A process for the clarification and decolorization of thioamides

Abstract

The present application relates to the technical field of decoloring of thioamide, and discloses a thioamide clarification and decoloring process, which comprises the following steps: (1) collecting clarified thioamide by filtering thioamide raw materials through a hydrophobic ultrafiltration membrane; (2) adding calcium oxide into the clarified thioamide obtained in step (1) and stirring for 5-15 minutes; and (3) filtering the mixture after the reaction in step (2) with a microfiltration membrane, and the filtrate is a transparent and colorless thioamide product. The present application can realize the clarification and decoloring of thioamide at a low cost and obtain a transparent and colorless product.

Description

Technical Field

[0001] This invention relates to the field of decolorization technology of thiocyanates, and more specifically to a clarification and decolorization process for thiocyanates. Background Technology

[0002] my country is a major country in non-ferrous metal resources, ranking among the top in the world in terms of non-ferrous metal production and reserves. However, low-grade, polymetallic, and complex ores account for the vast majority of my country's sulfide mineral resources. As high-quality resources are continuously exploited, the limited mineral resources are becoming increasingly scarce, resulting in low comprehensive utilization of my country's sulfide mineral resources and resource shortage.

[0003] The utilization of sulfide mineral resources mainly refers to the maximum recovery of beneficial elements and their carrier minerals from sulfide ores. Since the advent of froth flotation in the early 20th century, flotation has been the primary method for the comprehensive utilization of sulfide ores. Flotation reagents include collectors, frothers, dispersants, depressants, flocculants, activators, and modifiers. Among these, collectors are flotation reagents that alter the hydrophobicity of the mineral surface, causing floating mineral particles to be adsorbed onto the froth; they are currently the most important and crucial type of flotation reagent.

[0004] As the world's largest producer of mineral processing reagents, my country still relies heavily on polluting collectors such as xanthates and black reagents, which fail to meet the demands for efficient resource utilization and severely hinder the improvement of the comprehensive utilization level of sulfide mineral resources. Therefore, we urgently need to increase research efforts on new, high-efficiency sulfide mineral collectors to improve the current state of flotation reagent use in my country. Compared with traditional xanthates and black reagents, thiocyanates are highly efficient and non-toxic, exhibit good mineral selectivity, and can achieve mineral flotation separation in low pH media. They also possess certain foaming properties, making them suitable for acidic or alkaline pulps. Thiocyanates have become one of the most widely used copper-sulfur separation collectors and represent one of the development directions for mineral processing reagents in my country.

[0005] The main production methods for thiocyanates include one-step catalytic synthesis, dimethyl sulfate method, monochloroacetic acid esterification method, haloalkane esterification method, and isothiocyanate alcoholysis method. Currently, the mainstream process in China is the monochloroacetic acid esterification method. Its advantages include high product purity and recovery rate. However, in actual production, it has been found that the product is turbid with low light transmittance. Obtaining a clear and transparent liquid requires long-term standing (generally more than 3 days), and any disturbance to the clarified liquid (such as transferring to another container, packing, or temperature drop) will cause the product to become turbid again. This is a common problem with this process. Currently, companies often use lengthy sedimentation, filtration, and distillation processes, which are costly and cumbersome.

[0006] Besides the turbidity issue, the product also suffers from discoloration. After entering the storage tank, the product's color changes from light yellow to red over time, gradually deepening. Therefore, decolorization is also a problem that needs to be addressed to improve product quality. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a clarification and decolorization process for thiouric acid esters, which can achieve the clarification and decolorization of thiouric acid esters at a lower cost and obtain a transparent and colorless product.

[0008] To achieve the above objectives, the technical solution of the present invention is: a thiouric acid ester clarification and decolorization process, comprising the following steps:

[0009] (1) Collect the clarified thiocyanate by filtering the thiocyanate raw material through a hydrophobic ultrafiltration membrane;

[0010] (2) Add calcium oxide to the clear thiouric acid ester obtained in step (1) and stir for 5 to 15 minutes.

[0011] (3) Filter the mixture after the reaction in step (2) using a microfiltration membrane. The filtrate is a clear and colorless thiouric acid ester product.

[0012] Furthermore, the hydrophobic ultrafiltration membrane mentioned in step (1) is made of one of polypropylene, polyvinylidene fluoride (PVDF), or polytetrafluoroethylene (PTFE), with a pore size of 0.001 to 0.2 μm.

[0013] Further; in step (2), the mass-to-volume ratio of calcium oxide to thiouric acid ester is (1-10) g: 100 mL, and the stirring speed is 100-1000 r / min.

[0014] Furthermore, the material of the microfiltration membrane mentioned in step (3) is selected from one of polypropylene, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE), with a pore size of 0.02 to 1 μm.

[0015] Research has revealed that the turbidity of the thiocyanate product is caused by free water, which exists in the form of water droplets. Therefore, the clarification issue is essentially a matter of separating the thiocyanate from the water. In this system, since the thiocyanate is the continuous phase and the water is the dispersed phase, a hydrophobic ultrafiltration membrane can be used as the filter medium to filter out the water and collect the thiocyanate.

[0016] Further research revealed that simply removing free water is insufficient to guarantee product clarity. This is because as the ambient temperature decreases, some of the water dissolved in the thiouric acid ester precipitates out, causing the clarified product to become cloudy again. Therefore, it is also necessary to remove the water dissolved in the thiouric acid ester. Dissolved water can be removed using various desiccants, such as silica gel and molecular sieves. Experiments show that the product, after drying and dehydration, can remain clear even when the temperature decreases.

[0017] Secondly, research revealed that the substance causing the discoloration of thiocyanate products is the mercaptoacetate salt dissolved in the thiocyanate, primarily sodium mercaptoacetate. Currently, acid washing is mainly used to address the color change, inhibiting the dissociation of mercaptoacetic acid and thus lightening the color, but not completely removing it. The inventors discovered that calcium salts can be used under alkaline conditions to precipitate the mercaptoacetate ions, completely removing the color.

[0018] Specifically, adding calcium oxide to the thiocyanate product after removing free water can achieve both dehydration and decolorization. This is because calcium oxide reacts with water to form calcium hydroxide, which has a dehydrating effect, and the calcium hydroxide reacts with thioglycolate to form a precipitate, which has a decolorizing effect. The reaction equation is shown in equation (1).

[0019] Ca 2+ +2SCH2COO - =Ca(SCH2COO)2

[0020] Equation (1)

[0021] The beneficial effects of this invention are:

[0022] (1) The process of the present invention can significantly improve the properties of thiocyanate products, changing the product from its initial turbid and colored state to a clear and colorless state.

[0023] (2) Low cost. First, the equipment investment is low. The hydrophobic ultrafiltration membrane uses mature products on the market and is inexpensive. Calcium oxide is also a common and inexpensive chemical raw material. Second, the operating cost is low. Since the thiouric acid ester product contains less water and discoloration impurities, the entire process will only produce a small amount of calcium salt, resulting in low operating cost. Attached Figure Description

[0024] Figure 1 These are graphs showing the dehydration effects of different dehydrating agents;

[0025] Figure 2 This is a comparison of high-performance gas chromatography (HPLC) images of clarified thiouric acid ester before and after decolorization;

[0026] Figure 3 yes Figure 2 A magnified schematic diagram of the impurity peaks. Detailed Implementation

[0027] Example 1:

[0028] A process for clarifying and decolorizing thiouric acid esters includes the following steps:

[0029] (1) The sulfur amino ester raw material (orange in color, with a water content of 2.1%) is pumped into the storage tank of the sulfur amino ester production equipment. The sulfur amino ester production equipment is the sulfur amino ester production equipment in patent CN202220509064.4. The hollow fiber membrane module II is a hydrophobic ultrafiltration membrane module. The hydrophobic ultrafiltration membrane module is composed of four layers of hydrophobic ultrafiltration membrane. The hydrophobic ultrafiltration membrane is made of polypropylene and has a pore size of 0.001μm. The clarified sulfur amino ester is collected from the outlet of the hollow fiber membrane module II.

[0030] (2) Add 1g of calcium oxide to 100mL of clear thiouric acid ester obtained in step (1), stir at 100r / min for 10 minutes, and no obvious heat generation was observed in the system;

[0031] (3) The mixture after the reaction in step (2) is filtered with a microfiltration membrane. The microfiltration membrane is made of polypropylene with a pore size of 0.1 μm. The filtrate is a clear and colorless thiouric acid ester product.

[0032] Comparative Example 1:

[0033] A clarification and decolorization process for thiocyanate, which, compared to Example 1, does not involve hydrophobic ultrafiltration of the thiocyanate raw material, includes the following specific steps:

[0034] (1) Add 1g of calcium oxide to 100mL of thiouric acid ester raw material, stir at 100r / min for 1 minute, the whole reaction system heats up significantly and the color darkens rapidly.

[0035] (2) The mixture after the reaction in step (1) is filtered with a microfiltration membrane. The microfiltration membrane is made of polypropylene with a pore size of 0.1 μm. The filtrate is clear and orange-red in color.

[0036] Comparative Example 2:

[0037] A clarification and decolorization process for thiouric acid esters, which, compared with Example 1, does not involve microfiltration, includes the following steps:

[0038] (1) The sulfur amino ester raw material is pumped into the storage tank of the sulfur amino ester production equipment. The sulfur amino ester production equipment is the sulfur amino ester production equipment in patent CN202220509064.4. The hollow fiber membrane module II is a hydrophobic ultrafiltration membrane module. The hydrophobic ultrafiltration membrane module is composed of four layers of hydrophobic ultrafiltration membrane. The hydrophobic ultrafiltration membrane is made of polypropylene and has a pore size of 0.001μm. The clarified sulfur amino ester is collected from the outlet of the hollow fiber membrane module II.

[0039] (2) Add 1g of calcium oxide to 100mL of clear thiouric acid ester obtained in step (1) and stir at 100r / min for 10 minutes. After standing at room temperature for 12 hours, the thiouric acid ester turns orange-red.

[0040] Comparative Example 3:

[0041] A clarification and decolorization process for thiocyanate, which differs from Example 1 in that 10g of calcium oxide is added to 100mL of clarified thiocyanate obtained in step (1). The final clear and colorless thiocyanate product is not significantly different from that in Example 1.

[0042] Comparative Example 4:

[0043] A clarification and decolorization process for thiocyanate, compared with Example 1, differs in that calcium oxide is replaced with calcium chloride, calcium carbonate, calcium bicarbonate, calcium citrate, and calcium lactate, respectively. The final thiocyanate products all have the same color as the thiocyanate raw material. This indicates that calcium chloride, calcium carbonate, calcium bicarbonate, calcium citrate, and calcium lactate have no decolorization effect.

[0044] Dehydration and decolorization verification

[0045] 1. Take the clear thiocyanate collected in step (1) of Example 1, and add molecular sieve (type 3A molecular sieve, analytical grade, white granules, diameter 3-5 mm, moisture absorption ≥50%), silica gel (blue color-changing silica gel, blue granules, diameter 2-4 mm, moisture absorption ≥35%), calcium oxide and other dehydrating agents to it. Conduct a dehydration experiment at room temperature, where the mass-to-volume ratio of dehydrating agent to thiocyanate is 1 g: 100 mL. The experimental results are as follows: Figure 1 As shown, the initial water content of thiocyanate was 1.79%. After 25 minutes of dehydration using molecular sieve, silica gel, and calcium oxide, the water contents of thiocyanate were 1.15%, 1.46%, and 1.45%, respectively. Compared to molecular sieve and silica gel, the water content of thiocyanate with added calcium oxide decreased more slowly, but the final dehydration effect of calcium oxide was similar to that of silica gel. Furthermore, after 25 minutes of dehydration, the color of thiocyanate with added calcium oxide changed from orange to colorless, while the color of thiocyanate with added molecular sieve and silica gel remained orange. This indicates that calcium oxide has both dehydrating and decolorizing effects.

[0046] Second: The clear thiocyanate collected in step (1) of Example 1 and the clear, colorless thiocyanate obtained in step (3) were compared using high-performance gas chromatography. Figure 2 As shown, the impurity peaks in the product after adding calcium oxide disappeared. This further verifies the decolorizing effect of calcium oxide.

[0047] The chromatographic conditions are as follows:

[0048] Column length / column inner diameter / liquid film thickness 50m / 0.25mm / 0.2μm Column temperature 140℃ vaporization chamber temperature 200℃ Detector temperature 200℃ <![CDATA[Average velocity of carrier gas (N₂)]]> 50cm / s airflow 300mL / min Hydrogen flow rate 30mL / min Flow split ratio 50:1 Injection volume 1.0μL

[0049] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims.

Claims

1. A clarification and decolorization process for thiouric acid esters, characterized in that, Includes the following steps: (1) Collect the clarified thiocyanate by filtering the thiocyanate raw material through a hydrophobic ultrafiltration membrane; (2) Add calcium oxide to the clear thiouric acid ester obtained in step (1) and stir for 5 to 15 minutes. (3) Filter the mixture after the reaction in step (2) using a microfiltration membrane. The filtrate is a clear and colorless thiouric acid ester product.

2. The clarification and decolorization process for thiouric acid esters according to claim 1, characterized in that: The hydrophobic ultrafiltration membrane mentioned in step (1) is made of one of polypropylene, polyvinylidene fluoride, and polytetrafluoroethylene, with a pore size of 0.001 to 0.2 μm.

3. The clarification and decolorization process for thiouric acid esters according to claim 1, characterized in that: In step (2), the mass-to-volume ratio of calcium oxide to thiouric acid ester is (1-10) g: 100 mL, and the stirring speed is 100-1000 r / min.

4. The thiouric acid ester clarification and decolorization process according to claim 1, characterized in that: The material of the microfiltration membrane mentioned in step (3) is selected from polypropylene, polyvinylidene fluoride, and polytetrafluoroethylene, and the pore size is 0.02 to 1 μm.

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