Low Total Acid Number Research Articles

Theoretical and experimental investigation of the impact of oil functional groups on the performance of smart water in clay-rich sandstones

This research investigated the effect of ion concentration on the performance of low salinity water under different conditions. First, the effect of injection water composition on interparticle forces in quartz-kaolinite, kaolinite-kaolinite, and quartz-oil complexes was tested and modeled. The study used two oil samples, one with a high total acid number (TAN) and the other with a low TAN. The results illustrated that reducing the concentration of divalent ions to 10 mM resulted in the electric double layer (EDL) around the clay and quartz particles and the high TAN oil droplets, expanding and intensifying the repulsive forces. Next, the study investigated the effect of injection water composition and formation oil type on wettability and oil/water interfacial tension (IFT). The results were consistent with the modeling of interparticle forces. Reducing the divalent cation concentration to 10 mM led to IFT reduction and wettability alteration in high TAN oil, but low TAN oil reacted less to this change, with the contact angle and IFT remaining almost constant. Sandpack flooding experiments demonstrated that reducing the concentration of divalent cations incremented the recovery factor (RF) in the presence of high TAN oil. However, the RF increment was minimal for the low TAN oil sample. Finally, different low salinity water scenarios were injected into sandpacks containing migrating fines. By comparing the results of high TAN oil and low TAN oil samples, the study observed that fine migration was more effective than wettability alteration and IFT reduction mechanisms for increasing the RF of sandstone reservoirs.

Conversion of soybean oil under subcritical water conditions into liquid biofuels with low oxygen contents

Although the hydrotreatment of natural triglycerides is a well-established route for producing sustainable aviation fuel and renewable diesel, its high hydrogen consumption is a concern. The hydrothermolysis of natural triglycerides is considered a highly promising alternative route; however, the correlation between process parameters and fuel properties and detailed chemical structures of the produced fuel have not been established. Herein, we investigated the conversion of soybean oil to gasoline-, jet fuel- and diesel-fraction hydrocarbons with low oxygen contents. The properties of fuels produced under various reaction conditions were analyzed comprehensively using simulated distillation, total acid number (TAN), and elemental analysis. Under the optimized reaction conditions of 420 °C, 4.5 MPa, an oil-to-water ratio of 6:1, and reaction time of 10 min, 26 % gasoline-, 62 % jet fuel-, and 90 % diesel-range hydrocarbons with a low oxygen content of 5.1 %, low TAN of 0.04 mg KOH g−1, and high calorific value of 42.7 MJ kg−1 resulted. To elucidate the reaction mechanism, the liquid products produced from soybean oil were analyzed using comprehensive two-dimensional gas chromatography combined with time-of-flight mass spectrometry. In addition, based on the oleic acid conversion under varying hydrothermal conditions, we proposed deoxygenation, cracking, cyclization, and aromatization pathways. The findings of this study present possibilities for producing sustainable biofuels with low oxygen contents for the aviation industry.

Understanding the effects of feedstock blending and catalyst support on hydrotreatment of algae HTL biocrude with non-edible vegetable oil

The performance of cobalt-molybdenum (CoMo) on hydrotreating of algae HTL biocrude and carinata oil was investigated. Commercial CoMo/Al2O3 (CoMo/Al) and synthesized CoMo supported on Douglas fir biochar (CoMo/DF), sulfided or unsulfided catalysts, were compared for hydrodeoxygenation (HDO), hydrodenitrogenation (HDN), hydrodesulfurization (HDS) and hydrodemetallization (HDM) reactions. Results showed that there lies a synergistic effect when HTL algae biocrude and carinata oil blends are hydrotreated. The yield of the upgraded blend (UB) oils retrieved over alumina catalyst was higher than the individual hydrotreated parent oils. For example, a 9% and 5% increase in yield was noted compared to the average of individual hydrotreated parent oils. The UB produced from sulfided CoMo/Al exhibited superior HDO activity primarily by decarbonylation. This was apparent in increased heating value, carbon addition, higher octane number, and lower total acid number than the oils obtained from the biochar-supported catalysts. Sulfided CoMo/DF catalyzed cracking reactions which lowered the viscosity, followed by high HDN and HDS activity compared to the commercial catalyst. The two supports showed different sorption behaviors. Interestingly, CoMo/DF had an effective sorption mechanism that helped in higher metal removal from the oil. Additionally, presulfiding and DF support exhibited positive results in term of less coke formation. In brief, biochar supports have higher acidic sites, inorganic mineral oxides, ion exchange capacity, high surface area, pore structure and connectivity. All of these make a substantial contribution to its unique catalytic behavior.

Recovery Observations from Alkali, Nanoparticles and Polymer Flooding as Combined Processes.

We have studied wettability alterations through imbibition/flooding and their synergy with interfacial tension (IFT) for alkalis, nanoparticles and polymers. Thus, the total acid number (TAN) of oil may determine the wetting-state of the reservoir and influence recovery and IFT. Data obtained demonstrate how the oil TAN number (low and high), chemical agent and reservoir mineralogy influence fluid–fluid and rock–fluid interactions. We used a laboratory evaluation workflow that combines complementary assessments such as spontaneous imbibition tests, IFT, contact angle measurements and selected core floods. The workflow evaluates wettability alteration, IFT changes and recovery when injecting alkalis, nanoparticles and polymers, or a combination of them. Dynamics and mechanisms of imbibition were tracked by analyzing the recovery change with the inverse bond number. Three sandstone types (outcrops) were used, which mainly differed in clay content and permeability. Oils with low and high TANs were used, the latter from the potential field pilot 16 TH reservoir in the Matzen field (Austria). We have investigated and identified some of the conditions leading to increases in recovery rates as well as ultimate recovery by the imbibition of alkali, nanoparticle and polymer aqueous phases. This study presents novel data on the synergy of IFT, contact angle Amott imbibition, and core floods for the chemical processes studied.

Optimization of bio-oil production from microwave co-pyrolysis of food waste and low-density polyethylene with response surface methodology

The applicability of waste to energy conversion technique is facing many issues because of current waste management practices. Focusing on the segregation issue of low-density polyethylene (LDPE) from food waste (FW), microwave (MW) co-pyrolysis of FW and LDPE was investigated in this study. Multifactor optimization of the operating parameters, viz., residence time, LDPE in feed and temperature, was done with response surface methodology to achieve maximum bio-oil yield with a low total acid number (TAN). Bio-oil yield and TAN varied from 17 to 42 wt% and 16–45 mg KOH/g respectively, in various experimental runs. The optimum conditions for maximum bio-oil yield with minimum TAN were residence time −7 s, LDPE in the feed-13% and temperature - 550 °C. A quadratic model was developed to predict bio-oil yield and TAN as a function of operating parameters with an error <8.1 %. Addition of LDPE improved the bio-oil yield (by 20 %). The bio-oil also exhibited reduction in moisture content and TAN (30% and 62 %) and increase in pH and higher heating value (HHV) (40 % and 44 %). Sugars (3.09 wt%), alkanes (1.64 wt%), acids (1.07 wt%), alcohols (0.85 wt%), phenols (0.59 wt%), furans (0.58 wt%) and ketones (0.55 wt%) were the major identified compounds in the bio-oil. Thus, the high HHV and chemical composition of bio-oil indicate its potential use in boilers, engines, turbines, transportation fuels and as a renewable feed for chemical synthesis. The main mechanism for bio-oil quality improvement was the synergetic effect of FW hydrocarbon and hydrocarbon radical (•HC) and hydrogen radical (•H) of LDPE. The energy consumption analysis showed an energy requirement of 13.11 kWh/kg for bio-oil production.

Fluid catalytic co-processing of bio-oils with petroleum intermediates: Comparison of vapour phase low pressure hydrotreating and catalytic cracking as pretreatment

For co-processing of bio-oil and conventional fossil feed in existing refinery fluid catalytic cracking (FCC) units, little attention has been paid to the increased aromatics and basic nitrogen content in the feed associated with the introduction of bio-oil and how it affects FCC performance. In this contribution, the effect of blending two bio-oils obtained from different catalytic treatment of wheat-straw pyrolysis vapors with atmospheric residue was tested using a microactivity testing unit (MAT). The catalysts used for the pyrolysis vapor phase upgrading included i) a Na/γ-Al2O3 deoxygenation catalyst, and ii) a Pt/TiO2 catalyst in combination with H2 atmosphere. The oxygen content of both bio-oils was similar at ~ 7–8 wt%, but the Na/γ-Al2O3 bio-oil had a lower total acid number (TAN) of 5 mg KOH/g and a higher basic nitrogen (BN) content of 0.7 wt% compared to the Pt/TiO2 bio-oil (15 mg KOH/g, 0.4 wt% BN).The processing of the upgraded bio-oils in blends with atmospheric residue in MAT increased the yields of dry gas, CO, CO2, and coke at the expense of naphtha (decrease by 2.8 percentage points) and decreased the conversion by ~ 2.5 percentage points. This is attributed to the high aromaticity and basic nitrogen content of the two bio-oils. The lower basic nitrogen content and higher degree of saturation for the Pt/TiO2 bio-oil may explain its slightly higher conversion (by ≤ 1 percentage points) compared to the Na/γ-Al2O3 bio-oil.This contribution provides important information for refinery operators interested in FCC co-processing of fossil oils and biomass-derived pyrolysis oils with elevated content of nitrogen and aromatics.

Variations in Wettability and Interfacial Tension during Alkali-Polymer Application for High and Low TAN Oils.

The injection of chemicals into sandstones can lead to alterations in wettability, where oil characteristics such as the TAN (total acid number) may determine the wetting state of the reservoir. By combining the spontaneous imbibition principle and the evaluation of interfacial tension index, we propose a workflow and comprehensive assessment to evaluate the wettability alteration and interfacial tension (IFT) when injecting chemical-enhanced oil-recovery (EOR) agents. This study examines the effects on wettability alteration due to the application of alkaline and polymer solutions (separately) and the combined alkali–polymer solution. The evaluation focused on comparing the effects of chemical agent injections on wettability and IFT due to core aging (non-aged, water-wet and aged, and neutral to oil-wet), brine composition (mono vs. divalent ions); core mineralogy (~2.5% and ~10% clay), and crude oil type (low and high TAN). Amott experiments were performed on cleaned water-wet core plugs as well as on samples with a restored oil-wet state. IFT experiments were compared for a duration of 300 min. Data were gathered from 48 Amott imbibition experiments with duplicates. The IFT and baselines were defined in each case for brine, polymer, and alkali for each set of experiments. When focusing on the TAN and aging effects, it was observed that in all cases, the early time production was slower and the final oil recovery was longer when compared to the values for non-aged core plugs. These data confirm the change in rock surface wettability towards a more oil-wet state after aging and reverse the wettability alteration due to chemical injections. Furthermore, the application of alkali with high TAN oil resulted in a low equilibrium IFT. By contrast, alkali alone failed to mobilize trapped low TAN oil but caused wettability alteration and a neutral–wet state of the aged core plugs. For the brine composition, the presence of divalent ions promoted water-wetness of the non-aged core plugs and oil-wetness of the aged core plugs. Divalent ions act as bridges between the mineral surface and polar compound of the in situ created surfactant, thereby accelerating wettability alteration. Finally, for mineralogy effects, the high clay content core plugs were shown to be more oil-wet even without aging. Following aging, a strongly oil-wet behavior was exhibited. The alkali–polymer is demonstrated to be efficient in the wettability alteration of oil-wet core plugs towards a water-wet state.

Thermo-Catalytic Reforming of spent coffee grounds

Conversion of spent coffee grounds through the Thermo-Catalytic Reforming system (TCR®) is evaluated in this study. While, the TCR® is a technology that has been developed by Fraunhofer UMSICHT, which combines an intermediate pyrolysis and a catalytic reforming. The temperature of the catalytic reformer is varied between 500 and 700 °C to achieve an optimum yield quantities and qualities of the products. The hydrogen concentration is maximized at a reforming temperature of 700 °C, and a gas yield up to 52 wt% is achieved. The thermal stable bio-oil produced at 700 °C has the highest calorific value of 36.8 MJ/kg with significantly low oxygen and water content, low viscosity and low TAN (total acid number). Furthermore, the maximum bio-oil and char yields are obtained at the lowest reforming temperature of 500 °C. Overall spent coffee grounds show a great potential as feedstock in the Thermo-Catalytic Reforming for energy and bio-chemicals production.

Effect of oil reactivity on salinity profile design during alkaline-surfactant-polymer flooding

This study focused on the influence of oil reactivity (ability to react with alkali to generate in situ surfactants) on salinity profile design during alkaline/surfactant/polymer (ASP) flooding. Two surrogate oils with different total acid number (TAN) were used. After determination of optimum salinity via phase behavior tests, 3 ASP corefloods with I-III-I, II-III-I (negative salinity gradient), and I-II-I salinity profiles were performed for each oil. ASP flooding was applied as a post-polymer enhanced oil recovery (EOR) method in this study. The results demonstrated: (1) for both low TAN oil and high TAN oil, when I-III-I salinity profile was employed, incremental oil recovery was less than 20% original oil in place (OOIP); (2) when negative salinity gradient was applied, high oil recovery from 33.5% to 38.5% OOIP was achieved over polymer flooding, resulting in cumulative recovery over 95% in spite of oil reactivity; (3) distinct trends were observed for corefloods with I-II-I salinity profile. For low TAN oil, an incremental recovery of only 20% OOIP was attained; by contrast, for high TAN oil, the incremental recovery was as high as 35.1%, which could be attributed to the generation of a large amount of in situ soaps that had lower optimum salinity compared to the added surfactants; and (4) ASP flooding proved to be an effective EOR approach to significantly reduce residual oil after polymer flooding if appropriate salinity profile was adopted. This study provides some guidance on salinity profile design when ASP flooding is considered for oils with different reactivity.

Scanning Kelvin probe study of steel/oil interfaces for corrosion evaluation

AbstractRust preventive oil (RPO) provides temporary protection to steel during storage and transit. Premature failure occurs as surface defects due to inefficient RPO quality. Conventional corrosion tests like salt spray and cyclic corrosion provide minimum information about corrosion mechanism. We applied separately three RPO, named here as A–C, on bearing steels and their corrosion performance was examined by scanning Kelvin probe (SKP). The corrosion potential of samples lowered after oil application. It seems that oil film delayed oxygen reduction reaction. Later, oiled samples were exposed in salt spray test (SST) and again examined by SKP at different time interval. The SKP result showed that oiled sample A corrosion potential increased during SST exposure. Oil A might develop passivity on steel surface. It is also supported by least red rust formed on oiled sample A in SST. Fourier transform infrared spectroscopy, inductively coupled plasma and chemical analysis of oils were performed to interpret the SKP outcome. Oil A possesses low oxidation peak, low total acid number, and high total base number that signify higher corrosion resistant. Finally, SKP findings are in‐line with the conventional corrosion tests‐salt spray and condensation water tests.

Oil Degradation in a Diesel Engine with Dual-Loop Lubricating System

ABSTRACT A common lubricating oil sump is used in most modern internal combustion engines for cooling, wear protection, and friction reduction. This requires compromises during base oil and additive selection as a result of differing needs for lubricant performance in engine subsystems. The use of a dual lubricating loop, providing separate oil sumps for the power cylinder and valve train subsystems, was investigated experimentally to determine the effect of system segregation on oil degradation. A small diesel engine was modified, installed in a commercial generator unit, and operated for one oil drain cycle. Oil sampling was tailored to assess base and acid numbers, oxidation, soot concentration, water content, and viscosity changes. The experiment complemented an earlier study that investigated the fuel economy benefits of such a lubricating configuration. These include longer drain intervals for the cylinder head and power cylinder subsystems, improved wear performance for the valve train, and opportunities for alternative material selection during engine design. The experiment demonstrated protection of the valve train subsystem from soot contaminants in the power cylinder. Lower total acid number and oxidation tendency was also observed in the valve train.

Upgrading low-boiling-fraction fast pyrolysis bio-oil using supercritical alcohol: Understanding alcohol participation, chemical composition, and energy efficiency

Herein, a supercritical methanol (scMeOH) route for efficient upgrading of the low-boiling fraction of fast pyrolysis bio-oil containing a large amount of low-molecular-weight acids and water was investigated. The effects of various reaction parameters, including the temperature, concentration, and time, were explored. The yield of bio-oil and the energy efficiency of the scMeOH upgrading process were determined based on the amount of methanol that participated in the reaction during upgrading and fractionation of the upgraded heavy-fraction bio-oils (UHBOs) and upgraded light-fraction bio-oils (ULBOs). Upgrading at 400°C with 9.1wt% bio-oil for 30min generated a high bio-oil yield of 78.4wt% with a low total acid number (TAN) of 4.0mg-KOH/g-oil and a higher heating value of 29.9MJkg−1. The energy recovery (ER) was 94–131% and the energy efficiency (EE) was in the range of 79–109% depending on the calorific values of the ULBOs. Compared with upgrading in supercritical ethanol and supercritical isopropanol, less alcohol participation, a lower TAN, and higher ER and EE were achieved with scMeOH upgrading. Plausible pathways for bio-oil upgrading in supercritical alcohols based on detailed compositional analysis of the UHBO, ULBO, and gaseous products were discussed.

Removal of naphthenic acids from high acid crude via esterification with methanol

Refining of high acid crudes (HACs) is seriously limited by extensive corrosion of refinery equipment due to the presence of intrinsic naphthenic acids (NAs). Herein, in the absence of a catalyst or external hydrogen, effective removal of the NAs contained in HACs was achieved using methanol at moderate temperature and moderate pressure. Several process variables, including the temperature, crude concentration, and reaction time are explored to optimize the removal of NAs from HACs. At 250°C, 6.4MPa, and 33.3wt% crude, a very low total acid number (TAN) of 0.08mg-KOH/g-oil (96.9% reduction efficiency) with a high oil yield (95wt%) is achieved. During the reduction of the TAN using methanol, some fraction of the resins and asphaltenes in the crude oil crack to form low-molecular-weight aromatic compounds. Compared to deacidification using methanol, pyrolysis (without methanol) results in a much lower TAN reduction efficiency (38.6%). The major deacidification mechanism using methanol is esterification, while that of pyrolysis (without methanol) is decarboxylation.

A data-driven approach for the study of coagulation phenomena in waste lubricant oils and its relevance in alkaline regeneration treatments

Coagulation phenomena can occur in certain types of waste lubricant oils (WLO) during regeneration processes involving alkaline treatments, causing plant shutdowns. In this context, this study addresses the nature of the compounds responsible for the coagulation phenomena after the alkaline treatment. For such, an empirical test was developed to assess the coagulation behaviour of WLO, consisting in the addition of KOH to the WLO followed by heating under stirring conditions. This test was performed on 133 samples and four coagulation classes were identified: A; B1; B2 and C. Moreover, a physicochemical characterization of WLO was carried out regarding viscosity at 40°C, saponification number (SN), total acid number (TAN), surface tension, water content, elemental analysis and functional groups (FTIR). 56 samples of fresh lubricant oils for different applications were also characterized and their properties assessed and compared. Multivariate methods were applied to WLO to discriminate among coagulation classes based on FTIR spectra. It was found that coagulation classes A and B1 exhibit statistically similar patterns for all properties determined. Spectral discriminating analysis did not reveal discriminant peaks for class B1 samples, and the presence of specific additives was pointed as the possible factor underlying the increase in viscosity in this oils. Class B2 presents the absence of additives and oxidation products as differentiating features. In addition, B2 samples showed lower TAN SN, and lower concentration of some elements. Lubricants from gear or hydraulic applications can give rise to this class of WLO. Oils of Class C are mainly composed by synthetic ester type base oils, which hamper regeneration processes using alkaline pretreatments. In future studies, WLO type A and B1 can be classified as a single class. The coagulation phenomena classification becomes A – negative, B – precipitate formation and C – positive.

Mechanistic Modeling of the Alkaline/Surfactant/Polymer Flooding Process under Sub-optimum Salinity Conditions for Enhanced Oil Recovery

Alkaline–surfactant–polymer (ASP) flooding is potentially the most efficient chemical EOR method. It yields extremely high incremental recovery factors in excess of 95% of the residual oil for water flooding on the laboratory scale. However, current opinion is that such extremely high recoveries can be achieved under optimum salinity conditions, i.e., for the Winsor Type III microemulsion phase characterized by ultralow interfacial tension (IFT). This represents a serious limitation since several factors, including alkali-rock interaction, the initial state of the reservoir water, and the salinity of injected water, may shift the ASP flooding design to either sub-optimum or over-optimum conditions. A recent experimental study of ASP floods, based on a single internal olefin sulfonate (IOS) in natural sandstone cores with varying salinity from sub-optimum to optimum conditions, indicated that high recovery factors can also be obtained under sub-optimum salinity conditions. In this paper, a mechanistic model was developed to explore the causes behind the observed phenomena. The numerical simulations were carried out using the UTCHEM research simulator (at The University of Texas at Austin), together with the geochemical module EQBATCH. UTCHEM combines multiphase multicomponent simulation with robust phase behavior modeling. An excellent match of the numerical simulations with the experiments was obtained for oil cut, cumulative oil recovery, pH profile, surfactant, and carbonate concentration in the effluents. The simulations gave additional insight into the propagation of alkali consumption, salinity, surfactant profiles within the core. The study showed that the initial condition of the core is important in designing an ASP flooding. Because of uncertainties in the various chemical reactions taking place in the formation, an accurate geochemical model is essential for operating an ASP flooding in a particular salinity region. The simulation results demonstrate also that, for crude oil with a very low total acid number (TAN), the ultralow IFT and low surfactant adsorption can be achieved over a wide range of salinities that are less than optimal. The results provide a basis to perform better modeling of the sub-optimum salinity series of experiments and optimizing the design of ASP flooding methods for the field scale with more-complicated geochemical conditions.

Spray Injection Direct Analysis in Real Time (DART) Ionization for Petroleum Analysis

Negative- and positive-ion direct analysis in real time (DART) ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was applied to characterize crude oil and its fractions. Crude oil samples dissolved in toluene were directly infused into a spray needle, which produced a continuous and long-time stable ion current for FT-ICR MS analysis to obtain mass spectra with a broad dynamic range and high signal-to-noise ratio. A comparison between negative-ion electrospray ionization [ESI(−)] and negative-ion DART for crude oil analysis was presented. The DART(−) ionized almost all of the compound classes found in ESI(−), while it exhibited high selectivity on naphthenic acids, which enabled the characterization of naphthenic acids in petroleum with a low total acid number (TAN). The method is suitable for the analysis of naphthenic acids in petroleum distillation cuts, even with a very high boiling point. Sulfides in petroleum were likely oxidized to sulfoxides and exhibite...

Demulsifier in Injected Water for Improved Recovery of Crudes That Form Water/Oil Emulsions

Summary Waterflooding for oil displacement becomes a challenge when water-in-oil (W/O) emulsion forms upon contact of injected water with oil in the porous media. We have recently reported very-high pressure drops and high pressure fluctuations for a number of crudes in waterflooding. In this work, we address the challenge by adding a small amount of a demulsifier in the injected water. The stability of W/O emulsion is affected by many factors, including oil chemistry, brine chemistry, and temperature. We find that the W/O emulsion formation may correlate closely to the low total acid number (TAN). In this work, we report the effectiveness of a demulsifier in significant reduction of pressure drop and elimination of pressure-drop fluctuations. The demulsifier can be dispersed in brine or water, and can be carried by injection fluid as an additive for improved oil recovery. Both micromodel observations and coreflooding results show that W/O-emulsion formation is avoided when 100 ppm demulsifier is injected in the carrier brine. Results also show that there is an increase in oil recovery.

Waxy Crude Oil Emulsion Gel: Chemical Characterization of Emulsified Phase Extract Components

Emulsions of several waxy crude oils exhibiting similar properties were prepared and characterized to better understand the nature of their polar components. Both crude oils and their corresponding emulsions were analyzed by negative-ion electrospray Fourier transform ion cyclotron resonance mass spectrometry [ESI (−) FT-ICR MS]. The most abundant classes found in these crude oils were neutral N, acidic O, and O2 heteroatomic compounds. The N class was present in higher relative abundance in all samples, followed by the O class (phenolic-like compounds). The O2 class was minor in all crude oils, corroborating their low total acid number (TAN) values. The O/O2 class ratios were directly correlated with their rheological properties. Higher O/O2 class ratios were associated with crude oils that formed gel emulsions, indicating that O class compounds play an important role in gel emulsion stabilization. The identified phenolic compounds possess a structure that allows for (i) intermolecular hydrogen-bonding i...

Monitoring the degradation and the corrosion of naphthenic acids by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and atomic force microscopy

Although the term “naphthenic acids” was originally used to describe acids that contain naphthenic rings, today this term is used in a more general sense and refers to all components in the acid extractable fraction. In crude oil, naphthenic acids exist as a complex mixture of compounds with broad polydispersity with respect to both molecular weight and structure. There has been increasing interest in the naphthenic acids in crude oil because of the corrosion problems that cause during oil refining. Herein, two powerful analytical tools, negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, ESI(-)FT-ICR MS and atomic force microscopy (AFM), were combined to monitor the thermal degradation of naphthenic acids and their corrosion effects on AISI 1020 steel, respectively. Two different acidic crude oils (TAN=2.38 and 4.79mgKOHg−1, and total sulfur=0.7993 and 1.0220wt%) have been submitted to thermal treatment at 280, 300 and 350°C during 2, 4 and 6h, and characterized by ESI(-)-FT-ICR MS, total acid number (TAN), and total sulfur. The AISI 1020 steel was analyzed by scanning electron microscopy (SEM) and AFM. Generally, heating the crude oil at 350°C in a period of 6h, it was observed that a high efficiency (≅80%) and selectivity of thermal decarboxylation process was monitored by decay of TAN (4.79→0.44mgKOHg−1). ESI(-)-FT-ICR MS results showed that naphthenic acid species remained after the heating have DBE ranging 1–12 and carbon number from C15 to C45. AFM topographic profile evidenced that the naphthenic acid corrosion of the crude oil with TAN of 4.73mgKOHg−1 on AISI 1020 steel was profoundly altered and a marked reduction in peak to peak height values (obtained by subtracting the value of the lowest peak by the highest peak in the topographic area examined). Optical images and microphotographs confirmed the presence of irregularities, characterizing the corrosion mechanism as pitting type. The naphthenic corrosion was also evidenced in samples with low TAN value (0.44mgKOHg−1).

Investigation on Pyrolysis of Low Lipid Microalgae Chlorella vulgaris and Dunaliella salina

Chlorella vulgaris and Dunaliella salina are two kinds of microalgae, which are widely distributed in China. Thermal decomposition of low-lipid C. vulgaris and D. salina were performed using thermogravimetric analysis. The effect of heating rates on pyrolytic characteristics was investigated, and thermal decomposition kinetics was determined as well. Furthermore, pyrolysis experiments were carried out on a fixed-bed reactor. The gas, char, and tar yields were analyzed, and the mass balance was from 88.4 to 96.8%. C. vulgaris had higher H2 yields and lower CH4 yields than D. salina during pyrolysis. The theoretical calorific value of the pyrolytic gas of D. salina was higher than that of C. vulgaris because D. salina had a higher amount of high heating value components, such as C2H6, C2H4, and C2H2. The biochar from microalgae had a smaller Brunauer–Emmett–Teller surface area than the char from pyrolysis of lignocellulosic biomass. Highest yields of pyrolytic oil were 49.2 and 55.4% (water-free basis) for C. vulgaris and D. salina at 500 °C, respectively. The characteristics of bio-oil from microalgae pyrolysis, including water content, density, acidity, and heating value, were investigated as well as the chemical composition at different pyrolysis temperatures. The microalgae pyrolytic oil was found to have significant levels of alkanes, alkenes, alkines, and esters and be particularly high in nitrogenous compounds. In comparison to the bio-oils from common lignocellulosic biomass, the microalgae oil had lower oxygen and water contents, a lower total acid number, and a higher heating value.