Issue 48/2015 - Research status and application progress of environmentally friendly corrosion and scale inhibitors

The rapid development of industrialization has led to water shortage and aggravation of water pollution has become a hot spot in the world today, and the formation of scale and dirt is the second largest hazard
in the industrial water system.
For this reason, people began the difficult journey
of developing corrosion and scale inhibitors.
China's research and development of corrosion and scale inhibitors began in the 70s of the 20th century (water quality stabilizers, etc.
), in the first 50 years has been the use of natural polymer corrosion and scale inhibitors and phosphorus-containing polymer corrosion and scale inhibitors, with the strengthening of people's awareness of environmental protection, considering the pollution of phosphorus to the water environment (causing eutrophication of water, etc.
), low phosphorus or no phosphorus and other environmentally friendly corrosion and scale inhibitors have gradually become the subject
of research at home and abroad.

Mainstream environmentally friendly scale and corrosion inhibitor

Adding scale and corrosion inhibitors to circulating water systems is a commonly used scale and corrosion inhibitor technology
.
The corrosion and scale inhibitors used in industry to treat sulfate scale and carbonate scale mainly include low molecular polymers and organophosphoric acid
.
Organophosphate is easy to hydrolyze, and it is easy to form organophosphate scale and cause environmental pollution, thus limiting its application
in high alkali, high hardness and high temperature water quality environment.
The low molecular polymer corrosion and scale inhibitor has attracted the attention
of researchers at home and abroad with its green environmental protection, degradable and other properties.

1.
Low molecular polymer type scale inhibitor polyaspartic acid (PASP) is a
polyamino acid surfactant with carboxylic acid chain, which has both dispersion and chelation properties and can be biodegradable green corrosion and scale inhibitor, which can replace acrylic acid in many fields, and is a green multi-functional polymer material with development prospects, which has become a hot spot
for scholars at home and abroad.

Yan Meifang et al.
of Beijing Normal University formulated PASP, sodium gluconate, surfactant FFA and itaconic acid homopolymer into a multi-phosphorus-free water treatment agent
in a specific proportion.
Experimental studies show that the water treatment agent has a dynamic fouling thermal resistance of only 1.
92×10-4m2·°C/W through the synergistic effect of the composite components, and the corrosion inhibition rate of carbon steel is as high as 96.
96%.

The biodegradation rate after 28 days is 88%, which has good degradability
.

In addition, polyepoxysuccinic acid (PESA) is suitable for high hardness and high alkali water system, and has the advantages of
easy biodegradation and good scale inhibition performance.
Adding a very small dose of PESA has a good corrosion and scale inhibition effect, and can be compounded with other agents to form a low phosphorus or non-phosphorus scale inhibitor with better performance
.

J.
M.
Brown et al.
of Wardham College in the United Kingdom studied the scale inhibition performance of PESA on scales such as barium sulfate and calcium carbonate under static conditions, and simulated it with industrial circulating water
.
The experimental results showed that when the mass concentration of PESA was 10mg/L, the calcium carbonate scale inhibition rate reached 97.
7%; When the mass concentration is 2.
5mg/L and 1.
0mg/L, the barium sulfate scale inhibition rate is 100% and 94.
4%, respectively, showing the excellent static anti-barium sulfate scale and calcium carbonate scale performance
of PESA.
Kao Co.
, Ltd.
of Japan has also conducted experimental research on the application performance of PESA, and the experimental results show that the scale inhibition performance of PESA is significantly better than tartaric acid, polymaleic acid and polyacrylic acid, and has certain corrosion inhibition properties
.
Research by Xiong Rongchun of Beijing University of Chemical Technology and others also confirmed the same results
.

Zeng Defang of Wuhan University of Technology used acrylonitrile and NaHS aqueous solution as raw materials to synthesize β-mercaptopropionic acid in the laboratory, and synthesized S-carboxyethylthiosuccinic acid (CETSA)
after polymerization with anhydrous maleic anhydride.
The corrosion and scale inhibition properties of CETSA were tested by experiments, and the experimental results showed that CETSA had strong adaptability to the water quality of the treated water and had excellent corrosion and scale inhibition properties
.
CETSA is compounded with zinc sulfate, methenamine, sodium gluconate, HPMA, etc.
at a specific ratio, and the corrosion inhibition rate of the obtained product is 1.
82 times that of CETSA under the same conditions, up to 93.
2%, which is significantly better than the traditional phosphorus-based corrosion and scale inhibitors (PAPE, PBTCA and ATMPS, etc.
) when the concentration is 30mg/L.


Polyglutamic acid (LMPGA) is a polymer that can be produced by large-scale fermentation, soluble in water, has good corrosion and scale inhibition performance, and meets the requirements of
environmentally friendly water treatment agents.
Xu Hao of Xi'an Shiyou University and others used LMPGA made in the laboratory as the experimental object to study the performance of LMPGA in inhibiting calcium sulfate and calcium carbonate scale and its influencing factors
.
The experimental results show that when the comparable molecular masses of LMPGA are 7.
0×103 and 5.
0×103, its performance of calcium carbonate scale inhibition is similar
.
When LMPGA was added to the treated water sample, when its concentration reached 20mg/L, the scale inhibition rate was 88%, and the calcium carbonate resistance performance of LMPGA decreased
with the increase of pH, constant temperature temperature, constant temperature time and Ca2+ concentration.
LMPGA also has excellent calcium sulfate scale inhibition performance, in the SO42- mass concentration of 0.
3g/L, Ca2+ mass concentration of 0.
2g/L, LMPGA concentration of 10mg/L, its calcium sulfate scale inhibition rate can reach more than
90%.
At the same time, it also has good corrosion inhibition performance
.

2.
Composite scale and corrosion inhibitor
In recent years, scholars at home and abroad have researched and developed environmentally friendly water treatment agents
such as polyaspartic acid type, polyepoxysuccinic acid type, and polyglutamic acid type.
Although they all have a certain corrosion and scale inhibition effect at the same time, a single water treatment agent is often difficult to meet the requirements of scaling and corrosion in the daily water treatment system, so researchers compound a single compound with other agents to enhance its scale and corrosion inhibition effect
.

Hu Xiaojing of Hebei University of Technology et al.
synthesized a multi-component all-organic water treatment agent
using PESA, polyaspartic acid carboxyl-containing derivatives (PASP-ASP), sodium gluconate and itaconic acid homopolymer as raw materials.
The biodegradation resistance and scale corrosion inhibition properties of the water treatment agent were measured by electrochemical experiment, biodegradation experiment, scale inhibition experiment and rotary hanging piece corrosion experiment, and the corrosion effect of the specimen and the scale sample generated by electron microscopy scanning were observed
.
The experimental results show that the main corrosion inhibition mechanism of the composite water treatment agent is to inhibit cathodic polarization, which has excellent chemical biodegradation performance and excellent corrosion and scale inhibition performance
.

Zeng Defang of Wuhan University of Technology and others synthesized a new type of phosphorus-free scale and corrosion inhibitor
using PESA, zinc salt, hydrolyzed polymaleic anhydride (HPMA), D-sodium erythorbate and sodium gluconate as raw materials.
Its scale inhibition and corrosion inhibition performance was determined by static scale inhibition test and
rotary hanging piece corrosion test.
The experimental results show that when the mass concentration of the sample is 50mg/L, the scale inhibition rate and corrosion inhibition rate can reach more than
98% and 90%, respectively.
In another experimental study, Zeng Defang compounded sodium benzoate, dipropylamide-dimethylpropanesulfonic acid, sodium erythorbate, sulfamic acid, zinc salt and other substances according to the mass ratio of 5:8:10:10.
9:0.
7 to obtain the compounding product
.
When added to industrial circulating cooling water, when the mass concentration is 40mg/L, the scale inhibition rate and corrosion inhibition rate can reach 97.
37% and 90.
4%, respectively, with excellent scale and corrosion inhibition performance
.

Industrial production applications

In recent years, various environmentally friendly scale and corrosion inhibitors have been more and more widely used in various production practices, and have achieved good environmental protection and economic benefits
.

The phosphorus-free scale inhibitors ECH-337 and ECH-337A, developed by Wang Wei of China University of Geosciences and Shanghai Washba Technology Co.
, Ltd.
, have been successfully applied to the water treatment process of corrosive circulating water in
steel plants.
ECH-337 and ECH-337A were put into use at the same time, debugging was normal, running for 6 months, the system was operating normally, the effect was good, and there was no obvious scaling and corrosion
.
Due to the use of phosphorus-free water treatment agent, the cost of wastewater treatment and secondary pollution
are greatly reduced.

In foreign countries, there have been cases of the application of PASP to suppress corrosion caused by CO2 in oil production pipelines for a long time
.
Polyaspartic acid developed by Rohm & Haas of the United States has a very good corrosion inhibition and cleaning effect on the production equipment; Through application practice, Monsanto Company of the United States has shown that the polyaspartic acid developed by it has obvious effects
on corrosion inhibition of steel when the amount of addition is 3% (30 °C, pH=10).

Developed by Wuhan Petrochemical Plant Equipment Monitoring and Protection Center, the environmentally friendly water treatment agent ZH800WS has been successfully applied in its third circulating water field, which has brought good economic and environmental benefits
to the company.
The ZH800WS used in the plant is compounded by WLH-2 phosphorus-free corrosion inhibitor, fluorescent tracer, hydrolyzed polymaleic anhydride, acrylic acid/2-methyl-2-propenamido-propanesulfonic acid copolymer and other trace additives in a specific proportion
.

Development and prospects

In order to meet the needs of sustainable development of society, the research and development of water treatment agents for corrosion and scale inhibition will continue to develop
in the direction of phosphorus-free, efficient and biodegradable greening.

Environmentally friendly corrosion and scale inhibitor should first be implemented in the production of greening, to ensure that in the production process as little as possible to produce environmentally unfavorable raw materials, reagents, etc.
and minimize the impact on human health, the selected production process to first ensure the production of no harmful products or by-products, the impact on the environment to minimize the impact, from the source to control pollution
。 In order to meet the requirements of today's green and sustainable development, the following three points must be paid attention to: First, when designing molecular structures, priority is given to elements or functional groups with strong activity and easy degradation, such as ester branched chains, carboxyl groups, amino groups and selective insertion of oxygen-containing and nitrogen elements; Second, give preference to natural products such as polyepoxysuccinic acid, polyaspartic acid, etc.
as the main raw materials, in the process of synthesizing modified polymers, it is necessary to minimize the generation of by-products, as well as reduce the problem of secondary pollution in the production process to maximize the utilization rate of raw materials; Third, pay attention to the impact on the environment in the production process, improve the production process, and try to use clean production processes in the process of program design and improvement
.

In addition, in the process of developing and developing new high-efficiency and environmentally friendly non-phosphorus-free corrosion and scale inhibitors, the focus should be on reducing product costs to ensure that the cost performance of the developed phosphorus-free corrosion and scale inhibitors is significantly better than the current traditional phosphorus-based corrosion and scale inhibitors, which is also the focus and difficulty of research in this field for a considerable period of time in the future, once a breakthrough, it will greatly improve its market share, so that environmentally friendly phosphorus-free corrosion and scale inhibitors are more widely used and developed
.