Acrylonitrile Production

These processes use expensive C2 hydrocarbons as feedstocks and thus have higher overall acrylonitrile production costs compared to the propylene-based process technology. The last commercial plants using these process technologies were shut down by 1970. 

The propylene-based process developed by Sohio was able to displace all other commercial production technologies because of its substantial advantage in overall production costs, primarily due to lower raw material costs. Raw material costs less by-product credits account for about 60% of the total acrylonitrile production cost for a world-scale plant. The process has remained economically advantaged over other process technologies since the first commercial plant in 1960 because of the higher acrylonitrile yields resulting from the introduction of improved commercial catalysts. Reported per-pass conversions of propylene to acrylonitrile have increased from about 65% to over 80% (28,68—70). 

AH iagredients in the polymerization recipe are not always added at the beginning of the process. For example, better latex stabHity can sometimes be achieved by starting with only part of the emulsifier, saving the rest for later addition. Sometimes a portion of the modifier is held out for late addition to aHow higher final conversion without premature consumption of aH of it. OccasionaHy, if a low acrylonitrile product is the objective, part of the acrylonitrile monomer wiH be saved for late addition so that a chemically more uniform copolymer is produced, which can sometimes enhance properties in critical appHcations. 

This new lower price changed the comparative economic advantages of some of the newer plastics and led to a search for new uses of acrylonitrile and its polymers and copolymers. A new route to Dacron was developed by du Pont using this lower priced acrylonitrile and the use of acrylic fabrics grew rapidly. There was also an increase in uses of ABS and acrylonitrile production capacity. 

Because acrylonitrile is readily volatile, significant releases to air may occur during acrylonitrile production and use (Hughes and Horn 1977 Miller and Villaume 1978). Kayser et al. (1982) estimated that 11,790 kkg/yr (metric tons per year) of acrylonitrile was released from these sources, accounting for 87% of all acrylonitrile released to the... 

Direct release of acrylonitrile to soil during acrylonitrile production and use is believed to be minimal (less than 1 kkg/yr) (Kayser et al. 1982). Accidental spills or leaks from hazardous waste sites could lead to local areas of soil contamination, and acrylonitrile has been detected in soil at 3 chemical waste sites (NPL and other sites) being investigated under Superfund (CLPSD 1988). 

Uses. Acrylic fibers account for about half the acrylonitrile production. Orion, Acrylon, and Dynel are polymers and copolymers of acrylonitrile. These fibers find extensive usage in apparel and household furnishings as well as in the industrial markets. 

Propene is used as a starting material for numerous other compounds. Chief among these are isopropyl alcohol, acrylonitrile, and propylene oxide. Isopropyl alcohol results from the hydration of propylene during cracking and is the primary chemical derived from propylene. Isopropyl alcohol is used as a solvent, antifreeze, and as rubbing alcohol, but its major use is for the production of acetone. Acrylonitrile is used primarily as a monomer in the production of acrylic fibers. Polymerized acrylonitrile fibers are produced under the trade names such as Orion (DuPont) and Acrilan (Monsanto). Acrylonitrile is also a reactant in the synthesis of dyes, pharmaceuticals, synthetic rubber, and resins. Acrylonitrile production occurs primarily through ammoxidation of propylene CH3- CH = CH2 + NH3 + 1.5 02—> CH2 = CH - C = N + 3 H20. 

Worldwide consumption of acrylonitrile increased 52% between 1976 and 1988, from 2500 to 3800 thousand tonnes per year. The trend in consumption over this time period is shown in Table 2 for the principal uses of acrylonitrile acrylic fibre, acrylonitrile-butadiene-styrene (ABS) resins, adiponitrile, nitrile rubbers, elastomers and styrene-acrylonitrile (SAN) resins. Since the 1960s, acrylic fibres have remained the major outlet for acrylonitrile production in the United States and especially in Japan and the Far East. Acrylic fibres always contain a comonomer. Fibres containing 85 wt% or more acrylonitrile are usually referred to as acrylics and fibres containing 35-85 wt% acrylonitrile are called modacrylics . Acrylic fibres are used primarily for the manufacture of apparel, including sweaters, fleece wear and sportswear, and home furnishings, including carpets, upholstery and draperies (Langvardt, 1985 Brazdil, 1991). 

Nitrile rubbers, the original driving force behind acrylonitrile production, have taken a less significant place as end-use products. They are butadiene-acrylonitrile copolymers with an acrylonitrile content ranging from 15 to 45%, and find industrial applications in... 

Surveys have reported full-shift personal exposures measured by the companies and the study investigators in four acrylonitrile production plants in the United States (Zey et al., 1989 Zey McCammon, 1990 Zey et al., 1990a,b). The monomer production operators had 8-h time-weighted average (TWA,) personal exposures of about 1 ppm [2.2 mg/m3] or less from about 1978 to 1986, with some TWAg levels greater than... 

Other chemicals present in acrylonitrile production or in other non-acrylonitrile operations on sites of the companies in the epidemiological study by Blair et al. (1998) include acetylene, hydrogen cyanide, propylene, ammonia, acetic acid, phosphoric acid, lactonitrile, hydroquinone, sodium hydroxide, sulfuric acid, acrylamide, acetone cyanohydrin, melamine, methyl methaciydate, zweto-methylstyrene, urea, methacrylonitrile, butadiene, ammonium hydroxide and ammonium sulfate (Zey et al., 1989, 1990a,b Zey McCammon, 1990). 

More than half of the worldwide acrylonitrile production is situated in Western Europe and the United States. In the United States, production is dominated by BP Chemicals, with more than a third of the domestic capacity. The export market has been an increasingly important outlet for U.S. production, exports growing from around 10% in the mid-1970s to 53% in 1987 and 43% in 1988. 

In this catalysis a surface allyl species is formed which combines with NO to form 3-nitrosopropene. Tautomerism and dehydration then lead to the acrylonitrile product. The coupling of the allyl and nitrosyl ligands in Ru(NO)(CO)(C3H5)L2 (231), via (112) represents a key step in the proposed reaction sequence and suggests the necessity of a bent nitrosyl, at least in a discrete complex case. 

A third catalytic system was proposed more recently and based on vanadium aluminum oxynitrides (VALON) [30]. The maximum acrylonitrile yield reported was about 30%, but with acrylonitrile productivity four times higher than for V/ Sb/W/Al/O catalysts and one order of magnitude than for Mo/V/Nb/Te/O. Other companies have studied and developed proprietary formulations but, in general, catalytic systems belong either to the antimonates family (Rhodia, BASF, Nitto, Monsanto) [31-33] orto the molybdates family. 

Acrylonitrile is commercially produced from propylene by a molybdate-based catalyst that has been optimized to produce a yield of around 80% acrylonitrile. Utilizing a less-expensive feedstock, the selective ammoxidation of propane to acrylonitrile has significant potential in reducing acrylonitrile production cost. The work-flow for this chemistry consisted of a primary scale evaporative synthesis station and 256-channel parallel screening reactor using a proprietary optical-based detection method. For the initial work shown here, secondary screening was done on a six-channel fixed-bed reactor. 

Commercially, lactic acid is manufactured by controlled fermentation of the hexose sugars from molasses, corn, or milk. Lactates are made by synthetic methods from acetaldehyde and lactonitrile, a by-product acrylonitrile production. 

Fluidized beds are used for both catalytic and noncatalytic reactions. In the catalytic category, there are fluidized catalytic crackers of petroleum, acrylonitrile production from propylene and ammonia, and the chlorination of olefins to alkyl chlorides. Noncatalytic reactions include fluidized combustion of coal and calcination of lime. 

The mass of gaseous emissions is five times the acrylonitrile production rate, because a large nitrogen amount is carried out with air. C02 is of significance too. 

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