Method for measuring content of polar compounds in waste lubricating oil

Abstract

The invention discloses a method for measuring the content of polar compounds in waste lubricating oil, which comprises the following steps: (1) mixing a waste lubricating oil sample to be measured with a solvent according to a certain proportion, placing in a round-bottom flask, connecting a condenser pipe, and heating and refluxing for a certain time; (2) transferring the heated and refluxed mixed sample into a centrifuge tube with scales, and centrifuging under a certain condition; and (3) after centrifugation, reading the volume of the lower layer precipitate in the centrifuge tube, and calculating the content of the polar compound according to the linear relation of the content of the polar compound-the volume of the lower layer precipitate. Compared with the prior art, the method disclosed by the invention has the following beneficial effects that expensive analytical instruments are not needed, the types of used reagents are few, the toxicity is small, the determination process is simple, and the consumed time is short.

Description

Technical Field

[0001] The invention relates to a waste lubricating oil analysis and detection method, in particular to a method for determining the content of polar compounds in the waste lubricating oil. Background Art

[0002] Waste lubricating oil refers to the lubricating oil replaced after being used in transportation vehicles (cars, trains, ships, etc.) or enterprise machinery and equipment. During the use process, due to the influence of external factors such as impurity contamination, oxidation or thermal decomposition, the original physical and chemical properties have changed and cannot be used anymore. my country produces a large amount of waste lubricating oil every year, which mainly comes from transportation oil and industrial oil. The main components of waste lubricating oil are alkanes, polycyclic aromatic hydrocarbons, olefins, benzene series, phenols, etc., and also contain impurities produced by oxidation or thermal decomposition during use. Waste lubricating oil contains a variety of toxic substances and has certain harm to human body and environment. Waste lubricating oil is not without utilization value. Only a few percent of it is deteriorated. It can be recycled by adopting scientific and reasonable process technology. It is a waste resource with high recycling value. Before recycling waste lubricating oil, it is necessary to focus on the content of polar compounds (colloids, asphaltene). The content of polar compounds can reflect the degree of deterioration of waste lubricating oil, and also seriously affect the cost and difficulty of its subsequent recycling. In addition to the polar compounds produced by natural deterioration, the recycled waste lubricating oil is also artificially mixed with low-quality oils such as asphalt residue, ethylene tar, and tire oil, which significantly increases the polar compound content of the waste lubricating oil and significantly reduces the quality of the recycled waste lubricating oil. Therefore, when recycling waste lubricating oil, it is very important to quickly and accurately determine its polar compound content to determine the recycling value of the waste lubricating oil.

[0003] At present, the method for determining the content of polar compounds in waste lubricating oil is mainly "Determination of Chemical Group Composition of Lubricating Oil Base Oil (Thin Layer Chromatography)" (SH / T 0753-2005). This method requires an expensive thin layer chromatograph with a hydrogen flame ionization detector, and the detection time is often more than 4 hours. It is costly, complicated, and time-consuming, and it is not convenient to quickly detect the content of polar compounds in waste lubricating oil when it is recycled. Therefore, based on the limitations of the current detection method, it is urgent to develop a new method for quickly determining the content of polar compounds in waste lubricating oil with low cost and simple process. Summary of the invention

[0004] The object of the present invention is to provide a method for determining the content of polar compounds in waste lubricating oil with low cost, simple steps and rapidity, so as to solve the technical problems mentioned in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for determining the content of polar compounds in waste lubricating oil, which comprises the following three steps: (1) Mix the waste lubricating oil sample to be tested with aliphatic hydrocarbon solvent in a certain proportion, place in a round-bottom flask, connect a condenser, and heat to reflux; (2) Transferring the mixed sample after heating and reflux into a graduated centrifuge tube and centrifuging it; (3) After centrifugation, read the volume of the lower sediment in the centrifuge tube and calculate the polar compound content through the linear relationship of "polar compound content-lower sediment volume".

[0006] Preferably, in step (1), the aliphatic hydrocarbon solvent is one of n-pentane, n-hexane and n-heptane.

[0007] Preferably, in step (1), the volume ratio of the waste lubricating oil sample to be tested to the aliphatic hydrocarbon solvent is 1:9 to 9:1 (total volume is 100 mL).

[0008] Preferably, in step (1), the reflux time is 5 to 30 min.

[0009] Preferably, in step (2), the volume of the centrifuge tube is 100 mL.

[0010] Preferably, in step (2), the centrifugal treatment conditions are: centrifugal temperature is 50-80°C, relative centrifugal force is 500-3000 g, and centrifugal time is 5-45 min.

[0011] Preferably, in step (3), the linear relationship of "polar compound content-lower layer precipitation volume" is obtained by the following method: A series of waste lubricating oil samples with known polar compound content were prepared, and the corresponding lower sedimentation volumes of the series of samples were obtained under the same conditions as the above three steps, and then the linear relationship of "polar compound content-lower sedimentation volume" was obtained through linear fitting.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The determination method of the present invention does not require expensive analytical instruments, uses fewer types of reagents with low toxicity, has a simple determination process, is short in time consumption, has a small relative error, and has a relatively stable determination result. The obtained result is basically consistent with the result of the existing thin layer chromatography method. DETAILED DESCRIPTION

[0013] The present invention will be further described below with examples, but the present invention is not limited thereto.

[0014] A method for determining the content of polar compounds in waste lubricating oil, first of all, it is necessary to establish a linear relationship between "polar compound content-lower layer sediment volume": A series of waste lubricating oil samples with known polar compound content were prepared. Each sample was mixed with n-heptane at a volume ratio of 3:7 (total volume of 100 mL), placed in a round-bottom flask, connected to a condenser, and heated to reflux for 20 min. The mixed sample after heating and reflux was transferred to a 100 mL centrifuge tube with a scale and centrifuged at 60°C and a relative centrifugal force of 600 g for 35 min. After centrifugation, the volume of the sediment in the lower layer of the centrifuge tube was read and correlated with the known polar compound content, and the linear relationship was obtained as y=1.557x+0.783, R 2 =0.99, where y is the content of polar compounds (in wt%) and x is the volume of the sediment in the lower layer of the centrifuge tube (in mL).

[0015] After establishing the linear relationship between "polar compound content-lower layer sediment volume", the waste lubricating oil samples with unknown polar compound content can be measured. Embodiment 1:

[0016] Take 30 mL of waste lubricating oil from Company A, add 70 mL of n-heptane and mix evenly, place in a round-bottom flask, connect a condenser, and heat to reflux for 20 min; transfer the mixed sample after heating and reflux to a 100 mL centrifuge tube with a scale, and centrifuge at 60°C and a relative centrifugal force of 600 g for 35 min; after centrifugation, read the volume of the lower sediment in the centrifuge tube as 0.25 mL, and calculate the polar compound content based on the linear relationship between "polar compound content-lower sediment volume" to be 1.17 wt%.

[0017] Comparative Example 1: The polar compound content of waste lubricating oil of Company A was measured by "Determination of Chemical Group Composition of Lubricating Oil Base Oil (Thin Layer Chromatography)" (SH / T 0753-2005), and the result was 1.13 wt%. If this is taken as the true value, the absolute error of the measurement result of the present invention is 0.04 wt%, and the relative error is 3.5%. Embodiment 2:

[0018] Take 30 mL of waste lubricating oil from Company B, add 70 mL of n-heptane and mix evenly, place in a round-bottom flask, connect a condenser, and heat to reflux for 20 min; transfer the mixed sample after heating and reflux to a 100 mL centrifuge tube with a scale, and centrifuge for 35 min at 60°C and a relative centrifugal force of 600 g; after centrifugation, the volume of the lower sediment in the centrifuge tube is read as 1.21 mL, and the polar compound content is calculated to be 2.67 wt% based on the linear relationship formula of "polar compound content-lower sediment volume".

[0019] Comparative Example 2: The polar compound content of waste lubricating oil of Company B was measured by "Determination of Chemical Group Composition of Lubricating Oil Base Oil (Thin Layer Chromatography)" (SH / T 0753-2005), and the result was 2.56 wt%. If this is taken as the true value, the absolute error of the measurement result of the present invention is 0.11 wt%, and the relative error is 4.3%.

[0020] Comparative Example 3: Referring to Example 2, n-heptane was replaced with toluene, and the other conditions remained the same as in Example 2; no precipitate was precipitated after centrifugation, and the precipitate volume was 0. The content of polar compounds could not be calculated.

[0021] It can be seen from the above embodiments and comparative examples that if the measurement result of "Determination of Chemical Group Composition of Lubricating Oil Base Oil (Thin Layer Chromatography)" (SH / T 0753-2005) is taken as the true value, the relative error of the measurement result of the present invention is small and the measurement result is more stable.

[0022] It should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for determining the content of polar compounds in waste lubricating oil, characterized in that: The steps include: (1) Mix the waste lubricating oil sample to be tested with an aliphatic hydrocarbon solvent, place it in a round-bottom flask, connect a condenser, and heat to reflux; (2) Transferring the mixed sample after heating and reflux into a graduated centrifuge tube and centrifuging it; (3) After centrifugation, read the volume of the lower sediment in the centrifuge tube and calculate the polar compound content through the linear relationship of "polar compound content-lower sediment volume".

2. The measuring method according to claim 1, characterized in that In step (1), the aliphatic hydrocarbon solvent is one of n-pentane, n-hexane and n-heptane.

3. The measuring method according to claim 1, characterized in that In step (1), the volume ratio of the waste lubricating oil sample to be tested to the aliphatic hydrocarbon solvent is 1:9 to 9:

1.

4. The measuring method according to claim 1, characterized in that In step (1), the reflux time is 5 to 30 minutes.

5. The measuring method according to claim 1, characterized in that In step (2), the volume of the centrifuge tube is 100 mL.

6. The measuring method according to claim 1, characterized in that In step (2), the centrifugal treatment conditions are: centrifugal temperature is 50-80°C, relative centrifugal force is 500-3000 g, and centrifugal time is 5-45 min.

7. The measuring method according to claim 1, characterized in that In step (3), the linear relationship of "polar compound content-lower layer precipitation volume" is obtained by the following method: A series of waste lubricating oil samples with known polar compound content were prepared, and the corresponding lower sedimentation volumes of the series of samples were obtained under the same conditions as the above three steps, and then the linear relationship of "polar compound content-lower sedimentation volume" was obtained through linear fitting.