Synthesis semi-continuous

Pera-Titus M, Mallada R, Llorens J, Cunill F, Santamari a J. Preparation of inner-side tubular zeolite NaA membranes in a semi-continuous synthesis system. J Membr Sci 2006 278(1-2) 401 09. 

Additionally, the influence of the life time of the micro-structured devices as well as the expenditure of the peripheral equipment was estimated in order to obtain insight into the ecological hot-spots of the system. A conventional macro-scaled semi-continuously operated batch process was chosen as a reference process. The comparison of both technological systems was performed by means of the two-step synthesis of m-anisaldehyde serving as model reaction. 

Continuous and Semi-Continuous Zeolite Synthesis The first report of continuous synthesis, rather than the usual batch-wise synthesis of zeolites, was from Mobil Oil in 1963 [172]. Another similar patent was from Alcoa Aluminum in 1969 [173]. 

Studies were carried out In a one-liter, mechanically-stirred autoclave operated In a semi-continuous fashion In that the catalyst and liquid carrier (normal-octacosane) remain In the reactor whereas synthesis gas is sparged to the reactor and volatile products removed overhead. The phases are well mixed, which simplifies Interpretation of experimental results. Moreover, the degree of mass transport can be controlled by varying the degree... 

Pina MP, Arruebo A, Felipe A, Fleta F, Bernal MP, Coronas J, Menendez M, and Santamaria J. A semi-continuous method for the synthesis of NaA zeolite membranes on tubular supports. J Membr Sci 2004 244 141-150. 

Nair and co-workers [8] have coupled of semi-continuous NF with the Heck reaction. The objective was the synthesis of trans-stilbene from styrene and iodobenzene using Pd(OAc)2(PPh3)2 as catalyst and Pjo-tolyljj as stabilizing agent. They used solvent-resistant membranes and different aqueous/solvent systems (ethyl acetate and acetone/H20 methyl tert-butyl ether and acetone/H20 tetra-hydrofuran/H20). The best conversion was obtained with the first-mentioned solvent mixture. A selectivity of 100% of trans-stilbene with a cumulative turnover number of 1200 was reported, where the rejection of the catalyst turned out to be as high as 97%. Therefore, the authors concluded that NF was a convenient technique to run catalytic reactions with catalyst recycling, since this method saves the catalyst, prevents the metal contamination of the products, and increases reactor productivity. 

The reactor system, where the kinetic experiments were carried out can be described as a semi-batch reactor. Only the synthesis gas (H2 and CO) was fed into the reactor continuously during the experiments, while 1-butene and the solvent were in the batch mode. All reactions took place in the liquid phase. The mass balance for an arbitrary component in the gas is given by... 

Straightforward. We have therefore employed XAD-4 to combine biocatalytic synthesis with simultaneous product extraction. The system (Figure 15.8) comprises a continuously stirred tank reactor, a starting material feed pump, a product recovery loop with a (semi-) fluidized bed of XAD-4, and a pump to circulate the entire reaction mixture through the loop." ° Preliminary studies indicated that XAD-4 had no detrimental effects on E. coli JMlOl (pHBP461), hence, separation of biomass and reaction liquid prior to catechol extraction was not required. The biocatalytic reaction was carried out at very low concentrations of the toxic substrate and product. This was achieved by feeding the substrate at a rate lower than the potential bioconversion rate in the reactor. 

All the optically active terpenes mentioned in this chapter are commercially available in bulk (>kg) quantities and are fairly inexpensive. Although many of them are isolated from natural sources, they can also be produced economically by synthetic methods. Actually, two thirds of these monoterpenes sold in the market today are manufactured by synthetic or semi-synthetic routes. These optically active molecules usually possess simple carbocyclic rings with one or two stereo-genic centers and have modest functionality for convenient structural manipulations. These unique features render them attractive as chiral pool materials for synthesis of optically active fine chemicals or pharmaceuticals. Industrial applications of these terpenes as chiral auxiliaries, chiral synthons, and chiral reagents have increased significantly in recent years. The expansion of the chiral pool into terpenes will continue with the increase in complexity and chirality of new drug candidates in the research and development pipeline of pharmaceutical companies. 

Due to their thermal instability fine chemicals often must be produced in the liquid phase at moderate temperatures. They are generally complex and multifunctional as well as chemo-, regio- and stereoselectivity play an important role. The reactor system of the choice are batch or semi batchwise operated multipurpose units. Bulk chemicals, mostly consisting of relatively small, thermostable molecules, can be produced in continuously operated fixed bed or fluidised bed reactors in the gas-phase allowing much higher space time yields, thus minimising investment costs1. These procedures can hardly be applied to the synthesis of e.g. fine and intermediate chemicals because of the relatively small... 

One of the biggest issues hindering the utilisation of macromarine compounds as drugs is that of supply. Total synthesis, partial synthesis and the semi-synthesis of natural products may reduce the demand pressure during commercial development however, the complexity of natural products extends the timeline for the realistic production of material needed for clinical testing. Sensible mariculture techniques will undoubtedly help to preserve the natural sources for these compounds while also allowing for testing to continue. 

Since for general clinical use morphine has a number of disadvantages the main one of which is its addictive property, many attempts have been made to modify the structure by semi-synthesis even before the structure had been fully established (ref.64). In parallel with the use of morphine and thebaine as natural intermediates many compounds having a simple structural resemblance to morphine have been studied for their potential analgesic activity without addictive and other side effects (ref.65), a search which continues to this day. 

In order to avoid a pronounced shift of the phase behaviour with the progress of the reaction one reactant can be fed to the reactor in a semi-batch mode. With this concept shift in phase behaviour may be compensated and the optimal state of the system is maintained during the whole reaction time. After phase separation at the most suitable temperature conventional product isolation follows. This sequence of process steps is also possible in a continuously operating process, as illustrated in Fig. 5.17 for the synthesis of 1-phenoxyoctane in a microemulsion stabilised by Triton X-100 [28],... 

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