Recycling of waste plastics is essential for reducing environmental degradation and ensuring future resource security. The quantity of domestic plastic waste recycled is increasing yearly, reaching 83 % in 2014. However, only 26 % and 4 % of the recycled waste plastic is treated by mechanical and feedstock recycling, respectively, whereas 70 % is treated by energy recovery (incineration). Therefore, the mechanical and feedstock recycling rates must be improved. This review examines the pyrolysis of waste plastics, which is a treatment method classed as feedstock recycling. Pyrolysis can convert waste plastics, which cannot be treated by mechanical recycling, into oils and gases. However, polyvinylchloride (PVC) and poly(ethylene terephthalate) (PET) produce corrosive gases and sublimating substances during pyrolysis, resulting in reduced quality of pyrolysis products, and damage to the treatment plant. Dehydrochlorination and dechlorination of PVC, in addition to catalytic pyrolysis of PET using Ca-based catalysts, have been developed. Recent studies into the pyrolysis of major plastics such as polyethylene (PE), polypropylene (PP), and polystyrene (PS) are summarized here, together with research on the dry and wet treatment of PVC and the catalytic pyrolysis of PET.
Supercritical fluid, which is defined as a state of fluid over the critical temperature and pressure, has high potential as a reaction and separation solvent. The development of chemical recycling of waste plastics by decomposition reactions in subcritical and supercritical fluids is reviewed including fundamental investigation and commercialization. Decomposition reactions proceed rapidly and selectively in supercritical fluids compared to conventional processes. Condensation polymerization plastics such as PET and nylon are relatively easily depolymerized to their monomers in supercritical water or alcohols. Crosslinked polymer can be recycled by selective decrosslinking reactions in supercritical fluid without severe decomposition of the backbone chains. Fiber reinforced plastics can also be recycled by depolymerization of the resin component to obtain recovered fibers and monomers. Pilot scale or commercial scale plants using subcritical and supercritical fluids have been developed for plastics recycling.
Pore size through silica based membranes prepared by using a counter diffusion chemical vapor deposition (CVD) method can be controlled precisely by using silica precursors having organic functional groups. These membranes were applied to hydrocarbon separation especially for propylene/propane system and methane/ethane system. In this paper, ethyltrimethoxysilane (ETMOS), propyltrimethoxysilane (PrTMOS) and hexyltrimethoxysilane (HTMOS) were used for the silica precursors. According to the thermal decomposition properties of the silica hydrolysis powder, the decomposition temperature of HTMOS (400 °C) is higher than those of ETMOS and PrTMOS. The pore sizes through the silica hybrid membranes deposited at 270 °C were approximately 0.40 nm that were independent of the sizes of alkyl groups in the silica precursors. The alkyl groups in the membranes can be partially decomposed during the deposition. Methane/ethane permeance ratio of 38 (methane permeance 2.8 × 10−9 mol m−2 s−1 Pa−1) was obtained through the ETMOS derived membrane deposited at 300 °C. The HTMOS derived membrane showed the propylene/propane permeance ratio of 414. The activation energy of C3H8 permeation was positive showing that the high permeation ratio was due to molecular sieve permeation mechanism. Amorphous silica based membranes showed the potential for hydrocarbon separation by controlling the deposition conditions.
Three methods of efficient pore size control for microporous carbon membranes were developed, (1) vapor-phase synthesis of furfuryl alcohol (FFA) carbon membranes, (2) pore size control by post-activation and (3) quaternary ammonium salt-mediated method for the direct synthesis of microporous carbon membranes with large pores. (1) At first, a H2-permselective FFA carbon membrane with pore size of 0.30 nm was prepared through optimization of the conditions of FFA deposition and carbonization process. (2) Next, the FFA carbon membranes were activated using various gases and vapors such as H2, CO2, O2 and steam (H2O). Different pore sizes and morphological changes were observed by changing the activation agent and temperature. After activation using H2 at 700 °C, the pore size of the microporous carbon membrane was increased from 0.30 to 0.45 nm. (3) Quaternary ammonium salt-mediated synthesis was developed for the direct synthesis of microporous carbon membranes with pore size larger than 0.40 nm. Using two types of cationic tertiary amines with different chain lengths, microporous carbon membranes with uniform pores of 0.4 nm and 0.5 nm were successfully synthesized. Using these methods, microporous carbon membranes with uniform pore sizes from 0.30 to 0.50 nm were successfully prepared, and were used in various H2 separation processes. These microporous carbon membranes showed superior H2-permselectivity in various H2 separation processes such as H2/CO, H2/CO2 and dehydrogenation of organic hydrides in a membrane reactor. The present techniques are expected to achieve precise pore size control of microporous carbon membranes.
Organic, inorganic, and metal-based materials for membrane technologies have been studied and developed, and membranes made from some of these materials have been applied to industrial applications. Various polyimides synthesized from combinations of several types of acid dianhydrides and diamines allow systematic molecular design of the membrane materials. Polyimide membranes applied to hydrogen recovery in the petroleum industry in the 1980 s are still used in various applications for gas and vapor separation such as nitrogen- or oxygen-enrichment by air separation, dehumidification, dehydration, carbon dioxide removal, and others. In particular, polyimides from 3,3’,4,4’-biphenyltetracarboxylic dianhydride (BPDA) have excellent fiber-forming properties with good thermal, chemical, and mechanical durability, so are used to manufacture asymmetric hollow fiber membranes for use in many membrane separation processes. This review introduces the material characteristics of polyimides, membrane properties of polyimide hollow fiber membranes, and applications as membranes for gas and vapor separation.
In the study, model based post-stack inversion technique was used to create pseudo logs at each seismic trace at the well location to constitute high resolution acoustic inverted impedance models. Interpretation of GR log, SP log, Caliper log, and seven sand bodies were marked as reservoir zones in well FG #X, which were identified as a hydrocarbon bearing reservoir. All of predicted gases bearing zones in the well FG #X show the low acoustic impedance (AI) values in inverted section analogous with the calculated AI value of logging data. The impedance value in an inverted section during 1660-1980 ms represents an image of the alteration of thin sand and a thick shale layer of Upper Bhubon formation. By observing the relatively lower AI values in the inverted section three locations have marked as additional well locations (PW 1, PW 2 and PW 3), which are more prospective for optimizing the gas recovery from this field.
Several supported transition metal oxides (X/Y, X＝WO3, Nb2O5, Y＝Al2O3, TiO2, SiO2) were investigated as solid acid catalysts for hydrolysis of dimethyl ether (DME). Among the transition metal oxide catalysts tested, Nb2O5/Al2O3 showed the highest catalytic activity in the temperature range appropriate for DME steam reforming. Using several types of Nb2O5/Al2O3 samples, the effects of Nb2O5 loading amounts and calcination temperature on the catalytic activity were studied to enhance the hydrolysis activity. XRD patterns showed AlNbO4 phase appeared when the calcination temperature was over 800 °C. The BET surface area decreased for the increase in the calcination temperature. For Nb2O5/Al2O3, the acid amount increased consistently with the Nb2O5 loading amounts up to 25 wt%, and it became almost constant for the further increase in the Nb2O5 loadings. 25 wt% Nb2O5/Al2O3 catalyst calcined at 500 °C exhibited the highest catalytic activity for DME hydrolysis, and consequently steam reforming of DME was carried out over the Nb2O5/Al2O3 mixed with Cu/ZnO/Al2O3. It was found that an optimal ratio of Cu/ZnO/Al2O3 to Nb2O5/Al2O3 was 1, which resulted in higher catalytic activity for steam reforming of DME than a mixture of Cu/ZnO/Al2O3 and γ-Al2O3.
Several configurations of membrane separation process were designed and evaluated for recovery and purification of hydrogen derived from dehydrogenation of methylcyclohexane for use in fuel cell vehicles (FCVs). Process conditions were assumed as follows: (a) Feed gas treated by the quenching process contains 98 % hydrogen and 2 % toluene; (b) Operating pressures of feed and permeate are 0.3 MPa and 0.1 MPa, respectively; (c) Target hydrogen recovery rate is 90 % with less than 0.3 ppm of residual toluene in purified hydrogen; (d) Purified hydrogen is stored at a pressure of 0.7 MPa; (e) Activity of the membrane stage follows the cross plug flow model. The single stage process required only specific power of 0.12 kWh Nm−3-H2 for compressing hydrogen into the storage tank. This process required the least energy but needed an ultra-high ideal separation factor of 280,000 at least. The two stage cascade process with a moderate ideal separation factor of 1000 to 1500 attained the recovery target and required specific power of 0.19 kWh Nm−3-H2 including recompression of the first stage permeate. The three stage process, which consists of the single stage followed by the two stage cascade, enabled membranes with an ideal separation factor of around 10,000 to achieve the target, and required specific power of less than 0.19 kWh Nm−3-H2. Membrane separation processes are competitive with pressure swing adsorption (PSA) processes.
A modified type analysis method (DS method) for heavy oil was conducted using a Liebig condenser as a column, which scale was about 1/4 as prescribed in the JPI standard (JPI-5S-22-83). Two kinds of maltenes (pentane soluble fractions), those from Middle East vacuum residue (ME) and Cold Lake oil sand bitumen atmospheric residue (CL), were separated into saturates, aromatics and resins by JPI and DS methods. The repeatability errors for the recoveries of respective saturates, aromatics and resins were within 2 wt% on each experiments. The recoveries of corresponding fractions between both methods were well agreed to each other, and also the results of elemental analysis. Those results indicate that the DS method is available as an alternative method to the JPI standard.
Saturate fractions separated by the JPI standard and DS methods, which is about a quarter-scale separation of the JPI standard, from maltenes (pentane-soluble fraction) in Middle East vacuum residue (ME) and Cold Lake oil sand bitumen atmospheric residue (CL), were analyzed by a HPLC system equipped a series of amino-modified silica-gel columns, an ultraviolet (UV, dual wavelength mode) detector and an evaporate light scattering detector (ELSD) using hexane as an eluent. All saturate fractions showed two peaks. The first one was assigned as nonaromatics, and the second one, monoaromatics, because only the second one showed a peak by UV detector at 270 nm, but no peaks at 320 nm. These peaks were determined after the correction of base line and intensity, since ELSD has an exponentially response with concentration. In an additional separation test by DS methods, the heptane eluent was collected into four subfractions, and those peaks were observed only in the first two subfractions. Another separation test was performed using a model sample (MO) including compounds having two benzene rings in a molecule (diphenyls). The heptane and toluene eluents were collected into four subfractions, respectively, then analyzed by gas chromatography. Diphenyls were observed in the last two subfractions of heptane and the first subfraction of toluene elutions. From the results, diphenyls could not determine by themselves, but as a part of polyaromatics. As a result, ME and CL contained practically no diphenyls. In conclusion, the combination of the JPI/DS methods and HPLC analysis provides the distribution of four types, nonaromatics, monoaromatics, polyaromatics and resins in maltene.
A certified reference material (CRM), NMIJ CRM 8302-a, for the quality control of biodiesel fuel analysis has been issued by the National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ, AIST). This CRM is based on 100 % fatty acid methyl esters (palm oil-based, B100 Biodiesel). The certified parameters are content of water and 6 elements (S, Na, K, Mg, Ca and P); density and kinematic viscosity. The methods for the accurate characterization of sulfur in biodiesel fuel certified reference material are described. The concentration (mass fraction) of sulfur was determined by three inductively coupled plasma tandem quadrupole mass spectrometer (ICP-MS/MS) methods and a combustion ion chromatography (CIC) method. The CIC result was validated by determining sulfur content in three certified reference materials (NIST SRM 2773, NIST SRM 2298 and NIST SRM 2299). The certified value of sulfur in the CRM 8302-a was determined as the weighted mean of the results of the above four methods.