Extruders reactions

Small commercial continuous extruders require a minimum of 100-1000 g of material for a typical experiment. Such extruder reactions may not be convenient for running a large matrix of screening experiments to optimize processing conditions, especially when limited amounts of valuable starting materials are involved. Most commercial REX processes are simple one-step chemical reactions between inexpensive and readily available starting materials. REX is particularly suited for just-in-time inventory control of a commercial polymer product because the total time involved in reaction and product finishing is often much shorter than in conventional continuous processes. 

Important processing methods mixing/compounding, injection molding, extrusion, Banbury mixer, two-roll mills, cold feed extruders, reaction injection molding... 

The technique involves the uses of rotatable sampling ports that enable the polymer to be removed and quenched as it passes particular zones (corresponding to different values of LID) as shown in Figure 1.37 (Van Duin et al, 2001). In this way 2g of polymer can be collected for off-line analysis in about 3-5 s. For the above polymers, the most common profile for product formation along the axis of the extruder was one that followed the profile for the decomposition of the peroxide with time (and thus distance along the extruder). Reaction of MA was very rapid, and there was an exponential growth in the amount of maleated polyolefin as the MA was consumed. 

Hydroxy-THISs react with electron-deficient alkynes to give nonisol-able adducts that extrude carbonyl sulfide, affording pyrroles (23). Compound 16 (X = 0) seems particularly reactive (Scheme 16) (25). The cycloaddition to benzyne yields isoindoles in low- yield. Further cyclo-addition between isoindole and benzyne leads to an iminoanthracene as the main product (Scheme 17). The cycloadducts derived from electron-deficient alkenes are stable (23, 25) unless highly strained. Thus the two adducts, 18a (R = H, R = COOMe) and 18b (R = COOMe, R = H), formed from 7, both extrude furan and COS under the reaction conditions producing the pyrroles (19. R = H or COOMe) (Scheme 18). Similarly, the cycloadduct formed between 16 (X = 0) and dimethylfumarate... 

There seem to be few limits to the kind of fragment extruded (Scheme 29), or to the nature of reactions preceding the fragmentation step. An illustrative example is the formation of a zwitterionic isomer before loss of ethylene (Scheme 30 Section 5.14.4.2.4) (70JOC584, B-73MI50301). 

Thiirane 1,1-dioxides extrude sulfur dioxide readily (70S393) at temperatures usually in the range 50-100 °C, although some, such as c/s-2,3-diphenylthiirane 1,1-dioxide or 2-p-nitrophenylthiirane 1,1-dioxide, lose sulfur dioxide at room temperature. The extrusion is usually stereospeciflc (Scheme 10) and a concerted, non-linear chelotropic expulsion of sulfur dioxide or a singlet diradical mechanism in which loss of sulfur dioxide occurs faster than bond rotation may be involved. The latter mechanism is likely for episulfones with substituents which can stabilize the intermediate diradical. The Ramberg-Backlund reaction (B-77MI50600) in which a-halosulfones are converted to alkenes in the presence of base, involves formation of an episulfone from which sulfur dioxide is removed either thermally or by base (Scheme 11). A similar conversion of a,a -dihalosulfones to alkenes is effected by triphenylphosphine. Thermolysis of a-thiolactone (5) results in loss of carbon monoxide rather than sulfur (Scheme 12). 

Difluoroaminofluorodiazirine (225) extrudes nitrogen at only 75 °C. Intramolecular stabilization gives trifluoromethylenimine (226) added tetrafluoroethylene is cyclopropa-nated. This type of dichotomy is not often found in carbene chemistry alkylcarbenes undergo intramolecular stabilization as a rule, whereas intermolecular stabilization is observed exclusively with alkoxycarbonylcarbenes and with difluorocarbene. In the latter case CF2 attacks its precursor when no other reaction partner is present. 

When the catalyst is expensive, the inaccessible internal surface is a liabihty, and in every case it makes for a larger reactor size. A more or less uniform pore diameter is desirable, but this is practically reahz-able only with molecular sieves. Those pellets that are extrudates of compacted masses of smaller particles have bimodal pore size distributions, between the particles and inside them. Micropores have diameters of 10 to 100 A, macropores of 1,000 to 10,000 A. The macropores provide rapid mass transfer into the interstices that lead to the micropores where the reaction takes place. 

The catalyst should be the copper-based United Catalyst T-2370 in 3/16 , reduced and stabilized, in extrudate form. Initially, 26.5 g of this should be charged to the catalyst basket. This catalyst is not for methanol synthesis but for the low temperature shift reaction of converting CO to CO2 with steam. At the given conditions it will make methanol at commercial production rates. Somewhat smaller quantity of catalyst can also be used with proportionally cut feed rates to save feed gas. 

Polymers containing oxazoline groups are obtained either by grafting the 2-oxazoline onto a suitable existing polymer such as polyethylene or polyphenylene oxide or alternatively by copolymerising a monomer such as styrene or methyl methacrylate with a small quantity (<1%) of a 2-oxazoline. The grafting reaction may be carried out very rapidly (3-5 min) in an extruder at temperatures of about 200°C in the presence of a peroxide such as di-t-butyl peroxide Figure 7.13). 

Reaction of alkali cellulose with carbon disulphide to produce a cellulose xanthate which forms a lyophilic sol with caustic soda. This may be extruded into a coagulating bath containing sulphate ions which hydrolyses the xanthate back to cellulose. This process is known as the viscose process and is that used in the manufacture of rayon. 

The transition state composition is, moreover, uncertain as regards the number of solvent molecules it contains. Thus, we might write for Eq. (6-1), carried out in water, a composition of [Fe(CN)5N2H4C>33 nH20]t. The number of water molecules is of more than academic interest here, in that the net reaction extrudes one molecule of water. It has been suggested (from chemical evidence,1 not as a deduction from the rate law) that water is eliminated first, and that the reaction may occur by way of the following transition state (or intermediate) ... 

On an industrial scale, PA-6 is synthesized from e-caprolactam with water as the initiator. The process is very simple if the reaction is earned out at atmospheric pressure. The polymerization is earned out in a VK-reactor (Fig. 3.23), which is a continuous reactor without a stirrer, with a residence time of 12-24 h at temperatures of 260-280°C.5,28 Molten lactam, initiator (water), and chain terminator (acetic acid) are added at the top and the polymer is discharged at the bottom to an extruder. In this extruder, other ingredients such as stabilizers, whiteners, pigments, and reinforcing fillers are added. The extruded thread is cooled in a water bath and granulated. The resultant PA-6 still contains 9-12%... 

The competition at 200°C between an aliphatic and an aromatic amine toward the formation of an imide is a very selective reaction (Fig. 5.1) for the formation of an aliphatic imide.141 This reaction suggests that the reactive processing in extruder, for example, could be used to transform a melt-processable polyimide with an oligomer end capped with an aliphatic amine. In order to get a perfecdy alternate block polyimide-block siloxane, Rogers et al. used low-temperature transimidization.142 An oligomeric aromatic imide was end capped... 

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