Pyrolysis separation system

The separation train of the plant is designed to recover important constituents present in the furnace effluent. The modem olefin plant must be designed to accommodate various feedstocks, ie, it usually is designed for feedstock flexibiUty in both the pyrolysis furnaces and the separation system (52). For example, a plant may crack feedstocks ranging from ethane to naphtha or naphtha to gas oils. 

The hollow-fiber systems for gas separation or the tubular microfiltration systems have to be pyrolyzed before mounting in the membrane housing, because of the large shrinkage during pyrolysis. That is the most critical step in the fabrication of a separation system. 

Lincoff, A.M., Separation System for Recovery of Ethylene and Light fniicts from a Naphtha-pyrolysis Gas Stream, Process Design Case Sidy, CACHE Corp., Austin, Texas (1983). 

CACHE (Computer Aids for Chanical Engineering CACHE Corporation, 2016) Process Design Case Studies represents an outstanding resource of many case studies. These are covered in 11 different volumes that span Separation System for Recovery of Ethylene and Light Products from Naphtha Pyrolysis Gas Steam in Volume 1, all the way to Conceptual Design of an Aromatics Plant from Shale Gas in Volume 2. 

SEC in combination with multidimensional liquid chromatography (LC-LC) may be used to carry out polymer/additive analysis. In this approach, the sample is dissolved before injection into the SEC system for prefractionation of the polymer fractions. High-MW components are separated from the additives. The additive fraction is collected, concentrated by evaporation, and injected to a multidimensional RPLC system consisting of two columns of different selectivity. The first column is used for sample prefractionation and cleanup, after which the additive fraction is transferred to the analytical column for the final separation. The total method (SEC, LC-LC) has been used for the analysis of the main phenolic compounds in complex pyrolysis oils with minimal sample preparation [974]. The identification is reliable because three analytical steps (SEC, RPLC and RPLC) with different selectivities are employed. The complexity of pyrolysis oils makes their analysis a demanding task, and careful sample preparation is typically required. 

In the thermal desorption technique excavated soil is heated to around 200 to 1000°F (93 to 538°C). Volatile and some semivolatile contaminants are vaporized and carried off by air, combustion gas, or inert gas. Off-gas is typically processed to remove particulates. Volatiles in the off-gas may be burned in an afterburner, collected on activated carbon, or recovered in condensation equipment. Thermal desorption systems are physical separation processes that are not designed to provide high levels of organic destruction, although some systems will result in localized oxidation or pyrolysis. 

Pyrolysis-Gas Chromatography-Mass Spectrometry. In the experiments, about 2 mg of sample was pyrolyzed at 900°C in flowing helium using a Chemical Data System (CDS) Platinum Coil Pyrolysis Probe controlled by a CDS Model 122 Pyroprobe in normal mode. Products were separated on a 12 meter fused capillary column with a cross-linked poly (dimethylsilicone) stationary phase. The GC column was temperature programmed from -50 to 300°C. Individual compounds were identified with a Hewlett Packard (HP) Model 5995C low resolution quadruple GC/MS System. Data acquisition and reduction were performed on the HP 100 E-series computer running revision E RTE-6/VM software. 

In gas separation applications, polymeric hollow fibers (diameter X 100 fim) are used (e.g. PAN) with a dense skin. In the skin the micropores develop during pyrolyzation. This is also the case in the macroporous material but is not of great importance from gas permeability considerations. Depending on the pyrolysis temperature, the carbon membrane top layer (skin) may or may not be permeable for small molecules. Such a membrane system is activated by oxidation at temperatures of 400-450 C. The process parameters in this step determine the suitability of the asymmetric carbon membrane in a given application (Table 2.8). 

It thus seems reasonable to expect that in the process of separation of CjH into 2 CHS radicals there is a distance in the neighborhood of 2.0 to 2.5 A. in which the system has a considerable amount of ionic character. It is our feeling that only such intermediates, particularly of the H-bonded type, are capable of explaining the very high A factors for C2H6 pyrolysis and the high collision efficiencies for radical-radical recombinations. 

Pyrolysis GC-MS Analysis. Flash pyrolysis was performed by using a pyroprobe 100 (Chemical Data Systems) temperature-control system. Samples were pyrolyzed from 150 to 750 °C with a temperature program of 20 °C/ms and a final hold for 20 s. After pyrolysis, the fragments were separated on a 25-m CP WAX 57 fused silica capillary column (temperature program 25-220 °C at 3 °C/min), followed by MS on a R 10-10 C (Ribermag, Rueil-Malmaison, France) operated at 70 eV and scanned from 20 to 400 m/z. 

Solvent-Refined Coal Process. In the 1920s the anthracene oil fraction recovered from pyrolysis, or coking, of coal was utilized to extract 35—40% of bituminous coals at low pressures for the purpose of manufacturing low cost newspaper inks (113). Tetralin was found to have higher solvent power for coals, and the I. G. Farben Pott-Broche process (114) was developed, wherein a mixture of cresol and tetralin was used to dissolve ca 75% of brown coals at 13.8 MPa (2000 psi) and 427°C. The extract was filtered, and the filtrate vacuum distilled. The overhead was distilled a second time at atmospheric pressure to separate solvent, which was recycled to extraction, and a heavier liquid, which was sent to hydrogenation. The bottoms product from vacuum distillation, or solvent-extracted coal, was carbonized to produce electrode carbon. Filter cake from the filters was coked in rotary kilns for tar and oil recovery. A variety of liquid products were obtained from the solvent extraction-hydrogenation system (113). A similar process was employed in Japan during Wodd War II to produce electrode coke, asphalt (qv), and carbonized fuel briquettes (115). 

Pyrolysis. A technique by which nonvolatile samples are decomposed in the inlet system and the volatile products are separated in the chromatographic column. 

In considering the reactions for formation of acetylene in a combustion system, it is worth-while to note, first, the evidence as to the nature of the oxidation and pyrolysis reactions as separate processes. (No attempt is made to review all the voluminous literature in these fields but rather to consider results of significance to the immediate problem.)... 

Originally, extractive distillation was limited to two-component problems. However, recent developments in solvent technology enabled applications of this hybrid separation in multicomponent systems as well. An example of such application is the BTX process of the GTC Technology Corp., shown in Figure 6, in which extractive distillation replaced the conventional liquid-liquid extraction to separate aromatics from catalytic reformate or pyrolysis gasoline. This led to a ca. 25% lower capital cost and a ca. 15% decrease in energy consumption (170). Some other examples of existing and potential applications of the extractive distillations are listed in Table 6. 

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