Method for purifying coal-to-ethanol by using glycerol
By using glycerol as the extractant, combined with an extractive distillation column and an ethanol-isopropanol separation column, the problems of high difficulty and high energy consumption in separating ethanol and isopropanol in coal-based ethanol production were solved, achieving efficient and low-loss purification of coal-based ethanol.
Patent Information
- Application Number
- CN202511652038.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-12
- Publication Date
- 2026-02-17
AI Technical Summary
In the current coal-to-ethanol purification process, the separation of ethanol and isopropanol is difficult and energy-intensive. Furthermore, existing methods require multiple distillation columns and a large amount of solvent, resulting in significant solvent loss.
Using glycerol as the sole extractant, a combination of an extractive distillation column and an ethanol-isopropanol separation column, along with a solvent recovery column, is used to achieve the sequential separation of water, n-propanol, and isopropanol. Only one solvent recovery column is needed to recover the solvent from two extractive distillation columns.
It achieves efficient separation of water, n-propanol, and isopropanol in coal-to-ethanol, reducing energy consumption and solvent loss, and simplifying the process.
Smart Images
Figure CN121537256A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of extractive distillation technology, specifically relating to a method for purifying coal to produce ethanol using glycerol. Background Technology
[0002] The main impurities in coal-derived ethanol are water, isopropanol, and n-propanol. Water can form an azeotrope with the other components, so it must be separated first. Extractive distillation using ethylene glycol for water removal is widely used. Of the remaining components, ethanol and isopropanol have similar boiling points, and currently, most are produced using conventional distillation, which faces the problem of a large number of trays and high energy consumption.
[0003] Although ethanol and isopropanol are not typical azeotropic systems, the presence of residual water and their close boiling points make separation difficult. Extractive distillation essentially alters the relative volatility of the two components to improve selectivity.
[0004] Selectivity (S) is an important criterion for analyzing and evaluating the separation ability of an extractant. For the separation of a two-component system, selectivity refers to the ratio of the activity coefficients of the two components, expressed by the following formula:
[0005] , These are the activity coefficients of component 1 and component 2 in the extractant, respectively. For a system where the gas phase is an ideal gas and the liquid phase is a non-ideal solution:
[0006] , These are the saturated vapor pressures of component 1 and component 2 at the equilibrium temperature, respectively, which can be calculated using the Antoni equation;
[0007] Where: P is pressure; T is temperature.
[0008] Therefore, there is a need to develop a method for purifying coal-based ethanol, which can improve the purity of coal-based ethanol while reducing energy consumption. Summary of the Invention
[0009] To address some shortcomings in existing technologies, this invention provides a method for purifying coal-derived ethanol using glycerol. This invention utilizes only glycerol as a solvent, sequentially introducing it into extractive distillation column B1 and ethanol-isopropanol separation column B2 to sequentially separate water, n-propanol, and isopropanol. Furthermore, the method requires only one solvent recovery column to recover all solvents from the two extractive distillation columns, reducing solvent loss and achieving the removal of water, isopropanol, and n-propanol impurities from coal-derived ethanol without the need for additional distillation columns, demonstrating excellent practicality.
[0010] To achieve the above-mentioned technical objectives, the present invention employs the following technical means: This invention first provides the application of glycerol in the purification of coal-to-ethanol.
[0011] The present invention also provides a method for purifying coal-to-ethanol using glycerol, wherein glycerol is the sole extractant.
[0012] Preferably, the method includes: (1) Coal-derived ethanol and glycerol are mixed in a mixer MIXER-1 and then introduced into extractive distillation column B1. The distillate from the top of the column is cooled to room temperature by a heat exchanger COOLER-1 and then sent to ethanol-isopropanol separation column B2. (2) Glycerol is introduced into the ethanol-isopropanol separation tower B2, and the distillate at the top of the tower is purified coal-derived ethanol; (3) The bottom liquid of extractive distillation column B1 and ethanol-isopropanol separation column B2 are fed into the mixer MIXER-2 for mixing, and then sent to solvent recovery column B3 for solvent purification. After purification, the liquid is cooled to room temperature by heat exchanger COOLER-2. Then, the feed stream is divided into two streams SOL-1 and SOL-2 by the splitter SPLIT and returned to extractive distillation column B1 and ethanol-isopropanol separation column B2 respectively.
[0013] Preferably, in step (1), the coal-derived ethanol contains, by mass fraction, 0.18%~5% isopropanol, 0.18%~5% n-propanol, 5%~10% water, and 80%~98% ethanol; The coal-to-ethanol is introduced into the extractive distillation column B1 from the 30th to 35th trays at a flow rate of 100-150 kg / h. The glycerol is introduced into the extractive distillation column B1 from above the 2nd to 5th trays at a flow rate of 100-150 kg / h.
[0014] Preferably, in step (1), the distillate from the top of the column flows out at a flow rate of 95~100 kg / h, at which point the contents of water and n-propanol can be reduced to below 1E-6; The distillate from the top of the column is cooled to room temperature by heat exchanger COOLER-1 and then fed into ethanol-isopropanol separation column B2 from above the 45th to 50th plates.
[0015] Preferably, in step (2), the glycerol is introduced into B2 from above the 2nd to 5th trays at a flow rate of 145~180 kg / h, and the mass flow rate ratio of the glycerol to the distillate from the top of the column in step (1) is 1.5:1. The purified coal-derived ethanol flows out at a flow rate of 95-100 kg / h, with an ethanol mass fraction exceeding 99.999%.
[0016] Preferably, in step (3), the liquid in the bottom of the tower is mixed and then fed into the solvent recovery tower B3 above the 3rd to 6th trays; After passing through solvent recovery tower B3, the bottom liquid flows out at a flow rate of 265~270 g / h, and the glycerol mass fraction in the bottom liquid exceeds 99.999%. The flow rates of SOL-1 and SOL-2 are 100~150kg / h and 145~180kg / h, respectively.
[0017] Preferably, the apparatus used in the method includes: an extractive distillation column B1, an ethanol-isopropanol separation column B2, and a solvent recovery column B3; The extractive distillation column B1 is provided with a feed inlet, a top outlet, and a bottom outlet. The feed inlet is connected to the mixer MIXER-1. The top outlet is connected to the first feed inlet of the ethanol-isopropanol separation column B2 via the first heat exchanger COOLER-1. The bottom outlet is connected to the solvent recovery column B3 via the mixer MIXER-2. The ethanol-isopropanol separation column B2 is equipped with a first inlet for the distillate flowing into the extractive distillation column B1, a second inlet for the glycerol flowing into the column, a top outlet and a bottom outlet. The bottom outlet is connected to the solvent recovery column B3 via a mixer MIXER-2. The solvent recovery tower B3 is also provided with a top outlet and a bottom outlet. The bottom outlet is connected to the first mixer MIXER-1 and the second inlet of the ethanol-isopropanol separation tower B2 via the second heat exchanger COOLER-2 and the splitter SPLIT, respectively.
[0018] Preferably, the extractive distillation column B1 has 75 to 85 theoretical plates and a molar reflux ratio of 0.8 to 1.2.
[0019] Preferably, the ethanol-isopropanol separation column B2 has 55 to 70 theoretical plates and a molar reflux ratio of 1 to 1.5.
[0020] Preferably, the solvent recovery tower B3 uses 12 to 18 theoretical plates and has a molar reflux ratio of 0.1 to 0.5.
[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention proposes for the first time a process that uses only glycerol as a solvent to sequentially separate water, n-propanol, and isopropanol by introducing it into an extractive distillation column B1 and an ethanol-isopropanol separation column B2. Simultaneously, a single solvent recovery column recovers all the solvent from both extractive distillation columns. Compared to existing technologies, this invention reduces solvent loss and eliminates the need for additional distillation columns. Attached Figure Description
[0022] Figure 1 The diagram shows the vapor-liquid equilibrium of ethanol (1) and isopropanol (2) in ethylene glycol and glycerol, respectively.
[0023] Figure 2 This is a process flow diagram of the present invention using glycerol as a solvent; the diagram includes: extractive distillation column B1, ethanol-isopropanol separation column B2, solvent recovery column B3, heat exchanger COOLER-1, heat exchanger COOLER-2, mixer MIXER-1, mixer MIXER-2, and splitter SPLIT.
[0024] Figure 3 Determine the flowchart for the parameters.
[0025] Figure 4 The diagram shows an existing conventional separation process flow, including: extractive distillation column B1, solvent recovery column B2, ethanol-isopropanol separation column B3, heat exchanger COOLER-1, heat exchanger COOLER-2, and mixer MIXER-1. Detailed Implementation
[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.
[0027] Example 1: In this embodiment, COSMOthermX software was used to compare the activity coefficients of each component after the introduction of solvent to measure the quality of the solvent, thereby screening solvents for purifying coal-to-ethanol. The results are shown in Table 1.
[0028] Table 1. Ratio of activity coefficients of ethanol and impurities in coal-derived ethanol under different solvents
[0029] The larger the absolute value of ln[γ(A) / γ(B)], the greater the selectivity of components A and B in that solvent. Table 1 shows that in the environments of glycerol and ethylene glycol, the absolute logarithms of the selectivity between ethanol and isopropanol are 0.49 and 0.38, respectively, much greater than those for dimethyl sulfoxide and N,N-dimethylformamide. The data in the table show that the separation effect of ethylene glycol is slightly worse than that of glycerol.
[0030] The extraction process for separating ethanol and isopropanol was simulated using glycerol and ethylene glycol as extractants, respectively. The simulation was performed using Aspen Plus software and the NRTL equation was selected as the method. First, the vapor-liquid equilibrium data of ethanol-isopropanol were simulated, and the results are as follows: Figure 1 As shown in the figure, the introduction of ethylene glycol or glycerol significantly increased the distance between the vapor-liquid equilibrium curve of ethanol and the diagonal line. This indicates that these two solvents can reduce the separation difficulty of the original system, with glycerol showing better separation performance.
[0031] Example 2: This embodiment provides an apparatus for purifying coal-to-ethanol, the structure of which is as follows: Figure 2 As shown. The apparatus includes: an extractive distillation column B1, an ethanol-isopropanol separation column B2, and a solvent recovery column B3; The extractive distillation column B1 is provided with a feed inlet, a top outlet, and a bottom outlet. The feed inlet is connected to the mixer MIXER-1. The top outlet is connected to the first feed inlet of the ethanol-isopropanol separation column B2 via the first heat exchanger COOLER-1. The bottom outlet is connected to the solvent recovery column B3 via the mixer MIXER-2. The ethanol-isopropanol separation column B2 is equipped with a first inlet for the distillate flowing into the extractive distillation column B1, a second inlet for the glycerol flowing into the column, a top outlet and a bottom outlet. The bottom outlet is connected to the solvent recovery column B3 via a mixer MIXER-2. The solvent recovery tower B3 is also provided with a top outlet and a bottom outlet. The bottom outlet is connected to the first mixer MIXER-1 and the second inlet of the ethanol-isopropanol separation tower B2 via the second heat exchanger COOLER-2 and the splitter SPLIT, respectively.
[0032] In the specific implementation process, the extractive distillation column B1 uses 75 to 85 theoretical plates and a molar reflux ratio of 0.8 to 1.2; the ethanol-isopropanol separation column B2 has 55 to 70 theoretical plates and a molar reflux ratio of 1 to 1.5; and the solvent recovery column B3 uses 12 to 18 theoretical plates and a molar reflux ratio of 0.1 to 0.5.
[0033] The theoretical number of trays, feed location, and reflux ratio for each column need to be analyzed using the "sensitive" module in Aspen Plus software. This is primarily determined based on the purity of the key components in the distillate or bottoms, aiming to ensure the purity of the key products, minimize the loss of key components, and keep energy consumption within a reasonable range.
[0034] First, the "theoretical plate number" needs to be determined. Then, based on this, the optimal "feed location" and "reflux ratio" need to be found, followed by the "solvent feed location." This completes one round of screening. However, as other parameters change, the optimal value of the "theoretical plate number" may change. In this case, it is necessary to re-screen for changes in other parameters, repeating this process until the optimal values of each parameter no longer change. The process is as follows: Figure 3 As shown. After verification, the detailed parameters of each tower in the apparatus of the present invention are shown in the following table:
[0035] Example 3: This embodiment discloses a method for purifying coal to produce ethanol using the apparatus described in Embodiment 2, specifically including the following steps: Ethanol (80%–98% by mass) mixed with isopropanol (0.18%–5% by mass), n-propanol (0.18%–5% by mass), and water (5%–10%) is introduced into extractive distillation column B1 from trays 30–35 at a flow rate of 100–150 kg / h. Glycerol is used as the solvent and is introduced from above trays 2–5 at the same flow rate. B1 uses 75–85 theoretical trays with a molar reflux ratio of 0.8–1.2. After passing through B1, the distillate flows out at a flow rate of 95–100 kg / h, with the water and n-propanol contents reduced to below 1E-6. This distillate is then cooled to room temperature by heat exchanger COOLER-1 and fed into ethanol-isopropanol separation column B2 from above trays 45–50.
[0036] Distillation column B2 has 55-70 theoretical plates with a molar reflux ratio of 1-1.5. Glycerol is also used as the solvent, introduced into B2 at a flow rate of 145-180 kg / h from above the 2nd to 5th plates. The mass flow rate ratio of solvent to the material to be separated is 1.5:1, i.e., a solvent ratio of 1.5:1. After passing through B2, the distillate flows out at a flow rate of 95-100 kg / h, with an ethanol mass fraction exceeding 99.999%. The bottom liquids from both B1 and B2 are fed into mixer MIXER-2, and after mixing, are sent to solvent recovery column B3 above the 3rd to 6th plates for solvent purification.
[0037] B3 uses 12-18 theoretical plates with a molar reflux ratio of 0.1-0.5. After passing through B3, the bottom liquid flows out at a flow rate of 265-270 g / h, with a glycerol mass fraction exceeding 99.999%. After being cooled to room temperature by heat exchanger COOLER-2, the feed stream is split into two streams, SOL-1 (100-150 kg / h) and SOL-2 (145-180 kg / h), using a splitter SPLIT, which are refluxed back to B1 and B2 respectively. The solvent loss is less than 1E-5 kg / h, replenished by the MAKEUP stream.
[0038] Example 4: This embodiment discloses a method for purifying coal to produce ethanol using the apparatus described in Embodiment 2, specifically including the following steps: Ethanol (80%–98% by mass) mixed with isopropanol (0.18%–5% by mass), n-propanol (0.18%–5% by mass), and water (5%–10%) is introduced into extractive distillation column B1 from trays 30–35 at a flow rate of 200–300 kg / h. Glycerol is used as the solvent and is introduced from above trays 2–5 at the same flow rate. B1 uses 75–85 theoretical trays with a molar reflux ratio of 0.8–1.2. After passing through B1, the distillate flows out at a flow rate of 190–200 kg / h, with the water and n-propanol contents reduced to below 1E-6. It is then cooled to room temperature by heat exchanger COOLER-1 and fed into ethanol-isopropanol separation column B2 from above trays 45–50.
[0039] B2 has 55-70 theoretical plates with a molar reflux ratio of 1-1.5. Glycerol is also used as the solvent, introduced into B2 at a flow rate of 285-300 kg / h from above the 2nd-5th plates. The mass flow rate ratio of solvent to the material to be separated is 1.5:1, i.e., a solvent ratio of 1.5:1. After passing through B2, the distillate flows out at a flow rate of 190-200 kg / h, with an ethanol mass fraction exceeding 99.999%. The bottom liquids from B1 and B2 are sent together to the mixer MIXER-2, and after mixing, are sent to the solvent recovery tower B3 above the 3rd-6th plates for solvent purification.
[0040] B3 uses 12-18 theoretical plates with a molar reflux ratio of 0.1-0.5. After passing through B3, the bottom liquid flows out at a flow rate of 265-270 g / h, with a glycerol mass fraction exceeding 99.999%. After being cooled to room temperature by heat exchanger COOLER-2, the feed stream is split into two streams, SOL-1 (100-150 kg / h) and SOL-2 (145-180 kg / h), using a splitter SPLIT, which are refluxed back to B1 and B2 respectively. The solvent loss is less than 1E-5 kg / h, replenished by the MAKEUP stream. Comparative Example 1:
[0041] This comparative example demonstrates a prior art method for purifying coal to produce ethanol. The specific steps are as follows, and the apparatus used is as follows: Figure 4 As shown: Ethanol (80%–98% mass fraction), a mixture of isopropanol (0.18%–5% mass fraction), n-propanol (0.18%–5% mass fraction), and water (5%–10%), is introduced from trays 35–41 at a flow rate of 100–150 kg / h. Ethylene glycol is used as the solvent, with a solvent mass flow rate to feed stream mass flow rate ratio of 1:1, and is introduced into plate B1 from trays 3–6. The main function of plate B1 is to remove water and n-propanol from the bottom bath. The molar reflux ratio is generally set at 0.8–1.2, the top pressure is 0.9–1.1 bar, and the overall pressure drop is 0.1–0.2 bar. After extractive distillation, the removal rate of water and n-propanol can exceed 99%.
[0042] The bottom liquid and distillate from B1 are introduced into the first solvent recovery tower B2 and the ethanol-isopropanol separation tower B3, respectively: the bottom liquid is sent to the solvent recovery tower B2 via the R-1-OUT stream. This recovery tower is generally equipped with 15 to 20 theoretical trays, and the feed position is set at 6 to 11 trays. The reflux ratio requirement is small, and 0.2 to 0.6 can meet the separation requirements. The ethylene glycol recovery rate exceeds 99.9%. After being cooled to room temperature by the heat exchanger COOLER-1, it is sent back to the extractive distillation tower B1. At the same time, the MAKEUP stream is used to replenish the ethylene glycol lost in the process, and the loss is less than 0.004 kg / h. The distillate from B1 is cooled to room temperature by heat exchanger COOLER-2 at a flow rate of 97.1 kg / h and then fed into the ethanol-isopropanol separation column B3 from the 33rd tray. Due to the close boiling points, under the conditions of using a conventional distillation column, in order to achieve the separation requirements, the number of trays exceeds 85, the molar reflux ratio exceeds 10, and the heat load of the reboiler exceeds 66,000 kW.
[0043] This method is conventional distillation, which has the problems of a large number of trays and huge energy consumption.
[0044] In summary, this invention provides a method for purifying coal-derived ethanol using glycerol. This invention utilizes only glycerol as a solvent, sequentially introducing it into extractive distillation column B1 and ethanol-isopropanol separation column B2 to sequentially separate water, n-propanol, and isopropanol. Furthermore, the method requires only one solvent recovery column to recover all the solvent from the two extractive distillation columns, reducing solvent loss while achieving the removal of water, isopropanol, and n-propanol impurities from coal-derived ethanol without the need for additional distillation columns, demonstrating excellent practicality.
[0045] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.
Claims
1. Application of glycerol in the purification of coal to produce ethanol.
2. A method for purifying coal to produce ethanol using glycerol, characterized in that, The method uses glycerol as the sole extractant.
3. The method according to claim 2, characterized in that, The method includes: (1) Coal-derived ethanol and glycerol are mixed in a mixer MIXER-1 and then introduced into extractive distillation column B1. The distillate from the top of the column is cooled to room temperature by a heat exchanger COOLER-1 and then sent to ethanol-isopropanol separation column B2. (2) Glycerol is introduced into the ethanol-isopropanol separation tower B2, and the distillate at the top of the tower is purified coal-derived ethanol; (3) The bottom liquid of extractive distillation column B1 and ethanol-isopropanol separation column B2 are fed into the mixer MIXER-2 for mixing, and then sent to solvent recovery column B3 for solvent purification. After purification, the liquid is cooled to room temperature by heat exchanger COOLER-2. Then, the feed stream is divided into two streams SOL-1 and SOL-2 by the splitter SPLIT and returned to extractive distillation column B1 and ethanol-isopropanol separation column B2 respectively.
4. The method according to claim 3, characterized in that, In step (1), the coal-derived ethanol contains, by mass fraction, 0.18%~5% isopropanol, 0.18%~5% n-propanol, 5%~10% water, and 80%~98% ethanol; The coal-to-ethanol is introduced into the extractive distillation column B1 from trays 30 to 35. The triglyceride is introduced into the extractive distillation column B1 from above the 2nd to 5th trays; The distillate from the top of the column is cooled to room temperature by heat exchanger COOLER-1 and then fed into ethanol-isopropanol separation column B2 from above the 45th to 50th plates.
5. The method according to claim 3, characterized in that, In step (2), the glycerol is introduced from above the 2nd to 5th trays, and the mass flow rate ratio of the glycerol to the distillate from the top of the column in step (1) is 1.5:
1. The mass fraction of ethanol in the purified coal-derived ethanol exceeds 99.999%.
6. The method according to claim 3, characterized in that, In step (3), the liquid in the bottom of the tower is mixed and then fed into the solvent recovery tower B3 above the 3rd to 6th trays; After passing through solvent recovery tower B3, the mass fraction of glycerol in the tower bottom exceeded 99.999%.
7. The method according to claim 2, characterized in that, The apparatus used in the method includes: an extractive distillation column B1, an ethanol-isopropanol separation column B2, and a solvent recovery column B3; The extractive distillation column B1 is provided with a feed inlet, a top outlet, and a bottom outlet. The feed inlet is connected to the mixer MIXER-1. The top outlet is connected to the first feed inlet of the ethanol-isopropanol separation column B2 via the first heat exchanger COOLER-1. The bottom outlet is connected to the solvent recovery column B3 via the mixer MIXER-2. The ethanol-isopropanol separation column B2 is equipped with a first inlet for the distillate flowing into the extractive distillation column B1, a second inlet for the glycerol flowing into the column, a top outlet and a bottom outlet. The bottom outlet is connected to the solvent recovery column B3 via a mixer MIXER-2. The solvent recovery tower B3 is also provided with a top outlet and a bottom outlet. The bottom outlet is connected to the first mixer MIXER-1 and the second inlet of the ethanol-isopropanol separation tower B2 via the second heat exchanger COOLER-2 and the splitter SPLIT, respectively.
8. The method according to claim 7, characterized in that, The extractive distillation column B1 uses 75-85 theoretical plates and has a molar reflux ratio of 0.8-1.
2.
9. The method according to claim 7, characterized in that, The ethanol-isopropanol separation column B2 has 55 to 70 theoretical plates and a molar reflux ratio of 1 to 1.
5.
10. The method according to claim 7, characterized in that, The solvent recovery tower B3 uses 12 to 18 theoretical plates and has a molar reflux ratio of 0.1 to 0.5.