Acrylic acid high pressure process

In September 1964 the Du Pont company announced materials that had characteristics of both thermoplastics and thermosetting materials. These materials, known as ionomers, are prepared by copolymerising ethylene with a small amount (1-10 % in the basic patent) of an unsaturated carboxylic acid such as acrylic acid using the high-pressure process. Such copolymers are then treated... 

The product mix of autoclave and tubular reactors are similar in terms of LDPE homopolymers (0.910-0.935 g/cc) and some specialty grades of polyethylene such as ethylene/vinyl acetate copolymers up to about 30 wt% vinyl acetate (VA). However, the autoclave process provides higher levels of vinyl acetate (40 wt%) in ethylene/VA copolymers and additional specialty grades of polyethylene such as ethylene/methyl acrylate, ethylene/acrylic acid and ethylene/n-butyl acrylate. Polyethylene molecular weight can be varied over a wide range with the high-pressure process, with Melt Index values (I ranging from 0.15 to 40. 

Theoretically, an almost infinite number of different grades can be produced in a high-pressure polyethylene plant, due to the high flexibility in polymerization conditions and the relative short transition times. In contrast to the lo v-pressure technology, where the polymerization is carried out by Ziegler/Natta, chromium, or metallocene catalysts, the high-pressure process can also use polar comonomers such as vinylacetate, acrylic acid, or N-butylacrylate to modify product properties. With all these opportunities, the resin producer can adjust the product portfolio to cover the market needs at the current economic environment. LDPE homopolymer resins with densities 0.917-0.934 g/cm at MFRs 0.15-100 g/10 min are available in the market. 

Ionomers are made in a two-stage process. In the first step, we copolymerize ethylene with small amounts of an organic acid containing a vinyl group, such as acrylic or methacrylic acid, in a high pressure reactor. In the second step, we neutralize the acid comonomers to form metal salts. We can create ionomers with a variety of metal salts, including sodium, calcium, and zinc. 

The oxidation process is carried out in the temperature range 300— 450°C, and generally studied at atmospheric pressure. Excess air is usually applied (with some exceptions) and substantial amounts of water vapour may be added to the feed. High initial selectivities (>95%) are feasible, and, although some further oxidation (combustion) of the product is unavoidable, yields of 70—90% are reported in the patent literature. The main by-products are carbon oxides, in addition to minor amounts of acrylic acid, acetaldehyde and formaldehyde. Acrylic acid may be a main product depending on specific catalyst properties and reaction conditions, as described in more detail in Sect. 2.2.3. 

This invention has its roots in Reppe chemistry. In the late 1930s, Reppe in Germany had developed a number of manufacturing processes for bulk chemicals, where acetylene was used as one of the basic building blocks. Even today BASF and Rohm Hass manufacture large quantities of acrylic acid and its esters by hydrocarboxylation of acetylene. This reaction, 4.12, is catalyzed by a mixture of NiBr2 and Cul. It involves high pressure (100 bar) and temperature (220°C), and mechanistically is not fully understood. 

In 1957 Standard Oil of Ohio (Sohio) discovered bismuth molybdate catalysts capable of producing high yields of acrolein at high propylene conversions (>90%) and at low pressures (12). Over the next 30 years much industrial and academic research and development was devoted to improving these catalysts, which are used in the production processes for acrolein, acrylic acid, and acrylonitrile. All commercial acrolein manufacturing processes known today are based on propylene oxidation and use bismuth molybdate based catalysts. 

Reppe s work also resulted in the high pressure route which was established by BASF at Ludwigshafen in 1956. In dais process, acetylene, carbon monoxide, water, and a nickel catalyst react at about 200°C and 13.9 MPa (2016 psi) to give acrylic acid. Safety problems caused by handling of acetylene are alleviated by the use of tetrahydrofuran as an inert solvent. In this process, the catalyst is a mixture of nickel bromide with a cupric bromide promotor. The liquid reactor effluent is degassed and extracted. The acrylic acid is obtained by distillation of the extract and subsequendy esterified to the desired acrylic ester. The BASF process gives acrylic acid, whereas the Rohm and Haas process provides the esters direcdy. 

Walter Reppe also used his new base to expand the chemistry of acetylene. His first major breakthrough, in the summer of 1939, was the addition of carbon monoxide to acetylene in the presence of alcohols (or water) and a nickel catalyst to form acrylates. Carbon monoxide had attracted attention for many years as a readily available, cheap and reactive carbon compound. I.G. Farben employed it in the Pier methanol synthesis, Ruhrchemie used it in the Fischer-Tropsch synthetic petrol process, and Du Pont had carried out research on the addition of carbon monoxide to olefins at very high pressure and temperatures. Additional impetus for the use of carbon monoxide in acetylene chemistry was provided by the introduction of covered carbide furnaces at I.G. Farben s Knapsack plant in 1938, which permitted the collection of by-product carbon monoxide. The polymers of acrylic esters were already used for treating leather and for paint, but acrylic acid was made from ethylene oxide, and consequently was rather expensive. Reppe s process reached the pilot plant stage by 1945, and was subsequently used on a large scale by BASF and its American partners. 

High-pressure copolymerization of ethylene with acrylic acid esters and with (meth)acrylic acid are other important technical processes that are run under supercritical conditions close to those of high-pressure ethylene polymerization (6, 6b). 

The carbonylative oxidation of alkenes catalyzed by palladium catalysts has been extensively studied owing to its industrial importance. The conversion of ethylene to acrylic acid has been developed into a commercial process by Union Oil (Scheme 10). The reaction is performed in a mixed solvent of acetic acid and acetic anhydride in the presence of a Wacker catalyst under high pressure of ethylene. 

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