CATALYTIC PROCESSING OF YELLOW PHOSPHORUS

 Development of “non-chlorine” synthetic methods of phosphorus derivatives directly from yellow phosphorus is one of priority problems of chemistry of phosphorus compounds and engineering chemistry in connection with increase of requirements of ecological purity and effectiveness of industrial processes. This problem is especially relevant for Kazakhstan as the largest producer of yellow phosphorus in the CIS. Phosphorus is one of the major industrial products with an extensive range of application. Phosphorus-containing derivatives are characterized by a huge variety of structures and properties, and they play a major role in the vital developments and exchange. For example, acids of phosphorus are applied in inorganic and organic synthesis, as reducers, in production of heat-resistant plastic, fodder and technical phosphates, in food, medical and military industry, synthetic scours, and esters of phosphorus acids found broad application as softeners, fire retardants, solvents, complex formers, heat carriers and efficient extragents of rare and transuranic elements.

The production of yellow phosphorus is based on reduction of phosphorites or apatites by coke in the presence of silicon dioxide in electric furnaces at 1300-1500 ^оC. Its main global manufacturers are the USA, Germany, Netherlands, and Canada. Today world production of phosphorus (without the CIS countries) makes about 1 million tons per year. Kazakhstan is included into quintuple of countries which possess 90% of world reserves of phosphorus, and also possesses the richest reserves of phosphorus-containing raw materials on the basis of fields of the basin of Karatau (South of Kazakhstan). The phosphoric branch of Kazakhstan provides 34,1% of production of chemical industry of the Republic (without production of petrochemistry) and the problem of increase in production of phosphoric and phosphorus-containing production is considered one of key for Republic economy.

In Kazakhstan the phosphoric branch is presented by the Kazfosfat LLP, Khimprom-2030 LLP, Kazazot LLP and JSC Reaktivnye fosfornye soli enterprises and about 100000 tons of yellow phosphorus are annually produced, and its export makes about 70%. The phosphoric industry of RK has the finished production cycle from extraction of phosphate rock to electric thermal production of phosphorus. In the late sixties for processing of the richest fields of phosphorites and coal in Kazakhstan three phosphoric plants were constructed and the Republic took the third place in the world on production of yellow phosphorus and its compounds.

The technological complex at these phosphoric enterprises begins with extraction of phosphoric ore, its processing and comes to an end with release and realization of ready raw materials and production for the chemical companies and consumers. The main part of all produced yellow phosphorus (~ 90%) is used for obtaining of phosphorus pentoxide (P₂O₅) and the thermal phosphoric acid applied in production of various phosphoric fertilizers and different phosphates. Production of yellow phosphorus is bound to formation of a large number of toxic waste, such, for example, as kiln gas, phosphoric slags and phosphoric slimes from products. Kiln gas has a high calorific value (~ 3000 kcal/m³) and can be applied as technological raw materials and synthesis of various organic compounds. However because of availability of harmful impurity, such as carbon oxide, hydrogen, toxic fire-dangerous and explosive corrosively active impurity of phosphorus-, sulfur-, fluorine-containing compounds, kiln gas is not used and incinerated. Electro-thermo-phosphoric slags are close on structure to metallurgical slags and thanks to the high content of oxides of calcium and silicon can be used in production of construction materials.

The traditional technology of organophosphorus compounds production is based on oxidation of yellow phosphorus by chlorine with the subsequent phosphorylation of an organic substrates by chlorides (PCl₃, PCl₅) and oxychlorides of phosphorus (POCl₃). The multistage commercial process is followed by liberation of a large amount of hydrogen chloride that causes padding expenses on its neutralization and reduces yield of phosphorus-containing products and also creates serious environmental problems.

On the level of the modern achievements and scientific prospects the modern chemistry of phosphorus can be compared to carbon chemistry. As a starting material for the industrial production of valuable acids of phosphorus and esters on their basis serves rather cheap and available yellow phosphorus (P₄). The selection opening of the tetrahedral molecule P₄ and its immediate functionalization gains the increasing value in connection with searching of new pollution-free processes of phosphoric products obtaining. The analysis of scientific and patent literature demonstrates that in recent time research teams in Russia, Germany, Italy, France and USA are engaged in development of scientific bases of such processes. They use various approaches, first of all, application of complexes of the transitional metals as platforms for activation and transformation of the P₄ tetrahedral molecule, chemical and electrochemical methods and also methods of external impact on a phosphorus molecule in the form of X-ray radiation, mechanical or ultrasonic processing. Despite the considerable achievements in coordination chemistry of yellow phosphorus, catalytic reactions with its participation are considerably less investigated.

The first example of a metal complex catalysis of organic reactions of yellow phosphorus was oxidizing reaction of P₄ by oxygen with formation of trialkylphosphates in alcohol-arene solutions of copper(II) chloride, discovered in laboratory of a homogeneous catalysis of D.V. Sokolsky Institute of organic catalysis and electrochemistry (IOCE, Almaty) by professor Dorfman Ya.A. with co-workers. They carried out systematic studying of the processes of a catalytic functionalization of yellow phosphorus based on interaction of elemental phosphorus with water, alcohols, amines and phenol in the presence of such oxidizers as oxygen, peroxide compounds, water and the various polar and non-polar solvents accelerated by individual and mixed catalysts on the basis of transitional metals complexes.

Scientists of laboratory of homogeneous catalysis of D.V. Sokolsky IOCE develop theoretical and applied aspects of reactions with participation of compounds of low-valence phosphorus and also catalytic ways of transformation of yellow phosphorus and wastage of its production in valuable inorganic and organic compounds for a number of years. In 1991 on the Jambyl JSC Khimprom the catalytic technology of obtaining pure carbon dioxide and ammophos from kiln gas of phosphoric production was tested. Impurity of sulfur- and fluorine-containing chemicals were caught by an alkaline solution, and phosphorus and phosphine were oxidized in catalytic copper-ammonia solution to inorganic phosphates.

In laboratory the new catalytic technology of organophosphorus compounds obtaining from elemental phosphorus and wastage of phosphoric production is developed. Use of catalysts allows replace toxic oxidizer chlorine with ecologically safe oxygen of air, to carry out process of oxidizing phosphorylation of an organic substrate to one stage and to use not only yellow phosphorus, but also phosphides of the transitional metals and hydrogen, polymeric red phosphorus, hypophosphites, arene extracts of poor phosphoric slimes. Withdrawal of yellow phosphorus from the commercial run significantly increases ecological safety of phosphorus compounds production. When using as organic substrates aliphatic alcohols C₁-C₅ in catalytic process with high yield and selectivity forms esters of phosphoric acid.

Trialkylphosphates are valuable organophosphorus compounds which are widely used as softeners, additives to fuels and lubricants, fire retardants and extragents necessary for complex processing of ores of rare, noble and radioactive metals. The integrated bench tests of a catalytic way of organophosphorus compounds obtaining from yellow phosphorus and alcohols allowed to offer the process flow diagram and to carry out pilot tests on the D.V. Sokolsky IOCE trial base. During tests the possibility of safe exercise of direct catalytic synthesis of tributylphosphate from P₄ and butanol in the soft conditions on a standard chemical processing equipment was shown.

Studies of oxidizing P-O coupling of low-valence phosphorus compounds with alcohol is a scientific basis for development of innovative catalytic processes of obtaining valuable element-organic compounds directly from products of the phosphoric industry.

         The recent scientific trend developed by Kazakh scientists – the functionalization of inorganic compounds of elemental and low-valence phosphorus, – attracts great interest of scientific community what successful realization together with scientists of Russia, Italy, France, Germany international projects, supported by the Soros funds testifies to (MY1000, 1994-1995), USAID (TA-MOU-CA13-041), INCO-Copernicus (ERB IC15-CT96-0746, 1997-2000), INTAS (00-00018, 2001-2004), ISTC (K-754 p, 2001; K-1284, 2006-2007) and leading European enterprises of the European Union as BASF AG (Germany) and Thermphos International (Holland).

The works of the Kazakh scientists of laboratory of a homogeneous catalysis were also performed according to programs of the basic researches conducted in D.V. Sokolsky IOCE since 1997 till present on subjects 05.H “New catalytic reactions with participation of phosphine, phosphorus, alcohols, olefins and other organic compounds as a basis of creation of new high technologies” (No. state registration 0197PK00487, 1997-1999), F.0184 “Ecologically safe catalytic syntheses of the organophosphorus derivatives from compounds of elemental and low-valence phosphorus” (No. state registration 0100PK00100, 2000-2002), F.0287 “Theoretical bases of catalytic processes of organophosphorus compounds obtaining from phosphorus and phosphides” (No. state registration 0103PK00320, 2003-2005), F.0354 “Scientific bases of eco-efficient catalytic syntheses of the element organic compounds from sulfur, derivatives of phosphorus and alcohols” (No. state registration 0106PK00452, 2006-2008), F. 0500 “Creation of scientific bases of ecologically optimized catalytic processes of organic phosphates and phosphites obtaining from yellow phosphorus” (No. state registration 0109PK00442, 2009-2011).

For the last 20-30 years there was a quantum leap in phosphorus chemistry. The searching of high performance of synthetic methods of phosphorus compounds which is carried out for a long time in many scientific centers of the world led to opening of a large number of new reactions and regularities of chemical behavior of phosphorus in relation to reagents of various nature were determined. The greatest development got direction on development of activation methods of yellow phosphorus in the coordination sphere of transitional metals complexes. In world scientific literature there are data by results of scientific research in coordination chemistry of yellow phosphorus and on reactions of P₄ with nucleophilic and electrophilic reagents in the conditions of chemical, electrochemical and catalytic activation.

Now the modern phosphoric industry has deficiency of qualitative and diverse phosphorus-containing production. In spite of the fact that in Kazakhstan phosphate rock is extracted and production of yellow phosphorus is arranged, production of acids of phosphorus and esters on their basis directly from P₄ is absent. Development of the alternate “non-chlorine” processes of synthesis of phosphorus inorganic and organic compounds directly from yellow phosphorus is important relevant task which will allow solve economic problems in the petrochemical, mining industry and agriculture by expansion of the range of phosphoric production and environmental problems because of constantly becoming tougher requirements to environment protection. At the same time, the catalysis of organic reactions of P₄, as well as catalytic chemistry of yellow phosphorus in general, still remains poorly studied area.

For the last 20-40 years the problem of activation and transformation of the P₄ molecule found the reflection and development in basic researches of a number of the known scientific centers, such as A.E. Arbuzov Institute of Organic and Physical Chemistry of the KazanSC of RAS (Sinyashin O.G., Budnikova Yu.G.), A.E. Favorskii Irkutsk Institute of Organic Chemistry of the Siberian Branch of the Russian Academy of Science (Trofimov B.A., Gusarova N.K.), “Institute of Inorganic Chemistry” at the University Cologne (Baudler M.), Technical University of Kaiserslautern (Sherer O.-Y., Sitzman H.), Institute of Organometallic Compounds (Sacconi L., Peruzzini M.), University of Florence (Stoppioni P.), Massachusetts Institute of Technology (Cummins C.C.).

Despite particular achievements in the field of coordination chemistry, chemical and electrochemical transformations of the molecule P₄ in the presence of various nucleophilic and electrophilic reagents, nevertheless poor attention is paid to oxidizing inorganic and organic reactions of P₄ in the catalytic mode, to the description of their kinetics and the mechanism, identification of the nature of catalytically active intermediates.

Now the Kazakh scientists from al-Farabi of Kazakh National University deal with a problem of searching of the alternate “non-chlorine” ways of yellow phosphorus transformation to valuable phosphorus compounds. Their works were performed according to programs of fundamental and applied researches in the period of 2015-2017 in Research Institute of New Chemical Technologies and Materials on a subject 3662/GF4 “Development of catalytic processes of oxidation and hydrogenation for the organic compounds obtaining from yellow phosphorus, alcohols and unsaturated hydrocarbons” (No. state registration 0115PK01013) and the Center of Physico-Chemical Methods of Research and Analysis for a subject 3444/GF4 “Scientific bases development of phosphorus-containing compounds obtaining on the basis of technogenic mineral raw materials” (No. state registration 0115PK00515).

For inclusion of Kazakhstan into number of the most developed states with competitive economy the President N.A. Nazarbaev set the task to create and develop the productions focused on export, joint ventures in the field of oil and gas and transport mechanical engineering, metallurgy, chemistry, and agrarian sector. As the main priority of long-term and stable development of Kazakhstan strengthening of competitive positions of chemical industry in the internal and external markets with use of scientific and technical capacity of branch would serve. On new height the chemical branch will be lifted by expansion of the range and improvement of consumer properties of socially oriented production, ensuring need for materials of strategic appointment.

 Doctor of Chemistry, associate professor,

Chair of physical chemistry, catalysis and petrochemistry

Department of chemistry and engineering chemistry

Al-Farabi Kazakh National University

Akbayeva Dina Nauryzbaevna