be included in electrochemical cells. For example, a membrane can contain sufficient immobilized ionic liquid to reduce ionic current density of at least one of protons and hydroxyl ions, relative to carbon-containing ionic current density. A gas stream containing carbon dioxide can be introduced on a cathode side, while a source of hydrogen gas can be introduced on the anode side of the membrane. Operation of an electrochemical cell with such a membrane can separate the carbon dioxide from the gas stream and provide it at a separate outlet.

Abstract: Carbon dioxide or other gases can be separated from gas streams using ionic liquid, such as in an electrochemical cell. For example, a membrane can contain sufficient ionic liquid to reduce ionic current density of at least one of protons and hydroxyl ions, relative to carbon-containing ionic current density. A gas stream containing carbon dioxide can be introduced on a cathode side, while a source of hydrogen gas can be introduced on the anode side of the membrane. Operation of an electrochemical cell with such a membrane can separate the carbon dioxide from the gas stream and provide it at a separate outlet.

Abstract: A layered structure can be formed having immobilized or segregated pH buffering groups that can be used to separate carbon dioxide or other gases. The pH buffering groups can be immobilized within a matrix, confined within a gel, or segregated by a semi-permeable membrane. The pH buffering groups can be configured to increase the efficiency of the system by maintaining a desirable pH profile within the cell and to permit the flow of the carbon-containing ions within the system while controlling diffusion of protons and/or hydroxyl ions.

Abstract: A method for separating CO2 from a processed fluid includes exposing a film to the processed fluid and reacting the CO2 with tetrahedrally coordinated zinc hydroxide moieties contained within the film to facilitate the transport of the CO2 through the film.

Abstract: A method for producing a crystalline silicoaluminophosphate (SAPO) membrane in which a porous support is contacted with SAPO seed crystals to form a SAPO seeded porous support. The SAPO seeded porous support is filled with an aqueous SAPO synthesis gel including a mixture of sources of aluminum, phosphorus, silicon, oxygen, water, and a templating agent, forming a gel-filled porous structure which is then heated to form a SAPO layer of SAPO crystals on a surface of and/or within pores of the porous support. The SAPO layer is calcined, thereby removing the templating agent and forming a supported porous SAPO membrane layer, which is then subjected to a pore size reduction post-synthesis treatment process, producing a reduced pore size supported porous SAPO membrane layer having an average pore size of less than about 0.38 nm.

Abstract: Porous composites comprise a porous membrane having a structure defining a plurality of pores extending therethrough, nonporous discontinuous surface layer affixed to said porous membrane, in which the nonporous discontinuous surface layer forms regions of gas permeability, and regions of gas impermeability, and a coating disposed upon the porous composite which renders at least a portion of the porous composite oleophobic.

Abstract: A gas-separation membrane module assembly and a gas-separation process using the assembly. The assembly includes a set of tubes, each containing gas-separation membrane elements, arranged within a housing. The housing contains tube sheets that divide the space within the housing into three separate, gas-tight spaces, with the tubes mounted in the central space. Feed gas enters the tubes through apertures positioned to feed multiple membrane elements within a tube in parallel, and one or more manifolds are used to collect residue gas from the membrane elements and direct the gas to the residue port or to a second group of membrane elements within the tube. The assembly can be used in various ways to carry out gas separation processes.

Abstract: A porous substrate with a seed crystal-containing layer for manufacturing a zeolite membrane includes: a ceramic porous substrate, and a seed crystal-containing layer containing a zeolite powder to function as a seed crystal for forming a zeolite membrane and a ceramic powder and being loaded on a surface of the ceramic porous substrate and fired to fix the seed crystal-containing layer on the porous substrate. The porous substrate with a seed crystal-containing layer used for manufacturing a zeolite membrane inhibits a defect such as a crack from being generated in the zeolite layer upon manufacture or use by manufacturing a zeolite membrane by the use of the substrate which then can be subjected to air-spraying, washing, and processing for the purpose of removing a foreign substance, etc., prior to hydrothermal synthesis.

Abstract: A carbon dioxide permeable membrane is described. In some embodiments, the membrane includes a body having a first side and an opposite second side; a plurality of first regions formed from a molten carbonate having a temperature of about 400 degrees Celsius to about 1200 degrees Celsius, the plurality of first regions forming a portion of the body and the plurality of first regions extending from the first side of the body to the second side of the body; a plurality of second regions formed from an oxygen conductive solid oxide, the plurality of second regions combining with the plurality of first regions to form the body and the plurality of second regions extending from the first side of the body to the second side of the body; and the body is configured to allow carbon dioxide to pass from the first side to the second side.

Abstract: Methods for separating carbon dioxide from a fluid stream at a temperature higher than about 200° C. with selectivity higher than Knudsen diffusion selectivity include contacting a porous membrane with the fluid stream to preferentially transport carbon dioxide. The porous membrane includes a porous support and a continuous porous separation layer disposed on a surface of the porous support and extending between the fluid stream and the porous support layer. The porous support comprises alumina, silica, zirconia, stabilized zirconia, stainless steel, titanium, nickel-based alloys, aluminum-based alloys, zirconium-based alloys or a combination thereof.

Abstract: A membrane suitable for separating a gas, in particular carbon dioxide, from a gas mixture containing the gas is provided by a blend of polyvinyl alcohol (PVA) and polyvinylamine (PVAm).

Abstract: The invention concerns a process for the removal of gaseous acidic contaminants, especially carbon dioxide and/or hydrogen sulphide, in two or more stages from a gaseous hydrocarbonaceous feedstream (1) comprising hydrocarbons and said acidic contaminants, using one or more membranes in each separation stages. The gaseous hydrocarbonaceous feedstream is especially a natural gas stream. The process is especially suitable for feedstreams comprising very high amounts of acidic contaminants, especially carbon dioxide, e.g. more than 25 vol. %, or even more than 45 vol. %. In a first stage (2) a pure or almost pure stream of acidic contaminants is separated from the feedstream, the acidic contaminants (4) stream suitably containing less than 5 vol % of hydrocarbons. The remaining stream (3) comprises the hydrocarbons and still a certain amount of gaseous acidic contaminants.

Abstract: A CO2-facilitated transport membrane of excellent carbon dioxide permeability and CO2/H2 selectivity, which can be applied to a CO2 permeable membrane reactor, is stably provided. The CO2-facilitated transport membrane is formed such that a gel layer 1 obtained by adding cesium carbonate to a polyvinyl alcohol-polyacrylic acid copolymer gel membrane is supported by a hydrophilic porous membrane 2. More preferably, a gel layer supported by a hydrophilic porous membrane 2 is coated with hydrophilic porous membranes 3 and 4.

Abstract: A membrane for use in an implantable glucose sensor including at least one crosslinked substantially hydrophobic polymer and at least one crosslinked substantially hydrophilic polymer; wherein the first and second polymers are different polymers and substantially form an interpenetrating polymer network, semi-interpenetrating polymer network, polymer blend, or copolymer. The membranes are generally characterized by providing a permeability ratio of oxygen to glucose of about 1 to about 1000 in units of (mg/dl glucose) per (mmHg oxygen). Three methods of making membranes from hydrophobic and hydrophilic monomers formed into polymer networks are provided, wherein according to at least two of the methods, the monomers may be substantially immiscible with one another.

Abstract: A gas separation process for treating flue gases from combustion processes, and combustion processes including such gas separation. The invention involves routing a first portion of the flue gas stream to be treated to a carbon dioxide capture step, while simultaneously flowing a second portion of the flue gas across the feed side of a membrane, flowing a sweep gas stream, usually air, across the permeate side, then passing the permeate/sweep gas to the combustor.

Abstract: A method of operating a membrane separation module is provided that includes the steps of directing a feed stream comprising a first component into the membrane separation module to separate the first component by permeating it across a membrane; and introducing a second component into the feed stream such that the second component has a higher permeability through said membrane than the permeability of the first component through said membrane.

Abstract: The present invention provides modified molecular sieve membranes with improved CO2/CH4 separation selectivity and methods for making such membranes. The molecular sieve membranes are modified by adsorption of a modifying agent, such as ammonia, within and/or on the membrane.

Abstract: Disclosed is a membrane-based method and system for treatment of flue gases from an oxy-combustion coal-fired boiler to recover approximately 90% (vol/vol) to approximately 95% (vol/vol) of the carbon dioxide in the flue gas and produce a carbon dioxide product having a carbon dioxide concentration of approximately 90% (vol/vol dry basis) to approximately 97% (vol/vol dry basis).

Abstract: The present invention discloses a novel method of making high performance mixed matrix membranes (MMMs) using stabilized concentrated suspensions of solvents, uniformly dispersed polymer stabilized molecular sieves, and at least two different types of polymers as the continuous blend polymer matrix. MMMs as dense films or asymmetric flat sheet or hollow fiber membranes fabricated by the method described in the current invention exhibit significantly enhanced permeation performance for separations over the polymer membranes made from the continuous blend polymer matrix. MMMs of the present invention are suitable for a wide range of gas, vapor, and liquid separations such as alcohol/water, CO2/CH4, H2/CH4, O2/N2, CO2/N2, olefin/paraffin, iso/normal paraffins, and other light gases separations.

Abstract: A membrane and method for separating carbon dioxide from a mixture of gases, where the membrane includes expanded polytetrafluoroethylene and polysiloxane. The membrane is highly stable and can separate carbon dioxide at high flux in harsh environments and high temperatures, such as exhaust gases from power plants.

Abstract: A method and system for diagnosing the effectiveness of a treatment on a porous material. For example, the porous material can include a porous low dielectric constant material. In particular, the method can utilize FTIR spectroscopy to characterize the porosity of materials, and assess the effectiveness of sealing pores in the material.

Abstract: The present invention is for novel high performance cross-linkable and cross-linked mixed matrix membranes and the use of such membranes for separations such as for CO2/CH4, H2/CH4 and propylene/propane separations. More specifically, the invention involves the preparation of cross-linkable and cross-linked mixed matrix membranes (MMMs). The cross-linkable MMMs were prepared by incorporating microporous molecular sieves or soluble high surface area microporous polymers (PIMs) as dispersed microporous fillers into a continuous cross-linkable polymer matrix. The cross-linked MMMs were prepared by UV-cross-linking the cross-linkable MMMs containing cross-linkable polymer matrix such as BP-55 polyimide. Pure gas permeation test results demonstrated that both types of MMMs exhibited higher performance for CO2/CH4 and H2/CH4 separations than those of the corresponding cross-linkable and cross-linked pure polymer matrices.

Abstract: A system and method of purifying gaseous carbon dioxide from a gaseous mixture obtained at low pressure from a flue gas by passing the gaseous mixture through a vacuum swing adsorption unit and then a gas purification unit to produce carbon dioxide having a purity of approximately 97% by volume or more.

Abstract: The present invention discloses blend polymer membranes comprising thermally rearranged polymers derived from aromatic polyimides containing ortho-positioned functional groups and methods for making and using these blend polymer membranes. The blend polymer membranes described in the current invention are prepared by heat treatment of blend polymer membranes comprising aromatic polyimides containing ortho-positioned functional groups such as —OH or —SH groups. In some instances, an additional crosslinking step is performed to improve the selectivity of the membrane. These blend polymer membranes have improved flexibility, reduced cost, improved processability, and enhanced selectivity and/or permeability compared to the comparable polymer membranes that comprise a single polymer.

Abstract: The present invention discloses a new type of high performance polymer membranes derived from aromatic polyimide membranes and methods for making and using these membranes. The polymer membranes described in the present invention were derived from aromatic polyimide membranes by crosslinking followed by thermal treating. The aromatic polyimide membranes were made from aromatic polyimide polymers comprising both pendent hydroxy functional groups ortho to the heterocyclic imide nitrogen and cross-linkable functional groups in the polymer backbone. The high performance polymer membranes showed significantly improved permeability for gas separations compared to the aromatic polyimide membranes without any treatment. The high performance polymer membranes also showed significantly improved selectivity for gas separations compared to the thermal-treated but non-UV-crosslinked aromatic polyimide membranes.

Abstract: A gas separation process for treating flue gases from combustion processes, and combustion processes including such gas separation. The invention involves flowing the flue gas stream to be treated across the feed side of a membrane, flowing a sweep gas stream, usually air, across the permeate side, then passing the permeate/sweep gas to the combustor.

Abstract: In order to synthesize semi-interpenetrating polymer networks (semi-IPNs) with molecular sieve characteristics, polyetherimide/bismaleimide (PEI/BMI) chromophore composites were made through sol-gel technique. A tunable and compatible chemical structure with fine morphology was obtained through in situ controlled sol-gel polymerization, crosslinking, chemical modification and membrane fabrication. The novel semi-IPN, synthesized and assembled by using ethanol as polar protic modifier and pore former, had a superior structure and morphology suitable for making gas separation membranes. These semi-IPN membranes gave fifteen times higher gas flux without significant decrease in their gas permselectivity than membranes prepared from pure PEL The chemical structures of these novel semi-IPNs were characterized by using FTIR, XPS and SEM.

Abstract: Disclosed is an improved method for the remineralization of process water in a desalination system. The method sequesters carbon dioxide gas (CO2) from seawater or concentrate (brine) of desalination process via a gas transfer membrane. The sequestered carbon dioxide gas (CO2) is thereafter used in the production of soluble calcium bicarbonate (Ca(HCO3)2). The calcium bicarbonate (Ca(HCO3)2) adds hardness and alkalinity to the resulting process water.

Abstract: A device for removal of at least a portion of carbon dioxide from an aqueous fluid includes at least one membrane through which carbon dioxide can pass to be removed from the fluid and immobilized carbonic anhydrase on or in the vicinity of a first surface of the membrane to be contacted with the fluid such that the immobilized carbonic anhydrase comes into contact with the fluid. The first surface exhibits carbonic anhydrase activity of at least 20% of maximum theoretical activity of the first surface of the membrane based on monolayer surface coverage of carbonic anhydrase in the case that the carbonic anhydrase is immobilize on the first surface.

Abstract: A gas-separation membrane assembly, and a gas-separation process using the assembly. The assembly incorporates multiple gas-separation membranes in an array within a single vessel or housing, and is equipped with two permeate ports, enabling permeate gas to be withdrawn from both ends of the membrane module permeate pipes.

Abstract: An air conditioning system comprising a gas-impermeable wall defining a space for air conditioning, and a selective separating member disposed in the wall as a part of the wall, having a function of allowing preferential permeation of oxygen and carbon dioxide and at the same time, blocking the permeation of hydrocarbon, nitrogen oxide, sulfur oxide and a fine solid component, in which the selective separating member comprises an organic polymer and satisfies the relationship of P1/P2>10 wherein P1 is the permeation coefficient of oxygen and carbon dioxide and P2 is the permeation coefficient of hydrocarbon, nitrogen oxide, sulfur oxide and a fine solid component.

Abstract: A process for the production of a carbon membrane comprising: (i) reacting a mixture of cellulose and hemicellulose with an acid; (ii) casting the mixture to form a film, (iii) drying said film; and (iv) carbonising said film.

Abstract: In the present invention high performance cross-linked polybenzoxazole and polybenzothiazole polymer membranes and methods for making and using these membranes have been developed. The cross-linked polybenzoxazole and polybenzothiazole polymer membranes are prepared by: 1) first synthesizing polyimide polymers comprising pendent functional groups (e.g., —OH or —SH) ortho to the heterocyclic imide nitrogen and cross-linkable functional groups in the polymer backbone; 2) fabricating polyimide membranes from these polymers; 3) converting the polyimide membranes to polybenzoxazole or polybenzothiazole membranes by heating under inert atmosphere such as nitrogen or vacuum; and 4) finally converting the membranes to high performance cross-linked polybenzoxazole or polybenzothiazole membranes by a crosslinking treatment, preferably UV radiation. The membranes can be fabricated into any convenient geometry.

Abstract: The present invention discloses a new type of high performance polymer membranes prepared from aromatic polyimide membranes by thermal treating and crosslinking and methods for making and using these membranes. The polymer membranes were prepared from aromatic polyimide membranes by thermal treating under inert atmosphere followed by crosslinking preferably by using a UV radiation source. The aromatic polyimide membranes were made from aromatic polyimide polymers comprising both pendent hydroxy functional groups ortho to the heterocyclic imide nitrogen and cross-linkable functional groups in the polymer backbone. The membranes showed significantly improved selectivity and permeability for gas separations compared to the aromatic polyimide membranes without any treatment. The membranes can be fabricated into any convenient geometry and are not only suitable for a variety of liquid, gas, and vapor separations, but also can be used for other applications such as for catalysis and fuel cell applications.

Abstract: A carbon dioxide separation system for a fuel cell system having a small volume and weight of a separation device and of a membrane, at simultaneous increase of the separated volume of carbon dioxide, comprises a separation device for containing a fluid phase, a carbon dioxide phase, and a two phase fluid including fluid and carbon dioxide. The separation device comprises a two phase fluid inlet, a fluid outlet, a carbon dioxide outlet, a carbon dioxide separation membrane, and a flow restrictor creating a backpressure which presses separated carbon dioxide through the carbon dioxide separation membrane. The flow restrictor comprises at least one narrow aperture, and is mounted downstream of the separation device. The carbon dioxide separation membrane is positioned in the separation device in such a manner that at least a part of the total membrane area is arranged above a two phase fluid level and is in touch with carbon dioxide contained in the separation device above the two phase fluid level.

Abstract: A method and apparatus for extracting CO2 from air comprising an anion exchange material formed in a matrix exposed to a flow of the air, and for delivering that extracted CO2 to controlled environments. The present invention contemplates the extraction of CO2 from air using conventional extraction methods or by using one of the extraction methods disclosed; e.g., humidity swing or electro dialysis. The present invention also provides delivery of the CO2 to greenhouses where increased levels of CO2 will improve conditions for growth. Alternatively, the CO2 is fed to an algae culture.

Abstract: A method and apparatus for extracting CO2 from air comprising an anion exchange material formed in a matrix exposed to a flow of the air, and for delivering that extracted CO2 to controlled environments. The present invention contemplates the extraction of CO2 from air using conventional extraction methods or by using one of the extraction methods disclosed; e.g., humidity swing or electro dialysis. The present invention also provides delivery of the CO2 to greenhouses where increased levels of CO2 will improve conditions for growth. Alternatively, the CO2 is fed to an algae culture.

Abstract: Ozone resistant O2/N2 gas separation membranes comprise a polymer membrane and an ozone reacting component, such as an antioxidant. The antioxidant may be included in the support layer of a composite membrane or included in the entire structure of an asymmetric membrane. The antioxidants in the separation membrane reduce oxidation and deterioration of the actual separation layer of the membrane.

Abstract: The present invention discloses mixed matrix membranes (MMMs) comprising ion-exchanged molecular sieves such as UZM-5 zeolite ion-exchanged with Li+ cation (Li-UZM-5) and a continuous polymer matrix and methods for making and using these membranes. These MMMs, comprising ion-exchanged molecular sieves, in the form of symmetric dense films, asymmetric flat sheets, asymmetric hollow fibers, or thin-film composites, have exhibited simultaneously increased selectivity and permeability (or permeance) over polymer-only membranes and the mixed matrix membranes made from molecular sieves that have not been ion exchanged for gas separations. These MMMs are suitable for a variety of liquid, gas, and vapor separations such as desalination of water by reverse osmosis, deep desulfurization of gasoline and diesel fuels, ethanol/water separations, pervaporation dehydration of aqueous/organic mixtures, CO2/CH4, CO2/N2, H2/CH4, O2/N2, olefin/paraffin, iso/normal paraffins separations, and other light gas mixture separations.

Abstract: An apparatus for producing hydrogen gas wherein the apparatus includes a reactor. In one embodiment, the reactor includes at least two conversion-removal portions. Each conversion-removal portion comprises a catalyst section configured to convert CO in the stream to CO2 and a membrane section located downstream of and in flow communication with the catalyst section. The membrane section is configured to selectively remove the CO2 from the stream and to be in flow communication with a sweep gas.

Abstract: A layered structure can be formed having immobilized or segregated pH buffering groups that can be used to separate carbon dioxide or other gases. The pH buffering groups can be immobilized within a matrix, confined within a gel, or segregated by a semi-permeable membrane. The pH buffering groups can be configured to increase the efficiency of the system by maintaining a desirable pH profile within the cell and to permit the flow of the carbon-containing ions within the system while controlling diffusion of protons and/or hydroxyl ions.

Abstract: Metal-organic framework (MOF)-polymer mixed matrix membranes (MOF-MMMs) have been prepared by dispersing high surface area MOFs (e.g. IRMOF-1) into a polymer matrix (e.g. Matrimid 5218). The MOFs allow the polymer to infiltrate the pores of the MOFs, which improves the interfacial and mechanical properties of the polymer and in turn affects permeability. Pure gas permeation tests show the incorporation of 20 wt-% of IRMOF-1 in Matrimid 5218 polyimide matrix results in 280% improvement in CO2 permeability without a loss of CO2/CH4 selectivity compared to those of the pure Matrimid 5218 membrane. This type of MOF-MMMs has significantly improved gas separation performance with dramatically high CO2 permeability (>35 barrer) and higher than 29 CO2/CH4 selectivity at 50° C. under 100 psig pressure, which are attractive candidates for practical gas separation applications such as CO2 removal from natural gas.

Abstract: Increasing the economic and environmental compatibility in treatment processes in sour gas production. For 25 yr, Mobil Erdgas Erdoel GmbH (MEEG) has been treating considerable amounts of sour gas in N. Germany. In 9 fields with different gas qualities, there are ca 30 producing wells. The main processes of the sour gas production and treatment are described. The gas is dried at the well site and if the reservoir pressure is not sufficient, compressed for transportation to the central processing facility. In most cases the use of sulfur solvents is necessary at the wells. Natural gas scrubbers for the total removal of hydrogen sulfide and Claus units with downstream units to obtain sulfur are utilized. To increase the environmental compatibility and economics, a number of secondary processes have been introduced for emission control; glycol stripping; and the Purisol, Selexol, Sulfinol, and Claus processes.

Abstract: Carbon dioxide is separated from a gas stream using a supported carrier liquid membrane having a selected concentration of carrier species, the method being especially suitable for use in anaesthesia under conditions of periodic flow.