Carbon dioxide from natural gas

Fluor Solvent A process for removing carbon dioxide from natural gas and various industrial gas streams by dissolution in propylene carbonate. Carbon dioxide is much more soluble than other common gases in this solvent at low temperatures. The process cannot be used when hydrogen sulfide is present. The process was invented in 1958 by A. L. Kohl and F. E. Miller at the Fluor Corporation, Los Angeles. It is now licensed by Fluor Daniel. The first plant was built for the Terrell County Treating plant, El Paso, TX in 1960 by 1985, 13 plants were operating. 

Figure 8.31 Flow scheme of one-stage and two-stage membrane separation plants to remove carbon dioxide from natural gas. Because the one-stage design has no moving parts, it is very competitive with other technologies especially if there is a use for the low-pressure permeate gas. Two-stage processes are more expensive because a large compressor is required to compress the permeate gas. However, the loss of methane with the fuel gas is much reduced...

Carbon dioxide/methane Carbon dioxide from natural gas Many plants installed but better membranes are required to change market economics significantly... 

In Europe, the TNO [27] and Kvaerner [19] are both developing contactors to remove water and carbon dioxide from natural gas. Glycol or amines are used as the absorbent fluid. The goal is to reduce the size and weight of the unit to allow use on offshore platforms, so oftentimes only the absorber, the largest piece of equipment in a traditional absorber/stripper, is replaced with a membrane contactor. Kvaerner has taken this technology to the demonstration phase and commercial units are expected to be introduced soon. 

Two processes are known by the Giammarco-Vetrocoke name. Both processes use an aqueous solution of sodium or potassium carbonate and arsenite to absorb acid gases. Some variations of the process use glycine instead of arsenite to activate the potassium carbonate solution. In one process, the solution is used to extract carbon dioxide from natural gas or synthesis gas. In the other, hydrogen sulfide is extracted from coke-oven or synthesis gas and yields elemental sulfur from a complex sequence of reactions. In 1992, more than 200 plants were operating1. 

Elf Activated MDEA An improved MDEA process for removing carbon dioxide from natural gas rich in hydrogen sulfide. The activator is a proprietary secondary amine that accelerates the reaction between the MDEA and the carbon dioxide. Developed by TotalFinaElf and IFP in the 1990s for use in the Lacq gasfield. 

In a more complete membrane process optimization or cost comparison of alternative membrane processes, the cost associated with any loss of the valuable gas component(s) needs to be considered as another operating expense just like any other utility expense. For example, in the case of the removal of carbon dioxide from natural gas (methane), there will be some amount of methane in the permeate (albeit in a small quantity) due to imperfect rejection of methane by the membrane. Since methane is, in this case, the desirable product component, its presence in the permeate represents a loss or an expense. The value of the loss should be included in any cost comparison. 

It may be added, however, that membrane systems have been used successfully to separate carbon dioxide from natural gas, notably in enhanced oil recovery operations. Here (supercritical) carbon dioxide is injected into a petroleum-bearing formation where the carbon dioxide acts to increase the oil mobility and its subsequent recovery. The carbon dioxide-rich gaseous effluent is recovered, and the carbon dioxide concentrated and re-injected. 

Use Plasticizer, fixative in perfumery, manufacture of cosmetics, specialty solvent, to remove carbon dioxide from natural gas, medicine (topical antifungal). 

At ambient temperature, carbon dioxide is three to five times more soluble in most organic solvents than in water (Table I). The differences among polar (e.g. methanol, = 0.139) and nonpolar (e.g. carbon tetrachloride, % = 0- 094) solvents are small. Two solvents which have recently been of practical interest in removing carbon dioxide from natural gas are propylene carbonate ( ) and monoethanolamine (10) - this last ought to be classified as an acid-base reaction. Judging from the number of entries in the 10th collective index to Chemical Abstracts, there is a substantial chemical engineering literature on this topic. 

Another industrial application of gas-separation membranes is the removal of carbon dioxide from natural gas. The CO2/CH4, selectivity is about 20 to 30 for polycarbonate, polysulfone, and cellulose acetate membranes at 35°C and 40 atm. A selectivity of over 60 can be obtained with Kapton , but this polymer is much less permeable than the others. Increasing the temperature raises the permeability of most polymers but generally causes a. slight decrease in selectivity. The operating temperature is chosen to be somewhat above the dew point of the residue gas. There is considerable COj absorbed in the membranes at high CO2 partial pressures, and the plasticization effect of CO2 increases the effective diffusion coefficients for all gases and makes the selectivity less than that based on pure-gas data. Methods of allowing for such nonlinear effects have been presented. ... 

Datta A. K., Sen P. K. 2006. Optimization of membrane unit for removing carbon dioxide from natural gas. Journal of Membrane Science 283 291-300. 

Sridhar, S., B. Smitha, and T.M. Aminabhavi, Separation of carbon dioxide from natural gas mixtures through polymeric membranes—A review. Separation and Purification Reviews, 2007. 36(2) 113-174. 

Other membrane-based gas-separation applications that developed in the late 1980s and the 1990s include the separation of carbon dioxide from natural gas, separation of organic vapors from air and nitrogen, and dehydration of air. Table 7.3 lists the major companies involved in the industry and their principal markets. Currently, total industry sales are estimated to be about US 200 million. Of all the industrial membrane-separation processes, gas separation is... 

Carbon dioxide. The design of a typical membrane system to remove carbon dioxide from natural gas is shown in Fig. 7.12. Two-stage designs are often used to reduce methane loss. The first carbon dioxide plants installed treated only a few million scfd of gas more recently, a number of large systems have been installed. Membrane-based units are particularly favored over amine absorption plants (the usual competitive technology) in offshore installations because of their smaller footprint and reduced weight. 

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