Life Cycle Assessment of A Hydrocarbon-based Electrified Cleaning Agent

The electrified cleaning agent requires a moderate volatilization rate, low ozone-depleting substances value, non-flammable, non-explosive and other characteristics. This study performed a whole life cycle assessment on a hydrocarbon-based electrified cleaning agent. The life cycle model is cradle-to-grave, and the background data sets include power grid, transportation, high-density polyethylene, chemicals, etc. The analysis shows that the global warming potential (GWP) of the life cycle of 1 kg of electrified cleaning agent is 2.08 kg CO2 eq, acidification potential (AP) is 9.49E-03 kg SO2 eq, eutrophication potential (EP) is 1.18E-03 kg PO4 3-

The electrified cleaning agent requires a moderate volatilization rate, low ozone-depleting substances value, non-flammable, non-explosive and other characteristics. This study performed a whole life cycle assessment on a hydrocarbon-based electrified cleaning agent. The life cycle model is cradle-to-grave, and the background data sets include power grid, transportation, high-density polyethylene, chemicals, etc. The analysis shows that the global warming potential (GWP) of the life cycle of 1 kg of electrified cleaning agent is 2.08 kg CO 2 eq, acidification potential (AP) is 9.49E-03 kg SO 2 eq, eutrophication potential (EP) is 1.18E-03 kg PO 4 3eq, respirable inorganic matter (RI) is 2.13E-03 kg PM2.5 eq, ozone depletion potential (ODP) is 4.91E-05 kg CFC-11 eq, photochemical ozone formation potential (POFP) is 2.89E-02 kg NMVOC eq, ionizing radiation-human health potential (IRP) is 3.16E-02 kg U235 eq, ecotoxicity (ET) is 2.69E-01 CTUe, human toxicity-carcinogenic (HTcancer) is 4.32E-08 CTUh, and human toxicity-non-carcinogenic (HT-non cancer) is 2.31E-07 CTUh. The uncertainty of the results is between 3.46-9.95%. The four processes of tetrachloroethylene production, D40 solvent oil production, tetrachloroethylene environmental discharge during product use, and electricity usage during product disposal have substantial effects on each LCA indicator, so they are the focus of process improvement. Changes in power consumption during production and transportation distance of raw materials have little effect on total carbon emissions. Compared with the production process of single-solvent electrified cleaning agent tetrachloroethylene and n-bromopropane, the production of the electrified cleaning agent developed in this study has its own advantages in terms of carbon footprint and other environmental impact indicators. Carbon emissions mainly come from the power consumption of each process, natural gas production and combustion, and other energy materials for heating. It is recommended to use renewable raw materials instead of crude oil to obtain carbon credits based on geographical advantages, and try to use production processes with lower carbon emissions, while the exhaust gas from the traditional production process is strictly absorbed and purified before being discharged.

Introduction
Electrified cleaning refers to cleaning operations performed under normal working conditions with a certain voltage. It is usually required that the electrified cleaning agent must have a moderate volatilization rate (i.e., not to freeze the line), low ozone-depleting substances (ODS) value, non-flammable, non-explosive and other characteristics. The electrified cleaning agent is mainly used for cleaning equipment and devices in use under high-voltage electric fields, such as locomotive substations, highvoltage substations and high-voltage lines. Traditional charged cleaning agents mostly use chlorinated hydrocarbons (e.g., Freon), bromo-hydrocarbons and other halogenated hydrocarbons, which are high specific resistance reagents with high ODS value and strong volatility. They may damage the atmospheric O 3 layer, and are easy to cause the line to freeze and increase the load of the line, affecting the normal operation [1].
The eco-friendly cleaning agent for high/low voltage equipment in use developed by this study is compounded with D40 solvent oil and tetrachloroethylene with extremely low ODS value as the base liquid, supplemented by butanol and other additives, which can effectively remove soil, dirt, oil stains and animal feces on the surface of charged devices. The electrified cleaning agent has a resistance value of more than 10 G ohms, and can be used in an electric field environment of up to 100,000 volts. It is mainly used for live cleaning of high-voltage circuits, substations, electrical equipment, etc. This research conducts a full life cycle assessment of the electrified cleaning agent, including the production, use and waste recycling process of the product.

Product Information
The research object of this study is: to access an electrified cleaning agent. The specific information is as follows : Specification number : DL1006-series Product category: Eco-environmental cleaning agent for high/low voltage live equipment (such as high voltage circuit, substation and electrical equipment). The target users of eco-environmental cleaning agents are the customers with high-voltage circuits, substations, electrical equipment and other equipment, including high-speed railways, motor vehicles, aircrafts, tanks, electrical equipment and instruments of ships. Shape and form: solution

Functional Unit and Benchmark Flow
Functional unit: 1 kg product

Data Representation
The representation of time, geography and technology is as follows: (1) Time representation: 2020 (2) Geographical representation: China

System Boundary
The system boundary of this study is from cradle to grave (from resource exploitation to waste treatment and recycle). The life process includes the production, use, recovery and waste solvent distillation of charged cleaners. Background processes include power grid, transportation, high density polyethylene for packaging, chemicals and sludge landfilling.

Selection Principle
The trade-off rules used in this study are based on the weight ratio of raw material to the product weight or the total process input. Specific rules are as follows: (1) When the weight of ordinary material is less than 1% of the product weight and the weight of material containing rare or high purity components is less than 0.1 % of the product weight, the upstream production data of the material can be ignored. Total negligible material weight shall not exceeding 5 %. (2) The material can be ignored if the low value waste is used as raw materials, such as fly ash, slag, straw, garbage and other upstream production data. The production equipment, plant, living facilities and other emissions are ignored.

Environmental Impact Indicators
Environmental impact indicators are summarized in Table 1. Data quality represents the difference between the target representativeness of LCA research and the actual representativeness of data. The data quality evaluation method in this report adopts the CLCD method. Note: eq. is the abbreviation of equivalent.

Software and Database
In this study, the eFootprint software system was used to establish a life cycle model of charged detergents and calculate the LCA results. The eFootprint software system is an online LCA analysis software developed by IKE Environmental Technology Co., Ltd (http://ike-global.com/). It supports full life cycle process analysis and has builtin China Life Cycle Basic Database (CLCD), European ELCD database and Swiss Ecoinvent database.
The China Life Cycle Basic Database (CLCD) used in the research was developed by IKE, which is an industry average database based on the core model of China's basic industrial system life cycle. The CLCD database includes inventory data sets of major domestic energy, transportation and basic raw materials.
The LCA model of the electrified cleaning agent was established in eFootprint software. The background data sources of this LCA study are shown in Table 2:   (30t)-diesel Note: In the benchmark model, only the transportation of D40 solvent oil and tetrachloroethylene, which account for the largest proportion, is considered. The upstream data sources of transportation data are all from the CLCD database.

Technical supplementary description:
The production is planned to use the existing equipment of a cleaning agent company in Jiangsu Suqian Dunjia Biotechnology Co., Ltd. The strict material and energy consumption balance calculations for the production process was performed by using ASPEN Plus. Figure 2 shows the flow chart of the simulation. D40 solvent oil and tetrachloroethylene (PCE), which are main raw materials of the charged cleaner, are added to the stirred tank 1 through pumps 1 and 2 (PUMP1 and PUMP2), respectively. The material is heated to 30°C by steam and stirred at 30°C for 30 minutes. After mixing, the materials are pumped by the pump 3 to the heat exchanger to cool to room temperature, and then enter the stirred tank 2. Butanol, isopropanol and ethyl acetate are added to the tank 2 at room temperature, and stirred for 30 minutes. Finally, the products are packed by the packaging machine and shipped.  Technical supplementary description: First, the air gun is used to remove dust from the equipment. Then, the spray gun is used to spray the charged cleaning fluid to clean the equipment. Finally, the air gun is used to evaporate the cleaning fluid, while the recycling and condensing equipment is operated to recover the solvent. In the benchmark model, it is assumed that 80% of the solvent can be recycled, i.e., 20% of D40 solvent oil and tetrachloroethylene and all additives are discharged into the atmosphere.

Electrified Cleaning Agent 【Disposal】
(1) Basic process information Process name: electrified cleaning agent【disposal】 Process boundary: from use to grave (2) Data representativeness Main data sources: chemical process simulation, database. The results do not represent industry average data Origin: China Base year: 2020 Process equipment: distillation equipment, sludge landfill Main raw material: Recycled electrified cleaning agent Main energy consumption: electricity Production scale: 2000 t/y Technical supplementary description: A two-stage distillation device is used to rectify the waste solution to separate tetrachloroethylene and D40 solvent oil. Figure 3 is a diagram of the two-stage distillation device for waste solvents simulated in ASPEN Plus. D40 solvent oil is simulated using a mixture of 50% decane and 50% undecane, and the sludge is simulated using ethyl palmitate. The used or unclean solvents in this process (i.e., detergents contain excessive soluble and non-volatile residues such as fatty acids, grease and oil) are first heated to above the boiling point of tetrachloroethylene (121°C) to recycle high-purity tetrachloroethylene (99% purity). Then, the distillate from the bottom of the tower enters the second-stage distillation tower and is heated to the boiling point of D40 mineral spirits (greater than 190°C) to volatilize and recover D40 mineral spirits. Residual impurities are left at the bottom of the kettle and become sludge due to their higher boiling point than D40 oil. Tetrachloroethylene and D40 solvent oil can be reused.

Sensitivity Analysis of Inventory Data
Inventory data sensitivity refers to the corresponding indicator change rate caused by the unit change rate of inventory data. By analyzing the sensitivity of the inventory data to each indicator and cooperating with the improvement potential evaluation, the most effective improvement points can be identified. Table 11 lists the inventory data with sensitivity> 0.5%.

Possible Process Improvement
(1) Tetrachloroethylene and D40 solvent oil are the necessary active ingredients in electrified cleaner products. It is recommended to optimize the production process to reduce environmental emissions, or to develop a cleaner production process. (2) Efforts should be made to reduce the environmental emissions of tetrachloroethylene and other solvents during the use of the product, develop the efficient solvent recovery equipment, and improve operating procedures. (3) Distillation for the recovery of waste solvents is a process with high energy consumption. Renewable energy should be used to replace electricity as much as possible to obtain carbon credits.

The Impact of Electricity Consumption during Production on Carbon Footprint
In the original model, the energy consumption of heating, stirring, cooling, and material transportation during the production process is considered. The power consumption estimated is 0.05 MJ. The simulated production process did not consider other processes that may be used, such as the energy consumption of the filtration process. It is estimated that all production energy consumption should be less than 0.1 MJ. Table 15 shows the impact of increasing power consumption from 0.05 MJ to 1 MJ on total carbon emissions. It can be seen that when the energy consumption increases to 0.1 MJ, the total carbon emissions only increase by 0.96%. When the electricity consumption further increases 10 times to 1 MJ, carbon emissions will increase by about 12%. Therefore, under the premise of paying attention to energy conservation in the production process, electricity consumption has little effect on the carbon footprint.

Impact of Transportation Distance on Carbon Footprint
In the original model, only the transportation of D40 solvent oil and tetrachloroethylene, which accounted for 64% and 33% of the components, respectively, was considered. The transportation distance was assumed to be 200 km, which is close to the national average goods transportation distance of 187 km. The data in Table 16 shows that increasing the transportation distance of D40 solvent oil to 2000 km will only increase the total carbon emissions by 4.33%. Therefore, the transportation distance of raw materials has little effect on total carbon emissions. In the original model, the product transport distance is 200 km. The data in Table  17 shows that when the product transportation distance is increased to 2000 km, the total carbon emissions only increase by 6.73%. Therefore, product transportation distance has little effect on total carbon emissions.

Comparison with LCA Indicators of Other Electrified Cleaner Production Processes
The LCA results of this study is further compared with the LCA indicators of other three common electrified cleaner production processes, including trichloroethylene, tetrachloroethylene and n-bromopropane (data source is the Ecoinvent 3.1 database).  It can be seen from the results of the LCA analysis (Table 18) that although trichloroethylene has a small carbon footprint and ionizing radiation, it is not selected for use because it is a flammable liquid that can cause fire and explosion when exposed to open flames and high heat. In comparison, the carbon footprints of the commonly used single-solvent electrified cleaning agents of tetrachloroethylene and n-bromopropane are 103.8% and 178.7% higher than the carbon footprint of the electrified cleaning agent of this study. And most of the other LCA indicators of these two electrified cleaning agents are also higher. Therefore, the production of the electrified cleaning agent developed in this study has its own advantages in terms of carbon footprint and other environmental impact indicators.

The Impact of Waste Solvent Recovery Efficiency on LCA Indicators
In the benchmark model, the recovery ratio of waste solvents is assumed to be 80%, i.e., 20% of tetrachloroethylene and D40 solvent oil are discharged as air emissions. Although the emission of D40 solvent oil is environmentally friendly, the emission of tetrachloroethylene has an obvious impact on photochemical ozone formation potential (POFP), ecological toxicity (ET), human toxicity-carcinogenic (HT-cancer), and human body Toxicity-non-carcinogenic (HT-non cancer) indicators. Moreover, the recovery efficiency is directly related to the waste solvent recovery process. Therefore, it is necessary to further study the influence of waste solvent recovery efficiency on various indicators of the whole life cycle.  From the data in Table 19, the recovery ratio of electrified cleaning agent is directly related to the power consumption of the waste process and the toxicity caused by environmental emissions. The higher the recovery ratio, the higher the energy consumption of the solution recovery process, which in turn leads to an increase in the carbon footprint (GWP), AP, EP, RI and IRP indicators of the whole life cycle. On the contrary, if the solvent is allowed to discharge to the environment, it will cause a significant increase in environmental toxicity indicators such as POFP, ET, HT-cancer and HT-non cancer. Therefore, the full cycle emissions of any product and process are closely related to the technical details of the entire process. The goal of reducing carbon footprint and other environmental impact indicators can be achieved only by choosing a low-emission and reasonable process.
As far as this process is concerned, a low-energy waste solvent recovery process should be developed, the power consumption of the current distillation recovery device should be reduced as much as possible, and renewable energy can be used to replace fossil energy. At the same time, the solvent recovery device needs to be improved to increase efficiency and minimize direct environmental emissions.

Estimation of the Carbon Footprint of the Upstream Tetrachloroethylene Production Process
The study further estimated the carbon emissions of the two upstream production processes (tetrachloroethylene and D40 solvent oil) that have the largest impact on the carbon footprint. Tetrachloroethylene (molecular formula C 2 Cl 4 , CAS-No. 127-18-4, also known as PCE or perchloroethylene) is a colorless and transparent liquid with an esterlike smell. It is not flammable and has no measurable flash point or flammability limit in air. Usually acetylene or ethylene is used as a raw material, and it is co-produced with trichloroethylene through chlorination and oxidation. The life cycle data of tetrachloroethylene comes from the Ecoinvent3.1 database of Europe, and the unit is 1 kg. The boundary map is as follows: Due to the confidentiality of commercial databases, the possible sources of upstream emissions can only be inferred through possible raw materials and reaction pathways. Table 20 summarizes the carbon emission (GWP) data of 1 kg of ethylene (C 2 H 2 ), chlorine (Cl 2 ), and tetrachloroethylene. Emissions from ethylene production originate from natural gas production, process heating, and oil refining. However, according to the analysis of the molecular formula and chemical reaction formula of tetrachloroethylene, ethylene production does not contribute much to the carbon footprint of the entire process. The main carbon emission of tetrachloroethylene comes from the chlorine production process. According to the production methods of different countries and regions, it can be seen that China uses the ion-exchange membrane method of chlor-alkali electrolysis to produce chlorine, producing carbon emissions of 1.68-2.51 kg CO 2 eq. The chlor-alkali electrolysis process (membrane technology), which is widely used in Europe and the United States, has a lower carbon emission of 1.04 kg CO 2 eq. According to the LCA boundary map ( Figure  17) and analysis results given by the commercial database, it can be seen that the carbon footprint sources of the production of chlorine include electricity, natural gas combustion and the energy consumption of the NaCl production process. The analysis shows that the main carbon emissions from the tetrachloroethylene production process are the electricity consumption of each process, the combustion of natural gas production and the combustion of other energy materials for heating. It is recommended to use renewable raw materials instead of crude oil to obtain carbon credits based on geographical advantages, and try to use production processes with lower carbon emissions, while the exhaust gas from the traditional production process is strictly absorbed and purified before being discharged.

Carbon Footprint Estimation of the Upstream D40 Solvent Oil Production Process
D40 solvent oil is made of distillate oil as raw material, after high-pressure hydrorefining and fractional distillation. Its main component is saturated alkanes, including nonane, decane and undecane. The production process is basically the same as naphtha. So in this study, the naphtha process was used instead of D40 solvent oil. The carbon footprint of the naphtha production process is estimated using data from commercial databases. The process diagram is shown in Figure 18, and the data of several databases is summarized in Table 21.
It can be seen from the process diagram that petroleum refining is a complex process. The data set includes drilling, crude oil production, processing, transportation of crude oil through pipelines, and ship transportation to the refinery. The whole process requires a lot of fuel to generate heat, steam and electricity. These fuels may be refinery gas, heating oil (residual oil), gasoline coke, middle distillate oil and liquefied petroleum gas. The output of petroleum refining is a series of products, and the quality of the product is closely related to the composition of the crude oil, the region and the refining technology used.  Analysis shows that the main carbon emissions from the production process of D40 solvent oil (naphtha) come from the production process of petroleum refining and natural gas production, and the emissions are closely related to the quality of crude oil and the refining process. It is recommended to improve the existing petroleum refining process, purchase cleaner crude oil as the raw material, and discharge the exhaust gas after strict absorption and purification.

Assumptions and Limitations
This study calculated the results of 10 indicators of the electrified cleaning agent production process. The detergent formula is determined by this research and does not represent the industry average. When simulating the calculation process, only the energy consumption of the core equipment is calculated. It is assumed that when the main equipment is increased, only electricity is consumed, and the process emissions are not increased. It is assumed that the production technology used for the raw materials is the same as the technology in commercial databases and public documents, and the emissions are the same.

Integrity Description
Strict mass balance and energy balance calculations were carried out for the production process of the electrified cleaning agent. The emission data were adopted from the literature and company measurement. The possible increase in power consumption in the process of production improvement has been discussed in detail in the carbon footprint analysis of power consumption in the section 4.5. The emission data of the production process and waste disposal was obtained from the public databases, and the emission data is highly reliable.

Data Quality Assessment
The report uses the CLCD quality assessment method to complete the uncertainty assessment of the model inventory data on the eFootprint system. The data quality evaluation results obtained are shown in Table 25.

Conclusions
This study analyzed the whole life cycle of the electrified cleaning agent developed. This electrified cleaning agent has the characteristics of non-phosphorus, green and environmental protection, and very broad market prospects. The life cycle model is cradle to grave, and the background data sets include power grid, transportation, high-density polyethylene, chemicals, etc. The production process uses computer simulation to carry out strict mass balance and energy consumption calculations. The study integrated the data from the manufacturer and the contents of the public literature to analyze the emissions.
(2) The four processes of tetrachloroethylene production, D40 solvent oil production, tetrachloroethylene environmental discharge 【 use 】 and electricity 【 product disposal】 have significant effects on each LCA indicator, so they are the focus of process improvement. (3) Changes in power consumption during production and transportation distance of raw materials have little effect on total carbon emissions.
(4) Compared with the production process of single-solvent electrified cleaning agent tetrachloroethylene and n-bromopropane, the production of the electrified cleaning agent developed in this study has its own advantages in terms of carbon footprint and other environmental impact indicators. (5) The higher the waste solvent recovery ratio, the higher the energy consumption of the solution recovery process, which in turn leads to an increase in the carbon footprint (GWP), AP, EP, RI and IRP indicators of the whole life cycle. On the contrary, if the solvent is allowed to discharge to the environment, it will cause a significant increase in environmental toxicity indicators such as POFP, ET, HTcancer and HT-non cancer. It is necessary to develop a low-energy waste solvent recovery process, or improve the current distillation equipment to reduce energy consumption. At the same time, the solvent recovery device needs to be improved to increase efficiency and minimize direct environmental emissions. (6) Estimates of carbon emissions from major upstream production processes show that carbon emissions mainly come from the power consumption of each process, natural gas production and combustion, and other energy materials for heating. It is recommended to use renewable raw materials instead of crude oil to obtain carbon credits based on geographical advantages, and try to use production processes with lower carbon emissions, while the exhaust gas from the traditional production process is strictly absorbed and purified before being discharged.

Suggestions
(1) The results of this study are not industry average, and the improved formula needs to be recalculated. (2) It is recommended to improve the existing petroleum refining process; purchase cleaner crude oil as raw materials; use renewable raw materials instead of crude oil to obtain carbon credits according to geographical advantages; and exhaust gas from the production process after strict absorption and purification before being discharged. (3) It is also necessary to pay attention to the recycling of packaging materials.

ACKNOWLEDGMENTS
We are grateful for the support from the School of Chemical Engineering and Pharmacy at the Wuhan Institute of Technology. We would also like to thank Mr. Rui Li from Mississippi State University for his assistance in the simulation of chemical processes.

CONFLICTS OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this paper.