Koon Fung Lam

Precious metal recovery by selective adsorption using biosorbents.

Silk sericin and chitosan biosorbents are low cost and highly efficient biosorbents derived from waste biomass. Both biosorbents displayed good capacity and excellent selectivity for gold adsorption. Silk sericin and chitosan adsorbed respectively 1 and 3.3mmolg(-1) of gold and have K(d) values of 450 and 34,000, respectively. Experimental evidence showed that gold adsorbed on the amide groups of the silk sericin, while gold and copper adsorbed on the amino groups of chitosan via charge-interactions and complexation. Binary (Au-Cu), five (Au-Co-Ni-Cu-Zn) and six (Au-Pd-Co-Ni-Cu-Zn) component separations consistently showed that silk sericin has better selectivity (Sel(Au)>2.4) than chitosan. It is possible to recover gold at 99.5% purity by silk sericin and 90% if the solution contained palladium.

Separation of precious metals using selective mesoporous adsorbents

The mesoporous NH2-MCM-41 adsorbent prepared by grafting aminopropyls on MCM-41 is selective towards gold and palladium adsorptions and can separate these precious metals from complex solutions containing other metal ions such as cobalt, nickel, copper and zinc. Adsorption is rapid and the adsorbent’s capacity for gold is better or comparable to most carbonaceous adsorbents including activated carbons. Furthermore, NH2-MCM-41 can separate palladium from gold solution at pH1.0 with excellent selectivity and capacity. Thus, it is possible to design a two steps separation process for the separation of palladium and then gold from the complex solution. A simple acid wash was sufficient to recover the adsorbed palladium and gold as concentrated, high purity (i.e., > 95%) metal salt solutions and the regenerated adsorbent was reused without lost of performance.

A comparative study on selective adsorption of metal ions using aminated adsorbents

It is well-known that chitosan consists of amino groups for the chelation of metal ions while NH2-MCM-41 has excellent adsorption selectivities for metals. This work compares both adsorption capacities and selectivities of chitosan and NH2-MCM-41. It has been found that chitosan has adsorption capacities of 1.76 mmol/g, 1.03 mmol/g and 1.30 mmol/g for Cu2+, Ni2+ and Zn2+ respectively whereas NH-MCM-41 has adsorption capacity of 1.52mmol/g, 0.8mmol/g and 0.83mmol/g for Cu, Ni and Zn. The higher adsorption capacity in chitosan is attributed to its higher loading of amine groups. The single component adsorption isotherms were well-fitted using Freundlich model. The binary adsorptions of Cu2+-Zn2+ and Ni2+-Zn2+ systems showed similar adsorption selectivities for both adsorbents. However, chitosan has no preferential adsorption for Ni2+-Zn2+ system while NH2-MCM-41 has a good selectivity towards Zn2+. It is believed that the difference can be attributed to the heterogeneous surface of chitosan due to its organic nature. The multi-component adsorptions were best described by a multicomponent extended Freundlich model. Despite the surface functional group, this work indicates the importance of the adsorbent support on selective adsorption.

Techno-economic Analysis of Distributed Hydrogen Production from Natural Gas

Abstract It is well established that hydrogen has the potential to make a significant contribution to the world energy production. In U.S., majority of hydrogen production plants implement steam methane reforming (SMR) for centralized hydrogen production. However, there is a wide lack of agreement on the nascent stage of using hydrogen as fuel in vehicles industry because of the difficulty in delivery and storage. By performing technological and economic analysis, this work aims to establish the most feasible hydrogen production pathway for automotives in near future. From the evaluation, processes such as thermal cracking of ammonia and centralized hydrogen production followed by bulk delivery are eliminated while on-site steam reforming of methanol and natural gas are the most technologically feasible options. These two processes are further evaluated by comprehensive economic analysis. The results showed that the steam reforming (SR) of natural gas has a shorter payback time and a higher return on investment (ROI) and internal rate of return (IRR). Sensitivity analysis has also been constructed to evaluate the impact of variables like NG feedstock price, capital of investment and operating capacity factor on the overall production cost of hydrogen. Based on this study, natural gas is prompted to be the most economically and technologically available raw material for short-term hydrogen production before the transition to renewable energy source such as solar energy, biomass and wind power.

Assessment of Sericin Biosorbent for Selective Dye Removal

Abstract The silk sericin is the main residue in silk production and it is found to be a low cost and efficient biosorbent. In this study, sericin was characterized with various techniques including SEM (scanning electron microscope), XRD, N 2 physisorption, FTIR (Fourier transformed infrared spectroscopy) and XPS (X-ray photoelectron spectroscopy). The nitrogen content of sericin was ca. 8.5 mmol·g −1 according to elemental analysis. Dye adsorption by sericin biosorbent was investigated with the acid yellow (AY), methylene blue (MB) and copper (II) phthalocyanine-3,4′4″4‴-tetrasulfonic acid (CuPc) dyes from water. Sericin displayed large capacity for AY and CuPc adsorption with adsorption capacities of respectively 3.1 and 0.35 mmol·g −1 , but it did not adsorbed methylene blue dye. This selectivity is due to the basicity of amide groups in sericin biosorbents.

Selective adsorbents from chemically modified ordered mesoporous silica

Abstract Ordered mesoporous silica (OMS) adsorbents were prepared by grafting amino, carboxylic and thiol-containing functional groups onto MCM-41 for the selective removal of dye and metal pollutants from wastewater. The amino containing OMS-NH 2 adsorbent has a large adsorption capacity and a strong affinity for the Acid blue 25. It can selectively remove Acid blue 25 from a mixture of dyes (i.e., Acid blue 25 and Methylene blue). The OMS-COOH is a good adsorbent for Methylene blue displaying excellent adsorption capacity and selectivity for the dye. The chemically modified OMS adsorbents were also tested for the selective removal and recovery of metals (i.e., lead and copper). The OMS-SH adsorbent can selectively remove lead from solutions containing Pb 2+ and Cu 2+ ions, whereas the OMS-NH 2 selectively adsorbed a large quantity of copper. The selectivity of the adsorbents for lead and copper is strongly influenced by pH. Indeed, by simply adjusting the pH, OMS-NH 2 can adsorb mainly lead or copper from a mixture containing both metals.

Recovery of high purity gold and silver using mesoporous adsorbents

Mesoporous silica containing amino surface groups displayed good capacity and excellent selectivity for adsorption of precious metals (i.e., Au and Ag). The adsorbed metals were recovered as high purity metal salt solution by simple acid wash and the regenerated adsorbents were reused without lost of performance.

Special Distillation Applications

The field of distillation has existed for millennia and has evolved from simple batch stills for alcohol and perfume extraction in antiquity to some of the largest pieces of equipment on most modern chemical plants. For some separations, however, boiling the feed mixture, as in standard distillation, must be avoided as some of the components might be destroyed, and for these, short path distillation is now routinely used in industry. Some separations are better performed in completely different configurations that do not rely on gravity but rather on centrifugal forces, as in high gravity, or HiGee, units. The scale of distillation operation in industry is continuously increasing and has resulted in larger and larger distillation column configurations. In recent years, however, small-scale operations down to milli- and microscale have become of interest as means of separation for integrated and intensified micro plants, or labs-on-a-chip. Distillation can also be achieved with the use of a membrane in membrane distillation, a configuration that is finding increasing interest within desalination. These nonstandard modes of distillation will be considered in this chapter. The main principles of the operation will be outlined, and a summary will be given of current work that has considered these processes, as well as where the main applications either can be found today or might be found in the future.