Ethylene polymerization with chromium-based catalyst and investigation of some effective parameters in polymerization

Dissertation for Master degree in Chemistry

(Applied Chemistry - Polymer)

Abstract:

Ethylene polymerization was successfully carried out in the presence of Phillips catalyst and in slurry phase. In the continuation of the work, the effect of some effective parameters in polymerization, including the effect of trialkylaluminum, the effect of 1-hexane comonomer, the effect of hydrogen, and also the effect of solvent replacement were investigated. Changes in the activity of the catalyst, the amount of product production, as well as the analysis of some of the most important characteristics of the obtained products, such as determining the melt flow rate, determining the density of the molten state and mass density, as well as the analysis of the particle size, show these effects well. Phillips catalyst; Slurry phase

Foreword:

Linear polyethylene, the most common type of plastic, was accidentally produced at Phillips Petroleum Company more than half a century ago, and it was found that chromium oxide deposited on silica has the ability to polymerize ?-olefins. A similar catalytic system in a modified state is used by many companies today, so that very large amounts of high-density polyethylene and some low-density polymers are produced by this system. Today, the new generation of these catalysts has a very high activity and the polymer products obtained from them are used for modern industrial uses with special applications. Despite more than half a century of global reviews and the publication of more than 700 articles, there are still many discussions around these catalysts. One of the long-standing problems in the development of these catalysts is the multiple oxidation states of chromium metal and the small number of active sites on these types of catalysts, which has caused obstacles to the further development of these catalysts. The score of these catalysts are leading, it is written.

1-1- Commercial polyethylene

1-1-1- History of polyethylene

LDPE was the first type of polyethylene produced commercially, which was produced and marketed by Imperial Chemical Industries (ICI) in 1938. [1-3]. The basis of this process was based on free radical polymerization under high pressure and the manufactured product included a wide range of polymer chains with short and long side branches. The speed of branching in this process is such that even the lateral branches are self-branching, a structure sometimes referred to as a "fluffy ball". The aforementioned structure prevents the polymer molecule from being entangled with its neighboring molecule, which significantly affects the behavior of the material during molding. The industrial processes of HDPE and LLDPE production were developed in the early 1950s as a result of the discovery of three types of catalysts completely independently, in three different places and with three different types of transition metals [2-10]. It is interesting to compare the approach taken by these researchers and the respective companies, summarized by J. P. Hogan [2, 4]. Like many great discoveries, all three of these discoveries were somewhat accidental.

     Phillips catalyst, which consists of Cr/silica or Cr/silica-alumina combination, was discovered in the second half of 1951 by J. Paul Hogan and Robert L. Banks at the research laboratory of the Phillips Company in Bartlesville, Oklahoma [8] and the first patent reports were published on January 27, 1953. became At the time, Hogan and Banks were trying to dimerize propylene, which unexpectedly yielded a polymeric product. The aforementioned discovery was then extended to polyethylene and polymers with a density of about 0.95-0.97 g/mL were obtained, which indicated the production of linear polyethylene.Phillips immediately developed an industrial process for the production of the catalyst, which succeeded in providing points in less than 4 years after the discovery of the catalyst. Phillips franchise includes site design, production of polyethylene in the amount of lb. 1000 for the development of the consumer market, helping to launch the site as well as the exchange of related information in full.

     Two years later, in October 1953, another accidental discovery was made by Karl Ziegler and his colleagues at the Max Planck Research Institute in Molheim, Germany [10]. The catalyst produced by Ziegler consisted of titanium chloride combined with aluminum alkyl. The first reports were quickly published as a patent on October 17, 1953, in which a polymer with a density of about 0.94 g/mL was reported. Ziegler patented the discovery in less than a year, in which he provided only the laboratory method and the purchasers of the patent were required to develop it independently. Hoechst company was one of the first buyers of this privilege. One of the first problems that existed and was not specifically mentioned in this score was how to control the molecular mass of the polymer [2]. The third catalytic system was discovered in the second half of 1950 by Alex Zletz at the Standard Oil Institute in Indiana [11, 12]. This catalyst consisted of reduced molybdenum on alumina. The first patents were published on April 28, 1951, in which a polymer with a density of about 0.96 g/mL was reported. This discovery was made in a different way than the previous discoveries. Apart from its importance, the concerned institution hired a consultant to try to improve the linear polyethylene produced, which the concerned consultant gave a discouraging assessment. His assessment led to a delay in the launch of commercial sites, and this continued until the Phillips and Ziegler systems launched their sites and were well on their way to commercial production [4, 13, 16]. In 1961, the first Indiana Standard Oil polyethylene technology site was launched in Japan, but unfortunately, this discovery had very little impact on the development of the linear polyethylene industry and the process died out in a short period of time. There is always a huge advantage in being the first in the consumer market; Because the first product always introduces the characteristics of the process that subsequent products (in other words, improved products) face. By 1954, enough information was available to set up a commercial Eschel Continuous Process. First, a site with a production of 1,000 pounds per day was built and was put into operation in early 1955. In the same year, the establishment of an industrial site with the production of 75 million pounds of HDPE per year along with another site with the annual production capacity of 180 million pounds of ethylene was approved. Due to the fact that no manufacturer could fully respond to the consumer market potential of this discovery, the board of directors of Philips decided to make its discovery a franchise. Although no commercial site had been set up and no consumer market existed by then, 9 companies from 7 countries quickly signed franchise agreements between 1955 and 1956 [2, 17]. These companies were: Union Carbide (USA), Allied (USA), British Petroleum (UK), Soltex-Celanese (USA), Rhone Poulenc (France), Solvay (Italy), Eletroteno (Brazil), BASF (Germany) and Showa Denko (Japan). For each of these companies, technical information, site design, as well as polymer samples from a developed site in Oklahoma were provided for market evaluation. Shortly thereafter, franchise sites were built and operated. Homopolymers with a melt index less than 1 were the first grades of HDPE introduced by the Phillips process. Sales of the product (referred to as Marlex) were slow in the early years due to its newness to the market, but after 1958, many applications for HDPE from the Philips system emerged.