Faizur Rahman

Nanostructured materials for water desalination.

Desalination of seawater and brackish water is becoming an increasingly important means to address the scarcity of fresh water resources in the world. Decreasing the energy requirements and infrastructure costs of existing desalination technologies remains a challenge. By enabling the manipulation of matter and control of transport at nanometer length scales, the emergence of nanotechnology offers new opportunities to advance water desalination technologies. This review focuses on nanostructured materials that are directly involved in the separation of water from salt as opposed to mitigating issues such as fouling. We discuss separation mechanisms and novel transport phenomena in materials including zeolites, carbon nanotubes, and graphene with potential applications to reverse osmosis, capacitive deionization, and multi-stage flash, among others. Such nanostructured materials can potentially enable the development of next-generation desalination systems with increased efficiency and capacity.

Characterization of foulants by autopsy of RO desalination membranes

Abstract A study was undertaken to identify various types of scales that were responsible for shortening the useful life span of the membrane permeators in a commercial reverse osmosis (RO) desalination plant. Compositions of the raw and treated feed water and of the reject brine were determined using the inductively coupled plasma (ICP) spectrometry and ion chromatography (IC). Various scaling index calculations showed that the feed and brine were non-scale forming with respect to CaCO 3 (calcite), SrSO 4 , CaSO 4 .2H 2 O (gypsum), and silica (SiO 2 ). Two completely fouled membrane permeators, retired from stage 1 and stage 2 of a commercial plant, were subjected to membrane autopsy using scanning electron microscopy (SEM), X-ray diffractometry (XRD), optical microscopy (OM), and energy dispersive x-ray florescence (XRF). The deposits were predominantly amorphous in nature. The membrane autopsy showed that CaCO 3 , SrSO 4 , and CaSO 4 .2H 2 O (gypsum) scales did not constitute a serious problem in the plant. The advanced phosphonate+polyacrylate based scale inhibitor had itself formed Ca phosphonate sludge, but the amount was quite small. Though below saturation, silica is believed to have been precipitated due to the catalyzing effect of trivalent Al 3+ and Fe 3+ ions. Iron fouling was the major cause of reduced life span of the membranes and, to a lesser extent, calcium-alumino-silicates.

Identification of scale deposits through membrane autopsy

A polyacrylate and hydroxyethylidene diphosphonate (HEDP) based advanced anti-scalant was tested against the conventional H2SO4 and sodium hexa-meta-phosphate (SHMP) inhibitors in a pilot plant which had parallel RO units, each fitted with identical hollow fine fiber (HFF) permeators which received same brackish feed water. At the end of the 3000 h trial, product TDS of unit #2 operating on the conventional treatment was only 180 ppm vs 620 ppm for unit #1 operating on the advanced anti-scalant, and it produced an average of 20% more product water. To identify the scale deposits, autopsy of the first and second stage permeators was carried out using visual observation, scanning electron microscopy (SEM), x-ray diffractometry (XRD), x-ray fluorescence (XRF), inductively coupled plasma (ICP) spectroscopy, ion chromatography (IC), and coulometry techniques. Whereas thick deposits of soft and non-adherent types of scales were found on the permeator fibers of unit #1, no scale was evident on unit #2 permeator fibers and no samples could be collected from them. Analyses of the solids removed from the unit #1 fibers revealed that bulk of the deposited scale was amorphous in nature which the SEM and XRD techniques were unable to charaterize. The XRF, ICP, and IC results suggested that the amorphous sludge was predominantly alumino-silicate type. In addition, membrane fibers of stage 1 had calcium/magnesium phosphonate, formed by the advanced anti-scalant itself by reacting with Ca2+ and Mg2+ of the brine. No CaCO3, SrCO3, CaSO4, SrSO4, or iron-based scales were detected, indicating that the advanced anti-scalant was effective against these scales.

Evaluation of SHMP and advanced scale inhibitors for control of CaSO4, SrSO4, and CaCO3 scales in RO desalination

Abstract Sodium hexa-meta-phosphate (SHMP), inhibitor-A (acrylic polymer), and inhibitor-B (polyacrylate+phosphonate), each at a dose level of 1 ppm (on active basis) were evaluated at 25°C for their efficacy against CaSO4, SrSO4, and CaCO3 scales in a synthesized brine which corresponded to 80% recovery from the locally available aquifer brackish water. At periodic time intervals brine pH was measured and samples were withdrawn and analyzed for Na+, Ca2+, Sr2+, SO42−, and total alkalinity (TA). The total time of equilibration was 168 h (7 days). The criterion adopted in comparing efficacy of the inhibitors was that if an inhibitor could achieve an induction period of at least 15 min, it would be considered an effective inhibitor at that dose level against that particular scalant. In the control experiment (no inhibitor added), there was an immediate drop in Ca2+, Sr2+, and TA levels and the solution became turbid much earlier than 15 min, suggesting that the brine was highly supersaturated and scale-forming with respect to CaCO3 and SrCO3 scales and would require injection of an inhibitor. In 168 h, there was no drop in SO42− concentration suggesting that the brine possessed no potential to form CaSO2.2H2O and SrSO4 scales. SHMP was able to keep the scale-forming constituents (Ca2+, Sr2+, and TA) in solution for 91 h, inhibitor-A for 50 h, and inhibitor-B for all of 168 h, suggesting that the inhibitors at 1 ppm gave completely scale-free operation up to 80% product recovery and that performance of inhibitor-B was the best.

Pilot plant evaluation of advanced vs. conventional scale inhibitors for RO desalination

Abstract An advanced anti-scalant, consisting of a polyacrylate and hydroxyethylidene diphosphonate (HEDP), was tested against the conventional H2SO4 and sodium hexa-meta-phosphate (SHMP) inhibitors in a pilot plant which had parallel RO units. The two units were fitted with identical brackish hollow fine fiber (HFF) permeators arranged in a two-stage mode which received the same brackish feed water, and were operated at the same feed pressure (27.6 bar/400 psig) and product water recovery (70%). Unit #1 was treated 9 ppm of as-received advanced anti-scalant, and unit #2 was treated with 6 ppm of SHMP and about 130 ppm of 98% H2SO4. The pilot plant trial lasted for 3,000 h. The techno-economic evaluation of the two scale control treatments was carried out in terms of pumping energy, the anti-scalants consumed, and the quality and total output of the product water produced in 3,000 h. The pumping energy and scale control treatment costs (as

OXIDATIVE DEHYDROGENATION OF PROPANE

/m3 of water produced) were same for the two treatments; but in terms of salt rejection, product TDS and output, performance of the advanced anti-scalant was inferior; after 3,000 h the salt rejection of unit #1 (which operated on the advanced anti-scalant) was about 81% vs. 94% for unit #2 (H2SO4+SHMP). Similarly, in 3,000 h unit #1 produced 20% less water of unacceptable quality (620 ppm) whereas unit #2 produced more water of excellent quality (180 ppm), providing a clear testimony to the superior performance of the conventional H2SO4+SHMP treatment over the advanced anti-scalant.

Hollow fine fiber vs. spiral-wound reverse osmosis desalination membranes. Part 2 : Membrane autopsy

The oxidative dehydrogenation of propane provides a highly selective catalyst for the oxidative dehydrogenation of propane to propylene, and a process for preparing the catalyst. The catalyst is a mixed metal oxides catalyst of the general formula MoaVbOx, where the molar ratio of molybdenum to vanadium is between 1:1 and 9:1 (a:b is between 0.5:0.5 and 0.9:0.1) and x is determined according to the oxidation state of the cations present. The catalyst is prepared by mixing the metals by sol-gel technique, heating the gel to dry the mixed oxides, further heating the dried product to induce auto-combustion, washing the product with isopropyl alcohol, and drying with a supercritical CO2 dryer. Oxidative dehydrogenation is carried out by contacting a stream of propane gas with the bulk mixed metal oxides catalyst at a temperature between 350° C. and 550° C. Propylene selectivity of 100% is reached at conversion rates between 1.9% and 4.8%.At temperatures near 650°C and residence times ofca. 3 s, the homogeneous oxidative dehydrogenation (OXD) of propane to propylene and ethylene approached oxygen limiting conditions, even when the reactor was filled with quartz chips. The addition of catalysts that are known to be effective in the OXD of ethane slightly increased the reaction rate, but the selectivities at a given conversion level were the same as those that were achieved in the homogeneous reaction.

Techno-economic evaluation of waste lube oil rerefining

Abstract A comparative evaluation of a holloe fine fiber (HFF) and a spiral-wound (SW) membrane was carried out by operating them in parallel units of an RO pilot plant. The two units received the same brackish feed water, identical scale control treatment (H2O+SHMP) and operated at the same recovery (70%). Unit #1, using the HFF membrane, was operated at a feed pressure of 27.6 bar (400 psig); unit #2, using the SW membrane, was operated at 15.2 bar (220 psig). The trial lasted 7500 h. The SW membrane produced water of excellent quality (86 ppm) vs. 470 ppm by the HFF membrane, and it consumed only half as much pumping energy, thereby outperforming the HFF membrane. Following the 7500 h trial, an autopsy of the two membranes was carried out to identify the scale deposits. Visual observation, scanning electron microscopy (SEM), X-ray diffractomery (XRD), inductively coupled plasma (ICP) spectroscopy, coulometry, photometric and gravimetric techniques were used. Both membranes were found in fouled condition. However, the HFF membrane was much more fouled. SEM and XRD analyses showed that 90–100% of the deposits were amorphous in nature. Results of the coulometric and photometric methods suggested that sodium hexa-meta-phosphate (SHMP) was effective in controlling the CaCO3 scale but was itself responsible for the fouling of both membranes by reversion to orthophosphate (PO43−). The ICP results showed that iron contributed to the fouling. Among the inorganic scales, calcium alumino silicate clay was the major scale; but the great bulk of the deposit on both membranes was organic matter or biomass.

Hollow fine fiber vs. spiral-wound RO desalination membranes Part 1: Pilot plant evaluation

Abstract This paper discusses the secondary use of used automotive lubricating oils. Current technologies for processing waste lube oil into new lubricants is outlined and the performance features of these products are compared with that of virgin materials. Process technology of Meinken and Mohawk were selected for techno-economic evaluation. A plant size of 50 000 TPA waste oil re-refining was considered for economic study of these processes. The estimated production cost for Meinken process was found to be

Effect of lower feedstock prices on economics of MTBE complex

348.8 per ton and for Mohawk process, assuming hydrogen supply to be made available from adjacent refinery, it was estimated to be