Dongri Energy Conservation: A good recipe for the radical treatment of waste acid pollution

A corner of the pilot project of Tohnichi silicone waste acid recycling

Industrial waste acid sources are extensive, industry dispersed, as many as dozens of chemical products in the production process of waste acid output, and waste acid concentration is generally low, impurity content is high, most of them also contain organic matter, direct use is more difficult
.
At the same time, China has strict requirements for the treatment of waste acid, and the harmless disposal and resource utilization of waste acid have become a problem
that plagues many chemical production enterprises.

In order to solve the above problems, Hangzhou Dongri Energy Saving Technology Co.
, Ltd.
(hereinafter referred to as Dongri Energy Conservation) adopts two innovative processes - dilute sulfuric acid vacuum concentration complete set technology and concentrated sulfuric acid hydrochloric acid deep desorption process, and has created a number of waste acid recycling demonstration cases in the chlor-alkali, silicone and methane chloride industries, which has provided a good prescription
for the eradication of waste acid pollution.

Dilute sulfuric acid vacuum concentration technology

Creating an "internal cycle" of by-product sulfuric acid

10,000 tons/year chlor-alkali dilute sulfuric acid concentration unit

China is a large producer and consumer of sulfuric acid, but the problem of waste sulfuric acid disposal has not been solved
.
The best way to dispose of waste sulfuric acid is to achieve recycling and reuse, so as to achieve harmless and resource utilization
.
However, the concentration of waste sulfuric acid is generally low, the impurity content is high, and it contains a large amount of organic matter, which is difficult to achieve purification treatment
.
In the chlor-alkali industry, high concentrations of sulfuric acid have good water absorption due to their very low partial pressure of water vapor and are used to dry chlorine and hydrogen chloride gas
.
After water absorption, the concentration of sulfuric acid is reduced and a balanced amount of chlorine and hydrogen chloride gas is dissolved, and how to recycle these sulfuric acids has become a technical problem
faced by the chlor-alkali industry.

Dongri Energy Saving has been deeply engaged in the chlor-alkali industry for many years, and has independently developed dilute sulfuric acid vacuum concentration technology
in response to the sulfuric acid treatment problems in the chlor-alkali industry.
According to the characteristics of by-product sulfuric acid in the chemical industry, this technology has carried out unique design and practice optimization in process design, equipment selection, energy saving and consumption reduction, solute removal, etc.
, which solves the problems
of low product concentration, serious equipment corrosion and inability to produce continuously on a large scale in the sulfuric acid concentration process.

In addition, the technology also has the advantages
of good anti-blocking performance, high reliability, and low "three wastes" emissions.
The anti-blocking performance is good because the sulfuric acid vacuum concentration device designed by Dongri Energy Saving adopts a unique internal structure design, so that the sulfate is not easy to block the pipeline, and it can also be cleaned and discharged
regularly with the wastewater in the wastewater tank.
The high reliability is due to the use of tantalum sulfuric acid heater, which has high mechanical strength, good corrosion resistance, strong ability to adapt to failure, and a service life of more than 25 years
.
The "three wastes" emission is low because the vacuum acquisition system of the device adopts a steam jet pump unit, which solves the problems of large alkali consumption and large amount of
wastewater discharged by the liquid ring vacuum pump.

In September 2017, Dongri Energy Saving successfully applied this technology in a chlor-alkali enterprise in Ningxia
.
The plant processes 5,000 tons of 75% (concentration) dilute sulfuric acid per year, and the acid concentration of the product exceeds 96%.

The project is also equipped with a caustic soda production unit of 2×1,000 tons/year to realize the recycling of sulfuric acid in chlor-alkali enterprises
.

Combined with the production experience of this set of sulfuric acid vacuum concentration unit, Dongri Energy Saving continued to optimize the process flow, and in December 2019, a chlor-alkali enterprise in Inner Mongolia successfully started a vacuum concentration unit that treats 10,000 tons of 75% dilute sulfuric acid per year, combining the sulfuric acid of the company's chlorine drying and hydrogen chloride drying process by-products, removing free chlorine and hydrogen chloride while increasing the sulfuric acid concentration, and the product acid is reused to the drying process
.
In this way, a set of sulfuric acid vacuum concentration device solves the concentration problem of two different sulfuric acids and realizes the recycling of sulfuric acid
.

Deep desorption process of hydrochloric acid by concentrated sulfuric acid

Crack the bottleneck of by-product hydrochloric acid treatment

100,000 tons/year chloromethane alcohol-containing dilute hydrochloric acid deep desorption (concentrated sulfuric acid method) device

By-product hydrochloric acid is one of the by-products in chemical production, which has fewer uses and low
market demand.
Most domestic enterprises use lime, calcium carbide slag or slaked lime for neutralization treatment to produce industrial-grade calcium chloride, polyaluminum chloride and other products, but the market capacity of these products is small, so the effective utilization of by-product hydrochloric acid has become a bottleneck
restricting the healthy development of chemical enterprises.

In view of the actual situation of by-product hydrochloric acid and hydrogen chloride gas in the chemical industry, Dongri Energy Saving independently developed a deep desorption process of hydrochloric acid by concentrated sulfuric acid, and used concentrated sulfuric acid extraction rectification to recover hydrogen
chloride.
The process uses the oxidation and reduction properties of sulfuric acid, based on the sulfuric acid vacuum concentration process, integrates innovation to carry out customized treatment of industrial waste acid, solves the problem of purification and treatment of waste acid, and realizes the resource reuse
of waste acid.

The deep desorption process of hydrochloric acid by concentrated sulfuric acid method can achieve continuous production and stable operation, and also has the characteristics of
low energy consumption, low COD of wastewater discharge and low chloride ion content.
It is particularly worth mentioning that the process solves the problems of traditional deep desorption processes such as calcium chloride method and pressure swing rectification method such as
unstable operation, easy blockage, and secondary pollution.

The essence of the calcium chloride method is salt extraction, by adding calcium chloride to hydrochloric acid, breaking the limit of its azeotropic point and separating hydrogen chloride
.
Because of the characteristics of calcium chloride solution, it is easy to scale at the wall of the heater hole and it is difficult to handle, and the impurities in hydrochloric acid are also easy to crystallize the calcium chloride solution and lead to the blockage of the device, so the calcium chloride method device is difficult to achieve continuous and stable operation
.
At the same time, the wastewater discharged by the calcium chloride method device has a high hydrogen chloride content, and a large amount of calcium chloride waste liquid will be discharged, which will cause secondary pollution
.

The pressure swing rectification method (or differential pressure method) is to let dilute hydrochloric acid into the vacuum distillation column for vacuum rectification, and the distilled water at the top of the column is partially refluxed after condensation, and the rest is used as a wastewater discharge system; The bottom of the tower is the concentrated constant boiling acid, which enters the pressurized desorption tower, and the top of the tower desorbs hydrogen
chloride.
Due to its process characteristics, salt impurities in hydrochloric acid will accumulate in the equipment because they cannot evaporate, resulting in equipment blockage, causing frequent maintenance of the desorption device, resulting in an increase
in the failure rate of desorption equipment and pipelines.

The basic principle of the concentrated sulfuric acid hydrochloric acid deep desorption process developed by Dongri Energy Saving is to use sulfuric acid and water to be completely miscible and the boiling point of concentrated sulfuric acid is higher than the boiling point of constant boiling hydrochloric acid, so that the water in dilute hydrochloric acid is transferred to concentrated sulfuric acid to form relatively dilute sulfuric acid, so as to extract hydrogen chloride, and the rarer sulfuric acid is dehydrated by evaporation, concentrated into concentrated sulfuric acid for recycling, and the evaporated water is acid wastewater
after condensation.
Compared with the above two methods, the concentrated sulfuric acid used in this process will not crystallize above room temperature, and the salt impurities brought into hydrochloric acid and sulfuric acid form sulfate, which can be separated by online crystallization during dilute sulfuric acid concentration without blocking the device
.
In addition, the process adaptability of this technology is good, and the impurity content in hydrochloric acid is not high; Low steam consumption, only 3.
5~6.
0 tons of steam per ton of 100% hydrogen chloride; Sulfate filtration and organic oxidation filtration are adopted, and the system has good anti-blocking performance; The hydrogen chloride content in wastewater can be stably controlled below 0.
3%, and the discharge cost is also low
.

Upgraded dilute hydrochloric acid desorption and sulfuric acid concentration technology

Cure the silicone industry

The dilute hydrochloric acid by-product of silicone production has a small amount of siloxanes, which have self-polymerization in the acid, and the accumulated polymer will cause the blockage of hydrochloric acid desorption device equipment and pipelines, resulting in calcium chloride method and pressure swing rectification hydrochloric acid desorption device can not operate
for a long time.
Frequent maintenance not only leads to an increase in operating costs, but also leads to an increase in the failure rate of equipment, which has become a technical problem
for the desorption of hydrochloric acid, a by-product of silicones.

The concentrated sulfuric acid hydrochloric acid deep desorption process developed by Dongri Energy Saving uses the characteristics of siloxane oxidized to silica by peroxymonosulfuric acid in sulfuric acid, and can realize online continuous solid-liquid separation
during the dilute sulfuric acid concentration process.
The specific principle is that in the sulfuric acid concentration stage, sulfuric acid will not crystallize due to temperature reduction like calcium chloride solution, and at the same time, the peroxy group formed by adding a small amount of hydrogen peroxide to the concentrated sulfuric acid has strong oxidation, which can oxidize the siloxane into the sulfuric acid to silica, and realize the online continuous filtration of siloxane in sulfuric acid, completely eliminating the siloxane
brought into the sulfuric acid during the hydrochloric acid treatment process.

In November 2020, the technology was successfully applied in a silicone enterprise in Jiangsu, and a 50,000 tons/year silicone-containing siloxane-containing dilute hydrochloric acid deep desorption device was built, and a successful start-up was carried out to produce qualified hydrogen chloride back to the methyl chloride unit for recycling
.

At the same time, in silicone production, the waste sulfuric acid emitted by the methyl chloride purification section contains a variety of organic substances
such as methyl chloride, dimethyl ether, methyl sulfate and siloxane.
Due to the easy polymerization of polymer organic siloxanes in sulfuric acid, if they are not effectively separated from the acid before concentration, siloxanes will polymerize and block the equipment during the stripping process of organic matter when dilute sulfuric acid is heated, resulting in the shutdown of the sulfuric acid treatment device accident
.
The silicone dilute sulfuric acid vacuum concentration process developed by Dongri Energy Saving uses the characteristics of siloxane oxidation to silica by peroxymonosulfuric acid in sulfuric acid, and realizes the oxidation and separation of siloxane in sulfuric acid during the dilute sulfuric acid concentration process, which solves the technical problem
of device blockage.

In December 2021, a silicone enterprise in Yunnan applied this technology to build a 15,000 tons/year silicone waste sulfuric acid recycling plant, and successfully started up at one time, producing qualified 96% regenerated concentrated sulfuric acid to return to the methyl chloride unit for recycling
。 This marks the realization of 10,000-ton industrial application of siloxane-containing dilute sulfuric acid concentration technology, and solves the technical problems of waste sulfuric acid treatment in silicone enterprises; It solves the problem of blockage caused by polymerization of siloxanes in waste sulfuric acid during the concentration process, and realizes the long-term operation of the device; The concentration of regenerated concentrated sulfuric acid exceeds 96%, which meets the quality requirements of concentrated sulfuric acid for the drying of silicone chloromethane, and realizes no waste sulfuric acid emission
of the device.

Separation purification + vacuum concentration combination process

Eliminate the hidden dangers of methane chloride production

20,000 tons/year chlorinated polymer recovery concentrated hydrochloric acid removal free chlorine system

China is the world's largest producer of methane chloride, silicone and glyphosate
.
Methane chloride is produced by methanol hydrochlorine in the production process of methane chloride and silicone, and chloromethane is by-product in the synthesis of dimethyl phosphite, the raw material of glyphosate, resulting in the by-product of methane chloride, silicone and glyphosate in the production process of dilute sulfuric acid
containing organic substances.

Taking the methane chloride plant as an example, the waste sulfuric acid emitted by it contains methyl sulfate, methyl chloride, methyl ether and other organic compounds, which need to be pretreated to remove macromolecular organic matter
before concentration.
If these organics cannot be safely and effectively removed before concentration, the concentrated sulfuric acid cannot be returned to the methane chloride production plant for recycling
.
Moreover, organic substances methyl chloride and dimethyl ether are flammable and explosive substances, which are enriched in the vacuum system and have great safety risks
.
The highly toxic substance methyl sulfate in the waste acid will also enter the wastewater, causing serious secondary pollution
.

10,000 tons/year silicone waste sulfuric acid recycling device

In order to solve the above problems, Dongri Energy Saving has developed the patented technology
of "a washing methyl chloride waste sulfuric acid purification system and process".
This technology combines the separation and purification process of organic matter in dilute sulfuric acid and the vacuum concentration process of dilute sulfuric acid into a whole, purifies and concentrates the methane chloride by-product dilute sulfuric acid to more than 95%, and returns it to the methane chloride production device for recycling, which solves the problem of high organic matter content and difficult secondary utilization of methane chloride by-product, and can also recover methanol and methyl ether
in waste sulfuric acid.

As a practical sample of this technology application, the methane chloride plant of Jiangsu Liwen Industry Co.
, Ltd.
undertaken by Dongil Energy Saving to recover by-product hydrochloric acid to produce 80,000 tons/year monochloromethane and supporting 2,700 tons/year sulfuric acid concentration project, using the by-product waste acid of the existing production equipment as raw materials, through recycling and resource regeneration, reduce the total amount of chlorine-containing wastewater discharge and total hazardous waste in the whole plant, and recycle and produce monochloromethane for use in the silicone industry, practicing the concept of
low-carbon green cycle development 。 Previously, Jiangsu Science and Culture Industry has built a 160,000 tons/year methane chloride production line, with nearly 100,000 tons of 25% hydrochloric acid, more than 10,000 tons of 88% sulfuric acid, and more than 5,000 tons
of 75% sulfuric acid.
The storage of large amounts of by-product acids poses a major safety hazard
.

The project adopts Dongri energy-saving concentrated sulfuric acid hydrochloric acid deep desorption technology, eliminates the output of by-product hydrochloric acid from the process, and recovers hydrogen chloride to produce monochloromethane for use in the silicone industry, ensuring continuous and stable extraction of hydrogen chloride intermediate products, laying the foundation
for the production of chloroform with cost advantages 。 The project also solves the problem of by-product sulfuric acid treatment, purifies and concentrates 88% sulfuric acid produced in the production process of monochloromethane into 95% concentrated sulfuric acid as raw material replacement, returns to the methane chloride production unit for recycling, solves the problem of high content of methane chloride by-product dilute sulfuric acid organic matter and difficult secondary utilization, and creates better economic benefits
for enterprises.

The first phase of the project has been successfully started up in November 2021 and reached production that year, including a 40,000 tons/year chloromethane plant, a 100,000 tons/year hydrochloric acid deep desorption unit, and a 15,000 tons/year dilute sulfuric acid concentration unit
.
The second phase of the project was launched in April 2022 and is expected to complete the project construction
in April 2023.

Driving innovation with technology

Promote sustainable industry development

Dongri Energy Saving drives innovation with science and technology, with more than 50% of R&D personnel, and more than 50 chemical environmental protection technology patents, including 26 invention patents and 27 utility model patents
.
In January 2021, Zhejiang University of Technology and Dongri Energy Conservation established the Dongri Energy Conservation Engineering Technology R&D Center of Zhejiang University of Technology to establish long-term close industry-university-research cooperation and jointly promote the sustainable development of
the basic chemical industry.

Dongri energy-saving technology has been successfully applied to many subdivisions of the chemical industry, including chlor-alkali, silicone, methane chloride, glyphosate, etc
.
In particular, dilute sulfuric acid vacuum concentration technology and concentrated sulfuric acid hydrochloric acid deep desorption process have been applied
in methane chloride and silicone industries.
Not only that, Dongri Energy Saving Technology has completed the pilot scale of waste acid treatment in the fields of hydrometallurgy and electronic chemicals, and has also carried out technological development and research and development
in fluorine chemical industry, phosphorus chemical industry and other industries.
In addition, Dongri energy-saving salt-containing solid waste treatment technology and hydrogen chloride oxidation production chlorine gas technology are also being
further developed.

For a long time, Tohnichi Energy Conservation has been actively carrying out service-oriented transformation, from a single equipment buyer and manufacturer to today's personalized system solution provider, from providing a single product to providing "product + service", becoming an energy-saving and environmental protection comprehensive service provider
integrating chemical process services and waste acid resource treatment.
With the increasingly strict national environmental protection policies and the increasing demand for waste acid recycling, the sustainable development model of basic chemicals has shown some obvious trends
.
In the future, on the one hand, Tohnichi Energy Saving will go deep into the process research of more industries and provide personalized solutions for diversified waste acid treatment and recycling; On the other hand, it will also strengthen upstream and downstream peers and cross-industry cooperation in the environmental protection and energy-saving industry chain, expand the service market, and provide chemical enterprises with composite environmental protection and energy-saving solutions
.
Not only that, the company's environmental protection service mode will be technology-oriented, with the industrial park as the carrier, committed to providing more comprehensive and comprehensive waste acid treatment, chlorine balance solutions, and the establishment of waste acid intensive recycling center
.

(Photo courtesy of the company)