Low-water amine liquid for synergistically removing sulfur and carbon in biogas as well as preparation method and application of low-water amine liquid

Abstract

The invention discloses a low-water amine solution for synergistically removing sulfur and carbon in biogas as well as a preparation method and application of the low-water amine solution. According to the preparation method, a binary deep eutectic solvent (Gly-Urea DES) is designed and synthesized by regulating and controlling the molar ratio of glycine to urea, and then the Gly-Urea DES, EG and H2O are mixed and compounded according to different mass ratios, so that the water-less amine liquid for capturing carbon dioxide and hydrogen sulfide with high efficiency and low energy consumption is prepared. The Gly-Urea DES has good acid gas trapping capacity, but the regeneration energy consumption of an aqueous solution of the Gly-Urea DES is relatively high, so that an ethylene glycol solution with relatively low specific heat capacity is used for replacing a part of water to prepare a water-less amine solution, the gas absorption capacity of the absorbent can be ensured, and the high energy required by regeneration can be reduced. The low-water amine liquid has the advantages of good thermal stability, low price, high carbon dioxide and hydrogen sulfide absorption capacity, low regeneration energy consumption and the like, and provides technical support for high-efficiency one-step removal of acid gas in biogas and production of biogas.

Description

Technical Field

[0001] The invention belongs to the field of biogas purification, and specifically relates to a low-water amine liquid for synergistic removal of sulfur and carbon from biogas, and a preparation method and application thereof. Background Art

[0002] With the sustained and rapid development of my country's social economy and the continuous acceleration of urbanization, the consumption level of residents is getting higher and higher, which has led to a sharp increase in the amount of domestic waste. At present, there are three main ways to deal with domestic waste: landfill, incineration, and composting. For these three treatment methods, biogas can be produced through the incineration fermentation of domestic waste, composting fermentation, and anaerobic fermentation. Biogas is purified and converted into green, low-carbon, renewable biogas, realizing resource utilization, filling the gap in natural gas resources, and achieving the goal of "shifting the high-energy consumption structure dominated by coal consumption to low-energy energy development."

[0003] Biogas is an important renewable energy source, of which 55% to 70% is methane, which can be used as a substitute for natural gas after purification. The large amount of carbon dioxide (30% to 45%) in biogas will reduce the calorific value and energy density of biogas, greatly limiting the scope of biogas utilization; in addition, the hydrogen sulfide (50 to 5000 ppm) in biogas will corrode metal pipes and internal combustion engines, and the combustion will produce SO 2 、SO 3 , which causes corrosion and pollutes the environment when dissolved in water. By removing carbon and sulfur, the combustion efficiency and energy utilization efficiency of biogas can be improved, and its sustainability as an energy source can be enhanced. GB / T41328-2022 "Biogas" environmental protection standard stipulates that CO in natural gas produced after the purification of methane raw gases such as biogas, biomass pyrolysis gas, and landfill gas 2 The mass concentration does not exceed 3%, H 2 The mass concentration of S does not exceed 15 mg / m 3 , thus removing H from biogas 2 S and CO 2 , is the only way to achieve high added value utilization of biogas.

[0004] At present, the commonly used methods for decarbonization and desulfurization of biogas in industry mainly include pressure swing adsorption (PSA), membrane separation, biological desulfurization, chemical absorption, etc. Among them, the chemical absorption method mainly uses alcohol amine solution, but the single alcohol amine solution has problems such as small absorption capacity, low reaction rate, high regeneration energy consumption, and strong corrosiveness. Therefore, the development of new absorbents has become a hot spot for gas separation and purification. In recent years, ionic liquids have made some research progress in the field of gas absorption. Ionic liquids have the characteristics of low vapor pressure, wide liquid temperature range, and stable properties. The anions and cations in the liquid can be easily selected according to specific needs. However, the preparation time of ionic liquids is long, the raw materials are generally expensive, and the viscosity is large, which restricts its large-scale industrial application. Deep eutectic solvent is a mixed solvent similar to ionic liquids, which is formed by the intermolecular interaction of hydrogen bond acceptors and hydrogen bond donors to form hydrogen bonds. It is characterized by the melting point of the mixture being lower than the melting point of its components. It not only has the characteristics of ionic liquids, but also has simple synthesis, low cost, safety and non-toxicity. Deep eutectic solvent aqueous solution has the advantages of high absorption rate, low viscosity, good thermal stability, etc., but its high water content will lead to high regeneration energy consumption. The low-water amine solution uses a physical eutectic with low specific heat capacity to replace water, which can not only ensure the gas absorption capacity of the absorbent, but also reduce the regeneration energy consumption, and is expected to achieve a significant reduction in costs in engineering applications. Summary of the invention

[0005] The purpose of the present invention is to provide a low-water amine solution for the synergistic removal of sulfur and carbon from biogas, and its preparation method and application, to solve the problems of low carbon dioxide and hydrogen sulfide gas capture capacity and high regeneration energy consumption of traditional amine solutions. The present invention provides a gas separation and purification technology based on an aqueous solution of an amino acid deep eutectic solvent, using a physical eutectic agent ethylene glycol to replace part of the water to form a low-water amine solution, which is used to achieve high efficiency and low energy consumption to capture CO in biogas. 2 and H 2 The purpose of S.

[0006] The technical solution of the present invention is as follows: As a first aspect, a method for preparing a water-poor amine solution for the coordinated removal of sulfur and carbon from biogas is provided, comprising the following steps:

[0007] The hydrogen bond acceptor Gly and the hydrogen bond donor Urea were heated at 70°C for 6 h in a molar ratio of 1:3, and stirred continuously to obtain a single-phase transparent viscous liquid, which is the deep eutectic solvent (Gly-Urea DES);

[0008] Gly-Urea DES, EG and H 2 O was heated at 70°C for 1 h while stirring continuously to obtain a low-water amine solution (Gly-Urea-EG-H 2 O), wherein Gly-Urea DES, EG, H 2The mass fractions of O are 25wt%, 33wt% and 42wt% respectively.

[0009] Furthermore, the continuous stirring is at a speed of 500 rpm.

[0010] As a second aspect, the present invention provides a low-water amine solution prepared by the preparation method.

[0011] As a third aspect, the present invention provides an application of the low-water amine solution in the synergistic removal of sulfur and carbon from biogas.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1. The low-water amine solution prepared by the present invention is simple to synthesize, safe, non-toxic, and green and environmentally friendly.

[0014] 2. The low-water amine solution prepared by the present invention has good thermal stability and regeneration ability.

[0015] 3. Since Gly-Urea-EG can form hydrogen bonds, this interaction enhances the stability and compatibility of the solution, promotes the capture and stabilization of gas molecules, and improves the overall absorption of CO in biogas. 2 and H 2 The ability of S can help to realize the decarbonization and desulfurization of biogas and its conversion into biogas in engineering, reduce greenhouse gas emissions, help cope with climate change, and have good environmental benefits.

[0016] 4. The specific heat capacity of EG used in the low-water amine solution prepared by the present invention is lower than that of water, which can reduce the sensible heat required for desorption to increase the temperature of the amine solution, so the regeneration energy consumption is low, which can greatly reduce the regeneration cost in engineering applications and has good economic benefits. In addition, reducing energy consumption also helps to reduce the environmental burden and promote sustainable development. By optimizing the solvent system, not only the system efficiency is improved, but also the operating cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 CO in the biogas simulation gas of the present invention 2 and H 2 Diagram of the continuous absorption device of S;

[0018] Figure 2 The water-poor amine solution (Gly-Urea-EG-H 2 O) Thermogravimetric image. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below through specific embodiments, but the protection scope of the present invention is not limited thereto.

[0020] The continuous absorption device ( Figure 1 ) is a 100 mL reactor equipped with a heating and stirring device. The gas inlet of the reactor is connected to different gas cylinders (40% vol CO 2 and 60% vol CH 4 , 1000ppm H 2 S and 99.9% vol N 2 ) and equipped with a flow meter. Before the absorption experiment, take an appropriate amount of absorbent and place it in the reactor. Then seal the reactor and use a vacuum pump to remove the residual air. The temperature of the reactor is maintained at the required absorption temperature by a temperature controller, and the experimental gas is injected into it. Immediately after the gas is injected, stirring the absorbent at a speed of 500 rpm. During the experiment, the gas is collected every 10 minutes, and the collected gas is subjected to gas phase analysis. The absorption capacity Q (mol-gas / mol-absorbent) is calculated from the absorption curve using the following formula:

[0021]

[0022] Where V F is the inlet flow rate (ml / min), n is the amount of absorbent substance (mol), V m is the molar volume (22.4 L / mol under standard conditions), C in is the inlet gas concentration, t A is the saturation time (min), C out(t) is the outlet gas concentration (ppm).

[0023] Example 1: Low-water amine solution (Gly-Urea-EG-H 2 O) preparation process

[0024] Glycine (Gly) and urea (Urea) were placed in a sealed container at a molar ratio of 1:3, heated at 70°C for 6 hours, and stirred at 500 rpm to prepare a single-phase transparent viscous deep eutectic solvent (Gly-Urea DES) liquid. After it stabilized, ethylene glycol (EG) and deionized water were added and heated and stirred (heated at 70°C for 1 hour, stirred at 500 rpm) to obtain a water-poor amine solution (Gly-Urea-EG-H 2 O), of which Gly-Urea DES, EG, H 2 The mass ratios of O are 25wt%, 33wt% and 42wt% respectively.

[0025] In this embodiment, the hydrogen bond acceptor Gly is cheap, non-toxic, and has good biocompatibility. It is easy to form Gly-Urea DES with the hydrogen bond donor Urea, which has good CO 2 and H 2S absorption capacity. Gly-Urea DES can absorb CO through physical and chemical reactions 2 and H 2 S. Gly A-NH 2 Can be used with CO 2 An oxygen atom and H 2 The sulfur atom of S forms hydrogen bonds and has a certain degree of van der Waals force; Gly can form hydrogen bonds with CO 2 and H 2 S reacts chemically to form the corresponding amino acid salt, and Urea can react with CO 2 Chemical reaction occurs to form carbamate, which reacts with H 2 S forms an amino compound. However, Gly-Urea DES is a complex formed by Gly as HBA and Urea as HBD through strong hydrogen bonding. Hydrogen bonding makes DES polar. The extensive hydrogen bonding network between molecules reduces the mobility of free species inside DES, making DES have high viscosity at room temperature. High viscosity may reduce the diffusion rate of gas in liquid, thereby slowing down the absorption rate of gas and affecting its absorption effect. This DES has good acid gas capture ability, but its aqueous solution regeneration energy consumption is high. Therefore, it is proposed to replace part of water with ethylene glycol solution with lower specific heat capacity to prepare less water amine solution, which can not only ensure the gas absorption capacity of the absorbent, but also reduce the high energy required for regeneration.

[0026] Example 2: Effect of low-water amine solution on CO 2 and H 2 Continuous absorption experiment of S

[0027] Take 10 ml of the low-water amine solution (Gly-Urea-EG-H 2 O) was placed in a reactor and stirred, the reactor was sealed and the residual air was evacuated using a vacuum pump, the temperature of the reactor was maintained at the required absorption temperature (30°C) by a temperature controller, and the experimental gas was injected into it, the flow rate was set to 20ml / min, the reactor outlet was opened, the gas was collected every 10min, and the collected gas was analyzed for gas phase until the absorbent was saturated. The carbon dioxide absorption capacity is 0.529mol-CO 2 / mol-absorbent, the hydrogen sulfide absorption capacity is 0.00184mol-H 2 S / mol-absorbent.

[0028] Example 3: Effect of low-water amine solution on CO 2 and H 2 Continuous absorption experiment of S

[0029] Take 10 ml of the low-water amine solution (Gly-Urea-EG-H2 O) was placed in a reactor and stirred, the reactor was sealed and the residual air was evacuated using a vacuum pump, the temperature of the reactor was maintained at the required absorption temperature (40°C) by a temperature controller, and the experimental gas was injected into it, the flow rate was set to 20ml / min, the reactor outlet was opened, the gas was collected every 10min, and the collected gas was analyzed for gas phase until the absorbent was saturated. The carbon dioxide absorption capacity is 0.518mol-CO 2 / mol-absorbent, the hydrogen sulfide absorption capacity is 0.00181mol-H 2 S / mol-absorbent.

[0030] Example 4: Effect of low-water amine solution on CO 2 and H 2 Continuous absorption experiment of S

[0031] Take 10 ml of the low-water amine solution (Gly-Urea-EG-H 2 O) was placed in a reactor and stirred, the reactor was sealed and the residual air was evacuated using a vacuum pump, the temperature of the reactor was maintained at the required absorption temperature (50°C) by a temperature controller, and the experimental gas was injected into it, the flow rate was set to 20ml / min, the reactor outlet was opened, the gas was collected every 10min, and the collected gas was analyzed for gas phase until the absorbent was saturated. The carbon dioxide absorption capacity is 0.501mol-CO 2 / mol-absorbent, the hydrogen sulfide absorption capacity is 0.00175mol-H 2 S / mol-absorbent.

[0032] Example 5: CO in a low-water amine solution 2 and H 2 S desorption performance experiment

[0033] The desorbed amine rich solution in Example 2 was used for desorption regeneration. The rich solution was heated to a regeneration temperature of 110°C and the desorption time was 30 minutes. The desorbed lean solution was further subjected to absorption experiments at an absorption temperature (30°C) and an absorption flow rate (20 ml / min). The carbon dioxide absorption capacity was 0.506 mol-CO 2 / mol-absorbent, the hydrogen sulfide absorption capacity is 0.00181mol-H 2 S / mol-absorbent, the carbon dioxide regeneration ratio reaches 95.7%, and hydrogen sulfide can achieve a regeneration ratio of 98.4%.

[0034] Figure 2 It is a water-less amine solution (Gly-Urea-EG-H 2O) shows that the water-poor amine solution (Gly-Urea-EG-H 2 O) has good thermal stability and its degradation rate is significantly lower than that of the aqueous solution of the absorbent. 2 Part of the water in O can not only ensure the acid gas absorption behavior similar to that of DES aqueous solution, but also significantly reduce the sensible heat required to increase the temperature of the amine solution during desorption, thereby reducing the regeneration energy consumption and significantly reducing its regeneration cost in engineering.

[0035] First, the regeneration energy consumption mainly includes three aspects: first, the desorption heat, which is the energy required for the reverse reaction between the acid gas and the amine; second, the vaporization heat, which is the energy required for the water vaporization that brings the acid gas from the liquid phase to the gas phase; third, the sensible heat required for desorption to increase the temperature of the amine solution. Since the specific heat capacity of EG is lower than that of water, the sensible heat required for desorption to increase the temperature of the amine solution can be significantly reduced. Secondly, from the perspective of kinetics and mass transfer phenomena on a laboratory scale, when comparing Gly-Urea-EG-H 2 O and Gly-Urea-H 2 CO in O 2 and H 2 When the absorbance of S was increased, the absorbance of EG-based solvents decreased only slightly despite their higher viscosity and thermodynamically unfavorable behavior.

[0036] Less water amine solution (Gly-Urea-EG-H 2 In the thermogravimetric curve of (O), Urea begins to degrade, with an obvious weight loss at 130 °C, and finally completely evaporates at 150-200 °C. Subsequently, Gly and EG begin to degrade and finally completely evaporate at 270 °C to 310 °C.

[0037] It should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Without making creative work, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a low-water amine solution for the coordinated removal of sulfur and carbon from biogas, characterized in that: The following steps are involved: Gly-Urea DES was obtained by heating glycine and urea at a molar ratio of 1:3 at 70 °C for 6 h while stirring continuously; Heat Gly-Urea DES, EG and H2O at 70°C for 1 h while stirring continuously to obtain a low-water amine solution, so that the mass fractions of Gly-Urea DES, EG and H2O are 25wt%, 33wt% and 42wt%, respectively.

2. The preparation method according to claim 1, characterized in that The stirring was continued at a speed of 500 rpm.

3. A low-water amine solution prepared by the preparation method according to claim 1.

4. Use of the low-water amine solution according to claim 3 in the synergistic removal of sulfur and carbon from biogas.

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