titanium dioxide production

Two Titanium Dioxide Production Processes: Sulfate And Chlorination

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Titanium dioxide is an important pigment widely applied in different industries, such as ink, coatings,masterbacth, PVC, paper, and cosmetics. knowing the titanium dioxide production process is key to understand the complex and accuracy in the production of titanium dioxide. We will get idea of different steps of process needed in the production. By understanding this process, we can better value the importance of titanium dioxide in various applications.

Two Production processes of Titanium Dioxide

There are two different production process of titanium dioxide, which are the production process of chloride method and the production process of sulfuric acid method.By sulfuric acid process, titanium powder will be reacted with concentrated sulfuric acid to get titanium sulfate. With hydrolyzation, metatitanic acid can be generated. Then with calcination and crushing, titanium dioxide can be obtained. Both Rutile and Anatase titanium dioxide can be produced in this way.

There are several advantages by sulfuric acid process. Its raw material is ilmenite and sulfuric acid, and they are easy to get. Its production technology is relatively mature which requires simple equipment.Also its anti-corrosion materials are easy to handle. But sulfate process also has some disadvantages. Its production process is long and can only be operated intermittently. It is by wet method operation which costs high consumption of water and sulfuric acid. There are various wastes by-products which may lead to pollution to the enviroment.

By chlorination process, rutile or high-titanium slag powder are mixed with coke. And titanium tetrachloride can be produced by high-temperature chlorination. With  oxidization at high temperature, titanium dioxide can be obtained after filtering, washing, drying and crushing. And only rutile type titanium dioxide can be produced by chloride process.

Chlorination process also has advantages. Its production process is short, continuous automation is high, the production capacity can beexpand easily, and its energy consumption is much lower. Three wastes are lower,  but higher quality products can be produced. But it also has some disadvantages. It requires high investment, complex equipment, higher quality raw materials. Its material also needs good resistant to high temperature and corrosion. The maintenance of the device and R&D is difficult.

Titanium dioxide

Titanium Dioxide by Sulfate Process

The sulfate process is mainly grouped into five steps: preparation of titnaium ore or titanium slag; preparation of titanium sulfate; preparation of hydrated titanium dioxide; calcination of hydrated titanium dioxide; after-treatment of titanium dioxide.

The above five steps includes following segments: drying, magnetic separation and grinding, acid hydrolysis, purification, concentration, crystallization and hydrolysis, water washing, bleaching and washing after bleaching, salt treatment, calcination,  dispersion and classification of titanium dioxide, inorganic surface treatment, water washing, drying, airflow crushing and organic treatment, packaging, recycling, by-products treatment and utilization. Various types of titanium dixoide such as anatase, rutile, and enamel type can be obtained through the sulfuric process.

Main segments in sulfate process production process

Acid hydrolysis. The titanium slag or dryilmenite is acidolyzed with concentrated sulfuric acid at a temperature of 150-180°C.The higher dilution of sulfuric acid is used when the ilmenite has lower titanium content. 85% of sulfuric acid concentration is suitable for treatment of rock ore; while 91-92% of sulfuric acid concentration is suitable for treatment of titanium slag. In the acidolysis process, ferric iron needs to be turned into ferrous iron.

Ferric iron is easy to be adsorbed on the surface of titanium dioxide particles, which will lead to the lower whiteness titanium dioxide.So it is quite important to maintain iron in a divalent form in the production process. Also the acid hydrolysis will produce the most of the air pollution. During the reaction, a big amount of acid mist, sulfur oxides, and unreacted raw material particles are produced in a short time.

Sedimentation and filtration. The cooled acidolysis solution, solid inert substances and unreacted raw material residue solution will be transfered from thebottom of acidolysis tank into the settling tank. Itspurpose is to remove soluble residues caused by titanium ore impurities.

These residues may include zircon,sulphate,  silica, rutile or leucolite. By adding starch, casein, or other organic flocculants, the liquid settles in the settling tank with simple gravity decomposition. First the solid matter is removed from the tank. Then raw materials will be recovered with washing of waste acid. Also the residual liquid will be washed by water. With fine filtering, the residual particles will be removed from settled titanium solution. These residues and other solids collected in the settling tank will be delivered to the storage yard.

Hydrolysis.Water-insoluble hydrated titanium dioxide precipitate or metatitanic acidcan be obtained with the hydrolyzation of soluble titanyl sulfate at 90°C. To getqualified hydrolyzed products at required particle size,the heating rate, ferrous ions content, tetravalent titanium ion content and other factors of titanium liquid need to be strictly controlled. The control of ferric ions is the key in this process. During rehydrolysis,crystal seeds is necessary to be added to control the hydrolysis rate, the filtration and washing performance. This can make the final product with better fineness and other quality indicators.

Seeds can be added in two ways: self-seeding and external seeding. The self-seeded crystal added during the carry out of the hydrolysis process and no additional preparation of the crystal seed is required. External crystal seed is to add rutile or anatase seed crystals to the titanium solution. Adsorbed iron and other metals can be removed under acid-leached with sulfuric acid after the hydrolyzed sediment slurry is filtered and washed. It is also referred as bleaching. This is the main step for causing waste acid in the sulfuric process.

Calcination.At 900-1250°C,the hydrated titanium dioxide is calcined. During the  calcination process, water and sulfur trioxide can be deducted. At the same time, anatase titanium dioxide can be transformed into the rutile type. Calcination can determine the particle size of the final titanium dioxide and enhance the chemical inertness. Titanium dioxide is grind into particles and then will be after-treated. In the calcination stage, some fine titanium dioxide particles are entrained with the discharge of sulfur trioxide and acid mist. This is the main source of waste gas in the sulfuric process.

After-treatment. After treatment process has following aspects:wet grinding, inorganic coating, drying, jet milling, and organic coating.

 

Different Stages In After Treatment Process

During wet grinding, titanium dioxide particles will be dispersed together with organic or inorganic dispersants. The aggregated titanium dioxide particles have to be depolymerized as much as possible, which can facilitate the inorganic coating. Wet milling equipment mainly includes ball milling machine, sand mill, dense medium mill, organic ball mill, etc.

After wet grinding and depolymerization, titanium dioxide needs to be treated with inorganic coating. This can shield ultraviolet light and strengthen its weather resistance. Inorganic coating agents are aluminum oxides, silicon oxides, water and hydroxides. In recent years, zirconium has been adopted for mixed coating to achieve better gloss and weather resistance. In drying process, a belt dryer or a spray dryer is used.

After inorganic coating, jet crushing and organic coating is made. Flat airflow pulverizers are commonly used currently. Different organic coating agents are added in this process. On the one hand, organic coating can help in neutralizing the surface energy of titanium dioxide to avoid its re-agglomeration. On the other hand, it can change the physical and chemical properties of titanium dioxide, which help improving its compatibility in the paint and plastics formulation. In paint application, amines, alcoholamines, and silanes are used for organic coating. In plastics application, dimethylsilane, polyethanol, and triethanolamine are used.

titanium dioxide production

Chlorination production process of titanium dioxide

Chlorination production process of titanium dioxide are as follows:  preparation of raw ore,  preparation of titanium chloride, titanium chloride, titanium dioxide surface treatment. It includes following segments: ore coke drying, ore coke crushing, chlorination, titanium chloride refining,oxidation of titanium chloride , dispersion and classification of titanium dioxide, inorganic surface treatment, water washing, drying, air crushing and organic treatment.

Differnt Segments in the Chlorination production process

Chlorination section

Titanium ore will be added into the boiling furnace from the boiling layer with certain proportion of petroleum coke. The circulating chlorine gas back from the oxidation process will be added in from the bottom of the furnace. This reaction is carried out at 925~1010℃ in a continual process. TiO2 and oxides of iron, silicon, alum, calcium, magnesium and other metals are transformed into corresponding chlorides. They will get out of the chlorination furnace with gas. The reaction gas needs to go through the cyclone separator.

And unreacted solid dust and non-volatile chloride in the reaction gas will be separated. After cooling and condensing, the ferrous chloride is separated first, and then ferric chlorine is separated. After this, low-boiling titanium tetrachloride (containing silicon tetrachloride and alum trichloride, etc.) will be collected by using cold titanium tetrachloride spray. After mud removing, crude tetrachloride is obtained. Crude titanium tetrachloride will be made into high-purity refined titanium tetrachloride by removing low-boiling impurities such as silicon tetrachloride.

Oxidation Section

the oxidation reactor needs refined titanium tetrachloride preheate, oxygen preheated, nucleating agent and crystal transformation accelerator to react in it. The initiation temperature of the oxidation reaction is above 800 °C. The main reaction is generally processed at 1300-1800 °C. The airflow from the reactor (entraining the titanium dioxide particles generated by the reaction) is quenched with low-temperature circulating chlorine gas to below 700 ° C, and then cooled to 200 ° C through the pipeline along the way, and the titanium dioxide is gradually separated from the cyclone separator and bag collector The chlorine gas is separated, and the titanium dioxide is sent to the post-treatment process after dechlorination treatment.

Post-processing stage

The post-treatment section includes following process: beating, grinding, chemical preparation, surface treatment, filtration and washing, spray drying, micro-grinding and packaging. Following are the details.

After oxidation process , the TiO2 powder will get into the beating tank. Dispersant and desalted water are measured and put into the beating tank. The qualified slurry will go to the grinding process.

After beating, the slurry enters into sand mill’s feedtank and get redispersion. By the feed pump, the slurry gets into sand mill. It will be ground to slurry with particle size less than 1 μm. After grinding, the slurry will go to the storage thank of sand mill. It will be pumped in the classifier as per different grades. The coarse material gets back to sand mill again. The fine material gets to the surface treatment tank.

After measuring, the slurry comes into the surface treatment tank. Different surface treatment agents are added in to the slurry. After the reaction, it goes into the filtration process.

The treated slurry gets pumped into the suction tank. In the suction tank, the leaf filter is vacuum-filtered . After the film loads up, the bridge crane get up the leaf filter. It is put into desalted water for washing. After it meets the requirement, the bridge crane gets up the leaf filter and unloads the slurry in the discharge tank.

The powder will go into airflow conveying system. At the entrance of the airflow mill, a pump delivers the powder. After adding crushing aids, the powder will get crushed into an average particle size of around 0.3μm. The bag filter separates the entrained TiO2 powder. The powder cools down by the air and gets seperated by cooling cyclone. The air flows out of the bag filter and goes into the atmosphere through the big fan. After the cooling cyclone and bag filter, the Tio2 powder gets into packaging process.

The TiO2 finished product comes into the screw conveyor. And it will go into the finished product warehouse. The package of TiO2 is 25 kg/bag or 1000 kg/bag by packaging machine as per customer needs

 

The Current Capacity Situtaion For Two Processes

Chloride process of titanium dioxide is the development trend. The chlorination method and the sulfuric method will exist together for a long time. Instead of a substitute relationship, they are complementary. In china, the total capacity of Chloride titanium dioxide from China is around 40MT. And the total capacity of sulfate titanium dioxide in China is 3.3million MT. The production capacity of chloride titanium dioxide increases in recent 10 years. The producers of chloride titanium dioxide in China has increased from 1 producer to 5 producers.

 

We have stated about the two different production process and each section of the titanium dioxide production process. It provides the chemical transformations and equipment involved in different process. And you will get a clear idea about the quality control of titanium dioxide.

Silicone-oil-factory

How is Silicone Oil Manufactured? A detailed Overview.

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You might have heard the phrase “We are living in a plastic world” because plastic is everywhere, incorporated into almost every aspect of our lives. Here at Hengyi Tek, we have our phrase “We are living in a silicone world”, silicone has been an integral part of our daily chores such as using silicone chips in our computers and automotive vehicles. Silicone has an excellent reputation for its existence in various physical forms which gives it a headstart over its counterparts. Silicone exists in the solid state as the general public knows it. Silicone also exists in the gel-like material such as in silicone implants. The last known physical state of silicone to a common is liquid silicone which is often termed silicone oil or silicone fluid. Although it is not commonly known that silicone also exists in liquid form, the uses of silicone oil or silicone fluid are very crucial and are used in several industries.

You might be pondering about the manufacturing process of silicone oil, but before that, it is a must that we talk briefly about the uses of silicone oil and its properties. Silicone-oil-factory

 Let’s discuss the later part first, the properties of silicone oil:

Properties:

The linear structure of silicone fluids (polydimethylsiloxanes) is primarily responsible for all the beneficial properties exhibited by them.

High Molecular Weight:

It is one of the very few materials which maintains a liquid consistency at such high molecular weight making it useful.

Stable Viscosity-Temperature profile:

High molecular weight and the linear structure helps silicone oil maintain a constant or minor change in viscosity over a wide range of temperatures. This is one of the most important properties which makes it the best for various uses.

Thermal and Oxidative Stability:

Silicone oil is semi-inorganic which makes it somewhat resistant to thermal degradation and oxidative degradation. While organic fluids are particularly prone to both kinds of degradations.

Doesn’t absorb UV and X-Rays:

Silicone oil is also used in the medical and healthcare industry so this property of inability to absorb UV and X-rays comes in handy while being used in medical settings.

Low Surface Tension:

This property is of particular importance for its use in various industries.

Low Vapor Pressure.

Low Volatility.

High Flash and Ignition Point.

High Specific Resistance.

Water Insolubility.

Dielectric Properties.

Now that we have discussed the properties briefly, let’s move on to discuss the uses of silicone oil in brief:

Uses of Silicone fluid: 

The properties mentioned above provide silicone fluids with the liberty of usage in several industries. Silicone fluids are used as lubricants and release agents in their pure forms. The use of silicone oils as lubricants has been around for a while, especially in hydraulic aircraft engines. The food industry owes a bundle of thanks to silicone fluids as it is used as releasing agent in cooking sprays and for baking purposes. The textile industry has also seen a major boom in the use of silicone fluids for smooth touching in fabrics. The paint industry is also one of those reaping benefits from this magical fluid.

How to Manufacture Silicone oil?

Before diving into the exact process of how silicone fluids are made. We must develop an understanding of the structure of silicone and its various compounds. Commonly used Silicones are polymeric compounds of silicone having a silicone-oxygen chain with both of these at alternating positions (Si-O-Si), this alternating chain of silicon and oxygen atoms makes up the backbone of Silicone compounds.

Silicone-oil-in-glass-jar

Depending upon the extent to which a silicone compound can bear functional groups, they can be classified as monofunctional, difunctional, trifunctional, and tetrafunctional. The structural formulas for all of them are given below:

Monofunctional Silicone Compounds:

They are also known as end groups. The degree of Polycondensation and viscosity of the polymer depends upon the monofunctional group present in organo-poly siloxane which limits the chain length affecting these parameters.

Molecular Formula:                              R3SiO1/2

Starting Silane:                                     R3SiCl

Difunctional Silicone Compounds:

Difunctional functional groups tend to have a higher degree of molecular chains.

Molecular Formula:                                  R2SiO2/2 

Starting Silane:                                         R2SiCl2 

Trifunctional Silicone Compounds:

These often tend to produce 3-D structures which are cross-linked.

Molecular Formula:                                  RSiO3/2 

Starting Silane:                                         RSiCl3 

Tetrafunctional (Quaternary) Silicone Compounds:

Molecular Formula:                                  SiO4/2 

Starting Silane:                                         SiCl4 

Mono and difunctional silicone compounds are the primary components for linear chain silicone oils, so our discussion will be limited to these two.

Another categorization of organosilanes is based on the type of substituent (R) present in the structure of the silicone oil.

Dimethyl Siloxane: 

When methyl (CH3) is present as a substituent on two positions in a linear chain of siloxane, it is called dimethyl siloxane or dimethyl silicone oil. The majority of organosilanes have dimethyl silicone in their structure. Trimethylsilyl-terminated dimethylpolysiloxane is also a major contributor to organosilanes.

Some other types of methyl silane are considered important such as

Methylhydrogensiloxanes:

This type of silicone has hydrogen in place of one of the methyl groups present on the difunctional unit.

Phenymethylsilicone Fluids:

The methyl group present in the backbone of dimethyl silicone is replaced by phenyl groups. They tend to show somewhat different extents of properties

Different properties can be achieved by changing the proportion of phenyl to methyl groups present on the backbone of silicone oil structures.

There are a lot of modifications that can be incorporated into the alternating silicone oil backbone and there is a significant number of silicone oils that are produced each year.

Glycolfunctional Siloxanes are another modified silicone that is water soluble, their silicone backbone contains glycol chains consisting of ethylene oxide or polyepoxide.

The use of silicone oils in the aqueous environment depends upon what kind of bonding they have for silicone with adjacent atoms. Bonds can be formed between silicone, oxygen, and carbon such as Si-O-C, these types of bonds are subjected to hydrolysis, also the bonds can be formed between silicone and carbon such as Si-C, the best property exhibited by this type of linkage is that they are unsaponifiable.

The procedure for the production of Silicon Fluids/Silicone Oil: 

We have already stated that our focus in this article will be the production method or manufacturing method of dimethyl silicone oil as it is one of the basic and most important forms. 

There are a few basic reactions that take place in the production of dimethyl silicone fluids, these reactions are considered to be of fundamental importance in all organo-silicone compound chemistry.

Silicone-oil-manufacturing

Before going into details of all these fundamental reactions, let’s list them all:

‌Müller-Rochow Synthesis

‌Hydrolysis, Methanolysis, Condensation

‌Polymerization Reaction

‌Equilibration Reaction

Transesterification Reaction

Hydrosilylation Reaction

Direct Synthesis Reaction

Now Let’s discuss all of them in a little detail:

‌Müller-Rochow Synthesis

Methylchlorosilanes are produced with the help of this reaction. These are cheaper to produce in terms of finances. Silicone and methyl chloride (in gaseous form) are primarily required for the reaction. A high temperature of 260-320°C is required with the presence of copper as a catalyst. Reactions take place in a gas/solid state. The equation of the above-said reaction is shown below, and it leads to the production of dimethyldichlorosilane as follows:

Si + 2CH3CI → (CH3)2SiCl2

‌Hydrolysis,methanolysis, and Condensation.

These three steps take place after the synthesis of organocholosilanes. Hydrolysis and methanolysis generally take place before condensation; both have organocholosilanes as their targets. After hydrolysis and methanolysis, the next step is condensation which leads to silane production. During these three processes, the acid chloride of silicic acid reacts with water and methanol. Details of the reaction are given below in the following:

(CH3)2SiCI2+ 2H2O→(CH3)2Si (OH)2 +2HCI 

n(CH3)2Si(OH)2→HO一[(CH3)2SiO]n一H + (n一1) H2O

nSi + 2nCH3OH →rnHO一[(CH3)2SiOH]x一 f (n一rn)H20 

The above reaction depicts the condensation of dimethyl dichlorosilanes after hydrolysis had already taken place. During this reaction, the elimination of water from silanol groups results in the production of high molecular siloxanes. The biggest drawback of hydrolysis reaction is that it results in a considerable amount of HCL gas production which leads to pollution. Methanolysis, on the other hand, is pollution free in this regard and fact more economical because the chlorine produced can be reused in the production of methyl chloride. 

Polymerization Reaction:

Out of many ways to produce silicone oils, one is called the polymerization reaction. As the name suggests, polymerization reactions result in the production of high molecular linear polysiloxanes from those siloxane rings which are free from hydroxyl groups.

Equilibration Reaction:

It is one of the mega players in the production of silicone fluids. The main goal of the reaction is to homogenize the siloxane mixtures which have a different molecular weight. This reaction is catalyzed in such a way that the final siloxane mixture is a gaussian molecular weight mixture. Silicone fluids with desired viscosity can be drawn out using an equilibration reaction and also stable uniform distribution can be achieved using this reaction.

Direct Synthesis Reactions:

In this type of synthesis, the reactants are either silicone or SiH containing silanes and chlorobenzene. After silicone and chlorobenzene react to produce phenylchlorosilanes which are repeatedly hydrolyzed to produce silicone oil.

Hydrosilylation reaction: 

It is a catalytic reaction in which noble metals act as a catalyst and they add ω-terminated olefinic molecules to SiH silanes.

Transesterification Reaction: 

Alkosilyl groups are transesterified by a silanol group-containing siloxanes which yield silicone oil.

Insertion Reactions are also one way to produce silicone oil.

All these processes can be used to produce silicone oil. Some of them are more economical and more frequently used but that is not our concern for today.