Current scenario and potential of biodiesel production from waste cooking oil in Pakistan:An overview☆

2019-02-09 06:40:04HarisMahmoodKhanChaudhryHaiderAliTanveerIqbalSaimaYasinMuhammadSulaimanHamayounMahmoodMuhammadRaashidMohsinPashaBozhongMu

Chinese Journal of Chemical Engineering 2019年10期

Haris Mahmood Khan ,Chaudhry Haider Ali,* ,Tanveer Iqbal,Saima Yasin,Muhammad Sulaiman,Hamayoun Mahmood,Muhammad Raashid,Mohsin Pasha,Bozhong Mu

1 Department of Chemical,Polymer and Composite Materials Engineering,University of Engineering&Technology,KSK Campus,Lahore 54890,Pakistan

2 East China University of Science and Technology,Shanghai 200237,China

Keywords:Biodiesel Waste cooking oil Feedstock sustainability Energy demand Pakistan

ABSTRACT Biodiesel utilization has been rapidly growing worldwide as the prime alternative to petrodiesel due to a global rise in diesel fuel demand along with hazardous emissions during its thermochemical conversion.Although,several debatable issues including feedstock availability and price,fuel and food competition,changes in land use and greenhouse gas emission have been raised by using edible as well as inedible feedstocks for the production of biodiesel.However,non-crop feedstocks could be a promising alternative.In this article,waste cooking oils have been recommended as a suitable option for biodiesel production bearing in mind the current national situation.The important factors such as the quantity of waste cooking oil produced,crude oil and vegetable oil import expenses,high-speed diesel imports,waste management issues and environmental hazards are considered.Moreover,process simulation and operating cost evaluation of an acid catalyzed biodiesel production unit are also conducted.The simulation results show that the production cost of waste cooking oil-based biodiesel is about 0.66USD·L-1.We believe that the present overview would open new pathways and ideas for the development of biofuels from waste to energy approach in Pakistan.

1.Introduction

The global total energy consumption is rising radically because of the expanding populace,modernization and individual's need for a higher expectation of everyday life.In 2015,the world total energy consumption was 575 quadrillions British thermal units(BTU)and it has been imagined to ascend by 28% by the year 2040 with an estimation of 736 quadrillions BTU[1].This rapid boom charge of energy consumption will ultimately trigger the environmental issues and greenhouse gas(GHG)emissions[2].Today,the world is satisfying 80%of its energy demands by non-renewable fossil fuels that eventually contributes to ecological and health problems[3,4].The enormous fossil fuel consumption has raised the issue for the choice of renewable energy[5].Therefore,massive struggle has been initiated globally to explore the most effective alternative fuels in order to overcome the financial and environmental impacts of petroleum-derived fuels[6-8].

In Pakistan,this problem has turned out to be more serious as production and transportation sides of the country are more reliant on inferior value energy resources delivering negative impacts on the national economy and additionally creating environmental concerns.Accordingly,it is essential to recognize substitute potentials in the country in order to explore feasible methods to control energy scenarios productively and in an environmental friendly way.In the financial year 2014-2015,energy consumption by transportation division was over 51%among all sectors,transportation side being the largest energy consumer in the country[9].The major energy carriers in Pakistan including gasoline and diesel should be supplanted with carbon-impartial fuels like biodiesel and bioethanol that can viably diminish the reliance on fossil-derived fuels.

The current manuscript is targeted at thoroughly scrutinizing different energy resources and needs in Pakistan,notably diesel fuel as a sustainable and acceptable mineral diesel substitute,with attention on its potentials of production and consumption.Waste cooking oil(WCO)is perceived to be the most compatible and economically feasible feedstock in Pakistan for biodiesel production after enquiring different generation feedstocks available in Pakistan alongside a brief overview of technologies currently being utilized for biodiesel production.In the end,economic feasibility is presented using WCO as a raw material for getting sustainable utilization of biodiesel.

2.Energy Sector in Pakistan

Fig.1.Trend in TPEC in Pakistan(1965-2016)[11].

Fig.2.Primary energy consumption by fuel in Pakistan[11].

Pakistan is a developing country with a total populace of around 200 million[10].The total primary energy consumption for(TPEC)the year 2016 was 83.2 Mtoe(million tons of oil equivalent)(Fig.1)[11]and primary energy consumption by fuel in Pakistan is shown in Fig.2.Most of the energy prerequisites in Pakistan are fulfilled by oil and gas resources as indicated in the Fig.2.Primitive resources of oil are not adequate to meet the energy demand of developing economy bringing about expanding import of oil from Arab countries,particularly from Saudi Arabia.The local generation of crude oil stayed 24.02 million barrels during July-March fiscal year 2016[9].The two noteworthy users of oil are transport and power sector.During the fiscal year 2012,the share of oil utilization in both sectors was 49%and 40%,respectively.During July-March period of fiscal year 2015,this portion expanded by 50% and 42% for both transport and power while during July-March period of fiscal year 2016,the share of transport and power in oil consumption remained 55%and 35%,respectively(Fig.3)[12].One justification could be shifting of the power sector to natural gas being less expensive compared to the oil,and the other might be slump in oil prices that has expanded its use in the vehicle sector.Import of crude oil is a financial liability on the public treasury as almost 17.2%of import bills are based on petroleum products.During July 2016,4.98 million metric tons were imported in contrast with 4.81 million metric tons of the corresponding period last year indicating a growth of 3.5%.In fact,the present circumstances reflect sole reliance of the transportation sector of the country on fossil fuels with no accessibility for renewable fuels in this sector.The principle petroleum oil lubricant POL items utilized as a part of Pakistan's transportation sector are diesel and gasoline.In addition,around 51.3% of the oil products were employed in the transportation sector during 2014-15(Fig.4)[13].Aside from the issues identified with the depletion of fossil fuels steadily with time,another major problem associated with the burning of fossil fuels is GHG discharges and ecological concerns.Indeed,fossil fuel burning was responsible for approximately 192.7 million tons of CO2in Pakistan in the year 2016 with a striking growth rate of 2.5% per annum since 2005(Fig.5)[14].In view of the BP energy outlook,in the year 2035,the worldwide emissions are anticipated to reach approximately twofold the value existed in 1990.On the other hand,approximately 7 million individuals pass away every year inferable from air contamination as per the facts presented by the World Health Organization(WHO)[15,16].Therefore,need is to move with the world and probing alternative resources of energy with the least environmental consequences.

Fig.4.Sector-wise petroleum products consumption in Pakistan(2014-2015)[13]

Fig.3.Sectorial share of oil consumption in Pakistan[12].

Fig.5.Total fossil fuel CO2emissions in Pakistan(2006-2016)[14].

2.1.Diesel fuel consumption in Pakistan

Fig.6.Global demand outlook for petroleum-based fuels 2014-2040(in million barrels per day)[17].

Diesel fuel is the sector's pioneer of petroleum-derived fuels.According to the data presented by the Organization of Petroleum Exporting Countries(OPEC),worldwide diesel consumption in 2012 was more than 4 billion liters per day,satisfying full petroleum-based fuel needs up to 29%.Diesel usage has been anticipated to reach 5.7×109L·d-1by the year 2035(Fig.6)[17]because of developing transportation and industrial regions.What's more,diesel fuel will be extra engaged in the marine sector from 2020 to 2040 because of stricter environmental regulations[18].Pakistan petroleum-based fuel consumption pattern is skewed toward the use of diesel fuel in parallel with a global pattern.High-speed diesel(HSD)consumption in Pakistan was 8.49 million metric tons in the year 2016-2017 with a growth rate of 9.6%(Fig.7)[19].For example,quantum imports of all POL items(particularly high-speed diesel and petrol),have recorded noteworthy growth in the year 2017,demonstrating strong transport sector activity(Fig.8)[20].This has also corresponded with a hefty increase in imports of busses and heavy-duty commercial vehicles as a consequence of an expansion in the populace growth,speedy industrialization,creating nation-wide transportation systems,and lastly the legislative methodologies to urge the natives to use local transport.Furthermore,the caretaker government has expanded the cost of gasoline,diesel,and kerosene oil for the month of July 2018,as suggested by the Oil and Gas Regulatory Authority(OGRA).The new prices will be gasoline 0.82 USD·L-1,diesel 0.99 USD·L-1and kerosene oil 0.72 USD·L-1[21].As high-speed diesel is widely used in transport and agriculture sectors and therefore steep rise in its prices would directly influence the life of the consumers who would be witnessing hike inflationary rates in the country.Other than the threat of petrol-diesel exhaustion,using the immense measures of this petroleum-derived diesel fuel has generated elevated levels of atmospheric contamination,prompting extreme ecological and health issues and hence misfortunes of Pakistan's national assets.The critical air contaminants delivered by dieselburning include suspended particulate matters(SPM),sulfur mixes,and nitrogen oxides.Nitrogen oxides(NOx)and sulfur oxides(SOx)released largely by the fuel combustion are the fundamental contributors to corrosion,acid rain,and damages to trees and plants[22,23].In addition,exhaust emissions of diesel cause reduction in visibility and ground-level ozone[24,25].Furthermore,it is well recorded that diesel engine exhaust emissions exhibit organic constituents which contain cancer-causing compounds like nitro-polyaromatic hydrocarbons[26].As a matter of fact,diesel is being assigned as the principal offender for the most threatening emissions like N2O,SO3,and SPM,released in the country.

3.Biodiesel as a Potential Renewable Energy Source

Fig.7.High speed diesel(HSD)consumption in Pakistan(2004-2017)[19].

The monoalkyl ester of long chain fatty acid is called biodiesel which is a promising renewable substitute for the petroleum-derived diesel fuel,non-renewable in nature[27-29].The unique highlights of biodiesel including higher flash point,less sulfur content,more cetane number as compared to mineral diesel,positive energy balance,intrinsic lubricity,renewability and the most imperatively,its compatibility with present fuel distribution setup have made biodiesel acceptable in the energy market[30,31].In addition,its burning releases 20%,30%,and 50% fewer hydrocarbons,carbon monoxide and smoke,respectively,in contrast with mineral diesel[32,33].However,it is important to mention that biodiesel displays 2%lower brake thermal efficiency and 13%higher specific fuel consumption as compared to derived diesel[32].But there exists an option of making a blend of biodiesel with derived diesel in any extents in order to produce a balanced blend with exclusive features that can be further used without engine modification[34].However,a source of biodiesel is either virgin/utilized plant oils or animal fats so it is non-toxic and biodegradable[35].Moreover,its contribution to the mitigation of greenhouse gas emissions could lessen pollution challenges alongside diminishing dependence on petroleum products[34].Significant reduction in total unburned hydrocarbons(HC)up to 90% and reduction in polycyclic aromatic HC up to 75%-90% can be achieved through burning of the neat biodiesel(B100)[36].Ecological benefits,financially competitive,adequate quantity production and positive net energy balance ratio are certain qualities that made biodiesel an incredible alternate for mineral diesel and petrol as a transportation fuel[37].Biodiesel showed 10.3%growth in production to meet the world level of 29.7 billion liters in the year 2014 owing to it's across the board acknowledgment all over the world[38].As demonstrated in Fig.9,the United States remained the top listed biodiesel producer in the year 2014 with an annual production of 4.7 billion liters of biodiesel.

3.1.Sustainability controversy of biodiesel feedstocks

Fig.8.Pakistan's imports of Petroleum Products(quarterly basis)[20].

Fig.9.Biodiesel production by various countries in the year 2017[38].

Biofuels along with biodiesel are usually characterized on the premise of feedstock and production techniques into five generations viz.:edible oil seeds,non-edible oil crops,waste-based biodiesel,algae and the latest genetically engineered crops(Fig.10).The major challenge identified by production is the supply of feedstock on which more than 70%of the overall biodiesel production cost is dependent{Gude,2013#179;Tabatabaei,2015#181}[37,40].The other point of concern is the accessibility of feedstock which relies upon various factors including the region geographical condition and the nature of oil resources.At present,over 95%of the global biodiesel production is based on the first generation feedstock[41].First generation biodiesel considers to be more feasible and sustainable in the countries where agricultural land and water resources are effortlessly available[42].However,this is not always acceptable as its consequences appear as food shortage issues[43-45].In fact,biofuels produced from food crops fundamentally enhance land use chage(LUC)that prompts lessen the supply of wheat and other important crops in the future[46].Ultimately,shrinkage of land patch devoted for food crop cultivation is occurring as a result of first-generation biofuel production and even turns into a noteworthy reason for crop price hikes[46].The second and third generation biofuels,typically biodiesel,are produced from non-edible crops and oil wastes respectively.Such resources incorporate either waste cooking oil,animal fat and grease or non-edible energy crops.In the case of nonedible crops,there exists no immediate clash over food crops but LUC and water security criteria can be affected[47].Although non-edible crops are non-agricultural but for their maximum yield,applying fertilizers,irrigation,and harvest practices is unavoidable[48-50].Waste produced from edible oil utilization,an inherent part of human diet,is inevitable.Since more than 80% portion of vegetable oils is used in food applications[51],an enormous quantity of waste could be generated.Therefore,waste resource utilization approach for production of biodiesel not only avoids the surplus cost and ecological difficulties but also eliminates competition over food,water,and land.In addition,waste resources are thought to be guaranteed raw material as they are available in abundance and more diversified[52].According to categories of biodiesel generations,the fourth and fifth generations included the production of biodiesel from microalgae and genetically engineered crops.It is imperative to elaborate that immense research directed on biodiesel production from microalgae[53-58]showed high production cost as compared to petroleum-derived diesel[59].Therefore it can be deduced that only the third generation biodiesel could be feasible keeping in view feedstock sustainability and financial suitability.

3.2.Biodiesel production in Pakistan

With the aim of biodiesel production and utilization as an alternative energy source in Pakistan,the Alternate Energy Development Board(AEDB)has enunciated strategy recommendations with the essential targets of minimizing the imported fuel bills,addressing the demand of raw material for biodiesel and advancing a contamination free ecosystem.Furthermore,starting from 14th Feb.2008,the Economic Coordination Committee(ECC)of the National Cabinet has allowed the strategy for the use of biodiesel as an alternative energy source in its meeting.Vital purposes of the canon are as follows:

1.AEDB might be the essential planning and encouraging body for the National Biodiesel Program.

2.The steady introduction of biodiesel fuel blends with petroleum diesel in order to accomplish a minimum share of 5%by volume of the total diesel consumption in the country by the year 2015 and 10%by 2025.

3.The Ministry of Petroleum&Natural Resources might concoct the fuel quality standards for B-100(neat biodiesel)and blends up to B-20(20%biodiesel/80%petro-diesel blend).

4.Oil Marketing Companies(OMCs)are to buy biodiesel(B-100)from biodiesel manufactures;and sell this biodiesel blended with petroleum diesel(starting with B-5)at their points of sale[60,61].

In 2010,Pakistan State Oil(PSO)in participation with the AEDB and the Pakistan Agricultural Research Council set up the biodiesel pilot project.The success of the pilot plant 2012 contributed to the biodiesel blending by the oil marketing companies from 2013[62].

4.Research and Development Status in Pakistani Institutions

Fig.10.Biodiesel feedstock classification based on the sustainability issue[39].

In Pakistan,various universities and ventures have started activities on biodiesel innovation.Sadly,all endeavors have been led exclusively and evidently,there was insignificant learning cooperation between and among institutions.This effort is an exertion at gathering the statistics delivered by various country associations and aims to display it in a comprehensive way[63].

The endeavors carried out by Pakistan in raising and tackling plants of Jatropha and pongame for the production of biodiesel is admirable.Research and advance detailing are likewise continuous and outcomes are persistently examined and assessed[63].

4.1.Status of Jatropha cultivation in Pakistan

There has been reported several times the presence of Jatropha in Sindh[64].It is privately distinguished as RatanJothor,Jamal Ghota or Karanga and was utilized to cure a few illnesses in towns[65].Jatropha has been for the most part cultured on the little scale by private moguls using imported seeds[64].Since 2006 to 2008 their farming has expanded to greater than 400 acres of land as appeared in Fig.11.This expansion in Jatropha cultivation was fundamental because of a forceful crusade began by the AEDB[64].In the private part,various associations are occupied with developing Jatropha nurseries at a few areas in Punjab,Baluchistan,and Sindh.These nurseries have turned into the root for an amount of Jatropha farms in similar territories.In these farms,the typical age of a plant may extend from a few weeks to around year and a half[64].In 2005,around 2 acres of land were developed for Jatropha cultivating[64].Notwithstanding,the private area began mounting nurseries to promote development.Over 10000 saplings were given by proprietors to a few cultivators in Punjab and Sindh for transplantation into the ranches in 2006[66].Essentially in 2007,these fields exhibited around 50000 saplings for transplantation to different producers in Baluchistan and in Sindh[64].However,because of more interest,comprehension,and possible financial pick ups in developing Jatropha,agrarians in Sindh exhibited more focus,and due to the substantial scale openness of saplings in the nurseries,over 200000 saplings were given by several nurseries in Sindh for transplantation during 2008[63].

Pakistan State Oil(PSO)additionally came up with Jatropha seeds for creating nurseries and for developing around 20000 plants in their particular farmhouse[64].Presently,the PSO owns around 10000-20000 saplings for transplantation[68].Upon estimation,their nurseries found nearby Karachi had already over 200000 saplings in the quarter of 2009 and were set up to offer extra saplings if asked.PSO led an experimental venture focused on saddling Jatropha curcas plants from its farmhouses for the production of biodiesel on a business scale.The anticipated results for Pakistan are accompanying[69].

·For promoting green ecosystem sixty lac plants will be grown.

·Five hundred growers will be leased to achieve the plant cultivation on 5000 acres of land.

·Twenty-four million kilograms of seeds will be generated every year from this farming activity.An aggregate of 7.2 million liters of biodiesel will be produced/year which is equivalent to 17 Mt of biodiesel/day.

Fig.11.Trend of Jatropha cultivation in Pakistan[64].

The academic institutions in Pakistan that affirmed outcomes for the production of biodiesel through transesterification of Jatropha curcas oil included the Nadir Edulgee Dinshaw(NED)University in Karachi[70],the Government College University,Faisalabad[61]and the Quaid-IAzam University in Islamabad[71].Then again,PSO itself likewise has partnered with numerous different academic institutions in Pakistan for the same reason[69].

4.2.Collaboration with local academic institutions

The AEDB has adequately finished their first investigative work of biodiesel resources in 2009.Pongamia pinnata,castor bean,and rapeseed were perceived to be the potential oil resources for the production of biodiesel.The association productively approved B10 and B20 fuels from these indigenous resources in vehicles.The AEDB additionally effectively settled an examination lab at Quaid-I-Azam University Islamabad and a fuel-testing lab at the University of Engineering and Technology,Taxila[72].

4.3.Commercial projects

Clean Power(Pvt.)Ltd.alongside AEDB has begun commercial level manufacturing of biodiesel with the plant capacity of 400 L·d-1.The multiple targets of this project involved plantation of crops in squander regions,cultivation of Jatropha and Pongamia plants and the utilization of waste vegetable oil.The organization additionally worked withPakistan Railways to develop Pongame seeds in a few zones of the country[70].

On the contrary,there has been a burden on the administrative and decision-making organizations to build manageable models for Jatropha cultivation and utilize it as a biofuel raw material.There are multiple problems concerning Jatropha including water management and irrigation,carrying capacity of the land,toxicity,composts and manures,soil impacts,soil planning and yields.There ought to be a detailed evaluation of Jatropha,as it still can't seem to convey its guarantees.However,the major risk that Pakistan bears today is water scarcity.As per the International Monetary Fund(IMF),Pakistan is the third most waterstressed country in the world.Its per capita yearly water accessibility is 1017 m3—unsafely near the shortage limit of 1000 m3.Pakistan's water accessibility was around 1500 m3in 2009[73].

In spite of the presence of rich prolific soils in Pakistan,it isn't hence sensible to commit any water supply to inundate first and second generation energy crops.Then again and as specified before,the economic and sustainable use of the fourth and fifth generation feedstocks does not appear to be sensible because of the availability of premature technologies.As a result,the main presently most-accessible feedstock in Pakistan to somewhat supplant mineral diesel utilization would be a waste-based vegetable and animal oils.

5.Waste Oil-based Biodiesel

In accordance with the above discourse,the main accessible cheap raw materials in Pakistan would be vegetable and animal waste oil including chicken fat,slaughterhouse waste,waste cooking oil and tallow.It is significant that for vegetable oil importing countries like Pakistan(Table 1)[74],the issue related to waste oil recycling should be additionally highlighted keeping in mind the end goal to get the benefit of the income spent on consumable oil imports.The resources for the collection of waste oils can be domestic and commercial zones where any sort of waste is generated and must be discarded.Waste cooking oil is gathered from industrial deep fryers and food manufacturers,for example,potato snack factories,restaurants,catering agencies,fast-food suppliers and from the millions of houses which use frying oil for food making purpose.For instance,eateries and inns in the U.S.only createover 11 billion liters of waste cooking oil every year,the dominant part of which is discarded[75].The worldwide vegetable oil production quantified to around 182 million metric tons in 2016/2017.The statistics show the global consumption of vegetable oils from 2013/2014 to 2016/2017,by oil type,and provide a forecast for 2017/2018(Fig.13)[76].

Table 1 Production and import scenario of vegetable-oil importing countries[74]

Sunflower,Canola,Rapeseed/Mustard and Cotton are the major oilseed crops grown in the country.The total accessibility of edible oil was 3.523 million tons during the year 2014-2015.Among that,2.967 million tonnes was imported and remaining 0.556 million tonnes was locally produced.The import bill of edible oil during the year 2014-2015 was Rs.269.412 billion(2.663×109USD).During the year 2015-2016(July-March),2.205 million tons of eatable oil of significant worth Rs.136.920 billion(Agriculture 311.392×109USD)were purchased in demonstrating an expansion of 24.5%against the same duration 2014-2015(July-March).The quantity of locally produced edible oil during 2015-2016(July-March)is assessed at 0.462 million tons.(See Fig.12.).Total availability of oil from all sources is assessed at 2.667 million tons during 2015-2016(July-March)[77].Fig.14 indicates the production and import of vegetable oil in Pakistan from 2006 to 2015.

Zubair Tufail,President,Federation of Pakistan Chambers of Commerce and Industry,said that per-capita consumption of cooking oil in Pakistan is among the highest in the world.

He said Malaysia and Indonesia remained two big sources of import of oil into Pakistan.He asked Malaysia and Indonesia to increase investment in the edible oil industry in Pakistan,as they can take benefit of transit trade to Afghanistan and Central Asian countries via Pakistan[79].

It is difficult to get reliable statistics on WCO currently in Pakistan and barely any data on WCO traded globally.Two alternative methodologies can be applied in order to estimate the collectible potential of including a top-down approach and the bottom-up approach.Each approach has its own pros and cons.Top-down estimate requires a meaningful ratio of a virgin to waste oil that is very challenging to find out.

It revealed that even some fast-food chains producing around 4 t of WCO per restaurant every year are not able to decide a significant virgin cooking oil to WCO proportion due to various affecting parameters.At fast-food eateries with a substantial turnover,the greater part of the oil goes out with the consumer items,so less is left in the fryer toward the end or conclusion of the day as waste.Fast-food eateries with a lower turnover create more WCO,as for example a lower quantity of fried foods absorbing the oil has been sold.In both sizes of restaurants,the cooking oil must be replaced with fresh oil with a similar recurrence,yet the measure of utilized oil is higher in less frequently visited fastfood eateries.

In Pakistan,sources of WCO include hotel chains,restaurants,confectionaries and domestic cooking.Pakistan is basically a agricultural country and because of diverse ecological conditions,the population is majorily dependent on agricultural products.Edible oil yielding crops and plants are cultivated on extensive scale in the country for cooking purposes.These edible oils are used in huts,hotels,local shops and every home of Pakistan.Other sources of waste oil also incorporate animal fats obtained from livestock and poultry.Pakistani people use meat of buffaloes,cows,goat,camels and poultry on large scale.They also use fats for cooking purposes.These are the major sources for collection of WCO.

According to the Pakistan Oilseeds and Products Annual report(2017),per capita consumption of edible oil is 24 kg[80].WCO is assessed to represent about 20%-30%of edible oil's consumption[81].Jiang et al.reported the vegetable oil consumption to substitute edible oil and picks 30% as the percentage of WCO generate from edible oil[82].This paper chooses 20%as the percentage of WCO produce from edible oils(an estimate on the very low side).Therefore,the WCO production is calculated by Eq.(1)

Fig.12.Production of vegetable oil in Pakistan[67].

Fig.13.Vegetable oils global consumption by oil type[76].

With current population of approximately 200 million,estimated quantity of 960 million kilograms of WCO is available every year in Pakistan from all provinces(Punjab,Sindh,KPK and Balochistan).

If the process of recycling is not carried out suitably,oil wastes often cause clogging of channels.Backups and unpleasant odor at the same time imposing additional expenses on wastewater processing setup by going into a system of sewers[83].A plentiful quantity of oil waste recycling is additionally critical for the ecosystem in order to avoid water and land pollution[37].

It is important that as currently animal fats and eatery grease are mostly dedicated to industrial utilization,some creating environmental and medical related issues.These applications incorporate the production of cosmetic products and animal feed.The previous could conceivably bring about hypersensitivity,dermal maladies,and non-compensable wounds[84]while the last could be a possible reason for human medical issues.

5.1.Waste oil-based biodiesel processing:production challenges

Fig.14.Production and import of vegetable oil in Pakistan(2006-2015)[78].

Some foremost firms that produce biodiesel from waste cooking oils are listed in Table 2.Multiple methods employed for producing biodiesel specifically transesterification process,have been broadly studied throughout the recent previous years[88-89].The process through which an oil and an alcohol react in the presence of a homogeneous or heterogeneous catalyst is called transesterification.Fatty acid methyl esters(FAME)and glycerol are the main and co-products as a result of the acidic,basic,or enzymatic-catalyzed transesterification reaction[91].Since the enzymatically catalyzed reaction is limited by its meticulous reaction conditions and catalytic activity loss,therefore it cannot be employed commercially for biodiesel production to date[89].Comparative information on the pros and cons of homogeneous vs heterogeneous catalyzed reactions has been shown in Tables 3 and 4.WCO needs filtration to remove solid particles,FFA,and water before its conversion to biodiesel[92].The presence of free fatty acids(FFA)and water in WCO are vital parameters for finding out the feasibility of the oil transesterification method.This makes biodiesel manufacturing from WCO difficult to obtain and has driven researcher to probe alternative techniques for getting the best production conditions.Even though high biodiesel yield is obtained through homogeneous alkali catalyst at low pressure and temperature but waste oil feedstocks demand to tackle severe problems including soap formation and low biodiesel yield due to the high percentage of FFA and water.The optimum levels of FFA and water for feedstocks must be less than 1 wt%and 0.5 wt%for FFA and water respectively for carrying the alkali-catalyzed reaction to completion.In fact,the level of FFAs in WCO is significantly more than 15%for both yellow and brown waste vegetable oil[94,95].Therefore,using conventional technologies for direct base-catalyzed transesterification reaction are undesirable and various pre-treatment methods are to be introduced to avoid yield loss and saponification in reactor[96-98].Still,it is worth mentioning thatnowadays most of the biodiesel units are operating using homogeneous base catalysts because they are cost effective as compared to heterogeneous catalysts[89].

Table 2 Firms using waste oils as feedstock for biodiesel production[85-87]

Table 3 Homogeneous and heterogeneous-catalyzed transesterification reaction comparison[89,92,93]

In spite of the efforts of introducing low-cost feedstock and favorable catalysts for biodiesel commercialization,various studies have also been carried out on process intensification using advanced technologies[97,99].Moreover,some technological enhancements and novel strategies are applied to deal with the post-treatment problems of operation such as alcohol and catalyst recovery,glycerine separation,and water separation from the product[100-103].Table 5 indicates a number of these successfully commercialized technologies.

6.Economic Evaluation of Biodiesel Production from WCO in Pakistan

The initial phase in economic feasibility analysis of the use of alternative is to investigate the major parameter influencing its acceptance,which is the price.In countries like Pakistan where fuel cost is already very high,there is a need to find out relatively cheap alternative along with environmental mandates.WCO-biodiesel is the most economical one as raw material for biodiesel production.Waste cooking oil is available at no cost.Since the government of Pakistan has banned the recycling and resale of waste cooking oil to the unauthorized vendors due to its illegal use in recycling that creates severe health issues.Sometimes,it is disposed of in sewer lines causing environmental issues[39].Therefore,production of biodiesel from WCO not only resolves the disposal issues but also mitigates the illegal activity related to its recycling.The raw material in biodiesel production accommodates more than 80%of the total cost as indicated in Table 6.

In order to calculate per liter cost of biodiesel produced in Pakistan,a medium-sized plant having about 24 t·d-1production capacity was selected based on the modeling study performed by Zhang et al.[96].The lifetime of the plant was assumed to be 20 years and was operated three shifts per day.Aspen Hysys v10 was employed for the simulation purpose and Aspen Process Economic Analyzer v10 was used to calculate the total operating cost for the biodiesel production.A continuousacid-catalyzed process flowsheet using waste vegetable oil was developed(Fig.15a,b).Due to the presence of the highly polar components,methanol and glycerol,the non-random two liquid(NRTL)thermodynamic/activity model was used to predict the activity coefficients of the components in a liquid phase.The reaction conditions were set at a temperature of 80°C and pressure of 400 kPa.Heat flow associated with material and energy streams is shown in Table 7 and heat duties of major equipments in terms of power are presented in Table 8.Major energy consumers in biodiesel production plant include methanol recovery section,fame purification and glycerol purification with relatively high heat duties as indicated in Table 8.

Table 4 Merits and demerits of acid-catalyzed and base-catalyzed transesterification reaction[89,92,93,97]

Table 5 WCO transesterification to biodiesel conversion made by some of the successful process intensification technologies

Total operating cost for the plant operating under Pakistan's conditions is provided in Table 9 using the national market data.The price obtained for WCO biodiesel is 0.66 USD·L-1,even though,the income generated from crude glycerol(80%solution)was not included in calculating the total operating cost.On the contrary,diesel price in Pakistan is 0.99 USD·L-1that is quite higher than biodiesel produced from waste cooking oil.Numerous researchers performed studies to evaluate the price of biodiesel based on their country scenarios at different time periods.M.Hajjari et al.(2017)reported 0.611 USD·L-1biodiesel price produced from waste cooking oil[129].Similarly,Karmee et al.(2015)produced biodiesel from waste cooking oil at price of 0.8 USD·L-1[130].In Pakistan,labor is cheap,therefore it is more feasible to produce biodiesel at economical rates with the excessive availability of raw material(WCO)that contributes 80% in production cost accessible in cheap prices.

Table 6 Cost of production of Biodiesel[128]

7.Conclusions

For the production of biodiesel,waste oil/fats are the most suitable feedstocks with reference to the availability of raw material,cost,greenhouse gas emissions,land use changes and sustainability.The government of Pakistan is spending too much expense in high-speed diesel and oil imports to fulfill the consumer requirements.Therefore,it is the need of the day to get benefit from the existing resources of biodiesel production from WCO.This activity not only significantly minimizes diesel import bills but also adds value to cooking oil import in terms of converting its waste to energy after fulfilling the cooking requirement of the consumers.Secondly,the economic evaluation of biodiesel production from WCO using Aspen Process Economic Analyzer justifies a great relief to Pakistani people in terms of getting cheap fuel with estimated product price of 0.66 USD·L-1as compared to petrodiesel whose current price is 0.99 USD·L-1.Along with the benefits of waste oil disposal management(the biggest problem in the country),illegal WCO use elimination and reduction of GHG emissions as compared to those in case of petrodiesel are added advantages.Although regulatory authorities of the Country like AEDB and PSO are involved in formulating policies and achieving targets for biodiesel production,the need is to establish a systematically managed waste cooking oil collection service in Pakistan to convert a huge quantity of waste oils into biodiesel every year.This waste to energy approach not only drastically reduces the diesel import bills but also helps in developing a proper waste oil management system in the country and more importantly,participates in environmental pollution control.