A method for removing leather aldehyde vocs

Abstract

The present application belongs to the technical field of volatile organic compounds removal, and discloses a method for removing leather aldehyde VOCs. The method removes aldehyde VOCs in leather by elution, and by using anhydrous ethanol containing urea as an eluent, the urea and aldehyde and ketone in the leather respectively undergo Schiff base reaction, thereby removing volatile organic compounds in the leather. The method removes aldehyde VOCs by Schiff base reaction, avoids the defect of leather discoloration caused by advanced oxidation technology, is more targeted, has good reaction effect, uses urea, has low finished product, and is rich in amino groups and colorless and odorless.

Description

Technical Field

[0001] This invention relates to the field of volatile organic compound removal technology, and specifically to a method for removing aldehydes (VOCs) from leather. Background Technology

[0002] Volatile organic compounds (VOCs) are mainly classified into alkanes, aromatic hydrocarbons, esters, and aldehydes based on their chemical structure. Under ultraviolet light, they can undergo photochemical reactions with nitrogen oxides (NOx) and hydroxyl radicals (-OH), producing secondary pollutants that affect the atmospheric environment. Exposure to VOCs may lead to illnesses such as headaches, dry coughs, difficulty concentrating, and fatigue. Chemicals used in leather tanning, especially retanning agents, fatliquoring agents, finishing agents, and some functional auxiliaries, contain significant amounts of VOCs, which are released during the storage, transportation, use, and tanning processes of these materials.

[0003] In recent years, VOCs removal has typically been achieved through advanced oxidation methods, such as plasma or photocatalysis. However, oxidation reactions often damage coloring groups in leather, such as azo groups, leading to discoloration.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] To address the problems in the background art, the present invention provides a method for removing aldehyde VOCs from leather.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for removing aldehyde VOCs from leather involves using anhydrous ethanol containing urea as an eluent to wash the leather.

[0008] Preferably, the concentration of the urea is ≥12 mg / mL.

[0009] More preferably, the concentration of the urea is 12-16 mg / mL.

[0010] Preferably, the mass ratio of the leather to the volume ratio of the washing solution is ≤1:50g / mL.

[0011] More preferably, the mass ratio of the leather to the volume ratio of the washing solution is 1:(50-100)g / mL.

[0012] Preferably, during elution, an excess of anhydrous calcium chloride is added and eluted under ultrasonic conditions.

[0013] Preferably, the elution time is ≥90 min.

[0014] More preferably, the elution time is 90-120 min.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] This invention employs an elution method to remove aldehydes and VOCs from leather. Using anhydrous ethanol containing urea as the eluent, urea reacts with aldehydes and ketones in the leather via Schiff base reactions, thereby removing volatile organic compounds. This invention removes VOCs through a Schiff base reaction, avoiding the discoloration defects of advanced oxidation techniques. It is also more targeted, has better reaction results, uses urea, has lower yield, and is rich in amino groups, colorless, and odorless.

[0017] The eluent and eluent method provided by this invention do not damage the properties of the leather itself. Ethanol is used as a solvent, which has good recyclability, and the new eluent prepared with the recovered liquid does not lose its effectiveness, thus having sustainable significance. Attached Figure Description

[0018] Figure 1 (a) shows the hexanal content and removal rate in leather samples after elution with different system agents in Experiment 2; (b) shows the hexanal content and removal rate in leather samples after treatment with ethanol eluent of different urea concentrations in Experiment 2; (c) shows the hexanal content and removal rate in leather samples after treatment with different elution times in Experiment 2; (d) shows the hexanal content and removal rate in leather samples after treatment with different ethanol eluent-liquid ratios in Experiment 2.

[0019] Figure 2 (a) shows the function of Δf at 3, 5, and 7 MHz as a function of time during the adsorption of urea and hexanal in Experimental Example 3; (b) shows the function of ΔD at 3, 5, and 7 MHz as a function of time during the adsorption of urea and hexanal in Experimental Example 3; (c) shows the Df plot of the 3 MHz process (1-2) of the adsorption of urea and hexanal in Experimental Example 3 (K1-K3 represent the slopes of the three different stages); (d) shows the relationship between urea, hexanal, and the mixture of urea and hexanal and the supernatant in Experimental Example 3. 1 H NMR spectrum;

[0020] Figure 3 The FT-IR spectra of urea (1), hexanal (2), a mixture of urea and hexanal (3) and supernatant (4) in Experimental Example 3;

[0021] Figure 4 (a) shows the hexanal content in the leather samples before and after different treatments in Experiment Example 4; (b) shows the SEM images of the cross-section and surface of the leather samples before and after different treatments in Experiment Example 4. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0023] This invention provides a method for removing aldehyde VOCs from leather, using anhydrous ethanol containing urea as the eluent to wash the leather.

[0024] This invention uses elution to remove aldehydes and VOCs from leather. The key is that the eluent is anhydrous ethanol containing urea. The principle is that urea has two amino groups, which can react with aldehydes in leather to form a Schiff base reaction, thereby removing volatile organic compounds from the leather.

[0025] The Schiff base reaction refers to the nucleophilic addition of aldehydes, ketones, and amines to remove a water molecule and form a C=N bond. This reaction is a dehydration reaction, and the reaction can be promoted by removing the water produced in the reaction and providing an anhydrous reaction environment.

[0026] The concentration of urea is determined based on the content of residual volatile organic compounds (VOCs) in the leather and is not subject to special restrictions; it can be selected based on the removal effect. Generally, the higher the urea concentration, the better the removal effect on VOCs. However, once the urea concentration reaches a certain threshold, it no longer affects the removal effect. Those skilled in the art can select the concentration based on the removal effect and cost considerations. For example, if the hexanal concentration in the leather is below the odor threshold of 5.87 μg / g, the removal effect is considered achieved, and the urea concentration can be adjusted appropriately based on this effect. The urea concentration should be greater than or equal to 12 mg / mL, preferably 12-16 mg / mL.

[0027] In order to improve the washing effect during the washing process, the amount of washing solution can be increased. Generally speaking, the ratio of the mass of leather to the volume of washing solution is less than or equal to 1:50 g / mL, preferably 1:(50-100) g / mL.

[0028] To improve elution efficiency, elution can be performed in an ultrasonic environment. The cavitation effect of ultrasound can enhance mass transfer, which is more pronounced in porous leather. In heterogeneous systems, asymmetric and symmetric collapse can occur depending on the distance between the solid and the cavitation bubbles generated by ultrasound. Symmetrical collapse typically produces microscale turbulence and shock waves, while asymmetric collapse occurs when particles are very close to the collapsing bubbles, forming a powerful liquid jet. The resulting microjet or shock wave acts directly on the solid surface, further opening up the surface pores and thus improving the removal efficiency of aldehyde VOCs.

[0029] Adding anhydrous calcium chloride during elution can promote the reaction and shift the equilibrium to the right.

[0030] There is no specific limitation on the washing time; it is a commonly used technical parameter in the field. The appropriate washing time can be determined based on the amount of leather and washing solution used. Generally, the washing time is ≥90 minutes, preferably 90-120 minutes.

[0031] To make the technical solution of the present invention clearer, the following detailed description of the method and effect of removing aldehyde VOCs from leather is provided through several specific embodiments.

[0032] It should be noted that aldehydes and ketones are the main contributors to volatile organic compounds in leather. Hexanal, which has a high content, has a strong pungent odor and affects the eyes, mucous membranes and upper respiratory tract. Therefore, in the following embodiments of the present invention, hexanal is used as an example to simulate the removal of aldehyde VOCs from leather.

[0033] Example 1

[0034] Prepare an ethanol eluent by adding 6g of urea to anhydrous ethanol and bring the volume to 500mL.

[0035] At room temperature, 1g of leather sample was placed in a 150mL conical flask for elution. 50mL of ethanol eluent was added, and excess anhydrous calcium chloride was added. Elution was carried out under ultrasonic conditions for 120min.

[0036] Example 2

[0037] Prepare an ethanol eluent by adding 8g of urea to anhydrous ethanol and bring the volume to 500mL.

[0038] At room temperature, 1g of leather sample was placed in a 150mL conical flask for elution. 50mL of ethanol eluent was added, and excess anhydrous calcium chloride was added. Elution was carried out under ultrasonic conditions for 120min.

[0039] Example 3

[0040] Prepare an ethanol eluent by adding 7g of urea to anhydrous ethanol and bring the volume to 500mL.

[0041] At room temperature, 1g of leather sample was placed in a 150mL conical flask for elution. 50mL of ethanol eluent was added, and excess anhydrous calcium chloride was added. Elution was carried out under ultrasonic conditions for 120min.

[0042] Example 4

[0043] Prepare an ethanol eluent by adding 7g of urea to anhydrous ethanol and bring the volume to 500mL.

[0044] At room temperature, 1g of leather sample was placed in a 150mL conical flask for elution. 100mL of ethanol eluent was added, and excess anhydrous calcium chloride was added. Elution was carried out under ultrasonic conditions for 120min.

[0045] Example 5

[0046] Prepare an ethanol eluent by adding 7g of urea to anhydrous ethanol and bring the volume to 500mL.

[0047] At room temperature, 1g of leather sample was placed in a 150mL conical flask for elution. 75mL of ethanol eluent was added, and excess anhydrous calcium chloride was added. Elution was carried out under ultrasonic conditions for 120min.

[0048] Example 6

[0049] Prepare an ethanol eluent by adding 7g of urea to anhydrous ethanol and bring the volume to 500mL.

[0050] At room temperature, 1g of leather sample was placed in a 150mL conical flask for elution. 50mL of ethanol eluent was added, and excess anhydrous calcium chloride was added. Elution was carried out under ultrasonic conditions for 90min.

[0051] Comparative Example 1

[0052] Compared with Example 3, the only difference is that anhydrous ethanol is replaced with an equal amount of deionized water, and the rest of the methods are the same as in Example 3.

[0053] Comparative Example 2

[0054] Compared with Example 3, the only difference is that the mass of urea is changed to 1g, and the rest of the steps are the same as in Example 3.

[0055] Comparative Example 3

[0056] Compared with Example 3, the only difference is that the elution time is changed to 10 minutes, and the rest of the steps are the same as in Example 3.

[0057] Comparative Example 4

[0058] Compared with Example 3, the only difference is that the amount of ethanol eluent used during elution is changed to 10 mL, and the rest of the steps are the same as in Example 3.

[0059] Comparative Example 5

[0060] Compared with Example 3, the only difference is that the ethanol eluent is replaced with an equal amount of anhydrous ethanol (without urea) during elution, and the other steps are the same as in Example 3.

[0061] Experimental Example 1: Determination of hexanal content in leather samples after rinsing

[0062] Take 0.2g of leather samples (4×4mm) after VOCs removal from Examples 1-6 and Comparative Examples 1-4, and after air-drying for 1 day, place the leather pieces into a 500mL Tedlar gas sampling bag and flush with 300mL N2. 2， The samples were incubated in a 65℃ constant temperature oven for 2 hours. The released volatile organic compounds were adsorbed using Tenax tubes. 200 mL of the sample was drawn from the bag into the tube using a sampling pump, and then the hexanal content in the leather samples was detected using a thermal desorption gas chromatography-mass spectrometry (TD100-XR, 8890-5977B). The results are shown in Table 1.

[0063] Table 1

[0064]

[0065]

[0066] As can be seen from Table 1, the removal rate reached a maximum of 81.3%, and the remaining hexanal content was as low as 2.83 μg / g, which is lower than the odor threshold of 5.87 μg / g that the electronic nose can detect, indicating that the odor of hexanal is almost undetectable.

[0067] Experiments revealed that the optimal removal effect was achieved when the urea concentration in the eluent was 14 g / L, the liquid-to-liquid ratio was 75, and the reaction time was 120 min. Furthermore, under these optimal conditions, TVOCs decreased from 87.17 μg / g to 49.32 μg / g, representing a removal rate of 43.42%.

[0068] Experiment Example 2 investigates the effects of different system agents and factors on the hexanal content in leather samples after elution.

[0069] 2.1 Multiple experimental groups were set up to investigate the hexanal content and removal rate in leather samples after elution under different system agents, as detailed below:

[0070] Untreated leather was used as the control sample group;

[0071] EtOH group: Anhydrous ethanol was used as the ethanol eluent; at room temperature, 1g of leather sample was placed in a 150mL conical flask for elution, 50mL of ethanol eluent was added, and excess anhydrous calcium chloride was added. Elution was carried out under ultrasonic conditions for 120min.

[0072] Aqueous elutriant group: 7g of urea was added to deionized water to prepare ethanol eluent, and the volume was adjusted to 500mL. At room temperature, 1g of leather sample was placed in a 150mL conical flask for elution. 50mL of ethanol eluent was added, and excess anhydrous calcium chloride was added. Elution was carried out under ultrasonic conditions for 120min.

[0073] EtOH elutraint group: 7g of urea was added to anhydrous ethanol to prepare ethanol eluent, and the volume was adjusted to 500mL; at room temperature, 1g of leather sample was placed in a 150mL Erlenmeyer flask for elution, 50mL of ethanol eluent was added, and excess anhydrous calcium chloride was added and stirred for 120min.

[0074] EtOH elutraint / US group: 7g of urea was added to anhydrous ethanol to prepare ethanol eluent, and the volume was adjusted to 500mL; at room temperature, 1g of leather sample was placed in a 150mL Erlenmeyer flask for elution, 50mL of ethanol eluent was added, and elution was carried out under ultrasonic conditions for 120min.

[0075] EtOH elutraint / US / CaCl2 group: 7g of urea was added to anhydrous ethanol to prepare ethanol eluent, and the volume was adjusted to 500mL; at room temperature, 1g of leather sample was placed in a 150mL Erlenmeyer flask for elution, 50mL of ethanol eluent was added, and excess anhydrous calcium chloride was added for elution under ultrasonic conditions for 120min.

[0076] The hexanol content and removal rate in the leather samples after treatment in the above groups are as follows: Figure 1 As shown in (a).

[0077] 2.2 Multiple experimental groups were set up to investigate the hexanal content and removal rate in leather samples treated with ethanol eluent of different urea concentrations, as detailed below:

[0078] Ethanol eluents were prepared by adding 0g, 1g, 2g, 3g, 4g, 5g, 6g, 7g, and 8g of urea to anhydrous ethanol, respectively, and the volume was adjusted to 500mL to obtain 9 sets of ethanol eluents. At room temperature, 1g of leather sample was placed in a 150mL conical flask for elution. A total of 9 sets were prepared, and 50mL of the above ethanol eluents were added to each flask. Excess anhydrous calcium chloride was added and the mixture was stirred and eluted for 120min.

[0079] The hexanol content and removal rate in the leather samples after treatment in the above groups are as follows: Figure 1 As shown in (b).

[0080] 2.3 The content and removal rate of hexanal in leather samples after different elution times were investigated, as follows:

[0081] Ethanol eluent was prepared by adding 7g of urea to anhydrous ethanol and bringing the volume to 500mL. At room temperature, 1g of leather sample was placed in a 150mL conical flask for elution. 50mL of ethanol eluent was added, and excess anhydrous calcium chloride was added for elution by rotating and stirring. The hexanal content and removal rate in the leather sample were measured at 0min, 10min, 30min, 60min, 90min, and 120min.

[0082] The measurement results of hexanol content and removal rate in leather samples after each washing time are as follows: Figure 1 As shown in (c).

[0083] 2.4 Multiple experimental groups were set up to investigate the hexanal content and removal rate in leather samples after treatment with different ethanol eluent ratios, as detailed below:

[0084] Prepare an ethanol eluent by adding 7g of urea to anhydrous ethanol and bringing the volume to 500mL. At room temperature, place 1g of leather sample into a 150mL conical flask for elution. Prepare a total of 6 groups, adding 10mL, 25mL, 50mL, 75mL, and 100mL of ethanol eluent respectively, and add excess anhydrous calcium chloride and elute by rotating and stirring for 120min.

[0085] The measurement results of hexanol content and removal rate in leather samples after treatment with different ethanol eluent ratios are as follows: Figure 1 As shown in (d).

[0086] Experiment Example 3: Exploration of the hexanal removal mechanism

[0087] The adsorption and desorption kinetics of hexanal for urea were studied using a quartz crystal microbalance (QCM-D) model with a silica sensor (QSX 303 from Biosciences, Sweden).

[0088] A 5 g / L urea-ethanol solution was passed through the sensor installed in the detection unit at a rate of 50 μL / min until adsorption equilibrium was reached, and then passed through a 1 g / L hexanol-ethanol solution at 25 °C. Frequency and dissipation values ​​at 3, 5, and 7 MHz were continuously recorded using QSense Dfind software. The analysis was performed by considering Δf and ΔD as functions of time during the urea and hexanol adsorption processes at 3, 5, and 7 MHz, and by plotting the Df values ​​for stages (1-2) of the urea and hexanol adsorption process at 3 MHz (e.g., [image of Df plot]). Figure 2 As shown in the figure, a multilayer adsorption of hexanal, urea molecules, and the sensor was observed. This is likely because, in the initial stage of adsorption, urea molecules slowly form a tight, thin binding layer on the sensor. Then, with the continuous addition of hexanal, the original urea adsorption layer reacts with hexanal, and more molecules are adsorbed onto this adsorption layer, forming a more tightly bound adsorption layer. This indicates that urea has a removal effect on hexanal.

[0089] By analyzing the supernatant after the reaction and a mixture of urea, hexanal, and urea and hexanal in a 1:1 mass ratio using FT-IR (Nicolet 6700, Thermo Fisher) and a 600MHz NMR spectra (AV II-600, Bruker), it was found that the 1640 cm⁻¹ NMR spectrum of the supernatant and the mixture... -1 The strong absorption peaks on the left and right are absorption peaks of the stretching vibration of the Schiffki functional group C=N (e.g. Figure 3 (As shown). Meanwhile, the supernatant and the mixture... 1 The characteristic peak of (1H, C-CH=N) was found at around δ 8.12 ppm in the 1H NMR spectrum. In summary, urea and hexanal can undergo a Schiff base reaction, and hexanal removed from leather VOCs does indeed undergo a Schiff base reaction with urea.

[0090] Experiment Example 4

[0091] Take untreated leather samples and leather samples treated with ethanol eluent five times in Example 3, and measure the hexanal content in the leather samples before and after different treatments. The measurement results are as follows: Figure 4 As shown in Figure (a), the hexanal content of untreated leather was 15.17 μg / g, and the hexanal contents of leather treated with 1-5 cycles were 3.47, 3.58, 3.41, 3.57, and 3.63 μg / g, respectively. Figure 4 (b) shows the SEM images of the interface between the untreated leather sample and the leather sample after five cycles of treatment, where (1) and (3) are the cross-section and surface of the untreated leather sample, respectively, and (2) and (4) are the cross-section and surface of the leather sample after five cycles of treatment, respectively. Table 2 shows the leather properties before and after treatment.

[0092] Table 2. Leather properties before and after treatment

[0093]

[0094]

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for removing aldehyde VOCs from leather, characterized in that, The leather is eluted using anhydrous ethanol containing urea as the eluent; wherein the urea reacts with aldehyde VOCs in the leather via a Schiff base reaction to achieve removal, and the aldehyde VOCs are hexanal; the concentration of the urea is 12-16 mg / mL; and the mass ratio of the leather to the volume of the eluent is 1:(50-100) g / mL.

2. The method for removing aldehyde VOCs from leather as described in claim 1, characterized in that, During the elution process, an excess of anhydrous calcium chloride is added and eluted under ultrasonic conditions.

3. The method for removing aldehyde VOCs from leather as described in claim 1, characterized in that, The elution time is ≥90 min.

4. The method for removing aldehyde VOCs from leather as described in claim 3, characterized in that, The elution time is 90-120 minutes.

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