The LPG Process

Gas Conditioning and Processing Learn Oil and Gas Oil and Gas Processes

Following are the some important processes for the recovery of LPG

  • Membrane process
  • Catalytic hydro-cracking process
  • Dehydration process
  • Catalytic process

 

Membrane Process

The present invention is a process for recovering high purity LPG from a gas condensate stream, from any source such as refinery gases, especially gas condensate wells which contain hydrogen, methane, ethane/ethylene, light gases containing heteroatoms (sulfur, oxygen, nitrogen, e.g., mercaptans) as well as the C3+ fraction valued as LPG and simultaneously recovering a high purity hydrogen rich stream by the use of two membranes separation units. In the present invention, the first membrane separation unit is located before a first optional compressor and a knockout drum and the second membrane separation unit is located after the knockout drum with recycle of the C3+ rich stream from the second membrane unit for combination with the crude LPG feed for repassage through the knockout drum. The current invention results in the production and recovery of high purity LPG from the knockout drum and the production and recovery of high purity hydrogen retentate from the first membrane. This high purity hydrogen obtained from the first membrane unit is of sufficient purity to be utilized as a hydrogen stream component for a refinery hydroprocessing process. The retentate of the second membrane unit contains mainly other lighter hydrocarbons such as Ci and C2, i.e., a C2 enriched/LPG lean stream as is generally utilized as fuel gas.

The bulk of the crude LPG stream is sent first to a membrane separation unit under the pressure at which it is received from its source such as 50 to 1000 psi (no pre-compression step being practiced) and the crude stream is divided into a H2 lean and C3+ LPG enriched permeate stream and a H2 rich retentate stream. The permeate stream, at reduced pressure, and of reduced volume due to the removal of the H2 and some C2 retentate stream can be fed as such to the knockout drum or can be recompressed in a first optional compressor before being sent to the knockout drum. Because of the reduced volume of this stream, if a compressor is required in the present process, a smaller compressor can be utilized than if the hydrogen was not removed prior to the compression step upstream of the knock-out drum. This results is both lower investment costs and lower energy consumption.

In one embodiment of the process of the present invention as presented  raw LPG feed from whatever source is fed at whatever pressure it is received from its source, typically 50 to 1000 psi, via line  into a first membrane unit  wherein it is contacted with a rubbery polymer membrane . The raw LPG feed is separated by the membrane into a retentate product stream enriched in hydrogen, and into a lower/reduced pressure permeate stream enriched in  LPG hydrocarbons and a reduced concentration of hydrogen as compared to the feed stream. The lower pressure permeate stream enriched in C3+ LPG concentration but still containing some hydrogen albeit at a reduced concentration is passed via line  though optional valve to optional compressor wherein its pressure can be increased at least back up to the pressure of the of the crude LPG, e.g., 50 to 1000 psi and then through line to knockout drum  wherein high purity C3+ LPG is liquified and recovered as product via line and a vaporous phase is recovered as overheads via line and sent to a second membrane unit where it is contacted with a rubbery polymer membrane In the second membrane unit the vaporous overheads stream from knockout drum is separated into a retentate stream rich in C1 and C2 and of reduced C3+ LPG content and into a reduced pressure permeate stream rich in C3+ LPG. The permeate stream is fed via line without the use of the optional compressor shown as to a point upstream of compressor where it is combined with the permeate stream from the first membrane separation unit.

In another embodiment, if the pressure of the permeate stream in line is sufficient, compressor may be omitted. In this alternate embodiment, the permeate is fed to knockout drum via line . In the second membrane unit , the vaporous overheads stream from knockout drum is separated into a retentate stream  rich in C1 and C2 and of reduced C3+ LPG content and into a reduced pressure permeate stream  rich in C3+ LPG. The permeate stream is fed via line  to compressor which is employed in this embodiment. The compressed permeate stream is recycled via line  into line for combining therein with the permeate from line for introduction/reintroduction into the knockout drum .

While compressors and are identified as optional, one or the other is required to repressurize the stream(s) recovered at reduced pressure as permeate either from the first membrane separation unit stream or from the second membrane separation unit stream so as to facilitate the processing and/or recycling of these streams in the processing circuit. Passage through each membrane unit results in a permeate recovered at a pressure lower than that of the feed to the membrane unit. Compressor  can be omitted if the pressure of the reduced pressure permeate in line is still high enough to permit effective separation in the knockout drum membrane unit circuit. If not, then recompression in a compressor is necessary. If the pressure in line  is sufficient without recompression in compressor for passage to knockout drum and membrane unit  the permeate recovered from membrane unit in line will be at yet a still lower pressure  so recycle of this permeate for recycle to the knockout drum would require depressurization by compressor .

 

In the membrane separations units, gas molecules sorb (i.e., either absorb or adsorb) onto the polymer film used as the membrane on the feed side of the membrane, usually under pressure (usually an applied pressure). This sorption creates a concentration gradient of molecules from the feed side to the permeate side of the membrane film. Gas molecules diffuse through the membrane film from the feed side to the permeate side under the influence of the concentration difference with the sorbed materials desorbing from the permeate face of the membrane film into the lower pressure permeate side of the membrane separation unit. This pressure differential may be the result of a higher or applied pressure on the feed side of the membrane than the pressure on the permeate side of the membrane and/or the permeate side can be under a partial or full vacuum to create the necessary pressure differential.

In gas separation most of the membranes used are glassy polymers such as cellulose acetate, polysulfone, polyamide, polyimide, etc., and combination of such polymers. In glassy polymers the polymer molecule is rigidly packed in the membrane film, therefore diffusion in restricted and the diffusion rate controls the separation. Larger molecules have slower diffusion rates. Thus, glassy polymer membranes can be used to separate small molecules such as hydrogen (kinetic diameter 2.89 A) from larger molecules such as methane (kinetic diameter 3.8 A) and propane (kinetic diameter 4.3 A) but because of the reduced diffusion rate the rate of separation is low.

In the recovery of LPG, as practiced in the present invention use is made of rubbery polymer such as polysiloxane, polybutadiene, etc. In this rubbery state, the polymer molecules in the membrane film are packed relatively loosely resulting in high flexibility of the rubbery polymer film and flexibility between the different polymer strands that comprise the membrane. Thus, diffusion rate differences between smaller molecules and larger molecules are insignificant. Herein, the selective separation is primarily driven not by differentiation in molecular size but instead by affinity of the membrane for certain constituents in the feed. The sorption on the feed side in LPG recovery using these rubbery polymer membranes favors large C3 molecules rather than the smaller hydrogen, C1 or C2 molecules.

Because of the higher sorption of the C3+ molecules, more C3+ molecules sorb on the feed side resulting in more C3+ molecules permeating through the membrane to the permeate side resulting in the separation Of C3+ molecules from the hydrogen and C1 and C2 molecules present in feed. In a preferred embodiment, the process of the present invention will produce a C3+ rich product stream that has a C3+ purity of at least 70 mol%, more preferably at least 80 mol%. In a preferred embodiment, the process of the present invention produces a C3+ rich product stream wherein the

 

wt% of the C3+ component in the C3+ rich product stream is at least 80 wt% of the C3+ component in the hydrocarbon-containing feed stream to the process. More preferably the process of the present invention produces a C3+ rich product stream wherein the wt% of the C3+ component in the C3+ product stream is at least 90 wt% of the C3+ component in the hydrocarbon-containing feed stream to the process.

Similarly, a rubbery polymer membrane such as polysiloxane, polybutadiene, etc., can be utilized in the first membrane separation unit to produce a lower molecular weight hydrogen-rich stream as a retentate at high purities (greater than 70 mol%) and produce a C2+ rich permeate stream which can then be further purified for LPG recovery. In a preferred embodiment, the process of the present invention will produce a hydrogen rich product stream that has a hydrogen purity of at least 70 mol%, more preferably at least 80 mol%. In a preferred embodiment, the process of the present invention produces a hydrogen rich product stream wherein the wt% of the hydrogen component in the hydrogen rich product stream is at least 40 wt% of the hydrogen component in the hydrocarbon-containing feed stream to the process. More preferably the process of the present invention produces a hydrogen rich product stream wherein the wt% of the hydrogen component in the hydrogen rich product stream is at least 50 wt%, and even more preferably at least 60 wt% of the hydrogen component in the hydrocarbon-containing feed stream to the process.

The preferred rubbery polymers useful in the present process are those which have a glass transition temperature below 200C, i.e., which are rubbery at room temperature or higher (about 200C or higher). The same or different rubbery polymer membranes may be used in each membrane separation unit.

 

Catalytic Hydro raking

 

A catalytic hydro cracking process which provides for the simultaneous production of LPG and distillate hydrocarbons. The feedstock is introduced into a de-nitrification and de-sulfurization zone and then passed directly to a hot, high pressure stripper utilizing a hot, hydrogen-rich stripping gas to produce a first liquid stream boiling in the range of the feedstock
and a first vapor stream comprising hydro carbonaceous compounds boiling at
a temperature below the boiling range of the feedstock. The first liquid
stream is hydro cracked in a first hydro cracking zone and then passed to
the denitrification and desulphurization zone. At least a portion of the
first vapor stream is condensed to produce a second liquid stream
comprising hydro carbonaceous compounds boiling at a temperature below the
boiling range of the feedstock. At least a portion of the second liquid
stream is hydro cracked in a second hydro cracking zone containing a second

hydro cracking catalyst to produce LPG boiling range hydro carbonaceous
compounds.

Dehydration Process

In the dehydration process of gas condensate, we obtain LPG, natural gas and other higher hydrocarbon like naphtha kerosene oil etc.

In the dehydration process the gas condensate from the slug catcher move towards the three sections.

1 gas dehydration unit

2 LPG unit

3 water treatment unit

In the gas dehydration unit the gas pass through feed chiller, separators, gas filters, molecular sieve beds, murccury guard beds, dust filter and then it goes to the LPG section.

In the LPG unit condensate from the slug catcher refined after passing through condensate chiller, condensate coalaser filter, deeathanizer, debutanizer.

 Catalytic Process

This invention relates to a catalyst for producing a liquefied petroleum gas containing propane or butane as a main component by reacting carbon monoxide with hydrogen.

This invention also relates to a process for producing a liquefied petroleum gas containing propane or butane as a main component from a synthesis gas using the catalyst. This invention also relates to a process for producing a liquefied petroleum gas containing propane or butane as a main component from a carbon-containing starting material such as a natural gas using the catalyst.

Objective of The Catalytic Process

An objective of this invention is to provide a less deteriorative catalyst for producing a liquefied petroleum gas with a longer catalyst life, which can produce a hydrocarbon containing propane or butane as a main component, i.e., a liquefied petroleum gas (LPG), by reacting carbon monoxide and hydrogen, with high activity, high selectivity and high yield.

Another objective of this invention is to provide a process for stably producing LPG with a high concentration of propane and/or butane from a synthesis gas in a high yield for a long period, using the catalyst. A further objective of this invention is to provide a process for stably producing LPG with a high concentration of propane and/or butane from a carbon-containing starting material such as a natural gas in a high yield for a long period.

The present invention provides a catalyst for producing a liquefied petroleum gas, which is used for producing a liquefied petroleum gas containing propane or butane as a main component by reacting carbon monoxide and hydrogen, comprising a Pd-based methanol synthesis catalyst component. Moreover, the present invention provides a process for producing a liquefied petroleum gas, comprising the step of:

Reacting carbon monoxide and hydrogen in the presence of the catalyst for producing a liquefied petroleum gas as described above to produce a liquefied petroleum gas containing propane or butane as a main component.

Moreover, the present invention provides a process for producing a liquefied petroleum gas, comprising the steps of:

(1) producing a synthesis gas from a carbon-containing starting material and at least one selected from the group consisting of H2O, O2 and CO2 (Synthesis gas production process); and

(2) feeding the synthesis gas to a catalyst layer comprising the catalyst for producing a liquefied petroleum gas as described above to produce a liquefied petroleum gas containing propane or butane as a main component (Liquefied petroleum gas production process).

Herein, “synthesis gas” means a mixed gas comprising hydrogen and carbon monoxide, and is not limited to a mixed gas consisting of hydrogen and carbon monoxide. A synthesis gas may be, for example, a mixed gas comprising carbon dioxide, water, methane, ethane, ethylene and so on. A synthesis gas produced by reforming a natural gas generally contains, in addition to hydrogen and carbon monoxide, carbon dioxide and water vapor. A synthesis gas may be a coal gas produced by coal gasification or a water gas produced from a coal coke.

A catalyst for producing a liquefied petroleum gas according to this invention comprises a Pd-based methanol synthesis catalyst as a methanol synthesis catalyst component. The catalyst for producing a liquefied petroleum gas according to this invention can

produce a hydrocarbon containing propane or butane as a main component, i.e., a liquefied petroleum gas (LPG) with high activity, high selectivity and a high yield, by reacting carbon monoxide and hydrogen, and has a longer catalyst life with less deterioration.

First, on the methanol synthesis catalyst component, methanol is formed from carbon monoxide and hydrogen, while dimethyl ether is also formed by dehydro-dimerization of methanol. Then, methanol thus formed is converted to a lower-olefin hydrocarbon comprising propylene or butene as a main component at an active site in a pore in the zeolite catalyst component. In the reaction, methanol would be dehydrated to give a carbene (H2C:), which is subjected to polymerization to give a lower olefin. The lower olefin thus generated is released from the pore in the zeolite catalyst component and is rapidly hydrogenated on the methanol synthesis catalyst to give a paraffin comprising propane or butane as a main component, i.e., LPG.

Herein, a “methanol synthesis catalyst component” means a compound which can act as a catalyst in the reaction of CO+2H2→CH3OH. And a “zeolite catalyst component” means a zeolite which can act as a catalyst in a condensation reaction of methanol into a hydrocarbon and/or a condensation reaction of dimethyl ether into a hydrocarbon.

As a methanol synthesis catalyst, a Cu—Zn-based catalyst (a composite oxide containing Cu and Zn) and a Zn—Cr-based catalyst (a composite oxide containing Zn and Cr) are widely used. However, sufficient catalyst performance cannot be always achieved when using, in place of a Pd-based methanol synthesis catalyst, a Cu—Zn-based methanol synthesis catalyst or a Zn—Cr-based methanol synthesis catalyst as a methanol synthesis catalyst component in a catalyst for producing a liquefied petroleum gas in production of LPG by reacting carbon monoxide and hydrogen. Furthermore, sufficient catalyst performance cannot be always achieved when using a zeolite as a catalyst component in case a Pd-based methanol synthesis catalyst is used as a methanol synthesis catalyst component in a catalyst for producing a liquefied petroleum gas.

The reaction of carbon monoxide and hydrogen for producing LPG depends on a variety of factors. Therefore, the reason why the catalyst for producing a liquefied petroleum gas of this invention exhibits excellent performance is not clear, but the followings might be assumed.                                                                            A reaction of carbon monoxide and hydrogen for forming methanol (CO+2H2→CH3OH) is an equilibrium reaction. And, the equation: CO+2H2=CH3OH+100 kJ indicates that the equilibrium of methanol formation is more advantageous as a temperature is lower. However, when reacting carbon monoxide and hydrogen to produce LPG, methanol formed on a methanol synthesis catalyst component is rapidly converted to a lower-olefin hydrocarbon at

an active site in a pore in the zeolite catalyst component. There are, therefore, substantially no restrictions to the equilibrium of methanol formation. Thus, it is not necessarily required to conduct the reaction at a lower temperature for achieving a sufficiently high yield. On the other hand, it is advantageous to conduct the reaction at a higher temperature in terms of a reaction rate. In the light of activity of the zeolite catalyst component, it is desirable that the methanol synthesis catalyst component has great heat-resistance to some degree. Specifically, the methanol synthesis catalyst can be used preferably at 270° C. or higher, more preferably 300° C. or higher, further preferably 320° C. or higher.

Among methanol synthesis catalysts, a Cu—Zn-based catalyst is generally used at a relatively lower temperature (about 230 to 300° C.) and its heat resistance is not so higher than other methanol synthesis catalysts. When producing LPG by reacting carbon monoxide and hydrogen at an elevated temperature for achieving higher activity and higher yield, it is not necessarily preferable to use a conventional Cu—Zn-based catalyst as a methanol synthesis catalyst component.

On the other hand, among methanol synthesis catalysts, a Zn—Cr-based catalyst is generally used at a relatively higher temperature (about 250 to 400° C.). There does not appear to be a particular problem in using a Zn—Cr-based catalyst as a methanol synthesis catalyst component when making a reaction temperature higher.

However, when producing LPG by reacting carbon monoxide and hydrogen, a methanol synthesis catalyst component is required to act as a catalyst in a hydrogenation reaction of an olefin into a paraffin. A conventional Zn—Cr-based catalyst does not, however, have sufficient hydrogenating ability. Thus, when producing LPG by reacting carbon monoxide and hydrogen, it is not necessarily preferable to use a conventional Zn—Cr-based catalyst as a methanol synthesis catalyst component.

A Pd-based methanol synthesis catalyst, which is used as a methanol synthesis catalyst component in this invention, is known to act as a catalyst in the methanol synthesis reaction (CO+2H2→CH3OH), but it is not widely used as a methanol synthesis catalyst. However, in the light of its high thermal stability and hydrogenating ability, it is suitable as a methanol synthesis catalyst component in a catalyst used in producing a liquefied petroleum gas by reacting carbon monoxide and hydrogen, particularly at an elevated reaction temperature.

As a methanol synthesis catalyst component, it is particularly preferable to use a catalyst in which 0.1 to 10 wt % Pd is supported on a silica support having a specific surface area of 420 m2/g or more.

However, an important factor for a zeolite catalyst component may not be limited to a pore size and a SiO2/Al2O3 molar ratio. Other factors such as an acid strength, a pore structure and a crystal size may be also important for a zeolite catalyst component. Performance of a catalyst for producing a liquefied petroleum gas, particularly its activity and LPG selectivity, strongly depends on the balance among three parameters, the ability of a methanol synthesis catalyst component to form methanol, the ability of a methanol synthesis catalyst component to hydrogenate an olefin into a paraffin, and the ability of a zeolite catalyst component to form a hydrocarbon from methanol, and they are thought to be influenced by a variety of factors.

A nickel catalyst, for example, is widely used as a catalyst in a hydrogenation reaction of an olefin into a paraffin. But if a substance cannot act as a catalyst in a methanol synthesis reaction (CO+2H2→CH3OH), it is, of course, unpreferable as a methanol synthesis catalyst component used in this invention.

The reaction conditions are also important for stably producing LPG for a long period with a high conversion, a high selectivity and a high yield by reacting carbon monoxide and hydrogen in the presence of a catalyst for producing a liquefied petroleum gas of this invention. This invention may be particularly effective when carbon monoxide and hydrogen are reacted at a reaction temperature of 300° C. to 420° C. (both inclusive) and under a reaction pressure of 2.2 MPa to 10 MPa (both inclusive).

According to this invention, for example, even after 50 hours from the reaction beginning, the catalyst can exhibit such a high activity that a conversion of CO is 50% or more, specifically 60% or more, more specifically 70% or more, further specifically 80% or more, to give a hydrocarbon with the total content of propane and butane of 60% or more, specifically 70% or more.

Furthermore, according to this invention, LPG with the total content of propane and butane of 90 mol % or more, specifically 95 mol % or more (including 100 mol %), for example, can be produced. And, according to this invention, LPG with a content of propane of 50 mol % or more, specifically 60 mol % or more (including 100 mol %), for example, can be produced.

Detailed Description

Examples of a Pd-based methanol synthesis catalyst component include Pd, preferably metallic Pd, supported on a support. In the light of catalytic activity, Pd is preferably supported on a support in a highly dispersed manner.

The amount of supported Pd in a Pd-based methanol synthesis catalyst component is preferably 0.1 wt % or more, more preferably 0.5 wt % or more, particularly preferably 1 wt % or more. In the light of dispensability and economical efficiency, the amount of supported Pd in a Pd-based methanol synthesis catalyst component is preferably 10 wt % or less, more preferably 8 wt % or less, particularly preferably 6 wt % or less. By adjusting the amount of supported Pd in a Pd-based methanol synthesis catalyst component within the above range, propane and/or butane can be produced with a higher conversion, a higher selectivity and a higher yield.

By adjusting the amount of supported Pd to be 0.1 wt % or more, more preferably 0.5 wt % or more, particularly preferably 1 wt % or more, carbon monoxide and hydrogen can be converted into methanol with a higher conversion, and methanol produced can be converted into a liquefied petroleum gas comprising propane or butane as a main component with a higher selectivity. On the other hand, by adjusting the amount of supported Pd to be 10 wt % or less, more preferably 8 wt % or less, particularly preferably 6 wt % or less, methanol produced can be converted into a liquefied petroleum gas comprising propane or butane as a main component with a higher conversion.

A support for Pd may be selected from known supports without limitation. Examples of a support include silica (silicon dioxide), alumina, silica-alumina, carbon (activated charcoal); and oxides of zirconium, titanium, cerium, lanthanum, iron or the like, and composite oxides containing two or more types of these metals, and composite oxides containing one or more types of these metals and one or more types of other metals. Such supports may be used alone or in combination of two or more.

A support is preferably neutral to basic. By using a neutral to basic support, higher activity and selectivity can be achieved in methanol synthesis.

Among others, a preferable support for Pd is silica. By using silica as a support, methanol can be produced with a higher selectivity and a higher yield without producing a hydrocarbon and carbon dioxide as a by-product.

A silica support preferably has a specific surface area of 420 m2/g or more, more preferably 450 m2/g or more, particularly preferably 475 m2/g or more,

further preferably 500 m2/g or more. By using a silica support having a specific surface area within the above range, higher catalytic activity can be achieved and propane and/or butane can be produced with a higher conversion and a higher yield.

The upper limit of a specific surface area of a silica support is not particularly restricted, but is generally about 300 m2/g.

A silica support preferably has an average pore size of 5.5 nm or less, more preferably 5 nm or less, particularly preferably 4.5 nm or less, further preferably 4 nm or less. By using a silica support having an average pore size within the above range, higher catalytic activity can be achieved and propane and/or butane can be produced with a higher conversion and a higher yield.

The lower limit of an average pore size of a silica support is not particularly restricted, but is generally about 1 nm.

When silica is used as a support, it can support one or more types of basic metals, in addition to Pd. By supporting a basic metal in addition to Pd on a silica support, catalytic activity may be further improved and propane and/or butane may be produced with a higher conversion and a higher yield.

Herein, a “basic metal” means a metal whose oxide is a basic oxide.

Examples of a basic metal include alkali metals, alkaline earth metals, lanthanoid metals and low-valence transition metals; specifically, Ca, Sr, La, Nd, Mg, Li, Na and the like. Basic metals may be used alone or in combination of two or more.

Among others, a preferable basic metal is Ca. By using Ca as a basic metal, dispensability of Pd can be improved, and thus higher catalytic activity can be achieved and propane and/or butane can be produced with a higher conversion and a higher yield. The total amount of basic metals supported on a Pd-based methanol synthesis catalyst component is preferably 0.01 wt % or more, more preferably 0.5 wt % or more. The amount of supported basic metals within the above range can result in sufficient effect of supporting a basic metal on silica as described above.

On the other hand, the total amount of basic metals supported on a Pd-based methanol synthesis catalyst component is preferably 5 wt % or less, more preferably 3 wt % or less. By adjusting the amount

of supported basic metals within the above range, dispensability of Pd can be improved, and thus higher catalytic activity can be achieved and propane and/or butane can be produced with a higher conversion and a higher yield.

In this invention, a Pd-based methanol synthesis catalyst component may be a silica support on which other components, in addition to Pd and a basic metal, are supported as long as the desired effects of the catalyst are maintained.

A Pd-based methanol synthesis catalyst component in which Pd, a basic metal or the like are supported on silica, may be prepared by a known method such as an impregnation method and a precipitation method. Next, there will be described a process for producing a liquefied petroleum gas comprising propane or butane, preferably propane, as a main component by reacting carbon monoxide and hydrogen using a catalyst for producing a liquefied petroleum gas according to this invention as described above.

A reaction temperature is preferably 300° C. or higher, more preferably 320° C. or higher, particularly preferably 340° C. or higher. By controlling a reaction temperature within the above range, propane and/or butane can be produced with a higher conversion and a higher yield.

On the other hand, a reaction temperature is preferably 420° C. or lower, more preferably 400° C. or lower, in the light of the restrictive temperature for the use of the catalyst and easy removal or recovery of the reaction heat. A reaction pressure is preferably 2.2 MPa or higher, more preferably 2.5 MPa or higher, particularly preferably 3 MPa or higher. By controlling a reaction pressure within the above range, propane and/or butane can be produced with a higher conversion and a higher yield, and the deterioration with time of the catalyst can be reduced further, so that propane and/or butane can be produced for a further longer period with a higher conversion and a higher yield. In particular, by controlling a reaction pressure to be 3 MPa or higher, propane and/or butane can be produced with a sufficiently high conversion and a sufficiently high yield.

On the other hand, a reaction pressure is preferably 10 MPa or lower, more preferably 7 MPa or lower, in the light of economical efficiency.

A gas space velocity is preferably 500 hr−1 or more, more preferably 1500 hr−1 or more, in the light of economical efficiency. In addition, a gas space velocity is preferably 10000 hr−1 or less, more preferably 5000 hr−1 or less, in order that each of a Pd-based methanol synthesis catalyst component and a β-zeolite catalyst component may give a contact time achieving a further sufficient conversion. A

concentration of carbon monoxide in a gas fed into a reactor is preferably 20 mol % or more, more preferably 25 mol % or more, in the light of ensuring a pressure (partial pressure) of carbon monoxide required for the reaction in a gas fed into the reactor, and improving a specific productivity of the materials. In addition, a concentration of carbon monoxide in a gas fed into a reactor is preferably 45 mol % or less, more preferably 40 mol % or less, in the light of a further sufficiently high conversion of carbon monoxide.

A concentration of hydrogen in a gas fed into a reactor is preferably 1.2 moles or more, more preferably 1.5 moles or more per one mole of carbon monoxide, in order that carbon monoxide may react more sufficiently. In addition, a concentration of hydrogen in a gas fed into a reactor is preferably 3 moles or less, more preferably 2.5 moles or less per one mole of carbon monoxide, in the light of economical efficiency. In some cases, preferably, a concentration of hydrogen in a gas fed into a reactor may be reduced to about 0.5 moles per one mole of carbon monoxide. A gas fed into a reactor may contain carbon dioxide in addition to carbon monoxide and hydrogen, which are starting materials of the reaction. By recycling carbon dioxide discharged from the reactor, or by adding the corresponding amount of carbon dioxide, formation of carbon dioxide from carbon monoxide by a shift reaction in the reactor can be substantially reduced or be eliminated.

A gas fed into a reactor can contain water vapor. And a gas fed into a reactor can contain an inert gas. A gas fed into a reactor can be dividedly fed to the reactor so as to control a reaction temperature. The reaction can be conducted in a fixed bed, a fluid bed, a moving bed or the like, and can be preferably selected, taking both of control of a reaction temperature and a regeneration method of the catalyst into account. For example, a fixed bed may include a quench type reactor such as an internal multistage quench type, a multi tubular type reactor, a multistage type reactor having a plurality of internal heat exchangers or the like, a multistage cooling radial flow type, a double pipe heat exchange type, an internal cooling coil type, a mixed flow type, and other types of reactors.

When used, a catalyst for producing a liquefied petroleum gas according to the present invention can be diluted with silica, alumina or an inert and stable heat conductor for controlling a temperature. In addition, when used, a catalyst for producing a liquefied petroleum gas according to the present invention can be applied to the surface of a heat exchanger for controlling a temperature.

Process for Producing a Liquefied Petroleum Gas from a Carbon-Containing Starting Material.In this invention, a synthesis gas can be used as a starting gas for producing a liquefied petroleum gas (LPG).

Next, there will be described an embodiment of a process for producing LPG according to this invention, comprising the steps of producing a synthesis gas from a carbon-containing starting material (synthesis gas production process) and then producing LPG from the obtained synthesis gas using a catalyst of this invention (liquefied petroleum gas production process).

 Synthesis Gas Production Process

In a synthesis gas production process, a synthesis gas is produced from a carbon-containing starting material and at least one selected from the group consisting of H2O, O2 and CO2.A carbon-containing substance which can react with at least one selected from the group consisting of H2O, O2 and CO2 to form H2 and CO, can be used as a carbon-containing starting material. A substance known as a raw material for a synthesis gas can be used as a carbon-containing starting material; for example, lower hydrocarbons such as methane and ethane, a natural gas, a naphtha, a coal, and the like can be used.

Since a catalyst is generally used in a synthesis gas production process and a liquefied petroleum gas production process in this invention, a carbon-containing starting material (a natural gas, a naphtha, a coal and so on) preferably contains less catalyst poisoning components such as sulfur and a sulfur compound. When a carbon-containing starting material contains a catalyst poisoning component, a step of removing the catalyst poisoning component such as devocalization can be conducted before a synthesis gas production process, if necessary.

A synthesis gas can be produced by reacting the above carbon-containing starting material with at least one selected from the group consisting of H2O, O2 and CO2 in the presence of a catalyst for producing a synthesis gas (reforming catalyst).A synthesis gas can be produced by a known method. When a natural gas (methane) is used as a starting material, for example, a synthesis gas can be produced by a water-vapor reforming method, an auto thermal reforming method or the like. In these methods, water vapor required for a water-vapor reforming, oxygen required for an auto thermal reforming, or the like can be fed, if necessary. When a coal is used as a starting material, a synthesis gas can be produced using an aerating gasification furnace.

For example, a shift reactor may be placed downstream of a reformer, which is a reactor for producing a synthesis gas from the above starting materials, so that a synthesis gas composition can be adjusted by a shift reaction (CO+H2O→CO2+H2).In this invention, a preferable composition of a synthesis gas produced in a synthesis gas production process is a molar ratio of H2/CO is 7/3≅2.3 in terms of the stoichiometry for a lower paraffin production, and a ratio

of hydrogen to carbon monoxide (H2/CO; by mole) in a synthesis gas produced is preferably 1.2 to 3. A ratio of hydrogen to carbon monoxide (H2/CO; by mole) in a synthesis gas is preferably 1.2 or more, more preferably 1.5 or more, in order that carbon monoxide may react suitably, since hydrogen is generated by a shift reaction caused by water generated in a conversion reaction from a synthesis gas to LPG. It is only necessary to feed hydrogen in such an amount that carbon monoxide can react suitably to form a liquefied petroleum gas comprising propane or butane as a main component, and excessive hydrogen may increase the total pressure of a starting gas unnecessarily, leading to a lower economical efficiency. Thus, a ratio of hydrogen to carbon monoxide (H2/CO; by mole) in a synthesis gas is preferably 3 or less, more preferably 2.5 or less.

A concentration of carbon monoxide in a synthesis gas produced is preferably 20 mol % or more, more preferably 25 mol % or more, in the light of ensuring a pressure (partial pressure) of carbon monoxide suitable for a conversion reaction from a synthesis gas to LPG, and improving a specific productivity of the materials. In addition, a concentration of carbon monoxide in a synthesis gas produced is preferably 45 mol % or less, more preferably 40 mol % or less, in the light of a further sufficiently high conversion of carbon monoxide in a conversion reaction from a synthesis gas to LPG.A synthesis gas having the above composition can be produced by appropriately selecting reaction conditions such as a feeding ratio of a carbon-containing starting material and at least one material selected from the group consisting of steam (water), oxygen and carbon dioxide, a kind of a catalyst for producing a synthesis gas used, and others.

For example, a synthesis gas can be produced using a gas whose composition is steam/methane (molar ratio) of 1 and carbon dioxide/methane (molar ratio) of 0.4 as a starting gas under the operation conditions of a reaction temperature (an outlet temperature of a catalyst layer) of 800 to 900° C., a reaction pressure of 1 to 4 MPa, a gas space velocity (GHSV) of 20000 hr−1, in an external heating multi tubular tubular reactor type apparatus filled with a catalyst, a Ru or Rh/a magnesia made the surface area smaller by sintering. When using steam for reforming in a synthesis gas production, a ratio of steam/raw material carbon (S/C) is preferably 1.5 or less, more preferably 0.8 to 1.2, in the light of an energy efficiency. But such a low S/C value may lead to the considerable possibility of carbon precipitation formation.

Examples of the metal oxide in this catalyst include those containing at least one metal such as Mg, Ca, Ba, Zn, Al, Zr and La. An example of such a metal oxide is magnesia (MgO).

In a process in which methane and steam are reacted (steam reforming), the reaction is represented by the following formula (i):

CH4+H2O⇄3H2+C O (i)
In a process in which methane and carbon dioxide are reacted (CO2 reforming), the reaction is represented by the following formula (ii):
CH4+CO2⇄2H2+2 CO (ii)

In a process in which methane, steam and carbon dioxide are reacted (steam/CO2 mixed reforming), the reaction is represented by the following formula (iii):
3CH4+2H2O+CO2⇊?8H2+4CO (iii)

For steam reforming using the above catalyst, a reaction temperature is preferably 600 to 1200° C., more preferably 600 to 1000° C., and a reaction pressure is preferably 0.098 MPaG to 3.9 MPaG, more preferably 0.49 MPaG to 2.9 MPaG (G indicates that a value is a gauge pressure). When the steam reforming is conducted with a fixed bed, a gas space velocity (GHSV) is preferably 1,000 to 10,000 hr−1, more preferably 2,000 to 8,000 hr−1. A rate of steam to a carbon-containing starting material is preferably 0.5 to 2 moles, more preferably 0.5 to 1.5 moles, further preferably 0.8 to 1.2 moles of steam (H2O) per one mole of carbon in the carbon-containing starting material (excluding CO2).In a liquefied petroleum gas production process, a lower-paraffin-containing gas, which comprises propane or butane as a main component of the hydrocarbon contained therein, is produced from the synthesis gas obtained in the above synthesis gas production process, by using a catalyst for producing a liquefied petroleum gas according to the present invention. And then, water is separated from the lower-paraffin-containing gas produced, as necessary, and subsequently a low-boiling component having a lower boiling point or a lower sublimation point than the boiling point of propane (unreacted starting materials, hydrogen and carbon monoxide; by-products, carbon dioxide, ethane, ethylene and methane; and so on) and a high-boiling component having a higher boiling point than the boiling point of butane (by-products, high-boiling paraffin gases) are, if necessary, separated from the lower-paraffin-containing gas, so as to obtain a liquefied petroleum gas (LPG) comprising propane or butane as a main component. If necessary, the gas may be pressurized and/or cooled so as to obtain a liquefied petroleum gas.

In a liquefied petroleum gas production process, carbon monoxide and hydrogen are reacted in the presence of the above catalyst for producing a liquefied petroleum gas of this invention, to produce a paraffin comprising propane or butane as a main component, preferably a paraffin comprising propane as a main component.In this case, a gas fed into a reactor is the synthesis gas produced in the above synthesis gas production process. The gas fed into a reactor may contain, in

addition to carbon monoxide and hydrogen, other components such as carbon dioxide, water, methane, ethane, ethylene and an inert gas. The gas fed into a reactor may be a gas obtained by adding carbon monoxide, hydrogen or other components, if necessary, to the synthesis gas produced in the above synthesis gas production process. And the gas fed into a reactor may be a gas obtained by separating a certain component, as necessary, from the synthesis gas produced in the above synthesis gas production process.

A gas fed into a reactor may comprise carbon dioxide, in addition to carbon monoxide and hydrogen, which are starting materials for producing a lower paraffin. As the carbon dioxide, by recycling carbon dioxide discharged from the reactor, or by using the corresponding amount of carbon dioxide, formation of carbon dioxide from carbon monoxide by a shift reaction in the reactor can be substantially reduced or be eliminated.

A gas fed into a reactor may comprise water vapor.

A reaction temperature is preferably 300° C. or higher, more preferably 320° C. or higher, particularly preferably 340° C. or higher. On the other hand, as described above, a reaction temperature is preferably 420° C. or lower, more preferably 400° C. or lower.

A reaction pressure is preferably 2.2 MPa or higher, more preferably 2.5 MPa or higher, particularly preferably 3 MPa or higher. On the other hand, as described above, a reaction pressure is preferably 10 MPa or lower, more preferably 7 MPa or lower.

A gas space velocity is preferably 500 hr−1 or more, more preferably 1500 hr−1 or more. On the other hand, as described above, a gas space velocity is preferably 10000 hr−1 or less, more preferably 5000 hr−1 or less.

A gas fed into a reactor can be dividedly fed to the reactor so as to control a reaction temperature. The reaction can be conducted in a fixed bed, a fluid bed, a moving bed or the like, and can be preferably selected, taking both of control of a reaction temperature and a regeneration method of the catalyst into account. For example, a fixed bed may include a quench type reactor such as an internal multistage quench type, a multi tubular type reactor, a multistage type reactor having a plurality of internal heat exchangers or the like, a multistage cooling radial flow type, a double pipe heat exchange type, an internal cooling coil type, a mixed flow type, and other types of reactors.

When used, a catalyst for producing a liquefied petroleum gas according to the present invention can be diluted with

silica, alumina or an inert and stable heat conductor for controlling a temperature. In addition, when used, a catalyst for producing a liquefied petroleum gas according to the present invention can be applied to the surface of a heat exchanger for controlling a temperature.

A lower-paraffin-containing gas produced in the liquefied petroleum gas production process comprises a hydrocarbon containing propane or butane as a main component. In the light of liquefaction properties, it is preferable that the total content of propane and butane is higher in a lower-paraffin-containing gas. According to this invention, there can be obtained a lower-paraffin-containing gas having a content of propane and butane of 50 mol % or more, preferably 60 mol % or more, more preferably 70 mol % or more (including 100 mol %) to the hydrocarbon contained therein, in total. Furthermore, a lower-paraffin-containing gas produced in the liquefied petroleum gas production process preferably contains more propane in comparison with butane, in the light of inflammability and vapor pressure properties.

Thus, water, a low-boiling component and a high-boiling component are, as necessary, separated from a lower-paraffin-containing gas produced, so as to obtain a liquefied petroleum gas (LPG) comprising propane or butane as a main component. Separation of water, a low-boiling component or a high-boiling component can be conducted in accordance with a known method.

Water can be separated by, for example, liquid-liquid separation.

A low-boiling component can be separated by, for example, gas-liquid separation, absorption separation or distillation; more specifically, gas-liquid separation at an ambient temperature under increased pressure, absorption separation at an ambient temperature under increased pressure, gas-liquid separation with cooling, absorption separation with cooling, or combination thereof. Alternatively, for this purpose, membrane separation or adsorption separation can be conducted, or these in combination with gas-liquid separation, absorption separation or distillation can be conducted. A gas recovery process commonly employed in an oil factory (described in “Oil Refining Processes”, applied to separation of a low-boiling component.A preferable method of separation of a low-boiling component is an absorption process where a liquefied petroleum gas comprising propane or butane as a main component is absorbed into an absorbent liquid such as a high-boiling paraffin gas having a higher boiling point than butane, and a gasoline.A high-boiling component can be separated by, for example, gas-liquid separation, absorption separation or distillation.

For consumer use, it is preferable that a content of a low-boiling component in the LPG is reduced to 5 mol % or less (including 0 mol %) by separation, for example, in the light of safety in use.The total content of propane and butane in the LPG

thus produced may be 90 mol % or more, more preferably 95 mol % or more (including 100 mol %). And a content of propane in the LPG produced may be 50 mol % or more, more preferably 60 mol % or more (including 100 mol %). Thus, according to this invention, LPG having a composition suitable for a propane gas, which is widely used as a fuel for household and business use, can be produced.

In this invention, a low-boiling component separated from the lower-paraffin-containing gas can be recycled as a starting material for the synthesis gas production process.A low-boiling component separated from the lower-paraffin-containing gas includes substances which can be recycled as starting materials for a synthesis gas production process; for example, methane, ethane, ethylene and so on. And carbon dioxide in the low-boiling component can be back to a synthesis gas by a CO2 reforming reaction. In addition, a low-boiling component includes unreacted starting materials such as hydrogen and carbon monoxide. Therefore, the low-boiling component separated from the lower-paraffin-containing gas may be recycled as a starting material for a synthesis gas production process, leading to reduce a specific productivity of the materials.

The whole low-boiling components separated from a lower-paraffin-containing gas can be recycled to a synthesis gas production process. Alternatively, part of the low-boiling components may be removed outside the system, while the rest of low-boiling components may be recycled to a synthesis gas production process. Low-boiling components can be recycled to a synthesis gas production process after separating only desired components.

In a synthesis gas production process, a content of a low-boiling component in a gas fed into a reformer, which is a reactor; in other words, a content of a recycled material may be determined as appropriate, and it may be, for example, 40 to 75 mol %.

For the purpose of recycling a low-boiling component, a known technique, e.g., appropriately providing a recycle line with a pressurization means can be employed.

Industrial Applicability

As described above, a catalyst for producing a liquefied petroleum gas according to the present invention is a less deteriorative catalyst with a longer catalyst life, which can produce a hydrocarbon containing propane or butane as a main component, i.e., a liquefied petroleum gas (LPG), by reacting carbon monoxide and hydrogen, with high activity, high selectivity and high yield. Therefore, by using the catalyst of this invention, propane and/or butane can be stably produced for a

long period with high activity, high selectivity and high yield, from a carbon-containing starting material such as a natural gas or a synthesis gas. In other words, by using the catalyst of this invention, a liquefied petroleum gas with a high concentration of propane and/or butane can be stably produced for a long period with high yield, from a carbon-containing starting material such as a natural gas or a synthesis gas.

The LPG Process

  • Membrane process
  • Catalytic hydro cracking process
  • Dehydration process
  • Catalytic process
  • Objective of the catalytic process
  • Detailed description
  • Synthesis gas production process
  • Industrial applicability