A method for pre-treating methanol to synthesize formaldehyde

Abstract

The present application discloses a method for synthesizing formaldehyde by pretreating methanol, which belongs to the field of chemical technology. By pretreating methanol, impurity ions in methanol are removed and methanol molecules are activated, thereby realizing the silver method for producing formaldehyde under relatively mild conditions. The pretreatment method is used to remove impurities in crude methanol and improve substrate activity, so that methanol molecules are pre-activated before contacting a catalyst, accurately adsorbed on the active sites on the catalyst surface, reacting rapidly, and the generated products are quickly desorbed from the catalyst surface, thereby improving reaction selectivity while enhancing catalyst utilization efficiency, reducing catalyst poisoning, extending the catalyst service life, and improving production efficiency.

Description

Technical Field

[0001] The present application belongs to the field of chemical technology, and in particular relates to a method for pre-treating methanol to synthesize formaldehyde. Background Art

[0002] Formaldehyde, as an important organic chemical raw material and chemical intermediate, is widely used in a variety of fields, including chemicals, materials, and pharmaceuticals. According to global market research, formaldehyde production reached 45.6 metric tons in 2020 and is projected to grow at an annual rate of 4.65% between 2021 and 2028, reaching a market value of US$37.7 billion by 2028. my country has become the world's largest formaldehyde producer and consumer, accounting for 55% of global production capacity and 53% of global consumption. Existing formaldehyde production processes in China primarily rely on methanol oxidation. Depending on the type of catalyst used, these processes can be categorized as either "silver" or "iron-molybdenum." The silver catalyst process has a long history and boasts mature technology, a shorter process flow, low power consumption, minimal investment, and high single-series production capacity. Its disadvantages include high methanol consumption, a short catalyst life, and poor catalyst activity.

[0003] During methanol oxidation, the activation of methanol can be carried out on the surface of the catalyst. The dissociative chemical adsorption of methanol requires the configuration of an appropriate pair of acid centers and basic centers. The B-base center reacts with H to generate a hydroxyl group, and the methoxy group reacts with the adjacent matching L-acid center to form a corresponding surface adsorption group.

[0004]

[0005] The main formaldehyde preparation process in my country is still the "silver method" formaldehyde preparation process, accounting for about 90.2% of the total preparation. The raw material in the "silver method" formaldehyde preparation process is refined methanol, and crude methanol should not be used as a raw material. This is because the Fe in crude methanol 2+ 、S 2- Impurities such as these can easily poison and deactivate the electrolytic silver catalyst, shortening the catalyst's service life and increasing energy consumption. Using crude methanol as raw material can reduce raw material costs compared to using refined alcohol. The cost of preparing 1 ton of formaldehyde can be reduced by about RMB 200, with significant economic and social benefits. Summary of the Invention

[0006] The purpose of the present application is to provide a method for synthesizing formaldehyde by pretreating methanol, so as to solve the technical problems existing in the prior art of using refined methanol for formaldehyde synthesis, high raw material cost, and easy deactivation of the catalyst.

[0007] To achieve the above objectives, the technical solution adopted in this application is to provide a method for pretreating methanol to synthesize formaldehyde, which specifically comprises the following steps:

[0008] (1) modifying the adsorbent using an anionic organosilicon surfactant to obtain a modified adsorbent;

[0009] (2) pretreating methanol using a modified adsorbent to obtain pretreated methanol;

[0010] (3) Add pretreated methanol and electrolytic silver catalyst into a fixed bed reactor, introduce air, and produce formaldehyde through oxidation reaction of the pretreated methanol.

[0011] In one embodiment,

[0012] In step (1), the anionic organosilicon surfactant is a siloxane carboxylate, and the siloxane carboxylate is one or more of tetrasiloxane sulfonate (MeSi4K), trisiloxane sulfonate (MeSi3K, EtSi3K, PhSi3K) or disiloxane sulfonate (MeSi2K).

[0013] The specific structure is as follows:

[0014]

[0015] In one embodiment,

[0016] In step (1), the adsorbent is activated carbon or carbon nanotubes.

[0017] In one embodiment,

[0018] In step (1), the mass ratio of the anionic organosilicon surfactant to the adsorbent is 0.1-1:1. Preferably, the mass ratio of the anionic organosilicon surfactant to the adsorbent is 0.5-0.9:1.

[0019] In one embodiment,

[0020] The temperature of the modification treatment in step (1) is 60-100°C, and the treatment time is 2-6 hours.

[0021] In one embodiment,

[0022] The temperature of the pretreatment in step (ii) is 40-100°C.

[0023] In one embodiment,

[0024] The temperature of the oxidation reaction in step (3) is 200-400°C.

[0025] In one embodiment,

[0026] The feed rate of the pretreated methanol in step (3) is 10-30 ml / min.

[0027] In one embodiment,

[0028] In step (3), the air pressure is 0.2-0.5 MPa, preferably, the pressure is 0.2-0.3 MPa.

[0029] The present application provides a method for pretreating methanol to synthesize formaldehyde. Compared with the existing technology, the present application has the following beneficial effects: using the pretreatment method, impurities in crude methanol are removed and the activity of the substrate is improved, so that the methanol molecules are pre-activated before contacting the catalyst, accurately adsorbed on the active sites on the catalyst surface, and reacted quickly, and the generated products are quickly desorbed from the catalyst surface, thereby improving the reaction selectivity and the utilization efficiency of the catalyst, reducing catalyst poisoning, extending the catalyst service life, and improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0031] Figure 1 This is the pretreatment process flow chart for this application.

[0032] Explanation of symbols in the figure:

[0033] 1. Pretreatment fixed bed; 2. First storage tank; 3. Oxidation reaction fixed bed; 4. Second storage tank. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clear and understandable, this application is further described in detail. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0035] In the embodiment, the reaction outlet gas is effectively captured, and the methanol conversion rate and formaldehyde selectivity are calculated by the following formula:

[0036]

[0037]

[0038] The formaldehyde and methanol solutions in the receiving bottle were analyzed and determined according to the national standard GB / T 9009-2011 "Industrial Formaldehyde Solution" for methanol conversion and formaldehyde selectivity.

[0039] The tetrasiloxane sulfonate (MeSi4K), trisiloxane sulfonate (MeSi3K, EtSi3K, PhSi3K) or disiloxane sulfonate (MeSi2K) used in the present invention are synthesized according to the method disclosed in the reference: Huang Yue, Preparation and Performance Study of Anionic Silicone Surfactants, Doctoral Dissertation, Shandong University, 2020-12-05.

[0040] Example 1

[0041] A method for pretreating methanol to synthesize formaldehyde, specifically comprising the following steps:

[0042] (1) At room temperature, add 14 g of MeSi4K to 100 mL of deionized water, stir until fully dispersed, then add 20 g of activated carbon, heat to 80 °C for modification, keep stirring for 4 h, and filter to obtain modified activated carbon;

[0043] (2) Filling the modified activated carbon into a fixed bed reactor, preheating the fixed bed reactor to 80°C, and introducing crude methanol for pretreatment at a feed rate of 20 ml / min to obtain pretreated methanol;

[0044] (III) Preheat another fixed-bed reactor to 300°C, load an electrolytic silver catalyst (10 g), and keep warm for 1 hour. Then, add pretreated methanol at a flow rate of 20 ml / min, introduce air at a pressure of 0.35 MPa, and produce formaldehyde through oxidation reaction. After the feed reaction is continued for 2 hours, the formaldehyde and methanol solution in the receiving bottle are analyzed and determined according to the national standard GB / T9009-2011 "Industrial Formaldehyde Solution" for methanol conversion and formaldehyde selectivity. The methanol conversion rate is 58.6%, and the formaldehyde selectivity is 98.3%. The process flow is as follows: Figure 1 As shown, the modified activated carbon enters the pretreatment fixed bed 1 and is pretreated with the crude methanol, and the obtained pretreated methanol is temporarily stored in the first storage tank 2; the pretreated methanol enters the oxidation reaction fixed bed 3 for oxidation reaction, and the obtained formaldehyde is temporarily stored in the second storage tank 4.

[0045] Example 2

[0046] This example differs from Example 1 in that activated carbon is replaced with carbon nanotubes to prepare modified carbon nanotubes. The remaining operations are the same. After 2 h of reaction, the methanol conversion rate is 62.4%, and the formaldehyde selectivity is 98.5%.

[0047] Example 3

[0048] The difference between this embodiment and embodiment 1 is that the mass of MeSi4K is 2 g, and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 50.2%, and the formaldehyde selectivity is 93.4%.

[0049] Example 4

[0050] This embodiment differs from embodiment 1 in that the mass of MeSi4K is 6 g, and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 54.7%, and the formaldehyde selectivity is 95.7%.

[0051] Example 5

[0052] The difference between this embodiment and embodiment 1 is that the mass of MeSi4K is 10 g, and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 57.3%, and the formaldehyde selectivity is 97.6%.

[0053] Example 6

[0054] The difference between this embodiment and embodiment 1 is that the mass of MeSi4K is 18 g, and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 60.4%, and the formaldehyde selectivity is 98.4%.

[0055] Example 7

[0056] This embodiment differs from embodiment 1 in that the mass of MeSi4K is 20 g, and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 62.8%, and the formaldehyde selectivity is 98.6%.

[0057] Example 8

[0058] This embodiment differs from embodiment 1 in that MeSi4K is replaced with MeSi3K, and the remaining operations are the same. After 2 h of reaction, the methanol conversion rate is 57.3%, and the formaldehyde selectivity is 97.8%.

[0059] Example 9

[0060] This embodiment differs from embodiment 8 in that MeSi3K is replaced with EtSi3K, and the remaining operations are the same. After 2 h of reaction, the methanol conversion rate is 57.2%, and the formaldehyde selectivity is 97.2%.

[0061] Example 10

[0062] This embodiment differs from embodiment 8 in that MeSi3K is replaced with PhSi3K, and the remaining operations are the same. After 2 h of reaction, the methanol conversion rate is 56.8%, and the formaldehyde selectivity is 96.4%.

[0063] Example 11

[0064] This embodiment differs from embodiment 8 in that MeSi3K is replaced with MeSi2K, and the remaining operations are the same. After 2 h of reaction, the methanol conversion rate is 57.2%, and the formaldehyde selectivity is 97.5%.

[0065] Example 12

[0066] This embodiment differs from embodiment 1 in that the temperature of the modification treatment in step (1) is 60° C., and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 56.4%, and the formaldehyde selectivity is 97.2%.

[0067] Example 13

[0068] This embodiment differs from embodiment 1 in that the temperature of the modification treatment in step (1) is 100° C., and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 60.5%, and the formaldehyde selectivity is 98.3%.

[0069] Example 14

[0070] This embodiment differs from embodiment 1 in that the time of heat preservation and stirring in step (1) is 2 h, and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 56.4%, and the formaldehyde selectivity is 97.8%.

[0071] Example 15

[0072] This embodiment differs from embodiment 1 in that the time of heat preservation and stirring in step (1) is 6 h, and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 61.3%, and the formaldehyde selectivity is 98.7%.

[0073] Example 16

[0074] This embodiment differs from embodiment 1 in that the preheating temperature of the fixed bed reactor in step (ii) is 40° C., and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 57.3%, and the formaldehyde selectivity is 97.7%.

[0075] Example 17

[0076] This embodiment differs from embodiment 1 in that the preheating temperature of the fixed bed reactor in step (ii) is 60° C., and the remaining operations are the same. After 2 h of reaction, the methanol conversion rate is 58.1%, and the formaldehyde selectivity is 98%.

[0077] Example 18

[0078] This embodiment differs from embodiment 1 in that the preheating temperature of the fixed bed reactor in step (ii) is 100° C., and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 60.4%, and the formaldehyde selectivity is 97.9%.

[0079] Example 19

[0080] This embodiment differs from embodiment 1 in that the preheating temperature of the fixed bed reactor in step (iii) is 200° C., and the remaining operations are the same. After 2 h of reaction, the methanol conversion rate is 58%, and the formaldehyde selectivity is 98.1%.

[0081] Example 20

[0082] This embodiment differs from embodiment 1 in that the fixed bed reactor is preheated to 400° C. in step (iii). The remaining operations are the same. After 2 h of reaction, the methanol conversion rate is 66.3%, and the formaldehyde selectivity is 97.2%.

[0083] Example 21

[0084] This embodiment differs from embodiment 1 in that, in step (ii) and step (iii), the crude methanol feed rate and the pretreated methanol flow rate are both 10 ml / min, and the remaining operations are the same. After 2 h of reaction, the methanol conversion rate is 61.6%, and the formaldehyde selectivity is 98%.

[0085] Example 22

[0086] This embodiment differs from embodiment 1 in that in step (2) and step (3), the crude methanol feed rate and the pretreated methanol flow rate are both 30 ml / min, and the remaining operations are the same. After 2 h of reaction, the methanol conversion rate is 56.3%, and the formaldehyde selectivity is 98.1%.

[0087] Example 23

[0088] The difference between this embodiment and embodiment 1 is that the air pressure in step (iii) is 0.2 MPa, and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 58.1%, and the formaldehyde selectivity is 98.2%.

[0089] Example 24

[0090] The difference between this embodiment and embodiment 1 is that the air pressure in step (iii) is 0.5 MPa, and the other operations are the same. After 2 h of reaction, the methanol conversion rate is 60.2%, and the formaldehyde selectivity is 98.3%.

[0091] Example 25

[0092] This embodiment differs from embodiment 1 in that the method for treating the pretreated methanol in step (ii) is as follows: adding the modified activated carbon and 2400 ml of crude methanol to a reactor, starting stirring, raising the temperature to 80°C, maintaining the temperature with stirring for 2 h, cooling to room temperature, filtering to remove the modified activated carbon, and obtaining pretreated methanol. The remaining operations are the same. After 2 h of reaction, the methanol conversion rate is 59.6%, and the formaldehyde selectivity is 98.7%.

[0093] Comparative Example 1

[0094] A fixed-bed reactor filled with electrolytic silver catalyst was preheated to 300°C and kept warm for 1 hour. Untreated crude methanol was then fed into the liquid phase to prepare formaldehyde at a flow rate of 20 ml / min. After the reaction was continued for 2 hours, the formaldehyde and methanol solutions in the receiving bottle were tested: the methanol conversion rate was 32.4%, and the formaldehyde selectivity was 65.1%.

[0095] Comparative Example 2

[0096] Unmodified activated carbon was loaded into a fixed-bed reactor, which was preheated to 80°C and crude methanol was introduced at a feed rate of 30 ml / min. A fixed-bed reactor filled with an electrolytic silver catalyst was preheated to 300°C and kept warm for 1 hour. The treated methanol was then fed in liquid phase to prepare formaldehyde at a flow rate of 30 ml / min. After the reaction was continued for 2 hours, the formaldehyde and methanol solutions in the receiving bottle were tested to show a methanol conversion rate of 46.2% and a formaldehyde selectivity of 76.4%.

[0097] It can be seen from Examples 1-25 and Comparative Example 1 that when formaldehyde is prepared using methanol without pretreatment, or when formaldehyde is prepared using methanol pretreated with unmodified activated carbon in Comparative Example 2, the alcohol conversion rate and formaldehyde selectivity are lower than those of Examples 1-25.

[0098] The present application provides a method for pretreating methanol to synthesize formaldehyde, which comprises modifying an adsorbent with an anionic organosilicon surfactant to obtain a modified adsorbent; pretreating methanol with the modified adsorbent to obtain pretreated methanol; adding pretreated methanol and an electrolytic silver catalyst into a fixed bed reactor, introducing air, and producing formaldehyde through an oxidation reaction of the pretreated methanol; compared with the prior art, the present application has the following beneficial effects: by pretreating methanol, impurity ions in methanol are removed, and methanol molecules are activated, thereby realizing the silver method for producing formaldehyde under relatively mild conditions; using the pretreatment method, impurities in crude methanol are removed, and substrate activity is improved, so that methanol molecules are pre-activated before contacting the catalyst, accurately adsorbed on the active sites on the catalyst surface, reacting rapidly, and the generated products are quickly desorbed from the catalyst surface, thereby improving the reaction selectivity while improving the utilization efficiency of the catalyst, reducing catalyst poisoning, extending the catalyst service life, and improving production efficiency.

[0099] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0100] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for pretreating methanol to synthesize formaldehyde, characterized in that: The specific steps include: (1) modifying the adsorbent using an anionic organosilicon surfactant to obtain a modified adsorbent; (2) pretreating methanol using the modified adsorbent to obtain pretreated methanol; (3) adding the pretreated methanol and an electrolytic silver catalyst into a fixed bed reactor, introducing air, and producing formaldehyde through an oxidation reaction of the pretreated methanol; The anionic organosilicon surfactant in step (1) is one or more of tetrasiloxane sulfonate, trisiloxane sulfonate or disiloxane sulfonate; the specific structure of the anionic organosilicon surfactant is: The adsorbent is activated carbon or carbon nanotubes; The mass ratio of the anionic silicone surfactant to the adsorbent is 0.1-1:1; The air pressure in step (3) is 0.2-0.5 MPa.

2. The method for synthesizing formaldehyde from methanol by pretreatment according to claim 1, characterized in that: The temperature of the modification treatment in step (1) is 60-100°C, and the treatment time is 2-6 hours.

3. The method for synthesizing formaldehyde from methanol by pretreatment according to claim 1, characterized in that: The temperature of the pretreatment in step (2) is 40-100°C.

4. The method for synthesizing formaldehyde from methanol by pretreatment according to claim 1, characterized in that: The temperature of the oxidation reaction in step (3) is 200-400°C.

5. The method for synthesizing formaldehyde from methanol by pretreatment according to claim 1, characterized in that: The feed rate of the pretreated methanol in step (iii) is 10-30 ml / min.

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