CN110105190B

CN110105190B - Method for producing acrylic acid based on aqueous lactate solution

Info

Publication number: CN110105190B
Application number: CN201810101753.XA
Authority: CN
Inventors: 徐柏庆; 刘宗辉; 严波; 梁瑜
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2018-02-01
Filing date: 2018-02-01
Publication date: 2021-05-11
Anticipated expiration: 2038-02-01
Also published as: CN110105190A

Abstract

The invention provides a preparation method of acrylic acid based on lactate aqueous solution, which takes the lactate aqueous solution as a raw material, and leads the lactate to generate gas-phase selective dehydration reaction under the action of zeolite catalyst and/or hydroxyapatite catalyst to generate the acrylic acid.

Description

Method for producing acrylic acid based on aqueous lactate solution

Technical Field

The invention relates to the technical field of catalytic conversion and utilization of biomass resources, in particular to a preparation method of acrylic acid based on a lactate aqueous solution.

Background

Acrylic acid is an important organic chemical raw material and polymer monomer, mainly used for producing acrylic ester (about 55%) and super absorbent resin (about 32%), and has huge market demand (about 600 million tons). The industry mainly adopts propylene (or propane) catalytic oxidation based on non-renewable petroleum raw materials to prepare acrylic acid, and one of the technical approaches for realizing the sustainable development of acrylic acid production by utilizing biomass derivative lactic acid. However, lactic acid is expensive, has strong acidity (pKa of 3.85), is corrosive to reaction equipment, and has high production cost. Compared with the traditional petroleum-based route, the route for preparing acrylic acid by dehydrating biomass-based lactic acid has no economic feasibility for a while. At present, an economically viable process for the production of acrylic acid is urgently needed.

Disclosure of Invention

In view of this, it is necessary to provide a method for producing acrylic acid from an aqueous lactate solution, which addresses the problem of high cost of producing acrylic acid from lactic acid.

A method for preparing acrylic acid based on lactate aqueous solution takes lactate aqueous solution as raw material, and leads the lactate to generate gas-phase selective dehydration reaction under the action of zeolite catalyst and/or hydroxyapatite catalyst to generate acrylic acid.

In one embodiment, the aqueous lactate solution is an aqueous methyl lactate solution, an aqueous ethyl lactate solution, or a mixture of both.

In one embodiment, the partial pressure of the lactate in the gas-phase selective dehydration reaction is 10kPa or less, and the partial pressure of water is 10 to 50 kPa.

In one embodiment, the zeolite catalyst comprises a metal cation comprising one or more of an alkali metal ion, an alkaline earth metal ion, and a rare earth metal ion.

In one embodiment, the alkali metal ions comprise Li⁺、Na⁺、K⁺、Rb⁺、Cs⁺Including Mg, the alkaline earth metal ions including Mg²⁺、Ca²⁺、Sr²⁺、Ba²⁺The rare earth metal ion comprises La³⁺、Ce⁴⁺One or more of (a).

In one embodiment, the metal cations in the zeolite catalyst are two, the two metal cations being Na⁺And K⁺、Na⁺And Rb⁺Or Na⁺And Cs⁺。

In one embodiment, the metal cation in the zeolite catalyst is K⁺And Na⁺Said K is⁺And Na⁺The molar ratio of (A) is 50/50-100/0.

In one embodiment, the zeolite catalyst comprises one or more of ZSM-5, beta, MCM-22, MOR, ZSM-22, ZSM-35, and zeolite X.

In one embodiment, the ratio of the total charge number of the metal cations to the number of aluminum atoms in the zeolite catalyst is greater than or equal to 0.8.

In one embodiment, the zeolite catalyst comprises SiO in the zeolite framework₂/A1₂O₃The molar ratio of (A) to (B) is 15 to 40.

In one embodiment, the volume space velocity (GHSV) in the gas phase selective dehydration reaction is 1000h^-1～9000h^-1The reaction temperature is 300-400 ℃.

In one embodiment, the hydroxyapatite catalyst has the general formula M₁₀(XO₄)₆Y₂Wherein M is a divalent cation Ca²⁺、Sr²⁺、Pb²⁺One or more of; XO₄Is PO₄ ^3-、VO₄ ^3-One or more of; y is OH^-、F^-One or more of them.

In one embodiment, the hydroxyapatite catalyst is calcium hydroxy phosphate, the Ca/P molar ratio of the calcium hydroxy phosphate is less than or equal to 1.67, and the roasting temperature in the preparation process of the hydroxyapatite catalyst is less than or equal to 700 ℃.

In the preparation method of acrylic acid based on the lactate aqueous solution, the lactate aqueous solution is converted into acrylic acid under the action of the catalyst, so that the raw material cost is low, the corrosion of the lactate to equipment is low, and the equipment cost is lower. Therefore, the synthetic route for preparing acrylic acid by selective catalytic dehydration of lactate aqueous solution has more research value and application prospect, and the industrial large-scale production and low cost of acrylic acid become possible.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the method for producing acrylic acid based on an aqueous lactate solution according to the present invention will be further described in detail by way of examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

A process for preparing acrylic acid from the aqueous solution of lactate features that the aqueous solution of lactate is used as raw material, and under the action of zeolite catalyst and/or hydroxyapatite catalyst, the lactate is subjected to gas-phase selective dewatering reaction to obtain acrylic acid.

The concentration of the lactic acid ester in the aqueous solution of a lactic acid ester is preferably 5 to 90 wt%, and more preferably 50 wt% or less. The lactate is preferably methyl lactate and/or ethyl lactate, and the methyl lactate and/or the ethyl lactate are used as reaction raw materials, so that not only is the raw material cost low, but also the methyl lactate and the ethyl lactate have low corrosivity on equipment, and the equipment cost is lower. The methyl lactate or the ethyl lactate can be prepared by a catalytic oxidation process with glycerin, a byproduct of biodiesel, as a raw material and low-carbon alcohol as a solvent. The production technology of biodiesel has increased several times over the last decade, and glycerol, which is a by-product of the biodiesel industry, is available in large quantities, and the lactate can be obtained in large quantities from glycerol.

The gas phase selective dehydration reaction preferably comprises the steps of:

inputting the lactate aqueous solution into a reactor filled with the catalyst by using a sample injection pump, mixing the lactate aqueous solution with inert carrier gas, and preheating the mixture into a gas phase; and

and contacting the raw material containing lactate with the catalyst to perform dehydration reaction to obtain acrylic acid. The reactor can be a fixed bed reactor, a fluidized bed reactor, a moving bed reactor and the like. The inert gas may be nitrogen, carbon dioxide gas, water vapor, air, or the like. The reaction feed process preferably heats the lactate to a temperature at least already at the time of reaching the catalyst bed in a gaseous state.

Mixing the lactate with an inert carrier gas in order to adjust the partial pressure of the lactate and water in the feed gas, wherein the partial pressure of the lactate is lactate pressure/(lactate pressure + water pressure + inert carrier gas pressure), the partial pressure of the lactate is preferably 20kPa or less, more preferably 10kPa or less, the partial pressure of the lactate is preferably controlled to be 3.9kPa or less, and particularly preferably 3kPa or less; the partial pressure of water is preferably 5 to 85kPa, more preferably 10 to 50kPa, and particularly preferably 15 to 35 kPa.

In the gas phase selective dehydration reaction, the flow rate of the raw material gas is expressed by the volume of the raw material gas treated on the unit volume of the catalyst per unit time (namely volume space velocity: GHSV), and the volume space velocity (GHSV) is preferably 10000h^-1Below, for example, 1000h^-1～9000h^-1More preferably 5000h^-1Hereinafter, 2000h is particularly preferable^-1The following. Selectivity of the gas phaseThe dehydration reaction temperature is a set temperature of a heat medium or the like for controlling the temperature of the reactor, and the reaction temperature in the present invention is preferably 250 to 500 ℃, more preferably 300 to 400 ℃, and particularly preferably 350 to 380 ℃. For the gas phase selective dehydration reaction of the lactic acid ester, too low or too high a reaction temperature lowers the yield of acrylic acid.

The gas phase selective dehydration reaction generates an acrylic acid solution, and more preferably, the method further comprises recovering acrylic acid obtained by the reaction as an acrylic acid solution by condensation, solvent capture, or the like. The method may further include a trapping and separating step of trapping the acrylic acid-containing gas with a liquid medium, or a condensation and separation process of condensing and trapping the acrylic acid-containing gas. Acrylic acid of high purity can be obtained by purifying the acrylic acid solution by conventional methods such as distillation, rectification or crystallization.

The catalyst comprises a zeolite catalyst comprising metal cations that function to balance the negative framework charge. In the present invention, although the kind of the metal cation in the zeolite catalyst is not particularly limited, it is preferable that the zeolite catalyst contains an alkali metal ion (Li)⁺、Na⁺、K⁺、Rb⁺、Cs⁺) Alkaline earth metal ion (Mg)²⁺、Ca²⁺、Sr²⁺、Ba²⁺) And rare earth metal ion (La)³⁺、Ce⁴⁺Etc.), and further preferably contains one or more alkali metal ions.

Preferably, the zeolite catalyst of the present invention is preferably at least two metal cations selected from alkali metal ions and alkaline earth metal ions as the metal cations that balance the negative charge of its framework. When such zeolite is used as a catalyst for producing acrylic acid from lactic acid esters, a high yield of acrylic acid can be obtained. More preferred are zeolite catalysts containing two or more alkali metal ions. From the viewpoints of ease of catalyst preparation, production cost and the like, Li is preferred⁺、Na⁺、K⁺、Ca²⁺And Mg²⁺As alkali metal ions and alkaline earth metal ions.

Further from the viewpoint of catalyst performance, the cation in the zeolite of the present invention is more preferably Na⁺And K⁺。

Still further, the zeolite of the present invention contains Na⁺And K⁺In the case of (1), K⁺And Na⁺The ratio of (A) to (B) is not particularly limited, but K⁺And Na⁺The molar ratio of (a) is preferably greater than 50/50, more preferably 80/20 or greater, and particularly preferably 90/10 or greater. On the other hand, as K⁺And Na⁺The upper limit of the molar ratio of (3) is preferably 98/2 or less.

The ratio of the total charge number of the cations in the catalyst, preferably the zeolite catalyst, to the molar content of aluminum atoms is more than or equal to 0.80. Further preferably, the ratio of the total charge number of the metal cations in the zeolite catalyst to the molar content of aluminum atoms is not less than 0.90.

The alkali metal in the zeolite catalyst is present in the form of an equilibrium cation. M represents a metal ion substituted for Na ion, x represents the degree of ion exchange, and y represents SiO in the zeolite framework₂With Al₂O₃In a molar ratio of (a). According to the type of alkali metal ion (K)⁺、Rb⁺Or Cs⁺) Degree of ion exchange (x ═ M)]/([M]+[Na])，SiO₂With Al₂O₃The resulting catalyst was represented by MxNa1-xW _ y, W being the kind of zeolite catalyst framework, wherein the values of X and y were each measured by X-ray fluorescence spectrum analyzer XRF. The framework type of the zeolite catalyst may preferably be ZSM-5, beta, MCM-22, MOR, ZSM-22, ZSM-35 or X-type zeolite. For example, the framework of the zeolite catalyst is ZSM-5, which is denoted by MxNa1-xZSM-5_ y.

The zeolite catalyst, preferably, SiO of the zeolite catalyst₂With Al₂O₃The molar ratio is 15 to 40. Preferably, the zeolite catalyst is SiO₂With Al₂O₃In a molar ratio of from 18 to 30.

Further preferably, the zeolite catalyst is preferably K_0.95Na_0.05ZSM-5-27. Said K_0.95Na_0.05SiO in ZSM-5_27 zeolite framework₂With Al₂O₃In a molar ratio of 27, with Na⁺And K⁺Are metal cations that balance the negative charge of the framework.

The ZSM-5, beta, MCM-22, MOR, ZSM-22, ZSM-35 or X type zeolite and hydroxyapatite related to the invention can be commercial products or commercial products, and can also be prepared by a traditional method. However, the zeolite catalyst of the present invention is preferably prepared by cation exchange as required.

Preferably, the preparation method of the zeolite catalyst comprises the following steps:

s10, placing commercial or ZSM-5, beta, MCM-22, MOR, ZSM-22, ZSM-35 or X type zeolite powder prepared by the traditional method into a muffle furnace, roasting for 1-12 hours at 400-650 ℃ under static or flowing air, removing the template agent in the zeolite, and obtaining the H-containing zeolite⁺Or Na⁺Zeolites that balance the negative framework charge cations are designated as HZ or NaZ.

S11, adding the HZ or NaZ zeolite into a solution containing cation A, heating and stirring to perform a cation exchange reaction to obtain the zeolite with A as an equilibrium cation.

More preferably, the zeolite having a cation as the equilibrium cation is added to a solution containing a cation B and then exchanged with B, whereby a zeolite containing both cations a and B can be obtained.

The degree of cation exchange can be adjusted by operating parameters such as the concentration of the target metal cation in the solution, the temperature and time of the exchange reaction, and the number of exchanges. If the operation of one ion exchange reaction does not achieve a desired degree of cation exchange, it is preferable to increase the number of times of the operation of the ion exchange reaction and repeat the operation of the ion exchange reaction a plurality of times to increase the degree of cation exchange to a desired degree.

The cation-exchanged zeolite S12 may be subjected to drying and/or calcination treatment as needed. For example, the baking treatment may be performed by heating the sample to 400 to 650 ℃ in an air atmosphere for 1 to 12 hours.

When the catalyst is hydroxyapatite, the general formula of the hydroxyapatite catalyst is M₁₀(XO₄₎₆Y₂Wherein M is a divalent cation Ca²⁺、Sr²⁺、Pb²⁺One or more of the following; XO₄Is PO₄ ^3-、VO₄ ^3-One or more of the following; y is OH^-、F^-One or more of them. The hydroxyapatite of the present invention may be a commercial product or a commercial product, and may be prepared by a conventional method. Preferably, the compound is prepared by a precipitation method.

The catalyst hydroxyapatite (M)₁₀(XO₄)₆Y₂) The preparation method comprises the following steps:

s20, adding M²⁺And XO₄ ^3-Adding aqueous ammonia, NaOH or KOH and other alkali solution into the solution;

s21, continuously stirring, and adjusting the pH value of the solution to 7-12;

s22, standing and aging the precipitate obtained by the reaction, filtering, washing and the like to obtain the hydroxyapatite.

From the viewpoint of obtaining good catalytic performance, it is preferable that the method further includes the step of calcining the hydroxyapatite catalyst in step S23. The hydroxyapatite is required to be roasted, the roasting temperature is preferably below 700 ℃, more preferably the roasting temperature of the hydroxyapatite catalyst is less than or equal to 500 ℃, and even more preferably the roasting temperature of the hydroxyapatite catalyst is less than or equal to 400 ℃.

Preferably, the hydroxyapatite catalyst is calcium hydroxy phosphate.

For example, in the preparation of calcium hydroxy phosphate, an optional calcium source such as calcium nitrate, calcium chloride, calcium hydroxide, etc., and an optional phosphorus source such as a soluble phosphate salt, preferably, ammonium phosphate and ammonium hydrogen phosphate.

The calcium hydroxy phosphate has strong ion exchange performance and Ca in crystal structure²⁺、PO₄ ^3-And OH^-Can exchange with other ions to make Ca²⁺And PO₄ ^3-The molar ratio of (i.e., Ca/P ratio) is changed.

Calcium hydroxyphosphate with different Ca/P ratios can be obtained by adjusting the ratio of the added calcium source and phosphorus source and the pH of the solution during the reaction. The heating temperature range during synthesis is 0-100 ℃, and the stirring time is 1-12 h. The prepared hydroxyapatite can be dried or roasted according to the requirement. The roasting treatment can be carried out in an air environment, and the sample is heated to 300-800 ℃ and kept for 1-12 h.

Ca contained in said calcium hydroxyphosphate couple of the present invention²⁺And PO₄ ^3-The molar ratio of (a) to (b) is not particularly limited. Preferably, the Ca/P molar ratio of the calcium hydroxy phosphate is less than or equal to 1.67. More preferably, the Ca/P molar ratio of the calcium hydroxyphosphate is preferably less than or equal to 1.63. Still more preferably, the calcium hydroxyphosphate has a Ca/P molar ratio of ≤ 1.60.

The catalyst of the present invention may contain other components in addition to the zeolite such as ZSM-5, beta, MCM-22, MOR, ZSM-22, ZSM-35 or X-type or the hydroxyapatite. For example, it may also be said zeolite or said hydroxyapatite supported on a specific carrier, i.e. a supported zeolite or hydroxyapatite catalyst. The carrier material may be inorganic oxide or composite oxide such as silica, alumina, titania, zirconia, etc., other crystalline silicate such as zeolite molecular sieve containing hetero atom, inorganic matter such as active carbon, silicon carbide, etc., metal or alloy such as stainless steel, aluminum, etc.

The catalyst of the present invention may also be an unsupported catalyst. For example, a binder may be added to zeolite to prepare various existing molded catalysts, and a zeolite catalyst containing no binder at all can be prepared by converting a silica carrier having a specific shape to zeolite or the like.

The shape of the catalyst of the present invention may be spherical, granular, columnar, annular, saddle-shaped, honeycomb-shaped, powdery, etc.

The catalyst of the metal cation-containing zeolite or hydroxyapatite of the present invention can be prepared by the above method. The use of these catalysts in the dehydration reaction of lactic acid esters can improve the conversion and selectivity for producing the acrylic acid.

Example 1

[ PREPARATION OF CATALYST ]

Mixing SiO₂/Al₂O₃Sodium ion (Na) at a molar ratio of 27⁺) The ZSM-5 type zeolite powder for balancing negative charges and cations of the framework is placed in a muffle furnace to be roasted for 5 hours at 500 ℃ to obtain NaZSM-5_ 27. Weighing 3g of calcined NaZSM-5-27, soaking in 60ml of KBr aqueous solution with the concentration of 0.1mol/L, stirring at 80 ℃ for 1 hour to perform ion exchange reaction, performing suction filtration and drying, and finally calcining at 500 ℃ for 3 hours to obtain the first Na-base catalyst⁺And K + is a ZSM-5 zeolite catalyst balancing the negative framework charge cations, and this catalyst is designated K_0.95Na_0.05ZSM-5_27。

[ PREPARATION OF ACRYLIC ACID ]

The vapor phase selective dehydration reaction of the ethyl lactate aqueous solution was carried out under normal pressure on a continuous flow quartz fixed bed reactor (length: ca.50cm, inner diameter: ca.9mm).

The method comprises the following specific steps: taking 500mg of K_0.95Na_0.05The ZSM-5_27 catalyst (20-40 meshes) is filled in the middle of the reaction tube and clamped between two layers of quartz wool, and the upper part of the upper layer of quartz wool is filled with about 2ml of quartz sand (20-40 meshes) for preheating reaction raw materials. The catalyst before reaction is at the reaction temperature (360 ℃) for 25ml min^-1Dry N of₂Medium blowing is carried out for 1.5 h; an aqueous solution of ethyl lactate having a molar concentration of 5% was injected into the reactor at a rate of 0.9ml/h using a micro-syringe pump, and the feed gas had a composition such that the ethyl lactate partial pressure was 1.8kPa, the water partial pressure was 35.1kPa, and the nitrogen partial pressure was 63.1 kPa. The reaction product was collected in a condenser tube in an ice water bath (0 ℃ C.) and sampled every hour for analysis.

Based on the measurement results of the gas chromatography, the conversion rate of lactate (EL conversion rate), acrylic acid selectivity (AA selectivity), and acrylic acid yield (AA yield) were calculated according to the following calculation formulas.

EL conversion (%) × (number of moles of lactate consumed in the reaction)/(number of moles of lactate fed to the reactor) × 100%.

AA selectivity (%) × (number of moles of carbon atoms in acrylic acid produced in the reaction)/(number of moles of carbon atoms in lactic acid consumed in the reaction) × 100%.

AA yield (%) ═ EL conversion × AA selectivity × 100.

TABLE 1a influence of different reaction times on the conversion in example 1

Reaction time (h)	Reaction raw material	Lactate partial pressure (kPa)	Partial pressure of water (kPa)
				10	Lactic acid ethyl ester	1.8	35.1
50	Lactic acid ethyl ester	1.8	35.1
				100	Lactic acid ethyl ester	1.8	35.1
150	Lactic acid ethyl ester	1.8	35.1
				200	Lactic acid ethyl ester	1.8	35.1
250	Lactic acid ethyl ester	1.8	35.1

Example 1b Effect of different reaction times on conversion

The effect of different reaction times on the conversion in example 1 is shown in tables 1a and 1b, said K_0.95Na_0.05The conversion rate of ethyl lactate on a ZSM-5-27 catalyst is reduced rapidly (ca.7%) 50h before reaction, but the conversion rate of ethyl lactate is reduced by less than 5% 50-250 h and can still be maintained above 80%, and good stability is shown; and the selectivity of the target product can be maintained above 90% in the reaction process.

TABLE 1c influence of different reaction temperatures on the conversion in example 1

TABLE 1d influence of different space velocities of the reaction volumes on the conversion in example 1

The results for different reaction temperatures and different space velocities are shown in tables 1c and 1d, by K_0.95Na_0.05ZSM-5-27 catalyst, the selectivity of acrylic acid is more than 60% at the reaction temperature of 340 ℃, 350 ℃, 360 ℃ and 370 ℃, and the catalyst shows high selectivity and the volume space velocity of 2460h^-1、3690h^-1、4920h^-1、6150h^-1In this case, the acrylic acid selectivity is greater than 60%.

Example 2

[ PREPARATION OF CATALYST ]

The catalyst was prepared in the same manner as in example 1.

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 1 except that the molar concentration of the reaction material was 5% in the methyl lactate aqueous solution. The results of the effect of different reaction times on the conversion of example 2 are shown in tables 2a and 2 b.

Example 2a Effect of different reaction times on conversion

Reaction time (h)	Reaction raw material	Lactate partial pressure (kPa)	Partial pressure of water (kPa)
				10	Lactic acid methyl ester	1.8	35.1
50	Lactic acid methyl ester	1.8	35.1
				100	Lactic acid methyl ester	1.8	35.1
150	Lactic acid methyl ester	1.8	35.1
				200	Lactic acid methyl ester	1.8	35.1
250	Lactic acid methyl ester	1.8	35.1

Example 2b Effect of different reaction times on conversion

K_0.95Na_0.05The methyl lactate gas-phase dehydration reaction on the ZSM-5-27 catalyst also shows good stability and selectivity (more than 85%) of the target product.

Example 3

[ PREPARATION OF CATALYST ]

The catalyst was prepared in the same manner as in example 1.

[ PREPARATION OF ACRYLIC ACID ]

Changing the reaction raw material from 5 mol% ethyl lactate aqueous solution to 10 mol% ethyl lactate aqueous solution with the sample amount of 1.2ml/h, and adjusting N₂The total space velocity and the water partial pressure were kept constant, and the composition of the feed gas was 3.9kPa ethyl lactate, 35.1kPa water partial pressure, and 61.0kPa nitrogen partial pressure. Other reaction conditions were the same as in example 1, and the obtained reaction results are shown in tables 3a and 3 b.

Example 4

[ PREPARATION OF CATALYST ]

The catalyst was prepared in the same manner as in example 1.

[ PREPARATION OF ACRYLIC ACID ]

Changing the reaction raw material from 5 mol% ethyl lactate aqueous solution to 20 mol% ethyl lactate aqueous solution with the sample amount of 1.8ml/h, and adjusting N₂The total space velocity and the water partial pressure were kept constant, and the composition of the feed gas was 8.8kPa ethyl lactate, 35.1kPa water partial pressure, and 56.1kPa nitrogen partial pressure. The other reaction conditions were the same as in example 1, and the reaction results were shown in tables 3a and 3 b.

Example 5

[ PREPARATION OF CATALYST ]

The catalyst was prepared in the same manner as in example 1.

[ PREPARATION OF ACRYLIC ACID ]

The reaction raw material is changed into pure ethyl lactate from 10mol percent ethyl lactate water solution, the sample amount is 0.5ml/h, and N is adjusted₂The total space velocity was kept constant at which the feed gas had a composition of 3.9kPa ethyl lactate/0 kPa water/96.1 kPa N₂. Other reaction conditions were the same as in example 3, and the obtained reaction results are shown in tables 3a and 3 b.

Example 6

[ PREPARATION OF CATALYST ]

The catalyst was prepared in the same manner as in example 1.

[ PREPARATION OF ACRYLIC ACID ]

Changing the reaction raw material from 10 mol% ethyl lactate aqueous solution to 4.5 mol% ethyl lactate aqueous solution with the sample amount of 2.2ml/h, and adjusting N₂The total space velocity was kept constant at the feed gas composition of 3.9kPa ethyl lactate partial pressure, 84.0kPa water partial pressure and 12.1kPa nitrogen partial pressure. The reaction results obtained under the same other reaction conditions as in example 3 are shown in tables 3a and 3 b.

TABLE 3a influence of different partial pressures on the conversion

TABLE 3b Effect of different partial pressures on conversion

Comparative examples 1, 2, 3, 4, 5 and 6 show that K is significantly affected by both the ethyl lactate partial pressure and the water partial pressure_0.95Na_0.05Performance of vapor phase dehydration reaction of ethyl lactate over ZSM-5 — 27 catalyst. According to the data, the partial pressure of the lactate is less than 10kPa, the selectivity of acrylic acid can reach more than 78%, when the partial pressure of the lactate is less than 3.9kPa, the selectivity of acrylic acid can reach more than 80%, and the conversion rate of the lactate can reach more than 58%. The partial pressure of the lactate is preferably 3.9kPa or less; the partial pressure of water is preferably 5 to 85kPa or higher. Example 1, when the partial pressure of water was 35.1kPa, the lactate partial pressure (kPa) was 1.8, and the partial pressure of water (kPa) was 35.1, the lactate conversion was 94%, and the acrylic acid selectivity was 86%.

Example 7

[ PREPARATION OF CATALYST ]

SiO in example 1₂/Al₂O₃Changing NaZSM-5 with the ratio of 27 into SiO₂/Al₂O₃NaZSM-5 with a ratio of 13, prepared under otherwise identical conditions to example 1, and the catalyst obtained was designated K_0.95Na_0.05ZSM-5_13。

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3, and the reaction results were shown in Table 4.

Example 8

[ PREPARATION OF CATALYST ]

SiO in example 1₂/Al₂O₃Changing NaZSM-5 with the ratio of 27 into SiO₂/Al₂O₃NaZSM-5 with a ratio of 18, the other preparation conditions being the same as in example 1, the catalyst obtained being denoted K_0.95Na_0.05ZSM-5_18。

[ PREPARATION OF ACRYLIC ACID ]

Example 9

[ PREPARATION OF CATALYST ]

The preparation conditions were the same as in example 1, and the catalyst obtained was designated K_0.95Na_0.05ZSM-5_27。

[ PREPARATION OF ACRYLIC ACID ]

Example 10

[ PREPARATION OF CATALYST ]

SiO in example 1₂/Al₂O₃Changing NaZSM-5 with the ratio of 27 into SiO₂/Al₂O₃NaZSM-5 with a 48 ratio, prepared under otherwise identical conditions as in example 1, and the catalyst obtained was designated K_0.95Na_0.05ZSM-5_48。

[ PREPARATION OF ACRYLIC ACID ]

Example 11

[ PREPARATION OF CATALYST ]

SiO in example 1₂/Al₂O₃Changing NaZSM-5 with the ratio of 27 into SiO₂/Al₂O₃NaZSM-5 with a ratio of 75, the other preparation conditions being the same as in example 1, the catalyst obtained being denoted K_0.95Na_0.05ZSM-5_75。

[ PREPARATION OF ACRYLIC ACID ]

TABLE 4 different SiO₂/Al₂O₃Influence of the ratio on the conversion

As shown in Table 4, SiO of the zeolite catalyst₂With Al₂O₃At a molar ratio of 13, the conversion of acrylic acid is 34% and the selectivity of acrylic acid is 61%; SiO of the zeolite catalyst₂/Al₂O₃At a molar ratio of 18, the conversion of acrylic acid is 53% and the selectivity of acrylic acid is 74%; SiO of the zeolite catalyst₂With Al₂O₃When the molar ratio is 27, the conversion rate of the acrylic acid is 60 percent, and the selectivity of the acrylic acid is 85 percent; SiO of the zeolite catalyst₂With Al₂O₃At a molar ratio of 48, the conversion of acrylic acid was 25% and the selectivity of acrylic acid was 35%. Altering SiO in the zeolite catalyst₂With Al₂O₃The molar ratio, the conversion of lactate and the selectivity to acrylic acid in the reaction result may vary.

As can be seen from the data in Table 4, the SiO in the zeolite catalyst₂/Al₂O₃The molar ratio significantly affects the performance of the gas phase selective dehydration reaction of ethyl lactate as described above.

Example 12

[ PREPARATION OF CATALYST ]

The KBr concentration in example 1 was changed from 0.1mol/L to 0.01mol/L under the same preparation conditions as in example 1, and the catalyst obtained was designated as K_0.54Na_0.46ZSM-5_27。

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3. Comparison of example 3 with example 12 shows that when K is present in the zeolite as a catalyst⁺And Na⁺When the molar ratio of (A) is reduced from 95/5 to 54/46, the selectivity of acrylic acid is 55%.

Example 13

[ PREPARATION OF CATALYST ]

SiO in example 1₂/Al₂O₃Changing NaZSM-5 type zeolite with 27 ratio into SiO₂/Al₂O₃The Na beta zeolite having a ratio of 42 was prepared under the same conditions as in example 1, and the catalyst was designated as K_0.95Na_0.05β_42。

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3, and the reaction results were shown in Table 5. K_0.95Na_0.05The conversion of ethyl lactate over the β _42 catalyst was 50% and the selectivity to acrylic acid was 53%.

Example 14

[ PREPARATION OF CATALYST ]

SiO in example 1₂/Al₂O₃Changing NaZSM-5 type zeolite with 27 ratio into SiO₂/Al₂O₃The catalyst obtained with a NaMCM-22 type zeolite having a ratio of 26, but under otherwise identical conditions to those of example 1, was designated K_0.97Na_0.03MCM-22_26。

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3, and the reaction results were shown in Table 5. K_0.97Na_0.03The conversion rate of ethyl lactate on the MCM-22-26 catalyst is 40%, and the selectivity of acrylic acid is 50%.

Example 15

[ PREPARATION OF CATALYST ]

SiO in example 1₂/Al₂O₃Changing NaZSM-5 type zeolite with 27 ratio into SiO₂/Al₂O₃A catalyst of the NaMOR type with a ratio of 20, prepared under otherwise identical conditions to those of example 1 and reported as K_0.94Na_0.06MOR_20。

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3, and the reaction results were shown in Table 5. K_0.94Na_0.06The conversion of ethyl lactate over MOR — 20 catalyst was 10% and the selectivity to acrylic acid was 30%.

Example 16

[ PREPARATION OF CATALYST ]

SiO in example 1₂/Al₂O₃Changing NaZSM-5 type zeolite with 27 ratio into SiO₂/Al₂O₃A catalyst K was prepared using NaZSM-35 type zeolite having a ratio of 28 under the same preparation conditions as in example 1_0.90Na_0.10ZSM-35_{_}28。

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3, and the reaction results were shown in Table 5. K_0.90Na_0.10The conversion of ethyl lactate over the ZSM-35 — 28 catalyst was 30% with acrylic acid selectivity of 10%.

Example 17

[ PREPARATION OF CATALYST ]

SiO in example 1₂/Al₂O₃Changing NaZSM-5 type zeolite with 27 ratio into SiO₂/Al₂O₃A catalyst K was prepared using NaZSM-22 type zeolite having a ratio of 50 under the same preparation conditions as in example 1_0.96Na_0.04ZSM-22_{_}50。

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3, and the reaction results were shown in Table 5. K_0.96Na_0.04The conversion of ethyl lactate over the ZSM-22-50 catalyst was 20% and the selectivity to acrylic acid was 30%.

TABLE 5, K⁺And Na⁺Effect of exchanging different zeolite catalysts on dehydration reaction of Ethyl lactate

As can be seen from table 5, the type of zeolitic molecular sieve significantly affects the performance of the gas phase selective dehydration reaction of the ethyl lactate on the catalyst, preferably a zeolite containing the ZSM-5 type framework. K⁺And Na⁺The ratio of (A) significantly affects the conversion of the lactate and the selectivity of acrylic acid, preferably the K⁺And Na⁺The molar ratio of (A) is 50/50-100/0, with K⁺The selectivity of acrylic acid increases with an increase in the ratio of (A) to (B).

Example 18

[ PREPARATION OF CATALYST ]

150ml of 0.250mol L were added in a water bath at 40 ℃ with continuous stirring^-1(NH)₄)₂HPO₄The aqueous solution is added dropwise to a container containing 250ml of 0.251mol L^-1Ca (NO) of₃)₂·4H₂Adding concentrated ammonia water dropwise into the O aqueous solution to keep the pH of the solution at 10 +/-0.1; after the dropwise addition, continuously stirring for 1h, and aging the obtained precipitate suspension in a drying oven at 40 ℃ for 12 h; then, a white solid precipitate filter cake is obtained by suction filtration through a sand mold funnel, the filter cake is pulped, stirred and washed by deionized water, and the operation is repeated until the conductivity of the filtrate is less than 10 mu S cm^-1Until the end; finally, the filter cake was dried at 110 ℃ overnight and placed in a tube furnace with flowing air (100ml min)^-1) Roasting at 360 ℃ for 5 h. The Ca/P ratio of the prepared catalyst is 1.62, and the calcination temperature is 360 ℃ and is recorded as HAP_1.62-360 (calcium hydroxyphosphate).

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3, and the reaction results were shown in Table 6. HAP_1.62-conversion of ethyl lactate over 360 (calcium hydroxy phosphate) catalyst 65% and selectivity of acrylic acid 52%.

Example 19

[ PREPARATION OF CATALYST ]

Ca (NO) in example 18₃)₂·4H₂The concentration of the O aqueous solution is from 0.251mol L^-1Changed to 0.239mol L^-1Otherwise, the catalyst was prepared under the same conditions as in example 18, the Ca/P ratio was 1.60, and the calcination temperature was 360 ℃Is HAP_1.60-360 (calcium hydroxyphosphate).

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3, and the reaction results were shown in Table 6. When the Ca/P ratio in the calcium hydroxyphosphate is decreased from 1.62 to 1.60, the selectivity to acrylic acid is 57%.

Example 20

[ PREPARATION OF CATALYST ]

Ca (NO) in example 18₃)₂·4H₂The concentration of the O aqueous solution is from 0.251mol L^-1Changed to 0.263mol L^-1Otherwise, the same preparation conditions as in example 18 were used, and the Ca/P ratio of the catalyst obtained by the preparation was 1.68, and the catalyst obtained by calcination at 360 ℃ was designated as HAP_1.68-360 (calcium hydroxyphosphate).

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3, and the reaction results were shown in Table 6. When the Ca/P ratio in the hydroxyapatite was increased from 1.62 to 1.68, the selectivity to acrylic acid was 42%.

Example 21

[ PREPARATION OF CATALYST ]

The calcination temperature of the sample in example 18 was raised from 360 ℃ to 500 ℃ under the same conditions as in example 18, and the Ca/P ratio of the catalyst obtained was 1.62, and the calcination temperature was 500 ℃ and was recorded as HAP_1.62-500 (calcium hydroxyphosphate).

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3, and the reaction results were shown in Table 6. When the roasting temperature of the hydroxyapatite is increased from 360 ℃ to 500 ℃, the selectivity of the acrylic acid is 47 percent.

Example 22

[ PREPARATION OF CATALYST ]

The calcination temperature of the sample in example 18 was raised from 360 ℃ to 700 ℃ under the same conditions as in example 18, and the Ca/P ratio of the catalyst obtained was 1.62, and the catalyst obtained at a calcination temperature of 700 ℃ was designated as HAP_1.62700 (calcium hydroxyphosphate).

[ PREPARATION OF ACRYLIC ACID ]

The reaction conditions were the same as in example 3, and the reaction results were shown in Table 6. When the roasting temperature of the calcium hydroxy phosphate is increased from 360 ℃ to 700 ℃, the selectivity of the acrylic acid is 46 percent.

TABLE 6 dehydration reaction Performance of Ethyl lactate over hydroxyapatite catalyst

As can be seen from Table 6, both the Ca/P ratio of the calcium hydroxy phosphate and the calcination temperature significantly affect the gas phase selective dehydration reaction performance of the ethyl lactate. When the Ca/P ratio of the calcium hydroxy phosphate is less than 1.68, the conversion rate of the ethyl lactate is gradually increased as the Ca/P ratio is reduced.

When the roasting temperature of the calcium hydroxy phosphate is less than 700 ℃, the conversion rate of the ethyl lactate is reduced along with the reduction of the roasting temperature, and the conversion rate of the ethyl lactate is gradually increased. Preferably, the conversion rate of lactate of HAP1.60-360(HAP is calcium hydroxy phosphate) reaches 75%, and the selectivity of acrylic acid reaches 57%.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A preparation method of acrylic acid based on lactate aqueous solution is characterized in that the lactate aqueous solution is used as raw material, and the lactate is subjected to gas phase selective dehydration reaction under the action of zeolite catalyst or under the action of the zeolite catalyst and hydroxyapatite catalyst to generate acrylic acid;

wherein the zeolite catalyst is a ZSM-5 type zeolite catalyst, the ZSM-5 type zeolite catalyst comprises metal cations, the metal cations exist in a form of cations balancing negative charges of a zeolite framework, and the metal cations are K⁺And Na⁺Said K is⁺And Na⁺In the zeolite framework of the zeolite catalyst, SiO is contained in the zeolite framework of the zeolite catalyst in a molar ratio of 50/50-100/0₂/A1₂O₃The molar ratio of the metal cations to the aluminum atoms in the zeolite catalyst is more than or equal to 0.8;

the reaction conditions are as follows: the lactate partial pressure is 3.9kPa, the water partial pressure is 35.1kPa, the reaction temperature is 360 ℃, the mass of the zeolite catalyst is 500mg, the lactate aqueous solution sample injection speed is 1.2ml/h, and the volume space velocity (GHSV) of a gas raw material in the gas phase selective dehydration reaction is 1000h^-1~9000 h^-1The reaction temperature is 300-400 ℃.

2. The method for producing acrylic acid based on an aqueous lactate solution according to claim 1, wherein the aqueous lactate solution is an aqueous methyl lactate solution, an aqueous ethyl lactate solution, or a mixture of both.

3. The method for producing acrylic acid based on an aqueous lactate solution according to claim 1, wherein K is⁺And Na⁺The molar ratio of (A) is 80/20-100/0.

4. The method for producing acrylic acid based on an aqueous lactate solution according to claim 1, characterized in that,said K⁺And Na⁺The molar ratio of (A) is 90/10-100/0.

5. The method for producing acrylic acid based on an aqueous lactate solution according to claim 1, wherein K is⁺And Na⁺The molar ratio of (A) is 90/10-98/2.

6. The method for producing acrylic acid based on an aqueous lactate solution according to claim 1, wherein the ratio of the total number of charges of metal cations to the number of aluminum atoms in the zeolite catalyst is not less than 0.9.

7. The method for producing acrylic acid based on an aqueous lactate solution according to claim 1, wherein SiO is present in the zeolite framework of the zeolite catalyst₂/A1₂O₃The molar ratio of (A) to (B) is 18 to 30.

8. The method for preparing acrylic acid based on an aqueous lactate solution according to claim 1, wherein the hydroxyapatite catalyst has a general formula of M₁₀(XO₄)₆Y₂Wherein M is a divalent cation Ca²⁺、Sr²⁺、Pb²⁺One or more of; XO₄Is PO₄ ^3-、VO₄ ^3-One or more of; y is OH^-、F^-One or more of them.

9. The method according to claim 1, wherein the hydroxyapatite catalyst is calcium hydroxy phosphate, the calcium hydroxy phosphate has a Ca/P molar ratio of 1.67 or less, and the calcination temperature during the preparation of the hydroxyapatite catalyst is 700 or less^oC。