Base, scavenging

There is a Gas Research Institute (GRI) evaluation of a solid-based scavenger (Sulfa Treat ). Full-scale evaluations have been conducted at a production plant in central Texas. The reference is GRI-95/0161. 

Zinc-Base Scavengers. There are two types of zinc-base scavengers available. These are ... 

The silica-based scavenger has much faster kinetics which allows it to scavenge HOBt in only five minutes (Table 3.1). 

Cross-coupling of terminal alkynes with aryl and vinyl halides are usually carried out in organic solvents, such as benzene, dimethylformamide or chloroform with a palladium-based catalyst and a base scavenger for the hydrogen halide. Copper(I) iodide is a particularly effective co-catalyst allowing the reaction to proceed under mild conditions. 

Advances made in solid phase extraction (SPE) and in development of resin-based scavengers have increased the versatility of chemistries implemented for synthesis of... 

A detailed study on scavenging HCl by calcium-based sorbents (Ca-C sorbent, consisting of 90 wt% of CaCOs and 10 wt% of phenol resin) during or after pyrolysis has been completed recently by Bhaskar et al. [36] and is planned for technical application at a municipal plastic waste pyrolysis plant at Mizushima, Japan. Calcium-based scavenging is a strategy already followed in industry and studied deeply for fluidized-bed pyrolysis of thermoplastics by Sinn and Kaminsky [37-39]. 

Dialyze the carrier protein against 10 mM potassium phosphate buffer, pH 7.2. At ust the carrier concentration to about 20 mg/mL. Weigh out the solid peptide and dissolve it in the same buffer at 5 mg/mL. Thiol-based scavengers, used to preserve free -SH groups in the peptide, are often present in peptide preparations and will need to be removed from the peptide solution by desalting on a Bio-Gel PIO column in 10 mM potassium phosphate buffer, pH 7.2. A brief nasal inspection is often sufficient to determine their presence. On the other hand, stock solutions of peptide (e.g., in PBS) may become oxidized if stored for extended periods, and so are best pretreated with 100 mMDTT (30 min at room temperature is adequate) to reduce the dissolved peptide before use. As the DTT will interfere with the conjugation, the reduced peptide should then be desalted on a PIO column as above. 

The SulfaTreat process also uses an iron-based scavenger for trace H2S removal. It has the advantage over the traditional iron sponge process of being non-pyrophoric. 

Since the discovery of solid phase peptide synthesis in 1963 [4], the venerable polystyrene resin has remained the cornerstone of combinatorial chemistry over the years and continues to be utilized as the primary mode of support for immobilizing reagents and scavengers. This section briefly outlines the latest developments of resin-based scavengers. 

Another interesting development is the use of fluorous-based scavengers in conjunction with microwave synthesis and fluorous solid-phase extraction (F-SPE) for purification. This was recently illustrated by Werner and Curran [74] in their investigation of the Diels-Alder cycloaddition of maleic anhydride to diphenylbutadiene (Scheme 11.23). After performing microwave-assisted cycloaddition (160 °C, 10 min) with a 50% excess of the diene, the excess diene reagent was scavenged by a structurally related maleimide fluorous dienophile under the same reaction conditions. Elution of the product mixture from an F-SPE column with Me0H-H20 provided the desired cycloadduct 89 in 79% yield and 90% purity. Subsequent elution with diethyl ether furnished the fluorous Diels-Alder cycloadduct. 

The most obvious benefit of using an oxygen scavenging film versus a sachet is that it does not appear as a foreign object. Moreover, the polymer-based film, unlike the metal-based scavenger, is also completely independent of moisture and has no effect on metal detection systems. 

It has also been observed that sulfide scavengers are categorized into three classes water-soluble, oil-soluble, and metal-based scavengers (Baker Hughes 2011). The indices of selection depend on the intended application in the oil and gas industry. The types are highlighted as follows ... 

Metal-based scavengers These scavengers have answered the specific needs of very high-temperature and high-H2S concentration applications. Examples are the drilling application when H2S contact is suspected as these additives can be used at temperatures in excess of 350°F (177°C) to form thermally stable products and are able to provide H2S reduction levels that other H2S scavengers cannot achieve. 

It should be noted that in the Cu" form, a copper-based scavenger is only half as efficient as when it takes the Cu + form. 

In many ways, copper-based scavengers fit the criteria previously listed for an ideal scavenger, but copper has one serious limitation—corrosion of metallic iron resulting from spontaneous metallic copper plating. For this reason, the basic copper carbonate that was once widely used has been replaced by its zinc counterpart. 

Problems are caused by clay flocculation, but these often can be minimized by adding more deflocculant. In fact, some early commercial zinc-based scavengers contained a lignosulfonate for this purpose. This combination was abandoned because deflocculation is not always desirable in conjunction with a scavenger treatment (Garrett et al. 1979). 

Six iron-sulfur minerals are stable enough to exist in nature all contain the ferrous (Fe +) form of iron. Those minerals with iron-to-sulfur ratios of 1 1 (FeS) are mackinawite and pyrrhotite. Those with iron-to-sulfur ratios of 3 4 0 0384) are greigite and smythite. All the iron sulfides with ratios of 1 1 and 3 4 are soluble in mild acids with formation of H2S. Those minerals with iron-to-sulfur ratios of 1 2 (FeSj) are pyrite and marcasite. Pyrite and marcasite are distinguished from the other four iron sulfides by their insolubility in concentrated HCl. Pyrite is highly pH- and temperature-stable. Due to this, it is found often in nature. This inertness also makes pyrite a desirable reaction product for sulfide removal using an iron-based scavenger. Various iron sulfides can be formed chemically from iron compounds reacting with soluble sulfides at ambient conditions in aqueous systems. The specific reaction conditions control both the products formed and the rate of reaction. 

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