Association desalting

Both the failure of the isolation valves to hold and the difficulty in draining the system were due to solid build up in the circuit. In the previous two-year period, the refinery had changed its crude feedstock resulting in operating difficulties on the unit desalter. Carryover of salts led to accelerated corrosion in the crude column and associated piping circuits. 

Figure 9. Apparent molecular weight distributions representing a homologous series of kraft lignin samples secured by desalting after association and dissociation in aqueous alkaline solutions for (1) 300 h, (2) 144 h and (3) 48 h at 170 gL1 in 1.0 M ionic strength aqueous 0.40 M NaOH (4) 0 h (5) 144 h and (6) 644 h at 0.50 gL 1 in aqueous 0.10 M NaOH. (Sephadex GlOO/aqueous 0.10 M NaOH elution profiles monitored at 320 nm.)...

Figure 16. Zimm plot of 514.5 nm light-scattering data characterizing associated kraft lignin sample in DMF following desalting after incubation at 170 gL 1 for 300 h in 1.0 M ionic strength aqueous 0.40 M NaOH.

Wangnick, K. 1998. IDA Worldwide Desalting Plants Inventory Report No. 15. Produced by Wangnick Consulting for International Desalination Association. 

A recent development is to combine filtration with solid-phase extraction separation. These filter modules contain a unique silica gel membrane that binds up to 20 pg of DNA in the presence of a high concentration of chao-tropic salt and allow eventual elution in a small volume of low-salt buffer. They also contain an asymmetric laminar membrane with a gradation of pore sizes for efficient removal of material precipitated in the lysate. Such membrane filters eliminate time-consuming phenol-chloroform extraction and alcohol precipitation. The impregnation of silica in the membrane matrix also prevents the problems associated with loose resins and slurries. High-purity plasmid DNA eluted from such modules is ready to use and often needs no further precipitation, concentration, or desalting. 

IMULSIONS OF OIL AND WATER are one of many problems directly associated with the petroleum industry, in both oil-field production and refinery environments. Whether these emulsions are created inadvertently or are unavoidable, as in the oil-field production area, or are deliberately induced, as in refinery desalting operations, the economic necessity to eliminate emulsions or maximize oil-water separation is present. Furthermore, the economics of oil-water separation dictate the labor, resources, and monies dedicated to this issue. Before we describe the methods and economics of emulsion breaking at commercial facilities, we will restate several key concepts concerning emulsions and the petroleum industry. 

Within the refining environment, the field of crude-oil dehydration is viewed somewhat differently. The first process a crude oil (or blend of crude oils) is subjected to is the desalting process. This process was developed with the expectation that a crude oil will have a known water content (less than 0.5%) and a soluble inorganic chloride salts content associated with this water (formation waters from oil-field production may have salt contents approaching 300,000 rngl ). Salts may also occur in crystalline form dispersed within the oil. As these salts have considerable negative effects in the downstream processes of the refinery, it is desirable to remove them. 

Historically, the chemical selection process has been performed on a bench-top scale. Bottle tests (including ratio, elimination, and confirmation test), jar tests, and portable electric desalter tests fall into this test category. No effort will be made to describe these tests or the associated analytical procedures in detail, as they are described in Chapters 3 and 10. Furthermore, significant variation in testing procedures will exist between various chemical companies, oil producers, and refiners. Each test procedure is also tailored to each treating facility. 

Desalter An oil-field or refinery apparatus used to separate water and associated dissolved salts from crude oil. 

The other two techniques, FlashQuant and LDTD MS, both utilize laser desorption to facilitate samples introduction into mass spectrometer. In FlashQuant workstation, samples were spotted on a stainless steel plate after desalting (Figure 4.9). The desalting step is critical in this technique to ensure the formation of uniform crystals on each sample spot and the reproducibility of the results. Samples are then introduced into the mass spectrometer through MALDI. The matrix interference associated with using MALDI is resolved by using a noninterfering matrix as well as the specificity of tandem mass spectrometry (MS/MS) [121,122],... 

Salts dissolved in an aqueous fraction associated with the organic liquid. For instance in crude oil processing steps are taken to "desalt" the hydrocarbon but there may be some "carry over" in the organic liquid stream. 

Wangnick, K. 1985. Desalting plant inventory report. International Desalination Association (IDA) Report. 

Mobile phases containing phosphate buffers have often been used in the preparative purification of oUgodeoxynucleotides. However, the necessity to subsequently desalt the product limits the use of such mobile phases furthermore, problems associated with intramolecular and intermolecular interactions (hydrogen bonding) can occur, although these can largely be overcome by including formamide in the eluent (Newton et al., 1983). An alternative mobile phase is aqueous triethylammonium acetate which can be removed by lyophilisation and in which these molecular interactions are limited (Fig. 11.1.11). 

J. Kieman, A.J.M. von Gottberg, Selection of EDR desalting technology rather than MF/RO for the City of San Diego Water Reclamation Project, Paper presented at the 1998 American Desalting Association, North American Biennial Conference Exposition, August, 1998. 

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