KR101188038B1 - Separation of propylene oxide from a mixture comprising propylene oxide and methanol - Google Patents

Abstract

The present invention relates to a process for separating propylene oxide from a mixture (M) comprising 5% to 50% by weight propylene oxide and 50% to 85% by weight methanol.

(i) introducing said mixture (M) into an extractive distillation column;

(Ii) further introducing a polar solvent into said extractive distillation column; And

(Iii) distilling propylene oxide from the extractive distillation column overhead at a pressure of 300 mbar to 750 mbar and a bottom temperature of 40 ° C. to 70 ° C.

Disclosed is a method comprising a.

Description

Process for separating propylene oxide from a mixture comprising propylene oxide and methanol TECHNICAL FIELD

The present invention relates to a process for separating propylene oxide from a mixture (M) comprising 5% to 50% by weight of propylene oxide and 50% to 85% by weight of methanol. The method

(i) introducing said mixture (M) into an extractive distillation column;

(Ii) further introducing a polar solvent into said extractive distillation column; And

(Iii) distilling propylene oxide from the extractive distillation column overhead at a pressure of 300 mbar to 750 mbar and a bottom temperature of 40 ° C. to 70 ° C.

It includes.

According to a preferred embodiment of the invention, the mixture M is formed by reacting propene with hydrogen peroxide in the presence of a titanium zeolite fixed bed catalyst in methanol as a solvent. Accordingly, the present invention also provides a process for producing propylene oxide, wherein the reaction comprises reacting propene with hydrogen peroxide in the presence of a titanium zeolite fixed bed catalyst in methanol as a solvent. According to this epoxidation reaction, either directly or after one or more aftertreatment steps, a mixture (M) comprising 5% to 50% by weight of propylene oxide and 50% to 85% by weight of methanol is formed, Way

(i) introducing said mixture (M) into an extractive distillation column;

(Ii) further introducing a polar solvent into said extractive distillation column;

(Iii) distilling the propylene oxide from the top of the extractive distillation column at a pressure of 300 mbar to 750 mbar and a bottom temperature of 40 ° C. to 70 ° C.

.

Due to the entrainment of the azeotrope, propylene oxide and methanol are at atmospheric or superatmospheric pressure, substantially 1 bar to 5, only when a distillation column with a very large number of theoretical plates is used and the reflux ratio is set very high. It can be separated by distillation in the bar range.

Such mixtures comprising propylene oxide and methanol are formed, for example, in an epoxidation process in which propene is reacted with a hydroperoxide such as hydrogen peroxide in the presence of methanol as solvent.

US 5,849,938 discloses a process for the extraction of propene from methanol in crude olefin epoxidation products by extractive distillation, wherein relatively heavy polar solvents having hydroxy groups such as water or propylene glycol are used as extraction solvents. It is mentioned that propylene glycol is particularly preferred. According to the prior art of this document, the distillation columns used usually have 20 to 60 theoretical stages, and the reflux / distillate ratio is generally in the range of 5 to 15. According to an embodiment, the typical ratio is nine. Typical bottom temperatures are from 90 ° C. to 120 ° C. and the pressure at which distillation is carried out is from 0.55 bar to 3.44 bar. According to an embodiment, the preferred bottom pressure of the distillation column is 2.76 bar and therefore higher than the standard pressure. A fraction comprising 300 or 1,500 ppm of methanol is obtained as a typical propylene oxide fraction. The bottom fraction obtained according to the examples contains up to 6,300 ppm of propylene oxide.

US 6,500,311 B1 discloses a process for separating methanol and propylene oxide. As extraction solvents, nonpolar solvents, ie C7-C9 hydrocarbons such as n-octane, are used.

It is an object of the present invention to provide propylene oxide from methanol, wherein the top and bottom streams are provided with improved energy balance compared to the processes described in the prior art and at the same time containing less impurities to methanol and propylene oxide, respectively. It is to provide a way to separate.

Another object of the present invention is to provide a process for separating propylene oxide from methanol, wherein mild distillation conditions are used as compared to the prior art and cheap extraction solvents are used.

Yet another object of the present invention is to provide a process for producing propylene oxide during the separation of propylene oxide from methanol, wherein the separation of propylene oxide has the advantages mentioned above and thus the process for producing propylene oxide Compared with the prior art, it is advantageous in terms of energy and purity of the distillation fraction.

Summary of the Invention

The present invention provides a process for separating propylene oxide from a mixture (M) comprising 5 wt% to 50 wt% propylene oxide and 50 wt% to 85 wt% methanol.

(i) introducing said mixture (M) into an extractive distillation column;

(Ii) further introducing a polar solvent into said extractive distillation column; And

(Iii) distilling the propylene oxide from the top of the extractive distillation column at a pressure of 300 mbar to 750 mbar and a bottom temperature of 40 ° C. to 70 ° C.

It relates to a method comprising a.

The present invention provides a process for separating propylene oxide from a mixture (M) comprising 5 wt% to 15 wt% propylene oxide, 50 wt% to 85 wt% methanol, and 10 wt% to 25 wt% water. Way

(i) introducing said mixture (M) into an extractive distillation column;

(Ii) further introducing water to the extractive distillation column in an amount of up to 2% by weight of the mixture (M);

(Iii) distilling the propylene oxide from the top of the extractive distillation column at a pressure of 300 mbar to 750 mbar and a bottom temperature of 40 ° C. to 70 ° C.

It relates to a method comprising a.

The present invention provides a process for separating propylene oxide from a mixture (M) comprising 5 wt% to 15 wt% propylene oxide, 50 wt% to 85 wt% methanol, and 10 wt% to 25 wt% water. Way

(i) introducing said mixture (M) into an extractive distillation column;

(Ii) further introducing water into said extractive distillation;

(Iii) distilling the propylene oxide from the top of the extractive distillation column at a pressure of 300 mbar to 750 mbar and a bottom temperature of 40 ° C. to 70 ° C.

Wherein the distillate is partially refluxed in the extractive distillation column and the mass ratio of reflux to distillate is 4 or less.

The present invention provides a process for separating propylene oxide from a mixture (M) comprising 5 wt% to 15 wt% propylene oxide, 50 wt% to 85 wt% methanol, and 10 wt% to 25 wt% water. Way

(i) introducing said mixture (M) into an extractive distillation column;

(Ii) further introducing water into said extractive distillation;

(Iii) distilling propylene oxide from the top of said extractive distillation column at a pressure of 300 mbar to 750 mbar and a bottom temperature of 40 ° C. to 70 ° C .;

(Iii) recovering a bottoms stream comprising up to 100 ppm of propylene oxide from the extractive distillation column and recovering a tops stream comprising up to 100 ppm of methanol from the extractive distillation column

It relates to a method comprising a.

The present invention provides a process for separating propylene oxide from a mixture (M) comprising 5 wt% to 15 wt% propylene oxide, 50 wt% to 85 wt% methanol, and 10 wt% to 25 wt% water. Way

(i) introducing said mixture (M) into an extractive distillation column;

(Ii) further introducing water into the extractive distillation column as steam at a pressure of up to 2 bar;

(Iii) distilling the propylene oxide from the top of the extractive distillation column at a pressure of 300 mbar to 750 mbar and a bottom temperature of 40 ° C. to 70 ° C.

It relates to a method comprising a.

The present invention provides a process for separating propylene oxide from a mixture (M) comprising 5 wt% to 15 wt% propylene oxide, 50 wt% to 85 wt% methanol, and 10 wt% to 25 wt% water. Way

(i) introducing said mixture (M) into an extractive distillation column;

(Ii) further introducing water to the extractive distillation column in an amount of up to 2% by weight of the mixture (M);

(Iii) distilling propylene oxide from the top of said extractive distillation column at a pressure of 300 mbar to 500 mbar and a bottom temperature of 40 ° C. to 70 ° C .;

(Iii) recovering a bottoms stream comprising up to 100 ppm of propylene oxide from the extractive distillation column and recovering a tops stream comprising up to 100 ppm of methanol from the extractive distillation column

It relates to a method comprising a.

The present invention comprises reacting propene with hydroxide in methanol as a solvent to contain 5% to 15% by weight of propylene oxide, 50% to 85% by weight of methanol and 10% to 25% by weight of water. A process for preparing propylene oxide, comprising obtaining a mixture (M), or obtaining a mixture which provides, according to workup, the mixture (M).

(i) introducing said mixture (M) into an extractive distillation column;

(Ii) further introducing water to the extractive distillation column in an amount of 0.45% to 1% by weight of the mixture M as steam at a pressure of up to 2 bar;

(Iii) distilling propylene oxide from the top of said extractive distillation column as a top stream at a pressure of 450 mbar to 500 mbar and a bottom temperature of 50 ° C. to 60 ° C .;

(Iii) recovering a bottoms stream comprising up to 100 ppm of propylene oxide from the extractive distillation column and recovering a tops stream comprising up to 50 ppm of methanol from the extractive distillation column

It relates to a method further comprising.

1 is a view showing a preferred embodiment of the present invention.

2 shows a process of the prior art.

3 is a view showing still another process of the prior art.

According to the invention, the propylene oxide is separated from the mixture M comprising 5% to 50% by weight propylene oxide and 50% to 85% by weight methanol. In a preferred embodiment of the invention, the mixture (M) is 5% to 15% by weight, preferably 6% to 12% by weight, particularly preferably 8% to 10.5% by weight of propylene oxide, and 55% % To 85% by weight, preferably 60% to 80% by weight, particularly preferably 65% to 75% by weight of methanol.

In the context of the process of the invention, the mixture (M) may comprise one or more further compounds. For these compounds, there are no particular restrictions on the conditions under which propylene oxide can be distilled from the top of the extractive distillation column in order to separate propylene oxide from the methanol contained in (M).

According to a preferred embodiment, the mixture (M) is also up to 25% by weight, more preferably 1 to 25% by weight, even more preferably based on the total weight of the water, more preferably the mixture (M) 2 wt% to 25 wt%, even more preferably 3 wt% to 25 wt%, even more preferably 4 wt% to 25 wt%, even more preferably 5 wt% to 25 wt%, more Even more preferably from 6 wt% to 25 wt%, more preferably from 7 wt% to 25 wt%, more preferably from 8 wt% to 25 wt%, even more preferably from 9 wt% to 25% by weight and even more preferably 10% to 25% by weight of water. Thus, the mixture M can be, for example, 10% to 25% or 10% to 20% or 10% to 15% or 15% to 25% by weight based on the total weight of the mixture M. Weight percent or 15 weight percent to 20 weight percent or 20 weight percent to 25 weight percent water.

According to a preferred embodiment wherein (M) comprises from 10% to 25% by weight of water, (M) is preferably from 5% to 45% by weight, more preferably based on the total weight of the mixture (M) Is 5 wt% to 40 wt%, even more preferably 5 wt% to 35 wt%, even more preferably 5 wt% to 30 wt%, even more preferably 5 wt% to 25 wt%, Even more preferably 5% to 20% by weight and even more preferably 5% to 15% by weight of propylene oxide.

Thus, the present invention also provides that the mixture (M) comprises from 50% to 85% by weight of methanol, from 5% to 15% by weight of propylene oxide and from 10% to 25% by weight based on the total weight of the mixture (M). It provides a method as described above comprising water.

In addition to methanol, propene and preferably water, the mixture (M) may comprise one or more further compounds.

According to a preferred embodiment of the invention, the mixture (M) is formed directly or indirectly from the process of producing propylene oxide by reacting propene with hydroperoxide in the presence of methanol as solvent. Thus, the mixture M may also comprise unreacted propene and / or unreacted hydroperoxide and / or one or more by-products of the epoxidation reaction, such as propylene glycol and / or acetaldehyde.

The reaction mixture obtained from the epoxidation reaction can be introduced directly as mixture (M) in step (i) when the content of (M) in methanol, propylene oxide and preferably water is in the above-mentioned range.

According to a particularly preferred embodiment of the invention, the reaction mixture obtained from the epoxidation reaction is worked up before being introduced into step (i) of the process of the invention. The workup of the reaction mixture obtained from the epoxidation reaction can be carried out in such a way that each can be envisaged for the conditions under which the mixture M which can be introduced in step (i) is obtained. The workup may comprise separating and / or adding one or more compounds from and / or to the mixture obtained from the epoxidation reaction. Preferably, one or more compounds are separated from the mixture obtained from the epoxidation reaction.

According to a more preferred embodiment of the present invention, propylene oxide, methanol and, preferably, at least one compound having a lower boiling point than water are separated from the mixture obtained during the workup from the epoxidation reaction.

Depending on the reaction conditions applied and the reactants used in the epoxidation reaction, these low boilers can be, for example, unreacted propene and / or propane, the latter propane being for example chemical grade propene of propene: propane When used as a reactant with a volume ratio of about 99.5: 0.5 to 94: 6, it can be introduced into the epoxidation reaction.

According to another preferred embodiment of the invention, the unreacted propene is separated from the reaction mixture obtained by the epoxidation reaction in one or more distillation columns, the respective amounts of which are mentioned above in relation to methanol, propylene oxide and water. The high boiling fractions contained within are introduced as (M) in step (i) of the process of the invention.

Accordingly, the present invention also relates to reacting propene with hydroperoxide in methanol as a solvent to provide 5 to 15 weight percent propylene oxide, 50 to 85 weight percent methanol and 10 to 25 weight percent water. Provided is a process for preparing propylene oxide, comprising providing a mixture (M) comprising, or preferably a mixture comprising propylene oxide, methanol, water, unreacted propene and optionally propane, wherein the latter The mixture was subjected to workup to give a mixture M comprising 5 wt% to 15 wt% propylene oxide, 50 wt% to 85 wt% methanol, and 10 wt% to 25 wt% water, the mixture at least as described above. And as mentioned later, in addition to steps (i) to (iii). According to this embodiment of the invention, the aftertreatment is preferably carried out by distillation of propene and, if present, preferably also propane and / or acetaldehyde, preferably up to 500 ppm, preferably up to 400 ppm and especially Preferably at most 350 ppm propene and at most 50 ppm propane, preferably at most 25 ppm and particularly preferably at most 10 ppm propane, and preferably at most 200 ppm, more preferably at most 150 ppm and particularly preferably Comprises providing a mixture (M) comprising not more than 100 ppm acetaldehyde. Thus, particularly preferably a mixture M comprising 350 ppm or less propene, 10 ppm or less propane and 100 ppm or less acetaldehyde is obtained. According to another preferred embodiment of the present invention, the mixture M introduced in step (i) has a high boiling point of 1% by weight or less, more preferably 0.75% by weight or less and particularly preferably 0.65% by weight or less. Compounds such as methoxypropanol and / or hydroperoxide.

In the context of the present invention, the term "hydroperoxide" means a compound of the formula ROOH. A detailed description of the preparation of hydroperoxides and in particular the hydroperoxides that can be used in the process of the invention can be found in DE-A-198 35 907, the contents of which are incorporated herein by reference. Examples of hydroperoxides that can be used for the purposes of the present invention are in particular t-butyl hydroperoxide, ethylbenzene hydroperoxide, t-amyl hydroperoxide, cumene hydroperoxide, cyclohexyl hydroperoxide, methylcyclohexyl Hydroperoxide, tetrahydronaphthalene hydroperoxide, isobutylbenzene hydroperoxide, ethylnaphthalene hydroperoxide, peracids such as peracetic acid and hydrogen peroxide. Mixtures of two or more hydroperoxides may also be used according to the invention. In the process of the present invention, it is preferable to use hydrogen peroxide as the hydroperoxide, and it is also preferable to use an aqueous hydrogen peroxide solution. Most preferably, the aqueous hydrogen peroxide solution is present in an amount of 1% to 90% by weight, more preferably 10% to 70% by weight and particularly preferably 30% to 50% by weight, based on the total weight of the solution. Include. It is also possible to use mixtures of two or more different hydroperoxides.

The epoxidation reaction of the mixture (M) obtained directly or indirectly can be carried out in each suitable catalyst or in an appropriate combination of two or more catalysts. Particularly preferably, titanium containing zeolites are used, with zeolites known to those skilled in the art as "titanium silicalite" (TS). Such titanium containing zeolites, in particular zeolites having a crystalline structure of the MFI-type, as well as methods for their preparation, are described, for example, in WO 98/55228, EP-AO 311 983 or EP-AO 405 978. Each content disclosed in these patents is incorporated herein by reference. In addition to Si and Ti, the zeolitic material may contain additional elements such as aluminum, zirconium, tin, iron, cobalt, nickel, gallium, boron or small amounts of fluorine. It is also possible for the titanium of the zeolite to be partially or completely replaced by vanadium, zirconium or niobium, or any mixture of two or more of these components. Titanium-containing zeolites having MFI-structures are known to exhibit patterns characteristic of x-ray diffraction. In addition, these materials have vibration bands in the infrared (IR) at about 960 cm ⁻¹ . Thus, it is possible to distinguish titanium-containing zeolites from crystalline or amorphous TiO ₂ -phases or alkali metal titanates. In another preferred embodiment, the at least one zeolite catalyst comprises at least one of titanium, germanium, tellurium, vanadium, chromium, niobium, zirconium elements. Pentasil zeolite structures, in particular ABW-, ACO-, AEI-, AEL-, AEN-, AET-, AFG-, AFI-, AFN-, AFO-, AFR-, AFS- via X-ray diffraction , AFT-, AFX-, AFY-, AHT-, ANA-, APC-, APD-, AST-, ATN-, ATO-, ATS-, ATT-, ATV-, AWO-, AWW-, BEA-, BIK -, BOG-, BPH-, BRE-, CAN-, CAS-, CFI-, CGF-, CGS-, CHA-, CHI-, CLO-, CON-, CZP-, DAC-, DDR-, DFO-, DFT-, DOH-, DON-, EAB-, EDI-, EMT-, EPI-, ERI-, ESV-, EUO-, FAU-, FER-, GIS-, GME-, GOO-, HEU-, IFR- , ISV-, ITE-, JBW-, KFI-, LAU-, LEV-, LIO-, LOS-, LOV-, LTA-, LTL-, LTN-, MAZ-, MEI-, MEL-, MEP-, MER -, MFI-, MFS-, MON-, MOR-, MSO-, MTF-, MTN-, MTT-, MTW-, MWW-, NAT-, NES-, NON-, OFF-, OSI-, PAR-, PAU-, PHI-, RHO-, RON-, RSN-, RTE-, RTH-, RUT-, SAO-, SAT-, SBE-, SBS-, SBT-, SFF-, SGT-, SOD-, STF- , STI-, STT-, TER-, THO-, TON-, TSC-, VET-, VFI-, VNI-, VSV-, WIE-, WEN-, YUG-, ZON, and at least two or more of the above-mentioned structures Zeolite catalyst having a structure type that can be assigned to the structure type of the mixed structure of Particularly preferred. In addition, the use of a titanium-containing zeolite catalyst having a structure of ITQ-4, ITQ-9, SSZ-24, TTM-1, UTD-1, CIT-1 or CIT-5 is envisaged. Additional titanium containing zeolites are of the ZSM-48 or ZSM-12 structure type. Titanium-containing zeolites of the structures MFI, MEL or MFI / MEL mixed structures as well as MWW, BEA or mixed structures thereof are preferred in the present invention. In the present invention, titanium-containing zeolites exhibiting a structure heterogeneous to zeolite beta as well as titanium-containing zeolite catalysts generally referred to as "TS-1", "TS-2" or "TS-3" are also preferred.

It is also possible to carry out the reaction using a suspension catalyst, but it is preferable to use a heterogeneous catalyst, more preferably a fixed bed catalyst. Thus, according to this preferred embodiment of the invention, it is not necessary to separate the catalyst from the reaction mixture obtained from the epoxidation reaction.

Thus, the present invention also provides a process for separating propylene oxide from a mixture (M) comprising propylene oxide, methanol and preferably water as described above, wherein the mixture (M) is a solvent after one or more aftertreatment steps. In the presence of a fixed bed catalyst, preferably a fixed bed zeolite catalyst, more preferably a fixed bed titanium zeolite catalyst, even more preferably a fixed bed TS-1 type titanium silicalite catalyst in a hydroperoxide, preferably Obtained directly or indirectly from the epoxidation process with reaction with hydrogen peroxide, the catalyst is not separated from the reaction mixture formed by the epoxidation process.

Accordingly, the present invention also relates to reacting propene in a methanol as a solvent with a hydroperoxide, preferably hydrogen peroxide, from 5% to 15% by weight of propylene oxide, from 50% to 85% by weight of methanol and from 10% to 25%. Providing a mixture (M) comprising weight percent water, or preferably a mixture comprising propylene oxide, methanol, water, unreacted propene and optionally propane. Wherein the mixture is post-treated to provide a mixture M comprising 5 wt% to 15 wt% propylene oxide, 50 wt% to 85 wt% methanol, and 10 wt% to 25 wt% water, The mixture is further applied at least to the steps (i) to (v) mentioned above and hereinafter, wherein the epoxidation is a fixed bed catalyst, preferably a fixed bed zeolite catalyst, more preferably fixed bed titanium It is not necessary to separate the catalyst from the reaction mixture formed in the presence of a zeolite catalyst, even more preferably a fixed bed TS-1 type titanium silicalite catalyst, which is formed by the epoxidation process.

In step (i) of the present invention, any suitable extractive distillation column may be used. Preferably, the column has no more than 80 theoretical stages, such as 10-80 or 20-80 or 30-80 or 40-80 or 50-80 or 60-80 or preferably Preferably more than 60 to 80, such as 61 to 80 or 65 to 80 or 70 to 80 or 75 to 80 theoretical groups. Preferably, the column has more than 60 theoretical stages, such as 61 to 65 theoretical stages. Two or more columns may be used according to the invention, wherein two or more columns may be connected in series and / or two or more columns may be arranged in parallel. It is preferable to use one column.

According to step (ii) of the present invention, one or more polar solvents are added. With regard to the chemical properties of one or more polar solvents, there are no particular limitations on the conditions under which extraction distillation is possible, depending on the conditions of step (iii). Thus, hydrocarbons, in particular C7-C9 hydrocarbons such as n-octane, are not used alone as extraction solvents or in combination with polar solvents such as water.

Preferred polar solvents are water, alcohols having one or more hydroxy groups, such as one, two, three or more hydroxy groups, preferably monools and diols, or ethers, preferably one or more hydroxy groups, preferably one hydroxy group Branches are ether compounds such as 1-methoxy-2-propanol and / or 2-methoxy-1-propanol. Water is particularly preferred, as such water can be used, for example, demineralized water, drinking water, suitable industrial water, suitable wastewater, in particular suitably treated wastewater, suitable process water or mixtures of two or more thereof. The water introduced into the process of the invention should be substantially free of organic substances, in particular methanol. According to one example of the invention, the water introduced in step (ii) is process water from a suitable process as carried out in the epoxidation plant in which the process of the invention is carried out. According to one aspect of the invention, as in the case of step (v) described herein, the process water is taken from a process in an epoxidation plant where methanol and water, which are epoxidation reaction solvents, are separated from each other. Preferably, water is taken from the bottom of at least one distillation column where methanol and water, the epoxidation reaction solvent, are separated. More preferably, the water obtained from the separation process is optionally introduced in step (ii) after one or more further purification steps, and the methanol obtained from the separation process is a solvent in the epoxidation reaction, optionally after one or more further purification steps. As recycled. Thus, the present invention also provides for the separation of methanol and water from one another to work up a mixture comprising methanol and water, and the separated water to step (ii), optionally after one or more further purification steps, preferably without further purification steps. The above-mentioned process is carried out in which the integrated process is carried out by recycling the optionally separated methanol as a solvent to an epoxidation reaction in which the mixture (M), which is optionally introduced into step (i) after one or more further purification steps, is formed.

The present invention therefore also provides a process for separating propylene oxide from the mixture (M) described above, characterized in that in step (ii) water is introduced into the extractive distillation column as a polar solvent.

According to an even more preferred embodiment, no solvent other than water is introduced as polar solvent in step (ii). According to another preferred embodiment, propylene glycol is not used as polar solvent.

Preferred embodiments according to the invention in which water is used as the polar solvent but no propylene glycol is used, in particular, show the advantage that water is cheaper than propylene glycol and can be disposed of without ecologically adverse effects. When propylene glycol is used as a polar solvent, post-treatment and recycling of propylene glycol is necessary to make the process ecologically and economically efficient. However, the workup essentially involves one or more additional process steps that are unnecessary when water is used as the polar solvent.

According to a preferred embodiment of the invention, one or more polar solvents are introduced into the extractive distillation column in about 15 theoretical stages, more preferably about 10 theoretical stages below the top of the extractive distillation column.

One or more solvents, preferably water, may be introduced into the column as liquid or vapor, or as liquid and vapor. If two or more solvents are used, one or more solvents may be introduced as a liquid and one or more other solvents may be introduced as a vapor.

According to a preferred embodiment, water is used as the polar solvent and introduced into the extractive distillation column as liquid and / or steam, more preferably as steam. Even more preferably, the steam introduced in step (ii) has a pressure of 2 bar or less, more preferably 1 bar or less, even more preferably 900 mbar or less and particularly preferably 800 bar or less.

With regard to the amount of solvent, there is no particular limitation with regard to the polar solvent which is preferably introduced into the extractive distillation column according to step (ii). Preferably, the polar solvent, in particular water, is introduced in an amount of up to 2% by weight, based on the weight of the mixture (M). More preferably the solvent, even more preferably the polar solvent, is based on the weight of the mixture (M) at most 1.8% by weight, more preferably at most 1.6% by weight, even more preferably at most 1.4% by weight, even more preferably It is introduced in amounts of up to 1.2% by weight and more preferably up to 1% by weight. It is also preferred that the amount of polar solvent is at least 0.2% by weight, more preferably at least 0.25% by weight, even more preferably at least 0.3% by weight and even more preferably at least 0.4% by weight, based on the weight of the mixture (M). Do. Thus, for example, the preferred range is from 0.2% to 2% by weight, more preferably from 0.3% to 1.6% by weight, even more preferably from 0.4% to 1.2% by weight, based on the weight of the mixture (M). And more preferably 0.45% to 1% by weight.

Thus, the invention also provides in step (ii) that at least one polar solvent, in particular water, is present in an amount of 0.45% to 1% by weight, based on the weight of the mixture (M), preferably as a vapor at a pressure of up to 2 bar. A process for separating propylene oxide from the mixture (M) as described above, which is introduced, is provided.

The preferred mass ratio of propylene oxide contained in (M) to the extraction solvent added in step (ii) is from 0.6: 1 to 70: 1, more preferably from 1: 1 to 20: 1 and particularly preferably from 3: 1 to 8: 1, for example 4: 1 to 7: 1 or 5: 1 to 7: 1 or 6: 1 to 7: 1.

The distillation in step (iii) is carried out at a bottom temperature of 40 ° C. to 70 ° C. and a pressure in the range of 300 mbar to 750 mbar. Other preferred pressure ranges in which distillation is carried out are from 300 mbar to 700 mbar, more preferably from 300 mbar to 650 mbar, even more preferably from 300 mbar to 600 mbar, even more preferably from 300 mbar to 550 mbar and more Preferably from 300 mbar to 500 mbar, or from 350 mbar to 750 mbar, more preferably from 400 mbar to 750 mbar, even more preferably from 450 mbar to 750 mbar, even more preferably from 450 mbar to 700 mbar, more Even more preferably 450 mbar to 650 mbar, more preferably 450 mbar to 600 mbar, even more preferably 450 mbar to 550 mbar and particularly preferably 450 mbar to 500 mbar.

Thus, the present invention also provides for the separation of propylene oxide from the mixture M as described above, characterized in that in step (iii), distillation is carried out at a pressure of 300 mbar to 500 mbar, in particular 450 mbar to 500 mbar. Provide a method.

As used herein, the term "pressure at which distillation is performed" means the top pressure of the column where distillation is performed.

Particularly preferred bottom temperatures of the extractive distillation are, for example, 40 ° C. to 70 ° C. or 40 ° C. to 65 ° C. or 40 ° C. to 60 ° C. or 45 ° C. to 70 ° C. or 45 ° C. to 65 ° C. or 45 ° C. to 60 ° C. or 50 ° C to 70 ° C or 50 ° C to 65 ° C or 50 ° C to 60 ° C.

Particularly preferred combinations of pressure ranges and and bottom temperatures are, for example, 300 mbar to 750 mbar and 40 ° C. to 70 ° C. or 300 mbar to 500 mbar and 40 ° C. to 60 ° C. or 450 mbar to 500 mbar and 50 ° C. to 60 ℃.

Thus, the invention also provides that in step (iii) the distillation is carried out at a pressure of 300 mbar to 500 mbar and a temperature of 40 ° C. to 60 ° C., more preferably at a pressure of 450 mbar to 500 mbar and a temperature of 50 ° C. to 60 ° C. Provided is a process for separating propylene oxide from the mixture (M) as described above, which is carried out.

Thus, the present invention preferably uses water as the extraction solvent in an amount of up to 2% by weight based on the weight of (M) and the extraction distillation is at a pressure of up to 750 mbar, preferably from 300 mbar to 750 mbar, more Preferably a pressure of 300 mbar to 500 mbar and particularly preferably of 450 mbar to 500 mbar and at the same time a temperature of 70 ° C. or less, preferably 40 ° C. to 70 ° C., more preferably 40 ° C. to 60 ° C. and even more preferred. Preferably by extraction distillation, characterized in that it is carried out at a temperature of 50 ℃ to 60 ℃, such as about 51 ℃, 52 ℃, 53 ℃, 54 ℃, 55 ℃, 56 ℃, 57 ℃, 58 ℃ or 59 ℃ A process for separating propylene oxide from the mixture (M) is provided.

As the extractive distillation column, virtually any column can be used. Particular preference is given to using a distillation column consisting of a packing column, more preferably a regularly packed packing column. Such packing columns have high resolution per meter of packing and only show very small pressure drops. The regular packing mentioned may be of virtually any type, but packing having a specific surface area in the range of 100 m 2 / m 3 to 750 m 2 / m 3 is preferred. For example metal sheet packing from Montz (type B1 100 to B1 500) or Sulzer ChemTech (Mellapak 125 to Mellapak 750), or mesh from Montz (type A3 500 to A3 750) or Sulzer ChemTech (type BX or CY) Packing is available. The unit m 2 / m 3 means the geometric surface area of the material forming the packing per cubic meter of packing.

According to the invention, the propylene oxide fraction separated from methanol and water is preferably distilled from the top.

The propylene oxide fraction which is distilled from the top in step (iii) is preferably at least 99.0% by weight, more preferably at least 99.5% by weight, even more preferably at least 99.6% by weight and more based on the total weight of the propylene oxide fraction Even more preferably at least 99.7% by weight of propylene oxide.

The propylene oxide fraction distilled from the top in step (iii) is preferably at most 500 ppm, more preferably at most 200 ppm, even more preferably at most 100 ppm, even more preferably based on the total weight of the propylene oxide fraction. Comprises up to 50 ppm, even more preferably up to 20 ppm and even more preferably up to 10 ppm methanol.

The propylene oxide fraction distilled from the top in step (iii) is preferably at most 200 ppm, more preferably at most 100 ppm, even more preferably at most 50 ppm, even more preferably based on the total weight of the propylene oxide fraction. Comprises up to 25 ppm and more preferably up to 20 ppm water.

The propylene oxide fraction which is distilled from the top in step (iii) is preferably at most 0.5% by weight, more preferably at most 0.3% by weight and more preferably at most 0.25% by weight, based on the total weight of the propylene oxide fraction. Pens and propane.

In the extractive distillation conditions according to the invention, the high boiling fraction at the bottom of the column, in addition to water and methanol, is 100 ppm or less, preferably 75 ppm or less and particularly preferably 50 ppm or less, based on the weight of the high boiling fraction. Propylene oxide.

In the extractive distillation conditions according to the invention in which water other than propylene glycol is used as the extraction polar solvent in step (ii), the high boiling fraction is not more than 1% by weight, preferably based on the weight of the high boiling fraction, in addition to water and methanol Preferably up to 0.5% by weight, particularly preferably up to 0.2% by weight of propylene glycol.

According to a particularly preferred embodiment of the present invention, the propylene oxide fraction distilled from the top in step (iii) is partially refluxed to the extractive distillation column. According to even more preferred embodiments, the mass ratio of reflux: distillate is less than 5, more preferably 4.5 or less, particularly preferably 4 or less, such as about 3.5 or about 3.6 or about 3.7 or about 3.8 or about 3.9 or 4 .

Thus, the present invention also provides a mixture M as described above, characterized in that the distillate obtained from the top in step (iii) is partially refluxed into the extractive distillation column, and the ratio of reflux to distillate is 4 or less. It provides a method for separating propylene oxide from.

Thus, the extractive distillation process of the present invention combines the advantages of low distillation pressure, low distillation temperature and at the same time a low reflux: distillate ratio.

The propylene oxide fraction distilled from the top is either used on its own or through one or more further workup steps if the content of the fractions for propene, propane and / or acetaldehyde is too high than the intended content of propylene oxide. Can be used. Such aftertreatment may include, for example, fractional distillation in which low boilers are recovered from the top and the purified propylene oxide fraction is recovered as a bottom stream or side stream. This bottoms stream can then be subjected to one or more further purification processes, if necessary.

The bottoms stream recovered from the extractive distillation column of step (iii) may be used on its own or after one or more workup steps in one or more other processes, or may be recycled in the process of the invention. According to a preferred embodiment of the invention, the bottoms stream is worked up in one, two or more stages so that at least 97 wt% methanol, up to 2 wt% water and up to 50 ppm acetaldehyde based on the total weight of the mixture Providing a mixture, wherein the purified methanol is recycled in the process of the invention, preferably as a solvent for the epoxidation reaction to give the mixture (M).

Depending on the polar solvent used as extraction solvent in step (ii), the solvent can be properly separated from the bottoms stream and recycled in the process of the invention, preferably as the polar solvent of step (ii). A further advantage of the preferred process of the invention in which water is used as polar solvent is that it is recycled to step (ii) because water can be purchased cheaply unlike propylene glycol as described for example as preferred extraction solvent in US Pat. No. 5,849,938. It is not necessary to work up the bottoms stream obtained in step (iii) to obtain a purified polar solvent.

Accordingly, the present invention reacts propene with a hydroperoxide, preferably hydrogen peroxide, in methanol as a solvent, preferably in the presence of a fixed bed titanium silicalite catalyst, thereby producing propylene oxide, methanol, water, unreacted propene and optionally propane. To form a mixture comprising, and post-treat the mixture to substantially completely remove the unreacted propene, resulting in 15 wt% propylene oxide, 50 wt% to 85 wt% methanol, and 10 wt% to 25 wt% Provided is a process for preparing propylene oxide to form a mixture (M) comprising water, the process comprising

(i) introducing said mixture (M) into an extractive distillation column;

(Ii) water in the extractive distillation column as a polar solvent, preferably water, more preferably at most 2 bar, preferably at most 1 bar, more preferably at most 900 mbar and particularly preferably at 800 mbar pressure Further introducing in an amount of up to 2% by weight, preferably 0.45% to 1% by weight of the mixture (M);

(Iii) a pressure of 300 mbar to 750 mbar, preferably 300 mbar to 500 mbar and particularly preferably 450 mbar to 500 mbar and 40 ° C. to 70 ° C., preferably 40 ° C. to 60 ° C., from the top of the extractive distillation column. Distilling propylene oxide as a top stream, particularly preferably at a bottom temperature of 50 ° C. to 60 ° C .;

(Iii) recovering from the extractive distillation column a bottoms stream comprising not more than 100 ppm, preferably not more than 75 ppm, particularly preferably not more than 50 ppm, based on the total weight of the bottoms stream, From the distillation column, up to 500 ppm, preferably up to 200 ppm, more preferably up to 100 ppm, more preferably up to 50 ppm, more preferably up to 20 ppm, particularly preferably based on the total weight of the top stream Recovering a top stream comprising 10 ppm or less of methanol; And

(v) optionally recycling methanol contained in the bottoms stream of step (iii) as a solvent, at least partially during the reaction of propene reacting with hydroperoxide

.

The following examples and drawings are used to illustrate the present invention, but are not intended to be limiting.

DETAILED DESCRIPTION OF THE DRAWINGS

1 shows a preferred embodiment according to the invention. The mixture M and the extraction solvent 1 are introduced into an extractive distillation column K200 (steps (i) and (ii)). Propylene oxide is distilled from the top of (K200) as top stream (step (iii)). Heat exchanger W230 is used to condense the top stream of extractive distillation column K200. As the coolant 3 used for the heat exchanger W230, cold water and cooling water are used, respectively. In order to heat the reboiler of column K200, heat exchanger W200 is used, and low pressure steam 2 is used as the heat source. The heat exchanger W220 is used to preheat the mixture M before the mixture M is introduced into the column K200.

2 shows an embodiment in which a nonpolar solvent is not used for distillation. The mixture M is introduced into distillation column K100. Propylene oxide is distilled from the top of (K100) as a top stream, which is compressed in an electric compressor (C100), the compressed vapor stream is condensed in a heat exchanger (W100), and at least a portion of the heat of condensation is an extractive distillation column. It is delivered to the reboiler used for (K100). As shown in FIG. 2, the heat exchanger W110 is used only for initiation of the distillation process, ie this heat exchanger W110 is not used during the continuous distillation process. Subsequently, the cooling and condensation stream exiting the heat exchanger W100 is divided so that a portion of the stream is sent to the first heat exchanger W130. The cooling stream exiting heat exchanger W130 is then sent to second heat exchanger W140 where the stream is further cooled and finally recycled as reflux at the top of column K100. If necessary and / or suitable, a portion of the energy stored in the bottoms stream of the distillation column is used in an additional heat exchanger W120 to heat the mixture M before the mixture M is introduced into the column K100. Or preheat.

3 shows another embodiment in which a nonpolar solvent is not used for distillation. Unlike the process shown in FIG. 2, the process according to FIG. 3 comprises an additional heat exchanger W101. Depending on the amount of energy recovered from the compressed vapor stream and delivered to the reboiler used in the distillation column (K100), the compressed vapor stream is split to transfer a portion of the stream to the heat exchanger (W100) and the remainder to the heat exchanger (W101). ) Can be transferred.

An epoxidation unit outlet stream in which almost all of the hard boiling components are separated is applied to different PO / MeOH separation units (Examples 1 to 3). In all examples, these streams have a composition according to Table 1.

Composition of the stream Stream mass%  Propylene  0.013423  Formaldehyde  0.011839  Acetaldehyde  0.026834  Propylene oxide  9.446765  Methanol  71.97108  water  17.54493  Glycol ether  0.43074  Propylene glycol  0.051477  Other (heavy boiling water)  Add to 100

Example  1: vacuum extraction distillation with water

The process of Example 1 was carried out in the unit of the apparatus illustrated in FIG. 1. In FIG. 1, a heat exchanger W230 is illustrated in which the top stream of the extractive distillation column K200 is cooled using cold water and cooling water, respectively. In order to heat the reboiler of the column, a heat exchanger W200 was used, and low pressure steam 2 was used as the heat source. The mixture M, ie the feed according to Table 1, was preheated using a heat exchanger W220 before introducing into the column K200.

The above mentioned stream (Table 1) was fed to an extraction distillation tower (K200) with 80 theoretical stages. Low pressure steam 2 was used to heat the reboiler of the column through heat exchanger W200. The condenser W230 was operated with cold water 3 produced in a cold water unit (not shown in FIG. 1). The column K200 was operated in vacuo at a pressure of 500 mbar and water was used as the extraction solvent 1. The feed point was as follows: the feed stream of the column was fed from column top to column 45 and water as extractant was supplied from column column to column 12 at a flow rate of 5.2% relative to propylene oxide contained in the feed stream. Purified propylene oxide was obtained from the top of the tower. The tower was operated at a mass reflux ratio (reflux: distillate) of 3.9. The top propylene oxide stream contained 10 ppm MeOH and 55 ppm water in addition to the light boiling. The bottoms stream contained 50 ppm of propylene oxide, MeOH, water and all other heavy boilers.

Example  2: 2 bar Extractive distillation using (a) water and (b) propylene glycol in Martial arts )

The process of Example 2 was carried out in the unit of the apparatus illustrated in FIG. 1. In FIG. 1, a heat exchanger W230 is illustrated in which the top stream of the extractive distillation column K200 is cooled using cold water and cooling water, respectively. In order to heat the reboiler of the column, a heat exchanger W200 was used, and low pressure steam 2 was used as the heat source. The mixture M, ie the feed according to Table 1, was preheated using a heat exchanger W220 before introducing into the column K200.

(a) The aforementioned stream (Table 1) was fed to an extractive distillation tower (K200) with 80 theoretical stages. Column K200 was operated at a pressure of 2 bar. Water was used as the extraction solvent (1). Low pressure steam was used as an external heat source to heat the reboiler of the column. Condenser W230 was operated with cooling tower water. The reboiler efficiency was 31.5 MW and the condenser efficiency was 30.2 MW. The feed point is as follows: the feed stream of the column was fed from the column top to stage 50 and water as extractant was fed from the column top to stage 12 at a flow rate of 10.4% relative to the propylene oxide contained in the feed stream. . The column is operated at a mass reflux ratio (reflux: distillate) of 6.1. Purified propylene oxide was obtained from the top of the tower. The top propylene oxide stream contained 10 ppm MeOH and 1500 ppm water, in addition to the light boiling. The bottoms stream contained 50 ppm of propylene oxide, MeOH, water and all other heavy boilers.

(b) The above mentioned stream (Table 1) was fed to an extractive distillation tower (K200) with 80 theoretical stages. Column K200 was operated at a pressure of 2 bar. Propylene glycol was used as the extraction solvent (1). Low pressure steam was used as an external heat source to heat the reboiler of the column. Condenser W230 was operated with cooling tower water. The reboiler efficiency was 36.5 MW and the condenser efficiency was 34.5 MW. The feed point is as follows: the feed stream of the column is fed from the column top to stage 60 and propylene glycol as the extraction solvent is supplied from the column top to stage 2 at a flow rate of 30% relative to the propylene oxide contained in the feed stream. It was. The tower was operated at a mass reflux ratio (reflux: distillate) of 7.3. Purified propylene oxide was obtained from the top of the tower. The top propylene oxide stream contained 10 ppm MeOH in addition to the light boiling. The bottoms stream contained 50 ppm of propylene oxide, MeOH, water, added propylene glycol and all other heavy boilers.

Example  3: top of the distillation column Stream  Fractional distillation without polar solvent, including compression, Comparative example )

The process of Example 3 was performed in the unit of the apparatus illustrated in FIG. 3, respectively.

The above mentioned stream (Table 1) was fed to a distillation tower (K100) equipped with an electric compressor (C100) for compressing the top steam discharge stream at the top of the column and having 80 theoretical stages. This stream was used as a reboiler heat source for the distillation column. Column K100 was operated in vacuo at a pressure of 500 mbar. No extraction solvent was used. The feed point of the feed stream was only 68 from the column top. Purified propylene oxide was obtained from the top of the tower. The tower was operated at a mass reflux ratio (reflux: distillate) of 9.4. The reboiler efficiency is 49.5 MW. The top propylene oxide stream contains 10 ppm of MeOH in addition to the light. The bottoms stream contains 50 ppm of propylene oxide, MeOH, water and all other heavy boilers.

Table 2 below summarizes the examples described above:

Synthesis of the above-described embodiment Example One 2a 2b 3 Extraction solvent water water Propylene
Glycol --- Top pressure [bar] 0.5 2 2 0.5 Top part temperature [℃] 16.1 54.8 54.8 16.1 Top Steam Stream Compression radish radish radish U Theory 80 80 80 80 Feed point (from the top) 45 50 62 68 Extraction solvent feed point (from the top) 12 12 2 --- Mass ratio
Extraction solvent / propylene oxide [%] 5.2 10.4 30 --- Mass reflux ratio 3.9 6.1 7.3 9.4 Bottom temperature [℃] of (K100 / 200) 55.9 89.5 91.5 55.8 In bottom stream
Residual amount of propylene oxide [ppm] 50 50 50 50 Residual MeOH in the distillation stream [ppm] 10 10 10 10 Reboiler efficiency of (K100) or (K200) [MW] 22 31.5 36.5 49.5 Electric Condenser Energy Consumption [MW] (C100) --- --- --- 14.5 Condenser Cooling Tower Water Capacity [MW] (W230) --- 30.2 34.5 --- Condenser Cold Water Capacity [MW] (W230) 21.1 --- --- --- Cooling Tower [MW] (W130) --- --- --- 6.0 Cold Water [MW] (W140) --- --- --- 3.6 Heat source reboiler (K100 / K200) Low pressure
steam Low pressure
steam Low pressure
steam Compression top
Stream steam

Claims (14)

A process for separating propylene oxide from a mixture (M) comprising 5 wt% to 50 wt% propylene oxide and 50 wt% to 85 wt% methanol, (i) introducing said mixture (M) into an extractive distillation column; (Ii) further introducing a polar solvent into the extractive distillation column, wherein the polar solvent is water, monool, diol or an ether compound having one hydroxy group; And (Iii) distilling propylene oxide from the extractive distillation column overhead at a pressure of 300 mbar to 750 mbar and a bottom temperature of 40 ° C. to 70 ° C. ≪ / RTI > The method of claim 1, wherein the ether compound having one hydroxy group is 1-methoxy-2-propanol or 2-methoxy-1-propanol. The process according to claim 1 or 2, wherein the mixture (M) comprises 5 wt% to 15 wt% propylene oxide and further comprises 10 wt% to 25 wt% water. The process according to claim 1 or 2, wherein the polar solvent is introduced in an amount of up to 2% by weight of the mixture (M). The process according to claim 1 or 2, wherein the extractive distillation column has no more than 80 theoretical plates. The process according to claim 1 or 2, wherein water is used as a polar solvent. The method of claim 6, wherein the water is introduced as steam at a pressure of up to 2 bar. The process according to claim 1 or 2, wherein the distillate obtained from the top in step (iii) is partially refluxed into the extractive distillation column, wherein the ratio of reflux to distillate is 4 or less. The process of claim 1 or 2, wherein the top stream distilled from the top contains up to 100 ppm methanol. The process according to claim 1 or 2, wherein the propylene oxide content of the bottoms stream recovered from the extractive distillation column is 100 ppm or less. The process according to claim 1 or 2, wherein the mixture (M) is formed by reacting propene with hydrogen peroxide in the presence of a titanium zeolite fixed bed catalyst in methanol as a solvent. The method according to claim 1 or 2, wherein the mixture (M) comprises 5% to 15% by weight of propylene oxide, 50% to 85% by weight of methanol and 10% to 25% by weight of water, Way (i) introducing the mixture (M) into an extractive distillation column having up to 80 theoretical stages; (Ii) further introducing water to the extractive distillation column in an amount of up to 2% by weight of the mixture (M); (Iii) distilling the propylene oxide from the top of the extractive distillation column at a pressure of 300 mbar to 750 mbar and a bottom temperature of 40 ° C. to 70 ° C. Wherein, the distillate obtained from the top in step (iii) is partially refluxed to the extractive distillation column, wherein the ratio of reflux to distillate is 4 or less, and the top stream distilled from the top is 100 ppm or less. Containing methanol and the propylene oxide content of the bottoms stream recovered from the extractive distillation column is 100 ppm or less. The process according to claim 12, wherein the mixture (M) is formed by reacting propene with hydrogen peroxide in the presence of a titanium zeolite fixed bed catalyst in methanol as a solvent. The method of claim 12, wherein the water is introduced as steam at a pressure up to 2 bar.

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