◎ Du Mengcheng and Xia Yu, Shandong Yanggu Huatai Chemical Co., Ltd.
Ⅰ. Domestic New Situation of Environmental Protection
After reform and opening-up, economic development is the first priority in China and environmental protection takes a back seat. In the 21st century, the environmental problems such as “acid rain”, sand storm and deterioration of water quality in rivers, lakes, etc. frequently arise. On December 3, 2005, Decision on Implementing Scientific Concept of Development and Strengthening Environmental Protection by the State Council was issued, China transferred from emphasizing economic growth and neglecting environmental protection into emphasizing both economic growth and environmental protection, which is an important milestone in China’s history of environmental protection.
During the “11th five year”, the country mainly focused on the problems of discharging sulfur dioxide into the atmosphere and chemical oxygen demand of water; during the “12th five year”, haze drew high attention of the whole society, the country mainly planned atmospheric control on the basis of the “11th five year” to strengthen the discharge control of smoke, nitric oxide, volatile organic compounds and toxic waste; among 10 targets of the “13th five year” plan, strengthening the ecological civilization construction was included for the first time, General Secretary Xi Jinping pointed out that “lucid waters and lush mountains are invaluable assets”, the country ascended environmental protection to a new height. Environmental protection regulations, action plans, etc. were launched intensively during this period and environmental protection became a new normal.
On September 12, 2013, the State Council published Action Plan for Prevention and Control of Air Pollution (“Ten Measures for Air”). In January 2015, “the strictest” environmental protection law in the history was launched; in April, Action Plan for Prevention and Control of Water Pollution (“Ten Measures for Water”) was officially launched; in August, Atmospheric Pollution Prevention Law was revised again, VOCs was included in the monitoring range; and in November, Basic Thoughts of “13th Five Year” Plan of Environmental Protection was launched.
In January 2016, new Ambient Air Quality Standard was launched; in May, Action Plan for Prevention and Control of Soil Pollution (“Ten Measures for Soil”) was published. In June 2016, the Ministry of Environmental Protection issued the Instructions for Giving Full Play to Environmental Protection to Promote Supply-side Structural Reform to propose overall thought and key tasks. Promoted by central environmental supervisor, various provinces successively shut down many “small, scattered, messed and polluting” enterprises which did not reach the discharge standard and severely polluted the environment. The demand for pollution control of the industries with high pollution and high energy consumption such as petrifaction, steel, nonferrous metal, chemicals, coal and cement was further released.
In March 2017, the government work report of the State Council proposed to initiate the Blue Sky Protection Campaign, and it was required to reduce the average PM2.5 concentration and the number of heavy pollution days in “2+26” cities in Beijing, Tianjin and Hebei by over 15%. The pollution control effect was linked with the assessment performance of local government officers, the river chief system, central environmental protection supervision, special rectification action, etc. were successively carried out, and the intensity of punishment was unprecedented. In September 2017, Work Program on Prevention and Control of Pollution of Volatile Organic Compounds of “13th Five Year” pointed out that by 2020, the VOCs pollution prevention and control management system with improvement of ambient air quality as the core would have been established and perfected, discharge reduction of VOCs pollution in key areas and key industries would have been implemented, with the total discharge reduced by over 10%. By coordinated control of the pollutants such as NOx, sustainable improvement of ambient air quality should be realized.
On January 1, 2018, the Environmental Protection Tax Law of the People’s Republic of China was implemented, which, based on the exiting pollution discharge fee system, linking with the newly revised environmental protection law, according to the principle of “conversion of tax”, defined the systems on taxpayer, tax object, taxation basis, tax item and amount and management of taxation of environmental protection tax and gave full play to the important role of tax in controlling and reducing pollutant discharge as well as protecting and improving ecological environment.
From 2016 to 2017, Central Environment Protection Inspectorate realized thorough nationwide inspection on 31 provinces (districts and cities) in China to basically grasp the current situation of pollution prevention and control in China.
Ⅱ. Influence of New Situation on Rubber Chemicals Industry
In 2017, China’s total output of rubber chemicals was 1.14 million tons, with a year-on-year (same below) slight growth of 1.7%, to basically realize stable supply; the total sales revenue was 21.57 Billion Yuan, with a growth of 15%, which fully embodied the whole industry situation of rise in price caused by slightly intense supply of rubber chemicals; the export volume increased by 2.3%, and the export (volume) rate was 29.4%; the export amount increased by 15.4%, and the export (amount) rate was 30%, and the global difference in price of rubber chemicals was gradually reduced and even disappeared.
From 2005, the supply-demand relationship of rubber chemicals market started to incline, the market pattern with supply exceeding demand slowly occurred and the price also gradually declined accordingly. Since the second half of 2016, along with launch and implementation of new environmental protection of the state, under huge shock of environmental protection tide, rubber chemicals industry was not an exception, with sharp decline in the rate of operation, and the phenomenon of demand exceeding supply occurred for a short time. In addition, the raw materials of rubber chemicals (basic chemical raw materials) were also affected by the environmental protection tide and some had the conditions of outage, such as dicyclohexylamine, tert-butylamine and m-xylylenediamine, which promoted the rubber chemicals such as accelerant DZ, TBBS and PK900 to be in a situation of tension in supply.
In the pattern of domestic rubber chemicals enterprises, because of high pressure in environmental protection and survival of the fittest in the market, the Matthew Effect was enhanced, the production enterprise of various types of rubber chemicals tended to be large-scale and centralized, small enterprises reduced and a few large- and medium-scale enterprises occupied half of the county.
High pressure in environmental protection and forced mechanism required rubber chemicals industry to advance with the times, make continuous improvement, innovate from the aspects such as safety, environmental protection and process and equipment in an all-round way, adapt to the current new normal and realize new development of rubber chemicals industry.
Ⅲ. Current Situation and Improvement Measures of Environmental Protection of Rubber Chemicals Industry
1. Current Situation and Development Trend of Waste Water Treatment
At present, aiming at the characteristics of waste water of high salt content and high COD, rubber chemicals industry has basically formed unified control route - pre-treatment - multiple-effect evaporation/MVR evaporation - biochemical treatment.
The widely-used evaporation processes in China are mainly multiple-effect evaporation and MVR evaporation. MVR evaporation once was widely applied as more advanced technology, whose core advantage is energy conservation. There is a relatively large regional difference in cost of steam and power in China, and it is more suitable for those areas with lower cost of steam to choose multiple-effect evaporation.
Biochemical treatment technology is the cheapest and stable and effective treatment method, the most difficult part of which is how to realize stable operation. Data shows that over 70% of the biochemical sewage treatment factories in China can not stably reach the standard of discharge. Biochemical operation needs to strictly control various water inflow indexes and operation indexes; in addition, the cultivation of the strains is also very crucial.
Waste water of rubber chemicals possesses the characteristics of high organic content, high salt, difficult treatment, etc. Taking rubber accelerant as the example, the product yield of main varieties is generally 87% ~ 93%, and each ton of waste water contains 60kg ~ 80kg of organics and 100kg ~ 150kg inorganic salt. Without pre-treatment, the organics will affect the evaporation process and evaporation capacity of waste water. Pre-treatment technologies include flocculation precipitation, absorption, extraction, oxidation, etc.
(1) Flocculation precipitation pre-treatment
With the advantages such as high removal efficiency, wide scope of application, low treatment cost and easy operation and management, flocculation or coagulation has become the most commonly-used waste water pre-treatment method so far. By adding certain ratio of flocculant or coagulant, large-particle pollutants in the waste water are removed by being absorbed and precipitated through the formed bridge, thus reaching the purpose of improving B/C and lowering the pollutant concentration and biotoxicity.
(2) Absorption pre-treatment
With good absorption property, activated carbon has been widely used in clean water treatment and also applied in pre-treatment engineering of low-concentration chemical waste water; however, high treatment cost of high-concentration organic waste water affects its promotion and application in engineering. Developing high-efficiency and low-cost absorbent is the key to promotion and application of absorption treatment technology. At present, the research on macroreticular resin phenol removal mainly focuses on optimization of absorption and desorption conditions as well as discussion of absorption mechanism, expecting to realize relatively high environmental benefits and economic benefits.
(3) Extraction pre-treatment
Extraction is the method of purifying the waste water by adding the solvent (extraction agent) insoluble or poorly soluble in water into the waste water to transfer some pollutants (extracted substances) soluble in waste water to the extraction agent through the interface between the extraction agent and waste water. Extraction treatment method is generally used for treating the high-concentration industrial waste water containing phenol or aniline, benzene, acetic acid, etc.
(4) Oxidation pre-treatment
Oxidation mainly includes Fenton, microelectrolysis, electrocatalytic oxidation, photocatalytic oxidation, wet catalytic oxidation, etc.
Microelectrolysis is the process of treating waste water by forming primary cell with Fe and C according to the principle of metal corrosion, which is also called internal electrolysis and scrap iron filtration. Since this method has the advantages of wide scope of application, good treatment method, long service life, low cost and easy operation and maintenance, it has become the research hotspot in recent years. In the waste water treated with this method, not only the content of organic pollutants can be sharply reduced, the B/C ratio of biodegradability can also be correspondingly increased. The microelectrolysis filler produced with the existing process has overcome the disadvantage of hardening passivation and the filler can continuously and efficiently operate.
Wet catalytic oxidation technology is an in-depth treatment technology of carrying out oxygenolysis of the pollutants in high-concentration organic waste water such as COD, TOC, ammonia and cyanogen in one lump sum by virtue of the principle of catalytic oxidation under high temperature and high pressure, in a reactor filling with catalyst, with the water kept in the liquid status, under the action of oxygen or liquid oxygen. Such technology can directly transfer the organics into CO2, N2, water, etc. and simultaneously realize deodorization, decoloration and sterilization and disinfection. With huge investment in equipment and high operation expenses (lower than incineration operation expenses), this technology applies to the waste water with high concentration, difficult degradation and small water volume.
In recent years, through constant development and application, various environmental protection and control technologies are also sorted out and updated. Since the consumption of activated carbon is lowered due to development of activated carbon regeneration technology, absorption pre-treatment with activated carbon is developed and applied in chemical waste water. Some scholars have made progress in research on chemical extraction, thus chemical extraction is well applied in waste water pre-treatment of rubber accelerants.
In addition, domestic research on treatment process of chemical waste water tends to the combined process adopting multiple methods. For example, internal electrolysis, coagulating precipitation - anaerobic - aerobiotic process is adopted to treat medical waste water, macroreticular resin absorption and anaerobic - aerobiotic biological treatment - flocculation precipitation process is adopted to treat organic chemical waste water, combined flocculation - electrolysis process is adopted to treat ephedrine waste water, ozone - biological activated carbon process is adopted to remove the organic pollutants in the water, combined photocatalytic oxidation - internal electrolysis - SBR process is adopted to treat high-concentration chemical waste water, etc., the combined processes achieve relatively good results.
There is only “the most suitable one” instead of “the most advanced one” among the treatment technologies. Over 50% of COD in waste water of rubber accelerant can be removed by adding acid for precipitation, and the solid obtained can be utilized as a resource. There are various types of rubber chemicals and different waste water problems, how to choose suitable treatment technology still needs continuous exploration and sustainable development and improvement of waste water treatment technology of rubber chemicals have a long way to go.
2. Current Situation and Development Trend of Exhaust Gas Treatment
In recent years, haze weather frequently occurring in the North attracted more and more attention of the public to the air quality, the territorial scope affected by the haze is enlarging and the influence degree is also becoming heavier and heavier. In December 2016, there were phenomena such as class suspension, restriction of motor vehicles, highway closure and suspension of flying in most regions of Beijing, Hebei and Shandong. The major component of the haze is PM2.5 while an important premise for generation of PM2.5 is VOCs (Volatile Organic Compounds). VOCs are mainly from industrial production, combustion, traffic and transport, etc., the VOCs emission from industrial production accounts for over 50% of total VOCs emission in China, and most of the tail gases of rubber chemicals industry belong to VOCs exhaust gas.
End treatment technologies of industrial VOCs are divided into resourceful treatment technologies and non-resourceful treatment technologies, in which resourceful treatment technologies mainly include condensation recovery, absorption recovery, membrane separation, etc.; non-resourceful treatment technologies mainly include regenerative combustion, catalytic combustion, biodegradation, plasma, etc.
The advantages of resourceful treatment technologies are good economic benefits and saving of resources, and the disadvantages lie in low treatment efficiency and difficulty in reaching the discharge limit indexes.
Condensation recovery method is the most commonly-used and the simplest technology, whose principle is lowering the temperature of the exhaust gas to the dew point temperature of the organics to condense the organics into the liquid for sedimentation and separation, thus realizing the purpose of purifying the exhaust gas. Since most of the reactions of rubber chemicals have heating conditions and require organic solvent, the processes such as reaction process and solvent distillation and recovery are generally equipped with distillation and recovery equipment.
Absorption recovery method mainly utilizes porous substances with large specific surface area such as activated carbon, zeolite and resin to absorb VOCs gases and then utilizes steam or negative pressure for desorption, thus realizing the purpose of purifying the tail gas and refining and recovering the VOCs. The largest disadvantage of absorption recovery process is that the nation has listed the waste activated carbon as hazardous waste, the waste activated carbon causes secondary pollution and how to treat and the treatment cost become the bottlenecks.
Membrane separation method is separating the VOCs from the air under certain pressure by controlling the pore size and permselectivity of polymeric membrane or ceramic membrane, thus purifying the tail gas. The advantages of this method are high treatment efficiency and energy-saving and eco-friendly method without secondary pollution; and the disadvantages lie in large investment, large difference in service life of the membrane due to components and working conditions and narrow scope of application, and it only applies to the tail gases with single components of VOCs, high concentration and high recovery value.
Compared with resourceful treatment technologies, non-resourceful treatment technologies have the opposite advantages and disadvantages, which have poor economic benefits, generally high operation expenses but high treatment efficiency, thus they can stably reach the discharge standard.
Among exhaust gas treatment methods, the most widely-used combustion methods are mainly two technologies, regenerative thermal oxidation (RTO) and regenerative catalytic oxidation (RCO), and because of waste of resources and severe secondary pollution, direct combustion method is not popularized.
Regenerative thermal oxidation (RTO) is heating the organic tail gas to over 760 ℃ to oxidize and decompose the VOCs into carbon dioxide and water. High-temperature gas generated by oxidation passes through specially-made ceramic regenerator, thus the ceramic regenerator is heated and accumulates heat, then the subsequent organic tail gas is pre-heated to realize the purpose of saving fuels. This technology applies to the tail gas with a concentration of 100mg~3500mg/m3, and the decomposition efficiency can reach 95%~99%, thus it is widely used in the industries such as coating, chemical and electronics. Its disadvantages are high investment and high operation cost, thus the enterprise with low-concentration tail gases can not afford it at all.
Regenerative catalytic oxidation (RCO) technology is similar to RTO, and their difference lies in that RCO utilizes catalyst to lower the reaction temperature, improve the combustion efficiency, increase heat recovery rate and improve the tail gas purifying rate, some organics which can not be decomposed by RTO can be oxidized and de-composed in RCO. The oxidation temperature of RCO technology is generally 200℃ ~500℃ , the heat recovery efficiency can reach 95%, and the operation expense can be saved by 33%~50% compared with that of RTO. Therefore, in the market, RCO technology is gradually replacing RTO technology, and partial existing RTO equipment are being transformed into RCO equipment. RCO replacing RTO has become a trend; however, RCO also has some problems, among which the most important are the life and efficiency of the catalyst and treatment of waste catalyst, meanwhile, the problems of high investment and operation expense also exist.
Biodegradation, plasma, photocatalytic oxidation, etc., as new technologies, have certain technology and cost advantages; however, they have more limitation in use conditions and attenuating property in treatment efficiency. As for the tail gases of rubber chemicals, especially the enterprises within non-single products, the tail gases have complex components and different concentration degrees, separate use of this new technology can not satisfy the emission requirements.
At present, rotating wheel absorption + RTO/RCO has become a relatively advanced and thorough technology in domestic exhaust gas control industry, which has solved the difficulty problem that low-concentration exhaust gas does not apply to RTO/RCO. Its limitation is that at present, all rotating wheels rely on import and have a large investment cost, and whether the rotating wheel applies to the tail gases of rubber chemicals industry and whether the service life can be guaranteed are to be verified.
3. Current Situation and Development Trend of Solid Waste Treatment
Among various industries in China, solid waste treatment just starts. Organic solid wastes in rubber chemicals industry generally come from residues of reaction still or residues of distillation or rectifying still. At present, the best treatment method is recycling, and those which can not be recycled shall be reduced with organic solid waste incinerator or directly handed over to the qualified unit as hazardous waste for treatment. Taking the accelerant MBT as the example, a part of manufacturers have verified through experiment that its organic solid waste can react to obtain benzothiazole. Benzothiazole, as the production material of the peptizer DBD, has high added value. Since there are a variety of rubber chemicals, the recycling method of different organic sold wastes differs.
The largest solid waste in rubber chemicals industry is waste salt. The waste salt mainly comes from evaporation of waste water, and theoretically, there must be organics in waste salt. The direction and treatment method of waste salt is one difficult problem in China now, the country does not determine whether the waste salt shall belong to hazardous waste, general waste or by product, or the waste salt with different quality belongs to different classes. In newly-added chemical projects, general environmental impact assessment units determine waste salt as suspected hazardous waste and manage and operate it temporarily as hazardous waste. What is worth mentioning is that glyphosate industry determined the nature of its waste salt as by product in 2015 and drew up the national standard of by product salt of glyphosate. Glyphosate industry provides a reference for way out for chemical waste salt.
If the nature of waste salt is determined as by prod-uct or general solid waste, we must treat it effectively. At present, such treatment is divided into two classes, one is having pre-treatment to purify the waste water before evaporation, thus lowering the organics in the waste water to certain degree, and the waste salt after evaporation can get good quality. Pre-treatment generally adopts advanced oxidation, absorption, etc. Advanced oxidation has high operation expense and its treatment efficiency is generally 50%~70%; absorption is mainly activated carbon or resin absorption, the efficiency of activated carbon absorption is generally 70%~80%; however, the treatment problem after absorption is transferred into the problem of waste water and exhaust gas, the residues become hazardous waste, and its consumption cost and post-treatment cost are also expensive. The other is purifying the waste salt, the mainstream treatment technologies include incineration, solvent cleaning, oxidation, extraction, etc. The technologies such as solvent cleaning, oxidation and extraction have large technical limit and low efficiency while incineration is a relatively reliable and mature process. Incineration of waste salt needs to consider the operation cost, retreatment of incineration tail gas, material of refractory brick, etc.
After treatment of waste salt, the nature of the waste salt needs to be determined as by product or identified as general solid waste, which requires guidance of national policy and joint effort of all rubber chemical enterprises.
If rubber chemicals enterprises need to build themselves as eco-friendly and closed green industrial park with high standard requirements with no treatment “tail”, the investment cost and operation cost required are impossible to be cheap. However, along with increasingly perfection of national environmental protection regulations and increasingly high demand of the people for environment, rubber chemical enterprises shall be willing to invest and dare to invest, constantly improve self “three waste” treatment level, improve “three waste” treatment process, and reduce “three waste” and reduce the cost on the basis of stable and effective standard reaching. Environmental protection control surely will become an important weight for the next round of survival of the fittest.
Ⅳ . Current Status and Development Trend of Processes and Equipment
Rubber chemicals industry belongs to the field of fine chemicals, compared with large chemical, its scale and capacity are relatively small. Therefore, the production process of rubber chemicals generally stays in intermittent reaction, and to flexibly control the capacity, multiple sets of small-scale reaction stills are adopted generally. High material consumption and large solvent loss as a result of loading and unloading as well as unstable product quality not only cause relatively high cost, but also bring about pressure of environmental protection control.
In recent years, rubber chemicals industry has faced the situation of supply exceeding demand and fierce competition, and the law enforcement situation of high pressure in environmental protection has still existed, which requires the rubber chemicals enterprises to transform and upgrade toward the direction of green chemical and intelligent chemical, improve the process and equipment level and lower the production cost and improve the comprehensive competitiveness of the products on the premise of ensuring stable and reliable quality of the products.
At present, the development trend of chemical equip-ment in the world shows polarization of large-scale and miniaturization. Large-scale reaction still is to facilitate automation and continuity, reduce the material transfer, improve production efficiency, lower the material consumption and keep sable product quality. However, the miniaturization direction is the current relatively hot micro chemical technology, which has the advantage of process enhancement and possesses the features such as good heat and mass transfer property, good safety, easy control and direct enlargement, thus improving the process safety and production efficiency, lowering the material consumption, reducing “three waste” and displaying its unique superiority.
Micro chemical technology is also applied and tried in the field of rubber chemicals, although there is no large-scale industrial production device at present, it can be predicted that after scientifically choosing the products and processes suitable for micro chemical reform and overcoming the problems such as micro chemical blocking and corrosion, the demonstrative micro chemical engineering in the field of rubber chemicals will be gradually perfected. Once micro chemical technology is successfully developed and applied, it will exert a huge influence on the whole field of rubber chemicals and even change current world pattern.
Most of the products in rubber chemicals industry can be researched and developed in the aspect of micro chemical technology, those not suitable for development and with high difficulty can be researched in the direction of large-scale reaction still, continuity and automation. No matter which method is adopted, the final fundamental purpose is developing toward greening and intelligence. It is believed that along with social and scientific progress, by brainstorming and absorbing, the rubber chemicals industry surely will have new reform and development.
