Patent Application: US-23707208-A

Abstract:
the present invention discloses a device , which uses membranes , capable of separating olefins from paraffins . the device considers an ultramicroporous ceramic membrane module , zeolite or silicate based , containing a fixed carrier of copper i or silver ions inserted by ion exchange , or as a monolayer of cucl , agno 3 , cu or ag + . olefins have higher diffusivity and affinity to the membrane than the remaining species , therefore the bicomponent permeation selectivity becomes reinforced when compared to the ideal permeation selectivity . the purification of olefins by removal of dienes and / or alkynes , is accomplished with a zeolite membrane functionalized with ag + and having a specific catalyst in the permeate side , e . g . palladium nanoparticulated , for catalyzing the hydrogenation of the permeating dienes and alkynes to the corresponding olefins , thus increasing the selectivity and the driving force of the separation .

Description:
functionalized microporous ceramic membranes have a higher selectivity when compared to the corresponding functionalized ceramic adsorbents . indeed , the olefins show higher adsorption affinity and diffusivity when compared to the corresponding paraffins in the functionalized ceramic matrix . as the permeability of a membrane is the product between the adsorption and diffusivity , the ideal selectivity of a membrane is higher than the corresponding adsorption selectivity . furthermore , it can be experimentally observed that the real selectivity of a membrane ( the ratio between the bicomponent permeabilities ) is higher than the ideal selectivity ( obtained from the ratio between the monocomponent permeabilities ), when the permeating species present both higher adsorption affinity and higher diffusivity [ 5 ]. taking this into consideration , it is advantageous to separate the olefins from the paraffins using a membrane process than the corresponding adsorption one . the ceramic membrane precursors here described are the same as the ones presently used for synthesizing adsorbents for the olefin / paraffin separations . silicates can be used for synthesizing microporous membrane coated with a silver nitrate monolayer [ 2 ]. the membranes should be supported and can be tubular or flat . one of the most convenient supports is the alumina . type y zeolite membranes , exchanged with ag + or cu + have to be used for purifying the propylene by removing allene and propyne , and for the purification of ethylene by removing ethyne , once this material shows a high adsorption affinity towards these impurities [ 2 ]. as previously mentioned , the performance of these membranes can be largely improved if at the permeate side the impurities concentration becomes very low [ 2 ]. this can be attained by selectively hydrogenating the impurities to the corresponding olefins . the present invention also discloses the use of a specific catalyst for hydrogenating the mentioned impurities , such as palladium or platinum nanoclusters and located at the permeate side of the zeolite membrane . in this case , the zeolite membrane works as a catalytic membrane reactor functionalized with a facilitate carrier . the propylene stream containing small amounts of impurities of allene and propyne , for example , should be fed at a pressure between 0 . 2 and 1 . 6 mpa to a zeolite membrane functionalized with ag + or cu + and containing palladium nanoparticles at the permeate side . to the permeate side an hydrogen stream should be fed in counter - current at a pressure between 5 and 100 kpa , a temperature between 0 and 60 ° c . and a hydrogen flowrate slightly above the stoichiometric one . the impurities that selectively permeate the membrane , make contact with the catalyst at the permeate side and , with the presence of hydrogen , they originate the corresponding olefins . the hydrogen should be fed at a flowrate slightly above the stoichiometric value . the permeate pressure should be in the range of hundreds of pa while the retentate pressure should be the highest possible , ranging between deci - mpa to mpa . this configuration allows a significant reduction in the partial pressure of these impurities at the permeate side , therefore increasing the membrane selectivity [ 31 ], and decreasing the pressure driving force necessary for the separation . the fact that , it joins the chemical reaction to a membrane separation unit aiming the increase of the separation selectivity and the decrease of the driving force necessary to the separation is innovative and is one of the key disclosures of the present invention . this example illustrates the use of the present invention for the separation of olefins from paraffins originated from an alkylation unit with sulfuric acid as catalyst [ 13 ]. the referred stream is fed at a normal flowrate of 100 l min − 1 and containing 5 % of propane ( c 3 h 8 ), 27 % of isobutane ( c 4 h 10 ), 15 % of butane ( c 4 h 10 ), 3 % of isopentane ( c 5 h 12 ), 2 . 5 % of propylene ( c 3 h 4 ) and 47 . 5 % of butene ( c 4 h 4 ). the olefins permeate the membrane at a normal flowrate of 50 l min − 1 , containing 5 % of propylene and 95 % of butene . the paraffins are retained and the retentate flowrate is 50 l min − 1 , containing 10 % of propane , 54 % of isobutene , 30 % of butane and 6 % of isopentane . this example illustrates the use of the present invention on the olefins separation from paraffins and the hydrogenation of the impurities ( alkynes and dienes ). a typical feed of hydrocarbons [ 32 ], containing 1 . 15 % of acetylene ( c 2 h 2 ), 71 . 8 % of ethylene ( c 2 h 4 ), 13 . 59 % of ethane ( c 2 h 6 ), 0 . 4 % of propyne and of allene ( c 3 h 4 ), 12 . 65 % of propylene ( c 3 h 6 ) and 0 . 38 % of propane ( c 3 h 8 ) is fed to the process at a flowrate of 100 mol min − 1 . the permeate stream is 86 . 03 mol min − 1 and contains 84 . 83 % of ethylene ( c 2 h 4 ) and 15 . 17 % of propylene ( c 3 h 6 ). the retentate flowrate is ; 13 . 97 mol min − 1 , made of 97 . 28 % of ethane ( c 2 h 6 ), and 2 . 72 % of propane ( c 3 h 8 ). it can be observed in fig1 , a divulged device representation of the present invention , which purpose is non - limiting and exemplificative . the referred figure shows : 1 . device for separating the olefins from the paraffins and purification of the paraffins ; the separation device of olefins from paraffins and olefin purification ( 1 ) consists of two chambers , separated by a membrane ( 2 ). a mixture of paraffins and olefins ( that may contain alkynes or dienes impurities ) is fed to the retentate chamber ( 3 ) through the feed channel ( 5 ). this input is normally made under pressure . once in contact with the membrane ( 2 ) most of olefins cross it to the permeate chamber ( 4 ), where the pressure is lower than in the retentate chamber ( 3 ), and exit through the permeate outlet ( 8 ). the partial pressure difference of each olefin between the retentate ( 3 ) and permeate ( 4 ) sides works as the separation driving force . it is then possible to feed to the permeate side ( 7 ) a gas stream aiming to dilute the olefin , and then increasing the mentioned driving force and the olefins permeation through the membrane ( 2 ). the paraffins , less permeable through the membrane ( 2 ), cross the retentate chamber being withdrawn from the device ( 1 ) through the exit channel ( 6 ). if alkynes or dienes impurities are present in the feed stream , these permeate the membrane ( 2 ) together with the olefins and are hydrogenated at the catalyst presented at the permeate side ( 4 ) of the membrane . the mentioned catalyst converts these impurities in olefins that are collected through the permeate exit ( 8 ). for hydrogenation to occur , hydrogen must be fed through the inlet of the permeate chamber ( 7 ). — nymeijer , k ., visser , t ., assen , r . and wessling , m . ; “ super selective membranes in gas - 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