A process for solvent dewaxing of a fischer-tropsch synthesis oil

Abstract

The application provides a solvent dewaxing method of Fischer-Tropsch synthesis oil products, which does not need to use high-toxicity solvents such as ketone-benzene or easily-toxic solvents, and does not need to be melted, and can realize the separation of oil wax in the Fischer-Tropsch synthesis oil products by using simple process operation, and can obtain a higher oil recovery rate. The application provides a solvent dewaxing method of Fischer-Tropsch synthesis oil products, which comprises the following steps: stirring and uniformly mixing Fischer-Tropsch synthesis oil products to be dewaxed with an ester solvent, obtaining a filtrate through filtration, removing the ester solvent in the filtrate, and obtaining the Fischer-Tropsch synthesis oil products after dewaxing; wherein the ester solvent is selected from one or more of methyl acetate, ethyl acetate, propyl acetate and butyl acetate, preferably the ester solvent is methyl acetate and / or ethyl acetate, and more preferably the ester solvent is ethyl acetate.

Description

Technical Field

[0001] This invention relates to the field of wax removal processing in Fischer-Tropsch synthetic oils, and specifically to a solvent dewaxing method for Fischer-Tropsch synthetic oils. Background Technology

[0002] Fischer-Tropsch synthetic waxes are mainly composed of high-carbon straight-chain hydrocarbons, ranging from C20 to C100, and are characterized by high wax content (greater than 95%) and high pour point (60-100℃). Converting Fischer-Tropsch synthetic waxes into petroleum products typically requires hydrocracking or hydroisomerization. However, due to the high wax content and high pour point of Fischer-Tropsch wax feedstocks (such as Fischer-Tropsch synthetic petroleum products), the converted petroleum products often suffer from excessive wax content. For example, the vacuum residue obtained from hydrocracking contains more than 50% wax and can only be recycled through further cracking. While petroleum products obtained through hydroisomerization have a lower wax content (less than 5%), the presence of residual wax still causes the petroleum products to fail the cloud point test.

[0003] By introducing solvent dewaxing, the oil and wax phases can be effectively separated to obtain high-quality oil products. Currently, the mainstream industrial solvent dewaxing scheme uses ketone-benzene dewaxing technology with methyl ethyl ketone (MEK) and toluene as a composite solvent. However, since MEK is a controlled raw material for the manufacture of toxic substances and toluene is also highly toxic, the use of ketone-benzene solvents poses significant risks.

[0004] Patent document CN103789039B discloses a solvent dewaxing method. The specific process involves mixing molten dewaxing material with a solvent, cooling the mixture to the dewaxing temperature, and adding the solvent using a multi-point dilution method. Dewaxing oil and dewaxing wax paste are obtained by filtration at the dewaxing temperature. The solvent is a mixture of an asymmetric ether containing tert-butyl and C3-C6 fatty ketones. This method can increase the filtration rate of solvent dewaxing by 15%-35%, and increase the dewaxing oil yield by 1%-5% under conditions where the wax content of the dewaxing oil is comparable or lower. However, this document uses an ether-ketone system as a composite solvent, still employing solvents such as acetone and methyl ethyl ketone (MEK), which are easily used in the production of toxic substances.

[0005] Patent document CN1050737 discloses a method for solvent dewaxing of waxy petroleum products using at least one suitable solvent and a polyacrylate-based dewaxing aid. In this method, the product to be dewaxed is mixed with the solvent and the polymeric dewaxing aid, the resulting mixture is cooled, and the precipitated wax is separated. The dewaxing aid uses a mixture of the following polymers: a polymeric product P-1 formed by the esterification of acrylic acid and C10-C14 alcohols, and a polymeric product P-2 formed by the esterification of methacrylic acid and an alcohol containing 10% (by weight) or more branched alcohols. The weight ratio of component I) to component II) in the mixture is 1:20 to 20:1. This method, based on the traditional ketone-benzene solvent dewaxing process, introduces polyacrylate as a dewaxing aid, which can promote wax crystallization and improve the oil-wax separation effect. However, this method still requires the use of traditional ketone-benzene solvents, and the added polymeric esters only act as dewaxing aids and cannot replace the function of ketone-benzene. Summary of the Invention

[0006] In view of this, the present invention provides a solvent dewaxing method for Fischer-Tropsch synthetic oils. This method does not require the use of highly toxic solvents such as ketones or benzenes or easily manufactured toxic solvents, and does not require melting. It can achieve the separation of oil and wax in Fischer-Tropsch synthetic oils with simple process operations and can obtain a high oil recovery rate.

[0007] To achieve its objective, the present invention provides the following technical solution:

[0008] This invention provides a solvent dewaxing method for Fischer-Tropsch synthetic oils, comprising the following steps:

[0009] The Fischer-Tropsch synthetic oil to be dewaxed is stirred and mixed with an ester solvent, filtered to obtain a filtrate, and the ester solvent is removed from the filtrate to obtain the dewaxed Fischer-Tropsch synthetic oil.

[0010] The ester solvent is selected from one or more of methyl acetate, ethyl acetate, propyl acetate, and butyl acetate, preferably methyl acetate and / or ethyl acetate, and more preferably ethyl acetate.

[0011] In some embodiments, the stirring and mixing is carried out in a temperature range of 0-60°C. Preferably, the stirring and mixing is carried out in a temperature range of 20-40°C.

[0012] In some embodiments, the filtration is carried out in a temperature range of -30°C to 10°C, and the filtration temperature does not exceed the temperature at which the mixture is stirred.

[0013] In some embodiments, the amount of the ester solvent is 1-30% based on the total mass of the Fischer-Tropsch synthetic oil to be dewaxed and the ester solvent.

[0014] Preferably, based on the total mass of the Fischer-Tropsch synthetic oil to be dewaxed and the ester solvent, the amount of the ester solvent is 5-30%, preferably 5-20%.

[0015] In some embodiments, after the mixing is performed, the mixture is allowed to stand for 0-24 hours before proceeding with subsequent operations.

[0016] Preferably, the settling time is 0.5-2 hours.

[0017] In some preferred embodiments, the ester solvent is ethyl acetate and / or methyl acetate, and the amount of the ester solvent is 5-30% based on the total mass of the Fischer-Tropsch synthetic oil to be dewaxed and the ester solvent; the stirring and mixing are carried out in a temperature range of 20-40°C, and after stirring and mixing, the mixture is allowed to stand for 0-24 hours, then cooled to -30°C to 10°C, and then filtered; preferably, the ester solvent is ethyl acetate, the amount of the ester solvent is 5-20%, and the cooling is to 0-10°C. In some embodiments, the filtration is carried out by pressure filtration or vacuum filtration.

[0018] In some embodiments, the ester solvents in the filtrate are removed by distillation.

[0019] Preferably, the ester solvent removed from the filtrate is recycled as the ester solvent used in the stirring and mixing process.

[0020] The technical solution provided by this invention has the following beneficial effects:

[0021] This invention uses environmentally friendly solvents, eliminating the need for traditional ketone-benzene solvents, and achieves the separation of oil and wax in Fischer-Tropsch synthesis oils with simple process operations, while also ensuring a high oil recovery rate. Detailed Implementation

[0022] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" may be used herein to include any and all combinations of one or more of the associated listed items.

[0024] This invention provides a solvent dewaxing method for Fischer-Tropsch synthetic oils. The process is simple and short, mainly comprising the following steps: mixing the Fischer-Tropsch synthetic oil to be dewaxed with an ester solvent, filtering to obtain a filtrate, removing the ester solvent from the filtrate, and obtaining the dewaxed Fischer-Tropsch synthetic oil. The ester solvent is selected from one or more of methyl acetate, ethyl acetate, propyl acetate, and butyl acetate, preferably methyl acetate and / or ethyl acetate, and more preferably ethyl acetate. Using this method to remove wax from Fischer-Tropsch synthetic oils, the solvent used is environmentally friendly and low in toxicity. Furthermore, the material does not need to be in a molten state during the mixing process of the Fischer-Tropsch synthetic oil to be dewaxed with the ester solvent; the separation of oil and wax can be achieved through the specific solvent and process described above.

[0025] The method provided by this invention uses one or more of methyl acetate, ethyl acetate, propyl acetate, and butyl acetate as a dewaxing solvent, enabling the separation of oil and wax from Fischer-Tropsch synthetic oils with simple operation and mild process conditions. The inventors have found that, under the same experimental conditions, compared with other dewaxing solvents, ethyl acetate is preferred as the dewaxing solvent, achieving superior oil and wax separation while also maintaining a high oil recovery rate.

[0026] In some embodiments, the Fischer-Tropsch synthetic oil to be dewaxed is stirred and mixed with an ester solvent within a temperature range of 0-60°C. The method of the present invention achieves oil-wax separation without requiring a high stirring temperature or the material being in a molten state. Preferably, the stirring and mixing is carried out within a temperature range of 20-40°C. The inventors have found that, under the same experimental conditions, using the preferred stirring and mixing temperature, compared to higher or lower temperatures, is more conducive to wax crystal precipitation and growth, and thus promotes the separation of the oil and wax phases.

[0027] In some embodiments, filtration is carried out within a temperature range of -30°C to 10°C, and the filtration temperature does not exceed the mixing temperature. In some embodiments, if the mixing temperature is higher than the filtration temperature, cooling is performed before filtration; in some embodiments, the mixing temperature and the filtration temperature are the same, in which case the cooling process can be omitted. In some embodiments, the filtration temperature is -30°C, -20°C, -10°C, 0°C, 5°C, 10°C, etc. The filtration temperature can also be called the dewaxing temperature, which can be specifically determined within the range of -30°C to 10°C according to actual needs, such as based on the different requirements of the dewaxed oil product or based on the different ambient temperatures of the solvent dewaxing operation.

[0028] In some embodiments, based on the total mass of the Fischer-Tropsch synthetic oil to be dewaxed and the ester solvent, the amount of the ester solvent is 1-30%, for example, 1%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, etc.; the method of the present invention can achieve oil-wax separation with a relatively small amount of ester solvent. Preferably, based on the total mass of the Fischer-Tropsch synthetic oil to be dewaxed and the ester solvent, the amount of the ester solvent is 5-30%; more preferably, the amount of the ester solvent is 5-20%. The inventors have found that using the preferred amount of ester solvent (5-20%) is beneficial to destroying the network structure of wax crystals and reducing the phenomenon of wax encapsulation of oil; under the same experimental conditions, using the preferred amount of ester solvent (5-20%) can further improve the oil-wax separation effect, obtain oil with relatively more thorough dewaxing, and at the same time, achieve a higher oil recovery rate.

[0029] In some embodiments, after the mixing is performed, the mixture is allowed to stand for 0-24 hours before subsequent operations are carried out. Preferably, the standing time is 0.5-2 hours, which is beneficial for achieving both good separation efficiency and oil-wax separation effect.

[0030] In some preferred embodiments, the ester solvent is ethyl acetate and / or methyl acetate, more preferably ethyl acetate. Based on the total mass of the Fischer-Tropsch synthetic oil to be dewaxed and the ester solvent, the amount of the ester solvent is 5-30%, preferably 5-20%. The stirring and mixing are carried out in a temperature range of 20-40°C. After stirring and mixing, the mixture is allowed to stand for 0-24 hours (preferably 0.5-2 hours), and then cooled to -30°C to 10°C, preferably to 0-10°C, before filtration. Solvent dewaxing of the Fischer-Tropsch synthetic oil under the above conditions can better balance good oil-wax separation effect and high oil recovery rate.

[0031] Specifically, in the method of the present invention, the filtration can be performed using conventional filtration methods in the art to separate the solid and liquid phases, such as pressure filtration or vacuum filtration. Specifically, the removal of ester solvents from the filtrate can be performed using conventional solvent removal methods in the art, such as, but not limited to, distillation.

[0032] Preferably, the ester solvent removed from the filtrate is recycled as the ester solvent used in the stirring and mixing process, which can save solvent usage and reduce costs.

[0033] The method of this invention is particularly suitable for wax removal from Fischer-Tropsch synthetic oils. There are no particular limitations on the specific types of Fischer-Tropsch synthetic oils, such as, but not limited to, hydrocracking vacuum tail oil and hydroisomerization tail oil. This method can be used for wax removal from Fischer-Tropsch synthetic oils with various wax content levels. It can also achieve good oil-wax separation for Fischer-Tropsch synthetic oils with high oil content (i.e., relatively low wax content), for example, for Fischer-Tropsch synthetic oils with an oil content of 90% or even 99%, further improving the quality of such high-oil-content Fischer-Tropsch synthetic oils.

[0034] The present invention will be further illustrated by the following examples.

[0035] The detection methods involved in the following embodiments are described below:

[0036] Pour point: Tested according to GB / T 3535;

[0037] Cloud point: Tested according to GB / T 6986;

[0038] Wax content: Tested according to SY / T 0537-2008;

[0039] Oil content: 100% - Wax content;

[0040] Dewaxed oil yield: Dewaxed oil mass / Total feed oil mass * 100%;

[0041] Oil recovery rate: Dewaxed oil yield / Oil content of feedstock oil * 100%;

[0042] Solvent usage: Solvent mass / (solvent mass + raw material oil mass) * 100%.

[0043] The properties of the feedstock oils (i.e., the Fischer-Tropsch synthetic oils to be dewaxed) used in the following examples are shown in Table 1 below:

[0044] Table 1

[0045]

[0046]

[0047] Examples 1 and 2 use different raw materials

[0048] Example 1:

[0049] 80g of hydrocracking vacuum tail oil was mixed with 20g of ethyl acetate (solvent content was 20%) at a mixing temperature of 25℃. After stirring evenly, the mixture was allowed to stand for 1 hour and then cooled to 0℃ (dewaxing temperature). The filtrate (oil phase) was obtained by vacuum filtration, and the wax phase was removed by filtration. The ethyl acetate in the obtained oil phase was removed by distillation, and finally a clear and transparent oil was obtained (corresponding to the dewaxed oil in Table 1). The properties of the obtained oil are shown in Table 2 below.

[0050] Example 2:

[0051] 80g of hydroisomerized tail oil was stirred and mixed with 20g of ethyl acetate (solvent content was 20%) at a mixing temperature of 25℃ (i.e., stirring and mixing temperature). After stirring evenly, the mixture was allowed to stand for 1 hour and then cooled to 0℃ (i.e., dewaxing temperature). The filtrate (i.e., oil phase) was obtained by vacuum filtration. The wax phase was removed by filtration. The ethyl acetate in the obtained oil phase was removed by distillation, and finally a clear and transparent oil product (corresponding to the dewaxed oil in Table 1) was obtained. The properties of the obtained oil product are shown in Table 2 below.

[0052] In Examples 3-11 below, hydroisomerized tail oil was used for the experiment because the wax content in hydroisomerized tail oil is lower, making it more sensitive to the effect of solvents and more easily affected by product indicators.

[0053] Example 3: Refer to Example 2, except that methyl acetate is used as the solvent.

[0054] Example 4: Refer to Example 2, except that butyl acetate is used as the solvent.

[0055] Example 5: Refer to Example 2, except that the mixing temperature (i.e., stirring and mixing temperature) of the hydroisomerized tail oil and solvent is 40°C.

[0056] Example 6: Referring to Example 2, the difference is that the mixing temperature (i.e., stirring and mixing temperature) of the hydroisomerized tail oil and solvent is 0°C, and no cooling process is required. Vacuum filtration is performed at 0°C (i.e., dewaxing temperature).

[0057] Example 7: Refer to Example 2, except that the mixing temperature (i.e., stirring and mixing temperature) of the hydroisomerized tail oil and solvent is 60°C.

[0058] Example 8: Refer to Example 2, except that the amount of solvent used is 5%.

[0059] Example 9: Refer to Example 2, except that the amount of solvent used is 1%.

[0060] Example 10: Refer to Example 2, except that the solvent amount is 30%.

[0061] Example 11: Refer to Example 2, except that the dewaxing temperature is 10°C.

[0062] Example 12: Refer to Example 2, except that the dewaxing temperature is -30℃.

[0063] Table 2

[0064]

[0065] As can be seen from the experimental results of Examples 1-12 above, the solvent dewaxing method of the present invention can achieve oil-wax separation with simple process operation and mild process conditions, and obtain a high oil recovery rate, whether it is Fischer-Tropsch synthetic oil with low oil content or Fischer-Tropsch synthetic oil with high oil content (i.e. low wax content).

[0066] When evaluating the oil-wax separation effect of each embodiment, the difference obtained by subtracting the dewaxing temperature from the cloud point of the dewaxed oil can reflect the difference in the oil-wax separation effect of the solvent dewaxing experiment. The oil-wax separation effect with a positive difference is not as good as the oil-wax separation effect with a difference of zero or negative. The oil-wax separation effect with a difference of zero is not as good as the oil-wax separation effect with a difference of negative. When all the differences are negative, the oil-wax separation effect with a larger absolute value is worse than the oil-wax separation effect with a smaller absolute value.

[0067] The experimental results of Examples 2-4 show that ethyl acetate is preferred as a solvent for dewaxing. Under the same experimental conditions, for the same Fischer-Tropsch synthetic oil, the difference between the cloud point and the dewaxing temperature of the dewaxed oil is negative, and the absolute value of this negative value is larger. This reflects that, under the same experimental conditions, using ethyl acetate for dewaxing has a better oil-wax separation effect, and the wax phase in the dewaxed oil is removed more thoroughly. At the same time, using ethyl acetate as a solvent for dewaxing can also achieve a higher oil recovery rate.

[0068] As can be seen from the experimental results of Examples 2 and 5-7, under the same experimental conditions, dewaxing of the same Fischer-Tropsch synthetic oil and stirring and mixing at 20-40°C can achieve a higher oil recovery rate while maintaining excellent oil-wax separation effect.

[0069] As can be seen from Examples 2 and 8-10, under the same experimental conditions, a solvent dosage of 5-30% results in a higher oil recovery rate when dewaxing the same Fischer-Tropsch synthetic oil. A solvent dosage of 5-20% is preferred, as it can achieve both a higher oil recovery rate and better oil-wax separation effect compared to higher or lower solvent dosages.

[0070] As can be seen from Examples 11 and 12, by adjusting the dewaxing temperature based on Example 2, dewaxed oils with different cloud points can be obtained. It is evident that the method based on the present invention can obtain dewaxed oils with different cloud point requirements by adjusting the dewaxing temperature.

[0071] The experimental results of Examples 2-3, 5, 8, 10-12 and Examples 4, 6-7, 9, which conducted solvent dewaxing experiments on the same Fischer-Tropsch synthetic oil, show that the following conditions are preferred: the ester solvent is ethyl acetate and / or methyl acetate, the solvent volume is 5-30%, the stirring and mixing temperature is 20-40°C, after stirring and mixing, the mixture is allowed to stand for 0-24 hours, and the dewaxing temperature is -30°C to 10°C; these conditions can achieve both good oil-wax separation and oil recovery. Based on this, Examples 2, 5, 8, and 11 further adopted the following preferred conditions for solvent dewaxing: the ester solvent is ethyl acetate, the ester solvent volume is 5-20%, and the dewaxing temperature is 0-10°C; compared with other examples of solvent dewaxing experiments on the same Fischer-Tropsch synthetic oil, these conditions have better results, achieving both a relatively high oil recovery rate and excellent oil-wax separation.

[0072] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A solvent dewaxing method for Fischer-Tropsch synthetic oils, characterized in that, Includes the following steps: The Fischer-Tropsch synthetic oil to be dewaxed is stirred and mixed with an ester solvent at a temperature range of 20-40°C, then cooled to 0-10°C, and filtered to obtain a filtrate. The ester solvent is then removed from the filtrate to obtain the dewaxed Fischer-Tropsch synthetic oil. The amount of the ester solvent used is 5-20% based on the total mass of the Fischer-Tropsch synthetic oil to be dewaxed and the ester solvent. The ester solvent is ethyl acetate; The Fischer-Tropsch synthetic oil is a hydrocracking vacuum residue or a hydroisomerization residue.

2. The solvent dewaxing method according to claim 1, characterized in that, After mixing, let it stand for 0-24 hours before proceeding with subsequent operations.

3. The solvent dewaxing method according to claim 2, characterized in that, The settling time is 0.5-2 hours.

4. The solvent dewaxing method according to claim 1, characterized in that, The filtration is performed by pressure filtration or vacuum filtration. And / or, the ester solvents in the filtrate are removed by distillation.

5. The solvent dewaxing method according to claim 1, characterized in that, The ester solvents removed from the filtrate are recycled and used as ester solvents in the stirring and mixing process.

Images