Recovery paraffin

Since the Sorbex process is a liquid-phase fixed-bed process, the selection of particle size is an important consideration for pressure drop and process hydraulics. The exact particle size is optimized for each particular Molex process to balance the liquid phase diffusion rates and adsorbent bed frictional pressure drop. The Sorbex process consists of a finite number of interconnected adsorbent beds. These beds are allocated between the following four Sorbex zones zone 1 is identified as the adsorption zone, zone 2 is identified as the purification zone, zone 3 is identified as the desorption and zone 4 is identified as the buffer zone. The total number of beds and their allocation between the different Sorbex zones is dependent on the desired performance of the particular Molex process. Molex process performance is defined by two parameters extract normal paraffin purity and degree of normal paraffin recovery from the corresponding feedstock. Details about the zone and the bed allocations for each Molex process are covered in subsequent discussions about each process. 

In Sorbex terminology, a gasoline Molex unit is classified as a low purity and low recovery Sorbex unit since typical purity and recovery targets are greater than 85% n-paraffin purity while operating at greater than 90% feed n-paraffin recovery. 

The recovery process is a vapor phase fixed-bed adsorption technology featuring desorption with ammonia. This process has paraffins recovery and product purity in the high 90% s. Ammonia is a very efficient desorbent. Since it is easily separated from the n-paraffins product, fractionation capital and energy requirements are substantially reduced. Furthermore, ammonia has the added advantage of protecting the adsorbents from coking. 

The liquid-phase extraction process operates at 177°C and 24.6 kg/cm (g), whereas the vapor-phase extraction process operates at 310-350°C and 2.2 kg/cm (a). Most importantly, the n-paraffin product from either process can surpass 99% purity and attain paraffin recoveries exceeding 95%. 

In contrast to trace impurity removal, the use of adsorption for bulk separation in the liquid phase on a commercial scale is a relatively recent development. The first commercial operation occurred in 1964 with the advent of the UOP Molex process for recovery of high purity / -paraffins (6—8). Since that time, bulk adsorptive separation of liquids has been used to solve a broad range of problems, including individual isomer separations and class separations. The commercial availability of synthetic molecular sieves and ion-exchange resins and the development of novel process concepts have been the two significant factors in the success of these processes. This article is devoted mainly to the theory and operation of these Hquid-phase bulk adsorptive separation processes. 

Separation of Norma/ and Isoparaffins. The recovery of normal paraffins from mixed refinery streams was one of the first commercial appHcations of molecular sieves. Using Type 5A molecular sieve, the / -paraffins can be adsorbed and the branched and cycHc hydrocarbons rejected. During the adsorption step, the effluent contains isoparaffins. During the desorption step, the / -paraffins are recovered. Isothermal operation is typical. 

Naphthenic acids are normal constituents of nearly all cmde oils, but not all cmdes contain sufficient quantities of usable acids to make recovery an economic process. Heavy cmdes from geologically young formations have the highest acid content, and paraffinic cmdes usually have low acid content. 

Both vapor-phase and Hquid-phase processes are employed to nitrate paraffins, using either HNO or NO2. The nitrations occur by means of free-radical steps, and sufftciendy high temperatures are required to produce free radicals to initiate the reaction steps. For Hquid-phase nitrations, temperatures of about 150—200°C are usually required, whereas gas-phase nitrations fall in the 200—440°C range. Sufficient pressures are needed for the Hquid-phase processes to maintain the reactants and products as Hquids. Residence times of several minutes are commonly required to obtain acceptable conversions. Gas-phase nitrations occur at atmospheric pressure, but pressures of 0.8—1.2 MPa (8—12 atm) are frequentiy employed in industrial units. The higher pressures expedite the condensation and recovery of the nitroparaffin products when cooling water is employed to cool the product gas stream leaving the reactor (see Nitroparaffins). 

Norma/andBranc/jedAlip/jatic Hydrocarbons. The urea-adduction method for separating normal and branched aHphatic hydrocarbons can be carried out in sulfolane (38,39). The process obviates the necessity of handling and washing the soHd urea—normal paraffin adduct formed when a solution of urea in sulfolane is contacted with the hydrocarbon mixture. OveraH recovery by this process is typicaHy 85% normal paraffin purity is 98%. 

So, Sulfolane and Carom, ca 1997, are two current rival processes. Sulfolane has a slight advantage over Carom ia energy consumption, while Carom has 6—8% less capital for the same capacity Sulfolane unit. In 1995, Exxon (37) commercialized the most recent technology for aromatics recovery when it used copolymer hoUow-fiber membrane ia concentration-driven processes, pervaporation and perstraction, for aromatic—paraffin separation. Once the non aromatic paraffins and cycloparaffins are removed, fractionation to separate the C to C aromatics is relatively simple. 

Dichloroethane is produced commercially from hydrogen chloride and vinyl chloride at 20—55°C ia the presence of an aluminum, ferric, or 2iac chloride catalyst (8,9). Selectivity is nearly stoichiometric to 1,1-dichloroethane. Small amounts of 1,1,3-tfichlorobutane may be produced. Unreacted vinyl chloride and HCl exit the top of the reactor, and can be recycled or sent to vent recovery systems. The reactor product contains the Lewis acid catalyst and must be separated before distillation. Spent catalyst may be removed from the reaction mixture by contacting with a hydrocarbon or paraffin oil, which precipitates the metal chloride catalyst iato the oil (10). Other iaert Hquids such as sdoxanes and perfluorohydrocarbons have also been used (11). 

Liquid propane is a selective hydrocarbon solvent used to separate paraffinic constituents in lube oil base stocks from harmful asphaltic materials. It is also a refrigerant for liquefying natural gas and used for the recovery of condensable hydrocarbons from natural gas. 

Gutierrez M, Forster FI, McConnell SA, et al. The detection of CD2+, CD4+, CD8+, and WC1+ T lymphocytes, B cells and macrophages in fixed and paraffin embedded bovine tissue using a range of antigen recovery and signal amplification techniques. Vet. Immunol. Immunopathol. 1999 71 321-334. 

Benchekroun M, DeGraw J, Gao J, et al. Impact of fixative on recovery of mRNA from paraffin-embedded tissue. Diagn. Mol. Pathol. 2004 13 116-125. 

Notes HeLa cells (1 x 106) were formalin-fixed in an equal volume of 1% agarose. After histological processing and paraffin embedding, the cell plugs were rehydrated and resuspended in the indicated buffer. Total protein in the supernatants was assessed colorimetrically after heating at the indicated temperatures and times. The % recovery values are the mean, the standard deviation and relative to a fresh cell lysate from the sample number of cells (for more detail, see Reference 25). 

Fowler CB, Cunningham RE, Waybright TJ, et al. Elevated hydrostatic pressure promotes protein recovery from formalin-fixed, paraffin-embedded tissue surrogates. Lab. Invest. 2008 88 185-195. 

To suggest a set of directions for future research in antigen retrieval requires that one first state the objective(s) toward which that research is directed. There are a number of important research directions that are deserving of attention, two of which we will consider here—(1) the recovery of unmodified proteins in native conformation from formalin-fixed, paraffin-embedded (FFPE) tissue and (2) the development of new techniques for assessing the quantity and functional state of tissue proteins recovered from FFPE tissue. 

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