Resource recycling method of propane-containing waste liquid

Abstract

The invention belongs to the technical field of chemical engineering, and particularly relates to a resource recycling method of propane-containing waste liquid. The method comprises the following steps: (S1) mixing the propane-containing waste liquid with alkali liquor to obtain first mixed liquor; (S2) performing phase separation on the first mixed solution to obtain an upper-layer oil phase and a lower-layer water phase containing propylene and propane; the propane-containing waste liquid is waste liquid in an epoxidation process in a production process for preparing epoxypropane by a co-oxidation method. The invention also relates to application of the oil phase obtained by the method in a butane isomerization process. The method provided by the invention realizes refining and purification of the propane-containing waste liquid material, and the product can be used as a feed of a butane isomerization device after being mixed with butane, thereby effectively realizing resource utilization of the waste liquid. The separation of polymers in the propane-containing waste liquid material is also realized, and the stability of the waste liquid conveying system is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and in particular relates to a method for recycling propane-containing waste liquid. Background Art

[0002] Among the various production processes of propylene oxide (PO), the co-oxidation method has become one of the current mainstream production methods due to its environmental friendliness and production flexibility. The co-oxidation method generates PO through the reaction of peroxide and propylene, and is widely used in the production of chemicals such as polyether polyols, propylene glycol, dimethyl carbonate, as well as in many fields such as surfactants, medicines, pesticides and fragrances. However, in the process of producing propylene oxide by the co-oxidation method, the raw material propylene inevitably contains a small amount of impurity propane.

[0003] In order to maintain the effect of the co-oxidation reaction and prevent the accumulation of propane in the process system, the existing process usually designs a distillation tower to separate propylene and propane. However, the propane-containing waste liquid separated in this process has become a problem. The waste liquid contains not only propane, but also a large amount of impurities such as aldehydes, ethers, alcohols, esters, and epoxides. The presence of these impurities makes it difficult to directly use the waste liquid. At present, most manufacturers choose to incinerate this waste liquid as waste oil, but this practice undoubtedly causes a huge waste of resources.

[0004] In addition, alcohol impurities in the waste liquid, especially macromolecular polymers such as polyethylene glycol and polypropylene glycol, tend to gradually deposit in the pipeline due to their long residence time during the subsequent transportation process, causing system blockage, increasing maintenance costs and operating difficulties.

[0005] Therefore, finding an effective method to recycle and utilize the propane-containing waste liquid is of great significance for reducing material consumption and improving the profitability of the device. It also plays a positive role in alleviating scaling of the back-end system, reducing operations and saving manpower. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a method for resource recovery of propane-containing waste liquid, which can effectively remove aldehyde, ether, alcohol, ester and / or epoxy impurities in the propane-containing waste liquid generated in the process of preparing propylene oxide by co-oxidation, thereby improving the purity of hydrocarbons in the waste liquid, and the refined propane-containing waste liquid can be used as a feed raw material for a butane isomerization unit.

[0007] In order to achieve the above object, the present invention provides a method for recycling propane-containing waste liquid, the method comprising the following steps:

[0008] (S1) mixing the propane-containing waste liquid with an alkali solution to obtain a first mixed liquid;

[0009] (S2) performing phase separation on the first mixed liquid to obtain an upper oil phase containing propylene and propane, and a lower water phase;

[0010] The propane-containing waste liquid is the waste liquid generated in the epoxidation process of preparing propylene oxide by the co-oxidation method;

[0011] The concentration of the alkali solution is 0.01-0.06 mol / L, preferably 0.02-0.04 mol / L;

[0012] The mass ratio of the propane-containing waste liquid to the alkali solution is (2-10):1, preferably (4-8):1.

[0013] The upper oil phase obtained by the method described in the second aspect of the present invention is used as a feed raw material in a butane isomerization process. Preferably, the upper oil phase is mixed with mixed butane and used as a feed raw material for a butane isomerization unit.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The present invention realizes the separation of polymers in propane-containing waste liquid, effectively solves the scaling and blockage of the conveying system caused by the presence of macromolecular polymers such as polyethylene glycol and polypropylene glycol, and improves the operation cycle of the downstream propylene recovery tower used to treat propane waste liquid.

[0016] 2. Through the process flow of the present invention, the propane-containing waste liquid material is refined and purified, so that it can be used as a feed raw material for the butane isomerization process, effectively realizing the resource utilization of the waste liquid. DETAILED DESCRIPTION

[0017] The present invention is further described below by means of specific embodiments. The embodiments of the present invention are only used as illustrations of the present invention and do not mean that the scope of the present invention is limited thereto.

[0018] In this article, all percentages or percentage contents involved are mass percentages or mass percentage contents unless otherwise specified.

[0019] A first aspect of the present invention provides a method for recycling propane-containing waste liquid, the method comprising the following steps:

[0020] (S1) mixing the propane-containing waste liquid with an alkali solution to obtain a first mixed liquid;

[0021] (S2) The first mixed liquid is subjected to phase separation to obtain an upper oil phase containing propylene and propane and a lower water phase.

[0022] In the present invention, the propane-containing waste liquid comes from the waste liquid in the epoxidation process of the co-oxidation process for producing propylene oxide. The co-oxidation process uses peroxide prepared by peroxidation reaction to carry out epoxidation reaction with propylene to produce propylene oxide (PO), wherein the propylene raw material comes from the propane dehydrogenation process. Since propane and propylene have similar properties, even after the refining process, the propylene product still inevitably contains a small amount of propane impurities. The propylene raw material containing propane impurities reacts with peroxide to obtain PO and alcohol, and the unreacted propylene is separated from PO and alcohol through a propylene recovery tower. The tower bottom obtains a mixed solution of PO and alcohol for further downstream refining, and the tower top is propane, propylene and a small amount of PO. This stream of materials is further sent to a propylene circulation tower, and the propylene at the top of the circulation tower returns to the epoxidation feed system, and the circulating tower bottom obtains a propane waste liquid containing propylene, isobutane, PO and other impurities.

[0023] Furthermore, the co-oxidation method is selected from the isobutane co-oxidation method, ethylbenzene co-oxidation method or cumene co-oxidation method in the art.

[0024] In some embodiments, in addition to propane and propylene, the propane-containing waste liquid contains the following impurities:

[0025] Alcohol compounds, such as methanol, ethanol, ethylene glycol, propylene glycol and polymers thereof, with a content of, for example, 0.4-1.5%;

[0026] Aldehyde compounds, such as formaldehyde, acetaldehyde, glyoxal, etc., whose content is, for example, 0.1-1.2%;

[0027] Ether compounds, such as dimethyl ether, diethyl ether, etc., whose content is, for example, 0.2-1.0%;

[0028] Ester compounds, such as methyl formate, methyl acetate, etc., whose content is, for example, 0.2-1.0%;

[0029] The content of branched epoxy compounds, such as 4-methyl-1,3-dioxolane and 4,4-dimethyl-1,3-dioxane, is, for example, 0.5-1.5%.

[0030] The inventors have found that among the above impurities, aldehyde and ether impurities can be directly dissolved in water; among the alcohol impurities, small molecule alcohols such as methanol, ethanol, ethylene glycol, and propylene glycol have good water solubility, but the solubility of high molecular polymers such as polyethylene glycol and polypropylene glycol is affected by the concentration of alkali solution, the amount of alkali solution, the temperature and the degree of mixing; ester impurities such as methyl formate and methyl acetate are dissolved in water after undergoing a hydrolysis reaction under the action of alkali solution, and their hydrolysis degree and solubility increase with the increase of the amount of alkali solution; branched epoxy impurities themselves have relatively poor water solubility. Similarly, this type of impurities will be hydrolyzed into alcohols under the action of alkali catalysis. Similar to polyethylene glycol and polypropylene glycol, the hydrolysis product alcohols will also be affected by the concentration of alkali solution, the amount of alkali solution, the temperature and the degree of mixing.

[0031] The above oxygen-containing impurities are of many types (including alcohols, aldehydes, ethers, esters and epoxides) and have high contents. If they are directly used as feed for the butane isomerization unit, they will affect the life of the main reaction catalyst and the purity of the reaction products.

[0032] That is, in the present invention, the propane-containing waste liquid comprises propane, propylene, isobutane, alcohol compounds, branched epoxy compounds, and optionally aldehyde compounds, ether compounds and / or ester compounds.

[0033] Further, the alcohol compound is selected from at least one of methanol, ethanol, ethylene glycol, propylene glycol, polyethylene glycol or polypropylene glycol;

[0034] The branched epoxy compound is selected from at least one of a branched penta-dioxane, a branched hexa-dioxane and a branched hepta-dioxane.

[0035] In some embodiments, in step (S1), the alkaline solution is selected from at least one of sodium hydroxide solution, potassium hydroxide solution, and ammonia water. Depending on the strength of the alkalinity, sodium hydroxide solution and / or potassium hydroxide solution are preferred.

[0036] Furthermore, the concentration of the alkali solution is 0.01-0.06 mol / L, preferably 0.02-0.04 mol / L. If the concentration of the alkali solution is low, the hydrolysis reaction time of esters and branched epoxy impurities is long, and the depolymerization of high molecular alcohols such as polyethylene glycol is difficult; if the concentration of the alkali solution is high, although the hydrolysis reaction process will be accelerated, the solubility of some impurities will be reduced.

[0037] Furthermore, the mass ratio of the propane-containing waste liquid to the alkali solution for the mixing is (2-10):1, preferably (4-8):1.

[0038] The inventors have found that the use of dilute alkali solution promotes the hydrolysis and ring opening of epoxy impurities into alcohols, thereby improving their water solubility and achieving the separation of such impurities and hydrocarbons. However, increasing the amount of alkali solution will cause these alcohol products to polymerize again into macromolecular impurities that are difficult to dissolve in water, which may cause system blockage. Therefore, controlling the addition ratio of alkali solution is very critical for the removal effect of epoxy impurities and controlling production costs.

[0039] Therefore, the alkali solution concentration and mass ratio provided by the present invention can improve the dissolution effect of the alkali solution on soluble impurities, and at the same time improve the recovery rate of the upper oil phase in step (S2).

[0040] In the present invention, the mixing temperature is 20-100°C and the pressure is 1.0-3.0 MPag. In some embodiments, in step (S1), the mixing method is selected from at least one of static mixer mixing, pipeline mixing, mixing tank mixing and stirring mixing.

[0041] Preferably, the mixing method is mixing with a static mixer, and the material of the mixing unit of the static mixer is carbon steel, stainless steel or PVC, preferably stainless steel and / or PVC.

[0042] In the present invention, the temperature of the phase separation is 20-100°C and the pressure is 1.0-3.0 MPag. In some embodiments, in step (S2), the phase separation is carried out by at least one of gravity separation, centrifugal separation, membrane separation or coalescence separation.

[0043] Preferably, the phase separation is carried out in a coalescer in the art, which can coalesce small droplets with a particle size of more than 25 μm in the material into large-size droplets, thereby achieving complete separation of the oil phase and the water phase, thereby preventing the alkali solution entrained in the oil phase from entering the butane isomerization unit, resulting in poisoning of the hydrogenation and isomerization reaction catalysts;

[0044] Furthermore, a stainless steel corrugated plate coalescing filler is arranged in the coalescer, and the filler thickness is 20-120 mm, preferably 50-100 mm.

[0045] In some embodiments, in step (S2), in the upper oil phase, the content of hydrocarbons (i.e., propane, propylene, isobutane) is more than 99%, the content of polyethylene glycol is ≤100 ppm, the content of branched epoxides is ≤100 ppm, and the total content of other impurities is ≤200 ppm.

[0046] The second aspect of the present invention provides a use of the oil phase obtained by the above-mentioned propane-containing waste liquid resource recovery method as a feed raw material in a butane isomerization process.

[0047] In some embodiments, the oil phase can be used as a feed material for a butane isomerization process, and after being blended with mixed butane, it can be used as a feed material for a butane isomerization unit (requires a total alcohol content of ≤500ppm and a total oxygen content of ≤800ppm).

[0048] Those skilled in the art can understand that the main component of the feed material in the butane isomerization unit is a mixed butane of normal butane and isobutane (whose total content is ≥97%), which may also contain a small amount of propane and propylene. The main production process is to obtain isobutane by hydrogenation and isomerization of the mixed butane. At the same time, propane is generated after hydrogenation of propylene. Propane and isobutane are then refined and separated to obtain propane-rich gas and product isobutane. The propane-rich gas is sent to the propane dehydrogenation unit as a raw material. In view of the fact that the composition of the upper oil phase described in the present invention is C3 and C4 such as propane, propylene, and isobutane, it can be mixed with mixed butane as the feed of the butane isomerization unit.

[0049] The present invention will be further described below by specific examples. In the following examples and comparative examples:

[0050] The propane-containing waste liquid is derived from the process of preparing propylene oxide by isobutane co-oxidation, and its components are 71.08% propane, 11.58% propylene, 15.42% isobutane, 0.2% ethylene glycol, 0.31% polyethylene glycol, 0.17% acetaldehyde, 0.27% dimethyl ether, 0.24% methyl formate, 0.09% propylene oxide, and 0.64% 4-methyl-1,3-dioxolane.

[0051] Example 1 (A1)

[0052] (S1) in a static mixer (mixing unit made of stainless steel), at a temperature of 50° C. and a pressure of 1.5 MPag, the propane-containing waste liquid is mixed with an alkali solution (sodium hydroxide aqueous solution) to obtain a first mixed liquid; wherein,

[0053] The concentration of the alkali solution is 0.01 mol / L;

[0054] The mass ratio of the propane-containing waste liquid to the alkali solution is 2:1.

[0055] (S2) in a coalescer (using a stainless steel corrugated plate coalescing packing having a thickness of 50 mm), at a temperature of 50° C. and a pressure of 1.5 MPag, the first mixed liquid is subjected to phase separation to obtain an upper oil phase containing propylene and propane and a lower water phase; wherein,

[0056] The content of hydrocarbons (i.e., propane, propylene, and isobutane) in the upper oil phase is 99.27%, and meets the feed conditions of the butane isomerization unit. Then the upper oil phase is mixed with mixed butane (the total content of n-butane and isobutane is 99%, and the total content of propane and propylene is 2%) at a mass ratio of 1:10 and used as the feed of the butane isomerization unit for butane isomerization reaction. The reaction is carried out under the catalysis of metal platinum, with a reaction temperature of 150°C, a pressure of 3.2MPag, and a space velocity of 3h -1 After the reaction, the product was analyzed and the conversion rate of the butane isomerization reaction was calculated to be 49.31%.

[0057] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is 1.5 years.

[0058] Example 2 (A2)

[0059] Refer to Example 1, the only difference is:

[0060] In step (S1), the concentration of the alkali solution is 0.02 mol / L.

[0061] In step (S2), the content of hydrocarbons in the upper oil phase is 99.97%, and meets the feed conditions of the butane isomerization unit. The conversion rate of the butane isomerization reaction is calculated to be 50.28%.

[0062] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is 3 years.

[0063] Example 3 (A3)

[0064] Refer to Example 1, the only difference is:

[0065] In step (S1), the concentration of the alkali solution is 0.04 mol / L.

[0066] In step (S2), the content of hydrocarbons in the upper oil phase is 99.98%, and meets the feed conditions of the butane isomerization unit. The conversion rate of the butane isomerization reaction is calculated to be 50.41%.

[0067] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is 3 years.

[0068] Embodiment 4 (A4)

[0069] Refer to Example 1, the only difference is:

[0070] In step (S1), the concentration of the alkali solution is 0.06 mol / L.

[0071] In step (S2), the content of hydrocarbons in the upper oil phase is 99.38%, and meets the feed conditions of the butane isomerization unit. The conversion rate of the butane isomerization reaction is calculated to be 49.32%.

[0072] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is 1.5 years.

[0073] Example 5 (A5)

[0074] Refer to Example 1, the only difference is:

[0075] In step (S1), the mass ratio of the propane-containing waste liquid to the alkali solution is 4:1.

[0076] In step (S2), the content of hydrocarbons in the upper oil phase is 99.74%, and meets the feed conditions of the butane isomerization unit. The conversion rate of the butane isomerization reaction is calculated to be 49.48%.

[0077] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is 2 years.

[0078] Example 6 (A6)

[0079] Refer to Example 1, the only difference is:

[0080] In step (S1), the mass ratio of the propane-containing waste liquid to the alkali solution is 6:1.

[0081] In step (S2), the content of hydrocarbons in the upper oil phase is 99.97%, and meets the feed conditions of the butane isomerization unit. The conversion rate of the butane isomerization reaction is calculated to be 50.35%.

[0082] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is 3 years.

[0083] Example 7 (A7)

[0084] Refer to Example 1, the only difference is:

[0085] In step (S1), the mass ratio of the propane-containing waste liquid to the alkali liquid is 8:1.

[0086] In step (S2), the content of hydrocarbons in the upper oil phase is 99.98%, and meets the feed conditions of the butane isomerization unit. The conversion rate of the butane isomerization reaction is calculated to be 50.46%.

[0087] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is 3 years.

[0088] Embodiment 8 (A8)

[0089] Refer to Example 1, the only difference is:

[0090] In step (S1), the mass ratio of the propane-containing waste liquid to the alkali solution is 10:1.

[0091] In step (S2), the content of hydrocarbons in the upper oil phase is 99.04%, and meets the feed conditions of the butane isomerization unit. The conversion rate of the butane isomerization reaction is calculated to be 48.78%.

[0092] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is 1 year.

[0093] Comparative Example 1 (D1)

[0094] Refer to Example 1, the only difference is:

[0095] In step (S1), the concentration of the alkali solution is 0.005 mol / L.

[0096] In step (S2), the content of hydrocarbons in the upper oil phase is 98.35%, and meets the feed conditions of the butane isomerization unit. The conversion rate of the butane isomerization reaction is calculated to be 47.54%.

[0097] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is only 0.5 years.

[0098] Comparative Example 2 (D2)

[0099] Refer to Example 1, the only difference is:

[0100] In step (S1), the concentration of the alkali solution is 0.1 mol / L.

[0101] In step (S2), the content of hydrocarbons in the upper oil phase is 98.74%, and meets the feed conditions of the butane isomerization unit. The conversion rate of the butane isomerization reaction is calculated to be 47.31%.

[0102] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is only 0.5 years.

[0103] Comparative Example 3 (D3)

[0104] Refer to Example 1, the only difference is:

[0105] In step (S1), the mass ratio of the propane-containing waste liquid to the alkali solution is 0.5:1.

[0106] In step (S2), the content of hydrocarbons in the upper oil phase is 98.25%, and meets the feed conditions of the butane isomerization unit. The conversion rate of the butane isomerization reaction is calculated to be 46.33%.

[0107] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is only 0.4 years.

[0108] Comparative Example 4 (D4)

[0109] Refer to Example 1, the only difference is:

[0110] In step (S1), the mass ratio of the propane-containing waste liquid to the alkali solution is 15:1.

[0111] In step (S2), the content of hydrocarbons in the upper oil phase is 98.11%, and meets the feed conditions of the butane isomerization unit. The conversion rate of the butane isomerization reaction is calculated to be 45.87%.

[0112] According to evaluation, the operating cycle of the propylene recovery tower after using this process to treat propane waste liquid is only 0.3 years.

Claims

1. A method for recycling propane-containing waste liquid, characterized in that: The method comprises the following steps: (S1) mixing the propane-containing waste liquid with an alkali solution to obtain a first mixed liquid; (S2) performing phase separation on the first mixed liquid to obtain an upper oil phase containing propylene and propane and a lower water phase; The propane-containing waste liquid is the waste liquid generated in the epoxidation process of preparing propylene oxide by the co-oxidation method; The concentration of the alkali solution is 0.01-0.06 mol / L, preferably 0.02-0.04 mol / L; The mass ratio of the propane-containing waste liquid to the alkali solution during the mixing is (2-10):1, preferably (4-8):

1.

2. The method according to claim 1, characterized in that The propane-containing waste liquid contains propane, propylene, isobutane, alcohol compounds and branched epoxy compounds, and optionally contains aldehyde compounds, ether compounds and / or ester compounds; The alcohol compound is, for example, at least one selected from methanol, ethanol, ethylene glycol, propylene glycol, polyethylene glycol and polypropylene glycol; The branched epoxy compound is, for example, at least one selected from the group consisting of branched dioxopentacyclic, branched dioxhexacyclic and branched dioxheptacyclic.

3. The method according to claim 1 or 2, characterized in that: In step (S1), the alkali solution is selected from at least one of sodium hydroxide solution, potassium hydroxide solution and ammonia water; Preferably, the alkali solution is sodium hydroxide solution and / or potassium hydroxide solution.

4. The method according to any one of claims 1 to 3, characterized in that In step (S1), the mixing temperature is 20-100°C and the pressure is 1.0-3.0 MPag.

5. The method according to any one of claims 1 to 4, characterized in that The mixing method is selected from at least one of static mixer mixing, pipeline mixing, mixing tank mixing and stirring mixing; Preferably, the mixing is carried out in a static mixer.

6. The method according to claim 5, characterized in that The mixing unit of the static mixer is made of carbon steel, stainless steel or PVC.

7. The method according to any one of claims 1 to 6, characterized in that In step (S2), the phase separation temperature is 20-100°C and the pressure is 1.0-3.0 MPag.

8. The method according to any one of claims 1 to 7, characterized in that The phase separation method is selected from at least one of gravity separation, centrifugal separation, membrane separation or coalescence separation; Preferably, the phase separation is carried out by coalescence separation in a coalescence separator.

9. The method according to claim 8, characterized in that The coalescing separator is provided with a stainless steel corrugated plate coalescing filler, and the thickness of the filler is 20-120 mm.

10. Use of the upper oil phase obtained by the method according to any one of claims 1 to 9 as a feed raw material in a butane isomerization process, such as a butane isomerization unit as a feed raw material, preferably, the upper oil phase is mixed with mixed butane as a feed raw material for the butane isomerization unit; Preferably, the total content of n-butane and isobutane in the mixed butane is ≥ 97 wt%.