Issue 7/2014 - Research progress on rare earth cis-butadiene rubber production technology

Research progress of rare earth cis-butadiene rubber production technology□ Yan Feng
rare earth cis-butadiene rubber self-adhesive good, excellent processing performance, in wear resistance, fatigue resistance, heat generation, aging resistance and rolling resistance and other aspects of better than traditional nickel, titanium, cobalt cis-butadiene rubber, the tire made of it, not only can save driving fuel consumption, but also can effectively reduce the probability of
car slippage and puncture phenomenon when braking, in line with high-performance tires in high speed, safety, The development needs of energy saving and environmental protection are the fastest growing cis-butadiene rubber varieties
today.

1.
Each component of the three-way
catalyst system composed of neodymium carboxylate / alkyl aluminum / chlorine-containing compound is soluble in the solvent, easy to measure and transport, which is conducive to the adjustment of the formula and the operation of the production process, so it is currently the only catalyst
used for industrial production.
The research and development of new catalytic systems is the focus of
current research.

Tian Lin et al.
, School of Chemical Engineering, Changchun University of Technology, used Nd2O3, (CH3)3SiCl and ethylene glycol dimethyl ether (DME) as raw materials to synthesize NdCl3·2DME complexes and used them to catalyze butadiene polymerization
.
The results showed that when n(Nd):n(AlR3):n(methylaluminoxane, MAO)=1:30:45 and the aging temperature was 50 °C, the CIS-1,4 content of the obtained polybutadiene was as high as 98.
7% (IR), while the total content of 1,4-structure was as high as 99.
6% (1H NMR).


Liu Xianguang of Dalian University of Technology et al.
used neodymium neodecanoate (referred to as Nd)/n-butyllithium (referred to as Li)/diethylaluminum chloride (referred to as Al) as catalyst for butadiene polymerization
.
The results show that the catalyst has the highest catalytic activity when c(Li)/c(Nd) is 12 and c(Al)/c(Nd) is about 15, and the polymer yield can reach 100%.

Under the conditions of 0 °C, c(Li)/c(Nd) is 12, and c(Al)/c(Nd) is 15, polymers with high cis-1,4-structure (molar content 97.
6%) and narrow molecular weight distribution (molecular weight distribution index 1.
23) can be
obtained.
With the increase of polymerization temperature, the activity of the catalytic system increases, and the relative molecular mass and molar content of the obtained polymer decreases
as cis -1,4-structure.

Qi Jun of Beijing Yanshan Branch of Sinopec introduced butadiene into the traditional three-way catalytic system neodymium carboxylate/alkyl aluminum/alkyl aluminum chloride to polymerize
butadiene.
The experimental results show that under the conditions of Al/Nd (amount ratio of substances) = 12~16, [Nd]=9.
0×10-5~1.
5×10-4mol/L, cis-butadiene rubber
with suitable Mooney viscosity value and cis-structure content greater than 98% can be prepared.

Jiang Liansheng and others of Changchun Institute of Applied Chemistry, Chinese Academy of Sciences invented a rare earth catalytic system and butadiene polymerization process
.
The rare earth catalytic systems selected are (A) neodymium carboxylate compounds, (B) alkyl aluminum hydride or trialkyl aluminum, (C) halogen-containing compounds, and (D) conjugated diolefins
.
The molar ratio between the components of the catalytic system is B:A=5~50:1, C:A=0.
5~5:1 and D:A=5~30:1; the aging temperature is 0~90 °C
.
The catalytic system can maintain homogeneous phase at room temperature for more than 54 hours, and the molecular weight of the obtained polybutadiene is unimodal distribution, the distribution index Mw/Mn=3~3.
5, and the cis content is greater than 97%.


2.
Relative molecular mass distribution adjustment
At present, the method of adjusting the relative molecular mass distribution is mainly to adjust the composition of the catalyst, and it can also be adjusted
by adding a fourth component.

Lu Guigen of Jinzhou Petrochemical Co.
, Ltd.
and others invented a rare earth cis-butadiene rubber molecular weight distribution adjustment process
.
The catalytic system used is: (1) neodymium compound or alkoxyneodymium compound Nd(RO)3, where R is isopropyl and isobutyl; (2) alkyl aluminum compounds or alkyl aluminum oxane compounds; (3) Halogen-containing compounds
.
The catalytic system and polymerization process provided by the invention can produce rare earth cis-butadiene rubber with different molecular weight distributions on the same production device, and the molecular weight distribution index Mw/Mn ranges from 1.
8~10.
0
.

Jiang Liansheng et al.
of Changchun Institute of Applied Chemistry, Chinese Academy of Sciences invented a method
for regulating the molecular mass distribution of rare earth cis-butadiene rubber.
The ternary rare earth catalyst composed of rare earth carboxylate (Ln), alkyl aluminum (Al) and chloride (Cl), when the Al/Ln molar is relatively low, adopts the unique feeding method of adding a small amount of butadiene (Bd) to participate in aging (Ln+Bd+Al) + Cl, and when initiating the polymerization of diolefins, the addition of alkoxyaluminoxane (MAO or MMAO) can effectively improve the catalytic activity and adjust the molecular mass and molecular mass distribution
.

3.
Li Bo of
Jinzhou Petrochemical Co.
, Ltd.
and others have developed a rare earth cis-butadiene rubber adiabatic polymerization production technology
.
The composition of the rare earth catalytic system used is: a branched neodymium carboxylate compound
of carbon atoms.
alkyl aluminum compounds; halogen-containing compounds; Monomer butadiene and solvent are adjusted to 0~40 °C by precooler and preheater into the polymerization kettle, the catalyst described above is added for butadiene cis-polymerization, after the polymerization is completed, the polymerization glue is added to the antioxidant through the termination kettle, and continuously enters the post-treatment process, and rare earth cis-butadiene rubber products
are obtained by agglomerating, drying and packaging.
The production of rare earth cis-butadiene rubber according to the above polymerization method can reduce energy consumption by 30%~40%.


4.
Body polymerization processThe
main advantage of the bulk polymerization process is to eliminate the refining and recovery process of the solvent used in the solution polymerization system, simplifying the process, reducing the cost, and is conducive to environmental protection and energy saving
.
Jinzhou Petrochemical Company used a rare earth homogeneous catalyst with chlorosilane as the third component for butadiene bulk polymerization
.
The characteristic viscosity of the prepared polymer is between 1.
0~1.
5, the polymer almost does not contain gel, the molecular chain structure of the product is regular, the content of cis-1,4 is greater than 97%, the average molecular weight is high, the molecular weight distribution is wide, and the strength of raw rubber is significantly higher than that of nickel-based cis-butadiene rubber
.

5.
Compared with the solution polymerization process, the
vapor phase polymerization process can eliminate the polymer coalescence and solvent recovery system, reduce investment and operation costs, and reduce environmental pollution
。 The development of highly active solid catalysts is one of the keys to this technology, and the supported rare earth catalyst systems mainly include: (a) rare earth carboxylate/alkyl aluminum (aluminoxane)/Lewis acid three-component supported catalytic system; (b) Hydrogen-modulated molecular weight and three-component catalyst with rubber reinforcing agent; (c) Modified π-allyl neodymium catalytic system
.
The results show that the silica-supported Nd(naph)3-Al(i-Bu)3-Al(i-Bu)2Cl catalytic system has quite high catalytic activity and stereoorientation, and its optimal composition is: n(Al): n(Nd)=40~60,n(Cl):n(Nd)=3~7
.
Adding an appropriate amount of monomer butadiene can multiply the catalytic activity
.
The relative molecular mass of the obtained cis-butadiene rubber is hundreds of thousands to millions, the gel content is less than 6%, and the cis-1,4-link content reaches about
98%.

6.
The traditional cis-butadiene rubber synthesized by Ti, Co and Ni catalysts by chain end modification technology does not have an active chain end due to the chain transfer and chain termination reaction of the active center to the monomer or solvent during the polymerization process, so it is difficult to improve the physical properties
of cis-butadiene rubber with chain end modification technology
.
However, the polymerization activity center of Nd-series catalysts is relatively stable and the life is long, which can continue to convert the re-added monomer or the second monomer into a polymer, and the relative molecular mass of the polymer increases
with the increase of conversion rate.
Using this quasi-active characteristic of Nd-series catalysts, chain-end modification technology can be applied to further improve the physical properties of the product and achieve high performance of
the product.
Huang Guiqiu of Guangxi Qinzhou University used rare earth catalyst for the polymerization of butadiene, and introduced phosphorus trichloride for terminal modification during the polymerization process, and found that when the relative molecular mass of polybutadiene was 13200, the modification temperature was 50 °C, n(PCl3)/n(Al(i-Bu)2H)=1.
0, and the modification time was 30min, the coupling efficiency of polybutadiene reached 38.
6%, and the coupling degree was 1.
47
.

7.
New product developmentLi
Yang et al.
of Dalian University of Technology invented a method
for synthesizing star-branched polybutadiene in a rare earth catalytic system.
The polymer has the structure shown in An-C, where A is the polybutadiene branched chain prepared by rare earth catalyst, C is the astrobranching agent residue, the astrobranching agent is an epoxy compound, n is the degree of branching, and n is greater than or equal to 3; The weight-average molecular weight of star-branched polybutadiene is 10×104~100×104, and the weight-average molecular weight of polybutadiene branched chain A is 5×103~20×104;cis structure 1,4- content (wt%) is 80%~98%, 1,2-polybutadiene and trans structure 1,4-polybutadiene content sum (wt%) is 2%~20%.

The prepared rare earth polybutadiene rubber has the characteristics of
star branching and high cis-structure.

Cai Hongguang et al.
of Changchun Institute of Applied Chemistry, Chinese Academy of Sciences invented a method
for preparing liquid polybutadiene rubber using a sulfonic acid rare earth catalyst 。 The catalyst is composed of binary components, rare earth organic sulfonic acid compounds are the main catalysts, and alkyl aluminum is the co-catalyst; There is no need to add a third component during the catalyst preparation process, which improves production efficiency; The solvent replaces benzene, toluene, xylene, etc.
with hexane, which reduces the harm of toxic solvents to people and the environment, and reduces the production cost caused by solvent recovery treatment; In addition, the polymerization process is gentle and stable, and there is no need to add a heat withdrawal device; Liquid polybutadiene rubber
with a monomer conversion rate of > of 90%, a weight average molecular weight of 8800~22000, and a molecular weight distribution index of 4~6 can be obtained by polymerization.

8.
Conclusion Although the development of polymerization butadiene of
rare earth catalysts in China is relatively early, there are still problems such as
the high amount of catalyst used, the single means of adjusting the relative molecular mass of polymers (mainly alkyl aluminum), the large amount of alkyl aluminum and the viscosity of cis-butadiene rubber solution.
In the future, we should increase the research and development of new catalysts, explore the formation mechanism of active centers, improve the efficiency of rare earth catalysts, and reduce costs.
In terms of polymerization process, the development of
new process technologies such as butadiene gas phase polymerization process and bulk polymerization should be accelerated.
In addition, new grades with unique properties should be actively developed through coupling modification, end group and cyclization modification, so as to further improve the physical-mechanical properties of the product and its compatibility with reinforcing materials such as silica, so as to meet the needs of green tire development and meet market demand
.