Hydrocarbons, heavy

Compilation of physical properties for 321 heavy hydrocarbons. Vapor pressures at low pressures. ... 

For heavy hydrocarbons, it is preferable to use the Maxwell and Bonnel method described beiow. 

To prepare gas for evacuation it is necessary to separate the gas and liquid phases and extract or inhibit any components in the gas which are likely to cause pipeline corrosion or blockage. Components which can cause difficulties are water vapour (corrosion, hydrates), heavy hydrocarbons (2-phase flow or wax deposition in pipelines), and contaminants such as carbon dioxide (corrosion) and hydrogen sulphide (corrosion, toxicity). In the case of associated gas, if there is no gas market, gas may have to be flared or re-injected. If significant volumes of associated gas are available it may be worthwhile to extract natural gas liquids (NGLs) before flaring or reinjection. Gas may also have to be treated for gas lifting or for use as a fuel. 

Gas processing facilities generally work best at between 10 and 100 bar. At low pressure, vessels have to be large to operate effectively, whereas at higher pressures facilities can be smaller but vessel walls and piping systems must be thicker. Optimum recovery of heavy hydrocarbons is achieved between 20 bar and 40 bar. Long distance pipeline pressures may reach 150 bar and reinjection pressure can be as high as 700 bar. The gas process line will reflect gas quality and pressure as well as delivery specifications. 

Dehydration can be performed by a number of methods cooling, absorption and adsorption. Water removal by cooling is simply a condensation process at lower temperatures the gas can hold less water vapour. This method of dehydration is often used when gas has to be cooled to recover heavy hydrocarbons. Inhibitors such as glycol may have to be injected upstream of the chillers to prevent hydrate formation. 

Facilities for the treatment and compression of gas have already been described in earlier sections. However, there are a number of differences in the specifications for injected gas that differ from those of export gas. Generally there are no technical reasons for specifications on hydrocarbon dew point control (injected gas will get hotter not cooler) although it may be attractive to remove heavy hydrocarbons for economic reasons. Basic liquid separation will normally be performed, and due to the high pressures involved it will nearly always be necessary to dehydrate the gas to avoid water drop out. 

The most common solvent employed is carbon dioxide gas, which can be injected between water spacers, a process known as WaterAlternating Gas (WAG). In most commercial schemes the gas is recovered and reinjected, sometimes with produced reservoir gas, after heavy hydrocarbons have been removed. Other solvents include nitrogen and methane. 

Elastomers. Elastomers are polymers or copolymers of hydrocarbons (see Elastomers, synthetic Rubber, natural). Natural mbber is essentially polyisoprene, whereas the most common synthetic mbber is a styrene—butadiene copolymer. Moreover, nearly all synthetic mbber is reinforced with carbon black, itself produced by partial oxidation of heavy hydrocarbons. Table 10 gives U.S. elastomer production for 1991. The two most important elastomers, styrene—butadiene mbber (qv) and polybutadiene mbber, are used primarily in automobile tires. 

Trickle bed reaction of diol (12) using amine solvents (41) has been found effective for producing PDCHA, and heavy hydrocarbon codistiUation may be used to enhance diamine purification from contaminant monoamines (42). Continuous flow amination of the cycloaUphatic diol in a Hquid ammonia mixed feed gives >90% yields of cycloaUphatic diamine over reduced Co /Ni/Cu catalyst on phosphoric acid-treated alumina at 220°C with to yield a system pressure of 30 MPa (4350 psi) (43). 

The source of nitrogen is always air. However, hydrogen can be derived from a variety of raw materials including water, light and heavy hydrocarbons (qv) resulting from cmde oil refining, coal (qv), natural gas, and sometimes a combination of these raw materials. In all cases, part of the hydrogen produced is derived from water. 

Heavy Hydrocarbon-Based Partial Oxidation Processes. Two major partial oxidation processes are commercially available, the SheU process (38) and the Texaco process (39). Operating conditions in the gas generator vary from 1200°C to 1370°C and from 3100 kPa to 8270 kPa (450—1200 psig). Generally, heavy oils are the hydrocarbon feeds however, the process can also accommodate feeds from natural gas to residual oils. 

The diglycolamine (DGA) process also allows high (up to 60 wt % DGA) solvent concentrations for reduced chculation rate and energy requhements. High solvent costs and a higher tendency to absorb heavy hydrocarbons have limited the use of this solvent. 

The amount of combustion ait is tightly controlled to maximize sulfur recovery, ie, maintaining the appropriate reaction stoichiometry of 2 1 hydrogen sulfide to sulfur dioxide throughout downstream reactors. Typically, sulfur recoveries of up to 97% can be achieved (7). The recovery is heavily dependent on the concentration of hydrogen sulfide and contaminants, especially ammonia and heavy hydrocarbons, ia the feed to the Claus unit. 

Antimony trichloride is used as a catalyst or as a component of catalysts to effect polymerisation of hydrocarbons and to chlorinate olefins. It is also used in hydrocracking of coal (qv) and heavy hydrocarbons (qv), as an analytic reagent for chloral, aromatic hydrocarbons, and vitamin A, and in the microscopic identification of dmgs. Liquid SbCl is used as a nonaqueous solvent. 

Of the four commercial processes for the purification of carbon monoxide two processes are based on the absorption of carbon monoxide by salt solutions, the third uses either low temperature condensation or fractionation, and the fourth method utilizes the adsorption of carbon monoxide on a soHd adsorbent material. AH four processes use similar techniques to remove minor impurities. Particulates are removed in cyclones or by scmbbing. Scmbbing also removes any tars or heavy hydrocarbon fractions. Acid gases are removed by absorption in monoethanolamine, hot potassium carbonate, or by other patented removal processes. The purified gas stream is then sent to a carbon monoxide recovery section for final purification and by-product recovery. 

There are several important Hquid fuels, ranging from volatile fuels for internal combustion engines to heavy hydrocarbon fractions, sold commercially as fuel oils. The technology for the combustion of Hquid fuels for spark-ignition and compression-ignition internal combustion engines is not described here. 

The normal regeneration temperature for siUca gel is 175°C. In hydrocarbon service, higher temperatures (225—275°C) are recommended to desorb heavy hydrocarbons, which tend to foul the adsorbent during prolonged use (see Silicon compounds). 

Tanks cool and partially freeze solids form a layer of self-insulation. This complex case, which has been known to occur with heavy hydrocarbons and mixtures of hydrocarbons, has been discussed by Stnhlbarg [Pet. Refiner,. 38, 143 (Apr. 1, 1959)]. The contents in the center of snch tanks have been known to remain warm and liquid even after several years of cooling. 

Shell Gas B.V. has constructed a 1987 mVd (12,500 bbhd) Fischer-Tropsch plant in Malaysia, start-up occurring in 1994. The Shell Middle Distillate Synthesis (SMDS) process, as it is called, uses natural gas as the feedstock to fixed-bed reactors containing cobalt-based cat- yst. The heavy hydrocarbons from the Fischer-Tropsch reactors are converted to distillate fuels by hydrocracking and hydroisomerization. The quality of the products is very high, the diesel fuel having a cetane number in excess of 75. 

There are two main approaches to its solution. Traditional approach is based on preliminary separation of UGC samples to gaseous and liquid phases and their subsequent analyses [1]. This approach is well-developed and it allows obtaining quite precise results being used properly. However, this method is relatively complicated. Multi-stage procedure is a source of potential errors, then, it makes the analyses quite time consuming. More progressive approach is based on the direct analysis of the pressurized UGC samples. In both cases the determination of heavy hydrocarbons (up to C ) is made by capillary gas chromatography. 

Onshore or offshore gas plants are designed for either LNG rejection and gas injection, or LNG rejection and transmission for sale. In the case of offshore plants, onshore facilities further process the natural gas before transmission for sale. In either case, natural gas must be treated and then refrigerated to make rejection of heavy hydrocarbons possible. In plants where natural gas is treated for sale purposes, water and hydrocarbon dew points of the gas must also be controlled. 

Sealing of turboexpander and compressor process gas from die bearing housing differs for air separation and natural gas applications. The bearing housing is usually sealed in cold expanders and for cases when die process gas contains heavy hydrocarbon components, which may cause condensation in die bearing housing. 

At the central platform, water and hydrocarbon liquids are first removed in knockout drums. Then saturated natural gas, free of any liquid droplets, enters the twin expanders. The gas is cooled below its dewpoint, allowing heavy hydrocarbon components and water vapor to condense in the discharge stream. Turboexpanders were chosen for two main reasons They are more compact than competing methods of controlling the dewpoint and their operating costs are typically lower than those of many alternatives. 

DGA is preferred for cold climates and high (50-70wt%) solution strength for economy. By comparison, solution strength for MEA is 15-25 wt%, and for DEA, 25-35 wt%.- Provide good filtration for DGA because it has a greater affinity for heavy hydrocarbons than other amines. The feed gas must have at least 1% acid gas... 

The same disadvantages with heavy hydrocarbons in the feed as other physical solvents High priced chemicals and process royalty, but losses are low and the licensee receives many engineering services."... 

Effects. Trays can become damaged several ways. A pressure surge can cause damage. A slug of water entering a heavy hydrocarbon fractionator will produce copious amounts of vapor. The author is aware of one example where all the trays were blown out of a crude distillation column. If the bottom liquid level is allowed to reach the reboiler outlet line, the wave action can damage some bottom trays. 

They are effective as a means of removing heavy hydrocarbon vapors from emergency release streams, thus minimizing condensation problems in downstream equipment. 

Another example of an unsteady state condensible blowdown system is the design for a phenol condensible blowdown tank. A blowdown tank is used in phenol treating plants to handle streams containing phenol and heavy hydrocarbons (lubricating oil stocks). The blowdown tank is illustrated in Figure 4. The design basis is as rollows ... 

In addition to heavy hydrocarbons and water vapor, natural gas often contains other contaminants that may have to be removed. Carbon dioxide (CO2), hydrogen sulfide (H2S), and other sulfur compounds such as mercaptans are compounds that may require complete or partial removal for acceptance by a gas purchaser. These compounds are known as acid gases. H2S combined with water forms a weak form of sulfuric acid, while CO2 and water forms carbonic acid, thus the term acid gas. ... 

Molecular sieves are available with a variety of pore sizes. A molecular sieve should be selected with a pore size that will admit H2S and water while preventing heavy hydrocarbons and aromatic compound.s from entering the pores. However, carbon dioxide molecules are about the same size as H2S molecules and present problems. Even thougli die COi is non-polar and will not bond to the active sites, the CO2 will entci the pores. Small quantities of CO2 will become trapped in the pores In this way small portions of CO2 are removed. More importantly, CO ih obstruct the access of H2S and water to active sites and decrease the eflectiveness ot the pores. Beds must be sized to remove all water and to pi ovitte for interference from other molecules in order to remove all H i.S. 

Physical solvent processes have a high affinity for heavy hydrocarbons. If the namral gas stream is rich in C3+ hydrocarbons, then the use of a physical solvent process may result in a significant loss of the heavier molecular weight hydrocarbons. These hydrocarbons are lost because they a c released from the solvent with the acid gases and cannot be economically recovered. 

The concentration of heavy hydrocarbons in the feed is low. That is, the gas stream is lean in propane-plus. 

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