Ethylene production processes

Figure 1 Simplified block diagram for RLOC Ethylene Production Process...

Detailed stream data obtained from process simulation for the ethanol production process and the ethylene production process are provided in Tables 4.A.1 and 4.A.2. 

Integration of Separate Ethanol and Ethylene Production Processes... 

Table 4.2 shows the flows of energy to and from the biomass-to-ethylene production processes considering the different levels of process integration. The level of heat integration has a strong influence on the amount of excess solid residues and electricity that can be exported from the processes and therefore influences their overall energy efficiency. It can be seen that in Case I the largest net amount of elecdicity can be exported from the site, while the amount of excess solid residues is at a minimum. 

Table 4.A.3 Stream data with hot and cold utility of the combined ethylene production process...

The price of acetaldehyde duriag the period 1950 to 1973 ranged from 0.20 to 0.22/kg. Increased prices for hydrocarbon cracking feedstocks beginning in late 1973 resulted in higher costs for ethylene and concurrent higher costs for acetaldehyde. The posted prices for acetaldehyde were 0.26/kg in 1974, 0.78/kg in 1985, and 0.92/kg in 1988. The future of acetaldehyde growth appears to depend on the development of a lower cost production process based on synthesis gas and an increase in demand for processes based on acetaldehyde activation techniques and peracetic acid. 

Processes rendered obsolete by the propylene ammoxidation process (51) include the ethylene cyanohydrin process (52—54) practiced commercially by American Cyanamid and Union Carbide in the United States and by I. G. Farben in Germany. The process involved the production of ethylene cyanohydrin by the base-cataly2ed addition of HCN to ethylene oxide in the liquid phase at about 60°C. A typical base catalyst used in this step was diethylamine. This was followed by liquid-phase or vapor-phase dehydration of the cyanohydrin. The Hquid-phase dehydration was performed at about 200°C using alkah metal or alkaline earth metal salts of organic acids, primarily formates and magnesium carbonate. Vapor-phase dehydration was accomphshed over alumina at about 250°C. 

In 1991, the relatively old and small synthetic fuel production faciHties at Sasol One began a transformation to a higher value chemical production facihty (38). This move came as a result of declining economics for synthetic fuel production from synthesis gas at this location. The new faciHties installed in this conversion will expand production of high value Arge waxes and paraffins to 123,000 t/yr in 1993. Also, a new faciHty for production of 240,00 t/yr of ammonia will be added. The complex will continue to produce ethylene and process feedstock from other Sasol plants to produce alcohols and higher phenols. 

Olefins are produced primarily by thermal cracking of a hydrocarbon feedstock which takes place at low residence time in the presence of steam in the tubes of a furnace. In the United States, natural gas Hquids derived from natural gas processing, primarily ethane [74-84-0] and propane [74-98-6] have been the dominant feedstock for olefins plants, accounting for about 50 to 70% of ethylene production. Most of the remainder has been based on cracking naphtha or gas oil hydrocarbon streams which are derived from cmde oil. Naphtha is a hydrocarbon fraction boiling between 40 and 170°C, whereas the gas oil fraction bods between about 310 and 490°C. These feedstocks, which have been used primarily by producers with refinery affiliations, account for most of the remainder of olefins production. In addition a substantial amount of propylene and a small amount of ethylene ate recovered from waste gases produced in petroleum refineries. 

The process can be operated in two modes co-fed and redox. The co-fed mode employs addition of O2 to the methane/natural gas feed and subsequent conversion over a metal oxide catalyst. The redox mode requires the oxidant to be from the lattice oxygen of a reducible metal oxide in the reactor bed. After methane oxidation has consumed nearly all the lattice oxygen, the reduced metal oxide is reoxidized using an air stream. Both methods have processing advantages and disadvantages. In all cases, however, the process is mn to maximize production of the more desired ethylene product. 

The unit Kureha operated at Nakoso to process 120,000 metric tons per year of naphtha produces a mix of acetylene and ethylene at a 1 1 ratio. Kureha s development work was directed toward producing ethylene from cmde oil. Their work showed that at extreme operating conditions, 2000°C and short residence time, appreciable acetylene production was possible. In the process, cmde oil or naphtha is sprayed with superheated steam into the specially designed reactor. The steam is superheated to 2000°C in refractory lined, pebble bed regenerative-type heaters. A pair of the heaters are used with countercurrent flows of combustion gas and steam to alternately heat the refractory and produce the superheated steam. In addition to the acetylene and ethylene products, the process produces a variety of by-products including pitch, tars, and oils rich in naphthalene. One of the important attributes of this type of reactor is its abiUty to produce variable quantities of ethylene as a coproduct by dropping the reaction temperature (20—22). 

Most by-product acetylene from ethylene production is hydrogenated to ethylene in the course of separation and purification of ethylene. In this process, however, acetylene can be recovered economically by solvent absorption instead of hydrogenation. Commercial recovery processes based on acetone, dimetbylform amide, or /V-metby1pyrro1idinone have a long history of successfiil operation. The difficulty in using this relatively low cost acetylene is that each 450, 000 t/yr world-scale ethylene plant only produces from 7000 9000 t/yr of acetylene. This is a small volume for an economically scaled derivatives unit. 

As indicated in Table 4, large-scale recovery of natural gas Hquid (NGL) occurs in relatively few countries. This recovery is almost always associated with the production of ethylene (qv) by thermal cracking. Some propane also is used for cracking, but most of it is used as LPG, which usually contains butanes as well. Propane and ethane also are produced in significant amounts as by-products, along with methane, in various refinery processes, eg, catalytic cracking, cmde distillation, etc (see Petroleum). They either are burned as refinery fuel or are processed to produce LPG and/or cracking feedstock for ethylene production. 

Production of maleic anhydride by oxidation of / -butane represents one of butane s largest markets. Butane and LPG are also used as feedstocks for ethylene production by thermal cracking. A relatively new use for butane of growing importance is isomerization to isobutane, followed by dehydrogenation to isobutylene for use in MTBE synthesis. Smaller chemical uses include production of acetic acid and by-products. Methyl ethyl ketone (MEK) is the principal by-product, though small amounts of formic, propionic, and butyric acid are also produced. / -Butane is also used as a solvent in Hquid—Hquid extraction of heavy oils in a deasphalting process. 

Total Hydrocarbon Gontent. The THC includes the methane combined in air, plus traces of other light hydrocarbons that are present in the atmosphere and escape removal during the production process. In the typical oxygen sample, methane usually constitutes more than 90% of total hydrocarbons. The rest may be ethane, ethylene, acetylene, propane, propylene, and butanes. Any oil aerosol produced in lubricated piston compressor plants is also included here. 

Polymer Suspensions. Poly(ethylene oxide) resins ate commercially available as fine granular soHds. However, the polymer can be dispersed in a nonsolvent to provide better metering into various systems. Production processes involve the use of high shear mixers to disperse the soHds in a nonsolvent vehicle (72—74). 

Chemical Processing Intermediates and Other Applications. Monoethanolamine can be used as a raw material to produce ethylenedianiine. This technology has some advantages over the ethylene dichloride process in that salts are not a by-product. Additional reactions are requked to produce the higher ethyleneamines that are normally produced in the ethylene dichloride process. 

Reaction and Heat-Transfer Solvents. Many industrial production processes use solvents as reaction media. Ethylene and propylene are polymerized in hydrocarbon solvents, which dissolves the gaseous reactant and also removes the heat of reaction. Because the polymer is not soluble in the hydrocarbon solvent, polymer recovery is a simple physical operation. Ethylene oxide production is exothermic and the catalyst-filled reaction tubes are surrounded by hydrocarbon heat-transfer duid. 

Alternatives to oxychlorination have also been proposed as part of a balanced VCM plant. In the past, many vinyl chloride manufacturers used a balanced ethylene—acetylene process for a brief period prior to the commercialization of oxychlorination technology. Addition of HCl to acetylene was used instead of ethylene oxychlorination to consume the HCl made in EDC pyrolysis. Since the 1950s, the relative costs of ethylene and acetylene have made this route economically unattractive. Another alternative is HCl oxidation to chlorine, which can subsequently be used in dkect chlorination (131). The SheU-Deacon (132), Kel-Chlor (133), and MT-Chlor (134) processes, as well as a process recently developed at the University of Southern California (135) are among the available commercial HCl oxidation technologies. Each has had very limited industrial appHcation, perhaps because the equiHbrium reaction is incomplete and the mixture of HCl, O2, CI2, and water presents very challenging separation, purification, and handling requkements. HCl oxidation does not compare favorably with oxychlorination because it also requkes twice the dkect chlorination capacity for a balanced vinyl chloride plant. Consequently, it is doubtful that it will ever displace oxychlorination in the production of vinyl chloride by the balanced ethylene process. 

Union Carbide Corp. also uses a siUca-supported chromium catalyst in their extremely low cost Unipol gas-phase linear low density ethylene copolymer process, which revolutionized the industry when it was introduced in 1977 (86—88). The productivity of this catalyst is 10 —10 kg polymer/kg transition metal contained in the catalyst. By 1990, the capacity of Unipol linear low density polyethylene reactors was sufficient to supply 25% of the world s total demand for polyethylene. 

Removal of metal chlorides from the bottoms of the Hquid-phase ethylene chlorination process has been studied (43). A detailed summary of production methods, emissions, emission controls, costs, and impacts of the control measures has been made (44). Residues from this process can also be recovered by evaporation, decomposition at high temperatures, and distillation (45). A review of the by-products produced in the different manufacturing processes has also been performed (46). Several processes have been developed to limit ethylene losses in the inerts purge from an oxychlorination reactor (47,48). 

Ethyleneamines are used in certain petroleum refining operations as well. Eor example, an EDA solution of sodium 2-aminoethoxide is used to extract thiols from straight-mn petroleum distillates (314) a combination of substituted phenol and AEP are used as an antioxidant to control fouling during processing of a hydrocarbon (315) AEP is used to separate alkenes from thermally cracked petroleum products (316) and TEPA is used to separate carbon disulfide from a pyrolysis fraction from ethylene production (317). EDA and DETA are used in the preparation and reprocessing of certain... 

For the same production capacity, the oxygen-based process requires fewer reactors, all of which operate in parallel and are exposed to reaction gas of the same composition. However, the use of purge reactors in series for an air-based process in conjunction with the associated energy recovery system increases the overall complexity of the unit. Given the same degree of automation, the operation of an oxygen-based unit is simpler and easier if the air-separation plant is outside the battery limits of the ethylene oxide process (97). 

The RR developed by the author at UCC was the only one that had a high recycle rate with a reasonably known internal flow (Berty, 1969). This original reactor was named later after the author as the Berty Reactor . Over five hundred of these have been in use around the world over the last 30 years. The use of Berty reactors for ethylene oxide process improvement alone has resulted in 300 million pounds per year increase in production, without addition of new facilities (Mason, 1966). Similar improvements are possible with many other catalytic processes. In recent years a new blower design, a labyrinth seal between the blower and catalyst basket, and a better drive resulted in an even better reactor that has the registered trade name of ROTOBERTY . ... 

Petrochemical units generate waste waters from process operations such as vapor condensation, from cooling tower blowdown, and from stormwater runoff. Process waste waters are generated at a rate of about 15 cubic meters per hour (m /hr), based on 500,000 tpy ethylene production, and may contain biochemical oxygen demand (BOD) levels of 100 mg/1, as well as chemical oxygen demand (COD) of 1,500 to 6,000 mg/1, suspended solids of 100 to 400 mg/1, and oil and grease of 30 to 600 mg/1. Phenol levels of up to 200 mg/1 and benzene levels of up to 100 mg/1 may also be present. 

One illustrative example is presented in tliis final cliapter. It lias been adopted from tlie outstanding work of Kavianaian et al. and is concerned with an ethylene production plant. Tlie solution involves a prcliminaiy hazards analysis (PHA) and tlie development of a fault tree for tlie process. 

Butylenes (butenes) are by-products of refinery cracking processes and steam cracking units for ethylene production. 

The main source for ethane is natural gas liquids. Approximately 40% of the available ethane is recovered for chemical use. The only large consumer of ethane is the steam cracking process for ethylene production. 

Raw materials for obtaining benzene, which is needed for the production of alkylbenzenes, are pyrolysis gasoline, a byproduct of the ethylene production in the steam cracking process, and coke oven gas. Reforming gasoline contains only small amounts of benzene. Large amounts of benzene are further produced by hydrodealkylation of toluene, a surplus product in industry. 

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