CO Feed Ratio Research Articles

Synergistic effects on properties of biofuel and biochar produced through co-feed pyrolysis of Erythrina indica and Azadirachta indica biomass

Co-feed pyrolysis is a thermochemical conversion process that entails the simultaneous or sequential decomposition of various feedstock in an oxygen-free environment, concurrently improving the quality of the end products. The technique is widely used to produce a range of valuable products, including biofuels, chemicals and biochar, capitalizing on the synergies between various feedstock. The current study focuses on the synergistic effects of co-feed pyrolysis of Erythrina indica (EI) and Azadirachta indica (AI) biomass at different co-feed ratios (EI:AI) of 1:4, 1:3, 1:2, 1:1, 2:1, 3:1 and 4:1 on weight basis. The reactions were carried out at a temperature of 600 °C under a pressure of 1 bar using nitrogen as inert atmosphere. The bio-oil yield produced through the co-feed pyrolysis reactions ranged from 29.51 to 32.40 % by weight, while the biochar and non-condensable gases yields ranged from 38.25 to 42.48 % and 26.90 to 30.73 % by weight, respectively. Positive synergistic effects of co-feed pyrolysis led to a notable enhancement in physicochemical properties of the fuel phase, especially by virtue of calorific value, density and presence of low mol. wt. components when compared to their individual counterparts. Specifically, the fuel phase obtained at 1:1 co-feed ratio exhibited the peak calorific value of 36.80 MJ/kg along with lowest density of 0.82 g/ml and pH of 3.58 which is the pinnacle accomplishment of this work; and comparable with commercial gasoline. Gas chromatography and mass spectroscopy of biofuels revealed alkanes, alkenes, alcohols, aromatics, esters, nitro compounds and organosilicons as their main compounds. Specific compounds, including cyclopentane, methyl-, 1-cyclohexyl-2-propen-1-ol and 1-pentene, 3-methyl, are the most significant compounds at co-feed ratio of 1:1. Biochar produced at co-feed ratio of 1:1 also depicted excellent physiochemical properties with the highest elemental carbon of 79.23 wt % and lowest oxygen and hydrogen contents of 18.49 wt % and 2.28 wt %, respectively with a maximum calorific value of 29.23 MJ/kg; which can be utilized as solid fuels. The biochar produced from the co-feed pyrolysis reactions also possesses highly porous structure which can be useful as a soil conditioner, carbon sequestration water filtration or wastewater treatment. Additionally, non-condensable gases composed of 7.45 vol % hydrogen, 34.26 vol % carbon monoxide, 21.32 vol % methane and 36.97 vol % carbon dioxide when co-feed ratio is 1:1.

Thermochemical putrefaction of Delonix regia biomass and tube waste to produce high-quality pyrolytic bio-oil

In this study, the authors have reported pyrolysis of two different waste materials, lignocellulosic biomass, Delonix regia (DR), and butyl rubber tube waste, (TW), at 600 °C temperature and 1 bar pressure using nitrogen inert atmosphere. In pursuit of obtaining high-quality products, the thermochemical reaction between 95, 85, 75, 65 and 50 mass % of DR is tested with 5, 15, 25, 35 and 50 mass % of TW, respectively. The co-feed ratio 95:5, 85:15, 75:25, 65:35 and 50:50 of DR/TW correspondingly resulted in the bio-oil yield of 22.67, 24.00, 24.34, 25.00 and 36.67 mass % and bio-char yield of 37.00, 43.77, 44.67, 45.33 and 49.52 mass %. The higher heating values (HHV) of all bio-oils are in increasing order to that of the increasing fraction of TW in co-feed where 50:50 ratio resulted in bio-oil of maximum HHV with 32.61 MJ kg−1. Further increased mass % of tube waste may increase the energy content of the final liquid product; however, the present work focuses on co-feeding and management of both these two wastes and accordingly the mass % of tube waste has been limited to maximum of 50%. The bio-oil consists of more than 85 area % of aliphatic and aromatics, whereas phenols and acids occupy only 6.72 area % and 1.24 area %, respectively. Thus, this study provides waste minimization approach along with sustainable production of bio-oil that can be upgraded to transportation fuel, or utilized as furnace oil and for process heat purposes. The co-pyrolysis of these two waste materials resulted in popular hydrocarbons such as benzene, toluene, xylene, styrene and bigger fraction of C10 cut D-limonene.

A comprehensive study on upgradation of pyrolysis products through co-feeding of waste tire into rice straw under broad range of co-feed ratios in a bench-scale fixed bed reactor

A comprehensive study investigating all co-pyrolysis products (bio-oil, char, and gas) utilizing bench-scale reactor is essential for potential use in upscaling and techno-economic analysis for commercialization and integration of pyrolysis with conventional systems. This study explores the co-pyrolysis of rice straw (RS) and waste tire (WT) to assess the impact on products under a broad range of feedstock ratio (20, 40, 60, and 80 wt% of WT into RS) in fixed bed reactor at 550 °C. Results revealed that feedstock mass ratio played a crucial role to transform the oxygenates into hydrocarbons (HCs). Liquid yield, organic phase, pH, aromatics, and olefins increased with increase of WT proportion in blend. Bio-oil yield, aromatics and olefins reached to 45 wt%, 42%, and 30% at WT/RS (80:20) compared to 36 wt%, 2%, and 4% in the case of RS alone, respectively. Likewise, at the same blend ratio, 85% reduction in oxygenates was observed while higher heating value (HHV) of bio-oil (41.40 MJ/kg) was comparable to that of WT (41.50 MJ/kg). Significant positive synergy was achieved for non-condensable gas after incorporation of WT into RS. Hydrogen (H2) and methane (CH4) along with higher HCs were increased while oxides of carbon reduced with the addition of WT compared to RS alone. Char characteristics also improved with addition of WT into RS in terms of increased carbon content, HHV, and reduced ash content.

Comparative study on pyrolysis of Delonix Regia, Pinewood sawdust and their co-feed for plausible bio-fuels production

Individual and co-feed pyrolysis of various weight percentages of two solid waste biomasses, have been carried out in a tubular reactor at 625 °C and 1 bar. Both biomasses considered herein are having average calorific values of 18.33 MJ/kg and 18.5 MJ/kg. Experiments are performed individually on both the biomasses and then the co-feed in the ratio of 25:75, 50:50, and 75:25 taken for co-pyrolysis study. Further to be noted that pyrolysis experiments of each case and their product analyses in addition to feed characterization have been done thrice. These results are presented individually for each run in addition to their average and standard deviation values. The biomass feedstock, bio-oil, and biochar are thoroughly characterized by extensive advanced characterization techniques such as thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), gas chromatography-mass spectroscopy (GCMS), nuclear magnetic resonance (NMR), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) appropriately, as applicable for each case. The highest heating value of obtained pyrolytic bio-oil is from a co-feed ratio of 50:50 with an average HHV of 20.3 MJ/kg and having only 14.3 wt % of moisture content on average of three repetition experiments. The density of bio-oil obtained in all cases is approximately close to 1 g/cc, whereas their average viscosity varies between 2.07 and 3.61 mPa s. Thus, this study delivers that the rarely researched biomass considered for this study has almost similar potential to produce biofuels as that of extensively researched other biomass and their co-feed (1:1) pyrolysis is optimum for production of improved quality of pyrolytic bio-oil in terms of HHV, pH, density and moisture content.

Dry reforming of methane catalysed by molten metal alloys

Dry reforming of methane usually affords low-quality syngas with equimolar amounts of CO and H. Here we report the high conversion of CH and CO to syngas and solid carbon through simultaneous pyrolysis and dry reforming of methane in a bubble column reactor using a molten metal alloy catalyst (65:35 mol% Ni:In). The H to CO ratio can be increased above 1:1 using feed ratios of CH:CO greater than 1:1 to produce stoichiometric solid carbon as a co-product that is separable from the molten metal. A coupled reduction–oxidation cycle is carried out in which CO is reduced by a liquid metal species (for example, In) and methane is partially oxidized to syngas by the metal oxide intermediate (for example, InO), regenerating the native metal. Moreover, the H:CO product ratio can be easily controlled by adjusting the CH:CO feed ratio, temperature, and residence time in the reactor.

C to H effective ratio as a descriptor for co-processing light oxygenates and CH4on Mo/H-ZSM-5

Co-processing of H2O, CO2, and light (C1–2) oxygenates with CH4 at 950 K over Mo/H-ZSM-5 catalysts results in complete fragmentation of the oxygenate and CO as the sole oxygen-containing product. The C/Heff accounts for removal of O as CO and describes the net C6H6 and total hydrocarbon synthesis rates at varying (0.0–0.10) oxygenate and H2 to CH4 co-feed ratios.

Reduction of CO2 to CO at Cu–ceria-gadolinia (CGO) cathode in solid oxide electrolyser

The feasibility was investigated of using a Cu/CGO cathode for CO2 reduction to CO in a high temperature solid oxide electrolyser (CO2–CO, Cu/CGO|YSZ|YSZ/LSM|LSM, ambient air). An adherent layer of porous Cu/CGO electrode on YSZ electrolyte was achieved by sintering Cu/CGO paste at 1,000 °C for 5 h. Comparable performance was obtained with Ni/YSZ and Cu/CGO cathodes for CO2 reduction at 750 °C and a 50:50 CO2–CO feed; CO oxidation rates were faster than CO2 reduction rates. Ohmic and polarisation resistances of the Cu/CGO electrode all decreased with decreasing CO2:CO feed ratio. In the electrolytic mode, 100 % current efficiency for CO2 reduction to CO was achieved on the Cu/CGO cathode at potential differences up to 1.5 V, above which the electronic conductivity of the YSZ electrolyte increased, causing a loss in effective current efficiency. Further increase in potential difference to ca. >2.3 V caused irreversible damage to the YSZ electrolyte due to its partial decomposition. No significant performance degradation, Cu sintering/migration, carbon deposition or electrode delamination was evident during 2 h of operating the electrolyser at 1.85 V and 750 °C for CO2 reduction with a Cu/CGO cathode.

Mechanistic Modeling of Cobalt Based Catalyst Sintering in a Fixed Bed Reactor under Different Conditions of Fischer–Tropsch Synthesis

A three-step sintering mechanism is proposed for Co-based catalysts under Fischer–Tropsch reaction conditions. This mechanism includes an intermediate formation of oxide layer on cobalt metal nanoparticles in the presence of water. The partially reversibly oxidized surface accelerates sintering by both reducing the surface energy and enhancing the diffusion rates of cobalt particles. The proposed mechanism is then employed for a fixed-bed unsteady state reactor. The effect of particle growth on the catalytic activity was analyzed within a diverse range of operating conditions (syngas ratio = 1.5–4, water co-feed ratio = 0–6, inert co-feed ratio = 0–6). It is found that, at the same gas space velocity, sintering proceeds faster at higher H2/CO ratios. At the same initial conversion, a low H2/CO syngas ratio increases sintering severity, i.e., catalyst deactivation due to the crystallite growth, as it brings about higher relative water partial pressure. Dilution of syngas with different amounts of inert gas does not affect the cobalt sintering rate. Cobalt sintering proceeds more rapidly if water is co-fed during the reaction.

철 촉매를 이용한 Fischer-Tropsch 합성 반응과 수성 가스 전환 반응에 대한 반응 속도 연구

철 촉매를 이용한 Fischer-Tropsch 합성 반응과 수성 가스 전환 반응에 대한 반응 메커니즘과 반응 속도식을 5 채널 고정층 반응기를 이용하여 조사하였다. 실험 조건은, 반응물 합성가스 <TEX>$H_2$</TEX>/CO 비 0.5~2, 반응물 공급 유량 60~80 ml/min, 반응 온도 <TEX>$255{\sim}275^{\circ}C$</TEX>로서 반응 압력은 1.5 MPa을 유지하였다. F-T 합성 반응의 반응 속도식(<TEX>$r_{FT}$</TEX>)은 반응 속도 결정 단계로서 분자로 흡착된 CO와 기상의 수소 분자와의 반응을 바탕으로 하는 Eley-Rideal 반응 메카니즘을 통해 계산되었고, WGS 반응의 반응 속도식(<TEX>$r_{WGS}$</TEX>)은 formate 중간체 생성 반응을 반응 속도 결정 단계로 가정하여 결정되었다. 실험 결과, F-T 합성 반응의 반응 속도식과 WGS 반응의 반응 속도식은 각각 탄화수소 생성과 <TEX>$CO_2$</TEX> 생성에 대한 반응 속도 실험값을 잘 모사하였고, 또한 power law에 근거한 CO 전환 반응에 대한 반응 속도식도 실험값과 잘 일치하였다. 이처럼, 각각의 반응 메카니즘을 바탕으로 도출된 반응 속도식(<TEX>$r_{FT}$</TEX>, <TEX>$r_{WGS}$</TEX>, <TEX>$-r_{CO}$</TEX>)은 실험값과 여러 가지 기존 문헌에서 보고된 반응 속도식 모델과 잘 일치하였다. The kinetics of the Fischer-Tropsch synthesis and water gas shift reactions over a precipitated iron catalyst were studied in a 5 channel fixed-bed reactor. Experimental conditions were changed as follows: synthesis gas <TEX>$H_2$</TEX>/CO feed ratios of 0.5~2, reactants flow rate of 60~80 ml/min, and reaction temperature of <TEX>$255{\sim}275^{\circ}C$</TEX> at a constant pressure of 1.5 MPa. The reaction rate of Fischer-Tropsch synthesis was calculated from Eley-Rideal mechanism in which the rate-determining step was the formation of the monomer species (methylene) by hydrogenation of associatively adsorbed CO. Whereas water gas shift reaction rate was determined by the formation of a formate intermediate species as the rate-determining step. As a result, the reaction rates of Fischer-Tropsch synthesis for the hydrocarbon formation and water gas shift for the <TEX>$CO_2$</TEX> production were in good agreement with the experimental values, respectively. Therefore, the reaction rates (<TEX>$r_{FT}$</TEX>, <TEX>$r_{WGS}$</TEX>, <TEX>$-r_{CO}$</TEX>) derived from the reaction mechanisms showed good agreement both with experimental values and with some kinetic models from literature.

Membrane reactor modelling, validation and simulation for the WGS reaction using metal doped silica membranes

AbstractIn this work, a Matlab Simulink© model was developed to analyse and predict the performance of a metal doped silica membrane reactor for H2 production via both the high and low temperature water gas shift reaction. An activated transport model for mixed gas separation with combined reaction was developed to model the effects within a membrane reactor unit. The membrane reactor was modelled as a number of perfectly mixed compartments containing a catalyst bed and a gas selective membrane. The combined model provided a good fit to experimentally measured results for higher conversions up to equilibrium, which is generally the case for industrial applications. Simulation results showed that H2 separation and H2 recovery improved with pressure, due to the H2 concentration driving force across the membrane. For a single stage membrane reactor unit, a maximum conversion of 93% could be achieved with a H2 recovery rate of 95%. In addition, the membrane reactor efficiency increased at higher temperatures and lower H2O:CO feed ratios, allowing for CO conversion improvements by the membrane reactor. Copyright © 2009 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

GC × GC: A novel technique for investigating selectivity in the Fischer–Tropsch synthesis

Abstract A study has been conducted to illustrate the benefit of the GC × GC-technique over the classically used 1D-GC technique to analyse the selectivity of iron catalysed low temperature Fischer–Tropsch synthesis. The selectivity of the products obtained from the iron catalysed Fischer–Tropsch synthesis at 225 °C; H 2 /CO feed ratio = 1.5 and total pressure = 27 bars was evaluated. The selectivity results obtained from these methods were compared with special focus on the minor compounds such as oxygenates. The superiority of the GC × GC-technique above the 1D-GC technique were proven when minor product compounds such as the linear acids, secondary alcohols, ketones and aldehydes, and branched paraffins, olefins, alcohols, acids could be quantified using the GC × GC-technique but not using the 1D-GC system. It is further shown that the GC × GC-technique displayed a higher level of accuracy than 1D-GC system when detecting compounds in complex mixtures.

Intrinsic kinetics study of LPDME process from syngas over bi-functional catalyst

Abstract The intrinsic kinetics of the three-phase dimethyl ether (DME) synthesis from syngas over a bi-functional catalyst has been investigated in a agitated slurry reactor at 20–50 bar, 200–240 °C and H 2 /CO feed ratio from 1 to 2. The bi-functional catalyst was prepared by physical mixing of CuO/ZnO/Al 2 O 3 as methanol synthesis catalyst and H-ZSM-5 as methanol dehydration catalyst. The three reactions including methanol synthesis from CO and H 2 , methanol dehydration and water gas shift reaction were chosen as the independent reactions. A kinetic model for the combined methanol and DME synthesis based on a methanol synthesis model proposed by Graaf et al. [G.H. Graaf, E.J. Stamhuis, A.A.C.M. Beenackers, Kinetics of low pressure methanol synthesis, Chem. Eng. Sci. 43 (12) (1988) 3185; G.H. Graaf, E.J. Stamhuis, A.A.C.M. Beenackers, Kinetics of the three-phase methanol synthesis, Chem. Eng. Sci. 43 (8) (1988) 2161] and a methanol dehydration model by Bercic and Levec [G. Bercic, J. Levec, Intrinsic and global reaction rate of methanol dehydration over γ-Al 2 O 3 pellets, Ind. Eng. Chem. Res. 31 (1992) 399–434] has been fitted our experimental data. The obtained coefficients in equations follow the Arrhenius and the Van’t Hoff relations. The calculated apparent activation energy of methanol synthesis reaction and methanol dehydration reaction are 115 kJ/mol and 82 kJ/mol, respectively. Also, the effects of different parameters on the reactor performance have been investigated based on the presented kinetic model.

Kinetic study and modeling of Fischer–Tropsch reaction over a [formula omitted] catalyst in a slurry reactor

The kinetics of the Fisher–Tropsch synthesis is studied in a laboratory CSTR slurry reactor using a commercial Cobalt catalyst. The rates of CO consumption and of production of hydrocarbons are modeled using a mechanism that accounts for olefin readsorption. The rate expressions are expressed in terms of liquid phase concentrations. The rate parameters are determined from experiments performed at 220 ∘ C , 2 MPa and H 2 / CO feed ratios of 1.6–3.35. The model gives a good prediction of the paraffin distribution. The effect of olefin readsorption (deviation to ASF distribution) seems minor and the corresponding rate parameters are poorly determined. The effect of water concentration remains to be more deeply investigated.

Selective CO oxidation with real methanol reformate over monolithic Pt group catalysts: PEMFC applications

Alumina supported Pt group metal monolithic catalysts were investigated for selective oxidation of CO in hydrogen-rich methanol reforming gas for proton exchange membrane fuel cell (PEMFC) applications. The results are described and discussed in the present paper and show that Pt / γ Al 2 O 3 was the most promising candidate to selectively oxidize CO from an amount of about 1 vol% to less than 100 ppm. We have investigated the effect of the O 2 to CO feed ratio, the feed concentration of CO, the presence of H 2O and/or CO 2, and the space velocity on the activity, selectivity and stability of Pt/Al 2O 3 monolithic catalysts. Afterwards, the Pt/Al 2O 3 catalyst was scaled up and applied in 5 kW hydrogen producing systems based on methanol steam reforming and autothermal reforming. The hydrogen produced was then used as fuel for an integrated PEMFC.

Kinetics and modelling of dimethyl ether synthesis from synthesis gas

The kinetics of the dual catalytic methanol and dimethyl ether (DME) synthesis process over a commercial CuO/ZnO/Al 2O 3 (methanol forming) and a γ-alumina (dehydration) catalyst have been investigated at 250°C and 5 MPa using a gradientless, internal-recycle-type reactor. A kinetic model for the combined methanol+DME synthesis based on a methanol synthesis model proposed by Vanden Bussche and Froment (1996) J. Catal., 161, 1–10) and a methanol dehydration model by Bercic and Levec (1993) Ind. Engng Chem. Res., 31, 1035–1040) has been tested using results obtained from a wide range of CO 2 : CO feed ratios. Results at different CO x : H 2 ratio and catalyst loading ratios were also obtained. Catalyst deactivation was observed during DME synthesis at high space velocities and a large ratio of dehydration catalyst.

Activity decline and diffusional changes in a magnesium-promoted cobalt-silica catalyst

A Co-Mg/diatomaceous earth catalyst was prepared by slow precipitation. Transmission electron microscopy (TEM) indicated two separate phases: small needles of a Co-Mg phase and the large particles of the diatom fragments. Nitrogen sorption measurements indicated much higherpore volume (0.32 cm 3 g ) for the catalyst than for the control catalyst made by fast precipitation (0.10 cm 3 g ). The catalyst activity in the Fischer-Tropsch synthesis at 155 kPa declined at an unusually fast rate. The decline was accompanied by an increase of the methane selectivity and a decrease of the Schulz-Flory growth factor. Hydrogen treatments temporarily restored the catalyst activity but did not arrest the declines. Increasing the H 2:CO feed ratio for the deactivated catalyst not only restored the high activity but also stabilized the catalyst. An increase of the methane selectivity and a small decrease of the growth factor also accompanied these changes. The changes in catalyst activity and product selectivity correlate well with the anticipated diffusional changes from gas phase diffusion to diffusion through liquids which have been deposited in the pores during the course of the reaction. It is inferred that the diffusional changes cause significant changes in the steady-state concentrations of the reaction intermediates and these, in turn, affect the reaction rate (conversion) and the chain termination (growth factor).

Hydrocarbon selectivity from cobalt Fischer-Tropsch catalysts

A cobalt Fischer-Tropsch catalyst was studied in a continuous-flow, well-stirred slurry reactor at 220-240°C, 0.5-1.5 MPa, H 2 /CO feed ratios between 1.5 and 3.5, H 2 conversions between 6 and 68%, and CO conversions between 11 and 73%. Increasing space velocity (decreasing conversion) or decreasing reactor H 2 /CO ratio decreased the yield of (undesired) C 1 products and increased the yield of (desired) C 10 +products. Reactor temperature and pressure has little effect on the carbon number distribution

Intrinsic kinetics of the Fischer-Tropsch synthesis on a cobalt catalyst

The rate of synthesis gas consumption over a cobalt Fischer-Tropsch catalyst was measured in a well-mixed, continuous-flow, slurry reactor at 220-240 o C, 0.5-1.5 MPa, H 2 /CO feed ratios of 1.5-3.5, and conversions of 6-68% of hydrogen and 11-73% of carbon monoxide. The inhibiting effect of carbon monoxide was determined quantitatively and a Langmuir-Hinshelwood-type equation of the following form was found to best represent the results: −R H2+CO =aP CO P H2 /(1+bP CO ) 2 . The apparent activation energy was 93-95 kJ/mol. Data from previous studies on cobalt-based Fischer-Tropsch catalysts are also well correlated with this rate expression

Carbon deactivation of Fischer-Tropsch ruthenium catalyst

Carbon deactivation of a 0.5 wt % Ru/..gamma..-Al/sub 2/O/sub 3/ surface-impregnated catalyst was studied by using a Berty continuous-stirred, gas-solid reactor (CSGSR)-gas chromatograph setup. The experimental variables were as follows: temperature, 473-573 K; pressure, 2-6 atm; weight hourly space velocity, 0.85, 16.5 h/sup -1/; H/sub 2//CO feed ratio, 3 and 2; and synthesis time, 0.5-5 h. Carbon deposited in a synthesis run was measured by integrating the methane evolution profile during catalyst reduction at 723 K in H/sub 2/. Significant amounts of carbon were deposited, increasing to several monolayers during 5-h synthesis periods. The methanation rate decreased as the synthesis continued, while the selectivity for C/sub 2/-C/sub 4/ hydrocarbons showed a maximum during the initial stages of deactivation. The kinetic data could be correlated by assuming both hydrogen-assisted CO dissociation and hydrogenation of surface carbon to be rate determining. The turnover numbers for methanation (N/subCH/4/sub) and carbon deposition (N/C/Ru/sub) are given.

The higher alcohol synthesis over promoted Cu/ZnO catalysts

AbstractAlkali oxides added to methanol catalysts increase the formation of ethanol, n‐propanol and isobutyl alcohol. This result has been known for many years, yet few quantitative studies have been reported in the literature. Data obtained on a commercial copper‐zinc oxide catalyst promoted with K2 CO3 are presented and compared with published work. The optimum promoter concentration was about 0.5% by weight. The H2 to CO feed ratio was important in determining the higher alcohol selectivity. The rate of production of isobutyl alcohol varied as p p while for methanol, ethanol and n‐propanol both exponents were positive and less than 1.6. Decreasing the hydrogen to carbon monoxide ratio from 2 to 0.5 more than doubled the isobutyl alcohol selectivity. Chain growth schemes predicting the higher alcohol selectivity are presented and estimates of the parameters are given.