Glycols, dehydration

HjO/CH4 Dehydration Glycol absorption Cellulose acetate Polyimide Polyaramide Plant installed... 

Solvent loss elsewhere] upstream units, for example for glycol dehydration glycol dumped with hydrocarbons separated in upstream flash drum/loss in downstream solvent stripper. 

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. 

The most common contaminants in produced gas are carbon dioxide (COj) and hydrogen sulphide (HjS). Both can combine with free water to cause corrosion and H2S is extremely toxic even in very small amounts (less than 0.01% volume can be fatal if inhaled). Because of the equipment required, extraction is performed onshore whenever possible, and providing gas is dehydrated, most pipeline corrosion problems can be avoided. However, if third party pipelines are used it may be necessary to perform some extraction on site prior to evacuation to meet pipeline owner specifications. Extraction of CO2 and H2S is normally performed by absorption in contact towers like those used for dehydration, though other solvents are used instead of glycol. 

Perchloric acid Acetic acid, acetic anhydride, alcohols, antimony compounds, azo pigments, bismuth and its alloys, methanol, carbonaceous materials, carbon tetrachloride, cellulose, dehydrating agents, diethyl ether, glycols and glycolethers, HCl, HI, hypophosphites, ketones, nitric acid, pyridine, steel, sulfoxides, sulfuric acid... 

Some industrial processes produce predorninately latent air conditioning loads. Others dictate very low humidities and when the dew point falls below 0°C, free2ing becomes a major concern. Dehydration equipment, using soHd sorbents such as siUca gel and activated alurnina, or Hquid sorbents such as lithium chloride brine and triethylene glycol, may be used. The process is exothermic and may require cooling the exiting air stream to meet space requirements. Heat is also required for reactivation of the sorbent material. 

Diethylene glycol readily dehydrates using an acid catalyst to make 1,4-dioxane [123-91 -1] (eq. 5). 

Polyethers are also products of commercial importance. Ethers can be formed by thermal dehydration, as shown for the formation of dipropylene glycol from propylene glycol. CycHc ethers can form by elimination of water from di- or tripropylene glycol. 

Although most of the installed solvent dehydration systems have been for ethanol dehydration, dehydration of other solvents including 2-propanol, ethylene glycol, acetone, and methylene chloride, has been considered. 

Carbon dioxide is ordinarily dehydrated duriag the Hquefactioa cycle to preveat free2e-ups ia the coadeaser and flow valves ia the Hquid lines. Ia some cases brittie or cmmbly blocks of dry ice have beea formed. This difficulty has beea overcome either by varyiag the residual moisture coateat of the Hquid carboa dioxide, or by injecting minute quantities of colorless mineral oil or diethylene glycol iato the Hquid carboa dioxide entering the press. If the dry ice is to be used for edible purposes, the additive must meet FDA specificatioas. 

Partially dehydrated derivatives complexed with polyethylene glycol or propylene glycol exist. In the United of hydration has been replaced by glycine are particularly popular. Aluminum zirconium tetrachlorhydrex gly antiperspinant products. 

A selection of industrial appHcations of extractive distillation includes (/) the separation of the / -butane—butadiene azeotrope in mixed C -hydrocarbon streams using furfural [98-01-17, as the solvent (36) (2) the dehydration of ethanol using ethylene glycol [107-21-1] (37—39) (J)... 

Membrane Pervaporation Since 1987, membrane pei vapora-tion has become widely accepted in the CPI as an effective means of separation and recovery of liquid-phase process streams. It is most commonly used to dehydrate hquid hydrocarbons to yield a high-purity ethanol, isopropanol, and ethylene glycol product. The method basically consists of a selec tively-permeable membrane layer separating a liquid feed stream and a gas phase permeate stream as shown in Fig. 25-19. The permeation rate and selectivity is governed bv the physicochemical composition of the membrane. Pei vaporation differs From reverse osmosis systems in that the permeate rate is not a function of osmotic pressure, since the permeate is maintained at saturation pressure (Ref. 24). 

Natural gas must meet certain specifications before it qualifies for fuel. It should also meet certain dew point characteristics before entering a transmission pipeline. Water dew point is controlled and maintained by stationary equipment such as molecular sieves or dehydration by glycol. Hydrocarbon dew point, on the other hand, can... 

Here are two authoritative discussions " of troubleshooting in glycol dehydration plants. 

Glycol plant troubleshooting information is presented from the article Dehydration Using TEG by Manning and Thompson. 

Here is another discussion of glycol plant troubleshooting from the article How to Improve Glycol Dehydration by Don Ballard. 

The most obvious indication of a glycol dehydration malfunction is a high water content or dew point of the outgoing sales gas stream. In most cases, this is caused by an inadequate glycol circulation rate or by an insufficient reconcentration of the glycol. These two factors can be caused by a variety of contributing problems listed below. 

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