Method for realizing desalination of bio-heavy oil by using methanol

Abstract

The application discloses a method for mixing and emulsifying bio-heavy oil and methanol, and then using a high-speed centrifuge to demulsify and desalt. Metal salts in bio-heavy oil mainly exist in the form of fatty acid salts. As a strong polar organic solvent, methanol can dissolve the fatty acid salts in bio-heavy oil, but cannot be mutually soluble with bio-heavy oil which is weak in polarity and lipophilic. A cross-flow porous ceramic membrane emulsification device is used, methanol at normal temperature is taken as a dispersed phase, and the methanol is made to pass through the ceramic membrane holes at a constant flow rate through a constant-flow pump to form a bio-heavy oil MeOH / O emulsion. Then, the bio-heavy oil is desalted in a high efficiency through a centrifugal demulsification method by using the density difference between bio-heavy oil and methanol. The salt removal efficiency of bio-heavy oil is controlled by adjusting the methanol content, centrifugal speed, centrifugal time and continuous phase temperature. In addition, the methanol molecules have a solventization effect with the hydrophilic head group of the fatty acid salts, and also have a Van der Waals force with the hydrophobic carbon and hydrogen chain of the fatty acid salts. The Van der Waals force makes it difficult for the fatty acid salts as anionic surfactants to be adsorbed on the oil-water surface. The large particle size and relative thermodynamic instability of the bio-heavy oil MeOH / O emulsion improve the desalination rate.

Description

Technical Field

[0001] This invention discloses a method for desalting bio-heavy oil using methanol, relating to the fields of biomass resource utilization and crude oil desalting. Background Technology

[0002] Due to further development of biofuels, global biodiesel production reached 2.89 billion gallons by 2017. As a byproduct of biodiesel production, bio-heavy oil is a sustainable green fuel with high oxygen content, low sulfur content, and high calorific value, attracting increasing attention against the backdrop of growing energy shortages. However, my country's level of deep processing and utilization of bio-heavy oil lags far behind that of other countries, and it is often treated as industrial waste. Bio-heavy oil has a sulfur content of less than 0.05%, and its calorific value is higher than that of ordinary bio-heavy oil. # Light diesel oil has high purity, complete combustion, low exhaust pollution, and good fuel economy. Therefore, utilizing bio-heavy oil to replace traditional fossil fuels and transforming the production processes of my country's energy-intensive industries is of great practical and strategic significance for achieving the low-carbon transformation of my country's energy-intensive industries. However, the high metal salt content generated by alkaline catalysts used in biodiesel conversion means that directly using it as fuel may clog preheater tubes, cause nozzle wear, and corrode combustion system equipment. These salts mainly exist in the form of fatty acid salts in bio-heavy oil because alkaline catalysts neutralize free fatty acids during biodiesel production. Developing efficient bio-heavy oil desalting technology is an urgent need for the utilization of bio-heavy oil. Methanol, as a green and inexpensive organic solvent, contains a polar hydroxyl group (-OH) and a nonpolar methyl group (CH3) in its molecular structure, enabling it to interact effectively with a variety of organic and inorganic compounds, thus having wide applications in scientific research and industrial production. Methanol can dissolve fatty acid salts, mainly based on the chemical principle of "like dissolves like," but it is not miscible with lipophilic bio-heavy oil. Fatty acid salts are salts formed from long-chain fatty acids and metal ions, possessing a hydrophobic alkyl tail and a hydrophilic ionic head. This molecular structure enables them to exhibit unique solubility behaviors in certain solvents. In addition to solubilizing the hydrophilic head group of fatty acid salts, methanol molecules also exhibit van der Waals forces with the hydrophobic hydrocarbon chains of fatty acid salts. These van der Waals forces play a role in the overall solubilization process, making it difficult for fatty acid salts to adsorb onto the oil / methanol interface, thus reducing interfacial tension and forming relatively unstable, larger emulsion droplets, which is more conducive to the desalting of bio-heavy oils. Furthermore, membrane emulsification technology, relying on membrane structures, can achieve a uniform distribution of the dispersed phase in the continuous phase, obtaining controllable emulsion size and span, significantly increasing the driving force for mass transfer between the two phases, and has been widely used in heavy oil emulsification technology. Summary of the Invention

[0003] The purpose of this invention is to disclose a method for desalting biofuel using methanol, in order to overcome the defects in biofuel applications where biofuel is affected by alkaline catalysts with high salt content, causing preheating pipe blockage, nozzle wear, and corrosion of combustion system equipment.

[0004] This invention provides a method for desalting bio-heavy oil using methanol, comprising the following steps:

[0005] The bio-heavy oil in the container is thoroughly shaken to form a continuous phase, and methanol at room temperature is used as the dispersed phase. The emulsification medium is a ceramic or metal membrane. A constant flow pump is used to force methanol through the membrane pores at a constant dispersed phase flux, forming a bio-heavy oil MeOH / O emulsion in the continuous phase. Then, the bio-heavy oil can be efficiently desalted by centrifugation.

[0006] The initial salt content of the bio-heavy oil is 200-1000 mg / L, and it is shaken thoroughly to ensure the uniformity of salt content in the bio-heavy oil.

[0007] The bio-heavy oil, as a continuous phase, is heated to a preset continuous phase temperature in a constant temperature bath and flows through one side of a porous inorganic membrane tube.

[0008] The methanol content of the aforementioned bio-heavy oil MeOH / O emulsion is 5-25 wt%.

[0009] The bio-heavy oil MeOH / O emulsion was placed in a high-speed centrifuge, and a certain centrifugation rate and time were set. After a certain time, the lower oil phase was taken out, which is the desalted bio-heavy oil.

[0010] The preset temperature of the continuous phase is 25-65℃, the continuous phase flow rate is 0.15-0.25 m / s, and the dispersed phase flux is 170.56-511.7 L·m. -2 ·h -1 .

[0011] The porous inorganic membrane tube is made of ceramic or metal, with a pore size of 50-2000nm, preferably 100-600nm.

[0012] The centrifuge speed is set to 3000-7000 rpm, and the centrifugation time is 2 min-10 min.

[0013] The ceramic is selected from one or a mixture of several of the following: alumina, zirconium oxide, magnesium oxide, silicon oxide, titanium oxide, cerium oxide, yttrium oxide, barium titanate, cordierite, andalusite, forsterite, talc, silica-alumina-nitrogen ceramics, zircon, ferrates, silicon nitride, aluminum nitride, silicon carbide, hydroxyapatite, clay, ceramic slag, silica sand, ceramic stone, feldspar, and white sand.

[0014] The metal is selected from one or a mixture of several of titanium, stainless steel, palladium, nickel, aluminum, and iron.

[0015] Beneficial effects:

[0016] 1. This invention utilizes methanol, a green and inexpensive polar solvent, to dissolve fatty acid salts in bio-heavy oil while remaining immiscible with the lipophilic bio-heavy oil, providing a new approach for the removal of metal salts from heavy oil.

[0017] 2. This invention utilizes membrane emulsification technology, relying on the membrane structure to increase the driving force for mass transfer between the two phases, thereby improving the desalination rate.

[0018] 3. This invention utilizes the interaction between methanol and the hydrophobic hydrocarbon chains of fatty acid salts to easily form relatively unstable and larger emulsion droplets, which is more conducive to the desalting of bio-heavy oil.

[0019] 4. The present invention has a flux of 170.56-511.7 L·m -2 ·h -1 Under conditions of high dispersed phase flux, the membrane emulsification process has a short emulsification time, low methanol loss, low energy consumption, and is easy to industrialize. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a high-temperature membrane emulsification device for methanol desalination according to the present invention; wherein, 1, emulsification raw material and emulsion product inlet and outlet; 2, constant temperature circulating water tank; 3, peristaltic pump; 4, flow meter; 5, ceramic membrane module; 6, pressure gauge at the membrane module outlet; 7, pressure gauge at the membrane module inlet; 8, constant flow pump; 9, dispersed phase methanol storage tank; 10, emulsified product discharge tank; 11, emulsified product discharge valve.

[0021] Figure 2 This is a schematic diagram of the centrifuge device for methanol desalting according to the present invention;

[0022] Figure 3 The infrared characterization images of the bio-heavy oil, methanol, and desalted alcohol phase of the present invention, and the ultraviolet-visible absorption spectra of methanol and the diluted desalted alcohol phase are shown.

[0023] Figure 4 The effect of emulsification and centrifugation parameters on desalination rate in this invention. Detailed Implementation

[0024] The present invention will now be described with reference to the accompanying drawings.

[0025] This invention discloses a method for desalting bio-heavy oil by emulsifying it with methanol and then using a high-speed centrifuge to break up the emulsion. The metal salts in bio-heavy oil mainly exist in the form of fatty acid salts. As a highly polar organic solvent, methanol can dissolve the fatty acid salts in bio-heavy oil, but is not miscible with the weakly polar, lipophilic bio-heavy oil. A cross-flow porous ceramic membrane emulsification device is used, with methanol at room temperature as the dispersed phase. A constant flow rate is maintained through the ceramic membrane pores via a constant flow pump to form a bio-heavy oil MeOH / O emulsion. The density difference between bio-heavy oil and methanol is then utilized to achieve efficient desalting of the bio-heavy oil through centrifugal demulsification. The salt removal efficiency of the bio-heavy oil is controlled by adjusting the methanol content, centrifugation rate, centrifugation time, and continuous phase temperature. Furthermore, in addition to solvation with the hydrophilic head groups of fatty acid salts, methanol molecules also exhibit van der Waals forces with the hydrophobic hydrocarbon chains of fatty acid salts. These van der Waals forces make it difficult for fatty acid salts, as anionic surfactants, to adsorb onto the oil-water surface. The larger particle size and relative thermodynamic instability of the bio-heavy oil MeOH / O emulsion improve the desalting rate. Through the methanol desalination process under membrane emulsification, the polarity of methanol can dissolve the fatty acid salts of bio-heavy oil, and there are intermolecular interactions between methanol and the hydrophobic hydrocarbon chains of fatty acid salts. This achieves efficient desalination of bio-heavy oil while utilizing the green and inexpensive polar solvent methanol. It is expected to solve the problem of acidic wastewater generated by the current industrial use of sulfuric acid desalination, obtain high-quality bio-heavy oil, and lay the foundation for further development of bio-heavy oil combustion systems.

[0026] This invention adopts Figure 1 The device flow chart shown includes a constant flow pump 8 and a porous inorganic membrane module 5. The porous inorganic membrane module uses an α-Al2O3 ceramic membrane. One side of the porous inorganic membrane is connected to the emulsion feedstock and emulsion product inlet / outlet 1, a peristaltic pump 3, and a flow meter 4 to achieve continuous flow of bio-heavy oil. The feedstock and emulsion product inlet / outlet 1 is connected to a constant temperature circulating water tank 2 and an emulsion product outlet valve 11. The membrane module outlet pressure gauge 6 and the membrane module inlet pressure gauge 7 are located on both sides of the membrane module. Methanol at room temperature is stored as the dispersed phase in a storage tank 9. The generated bio-heavy oil MeOH / O emulsion product is placed in an emulsion product outlet tank 10.

[0027] This invention adopts Figure 2 The centrifuge apparatus diagram shown above indicates that the prepared bio-heavy oil MeOH / O emulsion 1 is placed in centrifuge 2, and after centrifugation, desalted bio-heavy oil 3 is obtained, with the upper layer being the desalted alcohol phase.

[0028] The salt content test method in this invention uses the microcoulometric method. The specific detection steps can be found in the prior art (doi.org / 10.1016 / j.seppur.2023.126241).

[0029] This invention performs Fourier transform infrared spectroscopy analysis on the upper desalted alcohol phase, pure methanol, and bio-heavy oil, and performs ultraviolet-visible absorption spectroscopy characterization on pure methanol and the diluted desalted alcohol phase, as follows: Figure 3 In the infrared spectrum, at 1560 cm⁻¹ -1 1405cm -1 Two new infrared absorption peaks appeared, which, after analysis, were identified as the antisymmetric stretching peak and the symmetric stretching vibration peak of the carboxylate, respectively. In the UV-Vis absorption spectrum, the absorption peaks of the diluted desalted alcohol phase were concentrated in the 200-300 nm range. All of these findings demonstrate the dissolution and removal of fatty acid salts in the desalted alcohol phase.

[0030] Figure 4 The effect of emulsification and centrifugation parameters on desalination rate in the example.

[0031] The method for achieving efficient desalting of bio-heavy oil by methanol desalting through membrane emulsification using the above-mentioned apparatus includes the following steps:

[0032] 1) Shake the bio-heavy oil in the container thoroughly to ensure the uniformity of salt content in the sample, and then use a microcoulometric analyzer to determine the initial salt content of the bio-heavy oil.

[0033] 2) The bio-heavy oil is added to the feed tank as the continuous phase in the high-temperature cross-flow membrane emulsification device. After being heated to the preset continuous phase temperature using a constant-temperature circulating water tank, it is circulated by a peristaltic pump. Methanol at room temperature is permeated through an α-Al2O3 ceramic tubular membrane at a constant flow rate using a constant-flow pump, forming a MeOH / O emulsion under the shear force of the bio-heavy oil. The methanol content of the emulsion is controlled by the level gauge of the dispersed phase methanol storage tank.

[0034] 3) Place the bio-heavy oil MeOH / O emulsion obtained in step 2 into a centrifuge, set the centrifugation rate and centrifugation time, determine the salt content of the lower oil phase after desalination, and calculate the desalination rate.

[0035] The initial salt content of the bio-heavy oil in step 1) is 427.09 mg / L.

[0036] In step 2), the preset continuous phase temperature is 25-65℃, the continuous phase flow rate is 0.15-0.25m / s, the methanol content is 5%-25wt%, the emulsifying medium is an α-Al2O3 ceramic tubular membrane with a pore size of 100-600nm, and the emulsification method is high-temperature cross-flow membrane emulsification.

[0037] In step 3), the centrifuge speed is set to 3000-7000 rpm, the centrifugation time is 2-10 min, the salt content after desalination is 143.54-23.92 mg / L, and the desalination rate is 66.39%-94.40%.

[0038] Example 1

[0039] A. Determination of initial salt content of bio-heavy oil: The raw bio-heavy oil was thoroughly shaken to ensure the uniformity of salt content. The initial salt content of the bio-heavy oil was determined using a microcoulometric analyzer, and the result was 427.09 mg / L.

[0040] B. Preparation of the bio-heavy oil MeOH / O emulsion: Bio-heavy oil was used as the continuous phase and heated to a preset continuous phase temperature of 25°C in a constant temperature bath, then flowed through one side of a porous inorganic membrane tube. Simultaneously, methanol at room temperature was used as the dispersed phase, and a constant flow pump was used to pump the emulsion at a constant dispersed phase flux of 341.1 L·m⁻¹. -2 ·h -1 Methanol is forced through the membrane pores to form a MeOH / O emulsion in the continuous phase, with a methanol content of 25 wt%.

[0041] C. Centrifugation demulsification and desalting of bio-heavy oil MeOH / O emulsion: The obtained bio-heavy oil MeOH / O emulsion was placed in a high-speed centrifuge, and a certain centrifugation speed of 7000 rpm and centrifugation time of 10 min were set. After a certain time, the lower oil phase was taken out, which is the desalted bio-heavy oil. The desalted salt content was tested, and the desalting rate was calculated.

[0042] Example 2

[0043] The difference between this embodiment and Embodiment 1 above is that:

[0044] In step B, a MeOH / O emulsion is formed in the continuous phase, with a methanol content of 20 wt%.

[0045] Example 3

[0046] The difference between this embodiment and Embodiment 1 above is that:

[0047] In step B, a MeOH / O emulsion is formed in the continuous phase, with a methanol content of 15 wt%.

[0048] Example 4

[0049] The difference between this embodiment and Embodiment 1 above is that:

[0050] In step B, a MeOH / O emulsion is formed in the continuous phase, with a methanol content of 10 wt%.

[0051] Example 5

[0052] The difference between this embodiment and Embodiment 1 above is that:

[0053] In step B, a MeOH / O emulsion is formed in the continuous phase, with a methanol content of 5 wt%.

[0054] Example 6

[0055] The difference between this embodiment and Embodiment 1 above is that:

[0056] In step B, the bio-heavy oil is heated to a preset continuous phase temperature of 35°C in a constant temperature bath and flows through one side of a porous inorganic membrane tube.

[0057] Example 7

[0058] The difference between this embodiment and Embodiment 1 above is that:

[0059] In step B, the bio-heavy oil is heated to a preset continuous phase temperature of 45°C in a constant temperature bath and flows through one side of a porous inorganic membrane tube.

[0060] Example 8

[0061] The difference between this embodiment and Embodiment 1 above is that:

[0062] In step B, the bio-heavy oil is heated to a preset continuous phase temperature of 55°C in a constant temperature bath and flows through one side of a porous inorganic membrane tube.

[0063] Example 9

[0064] The difference between this embodiment and Embodiment 1 above is that:

[0065] In step B, the bio-heavy oil is heated to a preset continuous phase temperature of 65°C in a constant temperature bath and flows through one side of a porous inorganic membrane tube.

[0066] Example 10

[0067] The difference between this embodiment and Embodiment 1 above is that:

[0068] In step C, the obtained bio-heavy oil MeOH / O emulsion is placed in a high-speed centrifuge, and a certain centrifugation speed of 6000 rpm and centrifugation time of 10 min are set. After a certain time, the lower oil phase is taken out, which is the desalted bio-heavy oil. The desalted salt content is tested, and the desalting rate is calculated.

[0069] Example 11

[0070] The difference between this embodiment and Embodiment 1 above is that:

[0071] In step C, the obtained bio-heavy oil MeOH / O emulsion is placed in a high-speed centrifuge, and a certain centrifugation speed of 5000 rpm and centrifugation time of 10 min are set. After a certain time, the lower oil phase is taken out, which is the desalted bio-heavy oil. The desalted salt content is tested, and the desalting rate is calculated.

[0072] Example 12

[0073] The difference between this embodiment and Embodiment 1 above is that:

[0074] In step C, the obtained bio-heavy oil MeOH / O emulsion is placed in a high-speed centrifuge, and a certain centrifugation speed of 4000 rpm and centrifugation time of 10 min are set. After a certain time, the lower oil phase is taken out, which is the desalted bio-heavy oil. The desalted salt content is tested, and the desalting rate is calculated.

[0075] Example 13

[0076] The difference between this embodiment and Embodiment 1 above is that:

[0077] In step C, the obtained bio-heavy oil MeOH / O emulsion is placed in a high-speed centrifuge, and a certain centrifugation speed of 3000 rpm and centrifugation time of 10 min are set. After a certain time, the lower oil phase is taken out, which is the desalted bio-heavy oil. The desalted salt content is tested, and the desalting rate is calculated.

[0078] Example 14

[0079] The difference between this embodiment and Embodiment 1 above is that:

[0080] In step C, the obtained bio-heavy oil MeOH / O emulsion is placed in a high-speed centrifuge, and a certain centrifugation speed of 7000 rpm and centrifugation time of 8 min are set. After a certain time, the lower oil phase is taken out, which is the desalted bio-heavy oil. The desalted salt content is tested, and the desalting rate is calculated.

[0081] Example 15

[0082] The difference between this embodiment and Embodiment 1 above is that:

[0083] In step C, the obtained bio-heavy oil MeOH / O emulsion is placed in a high-speed centrifuge, and a certain centrifugation speed of 7000 rpm and centrifugation time of 6 min are set. After a certain time, the lower oil phase is taken out, which is the desalted bio-heavy oil. The desalted content is tested, and the desalting rate is calculated.

[0084] Example 16

[0085] The difference between this embodiment and Embodiment 1 above is that:

[0086] In step C, the obtained bio-heavy oil MeOH / O emulsion is placed in a high-speed centrifuge, and a certain centrifugation speed of 7000 rpm and centrifugation time of 4 min are set. After a certain time, the lower oil phase is taken out, which is the desalted bio-heavy oil. The desalted salt content is tested, and the desalting rate is calculated.

[0087] Example 17

[0088] The difference between this embodiment and Embodiment 1 above is that:

[0089] In step C, the obtained bio-heavy oil MeOH / O emulsion is placed in a high-speed centrifuge, and a certain centrifugation speed of 7000 rpm and centrifugation time of 2 min are set. After a certain time, the lower oil phase is taken out, which is the desalted bio-heavy oil. The desalted salt content is tested, and the desalting rate is calculated.

[0090] The test results of Examples 1-17 are as follows:

[0091] Bio-heavy oil and methanol were emulsified using a high-temperature cross-flow membrane, and the resulting emulsion was then centrifuged to break the emulsion and desalt. The effects of different emulsification and centrifugation parameters on the desalination rate were investigated. The emulsification and centrifugation conditions and desalination rate results for different embodiments are shown in Table 2.

[0092] Table 2 Emulsification, centrifugation conditions and desalination rates of different embodiments

[0093]

[0094]

[0095] During biodiesel production, alkaline catalysts neutralize free fatty acids, resulting in metal salts in bio-heavy oil primarily existing as fatty acid salts. Methanol, a green and inexpensive polar solvent, can dissolve fatty acid salts in bio-heavy oil and is not miscible with the weakly polar and lipophilic bio-heavy oil. This invention utilizes a high-temperature cross-flow membrane emulsification method, using methanol at room temperature as the dispersed phase, to prepare a bio-heavy oil MeOH / O emulsion. Taking advantage of the density difference between bio-heavy oil and methanol, efficient desalination of the bio-heavy oil is achieved through centrifugal demulsification. Under the aforementioned emulsification conditions, Example 9 achieved a maximum desalination rate of 94.41%, with a methanol content of 25 wt%, a continuous phase temperature of 65°C, a centrifugation rate of 7000 rpm, and a centrifugation time of 10 min. This provides a possibility for high-throughput continuous preparation of bio-heavy oil MeOH / O emulsions for desalination.

[0096] The above describes a method for desalting bio-heavy oil using methanol via high-temperature cross-flow membrane emulsification; this is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiment. Any equivalent modifications or variations made by those skilled in the art based on the content disclosed in the present invention should be included within the scope of protection set forth in the claims.

Claims

1. A method for desalting bio-heavy oil using methanol, characterized in that, Includes the following steps: Bio-heavy oil is used as the continuous phase, methanol as the dispersed phase, and a ceramic membrane as the emulsifying medium. The bio-heavy oil flows through one side of the emulsifying medium, while methanol is forced through the membrane pores from the other side, forming a bio-heavy oil MeOH / O emulsion in the continuous phase. The emulsion is centrifuged to separate the bio-heavy oil from the alcohol phase, thereby desalting the bio-heavy oil. The bio-heavy oil is a byproduct of the biodiesel production process, and the metal salts in the bio-heavy oil mainly exist in the form of fatty acid salts. The methanol content of the bio-heavy oil MeOH / O emulsion is 5-25 wt%; The preset temperature of the continuous phase is 25-65℃, the flow rate of the continuous phase on the surface of the emulsion medium is 0.10-0.30 m / s, and the flux of the dispersed phase on the emulsion medium is 100-600 L·m. -2 ·h -1 ; The pore size of the emulsion medium is 50-2000 nm.

2. The method according to claim 1, characterized in that, The content of biological heavy oil salt is 200-1000 mg / L.

3. The method according to claim 1, characterized in that, The pore size of the emulsion medium is 100-600 nm.

4. The method according to claim 1, characterized in that, The centrifuge speed is set to 3000-7000 rpm, and the centrifugation time is 2 min-10 min.

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