A process for removing impurities from car urea

Abstract

The application discloses a kind of to the impurity removal process of biuret in vehicle urea, belong to urea purification technical field.The above-mentioned impurity removal process includes the following steps: the urea solution containing impurity biuret is handled with low-temperature precipitation: be placed in low-temperature environment, add pH regulator, after low-temperature precipitation impurity biuret, restore to room temperature, add extractant, impurity biuret is extracted and adsorbed, after solid-liquid separation, liquid-liquid separation again, obtain the urea solution of impurity biuret removal.This application is by using pH regulator, make the environment of urea solution present relatively strong alkaline environment, make impurity biuret as much as possible precipitate in low-temperature environment, but urea particle does not precipitate, simultaneously also add extractant, make the biuret that precipitates adsorbs and is wrapped in extractant, and filter through liquid-liquid separation device, can obtain low biuret content vehicle urea solution.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of urea purification, in particular to a process for removing biuret from urea for vehicle use. BACKGROUND

[0002] Urea for vehicle use acts on the SCR system, and in the SCR system, the urea for vehicle use serves as a reducing agent, and is pyrolyzed and hydrolyzed into ammonia and carbon dioxide under high temperature conditions, wherein the ammonia can convert nitrogen oxides in tail gas into harmless nitrogen and water.

[0003] The content of biuret impurities in urea for vehicle use affects the conversion efficiency of the SCR system NOx to some extent, and biuret will undergo polymerization under high temperature to form stone-like solids, which block the system pipeline and nozzle.

[0004] One of the necessary conditions for the synthesis of urea particles is high temperature and high pressure, and under high temperature conditions, urea will generate one of the by-products, biuret. At present, the existing urea particle production process obtains urea particles with a biuret content of generally more than 0.7%. The content of biuret in urea for vehicle use has a higher requirement, and in the actual use process, the temperature and exhaust pressure of the engine may cause the urea to be heated to generate a polymerization reaction, and convert into biuret, melamine and other higher polymers, causing vehicle failure. In order to avoid the occurrence of such a phenomenon as much as possible, in addition to controlling the temperature and pressure of the engine, the content of biuret in urea for vehicle use can also be reduced as much as possible. The lower the content of biuret in the product, the lower the probability of generating polymers. Biuret, as a conventional impurity in urea solution, is also an intermediate for synthesizing polymers. Reducing the content of biuret in the urea solution can effectively reduce the generation and accumulation of fouling in the vehicle SCR system, avoid blocking the SCR system, and avoid unnecessary maintenance costs.

[0005] At present, the method for reducing the content of biuret in urea solution mainly adopts recrystallization and organic solvent extraction to remove biuret in urea particles. Using the recrystallization method, the urea loss rate is high, the energy consumption is high, and the industrialization cost is also high; in the organic solvent extraction method, the effective extraction organic solvents are usually methanol and ethanol, and large-scale operation has certain risk, and the solubility of the two organic solvents is limited, the use cost is high, and it is difficult to promote and apply on a large scale. SUMMARY

[0006] The present application aims to provide a process for removing biuret from urea for vehicle use, which has low cost, simple process and high impurity removal rate.

[0007] Technical solution: The process for removing biuret from automotive urea of ​​the present invention comprises the following steps: subjecting a urea solution containing the impurity biuret to a low-temperature precipitation treatment: placing the solution in a low-temperature environment, adding a pH regulator, precipitating the impurity biuret at low temperature, and then returning the solution to room temperature; adding an extractant after the low-temperature precipitation treatment to extract and adsorb the impurity biuret, performing solid-liquid separation, and then liquid-liquid separation to obtain a urea solution for automotive use with the impurity biuret removed.

[0008] Furthermore, the mass concentration of urea in the urea solution is 40-50%.

[0009] Furthermore, the mass concentration of the impurity biuret in the urea solution is 0.87-1.05%.

[0010] Furthermore, the temperature of the low temperature environment is -11°C to -25°C.

[0011] Furthermore, it is characterized in that the pH regulator is ammonia water, sodium hydroxide or potassium hydroxide; and the added amount of the pH regulator is 0.1-3% of the urea solution.

[0012] Furthermore, the low-temperature precipitation time is 8-16 hours.

[0013] Furthermore, the extractant is dioctyl phosphate, tributyl phosphate or carbon tetrachloride; and the added amount of the extractant is 5-10% of the urea solution.

[0014] Furthermore, the low-temperature precipitation treatment step is repeated 1-3 times, and the best impurity removal effect is achieved when the repetition number is up to three times.

[0015] The invention utilizes the principle of a third phase generated between the aqueous and organic phases during the extraction process. Because the extractant produced during solvent extraction has insufficient solubility in the organic phase, exceeding saturation, it precipitates from the organic phase, and the solubility of the extractant is lower than that of the generated third phase. Experiments have shown that the solubility of biuret in urea is high in the third phase formed by a selected extractant (organic phase) and a urea aqueous solution (aqueous phase), while the solubility of urea is low. This property can be exploited to substantially reduce the biuret content in automotive urea.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0017] (1) A pH regulator is used to make the environment of the urea solution more alkaline, so that as much biuret as possible is precipitated under low temperature, but urea particles are not precipitated. An extractant is added to absorb and encapsulate the precipitated solid particles (i.e., biuret) in the extractant, and the urea solution is filtered through a liquid-liquid separation device to obtain a low-biuret content automotive urea solution.

[0018] (2) The operation is simple, and the implementation is convenient, so it can be widely used on a large scale.

[0019] (3) No other waste product is produced, and the obtained urea solution can be used as high-quality vehicle urea after dilution. DETAILED DESCRIPTION

[0020] The application will be further described below in combination with specific examples.

[0021] Example 1: The impurity removal process of biuret in vehicle urea is as follows:

[0022] A urea aqueous solution with a concentration of 40% is prepared in advance, the initial biuret concentration of the urea aqueous solution is 0.87%, and the urea aqueous solution is weakly alkaline. The solution with the concentration is placed in a low-temperature oven with a pre-adjusted temperature, the oven temperature is set to -11℃, 0.1g of potassium hydroxide is added to the pre-prepared urea solution, the alkalinity is simply measured by using pH test paper, then it is taken out after being placed in the oven for 10h of temperature reduction, and it is observed that a layer of white powder solid appears at the bottom of the liquid. After being restored to room temperature, diisooctyl phosphate is used for extraction and adsorption of solid particles, the solid and the liquid are separated, and a liquid-liquid separation device is used to separate the two liquids to obtain a high-concentration urea solution.

[0023] The obtained liquid is filtered and detected by GB 29518-2013, appendix A and appendix C, and the urea content is 39.86% and the biuret content is 0.29%.

[0024] The obtained urea aqueous solution is diluted into a vehicle urea solution with a concentration of 32.5% by using ultrapure water, and the biuret content is 0.24% detected by GB 29518-2013 appendix C.

[0025] Example 2: The impurity removal process of biuret in vehicle urea is as follows:

[0026] A urea aqueous solution with a concentration of 40% is prepared in advance, the initial biuret concentration of the urea aqueous solution is 0.87%, and the urea aqueous solution is weakly alkaline. The solution with the concentration is placed in a low-temperature oven with a pre-adjusted temperature, the oven temperature is set to -11℃, 0.1g of potassium hydroxide is added to the pre-prepared urea solution, the alkalinity is simply measured by using pH test paper, then it is taken out after being placed in the oven for 10h of temperature reduction, and it is observed that a layer of white powder solid appears at the bottom of the liquid. After being restored to room temperature, diisooctyl phosphate is used for extraction and adsorption of solid particles, the solid and the liquid are separated, and a liquid-liquid separation device is used to separate the two liquids to obtain a high-concentration urea solution.

[0027] The filtered liquid was detected by GB 29518-2013, Appendix A and Appendix C, and the content of urea was 39.86%, and the content of biuret was 0.29%.

[0028] The filtered urea solution was placed in a low-temperature oven with a previously adjusted temperature, the oven temperature was set to-15℃, and after 10h of cooling, it was taken out and restored to room temperature. A small amount of white powder was observed at the bottom of the liquid, and negative pressure filtration was used to separate the solid and liquid.

[0029] The filtered liquid was detected by GB 29518-2013, Appendix A and Appendix C, and the content of urea was 39.84%, and the content of biuret was 0.23%.

[0030] The obtained urea aqueous solution was diluted to 32.5% of the vehicle urea solution using ultrapure water, and the content of biuret was detected by GB 29518-2013 Appendix C to be 0.19%.

[0031] Example 3: The impurity removal process of biuret in the vehicle urea is as follows:

[0032] A 50% concentration urea aqueous solution was prepared in advance, the initial biuret concentration of the urea aqueous solution was 1.05%, and the urea aqueous solution was weakly alkaline. The solution with this concentration was placed in a low-temperature oven with a previously adjusted temperature, the oven temperature was set to-11℃, 0.1g ammonia was added to the previously prepared urea solution, and the alkalinity was measured by using pH paper, and then placed in the oven for 10h of cooling, and then taken out and restored to room temperature. A layer of white powder solid was observed at the bottom of the liquid, carbon tetrachloride was used for extraction and adsorption of solid particles, and the solid and liquid were separated, and then a liquid-liquid separation device was used to separate the two liquids, and a high-concentration urea solution was obtained.

[0033] The filtered liquid was detected by GB 29518-2013, Appendix A and Appendix C, and the content of urea was 49.88%, and the content of biuret was 0.45%.

[0034] The filtered urea solution was placed in a low-temperature oven with a previously adjusted temperature, the oven temperature was set to-15℃, and after 10h of cooling, it was taken out and restored to room temperature. A small amount of white powder was observed at the bottom of the liquid, and negative pressure filtration was used to separate the solid and liquid.

[0035] The filtered liquid was detected by GB 29518-2013, Appendix A and Appendix C, and the content of urea was 49.78%, and the content of biuret was 0.28%.

[0036] The obtained urea aqueous solution was diluted to 32.5% of the vehicle urea solution using ultrapure water, and the content of biuret was detected by GB 29518-2013 Appendix C to be 0.18%.

[0037] Example 4: The impurity removal process of biuret in the urea solution for vehicle is as follows:

[0038] A urea solution with a concentration of 45% was prepared in advance, and the initial biuret concentration of the urea solution was 0.93%. The urea solution was weakly alkaline. The solution with this concentration was placed in a low-temperature oven with a pre-adjusted temperature, and the oven temperature was set to -11°C. 0.2 g of ammonia water was added to the pre-prepared urea solution, and the alkalinity was measured using pH paper. Then, after being placed in the oven for 10 h and taken out, it was restored to room temperature. A layer of white powder solid was observed at the bottom of the liquid, which was restored to room temperature. Phosphoric acid diisooctyl ester was used to extract and adsorb the solid particles. The solid and liquid were separated, and a liquid-liquid separation device was used to separate the two liquids to obtain a high-concentration urea solution.

[0039] The obtained liquid was filtered and detected by GB 29518-2013, Appendix A and Appendix C, and the urea content was 44.99%, and the biuret content was 0.40%.

[0040] The obtained urea solution was diluted to 32.5% urea solution for vehicle using ultrapure water, and the biuret content was 0.29% detected by GB 29518-2013, Appendix C.

[0041] Example 5: The impurity removal process of biuret in the urea solution for vehicle is as follows:

[0042] A urea solution with a concentration of 45% was prepared in advance, and the initial biuret concentration of the urea solution was 0.93%. The urea solution was weakly alkaline. The solution with this concentration was placed in a low-temperature oven with a pre-adjusted temperature, and the oven temperature was set to -20°C. 0.3 g of ammonia water was added to the pre-prepared urea solution, and the alkalinity was measured using pH paper. Then, after being placed in the oven for 10 h and taken out, it was restored to room temperature. A layer of white powder solid was observed at the bottom of the liquid, which was restored to room temperature. Phosphoric acid diisooctyl ester was used to extract and adsorb the solid particles. The solid and liquid were separated, and a liquid-liquid separation device was used to separate the two liquids to obtain a high-concentration urea solution.

[0043] The obtained liquid was filtered and detected by GB 29518-2013, Appendix A and Appendix C, and the urea content was 44.85%, and the biuret content was 0.33%.

[0044] The obtained urea solution was diluted to 32.5% urea solution for vehicle using ultrapure water, and the biuret content was 0.24% detected by GB 29518-2013, Appendix C.

[0045] Example 6: The impurity removal process of biuret in the urea solution for vehicle is as follows:

[0046] A 50% urea solution was prepared in advance, and the initial urea solution had a biuret concentration of 1.05%. The urea solution was weakly alkaline. The solution was placed in a low-temperature oven with a pre-adjusted temperature, and the oven temperature was set to -20°C. 0.1 g of sodium hydroxide was added to the pre-prepared urea solution, and the alkalinity was measured using pH paper. After 10 hours of cooling in the oven, the solution was removed and returned to room temperature. A layer of white powder was observed at the bottom of the liquid, and the liquid was returned to room temperature. Carbon tetrachloride was used to extract and adsorb the solid particles. The solid and liquid were separated, and a liquid-liquid separation device was used to separate the two liquids, obtaining a high-concentration urea solution.

[0047] The filtered liquid was detected by GB 29518-2013, Appendix A and Appendix C, and the urea content was 48.96%, and the biuret content was 0.31%.

[0048] The obtained urea solution was diluted to 32.5% with ultrapure water, and the biuret content was 0.21% detected by GB 29518-2013 Appendix C.

[0049] Example 7: The impurity removal process of biuret in the urea solution is as follows:

[0050] A 50% urea solution was prepared in advance, and the initial urea solution had a biuret concentration of 1.05%. The urea solution was weakly alkaline. The solution was placed in a low-temperature oven with a pre-adjusted temperature, and the oven temperature was set to -20°C. 0.1 g of sodium hydroxide was added to the pre-prepared urea solution, and the alkalinity was measured using pH paper. After 10 hours of cooling in the oven, the solution was removed and returned to room temperature. A layer of white powder was observed at the bottom of the liquid, and the liquid was returned to room temperature. Carbon tetrachloride was used to extract and adsorb the solid particles. The solid and liquid were separated, and a liquid-liquid separation device was used to separate the two liquids, obtaining a high-concentration urea solution.

[0051] The filtered liquid was detected by GB 29518-2013, Appendix A and Appendix C, and the urea content was 48.96%, and the biuret content was 0.31%.

[0052] The above steps were repeated, and the filtered liquid was detected by GB 29518-2013, Appendix A and Appendix C, and the urea content was 49.78%, and the biuret content was 0.24%.

[0053] The obtained urea solution was diluted to 32.5% with ultrapure water, and the biuret content was 0.16% detected by GB 29518-2013 Appendix C.

[0054] Comparative Example 1: The impurity removal process of biuret in the urea for vehicle is as follows:

[0055] A urea solution with a concentration of 40% was prepared in advance, and the initial biuret concentration of the urea solution was 0.87%. No additional pH adjuster was added, and the urea solution was weakly alkaline. The solution with this concentration was placed in a low-temperature oven with a pre-adjusted temperature, and the oven temperature was set to -11°C. After 10 hours of cooling, it was taken out and restored to room temperature. A layer of white powder solid was observed at the bottom of the liquid. Phosphoric acid diisooctyl ester was used to extract and adsorb the solid particles. The solid and liquid were separated, and a liquid-liquid separation device was used to separate the two liquids to obtain a high-concentration urea solution.

[0056] The filtered liquid was detected by GB 29518-2013, Appendix A and Appendix C, and the urea content was 39.88% and the biuret content was 0.37%.

[0057] The obtained urea solution was diluted to 32.5% urea solution for vehicle using ultrapure water, and the biuret content was 0.30% detected by GB 29518-2013 Appendix C.

[0058] Comparative Example 2: The difference from Example 1 is that no third phase is generated during the extraction process, and the extractant used is octane.

[0059] A urea solution with a concentration of 40% was prepared in advance, and the initial biuret concentration of the urea solution was 0.87%. The urea solution was weakly alkaline. The solution with this concentration was placed in a low-temperature oven with a pre-adjusted temperature, and the oven temperature was set to -11°C. 0.1 g of potassium hydroxide was added to the pre-prepared urea solution, and the alkalinity was measured using pH paper. After 10 hours of cooling in the oven, it was taken out and observed that a layer of white powder solid appeared at the bottom of the liquid. It was restored to room temperature, and octane was used to extract and adsorb the solid particles. The solid and liquid were separated, and a liquid-liquid separation device was used to separate the two liquids to obtain a high-concentration urea solution.

[0060] The filtered liquid was detected by GB 29518-2013, Appendix A and Appendix C, and the urea content was 39.86% and the biuret content was 0.29%.

[0061] The obtained urea solution was diluted to 32.5% urea solution for vehicle using ultrapure water, and the biuret content was 0.28% detected by GB 29518-2013 Appendix C.

Claims

1. A process for the removal of biuret from car urea, characterized in that, The method comprises the following steps: low-temperature precipitation treatment of urea solution containing impurity biuret: placing in a low-temperature environment, adding a pH regulator, recovering to room temperature after low-temperature precipitation of impurity biuret, adding an extractant after the low-temperature precipitation treatment, extracting and adsorbing the impurity biuret, and then separating the solid and liquid, and then separating the liquid and liquid, to obtain the urea solution for vehicles with the impurity biuret removed; The mass concentration of urea in the urea solution is 40-50%, the mass concentration of impurity biuret in the urea solution is 0.87-1.05%, the temperature of the low-temperature environment is-11 to-25℃, the low-temperature precipitation time is 8-16h, the pH regulator is ammonia, sodium hydroxide or potassium hydroxide, the addition amount of the pH regulator is 0.1-3% of the urea solution, the extractant is diisooctyl phosphate, tributyl phosphate or carbon tetrachloride, and the addition amount of the extractant is 5-10% of the urea solution.

2. The process for removal of impurities from car urea against biuret according to claim 1, wherein, The low-temperature precipitation treatment is repeated 1-3 times.