CN103638951A - Catalyst for preparing acrylic acid through lactic acid dehydration and application thereof - Google Patents

Abstract

The invention discloses a catalyst for preparing acrylic acid by dehydrating lactic acid, which is characterized in that the catalyst is prepared in the following manner: using soluble alkaline earth metal M salt solution or hydroxide alkaline earth metal M solution and dilute sulfuric acid or alkali metal sulfate solution The alkaline earth metal sulfate is prepared by the reaction, and the obtained alkaline earth metal sulfate is precipitated and filtered, washed with distilled water, then placed in a drying oven for drying, and placed in a muffle furnace after drying, and calcined by temperature programming. The alkaline earth metal sulfate catalyst is environmentally friendly, simple to prepare, low in cost, high in catalytic activity, good in stability, high in acrylic acid selectivity and lactic acid conversion rate, and has potential commercial development value.

Description

Catalyst and Application of Dehydration of Lactic Acid to Acrylic Acid

technical field

The invention belongs to the field of chemical industry, and in particular relates to a new method for preparing acrylic acid by catalyzing dehydration of lactic acid with alkaline earth metal sulfate.

Background technique

Acrylic acid is an important unsaturated organic acid with a structural formula of H ₂ C=CH-COOH. It is a colorless and transparent liquid at normal temperature and pressure, and can be miscible with water in any proportion. There is a double bond and a carboxyl group in the structural formula of acrylic acid, so its chemical properties are lively and its acidity is strong. Acrylic acid is mostly used to prepare acrylates. Acrylic acid salts and esters can be homopolymerized or copolymerized, and can also be copolymerized with monomers such as acrylonitrile, styrene, butadiene, vinyl chloride and maleic anhydride. Has many excellent properties such as color retention, light resistance, heat resistance, oxidation resistance, aging resistance, super water absorption, etc. It is widely used in synthetic resins, adhesives, synthetic rubber, synthetic fibers, super absorbent resins, pharmaceuticals, leather, Textile, chemical fiber, building materials, water treatment, oil exploration, coatings and other fields. With the rapid progress of acrylic acid rectification technology, high-purity acrylic acid (glacial acrylic acid) is separated, which is especially suitable for the production of sanitary products for women and children. It can be seen that acrylic acid is an extremely important bulk chemical, and it is also one of the important raw materials for the synthesis of various high value-added products in industry. The total consumption of acrylic acid has also increased year by year due to the large increase in demand for women's and children's hygiene products and water-soluble architectural coatings.

According to the renewability of raw materials for the synthesis of acrylic acid, the process routes for the synthesis of acrylic acid can be mainly divided into two categories, namely bio-based routes such as dehydration of lactic acid to acrylic acid and glycerin dehydration oxidation to acrylic acid; non-bio-based routes such as propylene oxidation and propane oxidation , Acetylene carbonyl synthesis method. Among these preparation methods, the lactic acid dehydration method has attracted much attention, because the route is a sustainable development route; the technology of preparing lactic acid from starch or cellulose is becoming more and more mature, and the source of lactic acid is guaranteed; the high-temperature gas-phase dehydration of lactic acid to prepare acrylic acid made great progress. The catalysts for preparing acrylic acid from lactic acid dehydration mainly include metal salts, zeolite molecular sieves, and heteropolyacid salts. The first category: metal salt catalysts, such as CaSO ₄ , KHSO ₄ , K ₂ HPO ₄ , etc. Holmen [USP2859240,1958] reported that lactic acid was dehydrated under the catalysis of Na ₂ SO ₄ /CaSO ₄ in a fixed bed reaction device. When the concentration of lactic acid was 10wt%, the selectivity of acrylic acid reached 68% when the reaction temperature was 400°C. The catalyst is prepared by mixing a certain concentration of Na ₂ SO ₄ solution and superfine CaSO ₄ powder in a slurry state at a molar ratio of 1:25, and then drying. Sawicki[USP4729978,1988] used inorganic bases as pH regulators, and impregnated metal oxide carriers with phosphate solutions to prepare catalysts for catalyzing the dehydration of lactic acid. The experimental results found that the catalyst obtained by first impregnating the silica support with sodium dihydrogen phosphate solution and then drying it, and then impregnating it with Na ₂ CO ₃ solution for the second time and then drying it had the best reaction performance, and the highest selectivity for acrylic acid was 65%, corresponding to The conversion rate of lactic acid reaches 89%. In addition, this document also comparatively studies the reaction performance of catalysts prepared with different oxide supports such as silica, titania or alumina, and the silica support is the best. Paparizos et al. [USP4786756A, 1988] under the conditions of gas-solid reaction, pre-treated _AlPO with inorganic alkali catalyzed the dehydration of lactic acid or ammonium lactate aqueous solution to produce acrylic acid. After purging for 30 minutes, the best yield of acrylic acid was 61.1%, and the content of propionic acid in the product was also very small. Gunter et al. [Ind.Eng.Chem.Res, 34,974,1995] used a loaded phosphate catalyst for the dehydration of lactic acid to produce acrylic acid and the co-production of 2,3-pentanedione. Experiments have found that the catalyst made of silica with a low specific surface area as a carrier can inhibit the occurrence of side reactions such as decarbonylation and decarboxylation. The occurrence of these side reactions is mainly attributed to the high specific surface area of silica and the strong acid sites on its surface. The best reaction conditions and results: the reaction temperature is 300°C, the total pressure is 0.5MPa, and the highest total selectivity of acrylic acid and 2,3-pentanedione is 83% when the silica-supported sodium arsenate is used as the catalyst. , The yield of 3-pentanedione reaches 25%. Tan Tianwei et al. [ZL:200810113126.4] introduced a two-stage reaction method for producing acrylic acid or acrylate from lactic acid or lactate. The invention patent adopts a two-stage vertical reactor. The lactic acid raw material is preheated before the top, and the upper and lower stages are filled with different types of catalysts respectively, and the lower end is connected to a gas-liquid separator. When the upper and lower ends are respectively filled with 13X molecular sieve and praseodymium phosphate/calcium sulfate/copper sulfate composite salt as catalyst, with 60wt% methyl lactate as raw material, the catalytic effect is the best when the reaction temperature is 400°C, and the selectivity of acrylic acid is as high as 85. %. [The Canadian Journal of Chemical Engineering 2008, 86, 1047] studied the dehydration of lactic acid catalyzed by a sulfate composite catalyst under gas-solid phase conditions. The experimental results show that the catalyst composition m(CaSO ₄ ):m(CuSO ₄ ):m(Na ₂ HPO ₄ ):m(KH ₂ PO ₄ )=150.0:13.8:2.5:1.2, temperature 330°C, lactic acid concentration 26wt% , the contact time is 88s, the carrier gas is CO ₂ , and the yield of the target product acrylic acid is as high as 63.7%. The research results also show that the surface acidity of the catalyst can be effectively controlled after calcination, and carbon dioxide as a carrier gas can inhibit the occurrence of side reactions to a certain extent. Zhang et al [Ind.Eng.Chem.Res.2009,48,9083] used silica-supported phosphate to catalyze the dehydration of methyl lactate to methyl acrylate and acrylic acid, and evaluated the activity of this series of catalysts. It was found that SiO ₂ /NaH ₂ PO ₄ showed a higher overall selectivity of acrylate to acrylic acid than SiO ₂ /Na ₃ PO ₄ or SiO ₂ /Na ₂ HPO ₄ , and NaH ₂ PO ₄ had the best loading , The high selectivity is considered to be related to the acid strength and density of the P-OH at the end of the polyphosphoric acid chain after the catalyst is roasted. At the same time, it shows that the different mass ratios of Na ₂ O and P ₂ O ₅ in phosphate also affect the catalytic performance of lactic acid dehydration. In addition, the group [Molecular Catalysis, 23, 318, 2009] also studied the influence of different Na/P ratio sodium phosphate salt series catalysts on the conversion reaction of lactic acid. The catalyst is prepared by first mixing NaH ₂ PO ₄ with Na ₂ CO ₃ or H ₃ PO ₄ in different proportions, then loading it on silica gel by impregnation method, and finally roasting it. The research results show that when the ratio of Na/P is 1.2, the surface acid strength and acid density of the phosphate catalyst are appropriate, the reactivity of catalyzing the dehydration of lactic acid to prepare acrylic acid is the best, and the yield of acrylic acid is as high as 30%. The characterization results revealed that the high yield of acrylic acid was due to the moderate acidity of the polyphosphate terminal POH on the surface of the catalyst, and the POH was the active site of the reaction. Lee et al [Catal.Commun.2010,11,1176] investigated the influence of silica supports obtained by different preparation methods on the catalytic performance of supported calcium phosphate. The silica carrier is prepared by sol method, gel method, silicate precipitation method; the supported catalyst is prepared by wet impregnation or sol-gel method, and the loading of active component Ca ₃ (PO ₄ ) ₂ is between 70% ~95%. Among them, the silica prepared by the precipitation method using sodium silicate as the precursor is the best. The best experimental result is that when the catalyst composition wt(Ca ₃ (PO ₄ ) ₂ ):wt(SiO ₂ )=80:20, the catalytic effect is the best, the conversion rate of lactic acid reaches 73.6%, and the total amount of acrylic acid and methyl acrylate The selectivity was 77.1%. Characterization comparative analysis reveals that the high selectivity is attributed to the proper distribution of acid-base sites on the catalyst surface. Peng Shaojun et al [Journal of Beijing University of Chemical Technology (Natural Science Edition), 37,11, 2010] used silica gel as the carrier and alkali metal dihydrogen phosphate MH ₂ PO ₄ (M=Li, Na, K) as the active component. Three kinds of supported polymeric phosphate catalysts M ₂ HPO ₄ /SiO ₂ were prepared by the method, and the effects of different alkali metal ions on the reaction performance of methyl lactate dehydration to acrylic acid and co-production of methyl acrylate were investigated in a fixed-bed continuous flow reactor . Among the three catalysts, Na ₂ HPO ₄ /SiO ₂ catalyzed methyl lactate to produce acrylic acid and methyl acrylate with the highest overall selectivity. When the reaction temperature was 380°C, the conversion rate of methyl lactate was 99.5%, and the target product acrylic acid could be selected. up to 52%. Catalyst characterization and quantum chemical calculations show that alkali metal ions affect the acidity density of the catalyst surface and the acidity of the terminal P-OH of the polyphosphorus salt chain, and the medium acid strength and medium acid amount on the catalyst surface are beneficial to improve the total selectivity of the product. Hong et al [AppliedCatalysis A: General 2011,396,194] developed a compound salt catalyst for the dehydration of methyl lactate to acrylic acid and acrylate esters with high efficiency and high selectivity. This series of catalysts is prepared by mixing Ca ₃ (PO ₄ ) ₂ and Ca ₂ P ₂ O ₇ in different mass ratios through slurry mixing. The experimental results show that the composite catalyst with a ratio of 50:50wt% has the highest activity and product selectivity, the selectivity of acrylic acid reaches 75%, and the selectivity of methyl acrylate is 5%. Catalyst characterization analysis reveals that high-temperature calcination endows the surface of the catalyst with appropriate acid-base strength, so the catalyst has high catalytic performance. Wadley et al [Journal of Catalysis 1997,165,162] research group used silica gel-supported sodium nitrate as a catalyst to catalyze the dehydration of lactic acid under gas-solid phase reaction conditions, and found that sodium lactate is an active component. The active component sodium lactate is formed by proton transfer between lactic acid and sodium nitrate, and the additional nitric acid generated by the reaction is volatilized with the product. The experimental results show that high temperature, low pressure and short contact time are beneficial to the formation of acrylic acid. [Industrial & Engineering Chemistry Research 1993, 32, 2608] Lira et al [Industrial & Engineering Chemistry Research 1993, 32, 2608] used disodium hydrogen phosphate, phosphoric acid, and sodium hydroxide to catalyze the dehydration of lactic acid respectively in a near-critical aqueous medium, and to produce three kinds of product acrylic acid and by-product acetaldehyde The reaction pathways were studied and evaluated. The best molar yield of acrylic acid was 58% when the reaction temperature was 360℃. The experimental results show that adding a small amount of Na ₂ HPO ₄ to the lactic acid solution can significantly increase the molar yield of acrylic acid, and the selectivity of acrylic acid increases from 35% to 58%; the addition of NaOH makes the molar yield of acrylic acid only 45%; The addition of acrylic acid reduces the selectivity of acrylic acid. The application of the first-order reaction kinetic model reveals that adding a small amount of 0.04MNa ₂ HPO ₄ can increase the reaction rate constant of the formation of acrylic acid, but mostly weaken the occurrence of side reactions such as decarboxylation and decarbonylation. Recently, Ghantani et al [Green Chemistry 2013, 15, 1211] used hydroxyapatite to catalyze the dehydration of lactic acid to prepare acrylic acid, and obtained a yield of 60%.

The second category: molecular sieve catalysts. Such as Y molecular sieve, NaY molecular sieve, ZSM-5, etc. Shi et al [Chinese Chemical Letters 2007,18,476] studied the catalytic effect of modified zeolite molecular sieve on the dehydration of methyl lactate to methyl acrylate. The experiment found that the KNaY molecular sieve prepared by ion exchange between NaY molecular sieve and KCl solution has weakened acidity and improved catalyst performance compared with that before exchange. The experimental results showed that the molar yield of acrylic acid was 37.9% and the selectivity was 45.7%. Wang et al. [Catalysis Communications 2008,9,1799] investigated the use of NaY molecular sieves modified by rare earth metals to catalyze the production of acrylic acid from lactic acid, and discussed and analyzed the relationship between catalyst structure and catalytic performance in combination with characterization. The experimental results show that the NaY molecular sieve modified by La ³⁺ has the best catalytic performance, and the optimal loading of La ³⁺ is 2wt%. Combined with the characterization results, it was found that the introduction of La ³⁺ changed the surface properties of the catalyst, such as reducing the surface acid density, expanding the pore size and increasing the specific surface area. In addition, the special unit cell distortion caused by the entry of La ³⁺ into the NaY framework cage is the fundamental reason for the high selectivity of acrylic acid. At a deeper level, specific twists may affect the adsorption changes, activation energy, and conversion pathways of lactic acid in the reaction. Sun et al. [Catalysis Communications 2009, 10, 1345] also conducted a systematic study on the dehydration of lactic acid catalyzed by NaY molecular sieves. The experimental results show that compared with NaY molecular sieves, the 2.8K/NaY molecular sieves prepared by K ⁺ modification not only greatly improve the selectivity of the target product, but also increase the life of the catalyst. For example, acrylic acid selectivity can be increased from 14.8% to 50%. Characterization analysis shows that the optimal catalyst has moderate acidity and alkalinity and the electronic effect of K ⁺ endows the improvement of catalyst performance. Sun et al [Industrial & Engineering Chemistry Research 2010,49,9082] KNaY molecular sieves prepared by potassium salt ion exchange catalyzed the dehydration of lactic acid to acrylic acid, focusing on the influence of potassium salt anions on the reaction performance, and compared and analyzed the NaY type According to the experimental results before and after the modification of molecular sieves, it is found that the product selectivity corresponding to NaY type molecular sieves after modification is greatly improved. Among them, KNaY molecular sieve modified with KI has the best catalytic performance. When the reaction temperature is 325°C, the conversion rate of lactic acid reaches 97.6%, and the corresponding acrylic acid selectivity reaches 67.9%. The mechanism analysis reveals that the anion exerts a significant influence on the catalytic behavior through the electronic effect, and the selectivity of acrylic acid is improved at the macroscopic level. Yan et al [Chinese Journal of Catalysis 2011,32,405] studied Ba ²⁺ and La ³⁺ ion-modified NaY molecular sieves to catalyze the dehydration of lactic acid to acrylic acid, and investigated the influence of different preparation methods of the catalyst on the pore structure and catalytic performance of the catalyst. Yu et al [The Canadian Journal of Chemical Engineering 2011,89,484] investigated the use of NaY molecular sieves modified with La ³⁺ to catalyze the dehydration of lactic acid, and used a series of characterization methods to analyze and discuss the effect of different catalyst preparation methods on the surface micropore structure and catalytic performance. Impact. Experiments found that the introduction of La ³⁺ can improve the catalytic performance of NaY molecular sieves. At the same time, compared with the in situ synthesis, the La/NaY molecular sieve prepared by impregnation method showed high acrylic acid selectivity, because different preparation methods caused the different positions of La ³⁺ in the molecular sieve, and the position difference may affect Electric field distribution, reactant adsorption, activation energy and reaction path, etc. Yan et al [Journal of RareEarths 2010, 28, 803] investigated the NaY-type molecular sieve modified by Ba ²⁺ , La ³⁺ and K ⁺ metal ions to catalyze the production of acrylic acid from lactic acid, and optimized the reaction conditions. The experimental results show that the catalyst La/NaY molecular sieve has excellent catalyst performance, and the yield of acrylic acid reaches 56.3% when the reaction temperature is 325 °C. The results of comparative characterization show that the high selectivity of acrylic acid is attributed to the appropriate acid-base content on the surface of the La/NaY catalyst. Properly reducing the acid content and acid strength can weaken the formation of acetaldehyde, while increasing the base content and appropriately reducing the base strength is beneficial to acrylic acid. generation. Zhang et al [ACS Catalysis 2011,1,32] investigated NaY molecular sieve modified with alkaline earth metal phosphate to catalyze the production of acrylic acid from lactic acid, and optimized the reaction from the aspects of phosphate type and load, reaction temperature, liquid space velocity and lactic acid concentration . The best result was obtained: when the reaction temperature of lactic acid was 340℃, the yield of acrylic acid was 58.4% under the action of 14wt%Na ₂ HPO ₄ /NaY catalyst. At the same time, by comparing the characterization spectra of the catalyst before and after the reaction, it was found that sodium phosphate was mainly converted into sodium lactate during the reaction, and the sodium lactate generated in situ is a highly active component that catalyzes the target reaction, and the introduction of phosphate reduces the surface area of the catalyst. acidic. Holm et al [Science 2010,328,602] introduced the use of heterogeneous molecular sieves as catalysts to catalyze the conversion of sugars to prepare lactic acid derivatives, such as the preparation of methyl lactate. For example, when the reaction temperature is 160°C, the monosaccharide or polysaccharide is dissolved in methanol, and the transformation is catalyzed by Lewis acid type molecular sieves such as Sn-Beta. The experimental results found that when sucrose was used as the reaction substrate, the yield of methyl lactate reached 68%. Catalyst recycling experiments show that heterogeneous molecular sieves can be reused after calcination with little effect on product selectivity.

The third type of solid heteropolyacid catalyst. The dehydration reaction of lactic acid catalyzed by solid heteropolyacid is often accompanied by serious decarbonylation and decarboxylation side reactions, so it is mainly used in decarbonylation and decarboxylation reactions. For example, Katryniok et al [Green Chemistry 2010,12,1910.] used heteropolyacids to catalyze the decarbonylation of lactic acid to acetaldehyde. Under gas-solid catalytic reaction conditions, SBA-15 is used as the carrier, the loading capacity of silicotungstic acid is 20wt%, the conversion rate of lactic acid is over 91%, the selectivity of acetaldehyde is 83%, and the selectivity of acrylic acid is extremely low.

To sum up, the production process of acrylic acid from biomass lactic acid is generally carried out under gas-solid phase reaction, the reaction temperature is between 300 and 450 °C, and the research on using modified molecular sieve as catalyst is the most. According to the research results, the conversion rate of lactic acid is generally high, but the selectivity of acrylic acid is generally low, and the stability of the catalyst is poor. Therefore, the focus of the dehydration of lactic acid to acrylic acid process is still to develop efficient and stable catalysts.

Contents of the invention

The patent of the present invention mainly relates to the preparation of acrylic acid by catalyzing the dehydration of lactic acid with sulfate, especially the dehydration of lactic acid catalyzed by alkaline earth metal sulfate. The catalyst has good stability, high selectivity, low price, simple preparation and convenient popularization and application.

In one aspect of the present invention, it relates to a catalyst for preparing acrylic acid from lactic acid dehydration, characterized in that the catalyst is prepared in the following manner:

Alkaline earth metal sulfate is prepared by reacting soluble alkaline earth metal M salt solution or alkaline earth metal hydroxide M solution with dilute sulfuric acid or alkali metal sulfate solution, and its material ratio n(M ²⁺ ):n(SO ₄ ^2- )=1:1, filter the prepared alkaline earth metal sulfate precipitate, wash with distilled water for more than 3 times, then put it in a drying oven for 4-6 hours at 110-130°C, take it out and put it in a desiccator for later use ; Alkaline earth metal sulfate is placed in a muffle furnace, and is calcined by temperature programming and temperature control, with a heating rate of 3-4°C/min, until the set temperature is reached, and calcined at a constant temperature for 3-7 hours; Tablets at 8-10MPa, crushed and sieved to 40-50 mesh to obtain the desired catalyst; the set temperature is 300-800°C, preferably 450-600°C.

In a preferred embodiment of the present invention, the alkaline earth metal M is selected from one or a combination of calcium, magnesium and barium, preferably barium and/or magnesium.

Another aspect of the present invention also relates to the application of the above catalyst in catalyzing the dehydration of lactic acid to prepare acrylic acid.

In a preferred embodiment of the present invention, described application comprises the following steps:

Choose a quartz tube, take the above-mentioned catalyst with a particle size of 40-50 mesh and fill it in the center of the quartz tube, and seal the two sections of the catalyst with quartz wool; place the above-mentioned quartz tube filled with the catalyst in a tube furnace, and connect the feed line , The carrier gas pipeline and the end sample collection device are well connected; the feed pump is a constant flow pump; the carrier gas is nitrogen; the sample collector is a gas-liquid separator with a cold trap.

In a preferred embodiment of the present invention, the reaction conditions are that the feed concentration of lactic acid is 10-50%, preferably 15-25%; the LHSV (liquid space velocity) is 1-8h ^-1 , and the carrier gas is nitrogen , The reaction temperature is 300-450°C.

In a preferred embodiment of the present invention, the catalyst reacts continuously for more than 7 hours.

In a preferred embodiment of the present invention, the conversion rate of lactic acid is 95-100%, the selectivity of acrylic acid is 60-70%, and the selectivity of acetaldehyde is 8-32%.

Description of drawings

Figure 1 Stability performance of CaSO ₄ catalyst: Test conditions: reaction temperature 400°C, CaSO ₄ 0.5g, carrier gas N ₂ 1mL/min, feed rate 1mL/h, lactic acid concentration: 20wt%.

Figure 2 Stability experiment of BaSO ₄ catalyst: Test conditions: reaction temperature 400°C, BaSO ₄ 0.5g, carrier gas N ₂ 1mL/min, feed rate 1mL/h, lactic acid concentration: 20wt%.

Detailed ways

Embodiment one

Weigh 0.8-1.2g of unbaked BaSO ₄ , press into tablets, grind, take 20-40 mesh particles, install them in a quartz tube with a diameter of 3mm, fix the catalyst BaSO ₄ with quartz wool, and then place the catalyst-filled quartz tube Put the tube in the heating furnace, turn on the carrier gas (N ₂ ) and pass it in, turn on the heating device, and let the temperature reach the target temperature in the way of program temperature increase (3-5°C/min), keep the temperature constant, and pass in 20% lactic acid Aqueous solution, collect the product, it is a light yellow transparent liquid, analyze the product, use gas chromatography as the detection tool, use n-butanol as the internal standard, use FFAP capillary column, hydrogen flame (FID) detection, the detection result is the conversion rate of lactic acid It is 99.5%, and the selectivity of acrylic acid is 62%.

Embodiment two

Weigh 0.8-1.2 g of BaSO ₄ calcined at 300°C, press into tablets, grind, take 20-40 mesh particles, install them in a quartz tube with a diameter of 3 mm, use quartz wool to fix the catalyst BaSO ₄ , and then fill the Put the quartz tube with the catalyst in the heating furnace, turn on the carrier gas (N ₂ ) and pass it in, turn on the heating device, and make the temperature reach the target temperature in the way of program temperature rise (3-5°C/min), keep the temperature constant, and pass it in 20% lactic acid aqueous solution, collect the product, it is a light yellow transparent liquid, analyze the product, use gas chromatography as the detection tool, use n-butanol as the internal standard, use FFAP capillary column, hydrogen flame (FID) detection, test results The conversion rate of lactic acid was 99.5%, and the selectivity of acrylic acid was 63%.

Embodiment three

Weigh 0.8-1.2 g of BaSO ₄ calcined at 500°C, press into tablets, grind, take 20-40 mesh particles, install them in a quartz tube with a diameter of 3 mm, fix the catalyst BaSO ₄ with quartz wool, and then fill the Put the quartz tube with the catalyst in the heating furnace, turn on the carrier gas (N ₂ ) and pass it in, turn on the heating device, and make the temperature reach the target temperature in the way of program temperature rise (3-5°C/min), keep the temperature constant, and pass it in 20% lactic acid aqueous solution, collect the product, it is a light yellow transparent liquid, analyze the product, use gas chromatography as the detection tool, use n-butanol as the internal standard, use FFAP capillary column, hydrogen flame (FID) detection, test results The conversion rate of lactic acid is 99.5%, and the selectivity of acrylic acid is 64.5%

Embodiment four

Weigh 0.8-1.2 g of BaSO ₄ calcined at 700°C, press into tablets, grind, take 20-40 mesh particles, install them in a quartz tube with a diameter of 3 mm, fix the catalyst BaSO ₄ with quartz wool, and then fill the Put the quartz tube with the catalyst in the heating furnace, turn on the carrier gas (N ₂ ) and pass it in, turn on the heating device, and make the temperature reach the target temperature in the way of program temperature rise (3-5°C/min), keep the temperature constant, and pass it in 20% lactic acid aqueous solution, collect the product, it is a light yellow transparent liquid, analyze the product, use gas chromatography as the detection tool, use n-butanol as the internal standard, use FFAP capillary column, hydrogen flame (FID) detection, test results The conversion rate of lactic acid was 99.5%, and the selectivity of acrylic acid was 67%.

Embodiment five

Weigh 0.8-1.2 g of BaSO ₄ calcined at 900°C, press into tablets, grind, take 20-40 mesh particles, install them in a quartz tube with a diameter of 3 mm, fix the catalyst BaSO ₄ with quartz wool, and then fill the Put the quartz tube with the catalyst in the heating furnace, turn on the carrier gas (N ₂ ) and pass it in, turn on the heating device, and make the temperature reach the target temperature in the way of program temperature rise (3-5°C/min), keep the temperature constant, and pass it in 20% lactic acid aqueous solution, collect the product, it is a light yellow transparent liquid, analyze the product, use gas chromatography as the detection tool, use n-butanol as the internal standard, use FFAP capillary column, hydrogen flame (FID) detection, test results The conversion rate of lactic acid was 99.5%, and the selectivity of acrylic acid was 62.5%.

Embodiment six

Weigh 0.8-1.2 g of BaSO ₄ calcined at 700°C, press into tablets, grind, take 20-40 mesh particles, install them in a quartz tube with a diameter of 3 mm, fix the catalyst BaSO ₄ with quartz wool, and then fill the Put the quartz tube with the catalyst in the heating furnace, turn on the carrier gas (N ₂ ) and pass it in, turn on the heating device, and make the temperature reach the target temperature in the way of program temperature rise (3-5°C/min), keep the temperature constant, and pass it in 10% lactic acid aqueous solution, collect the product, it is a light yellow transparent liquid, analyze the product, use gas chromatography as the detection tool, use n-butanol as the internal standard, use FFAP capillary column, hydrogen flame (FID) detection, test results The conversion rate of lactic acid was 99.5%, and the selectivity of acrylic acid was 67%.

Embodiment seven

Weigh 0.8-1.2 g of BaSO ₄ calcined at 700°C, press into tablets, grind, take 20-40 mesh particles, install them in a quartz tube with a diameter of 3 mm, fix the catalyst BaSO ₄ with quartz wool, and then fill the Put the quartz tube with the catalyst in the heating furnace, turn on the carrier gas (N ₂ ) and pass it in, turn on the heating device, and make the temperature reach the target temperature in the way of program temperature rise (3-5°C/min), keep the temperature constant, and pass it in 15% lactic acid aqueous solution, collect the product, it is a light yellow transparent liquid, analyze the product, use gas chromatography as the detection tool, use n-butanol as the internal standard, use FFAP capillary column, hydrogen flame (FID) detection, test results The conversion rate of lactic acid was 99.5%, and the selectivity of acrylic acid was 67%.

Embodiment Eight

Weigh 0.8-1.2 g of BaSO ₄ calcined at 700°C, press into tablets, grind, take 20-40 mesh particles, install them in a quartz tube with a diameter of 3 mm, fix the catalyst BaSO ₄ with quartz wool, and then fill the Put the quartz tube with the catalyst in the heating furnace, turn on the carrier gas (N ₂ ) and pass it in, turn on the heating device, and make the temperature reach the target temperature in the way of program temperature rise (3-5°C/min), keep the temperature constant, and pass it in 30% lactic acid aqueous solution, collect the product, it is a light yellow transparent liquid, analyze the product, use gas chromatography as the detection tool, use n-butanol as the internal standard, use FFAP capillary column, hydrogen flame (FID) detection, test results The conversion of lactic acid was 99.5%, and the selectivity of acrylic acid was 64%.

Embodiment nine

Weigh 0.8-1.2 g of MgSO ₄ calcined at 500°C, press into tablets, grind, take 20-40 mesh particles, install them in a quartz tube with a diameter of 3 mm, fix the catalyst BaSO ₄ with quartz wool, and then fill the Put the quartz tube with the catalyst in the heating furnace, turn on the carrier gas (N ₂ ) and pass it in, turn on the heating device, and make the temperature reach the target temperature in the way of program temperature rise (3-5°C/min), keep the temperature constant, and pass it in 20% lactic acid aqueous solution, collect the product, it is a light yellow transparent liquid, analyze the product, use gas chromatography as the detection tool, use n-butanol as the internal standard, use FFAP capillary column, hydrogen flame (FID) detection, test results The conversion rate of lactic acid was 99.5%, and the selectivity of acrylic acid was 63%.

Embodiment ten

Weigh 0.8-1.2 g of ZnSO ₄ calcined at 500°C, press into tablets, grind, take 20-40 mesh particles, install them in a quartz tube with a diameter of 3 mm, fix the catalyst BaSO ₄ with quartz wool, and then fill the Put the quartz tube with the catalyst in the heating furnace, turn on the carrier gas (N ₂ ) and pass it in, turn on the heating device, and make the temperature reach the target temperature in the way of program temperature rise (3-5°C/min), keep the temperature constant, and pass it in 20% lactic acid aqueous solution, collect the product, it is a light yellow transparent liquid, analyze the product, use gas chromatography as the detection tool, use n-butanol as the internal standard, use FFAP capillary column, hydrogen flame (FID) detection, test results The conversion of lactic acid was 50%, and the selectivity of acrylic acid was 25%.

Embodiment Eleven

Weigh 0.8-1.2 g of NiSO ₄ calcined at 500°C, press into tablets, grind, take 20-40 mesh particles, install them in a quartz tube with a diameter of 3 mm, fix the catalyst BaSO ₄ with quartz wool, and then fill the Put the quartz tube with the catalyst in the heating furnace, turn on the carrier gas (N ₂ ) and pass it in, turn on the heating device, and make the temperature reach the target temperature in the way of program temperature rise (3-5°C/min), keep the temperature constant, and pass it in 20% lactic acid aqueous solution, collect the product, it is a light yellow transparent liquid, analyze the product, use gas chromatography as the detection tool, use n-butanol as the internal standard, use FFAP capillary column, hydrogen flame (FID) detection, test results The conversion rate of lactic acid was 99.5%, and the selectivity of acrylic acid was 30%.

Embodiment 12

The stability performance of barium sulfate catalyst and calcium sulfate catalyst was comparatively studied, and the stability of barium sulfate catalyst was better than that of calcium sulfate catalyst. For example, if the barium sulfate catalyst runs continuously for 80 hours, the conversion rate of lactic acid drops from 100% to 90%, and the selectivity of acrylic acid drops from 76% to 50%; while the calcium sulfate catalyst runs continuously for 5 hours, the conversion rate of lactic acid drops to 75%. The experimental results are shown in Figures 1 and 2.

The above description is a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (8)

1. a catalyzer for preparing acrylic acid by dehydration of lactic acid, is characterized in that described catalyzer is prepared in the following way: Alkaline earth metal sulfate is prepared by reacting soluble alkaline earth metal M salt solution or alkaline earth metal hydroxide M solution with dilute sulfuric acid or alkali metal sulfate solution, and its material ratio n(M ²⁺ ):n(SO ₄ ^2- )=1:1, filter the prepared alkaline earth metal sulfate precipitate, wash with distilled water for more than 3 times, then put it in a drying oven for 4-6 hours at 110-130°C, take it out and put it in a desiccator for later use ; Alkaline earth metal sulfate is placed in a muffle furnace, and is calcined by temperature programming and temperature control, with a heating rate of 3-4°C/min, until the set temperature is reached, and calcined at a constant temperature for 3-7 hours; Tablets at 8-10MPa, crushed and sieved to 40-50 mesh to obtain the desired catalyst; the set temperature is 300-800°C, preferably 450-600°C. 2. lactic acid dehydration according to claim 1 prepares the catalyst of acrylic acid, it is characterized in that described soluble alkaline earth metal salt or alkaline earth metal alkaline solution are selected from calcium chloride, lime water, calcium nitrate; Barium chloride, barium hydroxide , barium nitrate; strontium nitrate, strontium chloride, etc.; soluble alkali metal sulfates are selected from sodium sulfate, potassium sulfate, dilute sulfuric acid mostly comes from waste acid. 3. The catalyst for preparing acrylic acid by dehydration of lactic acid according to claim 1, wherein the alkaline earth metal M is selected from one or a combination of calcium, magnesium and barium, preferably barium and/or magnesium. 4. the application of the catalyst described in any one of claims 1-3 in the preparation of acrylic acid by catalyzing the dehydration of lactic acid. 5. The application according to claim 4, comprising the steps of: Choose a quartz tube, take the above-mentioned catalyst with a particle size of 40-50 mesh and fill it in the center of the quartz tube, and seal the two sections of the catalyst with quartz wool; place the above-mentioned quartz tube filled with the catalyst in a tube furnace, and connect the feed line , The carrier gas pipeline and the end sample collection device are well connected; the feed pump is a constant flow pump; the carrier gas is nitrogen; the sample collector is a gas-liquid separator with a cold trap. 6. The application according to claim 5, the reaction conditions are that the feed concentration of lactic acid is 10-50%, preferably 15-25%; the LHSV (liquid space velocity) is 1-8h ^-1 , and the carrier gas is Nitrogen, the reaction temperature is 300-450°C. 7. The application according to claim 5, wherein the catalyst reacts continuously for more than 7h. 8. according to the described application of claim 5 or 6, described lactic acid conversion rate is 95-100%, the selectivity of acrylic acid is 60-70%, and the selectivity of acetaldehyde is 8-32%.

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